24s BestechPower BMS Thread

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

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Re: 24s BestechPower BMS Thread

Post by dnmun » May 29 2013 11:06am

nono, not me. i usually will tape the plastic felt stuff onto the bottom pcb of the BMS to prevent it shorting to something but i always wanna be able to remove components and replace them so the plastic film is a problem.

but many BMS do have a thin layer of clear insulating film all over them. some controllers too.

post up a picture of the BMS and show how you were able to get around the problem of the shorted mosfet on the charging bank of mosfets.

i have been able to get the BMS to balance some outa balance cells but it takes alotta time. you should measure the gate voltage of the charging mosfet to see if it is still turned on when you are trying to make it balance and it seems to stop. if one cell is too high then it will block the charging and it can only balance by draining down then so it is slower. jmho.

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Bazaki   10 kW

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Re: 24s BestechPower BMS Thread

Post by Bazaki » May 29 2013 11:28am

I'll check the mosfet.

As for the liquid tape from plasti dip, you can peel it of without problems, just see it as liquid shrink tube.

You can dip your phone, car, and now also your BMS or Lipo, but that is just my opinion :mrgreen:

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Re: 24s BestechPower BMS Thread

Post by dnmun » May 29 2013 11:39am

you can spray shellac or polyurethane too and seal it that way but i worry about the heat from the shunt resistors.

on the BMSs where i have seen the shellac on the balancing shunt resistors it never seemed damage the shellac unless the resistor was obviously cooked and overheated. then the shellac looked all cloudy and foggy. but still intact. it is hard to burn with the soldering iron too if you try to unsolder the shunt resistor.

ps: i have abuncha those 100 ohm 2512 shunt resistors too now. a bunch.

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Re: 24s BestechPower BMS Thread

Post by izeman » May 29 2013 11:49am

Bazaki wrote:About the balancing I'm not sure, the resistors don't get hot anymore and I manually imbalanced cell 6 so one 6s pack has about 40mV imbalance and it doesn't seem to happen that the BMS is balancing it.
are you sure the cells are charged high enough? if this one cell is below the balancing voltage nothing will happen. all cells are pulled down to the balancing voltage of imho 3.6V for lipo. so if this one cell is below 3.6V nothing will happen. that's ok.

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Re: 24s BestechPower BMS Thread

Post by dnmun » May 29 2013 12:21pm

it doesn''t work quite like that. the cells that climb above the shunt transistor turn on voltage don't just immediately drop that voltage. you have the charger voltage, say it is maxed out at 63V for 15S in my case. and 14 have a voltage of 4.21 then the low cell can be .14V below 4.2 and the charger cannot push more current than just the balancing current. and 140mV of lipo is a lotta charge to deliver so it takes time.

but i don't yet have a handle on how the D131 works yet. i am gonna talk to silverheels and see if i can build up this 24S lipo pack using some JST plugs on the sense wires and attach it to the top of his packs like sacko is doing. then i may learn something about how the D131 works.

i still have not figured out how to do the 20S hack and conserve the HVC and LVC functions. may work that out today.

just overcharged my 15S to about 4.22-4.23 up to 4.24 on the 5200mAh pouches to see how long it takes to drain it off. but this just charged up so the mobile charge is still showing on the meter.

the cells already seem close since they have a .001V variation since the group of 5200mAh pouches are different so they don't count.

but the losest, shortest cell is only 3.85Ah and the highest is 5.2Ah so it was able to balance and protect the pack with that range of capacity. it shut off when it dropped below 2.7V under load of 5A. 1C.

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Re: 24s BestechPower BMS Thread

Post by sacko » May 29 2013 3:54pm

My BMS 900w charges up to 99.4v (as requested when ordered), but the green light doesn't come on when the charge has completed, as it says its meant to. It remains red and turns off.

Is this what it's meant to do with the BMS?

