DIY 7s Li-ion Pack with BMS and Fuel Gauge - Page 1
Forum section: electronics / projects

author: lja246
author_rank: Contributor
timestamp: November 14, 2024, 04:36:19 am
content: I'm planning on making a LED panel and powering it from a 7s Li-ion pack. As part of the pack I wanted to include a BMS and a fuel gauge. I'm planning on using the BQ76942 for the protection and the BQ34Z100 for the fuel gauge. I was wondering if anyone has had any experience with these parts and whether you think they would be suitable for this. I have attached a draft of the schematic which I made basically following the example schematics. I'm not sure if the schematic is right so if you have used these parts before I would appreciate it if someone could have a quick look over it to check for obvious mistakes. I haven't really made a complicated schematic before and didn't want to get a PCB ordered before getting it checked.

author: jbb
author_rank: Super Contributor
timestamp: November 14, 2024, 05:40:21 am
content: Secondhand, but someone over athttps://www.eevblog.com/forum/renewable-energy/how-to-predict-battery-status/msg5700489/#newdid mention having some trouble with the BQ34Z100. You might want to check that - or even message the user directly - before proceeding too far

author: lja246
author_rank: Contributor
timestamp: November 14, 2024, 09:58:11 pm
content: Thanks for that,I don't suppose you would know of any good alternatives? I've found some others but I guess they could all have their own issues that aren't documented.

author: mtwieg
author_rank: Frequent Contributor
timestamp: November 15, 2024, 02:37:37 pm
content: I'll re-post my original response on the BQ34Z100-G1:QuoteThe Maxim fuel gauge chip I had tinkered with a bit was the MAX17205. Ultimately that also wouldn't work for us because their firmware couldn't support PbA chemistries (no idea why), but at the very least their software tools seemed far more stable compared to BQstudio.However, I would still assume you will need support from the manufacturer (either TI or Maxim/ADI) somewhere. And from what I've seen, their user support forums (e2e, engineerzone, etc) do not offer sufficient support for these chips. Just search e2e for BQstudio or BQ34Z100-G1 and see how many issues actually get resolved, vs how many are left unresolved or are taken "offline" (meaning the user had access to more direct support). If you can't get that direct support (usually only an option if your EAU is thousands or more), you face a very difficult path...If you're working with an Li-ion battery and also want other BMS features (cell balancing, protection, etc), then that might make TI's parts more attractive, as they seem to have a more fleshed-out ecosystem. But AFAIK it all uses BQstudio, which is the main problem IMO.

author: lja246
author_rank: Contributor
timestamp: November 16, 2024, 10:01:54 pm
content: Thanks,I think for now i'll leave the BQ34Z100 in there but just not populate it and try to work something else out for SOC. I've tried to ask questions in the E2E forum at TI but I can't because I don't have a company so I can't really get any technical support from them that way.It's a shame because from the datasheet it looks like a really nice IC. I was only planning on programming the IC from a MCU anyway because to use BQStudio I think you need the EV2400 programmer which is like $400 AUD and i'm guessing if its a pain to get working with their own software and programmer it would be even worse to try and use my own.I think i'll try to stick with the BQ76942 for the protection because it looks promising but that may also have its own issues with programming.