Anyone use balancing PCB's ?

Batteries, Chargers, and Battery Management Systems.
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John in CR   100 GW

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Anyone use balancing PCB's ?

Post by John in CR » Dec 26 2013 7:20pm

I picked up a variety of these boards thinking they were BMS's, but what they do is constantly balance the pack at up to 50mA of current between series cells. There's no cell level HVC or LVC, so it doesn't carry any of the power or cut anything off. It just brings the cells all toward equal, and since it does so at any cell voltage the same PCB works for Lipo or LiFePo4 whether you charge to 4.10V or 4.15V or 4.20V it doesn't care.

I haven't heard of these things before, and I was wondering if anyone has seen or used them. I understand that they are used on some of the Chinese ebikes with the safe chemistries, so the bulk charger acts as the pack HVC and the controller as the pack LVC with a balancing PCB preventing the pack from getting out of whack until a cell dies.

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Re: Anyone use balancing PCB's ?

Post by torqueon » Dec 27 2013 7:59am

i just finished building and testing one. It works a charm. Its based off the lm431 shunt regulator and will shed 75 ma.

I bulk charge and as soon as one cell goes high, i turn down the amps to 75 ma and let the balance r level all the cells.

John in CR   100 GW

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Re: Anyone use balancing PCB's ?

Post by John in CR » Dec 27 2013 11:36am

Here are pics front and back of a 12s board set up for 10s. Let me know if better resolution is necessary.

I hope these puppies work out and that they use no current once balance is reached. Then I'll be able to get as close as possible to the convenience of my old Konion packs that don't have the oomph for my current ride.
Balance PCBs back sml.JPG
Balance PCBs front sml.JPG

dnmun   100 GW

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Re: Anyone use balancing PCB's ?

Post by dnmun » Dec 27 2013 12:35pm

can you test them to see what voltage they turn on the shunt transistor?

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fechter   100 GW

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Re: Anyone use balancing PCB's ?

Post by fechter » Dec 27 2013 12:39pm

Looks like a BMS board where they just didn't populate all the parts. I would question whether they really balance at any voltage. This could be tested. More typically, the shunt voltage is fixed depending on what chemistry you're using and it comes on when the cell reaches the set point.

With the 82 ohm resistors, you'll get about 50mA at 4.15v. If the charge current is higher than 50mA, the shunts can 'swamp' and fail to keep the voltage down. To really balance, you should charge at or below 50mA for as long as it takes to reach balance.

BesTech Power has an assortment of the balance only boards: http://www.bestechpower.com/
"One test is worth a thousand opinions"

dnmun   100 GW

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Re: Anyone use balancing PCB's ?

Post by dnmun » Dec 27 2013 12:47pm

bestechower won't sell just their balancing boards. i was able to talk henry into sending me that balance board for the D131 but he won't sell them. the one i got was for the lipo @ 4.2V so that was why i hoped he would test these to see what voltage they balance at.

John in CR   100 GW

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Re: Anyone use balancing PCB's ?

Post by John in CR » Dec 27 2013 7:34pm

They are the same boards used as BMS's with additional components, mosfets and whatnot from the pics I saw of Baleaf's BMS's. I need to get them connected to a pack and test if they really simply equalize the cells like I've been told.

I bought them thinking they were low power and cheap lipo BMS's with the intention of running only charge power from my solar modules to give me both balancing and a second level of charge cutoff, one top of charge limit with Fetcher's voltage cutoff, and a cell level cutoff. Then on the bike also wire up a visible or audible alarm that is tripped with the typical BMS cell level LVC. I hoped to obtain a reliable BMS functionality at minimal cost running only low power for my DC/DC converter thru the BMS. The idea is with only low current, what would kill the BMS?

Since they aren't a full BMS, now I'm trying to find a use for them. An any SOC any chemistry balancer seems pretty useful, so hopefully they work like I'm told.

John

John in CR   100 GW

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Re: Anyone use balancing PCB's ?

Post by John in CR » Dec 30 2013 7:13am

They balance alright, however (a big however), they keep drawing power and not evenly. I knew there was trouble when the largest black chips were all too hot to hold my finger on. I tried 2 of the 10s boards and they both behaved the same and continued the power draw.

I removed the duct tape from a 10s Konion pack I have. Amazing batteries...I taped this pack up back in 2009 after making sure it was balanced. It didn't see a lot of use as a range extender pack, but it hadn't been charged in a least 3 years. Every cell was still at 4.03v . So little self discharge and perfect balance is just incredible.

Back on topic, I discharged a couple of the 2p1s groups down to 3.9v and charged 2s2p up to 4.08v, and connected the balance board. It brought them into balance fairly quickly at 4.01v each, and since those chips were hot, I left it connected. 6 hours later the 3ah pack was down to 3.92v per cell except cells #1 and #6 . #1 was down to 3.82v and #6 was at 3.87v . Those weren't the cells that I knocked out of balance to start the test.

I'll try to get more info about the boards, and see if they behave differently at LiFePo4 voltages, but for now they aren't useful to me. I could live with a very slight power drain on a daily rider, but not that creates even a slight out of balance. Also, I didn't like how hot those chips were in open air. Closed up inside a battery enclosure seems begging for some kind of failure. After all heat is the enemy in our systems, though I guess the poor souls living in places cold now don't mind a bit of heat.

I'll update the thread if I find out anything useful.

dnmun   100 GW

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Re: Anyone use balancing PCB's ?

Post by dnmun » Dec 30 2013 9:54am

if they are lifepo4 balancing circuits then they will drain your lipo or konions down to the 3.6V level.

you can measure the cell voltage where the shunt transistor turns on to determine what they were manufactured for.

if the shunt transistor turns on at 4.2V then they are made for lipo balancing and if they turn on at 3.6V then they are made for lifepo4 balancing.

John in CR   100 GW

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Re: Anyone use balancing PCB's ?

Post by John in CR » Jan 02 2014 12:33pm

Quick update:
The 10s boards are in fact for LiFePo4, and each channel bleeds off at about 50ma if the voltage is above 3.65V +/-.01V . I'll check the other boards to see if they are all for Lifepo4 and all work the same. Right now my excitement level is pretty low, since I was expecting boards that balance a pack at whatever the average cell voltage is, less a small amount for losses.

I don't want to have to charge all the way to 100% just to get the balancing to kick in. Don't the electronics guys who come up with this stuff understand that charging batteries conservatively is a big component in greatly extending their useful life?

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