toolboy's Corner: Ryobi Inverters

In late 2018/early 2019, Ryobi introduced the 18v 150W Inverter model RYi150BG. Shortly thereafter Ryobi released the 40v 300W Inverter model RYi300BG. It was rumored that Ryobi would release a 40v 1500W Inverter (model RYi1802B5), and this model actually appeared briefly on the Home Depot website. Late in 2020 the larger inverter appeared on the Ryobi Tools website as an 1600W inverter model RYi1802B6 but it hadn't appeared on the Home Depot website as of 11-Feb-2021. However, I did notice that it on the Home Depot website on 08-Mar-2021 and it is listed as 1800W continuous power, not as 1600W continuous with and 1800W for just 3 minutes (though this is still what the manual states). The package clearly comes with two 6Ah batteries, and it's the extra-tall OP40602 models, not the "standard" sized OP40601. After initially advertising these units as "Inverter/Generators" Ryobi decided to start calling these units "Inverters" or "Power Sources" rather than "Inverter/Generators", which IMHO is far more appropriate. Read on for a discussion and comparison of these tools, beginning with the manufacturer specifications.

Model Ryobi 18v Model RYi150BG Ryobi 40v Model RYi300BG Ryobi 40v Model RYi1802B6
 
Dimensions 3" H x 4" L x 2.5" W 8" H x 4.5" L x 5.5" W 14.75"H x 18.25"L x 11.125" W
Weight 1 lb. 15 lb?
Manual RYi150BG Manual (743K) RYi300BG Manual (805K) RYi1802B6 Manual (3,016K)
Power Source One Ryobi 18v Battery (Any size) One Ryobi 40v Battery (Any size) 1-4 Ryobi 40v Batteries (Any size)
Rated AC Power 150W Continuous (120V, 1.25A) 300W Continuous (120V, 2.5A) 1600W Continuous (120V, 13.3A)
1800W (120V, 15A for 3 mins max)
3000W Starting Watts
AC Waveform Modified Sine Pure Sine Pure Sine
USB Outlets (2) USB-A, 5V @ 2.4A
Note: the 2.4A is shared between the two ports
USB-A (5/9/12 volts, up to 3A)
USB-C (5/9/12/20 volts, up to 2A)
Note: If USB-A is in use, USB-C is limited to 5v only.
(4) USB-A (5 volts, 2.1A)
(2) USB-C (5/12/20 volts, 3A)
Misc VERY small!
NOT parallel capable
NOT parallel capable PARALLEL capable!
Bluetooth interface and mobile app
Charger input port (80W)
Protective cover (fabric?)


What is an Inverter?

These tools use one Ryobi battery (or more) as input to produce 120V AC output which can be used to power compatible devices in place of a standard AC outlet. Which devices are compatible depends greatly on the device and the inverter model. Power-hungry devices may not be compatible with the smaller inverters, and even though a larger inverter may be capable of powering a device it may not be able to do so for long enough to matter.

What does the 150W/300W/1600W really mean?

The "W" stands for Watts, and this is a measurement of power. Every AC-powered device you can buy will (or should) be labeled with its power requirements. In most cases you'll see the power in Watts, or you'll see the voltage in volts and current in Amps. The relationship between these inverters is based on a variation of Ohm's Law where P=ExI and P = power in Watts, E= voltage in volts, and I = current in Amps.

What does "PARALLEL Capable" mean?

Two identical inverters (or generators) which are advertised as "parallel capable" can be wired together in order to provide 2X the output to power a device which requires more than one inverter (or generator) can supply by itself. The 150W and 300W inverters are NOT parallel capable, but the 1600W inverter is. So when wired in parallel, two 1600W inverters can generate 3200W continuous, 3600W for up to three minutes, and 6000W starting watts. When operated in parallel the voltage remains the same at 120V. Two 1600W inverters connected in parallel will NOT produce 240V!

I have no direct experience with sump pumps or well pumps, but a web search reveals that a typical 1/2 HP sump pump motor requires about 2100W startup and 1000W running. If your sump pump is 1/2 or smaller then the 1600W inverter will probably be able to get it started and run it for several minutes (depends on your supply of fresh batteries).

Well pumps are typically 240V and therefore they cannot be powered directly by the 1600W inverter. It won't work even if you buy two 1600W inverters and wire them in parallel. However, it may be possible to use a step-up transformer to convert the inverter's 120V output to 240V as needed by the well pump. If you have a very small well pump rated 1/2 HP or less and get a step-up transformer rated for at least 2500W, it might work. A more typical 1-1/2 HP well pump motor requires 5000W startup and 2500W running, so it might work with two 1600W inverters in parallel and a 6000W+ step-up transformer. If your well pump is larger than 1-1/2 HP (and many are!) then this solution will probably not work, even briefly. NOTE: I'm not advocating the use of the 1600W inverter to power sump pumps or well pumps, and I'm certainly I'm not suggesting that using a step-up transformer in this way is a good idea. I'm simply pointing out that this is theoretically possible.

Which Inverter model(s) can power my device(s)?

Answering this question accurately is harder than you might think. In order to power your device(s), the inverter must: If you're considering the 150W inverter, then even if all of the above are true you still may not be satisfied if your device(s) are sensitive to "dirty" power.

The smallest inverter (150W) is good for lights and select electronic devices. The 300W inverter is good for these plus a wider variety of electronic devices and even some devices with small motors. The 1600W inverter is good for all of these and even some devices with medium to large sized AC motors.

