How to charge the Ryobi 18v and 40v batteries directly from solar

[Eric P]

I hope this has been posted to the correct forum. I am looking for some advice on what it would take to charge the Ryobi 18v and 40v batteries directly from solar. I do not want to create a system with a bank of deep cell batteries, a charge controller, solar, and an AC inverter (yet). I just wanted to learn what it would take to charge the Ryobi batteries directly from solar. I think the 18v battery is the easiest because Ryobi has created an In-Vehicle charger.

18-Volt ONE+ In-Vehicle Dual Chemistry Charger for use with 12V DC Outlet
https://www.homedepot.com/p/RYOBI-1...ger-for-use-with-12V-DC-Outlet-P131/100342149

I currently have the Nomad 20 which is a foldable solar panel form GoalZero.
https://www.goalzero.com/shop/solar-chargers/nomad-20-solar-panel/

The Nomad 20 has a female 12v car adapter which could connect to the car adapter from the Ryobi In-Vehicle Charger. The specs for the solar output port on the Nomad 20 are 14-22V, up to 1.3A (20W max). They also make a Nomad 50 with 14-22V, up to 3.3A (50W max) and a Nomad 100 with 14-22V, up to 8A (100 max). The Nomad panels are also chainable up to 150 watts.

My first question would be is the 20 watts from the Nomad 20 enough to charge the Ryobi 18v 4Ah battery or would it be better to upgrade to the Nomad 50 or 100…I assume more watts from solar is better? It would be nice if I could get a full charge in 4-6 hours of good direct sunlight.

Next, what would it take to charge the Ryobi 40v battery directly from solar? Ryobi does not make an In-Vehicle charger for their 40v battery so we would have to create something ourselves. If I understand correctly I would need at least 40v+ of solar to be able to charge a 40v battery. I think that means hooking up two 24v solar panels in series so that I get a theoretical total of 48v from the solar. How many solar watts would be appropriate to charge a 40v 5-6Ah battery in about 4-6 hours of good direct sunlight?

Then I thought I would need a charge controller to keep the battery healthy and safe from overcharge, but another forum post said that the Ryobi battery has an internal battery management system (BMS).

DIY Ryobi 18V One+ Power Station (very cool project BTW)
https://diysolarforum.com/threads/diy-ryobi-18v-one-power-station.4229/

Is the internal BMS like a charge controller? If so, can I simply connect the output wires from the solar panels directly to the Ryobi 40v battery? Will its internal BMS kept the battery healthy and safe from overcharge and what about electricity flowing backwards? If that works, I guess the only way to tell the current charge status would be to use the built-in charge indicator on the battery? Would it be safer to use an charge controller?

Any thoughts or advice would be greatly appreciated.

Thanks

 

[Craig]

I have tried to charge cordless tools directly from DC without much luck. Seems they like the circuitry that is in the charger that comes with them.

 

[45North]

Or you could just charge them with your regular AC charger plugged in to a 12v inverter powered by solar.
Not as efficient as the new Ryobi car charger, yes, but more flexible - you already have the Ryobi AC charger and the inverter could be used for anything.

Edit: Sure it's not efficient - converting from DC to AC and back again. But it might be OK for occasional use and if your system is big enough to swallow the losses.

Thanks for the idea; i've been thinking about this myself. So, now I'll have to first plug my Ryobi AC charger into my wattmeter and see what it draws. Then I'll see if I can charge it with my 25W solar setup. What are the odds?

 

[namesgolden]

Use the official charger.

Don't get caught up in chasing efficiency. Except in mobile application overbuilding your array is more practical.

Get a sonoff device or timer. Set it to turn on after 2pm (or whenever your main bank is charged). Plug your 110v Ryobi chargers in after the timer.

That said, Ryobi packs are just 5s lithium packs. The BMS hasn't been reverse engineered, so you'd have to open them up and add charging/balance wires to charge them properly.

 

[Supervstech]

Could it be done? Sure... keep in mind those 18650 banks are what? 14S banks? Li nmc cells can’t do bad things if charged improperly.
I would use the factory charger and power that with solar powered inverter...

