Solved! Peak current Daly BMS

jai134

100 W
Joined
Sep 18, 2021
Messages
105
I have big problems with something turning power off when my bike reaches approx 250A. I am starting to beleive that it is the BMS. It is a Daly 14S, 48V, 250A BMS and I cant find anything about peak current. Does anyone know? 20211222_143250.jpg
 
If the BMS is shutting off at a high current load, then some of the cells are probably dropping in voltage enough to trigger it's LVC.

AFAIK those BMS have a BT app you can monitor them with, to see exactly what's happening at any time.
 
Sorry for not replying!
Yes, it has a BT app and I have it on the bike when I drive. I can see that it shuts off at something like 250-275A but I can't see what's happening with every cell because it is so small and I can't have a close look when I am driving.
I think that I have to raise "discharge overcurrent protection" in the BMS to somewhere close to 375A and "phase current" and "Battery limit" to 100% in the controller to be somewhere near what I want. I didn't realise that the BMS only could deliver 375A. I thought it was 500A.
 
I tried to set "Discharge overcurrent protection" to 370 in the BMS and both "current percent" and "battery limit" to 100 in the controller yesterday. The bike felt ok but slow acceleration. I had two cut outs and this time I was able to see that the BMS was delivering 406A at the first cut out and 307 second time. I dont think the app reacts so fast so I can see whats actually goes on.
Today I lowered "current percent" to 74 so it should match the BMS but now it shut down at approx 270A. It is really confusing this. What values do you need for helping me with this settings?
 
You have to look at the cell voltages, to see which ones are dropping down under load and causing the shutoff.

That's assuming it's a voltage drop causing it, but that is what usually does this--a cell or cells that are not working correctly, causing so much voltage drop on that cell group that it triggers the BMS's cell-level LVC.

So finding out which cell group(s) are dropping in voltage, and how far, will help you find out which cell groups to replace to fix the battery.

The BMS is just doing the job it is supposed to do by protecting the cells against damage that could cause a fire.
 
Ok.
Then I need to find something that's logging my system. The Daly BT app does not.
 
Here is a link to the recording: https://photos.app.goo.gl/izRHhjydLvvjVXqZ9

I can't see somethinh that's wrong so I think it is me that's the problem. Instead of just limiting the output it cuts off power when it reaches max.

I think I need a good monitoring system and display to be able to see where the red zone starts. I have one, Powerwatcher, but unfortunately it's not compatibel with Nokia cell phones. I am waiting for support from miromax.
 
The BMS has no way to do anything other than complete shutoff of power when a limit is reached. Only the controlller has the electronics to reduce power output when limits are approached or reached.

I don't see any cells dropping too low. But I don't see any current varying normally. It doesn't vary, it just jumps to the few values it ever displays, meaning the BMS isn't sampling it very often or else it isn't bothering to send that to the display app, or the display app isn't bothering to update the screen very often with the data it does get. Either way, it's pretty tough to tell what's really going on like that. :(

The only non-error current readings are -49.5A, at 56.3v, -213.3A at 53.1v, and -242.2A, and voltage reads 53.2v at that moment.

Except for those, everytime it shows any current reading, it shows an overcurrent error: once for negative 327.2A, voltage drop only to 50.3v, (when I see it shut off the charge and discharge FETS the first time) and once for 326.3Amps, and voltage sags to 49.7 volts at that moment, giving a Sum Volt Low Level 2, which is the total pack voltage below the limit (presumably 50v?), when it shuts off again.

Note that amps should read positive, but they always seem to read negative, so either there is a problem with noise in the BMS's current sensor or software, causing it to think it's negative when it's actually positive, or there's just a plain bug in the display app doing that. If the limits set in the BMS for current are positive numbers, maybe when it reads out a negative current it's shutting down because it considers that too far out of limit, for instance if it's set for say, 350A positive current as a limit, but it reads -326A, the difference betwee those is over 600A, and it may shutdown because even though it didn't reach 350A, the software still sees it as almost 700A difference and thinks that's almost double it's limit. Just a thought. If there is a way to set negative numbers for current, maybe that will make a difference?


It's possible there is just a plain fault with the BMS causing the shutdown problem, most likely a bug in the software inside the BMS itself if this is the issue.
 
Thank You! There it is! "Sum volt low protect" is set to 50.4V. I didn't know what to look for and focused on differences between the cells.
Can it be that it is negative because it is "used" amps and if I get regen going it will show as positive?
Can I go lower than 50.4V or is it dangerous in some way? "Cell volt low protect" is set to 3.2V so I don't understand why the "Sum volt..." should be much higher..
 
I lowered "Sum volt low protect" to 46V and went out for a ride. https://photos.app.goo.gl/HsTDyFziiZbjJZso8
As you can see I was able to stay at a high output for a longer time than before. I shuts down but now it's not the BMS that is doing it. Now it is the controller I think because I had to restart everything.
 
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