Power

You cannot use one of these inverters to supply power to a device that rated for more power than the unit can provide. So if your device's label indicates that it requires 500W, then it's safe to assume that the 150W and 300W inverters will not be able to power it. If your device doesn't list the power requirement in Watts but does mention volts and/or amps, then use the formula P=ExI. If your device's label reads "input: 110v AC at 3 amps" then the power requirement = (110v)(3A) = 330 Watts. If the label says only "Input: 5A" you'll need to ensure that the device is powered by a standard household outlet, and if so then assume 120v so it's (120v)(5A) = 600W. Some US devices are powered by 240v, and these are incompatible with the Ryobi inverter/generators. Other devices require a wall adapter which converts AC to DC, and if these devices are labeled with power requirements it will likely be the DC power requirements, not the AC power requirements, so it's important to be certain what you're looking at.

Say you want to power your cable modem and wireless router. Determining the power requirements on these devices can be very confusing as they're likely to use a wall adapter. The devices are likely to be labeled with the power requirements in volts DC and Amps or milliamps (e.g., 12v DC, 1A). The wall adapter may indicate a range of input voltages (e.g., "Input: 100-240v AC, 50-60Hz, 0.5A. Output: 12v DC, 1.5A"). 0.5A at 100v would be 50W, but 0.5A at 240v would be 120W! For this situation I'd suggest looking at the device's power input requirement and add 20% for conversion loss, or if the device isn't labeled then add 20% to the wall adapter's output power. For a device rated 12v@1A the power needed would be 12W, then add 20% for 14.4W. If the wall adapter says output 12V@1.5A the power output would be 18W, then add 20% for 21.6W. Be aware that the wall adapter may be rated to provide more power than the device requires. Generally, a device will only draw as much power as it needs, so the estimate from the device's label will be more accurate than the output label of the wall adapter. But either of these estimates (14.4W or 21.6W) will more accurately describe the actual power needs than what can be calculated from the variable input voltage label on the wall adapter (50W or 120W).

Motors

Even if the inverter you have in mind meets the power requirements of your device, it still may not be able to power the device, especially if your device contains an motor. That's because motors are typically rated for how much power they need to keep going once they've been started and have reached operating speed. The amount of power required to get the motor moving from a dead stop can be 2X, 3X, even 4X or more than the amount of power required to keep it going at its typical operating speed. If your device contains a motor and the label doesn't indicate the startup power requirements, there's really no way of knowing how much power will be needed without using an instrument to measure it.

What sort of devices contain a motor? Just about any device that "moves" when it operates contains a motor: fans, power tools, CPAPs, heaters with fans, etc. If your device contains a motor and its power requirements are the same or just a little less than the inverter you're considering, don't count on that inverter being able to get it started.

Case in point: Recently someone on the Home Depot website asked if the 40v 300W inverter could be used to power a space heater. The Ryobi 40v 300W inverter is rated to supply up to 300W, and most 120V space heaters are rated 1500W. Some space heaters have multiple heat settings, but even when on LOW these heaters will likely require 500W or more. However, if you have a "personal" space heater (rated under 300W) then this inverter MAY be able to power it. I own a Lasko MyHeat model 100 (rated 200W) and the Ryobi 300W inverter cannot be used to power it from a dead stop. The inverter will power the MyHeat for about 3 seconds before the it flashes red to indicate "overload". I watched the power-on power draw with a Kill-A-Watt in a standard AC outlet and observed that the little heater draws up to about 330W in the first five seconds, then slowly drops to 200W over the next 15 seconds where it stays until powered off. So even though the 300W inverter is rated to supply 50% more power than is required for the "personal" heater, it can't do the job because the heater requires more than 300W to get started.

Run Time

Run Time describes how long the inverter can provide power to your intended load. Why is this important? Well, say your goal is to power a TV and portable satellite dish while camping to watch a 2-hour movie. Your inverter may be capable or powering everything perfectly, but you won't probably be happy if it runs out of energy after 15 minutes. The way to estimate your run time is to compare the amount of energy available in your battery (or batteries) with the amount of energy required to power your device(s). For a realistic estimate, the comparison must consider several "hidden" factors:

Idle Current Draw

All of these inverters draw a little bit of power from the battery when they're switched "ON", even when there is nothing plugged in and drawing power. This is called the "idle" current draw. Typically this represents the amount of power required to illuminate the display and/or buttons and to energize the AC and USB output ports. The smaller your power requirement is, the greater the idle current draw will affect your run time estimate. I've measured the idle current draw of the 300W inverter at about 8.3W. I'd expect that the 150W inverter draws less and that the 1600W inverter draws more.

DC-to-AC conversion loss

It's not possible to convert 100% of the energy input from the battery into the AC or USB output. The conversion process will always experience some loss due to heating of the internal components or other factors. For these devices, the actual power loss depends mostly on circuit design and the actual load. I'd expect the conversion loss to be around 10% for these inverters, but a range 5%-15% would not be surprising.

Your Battery's ACTUAL Capacity

Ryobi (and all manufacturers) advertise their battery capacities based on the cell manufacturers' specifications. These specs are generated in near-perfect laboratory conditions which you'll never experience. It's very unlikely that your brand new battery will ever deliver more than 98% of the rated capacity, and 95% is more realistic. A battery's ACTUAL capacity will slowly deteriorate as it ages and is cycled. After a year or two of moderate use a battery may perform at 90% of it's rated capacity, and after two or three years it may perform at 80-85% of its rated capacity or less. If you're trying to estimate run time when new, assume 95% rated capacity. For a used battery, assume 90% of rated capacity.

Back to the question of run time estimation, let's consider examples with low, medium, and high power requirements.

