Author Options:

What powersupply or charger should I use? Answered

It is for a battery pack for a cordless drill made of good sony high drain cells from "died" makita packs. It is for another drill then makita.

I found this bms:


Should I use an Imax charger, or a regular notebook charger, about 19-21 volts?



I am guessing your Makita(r) battery pack is a series stack of 5 Li-ion cells, and this is why you are looking at a 5S BMS (battery management system).

Specifically you are wondering about the character of the charging source needed for this BMS. I think the answer to this is revealed in the first line of the "specification" table in the item description, although it is a little cryptic.

It says test item, "Charging voltage", wants criterion, "DC:22.5-25V CC/CV"

My interpretation of this, "DC:22.5-25V CC/CV", is it symbolizes a battery charger capable of implementing a real charging algorithm; i.e. constant current during first part of the charge, followed by constant voltage during the second part of the charge. The actual algorithm itself, I have seen described here,


Quote: "The basic
algorithm is to charge at constant current (0.2 C to 0.7 C depending on
manufacturer) until the battery reaches 4.2 Vpc (volts per cell), and hold the
voltage at 4.2 volts until the charge current has dropped to 10% of the initial
charge rate. The termination condition is the drop in charge current to 10%.
The top charging voltage and the termination current varies slightly with the

The ImaxB6(r) charger is what I would call a real battery charger, since it implements this CC followed by CV charging algorithm. In contrast, the power brick for a notebook simply supplies constant voltage, CV.

(I assume the CC-followed-by-CV algorithm needed for actually charging Li-ion batteries in an actual notebook computer, is provided by a circuit board inside the notebook.)

So I am guessing the ImaxB6, will work for this, and a constant-voltage laptop charger will NOT work.

By the way, I actually have one of these, a Imax B6, but I have only used it once or twice, because I, myself, am still figuring out Li-ion batteries, and the chargers, and protection circuits (also called BMS) for the same.

Well, I guess that's another BTW: You're getting advice from someone who is NOT an expert regarding building Li-ion battery packs. I'm still figuring this stuff out myself.

The part most confusing to me, is the question of overlapping rules of the BMS versus those of the battery charger. Or is there a possibility these rules could conflict, so that the BMS and battery charger start fighting with each other?

I think perhaps these rules are sort of chosen carefully, so they don't overlap. E.g. the termination voltage the ImaxB6, according to the manual, page 15, is 4.1 volts per cell, for Li-ion cells, but the voltage at which the BMS senses an overcharge condition, is intentionally set higher than this, at 4.325 volts per cell, according to the spec table on its eBay item page.

Also I am guessing maybe this is why the cell balancing connections are attached to a little plug. That is so the plug could be attached to BMS, or to the charger, but not both at the same time. My fear is that if both balancing circuits were connected to the battery, they might try to fight each other, and maybe that is the reason why the balancing connections are (often) connected to a little plug. So the user can choose one or the other, BMS or charger, to do the balancing.

Final BTW, it looks like there might be some Instructables linked the related panel on the right there, ----->

I haven't read them yet, but maybe some of those can more clearly inform, or answer your question.

ok but when using an imax charger without bms, the cells are not protected. i dont want to drain them empty and causing damage. or is therē something i can use to protēct them till about 2,5v reached and max 10a drain?

can i use then a regular charger for ni-cd 18v drill battry?


I think the thing needed for protecting a series stack of 5 Li-ion cells is a 5S-BMS, like the one sold on eBay you linked to above. This board gets permanently attached to the 5 cells, and then the main job of the BMS is to protect them from over-discharge while they attached to a load, i.e. powering your cordless drill, or whatever; i.e when the cell voltages get too low (typically, 2.5 volts per cell), the MOSFETs on the BMS are switched into open state so the load, the drill motor, cannot draw current from the cells.

Regarding the charger, for charging a stack of Li-ion cells you want a charging algorithm intended for charging Li-ion cells, NOT one with algorithm intended for charging Ni-Cd cells.

Li-ion and Ni-Cd do not have the same charging algorithm strategy. Compare:



So I would expect 18V charger for Ni-Cd drill battery to NOT work for charging a stack of Li-ion cells.

but as you said, would an IMAX charger do the trick or should it fight each other?

I think when cc CV algorithm is send to BMS the BMS would do nothing wrong except when it's little different in algorithm

I think it will work.

I mentioned I actually have that ImaxB6. I don't have any 5S Li-ion battery packs that I could test with it.

Although I do have a 3S Li-ion battery pack. It is not homemade. It is a HarborFreight(r) brand battery pack, made for one of their cordless drills:


Taking this battery apart, reveals it is a 3S stack of 18650 Li-ion cells, attached to BMS board that came with it.

