Can power tool lithium batteries run in series without damaging protection circuits?

I don’t know how the protection is set up on power tool batteries. I know we can run regular protected lithiums in series as they only really check for over and under cell voltage and limit current. Are power pack protection circuits the same, or do they have some other protection that would prevent them from being in series? Also, any clue what current the ryobi batteries will put out? I’m trying to get to 36V and figured I could use to Ryobi 18V batteries in series, but I don’t want to damage my batteries?

I’m not able to tell you the current output of Ryobi batteries, but I can tell you, since I’ve tested few hardware tool brands here in the shop where I work that i guess Ryobi sources one of the worst cells out there
I mean, we sell Makita, Hitachi, Bosch, AEG, Milwaukee, Ryobi and others, but the fault ratio on Ryobi it’s unbelivable, compared to real brands….like 5 fault batteries on 10 Ryobi tools, (drills, chansaws 36V…and other 18V stuff)… my boss continues to sell them, but I have to manage the RMA process, and everytime I could i tend to discourage the customer to buy Ryobi
Also capacity checks made me discover something interesting, Milwaukee had some flaws on M12 series batteries with crappy ICRs, MAKITA does a pretty good job. Now seems milwaukee is using new samsung stuff….yet to verify.

Sorry for the OT

Anyway If this could be helpful I could tell you that new products can take advantage of 2x 18V battery packs in series, like this

I have only come across one tool that had low voltage protection. It was a late model hilti drill. I think most (or all) brands use balance chargers of sorts but I could be wrong.

I see no reason why it wouldn’t work. You would have to charge each pack separately but for discharging each pack wouldn’t “know” it was being run in series with another one. As soon as any one cell discharged below the cutoff voltage the pack that contained that cell would shut down. Because the 2 packs are in series all current would stop.
I have a lot of used Ryobi 18V packs and have been meaning to verify that. I will be back home in 10 days and will check that out.
Someone has already posted that tools exist that run on 2 packs in series. I saw a Makita circular saw that ran on 2 18v packs and was called a 36v saw.

Checkout that clearance price!

It’s the only store ever to put that saw on clearance

I know some people have built ebikes that run DeWalt packs in series.

But there is a potential problem. If one pack discharges faster than the other one under load, you can get the “reverse charge” effect. Depending upon the circuity in the pack, it could damage it (the cells and/or the circuitry on the pack(s)).

My gut feeling is that if you try to connect these packs in series you need to start from identical packs. This could be complicated. If you buy the packs from multiple sources, you have no real idea of the use information or the level of cell matching. If I had a single source that can convince me of the "likeness" of the packs, I could go with this. Buying random packs for eBay; not so much.

I am still on vacation and have not yet confirmed what I believe to be true, that 2 Ryobi 18v drill packs can be used in series.
I have about 30 of these packs that I have rescued and repaired from the recycle bins. I have never seen a schematic of the circuit board in them but I have enough experience with them to be able to take an educated guess as to how they function.
Each board contains 2 power FETs. These 2 FETs are in the output/input circuit of the pack. I think one is used during discharge and the other during charging. Also on the board there are many components that are used to monitor the voltage of each 18650 cell while discharging or charging. During discharge, when ANY one of the 5 cells falls below about 2.5v, a signal is sent to the discharge FET shutting it off. This FET is in series with the 5 cells so the voltage across the pack at that point is zero. Because that FET is off, current from the second pack, which is in series, can no longer flow either. When ever a cell falls below 2.5v from which ever pack the discharge FET in that pack will cause all current flow to cease.
It is NOT necessary to have perfectly matched packs other than to maximize runtime. The 2 pack combo will shut down when the weakest cell amongst the 2 packs is fully discharged.
The charging FET works in like manner. First cell to charge up to 4.25v causes all charging to stop. The Ryobi packs have NO balance charging. Often times I will find a pack that just needs to be manually balanced charged. It was tossed due to poor run times because one cell was out of sync with the others.

I am planning on building a light similar to The light OL used and will use 2 Ryobi packs in series. After having said all this, I have yet to actually confirm it. As I have 30 functioning packs, I can “afford” to perform the experiment, and I will.

dchomak, you are doing the same think I am. I plan on powering a CXB3590 and I would like the ease of using the tool packs rather than making a pack. I don’t have near as many batteries as you do (I only have 6), but I don’t see a reason that they wouldn’t work. Some searching and I found this which is interesting

Actually not… inside the FET there is basically a diode across the source and drain. Switching the FET off, only blocks current flow in one direction. Voltage from the lower pack can flow into the upper pack if the lower one is on and the upper one is off.

Last night I wired 2 packs in series (42V fully charged) and discharged them through 7 ohms of power resistors rated at 285W total.
The penny is for scale.

The output FET on a Ryobi drill pack is an IRF1404z. During discharge I measured the voltage across the Drain-Source pins. I wanted to confirm what I thought to be true, that this FET acts as a switch, turned on when the pack is charged up and under load and turned off when any one cell in the pack is depleted.