Run Time example: Low Power Requirements

Let's say that you just want to power your combination internet modem/wireless router using a Ryobi 40v 300W inverter and a used 40v 4Ah battery. If the device is labeled with a power requirement of 12v at 900mA, we can calculate the power requirement in Watts using the formula P=ExI, so P=(12v)(0.9A) = 10.8W. All Ryobi 40v batteries are labeled with the rated battery capacity in Watt-hours, and for the 40v 4Ah battery this is 144Wh. We calculate the run time as the amount of available energy in the battery in Watt-hours divided by the power requirement in Watts to determine the run time in hours. So that's (144Wh)/(10.8W) = 13.3 hours.

But wait! We didn't factor in the idle draw, DC-to-AC conversion loss, or the battery's ACTUAL capacity!

We know the idle draw of the 300W inverter to be 8.3W, we can estimate the DC-to-AC conversion loss at 10% (=90% efficient), and for our used battery let's assume that the battery's ACTUAL capacity is 90% of it's rated capacity. The revised calculation is therefore (144Wh)(0.9 of rated capacity)(0.9 efficient)/(10.8W device + 8.3W idle) = 6.1 hours. That's less than half the run time we'd estimated without considering the other factors.

If we break this down into the three factors, we find that run time is reduced by 34% due to idle draw, 10% due to conversion loss, and 10% due to ACTUAL battery capacity. The biggest factor for this small load is the "idle" draw.

Run Time example: Extremely Low Power Requirements

Someone on The Home Depot website asked how long a 5Ah battery would run the built-in LED light. I've measured the LED bulb power draw at 2.1W. The calculation for run time with a used 5Ah battery would be (180Wh)(0.9 of rated capacity)/(2.1W device + 8.3W idle) = 15.6 hours.

This sounds absurd, doesn't it? The battery has 180Wh of energy and the LED consumes just 2.1W, so it seems like the run time should be 180Wh/2.1W = 85.7 hours! But no, the actual run time is 5X shorter due mostly to the idle draw.

If we break this down into the three factors, we find that run time is reduced by 80% due to idle draw, 0% due to conversion loss, and 10% due to ACTUAL battery capacity. The biggest factor BY FAR for this small load is the "idle" draw. There is no AC conversion loss because there is no power being consumed by the 120v AC outputs.

Run Time example: Medium Power Requirements

Let's use the same Ryobi 40v 300W inverter, 4Ah battery and internet modem/wireless router from before, but let's add a 60" Roku HDTV, a 20" box fan, two LED table lamps, and we also want to fast charge an iPad. If we use a Kill-A-Watt we measure the power requirements of the 60" HDTV at 170W, the 20" box fan on HIGH at 85W, and the two LED table lights at 5W each. The iPad draws 12W while charging. The total power requirement is 10.8W modem/router + 170W HDTV + 85W fan + 5W lamp + 5W lamp + 12W iPad = 287.8W. The revised calculation is (144Wh)(0.9 of rated capacity)(0.9 efficient)/(287.8W devices + 8.3W idle) = 0.3939 hours, or about 24 minutes. The 300W inverter and a 4Ah battery can power all of these things at once, but with an estimated 24-minute run time I doubt that this is the solution we'd be looking for.

If we break the losses down into the three factors, we find that run time is reduced by 1.3% due to idle draw, 10% due to conversion loss, and 10% due to ACTUAL battery capacity. The idle draw is negligible for a medium load.

Run Time example: High Power Requirements

Let's say you want to run a ceramic space heater with your Ryobi 1600W inverter and one 4Ah battery. I don't know what the 1600W inverter's idle draw is, but I'll guess 20W. The space heater is rated 1500W, so the calculation is (144Wh)(0.9 of rated capacity)(0.9 efficient)/(1500W devices + 20W idle) = 0.0767 hours, or just under 5 minutes. That's not long enough to heat up a cold room.

Let's say that instead of the one 4Ah battery you have four new 40v 7.5Ah batteries -- the largest capacity 40v battery that Ryobi currently sells. The 40v 7.5Ah battery label indicates that each has a rated capacity of 270W, and we'll assume that these new batteries are operating at 95% of their rated capacity. The calculation is (4 batteries)(270Wh)(0.95 of rated capacity)(0.9 efficient)/(1500W devices + 20W idle) = 0.6075 hours, or about 36 minutes. Even with four of the largest 40v batteries that Ryobi sells, you'll only be able to run that space heater for a half hour.

"Dirty Power" -- Not all DC-to-AC inverters are created equal!

Let's consider the 120V power which comes out of your household outlet to be "clean" power. Your power company works hard to ensure that this power is exactly 120V AC at 60Hz. AC stands for "Alternating Current", and what this means is that if you measure the voltage between the two wires of your electrical socket and plot your measurements as a function of time, you'll see that the voltage rises from 0 volts to 170v, then drops back to 0v, then keeps dropping to -170v, then rises back to 0v, at which point the cycle repeats itself. The change in voltage can be represented as a smooth sinusoidal pattern which repeats 60 times per second (60 Hz). The voltage between the two wires actually alternate from an amplitude of +170v to -170v or 340v peak-to-peak, so how can this be called 120v? AC voltage is generally described in terms of the RMS (root mean square) voltage, which I'll not try to explain in detail but I'll mention that it's calculated as the amplitude divided by the square root of two, or about (170)/(1.414) = 120.

