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48V/280A LifePo4 powerwall - BMS recommendation
#1
Hello to all,

I purchase 16 LifePo4 cells for building a 48V/280A power wall.
I'm now using an hybrid inverter WKS 5kVA/48V and 12 x 300W full black modul.
The 12 solar panel are now on configration : 3S4P due to limitaiotn on the max voltage admissible : 60 - 115VDC so in PV entry : 90VDC/40A
The specification of the hybrid inverter is the following :
- Max charge from AC : 60A
- Max charge from DC solar  : 80A

Which kind of BMS (Charge/decharge, common/separate port) can you advise to me?

Thanks to all for your answers.
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#2
For heavy duty - Batrium is a winner for me.  I use WM4 with 84 longmons (80kwh battery bank) and have had 2 yrs of good results so far. 

For lighter duty.... ($150 range)....
Was going to start a thread, but this one will do.   I've been trying to use Chargery 8T, 16T but after 2 failures in 2 days - I'm moving on and interested in responses here.

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Unfortunately - I can no longer recommend Chargery...

I recently went with Chargery because I want to see what's happening (voltage per cell) and using a phone app is not OK for me.

* Wednesday - one of 2 Cargery 16T I have on APC 3000 (wired to outside the APC at 75F room temp) became 'overly hot' as in too hot to hold the blue box.    The unit reported 4.5v on cell 8 and 1.2v on cell 12 (out of 14s) and instead of turning off the relay (cutting power from the battery) it went into a cycle where it would turn off the external relay, and then after couple of mins - turn on again and repeat.   Research showed no problem with the battery/cells/sense-leads after independent measurement.  

* Yesterday - After finding the battery OK and concluding the Chargery unit was the problem, I replaced it with a back up Chargery 16T - which reported all OK.  Unfortunately, when I poked the temp sensor into the case the tip brushed against a battery and 'sparked'.  *This kill the unit!    My bad but the temp sensor appeared to electrically protected? - clearly not good as I do better with units that have a little protection against myself Smile

1/2 of this is due to a failed unit and 1/2 to a combination of 'a bit sloppy on my part' + unexpected finicky temp sensor.  I can't afford this.  And what really bothers me is the failed unit didn't just disconnect the battery - but rather when into an on/off loop.  The whole point of a BMS is to disconnect the battery if the BMS thinks there is a problem - what if there had been an actual problem with the battery?.
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#3
Thanks OffGridInTheCity for your reply but my "small" battery can not affrod a Batrium BMS... it is more or less 1/3 of the total price of my battery installation...
Never try or no feedback about Dali BMS or equivalent model sold on chinese market?
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#4
(07-24-2020, 04:35 PM)duclos_laurent Wrote: Thanks OffGridInTheCity for your reply but my "small" battery can not affrod a Batrium BMS... it is more or less 1/3 of the total price of my battery installation...
Never try or no feedback about Dali BMS or equivalent model sold on chinese market?
Do you mean "Daly" - like this? - https://s.click.aliexpress.com/e/_dTCUHMJ

Don't have any info beyond random youtubes here and there - but Daly doesn't have visuals so its no good for me.   I'm sure you'll get some advice on what you're looking for Smile
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#5
Don't mean to hi-jack your thread - but to follow up on Chargery 16T fail described above...  just opened it up and you can see 'burnt component'!  It just flakes off as you pick at it and is the source of the burning smell.
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#6
It is not a thread hi-jack, I prefer to be aware than to burn a BMS... so no Chargery BMS for me
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#7
(07-24-2020, 06:34 PM)OffGridInTheCity Wrote: Don't mean to hi-jack your thread - but to follow up on Chargery 16T fail described above...  just opened it up and you can see 'burnt component'!  It just flakes off as you pick at it and is the source of the burning smell.

That's not the first time I've heard of problems with Chargery BMS/chargers, e.g. below from EndlessSphere

ElectricGod Wrote:I can't in good faith recommend that anyone buy this balance charger (Chargery C4012B). I wouldn't buy one and I've had 3 of them. I'm really disappointed in this charger!!! It is dangerous and can't be trusted [...]

It lasted less than an hour before it shut down for no apparent reason. I pulled the power chord, let it sit a while and plugged it back in. Everything seemed fine so I proceeded to test at 12S again...same thing...shut down in the middle of a charge, but now it wouldn't power up again. OK...time to take it apart and see what happened. I found that a heat sink with a single transistor on it got so hot that it melted the wires that were touching it. This created a short between the balancing board and the transistor and pitted the heat sink. That was the end of the beta version charger. I sent it back with the expectation of what I found receiving some form of correction. In a later version of the charger, I opened it up and found that the "solution" was a piece of kapton tape stuck over the heat sink. Really? Don't fix the over heating problem, just throw a band-aide on it. Well that was disappointing! This was the first hint I had that these chargers are garbage

Designing and testing Li-ion BMS & chargers requires a large amount of expertise and resources - which are often lacking in very small companies like Chargery. The company is reportedly a one-man show according to comments there, viz. "Chargery is a small company and had initial problems bringing both products to market early. Being a one man show means Jason is responsive to requests for small change".  When it comes to matters of safety, do you really wish to trust a "one man show"?



