diy solar

diy solar

Overkill 120A 12V 4S BMS overheating during stress testing

Sillyputty

Solar Enthusiast
Joined
Jul 21, 2020
Messages
188
I've contacted Steve from Overkill several times on this and haven't heard back. Perhaps others here can shed some light on what's going on. The discussion thus far:

"Hi Steve - I have two of the JBD Overkill BMS's for two separate 4S 280AH battery packs. One I've used throughout the year in a camp trailer, the other I've recently finally completed and have run a few cycles on.

On one occasion (with both BMS's) running within specs (~ 1000 watts continuous) I've experienced where the BMS overheats substantially (20+ degrees centigrade) over the already set discharge limit of 70c without shutting down or showing an overheating error in the app. The first time I shut it down, the second one (newer BMS) shut itself down at ~100c. Both times were while I was monitoring them so no harm done..."

I'm using the latest android app from your website.

Is this a know issue?


And:

"Hi Steve - I've received no reply on this. I have found it happening again, and for some reason it only happens when the charging is disabled in the BMS settings. When doing a stress test, I disable charging in the BMS settings to prevent the battery from being influenced at all from outside power from any solar panels or other chargers that may be hooked up.

Turning the charging back on in the BMS settings alleviates the overheating issue, at least AFAIK so far.

1) Is this normal?

2) What is causing this?"


EDIT: to include that the BMS's have the default settings that Overkill provides when it's ordered.

Thanks
 
Last edited:
Yes both ports need to be on while in use.
Any thoughts on why? So far, I've seen nothing in the Overkill manual that says this.

Seems quite dangerous to allow a setting to effectively disable a safety parameter without notice and/or good reason.
 
I don't know the circuits or components well enough to explain.
You are not the first to discover the issue. I believe the idea is to protect the cells, not to regulate charge or discharge independently.
 
I believe the idea is to protect the cells, not to regulate charge or discharge independently.
I think all of the temperature settings are a BMS specific (or battery overall specific, depending which temp sensor is being read) setting. In other words, it isn't a cell-level setting. In this case the discharge over-temperature of the BMS temperatures sensor (not the battery temp sensor) is not shutting off the discharge when the BMS settings say it should. Nothing I've found in the manual mentions this.
 
Last edited:
If you disable the charge path with the app, then the discharge current will overheat the fets, you should notice a slight drop is battery volts due the diode drop. This is explained clearly here,


Manual disconnect of the chargers or disable would be preferred .

It's somewhat worrying the over temp protection did not cause shutdowm.

Mike
 
If you disable the charge path with the app, then the discharge current will overheat the fets, you should notice a slight drop is battery volts due the diode drop. This is explained clearly here,


Manual disconnect of the chargers or disable would be preferred .

It's somewhat worrying the over temp protection did not cause shutdowm.

Mike
Thank you very much, Mike. It's nice to have an explaination and a work-around (be nice if it came from the vendor and was in the manual) and yes, it's quite worrying that it allowed things to get almost 25 degrees C above the threshold w/o tripping the safety features. I did note also that the inverter tripped due to voltage drop w/the charge path disabled. Once both charge and discharge were enabled things ran as they should. Also good to know why that had happened.
 
I think (someone correct me if I'm wrong) that the only way to be able to disable charging and/or discharging separately is to have a dual port BMS not a single port BMS. The thing is it seems most dual port BMS have very lackluster charging amps support.
 
Nobody corrected you so this must be the case.
Which stands to reason as the common port -ve leg controller bms can only switch the negative leg, open or closed which essentially both charge/discharge.
I’ve sprinkled this around the forum in similar threads for affirming and had no response.
Basically the reason I chose 4s2p, with 2bms’s was for redundancy. It would be nice if someone that understands the circuitry could confirm this premise.
I can’t see how it can be done without a switching circuit to an external contractor on I/O’s. eg
Tao , electrodacus, Orion etc
The config editor suggest you can turn either on or off which contrary to above. Odd.
I have not yet had the time to top balance or adjust parameters so here’s hoping someone short circuits my confusion.
 
Last edited:
The JBD BMS is considered a single port I believe, it has only one cable on the input side. But it can control charge/discharge separately.

Here's a good discussion on the topic:

 
Back
Top