DC-to-AC inverters attempt to recreate the same output signal as the utility company, but it's not exactly the same. Years ago, some inverters provided power as a square wave, but modern DC-to-AC inverters provide power as modified sine wave (MSW) or pure sine wave. The different outputs provide a different level of distortion which can affect how well the powered devices work. The output of the MSW inverter does not look like a smooth sinusoid, instead it jumps in "steps" from 0 volts to 170v where it holds, then it steps back down to 0 volts and holds, then it steps to -170v and holds, then back to 0 volts and holds. The pure sine wave inverter creates an output signal which looks like a smooth sinusoid, like the utility power. More complex components are required to create a pure sine wave output as compared to the MSW, so the pure sine wave inverters are typically more expensive.



Some devices do not operate as well (or at all) with a MSW signal. In particular, AC motors don't run as well on a MSW signal as compared to a pure sine wave. When powered by a MSW inverter as compared to pure sine wave, one may observe that an AC motor "hums", attains a slower maximum speed and generates more heat. For lights and electronic devices, the difference is often observed as flickering, static/noise, or an audible "hum".

The Ryobi 18v 150W inverter provides a MSW output, whereas the 40v 300W and 1600W inverters provide a pure sine wave output.

Unfortunately, not all pure sine wave inverters are created equal. "Low Frequency" (LF) and "High Frequency" (HF) are the two major inversion methods for pure sine inverters. I'll not go into great detail here, but be aware that inverters using a HF design are typically smaller, less expensive, and are less capable of operating devices which contain AC motors like pumps or power tools. Inverters with a LF design are typically larger, heavier (due to the use of an iron core transformer), more expensive, and are much more capable of operating high-surge loads.

The Ryobi 40v 300W and 1600W inverters are HF inverters.

The 1600W inverter contains a HF design, but in its specifications it states that it can handle a startup load of 3000W. That will be enough for many devices, but I wouldn't be surprised to learn that it's not enough oomph to start certain devices which are rated for less than 1600W but which require much more to start. The devices most likely to have trouble starting would be sump pumps, refrigerators/freezers, vacuums, circular saws, and stationary power tools.

Other factors affecting signal quality

The output signal may not cycle exactly at 60Hz, or even if the cycle is exactly 60Hz the signal may spend a little longer in the first half of the cycle than in the second half. It could be that the slope when going from zero to the maximum amplitude is slower than the curve back to zero. The peak amplitude may be 170v with no load, but as the load increases the peak amplitude may drop to 160v, 150v, or less. Actually, MSW inverters are typically designed to provide less than a 170v peak amplitude signal. The "pure sine" signal may be a bit jagged rather than smooth and may get worse as the load increases. A MSW output may "bounce" a little as it settles at each output level. The specifications for some inverters may include Total Harmonic Distortion (THD), an operating range for output voltage or frequency, or other factors as a way of describing how "clean" the output signal is.

Some MSW inverters may be better than others because they incorporate more "levels" or "steps". The picture above shows a MSW signal with three levels (steps from 0v to +170v to 0v to -170v to 0v), but some MSW inverters may have five levels or more. I've not investigated how many levels different MSW inverters have, but I remember reading years ago that a particular Xantrex MSW inverter designed for RVs had more than 30 levels.

"Dirty" power to a box fan

To help characterize what to expect from the "dirty" MSW AC signal of the 150W inverter, I'll use a cheap 20" box fan -- the kind which can be purchased for under $20 from the endcap display at your local hardware store in the middle of summer. My expectation is that the fan will "hum", rotate more slowly, and get warmer when powered by the 150W MSW inverter, but that when using the 300W pure sine inveter the fan will be no different than when on utility power.

While on household/utility AC I used a tachometer and measured the blade speed on LO/MED/HI to be 720/888/1044 rpm. On the 150W MSW inverter the blade speed measured 684/864/1008 rpm, or 95%/97%/97% as fast as on utility power. On the 300W pure sine inverter I measured 696/876/1020 rpm, or 97%/99%/98% as fast as on utility power. For a 5-bladed fan my tachometer has a resolution of +/- 12 rpm. On the 150W MSW inverter I could clearly hear a "hum" when the fan was on LO, I could still hear it faintly on MED over the increased fan noise, but on HI I couldn't really hear a hum anymore, probably because the fan noise was so great as to overwhelm any hum. I could not detect any hum with the 300W pure sine inverter at any speed.

For the temperature comparison I first attempted to use a non-contact IR thermometer, but I was dissatisfied with the consistency of the readings so I gave up on this approach. Eventually I settled on using a mini 6" Quick Clamp to hold an RTD against the square-ish laminated metallic section of the AC motor, I captured temperature data for an hour after starting OFF at ambient, and switching to LO on utility power. In about 15 minutes the temperature rose from 70.7F to 99.68F and over the next 45 minutes the temperature seems to drift between 98.78F and 101.66F with an average of 100.00F. The data between 15 and 30 minutes reveals that the min/max/avg are 98.96F/101.48F/100.00F and the data for the last 15 minutes the values are 98.96F/101.66F/100.32F. That's close enough to suggest that the temperature can be estimated as the average of the last 15 minutes of data if the fan has been running for at least 30 minutes.

The average fan motor temperatures when running on utility power LO/MED/HI were 100F/96.9F/97.5. On the 150W inverter the temperatures were 104.2F/100.0F/98.49F, and on the 300W inverter the temperatures were 101.6F/99.4F/97.24F. It's true that the motor runs hotter on the MSW Inverter as compared to pure sine, but the difference is very small.

As expected, the fan rotated more slowly with the 150W MSW inverter and the fan made an audible hum. But I did find it surprising that the rotation speed was at most 5% slower -- I was thinking the difference would have been much greater. I was also surprised to measure a slightly slower rotational speed with the 300W pure sine inverter as compared to utility power.

Why would anyone buy a 1600W inverter that can only run at full capacity for a half hour?!

