Cheapest Active Cell Balancer Project

Batteries, Chargers, and Battery Management Systems.
markz   100 GW

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Re: Cheapest Active Cell Balancer Project

Post by markz » Jan 22 2019 3:50pm

Vanarian wrote:
Jan 22 2019 8:21am
Keep me updated if you go this route please!

Edit : Wait actually if you can parallel plug batteries on modules it should work no ? I mean : You usually use a single BMS for a whole battery pack. Can it be made ?
I am not going this route, I would just buy a BMS from Besttech for my new 18650-25R's sitting in front of me right now. Debating which way to build it with my tab welder from https://avdweb.nl/popular/spotwelder/diy-spot-welder I like 10S because it keeps the speeds down for me, but I do like the occasional twist if you know what I mean :wink: so I just might go 48V(13S) but I dont like the # 13 so I might go 14S but my Makita's are all in 5S2P so there is that, and I think 15S is too much. There is the throttle hack I can do to limit the throttle to what I want in terms of speed. Plus with the extra 5S to my existing 10S, I would get more watts but not more discharge current, because there is no increase in parallel strings, just an increase in voltage, but additional 5S would mean each 18650 can would have a lower discharge because more 18650's in series in each string. I hope I am not fuckingthat up, I am too often wrong in my daydreaming plans.

You are right though, this threads called the "Cheapest Active Cell Balancer Project" and its great for small packs, like my bicycle light, which is one Makita of 5S2P, 21V 3Ah hose clamped right to my hand bars. Usually I balance manually with RC Charger. Another option is $2 cell phone charger from the Thrift store. Which brings me to an idea I've had for months now. Buy a bunch of them cheap cell phone chargers, not sure what voltage they are and use them to balance charge to the same voltage if your cell phone chargers are all the same voltage.

I am leaning away from electronics work now. I did look into FOC controllers (better eff. and stuff, search Justin_le I read thatshit last night, forgot already :oops: ), but expensive. Next is the Sinewave but the price is higher then cheap generic. Lebowski Controller is a DIY, I've looked into, not into soldering up pcbs, I am comfortable with the noice cheap generic trap trapezoidal waveform produces. What I am into is modifying the current sense shunts. Can't believe I put up with shitty 30A's stock, upped it to 45A stock with shunt mod to nonmeasured guessimation 55-60A. 3 shunts at 45A add one in parallel so 60A.

Rambling and bored gets me chatty. Gotta ebike for some food and Home Depot.
Wait actually if you can parallel plug batteries on modules it should work no ? I mean : You usually use a single BMS for a whole battery pack. Can it be made ?
Paralleling batteries you need to be careful, they need to be very close in voltage. I like to do it within 0.10V otherwise the equalization of current/voltage between the two battery packs will highly discharge one area of the battery to equal out the other part. Basic info for the LiPo balance charging, on them parallel boards with lots of tiny connectors on them. Hobbyking has them.

My battery pack I just solder on the used stuff I buy, the new pack will be tab welded so I am used to paralleling, reconfiguring and such. Have never done a BMS before, like I said manual balance every now and then with ultra stable Li-Mn chemistries, dont go too low because they unbalance.

Gotta go, rambling over.

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Vanarian   10 kW

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Re: Cheapest Active Cell Balancer Project

Post by Vanarian » Feb 12 2019 11:32am

markz wrote:
Jan 22 2019 3:50pm
Paralleling batteries you need to be careful, they need to be very close in voltage. I like to do it within 0.10V otherwise the equalization of current/voltage between the two battery packs will highly discharge one area of the battery to equal out the other part.
Thanks for the tip ! Ok so as long as voltage tolerance is tight, it can be done ! Good to know, I should try that with two cells (if it blows, at least the whole pack won't go down).
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markz   100 GW

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Posts: 10885
Joined: Jan 09 2014 11:38pm
Location: Alberta Canada

Re: Cheapest Active Cell Balancer Project

Post by markz » Feb 12 2019 4:32pm

Vanarian wrote:
Feb 12 2019 11:32am
Thanks for the tip ! Ok so as long as voltage tolerance is tight, it can be done ! Good to know, I should try that with two cells (if it blows, at least the whole pack won't go down).
Yeah you can try it, just dont have too much of a difference between both packs.
Too much of a difference then there will be an uncontrolled flow of current from the higher voltage pack to the lower voltage pack.
The current would be so high it could damage the batteries.

I=(V1−V2)/(R1+R2)

3V - 2V = 1V
divided by
0.02 + 0.03 = 0.05 ohms
equals 20A

Whereas if you only have a delta difference of 0.10V then 3.0 - 2.9 = 0.1V divided by 0.05ohms equals 2A

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