Overdischarged batteries, no grid connection

[houseofancients]

I could be wrong but I thought there are more supporters for JK-BMS on this forum than any other BMS. Obviously that doesn't necessarily make it better. Refresh my memory, which BMS are you using again? Does your BMS do pre-charge and have inverter communications built in?

Seplos and yes..
Jk has a proper BMS too...

The one you're using was developed for an e-bike/motor and may work fine for folks who know what they are doing and know the limitations of both their inverter and the BMS..

 

[houseofancients]

Lucky @Luk88 has a BMS with pre charge built in. The way it works is you short the BMS 3 or 4 times to the inverter caps, pausing 60 seconds after each short to wait for the BMS to recover, and voila! Precharged!

Yeah , this response proves exactly my point.

 

[kolek]

may work fine for folks who know what they are doing

Well that clearly excludes me. I've been confused since birth

 

[kolek]

the abusive absorb zone

absorb zone is the period of charging between about 80-90%?
sorry I don't get it. why is this abusive? difficult to balance through that stage?

 

[Skypower]

One thing about the JK. If it is rated for continuous discharge 200 amps, I’d believe that if it was in the open with a fan blowing on it. If it’s on the side of a box and it can do convection cooling I say 150 continuous. Enclosed 100 or less. There’s very little loss through the bms and it’s highly efficient but there’s still some heat buildup and it’s got to dissipate to somewhere.

 

[kolek]

still some heat buildup and it’s got to dissipate to somewhere.

Are there people reporting overheating with the JK-BMS enclosed in the battery box? I searched the forum here and nothing immediately pops up. It's relevant to me, because I have mine enclosed with the cells, with only about 1 inch of space between it and the lid of the box.

 

[Skypower]

absorb zone is the period of charging between about 80-90%?
sorry I don't get it. why is this abusive? difficult to balance through that stage?

No, I mean at a full state of charge, the point where your voltage hits a wall and stays there a bit. The algorithm in my inverters doesn’t give me access to absorb time, usually between 15 or 45 minutes. Once that’s done it the inverter won’t pick back up until it reaches the float voltage of 54 volts. Rinse and repeat next day.

 

[kolek]

Are there people reporting overheating with the JK-BMS enclosed in the battery box? I searched the forum here and nothing immediately pops up. It's relevant to me, because I have mine enclosed with the cells, with only about 1 inch of space between it and the lid of the box.

Researching my own comment further, I see this:
"Never "enclose" a BMS meaning don't cover/wrap it in anything, it needs air for passive cooling. They get warm when in use, warmer with higher amp draws, so it's important that they can shed that off."
Looks like I need to redesign how I'm doing that

 

[Skypower]

Are there people reporting overheating with the JK-BMS enclosed in the battery box? I searched the forum here and nothing immediately pops up. It's relevant to me, because I have mine enclosed with the cells, with only about 1 inch of space between it and the lid of the box.

Check out RCinFLA’s chart post #9

Lifespan of FET-based BMS?

I'm running a 271Ah 4S bank through a 120A JBD BMS. Has been working well for nearly a year now. I use it to run cooking equipment daily. So maybe an hour total on average I'd guess pulling 60A or so. But shorter periods of time pulling close to 120A. Should I expect a limited life out of my...

diysolarforum.com

 

[kolek]

Maybe putting a big passive CPU cooler on top of the JK-BMS and expose that cooler outside the case? Sound like a fun cludgy project.

 

[Skypower]

Maybe putting a big passive CPU cooler on top of the JK-BMS and expose that cooler outside the case? Sound like a fun cludgy project.

lol!!!!!

 

[kolek]

Check out RCinFLA’s chart post #9

Lifespan of FET-based BMS?

I'm running a 271Ah 4S bank through a 120A JBD BMS. Has been working well for nearly a year now. I use it to run cooking equipment daily. So maybe an hour total on average I'd guess pulling 60A or so. But shorter periods of time pulling close to 120A. Should I expect a limited life out of my...

diysolarforum.com

Wow after reading that comment I am definitely going to need to get that BMS out of the box. UGH. I hate you @Skypower. Reality is all your fault! Seriously, thank you for the alert about that.

It's sad that JK doesn't put a proper heat sink on their BMS given that post, rather than stick it in an aluminum box which would only exacerbate the problem.

 

[Skypower]

Happens to be my today’s project. Air blows in the plenum area, then across the tops of the batteries and out the top rear of the cover (seen in background). My bms’s are never much above ambient but my cells are getting warm in summer. I found that if I remove heat when it’s cooler 3AM to 10AM I can get way ahead of the heat later. Buss bars are excellent means of conducting heat out of the cells. Two of my batteries already have this but they are in the open under a bench top protecting them. A small fan connected to a smart plug blows air across the tops of them. When it gets hot the air is stagnant, no sense in blowing hot air on them just to heat them.

 

[kolek]

Looks great. You're way ahead of me.

 

[Skypower]

Wow after reading that comment I am definitely going to need to get that BMS out of the box. UGH. I hate you @Skypower. Reality is all your fault! Seriously, thank you for the alert about that.

It's sad that JK doesn't put a proper heat sink on their BMS given that post, rather than stick it in an aluminum box which would only exacerbate the problem.

Before you panic see how hot it gets. If it needs some help a tiny fan can help a ton.

 

[kolek]

Before you panic see how hot it gets. If it needs some help a tiny fan can help a ton.

Will do, and our household doesn't use much power so maybe it won't get too warm. Right, fan or even better, if it's enough, passive cooling. My first choice would be sticking copper heat sinks on the case with thermal paste / thermal epoxy. And only go to fans/active cooling if passive didn't cut it.

 

[kolek]

Like this: https://www.amazon.com/Heatsink-Skiving-3-93x1-96x0-59-Electronic-Cooling/dp/B07PLPBY5Z