 

[Eric P]

Thanks for the replies. Unfortunately I do not know anything about the inner workings of the Ryobi batteries (5s, 18650, 14s, etc...). I have considered that it would be easier to connect to an existing system that has solar, a charge controller, deep cell batteries, and finally an DC/AC inverter so I can use the standard out-of-the-box Ryobi charger...but I have no such system and creating one for this propose does not make sense at this time. I eventually want a system like that but its not financially possible at this time.

Let me ask this question another way. If I were working at a construction site that did not have access to power, or a remote site (think something like those Building Alaska shows) and you wanted to charge the Ryobi batteries from solar...how would you do it? I guess the simple answer is use a traditional generator (gasoline, propane, etc...) and an DC/AC inverter to the Ryobi charger? Seems so wrong to not just charge the batteries directly.

I suggested to GoalZero that they offer a device to allow their solar panels to charge the Ryobi batteries. They said it was a good idea and would consider it. I would think it would be easier to create something for the 18v vs. the 40v. I am not expecting them to create anything but who knows....it would be pretty cool.

I have two final questions. First, if I were to connect a GoalZero Nomad Solar panel to the Ryobi In-Vehicle charger what would be the best wattage choice (20,50, 100, or 150)? Second, from what I understand if I have a 12v battery bank, and I want to charge it from solar, the solar array needs to produce a little more than 12v...say 13-14v. Right? I assume the same is true for 24v and 48v battery banks...the solar needs to produce slightly more voltage than the battery. Right? So to charge a 40v 1Ah battery you would need slightly more voltage than 40v?

Thanks everyone.

 

[erik.calco]

Does Ryobi have a vehicle charger like Milwaukee has? If so, you could charge it from the batteries of a 12V or 24V solar system.

 

[Eric P]

Yes Ryobi does offer an In-Vehicle Charger for their 18v battery not the 40v.

18-Volt ONE+ In-Vehicle Dual Chemistry Charger for use with 12V DC Outlet
https://www.homedepot.com/p/RYOBI-1...ger-for-use-with-12V-DC-Outlet-P131/100342149

 

[erik.calco]

Yes Ryobi does offer an In-Vehicle Charger for their 18v battery not the 40v.

18-Volt ONE+ In-Vehicle Dual Chemistry Charger for use with 12V DC Outlet
https://www.homedepot.com/p/RYOBI-1...ger-for-use-with-12V-DC-Outlet-P131/100342149

Where you go from there just depends on your solar setup. You can get 12V sockets and spade terminals on ebay. Use to wire, then wire to 12V source such as your DC fuse box and your bus bar with ring terminals if DIY. Commercial portable systems typically come with 12V sockets.

40V would have to go through an inverter.

 

[Off grid Colorado]

Funny I've never charged my Ryobi batteries on the grid...

 

[Eric P]

Exactly how do you charge your Ryobi batters? Do you have a solar powered battery bank with an DC/AC inverter?

 

[Off grid Colorado]

Yes

 

[45North]

Thanks for the idea; i've been thinking about this myself. So, now I'll have to first plug my Ryobi AC charger into my wattmeter and see what it draws. Then I'll see if I can charge it with my 25W solar setup. What are the odds?

Tried it but the Ryobi charger draws 90W - too much for my small system.

 

[Off grid Colorado]

I use a 13$ 200w inverter in my truck with the ryobi chargers it works great...

 

[tictag]

My first question would be is the 20 watts from the Nomad 20 enough to charge the Ryobi 18v 4Ah battery or would it be better to upgrade to the Nomad 50 or 100…I assume more watts from solar is better?

All batteries have what's called a 'nominal' voltage but in truth, the voltage of most batteries vary depending on their state of charge. For example, a 12V lead-acid battery will vary from around 10V fully discharged to around 12.8V fully charged. In order to charge that battery you need to overcome the battery's own potential, then add some to force enough current through the battery's own internal resistance. That's why a lead-acid battery is typically charged at 14.8V.

Same will go for your 18V(nominal) battery.

I do not know what chemistry Ryobi uses, though NMC has been suggested. According to here, NMC has a nominal cell voltage of 3.7V, meaning the battery will likely have 5 cells connected in series (5 x 3.7V = 18.5V). NMC chemistry should be charged at 4.2V per cell, so 21.0V (5 x 4.2V = 21.0V) - no more, no less - and with a Constant Current / Constant Voltage (CC/CV) charge profile. The wattage of the panel will determine how quickly the battery can be charged e.g a 20W panel will charge twice as fast as a 10W panel.

