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NiMH powertool upgrade
#11
(05-02-2019, 07:31 PM)daromer Wrote: The balance part for me is cruical. Especially if you run 2nd hand cells. A balance charger does not cost that much so.

I"m still getting used to all the terminology.  I know its a balance charger if it has wires going to each series connection right?  So the unit I posted above would be considered a balance charger?
Mobilis in Mobili
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#12
Multiple protective functions including overcharge protection, overdischarge protection and short circuit protection

If it provides these protective functions on each cell in series I think you are right it would be self balancing

Would like to get feedback on this board. I have been looking for something similar but hoping for half that cost.
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#13
Go for a BMS with balancer, and a relatively low-current PSU. Or grab two PSUs, a big one to top your batteries quickly and a small one (max 200mA) to allow enough time for the balancer to balance the battery. You may omit the BMS completely ONLY if you use a balance charger for charging, but you're running on extra danger of damaging a cell that way due to over discharge, however it won't catch on fire, fire happens when charging the battery.
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#14
Okay, now I'm confused. I've been thinking of BMS and Balance Chargers as being the same thing, but it sound like they are different or is it that the BMS is doing the balancing, but the power for the BMS has to come from a charger with a little more brains than, say, a laptop power supply.

So in the case of this board, I thought I could just plug in a laptop power supply to the provided power jack and this circuit would manage the rest. It does claim to have overcharge protection. IF that's not the case, how does a person determine what is needed?
https://www.amazon.com/5Series-Battery-P...way&sr=8-3

If this is the case it would represent a pretty good deal overall as I could salvage the PSU and then the battery would cost $11 plus batteries and materials.

Just found a good breakdown here: https://www.youtube.com/watch?v=c3Z77MYYhL8

In this case the circuit he uses (4:34) doesn't have enough wires to be a balance circuit, so he adds an additional harness to use his IMAX B6 for charging/balancing. Otherwise if he put it in the regular tool charger (if it worked at all) it would charge blind and could unbalance.

So this makes me think the circuit I've linked IS a balancing BMS, and as Thanar suggests I could use it and a low current PSU. So here I go, placing the order. I'll give it a shot and let people know how it goes. This will be my first battery build of any type...
Mobilis in Mobili
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#15
Follow-up!  I've received the circuit board.  



- There was no manual or data sheet of any type included but the board is well marked enough to figure out what goes where
- Model number is XL-MH9959.  
- MOSFETs are SM3116NA which are apparently rated for 30V and 60A data sheet (http://www.sinopowersemi.com/temp/SM3116...asheet.pdf)
- Main IC is BM3451, a 3/4/5 charging protection and balancing chip data sheet (https://datasheetspdf.com/pdf/1098180/BY...s/BM3451/1)
- Wire for main battery connections appears to be 16AWG which is sufficient, but all the wires are very short and may need to be replaced
- The battery clips showed no hint of copper, unlike a Makita charging board I was comparing it to, so I thought maybe I'd got nickel plated steel, but after filing one of the clips there was copper in there.

So it seems legit and likely it will be able to handle the 20A it was marketed as rated for.  If anybody spots anything fishy or want more part info let me know.

Looking up the model number there is a blog from someone in Hungary reviewing the board for use in a DIY Drill Battery Build - update 2018-4-25 (https://electrodiy.blog.hu/2018/03/31/ak...sa_hazilag).  Google Translate does a decent job and it sounds like he he was happy with it after a few modification to work with his drill and charger.  

I plan to be making some modifications as well.  I'm hoping to set this up to be charged by a 20V lenovo laptop charger. Building the actual battery to go with it is going to be a bigger challenge.  I have the cells from other power tool batteries, but tossed everything else before I knew that tools often use thicker nickel or nickel plated copper for their connections.  I could have reused the nickel plates if I was more careful tearing the pack apart.  Going the straight nickel route (if I can find any, still looking) at 20A peak with 2p pack will require 2 layers at the series connections...probably going to end up looking ugly, oh well, function first.
Mobilis in Mobili
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