Dc Breakers

[PeSCaLo]

Hi Guys,
Questions about Dc Breakers in Series.

Let say I have 4 DIY 12V LFP batteries and each one has its own DC Breaker rated to 24V 63A.

If I decide to series connect them Together, i’ll get 48 V bank.
Will I be going over each breaker’s nomival voltage of 24Volts.? since the home pack is 48v?

 

[Don B. Cilly]

Yes, way over. You'd have to get a 60-80V (or more, whatever you can find) breaker.
Also, the batteries, you'd have to remove three BMSs and rewire just one - if it takes 16S. Probably best to re-arrange all cells...
-

 

[PeSCaLo]

So, the question is, can I use 24v breakers on each battery and then serial connect them all.

wont that breaker always “see” less than 24v?
wont that breaker need to extinguish <24v arc?
if all breaker work together?

 

[Hedges]

If all breakers are mounted side by side on a DIN rail and mechanically ganged, that works.
Midnight for instance sells 300V and 600V breakers made of two or four 150V poles.

If they trip independently, one will trip and experience entire voltage of pack.
Same goes for BMS; some can handle the voltage of being connected in series and some can't.

 

[rmaddy]

There is no reason to put a breaker on the batteries in series. Put a properly sized Class T fuse near the battery bank on the positive wire to the positive bus bar.

One other idea to consider - if you have 4 DIY 12V LiFePO₄ batteries that you want to put in series for 48V, why not get a 16S BMS and build an actual 48V battery? Eliminate all of the extra issues and effort of putting 12V batteries in series.

 

[Hedges]

What is the AIC rating of your "DC Breaker rated to 24V 63A"? (I find some rated 6k AIC.)
Your "DIY 12V LFP batteries" may have short circuit current capability greater than the breaker.

 

[chrisski]

Can your BMS be put in series for 48 volts? Not all can.

 

[PeSCaLo]

all breakers are mounted side by side on a DIN rail and mechanically ganged, that works.
Midnight for instance sells 300V and 600V breakers made of two or four 150V poles.

@Hedges Hi
Can we expand on that?
That was exactly my question. And that was exactly what I was thinking.


So, since the breaker/ fuse would only see the volt to where is connected.
Im asking because im looking into finding a solution to few problems problems:
- LFP have very low internal resistance. means that a small mistake mixing cables in shorting the bank will creat a huge fireball , sparks, and vaporize the metal eyelugs. From experience.
I dont want to expose family and friends to this kind of danger, above what SLA provides.
So Im looking to integrate a Short Circuit Prevention Mechanism into each battery. A Fuse would be great, ANL has 80v 500 amp relatively inexpensive. Breaker Tomnz 125A 250v 10Ka
- Individualy fusing or breaker, batteries that I can later serial connect to any voltage needed.
- low Volt Fuses are MUCH less expensive that HV fuses.

If I want to create a 384v bank, all the little fuses should protect the individual batteries.




can you please link to the midnight breakers?

 

[rhino]

https://www.midnitesolar.com/pdfs/breakers_11x17.jpg

 

[chrisski]

So Im looking to integrate a Short Circuit Prevention Mechanism into each battery. A Fuse would be great, ANL has 80v 500 amp relatively inexpensive.

I think the Class T fuse is pretty pricey, but it is less than the breaker, housing and mounting itself.

I do have both my 8S batteries fused with a Class T and then fused again after they are joined. Each Class T fuse needs to be mounted in a fuse holder, and each fuse holder is about six inches long, two inches wide, and three inches tall. First shock I had was how much each fuse and housing cost and then how much room they took up in my build. Still less price and space than a properly rated DC circuit breaker with a housing.

 

[rmaddy]

First shock I had was how much each fuse and housing cost

You can spend $50 for a Class T fuse and matching holder and cover at donrowe.com or you can spend more than twice that for the Blue Sea Systems versions. The fuse from donrowe.com is a high quality Littlefuse brand fuse.

 

[Hedges]

If I want to create a 384v bank, all the little fuses should protect the individual batteries.

You will need fuse or breaker able to interrupt > 384V.
Some from Midnight are rated 600V. Four poles in series, common trip.

Class T, even JLLS is only rated 300V

Class T Fuse - Industrial Power Fuses - Littelfuse

www.littelfuse.com

Here are 400VDC to 1000VDC fuses

McMaster-Carr

McMaster-Carr is the complete source for your plant with over 595,000 products. 98% of products ordered ship from stock and deliver same or next day.

www.mcmaster.com

What will the device be that is the load?
Some inverters for 400V input say 30A max short circuit current. They are meant for lower voltage battery plus boost converter.

 

[chrisski]

If I want to create a 384v bank, all the little fuses should protect the individual batteries.

You will need fuse or breaker able to interrupt > 384V.
Some from Midnight are rated 600V. Four poles in series, common trip.

Well, the 384 v requirement is more than I can speak to. Class T fuses definetly do not do that, nor any fuse I have used.

 

[sunshine]

Will I be going over each breaker’s nomival voltage of 24Volts.? since the home pack is 48v?

Probably....but since the nominal voltage will only be exceeded after the fuse has blown will that really matter since we are talking relatively low voltages?

Show me a blown fuse that would arc across 48v and not 24V !!

 

[Hedges]

Look at the interrupt rating vs. current for this one.
Maybe it wouldn't arc at 48V, but I wouldn't take the chance. Especially for a high short circuit current battery.

https://www.bluesea.com/products/5253/AMI___MIDI_Fuse_-_60_Amp

Well, the 384 v requirement is more than I can speak to. Class T fuses definetly do not do that, nor any fuse I have used.

DMM fuse, for one.
PV string fuses too.

 

[PeSCaLo]

Still less price and space than a properly rated DC circuit breaker with a housing

Here is the link for this breaker $15 from aliexpress. This Brand has been extensively reviewed on Youtube.

 

[PeSCaLo]

If we use this busbar for the Tomnz Breaker above, that would be a great solution for the 384Vdc battery.
Anybody knows the name of this kind of busbars with lug for MCB? or a link to buy one?

 

[PeSCaLo]

What will the device be that is the load?

This load will be a 40Kw UPS, Split-phase, with mppt 22Kw Solar controller. It needs 384Vdc battery to work.

ere are 400VDC to 1000VDC fuses

thanks, I was thinking of using Solar Fuses, <1000Vdc up to 50 amps available

 

[WYtreasure]

You get what you pay for (maybe) and $15 to protect a bunch of electronics does NOT seem like a good idea to me.

 

[PeSCaLo]

You are right.
Im thinking of a Cascade Effect, using multiple Breakers (China MCB) on each battery, and one Main Hight Quality Midnight DC Breaker Before the Load.
Same with Fuses.