Re: bargain-basement vs. reputable BMS. Likely many readers are not aware of the immense effort involved in the design of a top-tier BMS, e.g. those used in laptop battery packs. The safety standards used in designing such packs are extremely comprehensive, using industry standard methods of risk analysis such as FTA (fault-tree analysis), FMEA (failure mode and effects analysis), etc. The design typically incorporates multiple levels of failsafe redundancy. For example, the safety standards employed for laptop batteries consider hundreds of possible cases, even the case that a pet urinates on a PC, e.g. below from the IEEE 1625 Standard for Rechargeable Batteries for Portable Computing
[Image: 2Yk6U.jpg]
For example, to protect against overcharge there are at least two independent circuits monitoring each cell's voltage. Each IC has the capability to turn off the charge MOSFET and, if that fails (e.g. FET failed short), they can then blow a special type of fuse (chemical / 3-terminal) to disconnect the cells. Such fuses require only a small voltage on a 3rd terminal to trigger a disconnect. Because it requires only a small voltage to blow, it can function even when the battery voltage has dropped very low (e.g. due to a short-circuit). Analogous redundancy exists for other protection mechanisms (overcurrent, overtemperature, etc).

The probability of safety failure of a laptop battery is greatly reduced due to these multiple levels of redundant protection. By contrast, there is significantly less protection provided by protected cells and standalone chargers. Protected cells can fail simply from static shock (ESD), mechanical shock (drops), etc. Indeed, there are many reports on CPF and BLF of failed protection circuits on cells. Standalone chargers typically have little if any redundant protection, and are not designed to meet any reputable international standards

There is little chance that a small company has the expertise and resources in-house to reach similar levels of safety.  So be careful with bargain-basement solutions.
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#8
@OffGridInTheCity,

According to your experience and power storage capacity, do you have some trouble or power pack misfuncton due to temperature too high?
My concern is that I will implement my cells inside the swimming pool house (5m² = 50sqft) on which during summer, the swimmng pool pump heat the swiming pool house and i feear that temperature will go over 45°C.
Do you have a system to cool down your batery or maybe to warm up if temperature is below 0°C?
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#9
^^^ Higher temperatures greatly accelerate degradion. If you can't reduce temps then to help offset such you should consider charging to less than 100% SOC in order to help prolong life. For example, see the graphs below and note how much faster the cells degrade (lose capacity and IR increases) while aging at very high SOC. See here for further discussion and links

[Image: qwKvY.jpg]
Also, be careful that the entire pack is kept at uniform temperature, else you may suffer from the same problem many laptop packs did - that some part of the pack is heated more than others so it degrades more quickly than others (why you often find both good and bad cells when harvesting used laptop packs), e.g. see the thermal image below.

[Image: dgqsQ.jpg]

Image excerpted from Battery Monitoring Basics - TI training, by Texas Instruments.
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#10
(07-28-2020, 02:52 PM)duclos_laurent Wrote: @OffGridInTheCity,

According to your experience and power storage capacity, do you have some trouble or power pack misfuncton due to temperature too high?
My concern is that I will implement my cells inside the swimming pool house (5m² = 50sqft) on which during summer, the swimmng pool pump heat the swiming pool house and i feear that temperature will go over 45°C.
Do you have a system to cool down your batery or maybe to warm up if temperature is below 0°C?
My batteries are all under or in the house with a temp range of 55F - 75F.     Yes - 45C+ (115F+)  is pretty warm and while that might be 'within max specs'  of your cells I would make effort to cool things down to 80F.  Even 90F is better than 115F.  

At least a fan and measure the temps to see what's actually happening. 

OR

Perpahs a cheap ($250) AC like this - https://www.amazon.com/dp/B07RDM6RBZ/ref=as_li_ss_tl?ie=UTF8&linkCode=sl1&tag=vehicledwelling-20&linkId=bbd877674f88573bfd89455184121223&language=en_US
Here's a youtuber @DIY Solar Power with Will Prowse with a set of youtubes on this AC in his shed in Nevada (sunny/warm)...   only 1.5kwh / day if I remember correctly
Part 1: [color=var(--yt-endpoint-visited-color, var(--yt-spec-call-to-action))]https://youtu.be/2Qh14pX3IxA[/color]
Part 2:
[color=var(--yt-endpoint-visited-color, var(--yt-spec-call-to-action))]https://youtu.be/kclLbSPtI7E[/color]
Part 3: https://youtu.be/xAUPNNe2rCg
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