It seems to me that this device has a very niche market for consumers who require PORTABILITY, NO EMISSIONS, and POWER equivalent to a typical household outlet. If any one of these conditions is not true then more cost effective alternatives exist. This inverter will likely come in a kit with two 6.0Ah batteries (216Wh each), be priced around $700, and will provide a max of (216Wh)(2 batteries)= 432Wh of energy.

You could even buy an AC inverter and a bank of 12v SLA batteries and mount them to a hand truck. A 2000W pure sine inverter, one 12v 75Ah SLA battery (900Wh), cables, a hand truck, and a 12v charger can be had for well under $700. Need more runtime? Add as many 12v 75Ah batteries as you like. They're under $150 each and each adds 900Wh to the system.

If PORTABILITY to you means close proximity to your pickup truck, then you could just keep this setup in your truck and use an extension cord. For that matter, some pickups have space under the hood for a second battery. One could install a second battery and put a splitter on the alternator, so it charges that second battery when the engine is running. Pop the hood and clip on the AC inverter when you need it using 350A Anderson quick connectors, or mount your AC inverter under the back seat and run a 2/0 AWG power wire to the second battery. With this solution you get a very fast recharge time from your vehicle's alternator, and/or you could always top off the battery at home with a standard car battery charger.

The big 1600W inverter does appeal to me, but more as a novelty than as a serious solution to any power problem I might encounter. A luggable gasoline or propane generator rated 2000W and an extension cord would be cheaper and would provide power for hours. A conventional generator is not an option for indoor use, but that's why we have the extension cord.

It seems to me that the 1600W inverter is intended for applications which require short bursts of energy. For example, you might be able to power a miter saw all day if you're working alone installing flooring, trim or molding and making a cut or two every few minutes. You could use this inverter to power your blender to make frozen margaritas while camping! But don't bring your refrigerator as this inverter won't have the energy to keep a refrigerator running all night. This inverter could probably run a sump pump for several cycles during a power outage, assuming that it can provide enough energy to get the sump pump started (see above about HF inverters).

I mentioned using a miter saw in the previous paragraph and it's worth discussing this option a bit further. According to the 1600W inverter's specs it can only provide a continuous 1600W of output, but it can deliver 1800W for up to 3 minutes and 3000W startup current. Most 10" miter saws (and table saws) are rated 15 Amps, which is 1800W. I suspect that Ryobi was thinking of tools like a miter saw when they designed this inverter. I mean, how long do you typically use a miter saw to make a cut? I bet the blade is actually spinning for less than 10 seconds, then it spins down while you clear off whatever you're cutting and align the next piece to be cut. This may take another 10 seconds or more. The inverter cools while you're moving the material around and the blade isn't spinning, and you may be able to continue in this way until the batteries are depleted. Think about a 10" table saw, also rated 15A. Sure, you power it on and you may want leave it running for more than three minutes. But the saw doesn't draw the full 15A that whole time. The amount of energy required to keep the blade spinning with no load will be MUCH lower than when cutting. Even though the saw remains on, the inverter can cool down while the blade is not cutting. That 3 minutes of 1800W is probably plenty to handle the actual duty cycle of most human-operated tools.

Unfortunately, the 1600W inverter cannot be used as an Uninterruptible Power Supply (UPS) as it lacks a passthrough power function. But it does have an input for battery charging (rated 80W). So not only can the batteries be charged without removing them from the inverter but this may mean that an alternative energy source can be used for charging, such as a car accessory jack or solar panels. At 80W, the battery charger is certainly not designed to charge all batteries at once, and in fact is rather slow. The OP403/OP404 chargers are also rated 80W, so I'd expect batteries to be charged at a similar, agonizingly slow rate (e.g., 4 hours per 6Ah battery or 8 hours for two 6Ah batteries).

If you must have an emissions-free, noise-free solution and portability is not a requirement, you may want to consider a UPS as an alternative solution or build a battery bank with an inverter/charger, and you could even add an alternative energy option such as solar.

If you need portability but you're not concerned about emissions or noise, then a modest 2000W-3000W propane-powered generator is fairly quiet, will run for 12-14 hours at half-load on a 20lb tank of propane, and can be purchased for less than the cost of the 40v 1600W inverter even without any batteries. Propane can be stored in tanks for years (unlike gasoline) so it's easy to keep a multi-day supply on hand for emergencies.

I'm sure glad the 1600W inverter has a pure sine output, that would have been a deal breaker. But IMHO the 1600W inverter really missed the mark on two important aspects: passthrough power and charge options. Hopefully Ryobi will develop most or all of these features for their next version, rather than give up. I'd like to see:
Bear in mind that even if Ryobi attempts to delivers on all of the above, it may not work as well as you think due to phyical limitations. A typical household outlet is protected by a 15A circuit breaker, meaning that it can provide up to 15A * 120v = 1800W continuously. If Ryobi provides the passthrough power option, then when the load is 1800W a 15A outlet will have no power left for charging. With passthrough, charging would only be possible when the load is below 1800W.

Without passthrough power, couldn't we still perform charging while the system is under load? The inverter should be able to use the energy input on the charge port to help power the load, and if the load is less than the charge input then the Inverter should use the excess energy to charge the batteries. Say you're without utility power and you want to power your laptop, a fan, and charge your smartphone. This load is probably around 150W. You can easily power these with your Ryobi 1600W Inverter and one or more 40v batteries. With two 100W solar panels you should be able to run the load during the day without even draining your batteries. With three or more 100W solar panels you should even be able to charge your batteries while running the load.

Battery Recharge Time on the 1600W Inverter -- how long will it take?

