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TechDirect BYD BMS in pre-built units: Can anyone read this Chinese label?

Why does the english version of that chart have columns "Min, Standard, MAX" if you can't change any of the settings?

According to that chinese manual, the standard is referred to 25C degree, value may change depended on temperature.

Personally, I dont think max/std/min make sense to me
 
These are the pre-built units - no way to access the individual cells without tearing the whole unit apart - or finding a way to access BMS readings or use the built-in adapter connections. It's a quandary.

At least you can easily access the cells voltages at the BMS connector to measure them with a DMM.
 
I reset the circuit breaker on mine... but it does list a delay and a release voltage on the BMS specs.
Question: "The do on charge 200 ma"
What the heck does that mean? When does it start? And how would you know?
 
Bidule: I have to plead ignorance - could you explain that process to me? (DMM measurement at connector - please refer to photo) Thx.
 
"The do (cell balance when its) on charge (but the max balance current is) 200 ma"
 
I reset the circuit breaker on mine... but it does list a delay and a release voltage on the BMS specs.
Question: "The do on charge 200 ma"
What the heck does that mean? When does it start? And how would you know?

The question I asked him was "Does it do cell balancing and what is the balance current?"

That was the response, which seems to be what ytwytw stated above. Max balance current 200 ma during charging.

200 ma contradicts with what the "single cell balance current" row in the english table states? Or is it 200ma max balance current for all cells at the same time?
 
Bidule: I have to plead ignorance - could you explain that process to me? (DMM measurement at connector - please refer to photo) Thx.

This connector:

BMS unit - open top.jpg

It has one wire per cell positive plus the main negative. If you take a DMM or voltmeter you can measure between each wire (from 1 to 2, then 2 to 3, 3 to 4, etc...) and you'll have each cell voltage ;)
 
Thanks... so turn off circuit breaker - unplug "balance leaf" - apply pos DM lead to connector #1 position and neg DM lead to main neg (at BMS?). Correct? Any significance to red lead (Cell #1? perhaps).
Do you think theres anyway to get a y-connection to that setup for monitoring?
 
"The do (cell balance when its) on charge (but the max balance current is) 200 ma"
Does that mean the balancing starts on "any" charge - or that it only starts at a particular voltage? Thx.
 
Since my three units are cutting out at 28.0v it would seem that they will never get a chance to balance. Argh.
 
Since my three units are cutting out at 28.0v it would seem that they will never get a chance to balance. Argh.

200mA is not enough to balance it.

If you really really really need to monitor, consider buy a new BMS
 
Thanks... so turn off circuit breaker - unplug "balance leaf" - apply pos DM lead to connector #1 position and neg DM lead to main neg (at BMS?). Correct? Any significance to red lead (Cell #1? perhaps).

That's not correct.

The correct procedure:

- turn off circuit breaker
- unplug balance leads connector
- measure cell 1 voltage between pin 1 and pin 2 of the connector
- measure cell 2 voltage between pin 2 and pin 3 of the connector
- measure cell 3 voltage between pin 3 and pin 4 of the connector
...
- measure cell 8 voltage between pin 8 and pin 9 of the connector
- replug the connector
- turn on the circuit breaker

It doesn't matter which way around you put the voltmeter leads, the only difference will be a sign "-" on the screen but we don't care, we just want the voltages ;)

Previously I didn't say to turn off the circuit breaker and to unplug the connector because you can do the measurement without unplugging the connector but it's a bit more complicated if you're not familiar and there is greater risk to make a short-circuit between the connector pins with the voltmeter leads, so yeah, don't go this route.

Do you think theres anyway to get a y-connection to that setup for monitoring?

Yes, but you need to find the same connector which is used here and do the Y yourself.
 
Thanks again to both of you. As you can probably see, the reason I got these pre-built units is because of my unfamiliarity with LFP/BMS procedures. Old school lead-acid guy. I figured it was enough for me as a start to get my CC's and Inverter specs tailored correctly. And I'm also AC coupling - which throws another set of variables into the mix. Really appreciate the heads up.
 
That's not correct.

The correct procedure:

- turn off circuit breaker
- unplug balance leads connector
- measure cell 1 voltage between pin 1 and pin 2 of the connector
- measure cell 2 voltage between pin 2 and pin 3 of the connector
- measure cell 3 voltage between pin 3 and pin 4 of the connector
...
- measure cell 8 voltage between pin 8 and pin 9 of the connector
- replug the connector
- turn on the circuit breaker

It doesn't matter which way around you put the voltmeter leads, the only difference will be a sign "-" on the screen but we don't care, we just want the voltages ;)

Previously I didn't say to turn off the circuit breaker and to unplug the connector because you can do the measurement without unplugging the connector but it's a bit more complicated if you're not familiar and there is greater risk to make a short-circuit between the connector pins with the voltmeter leads, so yeah, don't go this route.



Yes, but you need to find the same connector which is used here and do the Y yourself.
Bidule, I started to follow the directions as stated, but first took a careful look at the connector. There are only 8 pins on the connector, not 9 - first pin being the red wire. How does that affect "- measure cell 8 voltage between pin 8 and pin 9 of the connector"? And how does "main negative" figure into the equation? Wanted to make sure I wasn't off base. Thx.
 
Ah, then they must use the B- for the first cell. That's not super good for accuracy.

So the procedure is the same but for the first cell you need to measure between the big black wire coming from the battery and the first wire of the 8 pins connector.

The first cell should be opposite to the red wire on the connector. But it can also be the red wire. There's no way to tell without measuring the voltage; if you measure almost battery voltage then it's the last cell, so start at the other side of the connector, if you measure about 3 V then you're on the correct wire.

Then follow what I described in my previous post for all the other cells ;)
 
Ah, then they must use the B- for the first cell. That's not super good for accuracy.

So the procedure is the same but for the first cell you need to measure between the big black wire coming from the battery and the first wire of the 8 pins connector.

The first cell should be opposite to the red wire on the connector. But it can also be the red wire. There's no way to tell without measuring the voltage; if you measure almost battery voltage then it's the last cell, so start at the other side of the connector, if you measure about 3 V then you're on the correct wire.

Then follow what I described in my previous post for all the other cells ;)

I don't think they get first cell positive from the B-.

I think maybe they have 8 leads, one for each cell and the negative line is the main neg?

At least that is what my testing of a stand alone Techdirect BYD BMS showed.
 
Bidule, I started to follow the directions as stated, but first took a careful look at the connector. There are only 8 pins on the connector, not 9 - first pin being the red wire. How does that affect "- measure cell 8 voltage between pin 8 and pin 9 of the connector"? And how does "main negative" figure into the equation? Wanted to make sure I wasn't off base. Thx.

Be careful measuring "Between the pins" if you short 2 pins you could have some trouble.

On the bottom side of the connectors there should be a little bit of exposed metal corresponding to each pin. Put the neg probe of your DMM on the main battery neg and the positive probe on one of the little metal bits on the bottom of the BMS connector to get the cell voltages... At least that is what I do. YMMV. Verify with an electrical engineer before following my advice though... :rolleyes:
 
Thank you both. Good advice. Now lets see if I can follow it...
 
I am finding this chart useful for my BYD packs...

Rule of Thumb State of Charge voltages for Various BYD LiFePO4 series configs attched.
 

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Any chance one of the resident design wizard on this forum could design a Y cable configuration with a bluetooth reader/sender to monitor cell voltages on these pre-built BYD units?
 

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