BMS alternative cell level charge protection only.

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

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BMS alternative cell level charge protection only.

Post by Ykick » Jul 29 2016 8:44am

Most of this posted in another thread viewtopic.php?f=14&t=82228 but I don’t wanna derail that fella’s topic and maybe those interested might not see it over there?

Anyway, the deal is with my RC Lipo commuter pack I feel better using cell level charge protection. As the years tick by I’ve come to realize discharge protection isn’t nearly as critical as charge protection. Basic pattern of fully attended discharge use outdoors seems to be much less risk of serious damage and deadly injury.

Here’s what I’ve taken to using for 16S RC Lipo ebike pack charge only BMS -
4SBMS.jpg
4SBMS.jpg (94.82 KiB) Viewed 1922 times
http://www.ebay.com/itm/201434924156?_t ... EBIDX%3AIT

It’s too early to declare a win but 4qty for $10 and they appear to play nicely together in series. I’m currently trying to determine how much parasitic drain while sitting? Also, still unsure if they draw power evenly from all cells? Or, is it the CellLog 8 problem of a couple cells powering the circuit and over long periods of time will drag the pack out of balance?

Got ‘em plugged into 4qty 4S Turnigy hardcase (16S, 60-67V) in the appropriate cell order and charge 2-5A through dedicated charge port using stock JST balance wiring/connectors. JST extensions soldered to the pads.
image1 copy 5.JPG
image1 copy 5.JPG (105.13 KiB) Viewed 1922 times
For discharge, I plug a cheap lighted volt meter into the battery charge port and if/when that goes OFF, I then know about a potential cell voltage problem even though power is not disrupted going to the bike. It shouldn’t be too hard to rig slightly more elaborate warning lights/buzzer that simply plugs into the battery charge port?

Basically, it’s cell voltage warning only during discharge and reliance on controller LVC but it's a reasonably well protected charge and none of that stupid-ass bleed balance resistor heat and shorted switching transistor nonsense. And @ $2.50ea plus a few similarly priced JST extension harnesses it's not an expensive solution. No mods to the battery packs either.

These boards have been terminating charge around 4.15-4.18V/cell. But keep in mind, I’ve only logged and compared a couple different channels so far. Other channels might be higher or even lower but I do like this cutoff range for the charger I’m using where the cells settle to about 4.1V once the charger turns off. If I ever want to maximize full SOC it’s simple matter to charge through the discharge port and bypass BMS boards.

If/when cells do ever go out of balance, I go in with a USB power bank along with a cell phone BMS or some other Lipoly 1S USB charger and merely bring up a low cell. Knowing when there’s a low SOC cell problem is most of the battle.

As the lawn power tool companies have apparently realized, discharge is the least of a battery pack fire hazard concern in these applications. Much like an ebike, lawn tools are used outdoors so smoke isn’t so much an issue while finding a reasonably non-flammable spot (middle of a paved road if nothing else) to dump it and get away isn’t too difficult. Plus, fire during discharge is much more likely to occur during lower SOC so there’s also less energy to dissipate and it's almost always an attended situation.

Charging however is a much more sinister/dangerous thing. Often happens indoors, unattended and cells are more likely to have their maximum or above full capacity available to dissipate into a building and/or enclosure. Living area, garage space, etc.
Last edited by Ykick on Aug 01 2016 10:19am, edited 1 time in total.
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Nordle   100 W

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Re: BMS alternative cell level charge protection only.

Post by Nordle » Aug 01 2016 2:39am

Should also be possible to stack two of these?
http://www.ebay.com/itm/Protection-Circ ... SwpDdVfkrz
Need 5*2S or 2*5S BMS for a 10S pack.
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Ykick   100 GW

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Re: BMS alternative cell level charge protection only.

Post by Ykick » Aug 01 2016 8:33am

Nordle wrote:Should also be possible to stack two of these?
http://www.ebay.com/itm/Protection-Circ ... SwpDdVfkrz
Need 5*2S or 2*5S BMS for a 10S pack.
They look similar to the 4S versions I’m using and might work in series for 10S application? But, they’re much more expensive ($12USD as opposed to $2.50USD each). For that difference in price it would probably be best to go with a 10S BMS use it for both charge/discharge protection or merely wire it for charge only protection.

Perhaps something like this -

http://www.ebay.com/itm/Battery-Protect ... 2291323634

I run 16S pack so my options are much more limited. Often costing $50-$80 for 30-60A BMS.

