bluetooth BMS?

Batteries, Chargers, and Battery Management Systems.
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Re: bluetooth BMS?

Post by glyndwr » Aug 05 2018 5:03am

Hi all,
whats your thoughts on using this style of bms for a home battery storage solution.
I have made up a 48v 120ah lifep04 battery that i used in a prius plug in conversion form a few years ago, but now moved to a full electric vehicle so these batteries became available for a new project.

I dont want to connect the 6AWG load cables through the bms, but rather only want the bms for its monitoring and balancing functions, i dont mind loosing the current monitoring, i can re use the jld404 and shunt i have for that puropse.
So, ideally i anly really want to connect the 16 cell tap wires to the bms and of course a battry pack pos and neg for pack voltage measurement. Do you think this will work ok in that configuration?

Thanks.

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izeman   10 GW

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Re: bluetooth BMS?

Post by izeman » Aug 05 2018 5:48am

sure this will work fine. you could even use it as designed. what's the expected wattage of your powerwall?
with 5 genuine 3077 i can do 60A all day long without issues. if you fully equip the BMS with 10 genuine parts you may be able to double that current (even though double current means 4x the heat, but as i said my BMS runs cool at 60A, and you can still add a big heat sink w/ or w/o fan if needed).
just don't expect any noticeable balancing. with those super small bleeding resistors it will take probably years to balance an unbalanced pack.

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Re: bluetooth BMS?

Post by izeman » Aug 05 2018 5:50am

ElectricGod wrote:
Aug 04 2018 11:06am
How do you re-calibrate the BMS?
good question. i have to look it up, what i think i saw a input field for shunt value in the windows software.

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flippy   10 kW

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Re: bluetooth BMS?

Post by flippy » Aug 05 2018 6:37am

With the 32S bms there is a "zero" option on the app to callibrate the shunt.
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Re: bluetooth BMS?

Post by glyndwr » Aug 05 2018 6:54am

Hi izeman,

I,ve got used to manually checking the pack like a human bms, and have manually bottom balanced the pack.

The hybrid solar inverter has got a max current charge and discharge rate of 2.5kw or 50 amps, but to be honest, after watching it all in operation, and with the lifepo4 sag the inverter auto throttles back the charge / discharge to about 1.5kw.
What i`ve noticed with the lifepo4 chemistry, even from new is sag can be abit of a drawback / problem. Ok, my cells now are a few years old and have seen a fair bit of useage coming from my plug in prius conversion.
What i`m seeing from max voltage around 54.4v is a 3v sag, then the pack sits pretty much stable at that rate through its discharge curve. The sag (or voltage increase) on charge is nigh on the same.

I have got a full nissan leaf pack here too, and have confirgured a pack from them in a 2p by 7 in series connected to a 6kw ups as an emergency power supply (i have a disabled child that needs some equipment running so ive built this in case of a power outage) with a 2.5kw load on the leaf cells connected to the bms i see a sag of only 0.4v.

The lifep04 pack is in my brothers house connected to his hybrid solar inverter, he isnt experienced with batteries although i look after them for him, so ive gifted him the lifep04 pack to learn from the characteristics of lithium and get used to managing them, plus if tings went awefully wrong, the lifep04`s are not as volatile therefore much safer.
I would like to fit this bms though for piece of mind and for him to have an instant visual display of what the individual cells are doing via a cheap tablet in his main living room.

I`m assuming if i dont connect the main load cables through the bms i havent got to worry about the cheap fet`s as they wont really be under any stress?

Thanks.

izeman wrote:
Aug 05 2018 5:48am
sure this will work fine. you could even use it as designed. what's the expected wattage of your powerwall?
with 5 genuine 3077 i can do 60A all day long without issues. if you fully equip the BMS with 10 genuine parts you may be able to double that current (even though double current means 4x the heat, but as i said my BMS runs cool at 60A, and you can still add a big heat sink w/ or w/o fan if needed).
just don't expect any noticeable balancing. with those super small bleeding resistors it will take probably years to balance an unbalanced pack.

glyndwr   10 mW

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Re: bluetooth BMS?

