BMS Balancing "optional"
- Thread starter WheezyRider
- Start date
Isn't there supposed to be an increase in temperature when the BMS is in the balancing phase? According to the shiny new Neoteck DMM and cheopo food thermometer gaffa taped to the top of my battery case, there isn't any increase in temperature during an hour after the charger light goes green, so perhaps my BMS doesn't have a balancing function? Ambient air temperature is 22 degrees C. Fully charged voltage as measured by the reasonably accurate ANENG 8008 is 42.05V, so perhaps no balancing is required? The DPC18 display is off, says it's 41.8V.
I bought these needle probes in the AliExpress sale, so if I'm feeling brave may measure cell bank voltages at some point.
I bought these needle probes in the AliExpress sale, so if I'm feeling brave may measure cell bank voltages at some point.
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Yes great fun. My guess is that if the cells are already in balance the BMS blocks the charging current rather than bleed all cells evenly. The battery and thermocouple need thermal insulation, balance current is small and the cells will warm up during charging. But what if you were to open the pack, discharge one group by a known amount and measure directly on the BMS?
You won't see any temp difference during balance as the balance current used is very low , 100ma or so. There is no big current transfer so no big heat transfer, if you want to measure heat connect a pair of batteries (same nominal ) with different SOC in parallel .
I'd certainly do that, if I had another BMS which definitely does balance, to replace this BMS with, if it turns out this BMS of mine doesn't actually do any balancing. I wouldn't mind a 30A BMS, so I can use the 25A continuous @Nealh said my battery is/was capable of producing, instead of it's current 22A. On the other hand it's a bit shagged out now, so maybe I shouldn't demand too much from it.
I've just fitted the AliExpress needle probes to DMM leads, so I might measure cell bank voltages next "balance" charge.
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You have to put your finger on the resistors to see if they're warm. I doubt you'd get anything on the outside of the battery.
Like @Woosh's BMS, the heatsink is riveted on. This is my only BMS, so I'm not going to drill out the rivets. Plenty of bleeding resistors, but I don't know which are bleed resistors.
I feared the BMS connector had been glued on...
...but it wasn't.
I don't fancy measuring cell bank voltages again anytime soon, my Central Serous Retinopathy addled eyes really aren't up to it. According to my shiny new and reasonably accurate ANENG 8008, the readings are:
4.195V
4.195V
4.198V
4.192V
4.197V
4.193V
4.196V
4.192V
4.189V
4.191V
The manual which arrived with my battery says I should charge while the battery is switched off, so I did this time. It's been a few hours, and the battery pack now measures 41.91V. My question for you clever battery boffins is: Has there been any balancing?
I feared the BMS connector had been glued on...
...but it wasn't.
I don't fancy measuring cell bank voltages again anytime soon, my Central Serous Retinopathy addled eyes really aren't up to it. According to my shiny new and reasonably accurate ANENG 8008, the readings are:
4.195V
4.195V
4.198V
4.192V
4.197V
4.193V
4.196V
4.192V
4.189V
4.191V
The manual which arrived with my battery says I should charge while the battery is switched off, so I did this time. It's been a few hours, and the battery pack now measures 41.91V. My question for you clever battery boffins is: Has there been any balancing?
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Apart from PCs, I've vigorously avoided having anything to do with the innards of electornic things all of my life, and practically know very little about this stuff. I usually stick to mucking about with software, and things of no discernable purpose. While reading these forums, long forgotten memories of physics lessons many decades past occasionally become unearthed. The only reason I learned to solder sortof properly a couple of years ago, is because I got an ebike and suddenly had to. There's also the curiosity factor. I think it's like the dustbin man training course - you pick it up as you go along.
Guerney your ten cell groups show the battery is perfectly well balanced as all are 4.19v or as near as damn it, One won't see balance much closer then the 0.01v you are seeing.
One can check whether balancing will occurr by checking the ten cell groups as it nears final charge voltage to see how close they are.
One can check whether balancing will occurr by checking the ten cell groups as it nears final charge voltage to see how close they are.