Of course this answer depends on how many batteries you have and the actual capacity of those batteries. However we know that the 1600W Inverter has a charger rated for 80W input. The OP403 and OP404 chargers are also rated for 80W input, so let's assume that the 1600W Inverter's charger behaves the same as an OP403. You can check the 40v Charger Testing pages ( Part 1 and Part 2) for all the details, but it is shown that an OP403 charger fully recharges a fully depleted 2.6Ah battery in ~1.5 hrs, a 4Ah battery in ~2.5 hrs, and a 6Ah battery in ~4 hrs.

If you have four fully depleted 6Ah batteries, then I'd guess that the 1600W Inverter's charger would take ~16 hours to fully recharge them.

If you want to recharge your batteries faster, I'd suggest that the best strategy would be to use one or more dedicated chargers. Use the Inverter's charger and three dedicated chargers (OP400, OP401, OP403, or OP404) to simultaneously recharge four 6Ah batteries in under 4 hours. If you don't own a dedicated charger, I'd recommend picking up an OP407 3-Port Quick Charger. The OP407 is rated 194W input and it can fully recharge one depleted 6Ah battery in about 1:40 or three 6Ah batteries in 5 hours. Charge the fourth battery on the 1600W Inverter and all 6Ah batteries will be fully charged in under 5 hours.

Efficiency for USB-A

I've attempted to objectively measure the efficiency of the USB-A charging ports. Why bother with this? Well if power is out and all you need to do is charge your cell phone, you'll probably want to use the most efficient solution to extend your battery charge as much as possible. What I did was measure the voltage and current input at the battery (18V or 40v) to determine Watts input, then I measured the voltage and current at the USB-A output to determine Watts output. To ensure the same load was applied to each inverter, I generated artificial loads using 10 Ohm 10W resistors. I measured with no load, one resistor, then 2, 4, and 5 resistors in parallel. This should approximate loads of 0W/0A, 2.5W/500mA, 5W/1A, 10W/2A, and 12.5W/2.5A. For comparative purposes I included Ryobi's P743 USB Inverter, a 40v OP403 charger, and an Anker USB wall charger in the results.

Device Measurement No Load 1x 10 Ohm
(~2.5W Load)
2x 10 Ohm
(~5W Load)
4x 10 Ohm
(~10W Load)
5x 10 Ohm
(~12.5W Load)
Anker A2620
(Mini USB Wall charger)
volts out 5.08v 4.98v 4.87v 4.75v 4.69v
amps out 0A 0.500A 0.950A 1.749A 2.053A
watts out 0W 2.49W 4.63W 8.31W 9.63W
watts in 0W 3.10W 5.70W 10.6W 12.8W
% Efficiency   80% 81% 78% 75%
Ryobi P743
Power Source
volts out 4.99v 4.89v 4.83v 4.71v 4.50v
amps out 0A 0.491A 0.944A 1.789A 2.087A
watts out 0W 2.40W 4.56W 8.43W 9.39W
watts in 0.41W 3.06W 5.90W 11.15W 12.76W
% Efficiency   78% 77% 76% 74%
Ryobi OP403
40v Charger
with USB port
volts out 5.00v 4.96v 4.89v 4.77v 4.71v
amps out 0A 0.483A 0.951A 1.668A 2.008A
watts out 0W 2.40W 4.65W 7.96W 9.46W
watts in 0.42W 4.16W 7.06W 11.62W 13.68W
% Efficiency   58% 66% 68% 69%
Ryobi RYi150BG
150W MSW Inverter
volts out 5.11v 4.95v 4.79v 4.55v 4.46v
amps out 0A 0.490A 0.934A 1.660A 1.943A
watts out 0W 2.43W 4.47W 7.55W 8.67W
watts in 3.72W 6.20W 8.66W 12.74W 14.36W
% Efficiency   39% 52% 59% 60%
Ryobi RYi300BG
300W Pure Sine Inverter
volts out 5.13v 5.00v 4.89v 4.72v 4.63v
amps out 0A 0.495A 0.954A 1.676A 2.037A
watts out 0W 2.48W 4.67W 7.91W 9.43W
watts in 7.44W 10.21W 13.06W 17.52W 19.55W
% Efficiency   24% 36% 45% 48%

From the above data it can be seen that for every device tested, the USB voltage decreases as the load increases. Also the inverters have a much higher "idle" current draw than the devices without an inverter, which makes them less efficient, especially for smaller loads. So let's say you go camping and you need 5v @ 1A (5W) to slow charge your smart phone overnight. Let's also say that you have a 40v 4Ah battery operating at 90% of rated capacity, an OP403 charger, and a RYi300BG 300W Inverter. How many hours of charging will you get from the OP403 vs the RYi300BG? Your battery will start with (144Wh)(.9) = 129.6Wh of energy. With a 5W load the OP403 is 66% efficient, so it will provide 5W for (129.6Wh)(.66)/(5W)= 17.1 hours. With a 5W load the RYi300BG is 36% efficient, so that's (129.6Wh)(.36)/(5W)= 9.3 hours.

A note about the 300W Inverter. I've noticed that if I measure the idle current draw immediately after powering on the inverter, I'll get readings of about 5.4W (e.g., 41.52v and 0.13A). For every minute that it's powered on, the inverter will experience a current surge of up to 4A lasting about 1 second. After a few minutes the source battery's voltage will not have changed much, but the current will have stepped up (e.g., 41.32v and 0.18A = 7.4W). The periodic surge adds about 15% to the total power draw, or 7.4W*1.15=8.5W

USB Charging your Phone/Tablet - How Many Times?