After TP voiced his concerns, I became concerned also. What he was reminded us of is that there are always “gotchas” out there that must be avoided. The gotcha that I then became concerned about was the voltage that the FET would see across the drain-source pins when it shut off. Normally with just 1 drill pack it would be the sum of all the cells in that pack, at most 21V. I looked up the Vdss of an IRF1404z and found that it is at minimum 40v. It occurred to me that when only one FET shuts off in a 2 pack series connection, it could possibly see all the voltage from both packs. Could be close to the 40v rating.
Anyway, I let the packs run down, measuring the voltage drop across the FET’s. While on, flowing about 7A. the voltage drop across the output FETs was only .015V. However when the pack shut down, the voltage across the FET that shut off went up to about 15v, not twice that, as I had feared.
Even had it doubled, I still think we would be OK as the actual Vdss of these FET’s is actually a little higher than 40v.
Besides, who here hasn’t been guilty of pushing the envelope of our semiconductors?

My conclusion is that for my purposes, it’s OK to run 2 of the Ryobi packs in series.

Hey guys, I’ve been playing fast and loose with these batteries for some time. I have them in my kids Power wheels. I get a new set each year when they go on sale 2/for 80-100$. These things are great for the power wheels. The 18V kicks the kids around a little quicker and makes them smile a about 1.5X more than the 12V batteries they came with. One older power wheel is a 6V “quad” so the 18V makes that one really cruise at 3x original speed. So… Long story short, I tried putting two of these batteries in series to get 36V… and well it took off when she hit the gas and then less than 1 full second later stopped. The lights no longer lit on the test button on one battery, so something cooked. I took it apart and it seemed there was some diode that was shot. Like an idiot I tried it again… got the exact same result. One battery gets nuked each time. Not sure if it’s the load… So… be careful putting these in series. Expensive mistakes. I even used these 3D printed caps, which actually end up melting due to the current being so high.

Also there’s this guy:

So what I’m wondering is- what am I doing wrong… do I need to have 4 batts? two parallel and two series? Or would some big old diodes on the main terminals prevent the issue I’m having? I know just enough to make these really dangerous, but not enough to fix them when they’ve stopped working… Any help greatly appreciated, I’d love to be able to put two of these in series to get 36V for these bigger power wheels. Thanks!

I tested the Ryobi’s in series and they survived.

BTW, I saw 2 packs of those 4Ah batteries for $59.00 yesterday :wink:

Could it be the excessive load in series that blew them out on me? maybe some in line fuses or diode between them?

It’s sometimes ok to over volt DC motors by 50, I did the same thing putting an 18V pack to a 12V tool but 300 is a bit much don’t you think? Even if the packs did survive the motors or some other integral part would not. Those same two 18V packs in parallel would keep them happy for a long time.

I just reread his post carefully, and realize he started having his problems when he tried to run his daughters older 6V power wheel on 36V!

That is the problem. 6 times the original voltage

Ryobismoker, there’s your problem.

No no, I didn’t run the 6V one at 36 (that indeed would be pretty crazy). The 6 volt one runs on 18v great. It’s 3x, yes, 300, However it was a slower item to begin with so the 3x actually puts it at only a HARE faster than the 12V’s on 18 at 150 or 1.5x. So I’ve run the 12V’s now on 18 for some time, and yes, it’s “ok”, but as it’s been a few years now (they have gotten plenty of fun and use), they are looking for the next level. So I thought taking the 12V ones to the 36V level would be there. However that’s not my only game in town. I also have a 24V Razor “kart” that is just too slow compared to the rest. So the 2x 18V to 36, would again get me that 1.5X fast ride. So before I go blowing out another 50$ battery, I’m wondering if there’s some simple protection I could build in between them so this doesn’t happen on the “kart”. Sorry for the lack of clarity and again, thanks for any help. I’ve actually thought if I can’t find a solution here I might just go back to some Nicd packs- could use the same charger but there would be much less circuit protection involved.

Well, all I can say is that you are sort of a pioneer. “Going where no one has gone before” :slight_smile:

Don’t forget, the Star Trek Enterprise was powered by di-lithium crystals. We, in this Century, are still stuck with only lithium.

So you want over current protection on two Ryobi packs in series? There might be some guru here who knows how to do that but generally speaking that’s more power (both volts and amps) than your average flashlight. Maybe ask the question on an E-bike forum, I imagine they would have a better knowledge bank for this type of application.

You’re putting two black boxes end to end. The protection circuits inside each are designed for the voltages and currents they were made to charge and discharge with and those circuits monitor each cell or pair of cells in the pack which probably can’t be easily done with something added on to the outside of both. It would be better to build a new pack with the cells and protection circuit designed for your new voltage. Otherwise your kids are Guinea pigs for a questionable and possibly very dangerous idea. 12-36 is another 300% uptick so I wouldn’t go there. Try starting with a higher voltage motor from a 36V lawnmower. You can use the charger and cells already made for it. Put a V-8 in that gremlin.

Ok. Having the same ryobi battery nuking problem when running in series. But… so far only the genuine batteries have nuked. The ebay knock offs seem to still be ok so far. Running 36 volts on kids peg perego diablo.