I am willing to try charging this 3S battery pack with my ImaxB6, and also write back and tell you if that worked or not.

thanks man, i will be happy with the results. I have to create a 12v pack too but first things first. I checked my drill ni-cd charger and says its compatible for 9.6 12 14,4 and 18 volts. So it seems to be a smarter charger but for ni-cd. Can it charge ni-mh also?

Is harbour freigt a good quality product like makita or more like let's say low budget or in the middle like black and decker?

I discovered my ImaxB6 charger, and 3S HarborFreight battery, do NOT work well together.

Bascially what happens is, I set up the ImaxB6 for the parameters it wants for charging a 3S Li-ion battery, connect to the it to the battery pack, then press "start".

Then, after about 5 minutes, the ImaxB6 goes be-be-bee-beep to anounce a successful charging cycle. Horay! The battery is fully charged!

But of course it isn't. Something is going wrong. I am guessing the BMS on the battery is doing something, like maybe disconnecting the battery? I don't know. However, I have tried this a few times, getting the same result: Charging starts, but stops prematurely after about 5 minutes, without charging the battery pack.

Regarding your question about the overall quality of HarborFreight(r), as a brand. Basically HarborFreight sells cheap tools. Typically they're the store that has the lowest prices, and also typically the lowest quality.

Actually, HF's reputation, for marginal just barely working tools, is well known. Or at least this reputation is well known in the Former US. But your profile says you're in the Netherlands, so maybe you had not heard of HF yet? Broadly speaking, they're the lowest of the low that's still well known. I'd say they're lower than Black and Decker(r), which itself is lower quality than Makita(r), which is essentially good, high quality.

This 3S-Li-ion drill I got from them, it seems to be pretty well put together. I've had it for a few years, and I haven't broken it yet. Although I did have one of its battery packs die mysteriously. I think its BMS failed, with the cells still good.

Anyway, I'm not sure what else to tell you about your battery charging plans, except maybe there are better answers still yet to found. Maybe in 'ibles people have written on this topic, like in the "related panel" ---->, or even other non-Instructables tutorials and blogs out there.

Some notes on the attached pictures: The first pic shows my setup for discharging this battery pack, through a 50 ohm resistor. The second pic shows the end of the failed charging attempt. Note the elapsed time on the display: 5 min + 6 sec.

The white thing I am using for a battery connector is homemade. It is a C-shaped piece of PVC pipe. It sort of clamps onto the battery pack, and holds in place the contacts, made from brass machine screws.


ok did you discharge the battery complete empty?

I als think the bms stops the IMAX from charging.

But Yeah hoe to solve this issues, maybe the bms is the cc-cv component, battery management system. So II think it will work with a regular power supply would do it?

The battery was pretty well discharged. After serveral attempts at charging it with ImaxB6, I plugged it into the HarborFreight(r) charger it came, and that charged it without any problems, in about an hour or two.

All I can conclude from this is that ImaxB6 and the HarborFreight BMS do not play well together. However, I think it would be a mistake to generalize this experience to every other BMS out there.

Also consider, the battery of Li-ion cells and the BMS do not have to be permanently connected, married together. This is the way cordless drill manufacturers do things, but it doesn't have to be done that way. I think for RC (radio controlled) toys, the BMS is on the toy car, copter, etc, and the battery consists of cells + power connector + balance connector. Thus for RC toys, the BMS stays connected to the toy, and is not connected to the battery while the battery is charging.

Another strategy for making things easier to take apart is to use cell holders. For example, this 'ible,
Noblenutria is using cell holders for his 18650 cells. His reasons for doing this, he says, are to facilitate removing failed cells, and also this is easier than spot-welding tabs onto cells. Actually this 'ible looks to me to be similar to your plan, making a new battery from old 18650 cells.

Final note: I do not think the BMS you linked to is implementing CC-CV charging. Like I said before, I think an actual CC-CV charger, specifically designed for charging Li-ion battery, is needed.

hi, thanks for your reply.

I think I'm gonna try it with the BMS and an imax charger. I have to order them both so it will take a while to create this. About the holders, that wont fit in my genuine housing. First things first, trying to reanimate a bricked makita battery. I've now 20 good batterys from 30 pcs (3 packs) .

I will create an instructable for it if it all works :)

Well it depends, how many batteries do you have, how are they wired together (in series or parallel), and what are the volts and amps of each cell?

Hi, 5s5p they are 2000 or 2100 mah each cell

Ok thanks, and the voltage of each cell? (I'm guessing 3.7 but I'm not sure)

I loaded some cells individually and reached 4,19 volts.