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Re: 24s BestechPower BMS Thread

Post by dnmun » May 29 2013 9:41pm

both of the leds remains red even when the charger is not pushing current? do you have an ammeter in the charging line so that you can measure the current flowing into the battery?

you can raise the charging voltage up to 100.8V if you are using the bestekpower BMS and it will balance around 4.2V/cell.

i burned up my 15S BMS by sending twice the maximum current through it. i put 5 of my 1500W electric heaters in parallel to discharge the little 5A 15S lipo pack which i charged to 63V and it pushed 30A briefly and it fell off to 25A then down to 20A as the voltage dropped but by then i had accidentally shorted 48v of the battery to the middle of the BMS when i let a loose alligator clamp slip and fall on the BMS, pop pop, but it looks like it hit in the top of the balancing circuits and only about 3-4S or 12-15V away so i hope there was not enuff voltage difference to damage one of the shunt transistors.

but that BMS is now ready to be rebuilt, ruined in one day. initially i had burned one of the three discharge mosfets, that seemed wrong that only 30A would cause on of them to blow. so after i cut the leg off the shorted one i restarted the discharge, and burned up the second one in no time. i thought these 4310 mosfets would handle more current than this.
Attachments
DSC01626.JPG
cut mosfets legs
DSC01626.JPG (148.28 KiB) Viewed 1338 times
DSC01627.JPG
removed shorted mosfets and remove BMS from battery
DSC01627.JPG (147.34 KiB) Viewed 1338 times

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Re: 24s BestechPower BMS Thread

Post by dnmun » May 30 2013 12:39am

tried a hack on the 24S BMS to cut it down to 20S, but no gate voltage on the discharge mosfet. it charged up to 82.6V and stopped when one cell got to 4.25v and is now draining back down to 4.15 before turning the charge on again. i can see the charging gate voltage swing up to 6v above the source. but the discharge mosfets have the gate voltage stuck at 3.77V or so, much too low and i think is turned off. in fact i think the charging gate voltage should be higher.

but i decided to hack this by lifting the resistor on the HVC and LVC signal lines on the channel above my last cell, so for 20S i went to the resistor that connects the LVC signal transistor and the HVC signal transistor to the signal lines running across the top of the BMS on channel #21. i thought this would give me a good gate voltage, not sure why it did not work.
Attachments
DSC01630.JPG
if you look closely on channel #21, you can see the missing resistor on the LVC signal line and at the very top the resistor is lifted and turned sideways and one end left attached but the link is open on the HVC signal line
DSC01630.JPG (150.1 KiB) Viewed 1347 times

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Re: 24s BestechPower BMS Thread

Post by sacko » May 30 2013 2:16am

Yup, its not going green. I need to get an ammeter to check amp draw, is there a way to use the CA as a charge meter?

Image

Image

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Re: 24s BestechPower BMS Thread

Post by izeman » May 30 2013 3:40am

isn't that an ampmeter in the second picture? sorry, it's so blurry and dark that i just can't identify it.

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Post by chroot » May 30 2013 5:19am

No, I'm seeing 99.2V on the multimeter in second blurred picture.
izeman wrote:isn't that an ampmeter in the second picture? sorry, it's so blurry and dark that i just can't identify it.
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Re: 24s BestechPower BMS Thread

Post by sacko » May 30 2013 5:31am

Sorry, didn't notice the picture quality was as bad as it was until I logged on to the computer.

It is a voltmeter reaqding 99.2v.

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Re: 24s BestechPower BMS Thread

Post by izeman » May 30 2013 8:35am

sacko wrote:Sorry, didn't notice the picture quality was as bad as it was until I logged on to the computer.

It is a voltmeter reading 99.2v.
ok. so voltmeter only. that's bad. a multimeter capable of measuring amps, resitors, checking diodes etc, is almost the same price, and looks the same.

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Re: 24s BestechPower BMS Thread

Post by sacko » May 30 2013 9:45am

It is meant to measure amps etc, it just doesn't work :)

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Re: 24s BestechPower BMS Thread

Post by dnmun » May 30 2013 9:51am

you would have to use the 10A range on the meter and switch the red prob over to the hole that says 10A.

but the red on the #2 led means it still has current flowing or the op amp will turn off the fan and the red of the led.

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Re: 24s BestechPower BMS Thread

Post by dnmun » May 30 2013 10:59am

finally got my 20S pack to balance. first balance. 84.1V charger, shunt balancing current just dropped below 50mA, all the cells are either 4.20 or 4.21V so that seems like it is fairly close in balancing. it gets really warm when all of the shunt resistors are carrying the full 170mA of balance current. but that helps it balance fast.

gonna remove it from the charger and watch the drain down and see where it ends up and then try a discharge.