My setup here covers the most important protection aspect (Charging, IMO) for $10 plus minimal wiring/connector costs.
Talent must not be wasted.... Those who have talent must hug it, embrace it, nurture it and share it lest it be taken away from you as fast as it was loaned to you.

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Nordle   100 W

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Re: BMS alternative cell level charge protection only.

Post by Nordle » Aug 01 2016 6:28pm

I have already one of those (white ones) on my actuall pack. use it for charge only and works so far. But what you say about price is totally true, just doubt about size now and maybe to built splitable packs to carry them on flights.
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Nordle   100 W

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Re: BMS alternative cell level charge protection only.

Post by Nordle » Aug 03 2016 1:27am

What's about this one
http://www.ebay.com/itm/Battery-BMS-Pro ... 1434924156
you think i could use this in a 1 x 4S + 2 x 3S configuration. Or do they have to be same voltage?
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Ykick   100 GW

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Re: BMS alternative cell level charge protection only.

Post by Ykick » Aug 03 2016 7:54am

Nordle wrote:What's about this one
http://www.ebay.com/itm/Battery-BMS-Pro ... 1434924156
you think i could use this in a 1 x 4S + 2 x 3S configuration. Or do they have to be same voltage?
Should work in series 3S or 4S but you just really won't know until you try.

But thanks for that link, they seem to be the same boards for 3S/4S in that listing and jumping the last cell connection for 3S configuration. I'm gonna try that on my versions 'cause I use 3S packs for another application and will report what happens. I just received a bag of 10 in my OP - I'm liking 'em a lot.

Might be a good way to air travel with packs under 100Wh? 5Ah 4S label says 74Wh which as I understand FAA rules for lithium batteries is practically an unlimited number in carry-on bags.
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Nordle   100 W

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Re: BMS alternative cell level charge protection only.

Post by Nordle » Aug 03 2016 10:36am

Me already curious if they work^^
Still searching some cheap 5S ones...
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Nordle   100 W

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Re: BMS alternative cell level charge protection only.

Post by Nordle » Aug 03 2016 11:02am

Ykick wrote: For discharge, I plug a cheap lighted volt meter into the battery charge port and if/when that goes OFF, I then know about a potential cell voltage problem even though power is not disrupted going to the bike. It shouldn’t be too hard to rig slightly more elaborate warning lights/buzzer that simply plugs into the battery charge port?
Would be nice to have that upside down, if when theres a problem a light/buzzer would go on.
4:20 Noob Hubz! BLAZE it
..sry for dat poor english..

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Ykick   100 GW

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Re: BMS alternative cell level charge protection only.

Post by Ykick » Aug 17 2016 9:48am

Nordle wrote:
Ykick wrote: For discharge, I plug a cheap lighted volt meter into the battery charge port and if/when that goes OFF, I then know about a potential cell voltage problem even though power is not disrupted going to the bike. It shouldn’t be too hard to rig slightly more elaborate warning lights/buzzer that simply plugs into the battery charge port?
Would be nice to have that upside down, if when theres a problem a light/buzzer would go on.
Don't think it would be hard to make a simple latching circuit to work in reverse? Charge port interruption turns a warning light or buzzer on?

But I do like the simplicity of a pilot lamp which merely turns OFF without any additional circuitry.

I'm liking these boards but with a such a low standby current (6uA) I haven't been able to determine if there's an uneven drain on the battery channels or not? I'll probably need to leave a setup connected for a month or so to figure that out?
Talent must not be wasted.... Those who have talent must hug it, embrace it, nurture it and share it lest it be taken away from you as fast as it was loaned to you.

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Ykick   100 GW

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Re: BMS alternative cell level charge protection only.

Post by Ykick » Sep 22 2016 8:39am

Be very careful here. I’m discovering a problem where the board on the negative side of the pack goes weird and allows the other series strings to overcharge.

I’m beginning to believe this isn’t gonna work for anything except single 4S BMS applications.

Back to the drawing board. I’m still a believer in charge side only BMS for outdoor devices but I think I’ll stick to small current BMS units wired for charge only.
Talent must not be wasted.... Those who have talent must hug it, embrace it, nurture it and share it lest it be taken away from you as fast as it was loaned to you.

- Frank Sinatra

Baron   100 W

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Re: BMS alternative cell level charge protection only.

Post by Baron » Feb 12 2017 4:23am

So those 4S boards are a no-go? I'm using the same hardcase lipos as you, in the same configuration (16S), what BMS/charger solution are you using? Thanks

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