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Proper rating for DC breaker for battery ?

Why not MRBF?
They are smaller and have a higher rating.
Good question. The only reason is that I have some ANL holders laying around from a different project.
When you mentioned the MRBF previously, I was thinking of the they were like the Class-T types.
Now I see what you mean.
Yeah, that could save some space. I'm still not sure what size enclosure I will use for this setup. Probably a Pelican type case.

Thanks for the tip... you guys have been really helpful (as always :) ).
 
The bluesea mrbf carriers fit a 3/8"(10mm) stud.
Littelfuse makes a terminal carrier that fits an 5/16"(8mm) stud.
I don't know of any carrier that fits a 1/4"(6mm) stud.
Learning point for me since I’ve never used these.

I think You just don’t place on any stud like a 4 stud bus bar. I believe you need to purchase a MRBF fuse block that attaches to a stud on that four position busbar.


To me, I picture this Kind of looks like a staircase when the fuse block is added to a bus bar.

Thanks.
 
Hi guys, real noob question, how is the math done behind figuring out how much the breaker must be able to handle?

I am trying to figure out how to dimension a breaker for a 16s 3.2v 280ah battery. Is it correct to assume that it must be able to handle more than 280a since the battery is “1C” (this seem to be how others have calculated)?

And lol, what the heck is “1C”? It obviously indicates that you are emptying the battery over 1 hour. But is this the max for these batteries? Or do you have to control that you don’t superseed the breakers capacity when you use it? (Seems unlikely that you would want to disconnect the battery with a manual switch when you are using a tremendous amount of power of course so I am sure that is fine, but just want to understand.)
 
Hi guys, real noob question, how is the math done behind figuring out how much the breaker must be able to handle?

I am trying to figure out how to dimension a breaker for a 16s 3.2v 280ah battery. Is it correct to assume that it must be able to handle more than 280a since the battery is “1C” (this seem to be how others have calculated)?

And lol, what the heck is “1C”? It obviously indicates that you are emptying the battery over 1 hour. But is this the max for these batteries? Or do you have to control that you don’t superseed the breakers capacity when you use it? (Seems unlikely that you would want to disconnect the battery with a manual switch when you are using a tremendous amount of power of course so I am sure that is fine, but just want to understand.)
What are the highest loads you expect to see.

Really based off the highest load you expect to see. Not just individually, but combined. From there, you go for an inverter big enough to run that.

I have a two batteries 8S 280 ah, so 560 ah total, and I fused each battery for 125 amps and 225 amps once combined and I have a 3000 watt inverter.

Formula for watts is

Inverter Wattage / Low Voltage Cutoff X Power Conversion Factor = Expected Amps

Expected Amps * 1.25 = what to fuse for. Round up to the next fuse size.

Much better explanation is here:

 
What are the highest loads you expect to see.

Really based off the highest load you expect to see. Not just individually, but combined. From there, you go for an inverter big enough to run that.

I have a two batteries 8S 280 ah, so 560 ah total, and I fused each battery for 125 amps and 225 amps once combined and I have a 3000 watt inverter.

Formula for watts is

Inverter Wattage / Low Voltage Cutoff X Power Conversion Factor = Expected Amps

Expected Amps * 1.25 = what to fuse for. Round up to the next fuse size.

Much better explanation is here:

Thanks! That is great! What is the Power Conversion Factor? Is that an estimated factor (1.25) that you apply at the end?
 
Thanks! That is great! What is the Power Conversion Factor? Is that an estimated factor (1.25) that you apply at the end?
The power conversion factor is listed in the inverter specs. My 12 volt inverter is 85% efficient, and the and my 24 volt inverter is 88% Efficient. When converting AC to DC, some energy is lost. When you pull a 1000 watt load and look on your inverter output readings, it reads 1000 watts, but it will take about 1150 watts from the battery to run it. If that was 3000 watt inverter, would be 3450 watts from the battery. It adds up and effects fuse sizing.

The 1.25 is for ”transient voltage.” Better described in the resource that was linked. Some loads may spike briefly when turing them on so this larger rating will avoid nuisance trips. Breakers are much more expensive then fuses, but are free to reset. Some of the fuses will cost $35+ so don’t want to blow those.
 
The power conversion factor is listed in the inverter specs. My 12 volt inverter is 85% efficient, and the and my 24 volt inverter is 88% Efficient. When converting AC to DC, some energy is lost. When you pull a 1000 watt load and look on your inverter output readings, it reads 1000 watts, but it will take about 1150 watts from the battery to run it. If that was 3000 watt inverter, would be 3450 watts from the battery. It adds up and effects fuse sizing.

The 1.25 is for ”transient voltage.” Better described in the resource that was linked. Some loads may spike briefly when turing them on so this larger rating will avoid nuisance trips. Breakers are much more expensive then fuses, but are free to reset. Some of the fuses will cost $35+ so don’t want to blow those.

Aha, so in my case with a 4kw inverter with 95% conversion that would give 4000w/40v (cut off voltage 48v battery of 16s 3.2v cells?) * 0.95 * 1.25 = 118.75As. With a 300A breaker we should be safe, right?
 
Aha, so in my case with a 4kw inverter with 95% conversion that would give 4000w/40v (cut off voltage 48v battery of 16s 3.2v cells?) * 0.95 * 1.25 = 118.75As. With a 300A breaker we should be safe, right?
Depends on the wiring. The wiring would need to handle the 300 amps. Would be better to get a 125 amp if available or a 150 amp if not available. 300 amp wiring, lugs, and corners are a little more expensive than 125 amp stuff.
 
Depends on the wiring. The wiring would need to handle the 300 amps. Would be better to get a 125 amp if available or a 150 amp if not available. 300 amp wiring, lugs, and corners are a little more expensive than 125 amp stuff.

Good point!

I’ve seen in YTs that they use like 70mm2 welding cables between the battery and the inverter, which I am sure are expensive (at the same time it’s not a very long distance). Does thick cables like that just enable you to use more power or do they also prevent losses?
 
To a point it helps. I lean to the conservative side. For my 24 volt 3000 watt system, I use 4/0. That’s what my calculations and wire ampacity charts said. Others use the 48 volts and not the inverter cutoff of 40 volts which will get you less amps and the same wattage with thinner wire, especially if the insulation rating is more than the 60c I use.

Where it really hurts, and you see this in Amazon 1 star reviews on inverters, My 12 volt 3000 watt inverter wiring for hot and it faulted out way before max output. Many times that is because wire way too thin is used and the wire heats up and loses voltage. Sometimes they even give the thickness of the wire, like 6 AWG.

That’s where it’s especially dangerous. No calculations done at all.

I did find the4/0 wire difficult to route because it was so much thicker than what I’m used to.
 
I did not read through this thread, just your question. I don't like CB, I like fuses for the catastrophic circuit protection. It is best to find the proper size wire to reduce voltage drop in the circuit and then size the fuse to the ampacity of that wire size. Most fuses and breakers have a response time that is found in their rating charts. As the amperes go above the ampere size of the fuse or CB, the fuse opens the circuit sooner at higher amperes and holds longer as the amperes drop nearer the fuse size. That is to allow for any surge current that may pass. 10 or 15 seconds is very fast.
 
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