DIY 100ah lithium battery

[ski3pin]

Here are two photos to clarify the issue that can get muddied in my narrative.

13.55V is right at what the BMS app indicates.


And at the battery terminals the voltage is 11.82V

It remains a puzzle. I will apply a load to the battery - as per Rando - and post the results.

 

[ski3pin]

Here is a new piece of data. I connected Will Prowse's recommended capacity tester from aliexpress and got quite a surprise.

First off, for a bench mark confirmation the unit works I connected it to my old AGM battery. The voltage reads 12.7V

I connected it to the new DIY battery and the voltage reads 1.94V! I went back and confirmed with the multi meter across the terminals that the multi meter still reads 11.82 as it did earlier. Wow.

 

[rando]

It looks like that there is either something wrong with your BMS or the BMS settings, the actual batteries look to be fine. What you are seeing is consistent with either the BMS being off or there being a fault with the BMS.

The only thing that stands out to me is the setting 'switch function' appears to be off. It is unclear to me whether this setting disables the 'switch function' or if it IS the 'switch function' and it is set to 'off'.

 

[ski3pin]

The only thing that stands out to me is the setting 'switch function' appears to be off. It is unclear to me whether this setting disables the 'switch function' or if it IS the 'switch function' and it is set to 'off'.

I believe that switch in the app turns on or off the optional external switch that I do not have. I've tried it both ways and it makes no difference. I am moving closer and closer to the BMS being at fault.

 

[ski3pin]

I spend time this morning continuing to troubleshoot without success, but I did encounter a change. After unplugging the balance leads push connector and then reconnecting, the BMS app now has both the charging and discharge off and will not allowing turning them on. Under protection it now reads "locking". Here's a photo -

Here is the "before" photo.

 

[pvstoy]

Would you need to disconnect everything and reattach in proper order???

 

[ski3pin]

Would you need to disconnect everything and reattach in proper order???

Although I've done that 2 or 3 times, I don't believe it's necessary as the only connection between the balance wires and the BMS is through that push connector.

 

[pvstoy]

Ski i don't know how it is wired, but is the wire that is a push connection supply 13.6 volts?

Measure voltage before pushing it in and after you push it in can you use a sewing pin pushed into the wire and read voltage on either side of the push in connection.

Don't forget the ground wires.

If you can't determine if there is a bad wire or connector then like Rando says it might just be a problem with the BMS.

 

[pvstoy]

any feature in the BMS for a reset?

 

[rando]

If you have already removed power from the BMS a few times (reseting it) and that hasn't fixed the problem, it seems pretty likely that the BMS has an issue. Before spending more time on this, does the BMS provider offer any tech support or a warranty?

 

[ski3pin]

I have confirmed there is no change in voltage coming out of the BMS with or without the balance leads connected and am satisfied it is an issue with the BMS and not operator error on my part. I have contacted the seller through aliexpress. It is beyond the 15 days after confirmation of receiving the item to open a dispute. I'll report on the response I receive.

 

[rando]

I have a 100A non-bluetooth BMS that has been sitting on the shelf since I upgraded to a bluetooth BMS a few years ago. I would be happy to send you if you want to get this up and running while you wait for resolution on the BMS you ordered. I can completely sympathize with the frustration of being this close to finishing a project only to be held up with something silly like this BMS issue at the last moment.

 

[ski3pin]

I have a 100A non-bluetooth BMS that has been sitting on the shelf since I upgraded to a bluetooth BMS a few years ago. I would be happy to send you if you want to get this up and running while you wait for resolution on the BMS you ordered. I can completely sympathize with the frustration of being this close to finishing a project only to be held up with something silly like this BMS issue at the last moment.

rando, thank you for your generous offer. Time is not critical in resolving this issue and the seller on aliexpress is communicating with me and may offer a solution. So, for right now I'll hold off on your offer but keep it ready on the shelf.

I'll report on what the seller does.

 

[ski3pin]

First off, a big thank you to rando and Imwilco1 for their generous offers of a replacement BMS. There are really nice people on Wander the West! I replaced my suspect BMS with one I received from Imwilco1. The battery and BMS both function now confirming it was a defective BMS.

I did two weeks of back and forth with the seller in China. After a list of "try this" finally the seller said I could return it to them at my expense. Not worth the time and effort on my part so I told them I'd just toss it in the trash.

Next up I did a capacity test as per one of Will Prowse videos. The result was 111 amp hours out of 120 amp hour cells.

The BMS app showed this.

 

[lmwilco1]

Did you top balance before your capacity test? I would hope that the cells will deliver their rated capacity.

Louis

 

[ski3pin]

Yes, I top balanced.