Post by glyndwr » Aug 05 2018 7:01am

after i bottom balance the lifep04 pack, connected it up to a meanwell psu through an energy monitor, and the pack took 7kwh from the wall till the worst cell hit 3.5v where i disconnected the meanwell.
So, for a pack thats quite a few years ld and seen alot of work, i`m quite impressed on how well the batteries are holding up.

Thanks.

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Re: bluetooth BMS?

Post by glyndwr » Aug 05 2018 7:52am

Which are the balacing resistors, are they the very small ones between the fet legs or the R404 resistors that are clear in the pic in page 25?

If they are accessible, thinking outside the box, could a 1watt resistor be soldered off the board over the original resistors to create a larger drain?

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Re: bluetooth BMS?

Post by izeman » Aug 05 2018 9:26am

glyndwr wrote:
Aug 05 2018 7:52am
Which are the balacing resistors, are they the very small ones between the fet legs or the R404 resistors that are clear in the pic in page 25?

If they are accessible, thinking outside the box, could a 1watt resistor be soldered off the board over the original resistors to create a larger drain?
i tried to do what you suggested, but it's a hard task, as there is very little space. you need to bend the resistor's pins and still it's a hassle. i would recommend against it.

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Re: bluetooth BMS?

Post by glyndwr » Aug 05 2018 10:26am

I d have a friend that works in a pcb manufacturing company that is very experienced and of course has professional soldering equipment including specialised solder irons that have very small tips for working of surface mount components, i`m sure if i was to ask they would solder the 16 resistors onto the pcb for me.
If it was possible with the correct equipment, which resistors are the right ones on the board, and what spec resistor would you recommend?

Thanks.

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Re: bluetooth BMS?

Post by ElectricGod » Aug 06 2018 12:14pm

glyndwr wrote:
Aug 05 2018 7:52am
Which are the balacing resistors, are they the very small ones between the fet legs or the R404 resistors that are clear in the pic in page 25?

If they are accessible, thinking outside the box, could a 1watt resistor be soldered off the board over the original resistors to create a larger drain?
There's really good reasons why I don't mess with the balance circuits when I mod a BMS. I just set the balance start voltage lower so that balancing starts sooner.

This is what you are looking for. You can't just replace the 2 rows of resistors. Those 3 legged components by the JST connectors are mosfets or bipolar transistors and they won't handle the higher balance current that lower resistance will create. You will need to double or triple up those tiny transistors. Then the traces on the board around the transistor become a problem. Can they handle 1 amp or more...maybe, but I'm skeptical. Finally, assuming you overcome all those other issues, the actual JST pins are designed for something like 1.2 amps...so that's going to be your absolute maximum balance current. I suspect, if you doubled up the resistors and transistors, that you could get away with 100mA balance current easily enough. Probably even 200mA (quadrupled parts) would be doable, but more than that is probably pushing your luck.

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flippy   10 kW

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Re: bluetooth BMS?

Post by flippy » Aug 06 2018 3:16pm

even if you pushed 1A on each leg you would burn off 4W easy per balance lead. you need the resistors to stand up and have a nice loud fan on them to keep the whole thing from burning up.
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Re: bluetooth BMS?

Post by glyndwr » Aug 06 2018 3:29pm

Thanks Electricgod,

great tech explanation, understood, not worth the grief.

I`m not too bothered about which smart bluetooth bms i buy, whats your thoughts on this one

https://www.aliexpress.com/item/Smart-D ... 20690.html

In the desrcription it says a 200ma balance rate.

Price is basically the same but this has a built in very accurate current sensor (how accurate though who knows) the pcb does look well made though, whats your thoughts on it?

Thanks.

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Re: bluetooth BMS?

Post by ElectricGod » Aug 06 2018 3:52pm

glyndwr wrote:
Aug 06 2018 3:29pm
Thanks Electricgod,

great tech explanation, understood, not worth the grief.

I`m not too bothered about which smart bluetooth bms i buy, whats your thoughts on this one

https://www.aliexpress.com/item/Smart-D ... 20690.html

In the desrcription it says a 200ma balance rate.

Price is basically the same but this has a built in very accurate current sensor (how accurate though who knows) the pcb does look well made though, whats your thoughts on it?

