Ryobi 18V lithium battery: charging without original charger

Thread Starter

ju1234

Joined Sep 15, 2018
13
I was trying to see if I could charge the Ryobi P102 Lithium battery without the original charger (a working battery). According to some videos I have viewed, all one needs to do is attach charging current, 20 or so Volt to the + and - terminals of the battery. I let the battery drain to 18V. Then I connected 19.2V from a laptop power supply, positive to battery marked + and negative to battery marked -. But it did not work. So, I searched a little further. The battery post has 3 terminals. 1 on the side marked with + , one on the other side marked -. The third one in front (or you can call it behind) is not marked. Commonsense would say that the charger should have current between the corresponding +/- terminals. NOT SO. In the charger, I connect the probes of the meter to the two side terminals. It shows no current. But if I touch the one in the front to one of the two on the side, I get 3 volt, the front one being positive. So front-left is 3V and front-right is 3V. And this thing charges an 18V battery.

Can any one please explain the above. And how would 3V charge a battery to 20V or so?

Any one knows a way of charging this battery without owning the charger and without having to open the battery to charge it. Thanks.
 

MrAl

Joined Jun 17, 2014
8,245
Lithium ion charging of a pack that has higher voltage than one cell has to be done very carefully. That is because the cells when powering the drill have to be connected in series. If they are kept in series that means they need careful monitoring so that one cell voltage does not go too high. This is very different than charging the old NiCd or NiMH cells which can put up with some overcharging. Li-ion cells are not like that and can get very hot if not charged properly.
With this in mind, it is going to be a risk to build a home built charger unless you are an expert in this area. Cell voltage should be monitored as well as cell temperature.
Maybe you can find a used one on a site that sells stuff. That would probably be the best bet.

Even better, go out and buy a quality drill. I bought a Ryobi several years ago and got two battery packs with it. They both went dead very soon afterward. I had to replace the cells and build my own charger to keep them topped off without damage because the charger that came with it just keep charging and charging. Never buy Ryobi again. I went to a Makita Li-ion type which works well and i had it for a while now too. My dad long time ago had a Makita too and it worked well for a long time too that's what sold me on mine. Came with a fast charger too.

So after all is said and done, it may not be worth it to even bother with a Ryobi just a waste of money.
 

Thread Starter

ju1234

Joined Sep 15, 2018
13
Is this the same battery?.

Yes. There is nothing wrong with my battery. In the charger it charges fine. It is just that I don't own this charger and I am going to use this battery for other purposes, other than Ryobi tools. So, I want to be able to charge it without the original charger. Is there a way I can allegator clip it and charge it. Either with a standard 19V (Laptop) charger, or I have a Black and decker 18V chager that has 4 prongs on it. #1 longer prong and other 3 shorter ones. The meter reads #2--1 and 3--1 as 5v each (#1 being negative) and 0 between #4--1. Can I alligator clip those to the 3 terminals of battery, will that work? Which to which? Thanks.
 

eflyguy

Joined Feb 10, 2021
7
The balancing logic is built into each battery, and there is some kind of communication between the in-battery charge controller and the charger that prevents charging by just hooking up to the +ve and -ve connections. I've done some research on this and have not come across any definitive information on how to make this work.

Personally, having switched to Ryobi tools many years ago, I have a bunch of chargers I never use. I've had one battery fail since I switched, I think 7 years ago. I have a total of 6 good batteries that are all about that age. They are good value, and the tools are great - I have virtually every one they make.

Anyway - I am sure someone local to you would have a spare charger they could sell. Don't know where you live but in the US we have a local marketplace called Craigslist where stuff like that is available. eBay might also be an option.
 

MrAl

Joined Jun 17, 2014
8,245
The balancing logic is built into each battery, and there is some kind of communication between the in-battery charge controller and the charger that prevents charging by just hooking up to the +ve and -ve connections. I've done some research on this and have not come across any definitive information on how to make this work.

Personally, having switched to Ryobi tools many years ago, I have a bunch of chargers I never use. I've had one battery fail since I switched, I think 7 years ago. I have a total of 6 good batteries that are all about that age. They are good value, and the tools are great - I have virtually every one they make.

Anyway - I am sure someone local to you would have a spare charger they could sell. Don't know where you live but in the US we have a local marketplace called Craigslist where stuff like that is available. eBay might also be an option.
Show us some pictures maybe one will be the right one for the OP.
 

kennybobby

Joined Mar 22, 2019
75
There is communication over the T1 tab between the pack and the charger which prevents using anything else to recharge a pack. i reversed the 40V packs and posted schematics over in the diy electric car forum; the 18V packs are nearly identical.
See here for more details, Ryobi pack schematics
 

MrAl

Joined Jun 17, 2014
8,245
Hello again,

If i was going to do a professionally designed multi cell pack i would definitely include feedback from each individual cell so i could monitor each cell and make sure there was no problem that would cause overheating and fire. This i believe a lot of manufacturers have done including Makita. Now on that pack i have i think the two main terminals are available where you might be able to charge using a high enough voltage source with current limit, but there would be no individual cell monitoring and so i think it would be a mistake. Is it that each cell has built in protection? Some cells do, but a lot of the higher current ones do not. That means it would be a risk for me to try to charge it that way thus i would never do it. Maybe at lower than usual current? I dont know, i'd have to think about that one. Cell over voltage could still occur meaning that there could still be a problem. At the very least i think the cells would get damaged so they would no hold a charge anymore.

Maybe measuring each and every terminal on the battery pack would reveal what each pin does. If there is hjgh tech electronics involved though it may depend on a data connection between the charger and the pack and that would be hard to duplicate without exact specifications for that pack.
 

kennybobby

Joined Mar 22, 2019
75
There are 2 big mosfets on the negative terminal side in the battery pack which must be ON for the pack to charge or discharge. These are controlled by 2 separate devices, one is a microcontroller and the other is a BMS chip, and they will shut down the pack for any anomaly.

So the + and - tabs on the battery housing that connect to the tools do not directly connect to the cells; that is why you can't charge one of these packs just by putting a power supply on the terminals.
 

eflyguy

Joined Feb 10, 2021
7
.. and the balance control is built into each battery.

The "charger" doesn't really do much more than provide the power needed, but it won't do that unless the pack communicates that the pack is ready and safe to charge - and the packs won't charge, unless there is good communication with the charger.

It's quite well designed - and pretty much makes trying to charge them as-is impractical.

Buy a used charger for $15, or buy a handful of 18650 cells.
 
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