How to verify BMS (Daly) is working?

jzpchen

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I bought a Daly 16s 120A BMS with common port. My battery are lifepo4 16 prismatic cells. After connecting them, I only got 9.5v for P+ and P-. I tried shorting P- and B- to activate, it has no effect. I should get the same voltage as the battery (now 53v), right? I use Victron Quattro 48/3000. I am not able to inverting. I am able to charging (with some issues to discuss separately) from AC source. What is the best way to validate the BMS is in good working order?
 

jzpchen

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For charging, it appears running fine for several hours from 3.29v. Then one of cells reached 3.75v and the rest are at 3.4v. That triggered BMS and stopped charging. I am not sure why. The battery cell with 3.75v seems fine. I lowered its voltage back to 3.3v. I am able to charge again. But then I will triage in 15 minutes. Then I tried to discharge and run into the issue I mentioned earlier. I can only discharge bypassing BMS.
 

electric

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Did you precharge your Victron when making initial connection? BMS could be damaged by initial inrush when connecting to the large inverter.
Your BMS charge protection is working as designed, stopping when first cell hits 3.75V. Of course the cell is fine because BMS worked. If it did not stop, your cell would not be fine after a few more minutes of imbalanced charge. What you are doing is called initial pack balance, perfectly normal process. Still doesn't explain why discharge is broken. Did you get any sparks when connecting to inverter?
 

Picasso

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This is why I dont care for these No display no UART BMS's. How the hell do you know what its doing. The new high amp Daly stuff is just one giant heatsink not even an LED.
 

jzpchen

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The proper discharge voltage (~53v) was not there (P+, P-) before I connected to Victron. I was wondering why it has this strange 9.5v when I first have the connection done. Since I was not trying to discharge I left BMS along and started focusing on charging. I didn't specifically doing pre-charge. I only started Victron configuration with out battery and through AC source before the battery is connected. When I charge, it appears working. P- and B- has a voltage of 0.65v. That is strange. I hope it should be very much close to 0.

A couple days ago, I asked Daly. They suggested if there is a load, there will be a proper voltage. But did have Victron load. However since the voltage is only 9.5v, Victron appears not started and maybe doesn't appear to be a load on BMS. I thought you can even measure using multimeter; that is not much a load.

I started to notice the problem is when I had some decent charging and unplugged AC source and expected the automatic transition to inverter. But it didn't happen. The Victron stopped completely.
 

jzpchen

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This is why I dont care for these No display no UART BMS's. How the hell do you know what its doing. The new high amp Daly stuff is just one giant heatsink not even an LED.
Now I started thinking the same. Daly BMS is a black box. I am not sure if it is doing its job. Do you have a few product recommendations? I'd like to know how exactly the balancing work. BTW, I am also curious on how exactly Daly BMS does its job. For example, the balancing is passive or active? It only says 30mA. Is that sufficient? Maybe fine since they did ask the difference among cells be less than 0.05v. Is balancing in action when P- is not used? Since now my P- is not working and not connected, I am wondering if it does the balance still.
 

MisterSandals

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BMS could be damaged by initial inrush when connecting to the large inverter.
I thought it was the capacitors in the inverter that got damaged by the inrush.
The BMS can be damaged too w/o pre-charging the inverter?

How large (watts) must the inverter be to where this becomes an issue?
 

jzpchen

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I thought it was the capacitors in the inverter that got damaged by the inrush.
The BMS can be damaged too w/o pre-charging the inverter?

How large (watts) must the inverter be to where this becomes an issue?
I was thinking about the same. If in a packaged battery such as battleborn, you are not able to access the connector behind the BMS. I thought it was more about the damage to the connector due to arc.
 

MisterSandals

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See time 2:00 in video; Will mentions pre-charging inverter because not sure if BMS will handle "the spark generated while charging the capacitors".

Not sure how authoritative that comment was meant to be...

 

electric

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Maybe this is why Battleborn sells this contraption https://battlebornbatteries.com/shop/current-surge-limiter/

Capacitors damage is a rare event and points to a weak design of the inverter. BMS damage is also subject to BMS design quality, so it's difficult to say if and when it happens, but it's certainly possible.