Thanks.
I have 2 of those BMS in 24S and 2 in 32S...good stuff and balance current is lots higher. If I had a need for more of them, I would not hesitate to buy more. They are also a lot more flexible and work with LTO...or just about anything you want to balance. The style I just upgraded is only good for LIPO and LION and maybe LIFE if you get that version. Those BMS are a bit interesting to set up. All the settings are in the andoid app, but you can set things wrong and the BMS stops working becasue of a settings conflict.
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Re: bluetooth BMS?

Post by ElectricGod » Aug 06 2018 5:01pm

flippy wrote:
Aug 06 2018 3:16pm
even if you pushed 1A on each leg you would burn off 4W easy per balance lead. you need the resistors to stand up and have a nice loud fan on them to keep the whole thing from burning up.
Ha! Yeah...didn't mention the heat produced. I guess if the resistors are stacked high enough they could sink from the aluminum that the mosfets use. Perhaps drop a little block of ceramic on top of each one to get them "in range" of the aluminum. Just DON'T want a short to happen!
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Re: bluetooth BMS?

Post by glyndwr » Aug 06 2018 6:01pm

Thanks ElectricGod,

it seems you have alot of confidence in that type of bms, do you personally prefer this bms over the other, i`m more inclined to buy this one now, my max current is 50 amps, the lowest bms board they do is 70 amp, ive watched maybe all the youtube videos i could find on this bms, some really interesting ones covering the full install, which is very good to see.
Would you say the screen was a useful item to have? or just utilise the bluetooth and use a tablet or phone?

i did see a commet on youtube from one user whose bluetooth module had failed, something to do with the 3.3v regulator on the bluetooth part of the pcb, anyhowss, he then installed an external bluetooth receiver.

any help greatly appreciated.

Anthony.

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Re: bluetooth BMS?

Post by ElectricGod » Aug 07 2018 1:07am

glyndwr wrote:
Aug 06 2018 6:01pm
Thanks ElectricGod,

it seems you have alot of confidence in that type of bms, do you personally prefer this bms over the other, i`m more inclined to buy this one now, my max current is 50 amps, the lowest bms board they do is 70 amp, ive watched maybe all the youtube videos i could find on this bms, some really interesting ones covering the full install, which is very good to see.
Would you say the screen was a useful item to have? or just utilise the bluetooth and use a tablet or phone?

i did see a commet on youtube from one user whose bluetooth module had failed, something to do with the 3.3v regulator on the bluetooth part of the pcb, anyhowss, he then installed an external bluetooth receiver.

any help greatly appreciated.

Anthony.
Consider the LCD to be a quick status. You can see voltage and current and cell status, but you can't change any BMS settings. I'm torn about the LCD. You can easily live without it. However, the app for your phone has no dashboard...so from that perspective, the LCD is your dashboard.

I wouldn't go with the 70A version. The cost for slightly more amperage is just not worth the few dollars less for the lower amperage version. I'd go with at least the mid range amperage.

I bet getting another BT board would be pretty easy. It's just a BT board that gets used in a zillion devices.
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Re: bluetooth BMS?

Post by glyndwr » Aug 07 2018 5:10pm

Thanks ElectricGod,

great advice, and much appreciated. Thank you.

Anthony

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Re: bluetooth BMS?

Post by ElectricGod » Aug 08 2018 12:10pm

glyndwr wrote:
Aug 07 2018 5:10pm
Thanks ElectricGod,

great advice, and much appreciated. Thank you.

Anthony
You are welcome...

I thought about this a bit more. The app doesn't provide anything like this data in any kind of a neat and easily read format.

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This is as good as it gets and it's pretty messy IMHO. So if no dashboard doesn't bother you, then don't get an LCD. The app for these BMS was really meant for programming, NOT monitoring.

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There's nothing like this in the app.

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Re: bluetooth BMS?

Post by Inwo » Aug 08 2018 12:36pm

Balance current.
The main thing that slows testing unknown batteries is low balance current. A charger cant charge faster than the balance circuit bleeds current from high cells.
What I need is an add-on 5 amp balance board, driven by bms.
A stand alone board may also be ok. A couple years ago, I made some stand alone boards, but only good for about 2 amps.
I did not have enough gain, so turn on was slow. If I can connect to bms circuit, turn on should be sharp.