The Ryobi Inverters make various claims wrt. the number of charges which will be possible with specific batteries, see the images below.. For example, the 300W Inverter advertising includes a table which indicates that a 40v Ryobi 4Ah battery can charge the average phone 15.1 times. Let's examine this claim.



A web search reveals that current cell phone batteries range in capacity from about 1500mAh to 4000mAh, but the average is 2500mAh. A 2500mAh battery will have a capacity of (2.5mAh)*(3.6v) = 9Wh. A 40v Ryobi 4Ah battery has a capacity of 144Wh. Therefore, one might conclude that a 4Ah battery can charge a typical 2500mAh battery (144Wh)/(9Wh) = 16 times. 16x is very close to the advertised claim of 15.1x, so on the surface this claim seems reasonable. But in reality this claim is very misleading.

Remember, as mentioned previously the 300W Inverter has an idle draw of 8.3W. The average cell phone charger provides about 10W for charging (5v @ 2A = 10W), so if the average battery is 9Wh the charge time should be 9Wh/10W = 54 mins. We'll assume that we have a used battery with only 90% of its rated capacity available for use. When charging from the 300W Inverter, the run time calculation is therefore (144Wh)(0.9 of rated capacity)/(10W charger + 8.3W idle) = 7.08 hours. Therefore the number of full charges is (7.08hrs)/(54 mins) = 7.8. This is about HALF of the advertised claim.

But the actual number of charges will be even smaller! You probably scoffed in the preceding paragraph when the calculation for charge time indicated that an average cell phone battery could be recharged fully in 54 minutes. I know I did when I wrote that. And yes, I understand that some phones can be fully charged in well under an hour. But the average cell phone charges at a "bulk" rate of about 2A at 5v, or 10W. The actual charge time will be longer than 54 minutes due to a number of factors, and the greatest factor is that most cell phones utilize multi-stage charging techniques which reduce the charge rate as the battery reaches a full charge. For example, the charge rate may decrease from 10W to 3W when the battery reaches 80% capacity, then the rate may decrease to 1W when 95% capacity is reached. (Actually a typical CC/CV charge curve is more likely. In Constant Current or CC mode a constant current is applied to the battery until a set voltage is reached such as 4.2v. When the battery reaches the set voltage, the charge circuit switches to constant voltage or CV mode where the voltage is held at the set point and the current slowly decreases to zero as the battery is "topped off". See any of the charger testing pages on this website for more details and graphs. For now I'll continue describing this as if it was a 3-stage CC charger as this model is a reasonable approximation and the math is simpler.) For this example, 80% of the battery's capacity is replenished at 10W, the next 15% of it's capacty is replenished at 3W, and the final 5% capacity is done at 1W. Let's do the math:

Charge time = (9Wh)(0.8)/(10W) + (9Wh)(0.15)/(3W) + (9Wh)(.05)/(1W) = 1.57 hrs

While the cell phone battery is charging, the Ryobi 40v battery must not only supply a total of 9Wh of energy to fully charge the battery, but it also must supply the Inverter's idle current of 8.3W for that entire time. So for one full charge of the 9Wh cell phone battery the 40v Ryobi battery must provide an additional (8.3W)(1.57hrs) = 13Wh. The "overhead" for using the 300W Inverter for this purpose is a whopping 13W! That's 144% of the energy that will be needed to recharge the cell phone battery!

At this rate, a 40v 4Ah battery can recharge the average cell phone (144Wh)(.9)/(9Wh + 13Wh) = 5.75 times.

But we haven't yet accounted for the DC-DC conversion loss! Some energy will be lost due to heat and other factors by the components which are used to convert the 40v battery's energy into 5v. It can be seen from the table above that some additional energy is consumed during the conversion. For example, when delivering 9.43W the 300W Inverter was observed to draw 19.55W, a difference of 9.61W. This is an additional 2.17W over the 7.44W idle draw. In a similar way, the conversion loss can be seen as 0.29W when delivering 2.48W. So that's an additional (2.17W)*(9Wh)(.8)/(10Wh) = 1.56W when charging up to 80%, then there's another (0.29W)(9Wh)(.15)/(3W) = 0.13W loss when charging the next 15% from 80% to 95%. I don't have a measurement for the conversion loss at 1W output, but surely it's less than the 2.48W rate and for 5% of the charge cycle that works out to about .04W. The total DC-DC conversion loss for one full charge can be estimated as 1.56W + 0.13W + 0.04W = 1.73W

With all of these considerations, a 40v 4Ah battery can recharge the average cell phone (144Wh)(.9)/(9Wh + 13Wh + 1.73W) = 5.46 times.

If your goal is to maximize the number of charges to your cell phone from a 40v battery, disconnect your phone from the charger and turn off your inverter when the phone reaches 80% charge level. In this way you make the best use of your 40v energy source by only drawing from the Inverter when the cell phone is charging at its maximum rate.

If you have an OP403 charger, consider using that instead of the 300W Inverter to charge your cell phone as its idle draw is much less -- 0.42W for the OP403 as compared to 8.3W for the 300W Inverter. So for one full charge of the 9Wh cell phone battery with an OP403 the 40v Ryobi battery must provide 9Wh + (0.42W)(1.57hrs) = 9.7Wh. The "overhead" for using the OP403 for this purpose is only 0.7W! That's only 8% of the energy needed to recharge the cell phone battery.

At this rate, a 40v 4Ah battery can recharge the average cell phone (144Wh)(.9)/(9.7Wh) = 13.37 times.

If you're going camping for the weekend and just need to recharge your phone 2-3 times, it doesn't matter whether you select the 300W Inverter or the OP403 charger. But if you plan to go camping for a week and you don't need the 120V AC, select the OP403 over the 300W Inverter because it's smaller/lighter and you'll probably be able to recharge your cell phone twice as many times with the same battery.

