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diy solar

balancing strategies as they relate to BMS

ArthurEld said:
Thanks, I have 100A MRBF but that seems too big. Should I get 30A MRBF? Or, 20A ATO fuses?

That is the size of the wires on my BMS. There are 4 of them.
Click to expand...
The fuse is to protect the wire and 100amps is withing spec for 6 awg.
The only failures I could see happening is a wiring mistake or a short in the charger and a 100 amp fuse will handle that.
The BMS also has overcurrent protection but I never trust a fet to fail open.
Also for quality fuses the lower the rating means the higher resistance.
 
smoothJoey said:
The fuse is to protect the wire and 100amps is withing spec for 6 awg.
Click to expand...
I am wondering why not use a 15a fuse when the charger is rated for 12a?

I get that the fuse protects the wire but as drawn in post #119, the positive leg should not exceed 12a if operating correctly.

Wouldn’t tighter tolerances on the fuse be better?

I would think if the positive leg somehow gets 90a, the charger rated at 12a is going to be smoking or worse.
 
MisterSandals said:
I am wondering why not use a 15a fuse when the charger is rated for 12a?

I get that the fuse protects the wire but as drawn in post #119, the positive leg should not exceed 12a if operating correctly.

Wouldn’t tighter tolerances on the fuse be better?
Click to expand...
Yes and no.
The ATC fuse aic=air interuppt capcity is very low and its possible the fuse might blow and still sustain an arc in a dead short.
 
smoothJoey said:
The ATC fuse aic=air interuppt capcity is very low and its possible the fuse might blow and still sustain an arc in a dead short.
Click to expand...
You kind of lost me but it sounds like the fuse type/design is the problem rather than the size.
If the fuse blows yet the break/gap is small enough to arc across is disturbing and new to me. Is that because its 48v?
 
MisterSandals said:
You kind of lost me but it sounds like the fuse type/design is the problem rather than the size.
If the fuse blows yet the break/gap is small enough to arc across is disturbing and new to me. Is that because its 48v?
Click to expand...

ATO / ATC Fuse - 15 Amp - Blue Sea Systems

Delivers fast-acting protection for electronics and other small loads
www.bluesea.com www.bluesea.com

MRBF Terminal Fuse - 100A - Blue Sea Systems

Space-saving ignition protected fuse for 30 to 300 Amp loads. Must use with Terminal Fuse Block.
www.bluesea.com www.bluesea.com

The atc/atc fuse is only rated for 32 volts with an aic of 1000 amps
The mrbf fuse is rated to 58 volts with an aic of 2000 amps

Breaking capacity - Wikipedia

en.wikipedia.org en.wikipedia.org
 
This is another reason that I favor making discretely fused batteries in parallel each with its own bms and fuse.
 
smoothJoey said:
The atc/atc fuse is only rated for 32 volts
Click to expand...
I wasn’t suggesting using an under rated fuse. That 15a atc is woefully inadequate.

My thought was that if a LOT more than 12a were on that line, my preference would be for a fuse to blow. A 100a fuse seems way too big to help the charger side.
 
MisterSandals said:
I wasn’t suggesting using an under rated fuse. That 15a atc is woefully inadequate.

My thought was that if a LOT more than 12a were on that line, my preference would be for a fuse to blow. A 100a fuse seems way too big to help the charger side.
Click to expand...
Nothing would get hurt if 100A went through. 100A is to keep the wire from burning up.
 
MisterSandals said:
You are saying that the 48v 12a charger will handle 100a?

I do not know but i suspect not.
Click to expand...

ArthurEld said:
Isn't the fuse to protect the battery from the charger? I don't think anything will send amps to the charger.
Click to expand...
The fuse protects the wire first.
It will also protect the battery.
We are not trying to protect the charger.
One of the scenarios we are protecting the wire and the battery from is a dead short in the charger.
 
I thought the main fuse connected to battery positive is to protect the cables in case of a short and everything else should have a separate fuse?
 
Gazoo said:
I thought the main fuse connected to battery positive is to protect the cables in case of a short and everything else should have a separate fuse?
Click to expand...
Its a single circuit with a single purpose.
How many fuses would you use and where would you put them?
 
smoothJoey said:
Its a single circuit with a single purpose.
How many fuses would you use and where would you put them?
Click to expand...
I took a closer look at the diagram. A single fuse would be ok and I would place the fuse as close to the cell positive as possible. I don't know of any reason it couldn't be placed on the negative side for that matter. Maybe I didn't read back far enough but what loads are planned?

I think he is using the same power supply I have. I have tested the power supply twice charging my Valence batteries and it does charge as advertised.
 
I think I have everything connected right. I still need to get some thin wire for battery connections to the coulomb meter.
I haven't turned on the power supply or BMS yet

IMG_20201023_152122103.jpgIMG_20201023_152140971.jpgIMG_20201023_152153781.jpg
 
ArthurEld said:
I think I have everything connected right. I still need to get some thin wire for battery connections to the coulomb meter.
I haven't turned on the power supply or BMS yet
Click to expand...
Yes that is fine. The Riden has two internal fuses. I am not sure about the actual power supply. Did you top balance the cells already?
 
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