You must not connect a solar panel directly to a battery (except in special cases) because the panel's output voltage will be different to the voltage required by the battery for a proper charge, and will vary as solar irradiance levels vary; you'll need a CC/CV buck/boost converter (also known as a battery charger!) to stabalise the charge voltage. These can be purchased as self-contained modules from, for example, Amazon. Obviously these don't come with all the bells and whistles that come as standard with a commercial battery charger.

It would be nice if I could get a full charge in 4-6 hours of good direct sunlight.

This is an easier question to answer, you say each battery is 4AH at 18V(nominal), right? So that's 72Wh, in order to generate 72Wh in 4 hours you would need an 18W power source (4AH x 18V = 18W). Two caveats:

1. The round trip charging efficiency is likely more that unity so more energy needs to put in than will be stored (this is normal).
2. Power ratings for solar panels are set in 'ideal' circumstances i.e. strong directly sunlight, low temperature etc.

With both of those in mind, my guess is that you could fully charge a 4AH pack in 5 or 6 hours with a 20W panel.

According to the website linked above you can charge NMC chemistry up to 0.7C, so 2.8A (4AH x 0.7C = 2.8A) so the fastest possibly way to charge the battery would be with a >59W panel (21.0V x 2.8A = 59W).

I have two final questions. First, if I were to connect a GoalZero Nomad Solar panel to the Ryobi In-Vehicle charger what would be the best wattage choice (20,50, 100, or 150)?

To charge one battery at the fastest possible rate, >60W would be required. It doesn't matter how much bigger, as you will see shortly.

Second, from what I understand if I have a 12v battery bank, and I want to charge it from solar, the solar array needs to produce a little more than 12v...say 13-14v. Right?

Yes, answered this above.


Other considerations:

1. The BMS that comes with the battery pack is there to protect the pack from bursting into flames, it can be ignored in regards to charging - your charging solution parameters simply need to stay within the BMS parameter e.g. charge rate etc.
2. The 18V(nominal) battery would need to be charged at 21V (no more, no less) and at no more than 2.8A (see above) using a CC/CV charge profile.
3. The CC/CV module will need to be specified for at least 59W, though I would recommend you at least double this because those things tend to get very hot!
4. Therefore your charging solution would look something like this:

To charge your 40V(nominal) batteries, I would assume these would be 11-cell batteries (11 x 3.7V = 40.7V), maybe 12? An 11-cell battery charged to 4.2V per cell would require a 46.2V source and to charge at the maximum rate of 2.8A would would require a supply of at least 129W e.g. a 120W or 150W PV panel, and again double this for the CC/CV module (e.g. at least 300W+)

Something like this or similar would allow you to charge multiple batteries simultaneously: https://www.amazon.com/dp/B076TTBKFG



As this device does not have a display, you would need a multimeter to set the CV [i.e. 21.0V for 18V(nominal) battery, or 46.2V for the 40V(nominal) battery] and CC [i.e. 2.8A].

Edit: Added clarifications e.g. how calculations were made.

 

[tictag]

Please note: I've made some pretty big assumptions in my post above, particularly on the battery chemistry and resulting charge voltages. These assumptions need to be checked! Lithium-ion battery technology is dangerous, especially during charging.

 

[Eric P]

Wow thank you very much for the detailed response. You gave me something to research. I am a little surprised that Ryobi or someone else like GoalZero has not produced a way to charge these 18v and 40v from solar. Oh and don't worry I will not blow my self up.

 

[tictag]

@Eric P Don't forget to 'like' the post if it offered you value ... not that there is any kind of contributor league table on here ... oh, wait...

 

[tictag]

 

[namesgolden]

Please note: I've made some pretty big assumptions in my post above, particularly on the battery chemistry and resulting charge voltages. These assumptions need to be checked! Lithium-ion battery technology is dangerous, especially during charging.

I can say the ryobi 18v packs are 5s, the balance leads are not exposed to the charger. I'm not sure what the stock BMS is capable of, but I do know the stock bms will let batteries drain below the voltage the stock chargers want to see before allowing a charge.

I have MANY ryobi tools, one of my first projects in mind when I make myself buy a spot welder is to build a 5s5p (or larger) pack.

I still feel as though this thread was over at "get a small cheap pure sine inverter"