The thing is, when I need it, like now, I have no time to build it. When I'm finished testing my 320 LiFePo4 75ah cells, I'll have time, but no desire. Like fixing the roof. :)
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Re: bluetooth BMS?

Post by Inwo » Aug 08 2018 12:43pm

Just thought of something, while looking at discharger picture.
Maybe these can be programmed in reverse. To start a 10a discharge when voltage goes high. doh!
Why reinvent the wheel? I can just buy a half dozen more.

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Re: bluetooth BMS?

Post by ElectricGod » Aug 08 2018 12:57pm

I googled for "xiaoxiang bms" and found a search result for an IOS app. It costs 99 cents. No point spending the money if it doesn't work.

https://itunes.apple.com/us/app/xiaoxia ... 05426?mt=8

Anyone ever try this IOS app in place of this android app?

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Re: bluetooth BMS?

Post by ElectricGod » Aug 08 2018 1:04pm

Inwo wrote:
Aug 08 2018 12:36pm
Balance current.
The main thing that slows testing unknown batteries is low balance current. A charger cant charge faster than the balance circuit bleeds current from high cells.
What I need is an add-on 5 amp balance board, driven by bms.
A stand alone board may also be ok. A couple years ago, I made some stand alone boards, but only good for about 2 amps.
I did not have enough gain, so turn on was slow. If I can connect to bms circuit, turn on should be sharp.

The thing is, when I need it, like now, I have no time to build it. When I'm finished testing my 320 LiFePo4 75ah cells, I'll have time, but no desire. Like fixing the roof. :)
I like that idea! Tap into the control lines for each cell and then pass those signals over to a parallel running board that can handle some significant amperage. There would need to be a custom made board for this that uses large resistors and larger SMT transistors, but it would not be hard to design. I think 2 resistors and a mosfet are all you need per channel on the add-on board. Snag the control signal from the gates for each mosfet on the BMS and send that over to the add-on board. The BMS should be none the wiser that it is balancing at 50mA or 5 amps.
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Re: bluetooth BMS?

Post by lionman » Aug 09 2018 1:22am

They should design the BMS with fewer, but more powerful discharge lanes.

Balancing performance would be a lot better in most situations if they had say 1/3 the number of lanes with 3x the discharge rating.

Just need some circuitry that ensures that 2 groups never connected to the same discharge lane, which some clever engineer could come up with.

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Re: bluetooth BMS?

Post by ElectricGod » Aug 09 2018 2:34pm

lionman wrote:
Aug 09 2018 1:22am
They should design the BMS with fewer, but more powerful discharge lanes.

Balancing performance would be a lot better in most situations if they had say 1/3 the number of lanes with 3x the discharge rating.

Just need some circuitry that ensures that 2 groups never connected to the same discharge lane, which some clever engineer could come up with.
Except that lots of people don't want an 8S BMS. 16S is pushing the lower limit for me. Most of my builds are 20S and I'm moving (slowly) forward on a 32S build.

What I wish is that BMS balancing had something to do with the current handling. 50mA balancing is pretty common despite the BMS being capable of 20 amps or 160 amps.

Balancing a 64 Ah pack at 50mA will take forever. It's fine for like 10 Ah, but for larger packs, it's just not enough balancing current. My band-aide is setting the balance start voltage low so that balancing gets a chance to do something on larger packs. The other option is to use multiple BMS's...which I also do.
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Re: bluetooth BMS?

Post by themelon » Aug 09 2018 2:52pm

ElectricGod wrote:
Aug 08 2018 1:04pm

I like that idea! Tap into the control lines for each cell and then pass those signals over to a parallel running board that can handle some significant amperage. There would need to be a custom made board for this that uses large resistors and larger SMT transistors, but it would not be hard to design. I think 2 resistors and a mosfet are all you need per channel on the add-on board. Snag the control signal from the gates for each mosfet on the BMS and send that over to the add-on board. The BMS should be none the wiser that it is balancing at 50mA or 5 amps.
Not cheap and not quite what you are talking about but I just happend across these:

https://www.ebay.com/itm/323194962541

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