Breaker Recommendation

[JustFloyd]

I just build a 52V battery with 304ah LFPO4 batteries, in a box kit. The kit came with a fuse (see Pictures) I'd like to replace it with a breaker. Looking for good quality and inexpensive if such a thing exists. Any recommendations?

 

[SparkyJJO]

"Inexpensive"

Well, how do you define that?

If you mean $20 - good luck, none of those are worth anything.

$80-100? Now you're getting close.

 

[JustFloyd]

"Inexpensive"

Well, how do you define that?

If you mean $20 - good luck, none of those are worth anything.

$80-100? Now you're getting close.

You'll notice I did say "if such a thing exists" Quality is priority over cheap. So what brand or brands would you recommend?

 

[HRTKD]

Look at the Midnite Solar breakers. I use their breakers, but not for OCP at the battery. The best OCP at the LiFePO₄ battery is a Class T fuse.

 

[JustFloyd]

I've looked at them, unless I missed it they don't have an 80v 400amp breaker. I found some on Amazon but am leery of them. I'm not sure what class fuse/fuse holder that is that came with the battery box, but getting a few spares may be the way to go. Unless something bad happens, I'll never pull enough from that battery to blow a 400a fuse! An external disconnect would be a good idea though.

 

[HRTKD]

Victron Energy makes a disconnect switch that is rated for 48 volt systems.

 

[Brucey]

Look at the Midnite Solar breakers. I use their breakers, but not for OCP at the battery. The best OCP at the LiFePO₄ battery is a Class T fuse.

Im pretty biased but I believe the mnedc175 or 250 breaker is the better ocp solution over a class t. AIC rating of 50,000A @125V, and can handle short term surges like inverter power up without needing to precharge etc. Doubles as disconnect. Really only downside are cost (which isn't a lot higher than a proper class t fuse holder and fuse) and physical space/mounting it needs.

 

[Brucey]

I've looked at them, unless I missed it they don't have an 80v 400amp breaker. I found some on Amazon but am leery of them. I'm not sure what class fuse/fuse holder that is that came with the battery box, but getting a few spares may be the way to go. Unless something bad happens, I'll never pull enough from that battery to blow a 400a fuse! An external disconnect would be a good idea though.

Looks like an 80V megafuse. Their AIC rating is pretty marginal for a 48V lfp battery, i.e it could open but the gap is insufficient to break the arc and power continues to flow.

 

[HRTKD]

Im pretty biased but I believe the mnedc175 or 250 breaker is the better ocp solution over a class t. AIC rating of 50,000A @125V, and can handle short term surges like inverter power up without needing to precharge etc. Doubles as disconnect. Really only downside are cost (which isn't a lot higher than a proper class t fuse holder and fuse) and physical space/mounting it needs.

How does the Class T fuse compare to the MNEDC250 breaker in terms of size? I fit a Class T fuse inside my 16s battery box. Also, how fast will the breaker open the circuit compared to the Class T? I haven't looked at the specs, so I don't know the answer. (It's not a rhetorical question)

 

[Brucey]

How does the Class T fuse compare to the MNEDC250 breaker in terms of size? I fit a Class T fuse inside my 16s battery box. Also, how fast will the breaker open the circuit compared to the Class T? I haven't looked at the specs, so I don't know the answer. (It's not a rhetorical question)

The mnedc250 is much bigger.

https://www.solar-electric.com/lib/wind-sun/MNEDC175-MNEDC250_specs.pdf

And the breaker trip curves, the ones I have are all 16, last page of document, F series.

https://www.stellavolta.com/content/CarlingBreakerTimeDelayValues.pdf

The Class t will absolutely open much sooner, the mnedc with type 16 trip curves allows for much more leeway for inductive loads/motors etc.

Edit to add, will trip at 313A steady state, so alot of leeway there.

 

[robbob2112]

At 400amps you are looking for a MCCB style breaker --- The Dih00l black brand will run you around $200ish... You might get a used ABB or Schneider breaker on ebay for around that.

I would replace that fuse with a class T like this

TFB2-400, 400A Class T Fuse Kit | DonRowe.com

The TFB2-400 offers 400 amps of over-current protection and provides safe operation of your inverter.

www.donrowe.com

Are you sure you need the 400 amp size? They provided that amperage because 304 cells usually run at 1C...

304a * 1.25 = 380a --- so 400amp fuse.

But if you have multiple of those batteries connected in parallel to say a 10k inverter

10000W/51.2v = 195a * 1.25 = 244a --- so 250amps would be enough to protect the battery and let the inverter run.

Also, you don't say what the amperage of the BMS is. If it is the typical 200amp BMS - then 250amps is also correct.
200a * 1.25 = 250a

If you are looking for a switch to turn the batteries on/off you might look at contactors -- like the one below -- one per battery -- then wire them to regular low current switches --- then you could turn them on/off easy -- note these are $175 full price, the $15 are probably still good, but they are EV vehicle pulls so some may be bad out of the box --- I have 16 of them and 2 weren't any good when received. They technically work, but appear to have burned contacts because the contact resistance varies with repeated cycling.

TE Connectivity EV200AAANA 500a 0-900vdc Tyco 12/24v

These were recovered from EV battery modules. These are VERY EXPENSIVE online. If you have any project that needs a high current relay this is your chance to save some money. Make a cheap 30a BMS into a 500a BMS. This will work for batteries in the 9-36v range so perfect for Lifepo4 and Lithium...

batteryhookup.com

 

[JustFloyd]

Are you sure you need the 400 amp size? They provided that amperage because 304 cells usually run at 1C...

304a * 1.25 = 380a --- so 400amp fuse.

I'll probably go with a Class T like you posted above.

But if you have multiple of those batteries connected in parallel to say a 10k inverter

I only have one of these batteries at the moment. My other batteries are EG4 LFP V2 six of them.

10000W/51.2v = 195a * 1.25 = 244a --- so 250amps would be enough to protect the battery and let the inverter run.

My inverter is an EG4 6000XP

Also, you don't say what the amperage of the BMS is. If it is the typical 200amp BMS - then 250amps is also correct.
200a * 1.25 = 250a

BMS for the DIY battery is a JK PB2A16S20P so yes it is 200a

If you are looking for a switch to turn the batteries on/off you might look at contactors -- like the one below -- one per battery -- then wire them to regular low current switches --- then you could turn them on/off easy -- note these are $175 full price, the $15 are probably still good, but they are EV vehicle pulls so some may be bad out of the box --- I have 16 of them and 2 weren't any good when received. They technically work, but appear to have burned contacts because the contact resistance varies with repeated cycling.

I got a blue sea manual disconnect switch that I'll install for on off of the battery. I was interested in a breaker so it would serve as a fuse replacement and an on off switch. Plus being able to reset it instead of having spare fuses in stock

 

[Brucey]

You will probably need to precharge the 6000xp when you first hook it up otherwise the surge will pop that class t fuse.