The data in the above table also shows that you'll get far more charges using the same Ryobi 18v battery from a P743 Power Source than you will from a 150W Inverter.

How do I get 12v out of an Inverter's USB port to directly power my 12v device?

The manual and specs for the 300W and 1600W Inverters indicate that the USB ports are capable of output voltages greater than 5v, such as 9v, 12v, and 20v. So one should be able to power a 12v device directly from one of these port, right? Well yes, but not really. There's no actual industry standard protocol for getting more than 5v out of a USB-A port. A device "negotiates" for a higher voltage by having a proprietary "conversation" over the D+ and D- lines. I put "conversation" in quotes because it is my understanding that this is not an actual serial communication; it's specific series of voltage level echoes and responses. If the Inverter recognizes the sequence, it will deliver the higher voltage. Perhaps the most widely known implementation of this charging technology was developed by Qualcomm and is called Quick Charge (QC).

For USB-C there is a standardized protocol called "Power Delivery" or PD for short. Two devices communicate serially to negotiate an optimal voltage and current, and this process actually takes into account the characteristics of the cable itself. PD is a bi-directional protocol, so either device could be the charging or receiving devices. In theory two connected smartphones with PD could negotiate to have one charge the other!

What does this means for powering your 12v device directly from one of these ports? Well it means that this will not be possible by simply wiring up your own cable as the cable will require some intelligence (e.g., trigger circuit) on the D+/D- lines to negotiate the higher voltage. Your best bet for the USB-A port will probably be to forget the 12v output and use a DC-DC step-up converter to go from 5v to 12v. To use 12v from USB-C, you can probably buy a cable with an integrated circuit which does the PD negotiation. NOTE: The Ryobi inverters don't actually mention that they implement QC on USB-A or PD on USB-C. Surely they do, but if so one might have expected them to mention this boldly in their published specs. Perhaps Ryobi reverse engineered these technologies and implemented proprietary/unlicensed/uncertified variants. This could explain why they do not make a claim of compatibility with QC and PD. (I have no actual knowledge about this, I'm just guessing.)

Efficiency for AC Inverter

When I first thought about how to test the Inverters I was thinking that I'd use a mix of resistive and inductive loads, thinking that in so doing the tests would not only measure efficiency but also demonstrate some of the difference of the MSW vs pure sine output. However, based on my experiments with a cheap box fan (see above) I've decide that resistive loads alone will be adequate. My test procedure will be to measure and compare the power draw from the battery against the power draw from various loads. I'll strive to test each Inverter at several load levels to determine how efficient they are at each level. I've already measured that the Inverters each have an "idle" load, so I expect that Inverter efficiency will increase with load. I wasn't sure how to accurately simulate small AC loads, but I can easily simulate small DC loads as I have a bin of LED bulbs with 4 to 24 5050 SMD LEDs and 7W walkway path incandescent bulbs. My strategy for loads under 25W will be to plug in a 12VDC @10A switching power supply and then measure the Power In and Power Out using various combinations of these bulbs. For larger loads I'll use a combination of incancescent bulbs rated 25W, 40W, 60W, 75W, and 100W; 2-level Halogen fixture which isn't marked but on utility power I've measured it to consume 139W on LO and 239W on HI, an LED bulb rated 10.5W; and a CFLs rated 13W and 42W. Before I began I measured the power consumption of each on utility power and observed that the incandescent and LED bulbs provided steady output power readings. But I observed that when first powered on the power consumed by the CFL bulbs was a few Watts below their rating, but as the bulbs remained on for a few minutes the power draw slowly rose up to a few Watts above the rated power then settled down close to the rated power. For this reason I'll try to avoid the CFLs during this test.

I measured Power In using my datalogger which has a resolution of 0.1W. Power Out was measured using my Kill-A-Watt which displays Watts to the tenth when the total power is under 100W or to whole Watt when over 100W (e.g., 1.2W, 12.3W and 123W). I discovered that the Kill-A-Watt is not particularly good at measuring the Power Out for the small loads. The output refreshes once per second and does not remain steady -- the actual readings bounced around by about +/-1W. This could be the Kill-A-Watt, but it could also be an artifact of the 12VDC power supply. For each reading I observed the output for 30 seconds, recorded the min and max values, then used the average of min and max.

At one point while testing the 300W Inverter near the 300W maximum load I added a 13W CFL to the existing load and my 300W Inverter went "pop" and is now dead. That's right -- it didn't trip the overload protection circuit. A component inside the inverter simply gave up. I'm not exactly sure why this happened. It could be that the inverter doesn't like to operate for long near its maximum output level, it could be that CFL bulbs have a weird power draw curve which pushed the Inverter "over the edge" because it was already near the maximum load limit, it could be that the 300W Inverter really doesn't like to operate near its load limit for long, or it could be something I haven't considered. At any rate, I do own a second 300W Inverter and I don't plan to ever use it loaded over 90% of its rated load capacity (270W). I did open up and inspect the fried 300W Inverter but I didn't see any components with the obvious look of being burned out. There's a 15A fuse on the battery (+) input which of course is intact. I also observed that the fried Inverter appears as a short circuit from the perspective of the input battery terminals, so when I get some time I should be able to determine which component(s) have shorted out and hopefully repair the unit.



It appears that for small loads (under 50W) the 150W Inverter is slightly more energy efficient, but that for larger loads the 300W Inverter is more efficient. I suspect that this is due to the greater idle current draw of the 300W unit.

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Last revised 29-Aug-2021
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