Dual identical batteries in parallel safety/simplicity Questions

[tomjasz]

I don't know details of my bms, so the possibility of charging safety issues gives me pause. My batteries are UPP brand, so not the highest or lowest quality, from what I gather: dont have a clue what sort of bms they use.

Sounds like the switch is safest way to go, though I'd much prefer a simple "Y" connector if I thought I could charge safely. I wonder if connecting both chargers and switching on both batteries, then activating both chargers simultaneously by using a plug strip with on/off toggle would eliminate the charging safety concerns for a "Y" connector without DPDT switch?

It still depends on the BMS design as noted previously--that behavior is what determines what happens in the case of one pack stopping charge for *any* reason while the other continues.

If you don't know which kind of BMS they have, it's possible to check by opening the packs to see if they have separate wiring from the charge and discharge ports to the BMS, so that the BMS has three independent thick wires from it: B- to battery cells, P- to discharge port, C- to charge port.

If P- and C- are the same electrical connection, or there is only a P- with both charge and discharge wires to it, then they are as safe as such things go to directly parallel.

If P- and C- are separate electrical connections, then the problems noted can happen and result in cell damage under certain conditions.

That’s overly complex for the average user and maybe even bad advice. Many packs are so marginally built as to make diving in a potential disaster. Your advice is always spot on but often well beyond average skill level. KISS for me…

 

[amberwolf]

Almost everything on this forum is overly complex for the "average user".

It's always up to the individual to judge their personal capabilities and not exceed them.

If any person chooses to do something outside their abilities, there are plenty of places on the internet for them to find ways to make bad things happen whether I post something or not. :/ (and most of the advice out there is almost certainly bad or wrong, by Sturgeon's Law)

At least if I do post it, someone that comes along looking for this type of thing and *is* capable will now know the difference to check for without guessing and potentially causing themselves problems trying to figure out how to find out.

 

[tomjasz]

Over simplifying is a real danger. A n00b ist equiped gi make a judgement without at least a simple disclaimer. All to often in 7 years of supporting kit customers i found this to be true. Its not s criticism, just a suggested awareness. Sometimes we forget how it was starting out. Take the suggestion FWIW. The biggest criticism I read regarding ES is exactly that. I for one is thankful for your detailed responses. Well done.

 

[amberwolf]

If I spent the time and forum space to write sufficient disclaimers and detail to ensure whoever follows the instructions can do so and/or can tell exactly what theyr'e getting into if they dont' already know that, it'd take me weeks or longer to write every post and they would be dozens to hundreds of pages long, and no one would ever read any of them, or use any of the information, making them all a complete waste of everyone's time.

(and this is aside from it being completely impossible to have every possible system and item out there to be able to personally examine and create the detailed warnings and instructions from, as that is not possible to do in sufficient detail without this)

That kind of detail would be required, since I cannot judge what someone else can do unless I am personally acquainted with them for their whole lives and know everything they are or are not capable of via direct experience... Since there are zero people on the planet that fit this qualification....

Maybe other people can do that sort of thing, but I can't, and I can't even imagine how anyone else could.


So...it's up to the reader to judge their own capabilities and whether or not to follow anything posted. There's literally no other practical way to do this sort of thing, helping people remotely over a forum.


When someone asks for more specific instructions and is willing to provide sufficient information for me to create those instructions, I can do so (and have done)...but that's a very very rare scenario.



FWIW, anyone simply giving advice to make sure voltages are the same and just connect batteries together without knowing sufficient details about them (or the user's capabilities), are providing potentially much more dangerous advice than I am.

 

[tomjasz]

at least a simple disclaimer.