In my experience, 12v/24v systems are usually OK without precharge, but 48v especially at 3kW and larger is at real risk of damaging inrush.
 

Supervstech

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I thought it was the capacitors in the inverter that got damaged by the inrush.
The BMS can be damaged too w/o pre-charging the inverter?

How large (watts) must the inverter be to where this becomes an issue?
I would think it is the voltage that is the limit.

12v inverters often are fine with the cap charge, but 24v 1000watt and up and anything 48v should be precharged. But it isn’t to protect the inverter... it is to protect the battery terminals and the BMS from huge amp surge.
 

jzpchen

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I will certainly be more careful on the pre-charge. I did read the Victron manual several times regarding how to connect to battery. It didn't mention pre-charge. I assume Victron side is fine. It is indeed running fine for either charging and inverting directly to the battery without BMS. So I think Victron designed properly for their capacitor area. I was concerned about arc to switches. So my main battery switch is rated for 48v and 275A. I hope it handles arc for its switch contacts. For BMS, I assume you cannot do it unless the system is not packaged. The battery terminal sits behind the BMS and will be in the case. BMS has to be designed to handle it or it cannot be packaged inside.
 

MisterSandals

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I would think it is the voltage that is the limit.
Ah! Large as in voltage large, that helps a lot!

This is the video i found where the guy shows the board in his blown inverter from inrush. Quite a good explanation of that starting at 8:00.

 

jzpchen

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I got some info from Daly to check.
 

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gehowi

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I started with a Daly BMS 16S 200A, with separate charge port and balancing; 125$.
It worked for 4 months and damaged after disconnecting the 16 wire connector.

Usually I do not trust electronic designs molded in resin without the need of absolute waterproof. May be they do to prevent fire when the circuitry get burned or just to hide the poor electronics..

Here you get 6 reasons not to buy such Daly crap:

1) Balancing 30mA on 200Ah batteries is ridiculous and has no effect. It's just a selling argument.
If you need balancing, buy a decent separate balancer with energy transfer.

2) Separate charge port limited to 30A or less for 200A BMS? Silly. It should be at least 50-100A. Probably cheap or too less mosfets used for charge port.

3) There should be at least 2 longer ground pins in the 16 pin connector to ensure that reference ground wires (B-) are connected first when plugging in.
If some positive pins are connected before the ground reference, damage to the control board is guaranteed. That's what happened with mine.
Daly use only 1 short ground pin (black wire). Unforgivable.

4) Not one led. You don't know any activity or error or whatever. Just hoping it does the job on the right time. If it does not, you only know when your cells are damaged already.

5) A BMS should turn off B- when a cell reaches +-2.6 or 3.65V. My Daly turned off lower than 2.45V, really too low.

6) No warranty. I contacted Daly and I got fast response. I had to measure the resistance amongst powercables and got diagnose: Dead.
I should send it back for repair. (How they should repair a moulded design?)
I asked for the return address in English and Chinese and up to now I did not get any respons anymore.

A BMS can also be damaged by connecting capacitive loads such as a large invertor or a huge short. These currents can be much higher than the current specified on the BMS. In good BMS designs, the inrush current should be limited or there should be enough parallel mosfets to handle it.
Keep in mind that every time the BMS turns on again after low battery, these currents will exist.
 

MisterSandals

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3) There should be at least 2 longer ground pins in the 16 pin connector to ensure that reference ground wires (B-) are connected first when plugging in.
If some positive pins are connected before the ground reference, damage to the control board is guaranteed. That's what happened with mine.
Daly use only 1 short ground pin (black wire). Unforgivable.

I am with you 100% on everything except this. Looks like maybe an RTFM error.
Step 1 is pretty clear.

FWIW, the Deligreen one page instruction manual is the best I've seen from Alibaba and Aliexpress by a long shot.
 

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jzpchen

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After digging into spec, I do feel the 30mA balancing current is low. My battery is 3.2v 150ah each. I don't see how 30mA is enough for a potentially 60A discharging (48v 3000w) and 30A charging. I just ordered an active BMS with 1.2A balancing current. I hope that is better. My Victron can provide other protection such as temperature, low voltage, over voltage, etc.
 
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