Yours has bleed resistors, as seen in the third photo. Typically, you'll see them in a row across the pcb, with one for each channel. In line with them are rows of other components that do the voltage sensing and switching, again one for each channel. Those rows of components start at the connector end.
The 2nd photo shows the shunts that measure the current - 5 x .005 in parallel = 1 x .001 to keep the temperature down.
Thanks nealh, it's good to know this pack composed of relatively inexpensive LG MH1 cells has held up well after at least 4,090km, with many full charges (first couple of years) and more recently some partial charges because charging takes so long. I'd rather wait and charge safer at 2A, than charge at a higher rate.
Thin silver needles on small white connector were quite hard to see, so I've put some heatshrink over the needles for next time, using a couple of those ultra thin heatshrink tubes they always package into sets I never normally find a use for.
I might also grab these while they're a quid or two cheaper than ebay, which the ebay seller may also ship from China:
That's a good idea - I can use my second DMM (Neoteck) or hook up one of these I bought in the AliExpress sale, if it turns out to be reasonably close to reasonably accurate.
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Intending to make my view of small things clearer and less scary, next time I measure cell bank voltages, I've just ordered this, when the price dropped temporarily to £10.06 for the short verson... so I ordered the longer version for a couple of quid more. Good offers like that (?) pop up in the AliExpress sales, and appear to disappear.
Can't be doing with crossed probes!
www.aliexpress.com
Can't be doing with crossed probes!
72LED 8X/10X NEW Illuminated Magnifier USB 3 Colors LED Magnifying Glass for Soldering Iron Repair/Table Lamp/Skincare Beauty - AliExpress 1420
Smarter Shopping, Better Living! Aliexpress.com
www.aliexpress.com
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Translated the text in the photo of my BMS, using Google image translate...
translate.google.com
...searched for the manual on their website, it isn't there, so I don't know if 22A is max current or max continuous.
Google Translate
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...searched for the manual on their website, it isn't there, so I don't know if 22A is max current or max continuous.
The magnifier mentioned in post #33 arrived yesterday, and I'm pleased to report they suprised me by sending the right version ie long, I was suprised further that the lens is glass not plastic, lens housing is aluminium, the clamp is mostly steel, the magnification provides a usefully clear view for the inserting of tiny pins into small BMS connectors.
I don't like that it doesn't run off the mains, uses USB instead, albeit 2A. The light isn't very bright, but bright enough held close, for close-up views of soldering and probing. I got the long version to easier keep my desk clear of kipple, but that will never be.
Well worth buying for those justifiably nervous of causing inadvertent catastrophic short circuits while attempting to measure ebike battery cell bank voltages - vast improvement over the warped view plastic lensed magnifier on my soldering "Helping hands", which can't be positioned at high enough elevation, and annoyingly changes position whenever I reposition the helping hands/crocodile clips.
When soldering things onto the bike in situ, this magnifier can be clamped to nearby furniture or stands etc. Here's are pointless photographs.
It's still on sale going cheap if solderists want one, it was about £2 cheaper last Sunday, might be again who knows?
www.aliexpress.com
I don't like that it doesn't run off the mains, uses USB instead, albeit 2A. The light isn't very bright, but bright enough held close, for close-up views of soldering and probing. I got the long version to easier keep my desk clear of kipple, but that will never be.
Well worth buying for those justifiably nervous of causing inadvertent catastrophic short circuits while attempting to measure ebike battery cell bank voltages - vast improvement over the warped view plastic lensed magnifier on my soldering "Helping hands", which can't be positioned at high enough elevation, and annoyingly changes position whenever I reposition the helping hands/crocodile clips.
When soldering things onto the bike in situ, this magnifier can be clamped to nearby furniture or stands etc. Here's are pointless photographs.
It's still on sale going cheap if solderists want one, it was about £2 cheaper last Sunday, might be again who knows?
72LED 8X/10X NEW Illuminated Magnifier USB 3 Colors LED Magnifying Glass for Soldering Iron Repair/Table Lamp/Skincare Beauty - AliExpress 1420
Smarter Shopping, Better Living! Aliexpress.com
www.aliexpress.com
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