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Re: 24s BestechPower BMS Thread

Post by izeman » May 30 2013 4:19pm

sacko wrote:It is meant to measure amps etc, it just doesn't work :)
maybe post a picture of the whole device, and we can show you what to connect where, and how to set it. just in case you don't have the manual. or if you know that it's broken, just ignore my post ;)

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Re: 24s BestechPower BMS Thread

Post by izeman » May 30 2013 4:22pm

dnmun wrote:..it gets really warm when all of the shunt resistors are carrying the full 170mA of balance current. but that helps it balance fast...
now that you know it gets cooking hot, you're still confident that it will get no problems? even though "resistors get warm for their living", it's still VERY hot. you know i want to be really sure that all is ok before if bolt things together and forget about it.

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Re: 24s BestechPower BMS Thread

Post by dnmun » May 30 2013 4:23pm

finally did the first discharge on this 20S pack and now that low cell seems rejuvenated. i got almost 5Ah outa these cells this time.

started at 35A discharge, 84V about 2700W into 5 of my electric heaters. the extension cord i plug the heaters into got warm, the shunt in the cheap watt meter got a little warm, but the D131 did not show any increase in temp. nothing i could detect. the battery got warm, but not the BMS. from 35A down to 27A. took maybe 10 minutes to discharge the entire 5Ah.

resting voltages after cutoff all about 3.6-3.7V.
Last edited by dnmun on May 30 2013 4:30pm, edited 1 time in total.

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Re: 24s BestechPower BMS Thread

Post by dnmun » May 30 2013 4:28pm

izeman wrote:
dnmun wrote:..it gets really warm when all of the shunt resistors are carrying the full 170mA of balance current. but that helps it balance fast...
now that you know it gets cooking hot, you're still confident that it will get no problems? even though "resistors get warm for their living", it's still VERY hot. you know i want to be really sure that all is ok before if bolt things together and forget about it.
it is not too hot to put your fingers on it. the big 5W resistors on the headway BMS would get hot fast when the shunt transistor cut in. this was an unbalanced pack and i overcharged to 84.4V to force it to fill all the cells up to full. then as it finally balanced them and all the temps went down i then reduced the balancing current by adjusting the charger voltage back down to 84.1V.

i was worried that my hack from 24S to 20S might not work because i could only guess about how the circuit worked so now that i know how to do that then if someone has a cell blow out and needs to drop the cell count then there is a fix for it. except that resistor is so tiny, so tiny~!!
Last edited by dnmun on May 30 2013 4:31pm, edited 1 time in total.

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Re: 24s BestechPower BMS Thread

Post by izeman » May 30 2013 4:29pm

dnmun wrote:...but the D131 did not show any increase in temp. nothing i could detect. the battery got warm, but not the BMS....
same here. pulling 45A through it, it didn't get warm at all.

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Re: 24s BestechPower BMS Thread

Post by sacko » May 31 2013 2:29am

Thanks guys :)
The manual didn't state those locations for the leads.

http://www.pollin.de/shop/downloads/D830348B.PDF

Something like this

Image

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Re: 24s BestechPower BMS Thread

Post by dnmun » May 31 2013 2:36am

no, put the dial on the 10A position. you have the red probe in the 10A plug so set the dial to 10A.

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Re: 24s BestechPower BMS Thread

Post by sacko » May 31 2013 2:37am

On a different note; my BMS doesn't get hot either. The are brand new packs and have been cycles a couple of times on my Cellpro PL6. The LED on the charger now goes green, I was just prematurely disconnecting the charger.

Love this setup and all cells are remaining balanced.

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Re: 24s BestechPower BMS Thread

Post by dnmun » May 31 2013 2:45am

it should only get hot from the shunt resistors and that is brief except when the pack is first balanced and then some of them stay on for a long time.

i was surprised when i burned up the mosfet on that D126 even though i was twice the legal limit. i figured those irf 4310 mosfets would handle 30A of current each, not just barely 7-8A like it seems like they did.

i find the lipo is easier to balance than the lifepo4. i think the standard deviation for the final balanced spread is less then half a millivolt.

you can charge the 24S lipo to 100.8V+

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