DC circuit breaker

blue · July 2018

I have 2awg cable from battery to inverter about 2.5 feet.

Estragon · July 2018

2ga wire seems pretty marginal IMHO for a circuit that could carry ~2500÷.85 efficiency ÷ 22v = 135ish amps, and may be able to surge much higher. The inverter manual should have a recommended wire and breaker/fuse size.

Likewise, fuse size for battery strings should be sized to be more than regular use current, but well under the ampacity of the wire used for interconnections.

mike95490 · July 2018

What gauge wire do you use from the batteries to the load ? The wire gauge determines the fuse size.

A 12V 2500w inverter can consume 400A peak surges. So, whatever your wire size, that drives the fuse size.

blue · July 2018

I have 2awg from battery to inverter and all batteries are wired with 2awg wire. I have had the inverter for a while. I am pretty sure it recommended 2awg.

mike95490 · July 2018

depending on the insulation rating, 2ga wire is good for 95A

https://lugsdirect.com/WireCurrentAmpacitiesNEC-Table-301-16.htm

Estragon · July 2018

Are you sure it was 2ga recommended, not 2/0? 2/0 is about finger-thumb size overall with the insulation. 2ga is more like pencil-sharpie size.

mike95490 · July 2018

2/O is rated 145A

#2 is rated 95A according to the chart in my earlier link, claiming to be NEC specs.

blue · July 2018

Thankyou for your help. I put the 60amp fuse in looks like we will have good sun today. Its been like a rainforest here the past couple of days. Okay I need to come clean. I was relying on memory. I went out and checked. I have 4awg cables on all batteries and to the inverter. I bought the cables from the auto parts store. I find no paper work on the inverter I believe it came that way. I cannot find the specs online I think it is discontinued. It is a jiecheng 24 volt 2500 watt pure sinewave inverter. It came with two cables that were wired with two cables each to one lug. They said 750 volts on one cable nothing else. Does that mean each of the two cables? The cables were not near long enough to separate the battery from the inverter. They were a 14 inches each. I had to replace them with 2 and a half foot 4awg cables. I am really shocked that 2/0 and 2 gage mean different things and I keep saying 2awg that I read on cables I thought all three meant the same. I am beginning to realize how little I know. I guess I should replace the 4awg battery cables with 2/0 cables. Are the 4awg cables ok for the batteries? Trying to help the planet. Ive kept the electric bill down to $30 a month. Always trying to do better. Must be safe. Thanks, Jim

Estragon · July 2018

4ga is for as little as 70a. The inverter can be a sustained load of nearly double that.

If it was me, I'd look at either; 1) replacing the wire with 4/0 for both inverter/bussbar and battery interconnects, and maybe put a bit more distance between inverter and batteries. 2 feet seems a bit close for comfort to me, or 2) rethink running 24v nominal battery if you really need 2500w.

blue · July 2018

Ok, I think I see awg and ga are the same. 2/0 has thicker strands which carry more load. Is replacing the inverter wire with 2/0 ok? What fuse would I need 150a? The batteries and the inverter and controller are in separate cabinets with separate ventilation. When your talking about rethinking 24v nominal battery are you saying I should go to 48v?

Estragon · July 2018

Yes, I'm just lazy and typing on phone, so ga is meant to be awg (American Wire Gauge)

With batteries and inverter in separate cabinets, proximity would be less of a concern for me.

Going to 48v would cut current in half vs 24v (maybe a bit more with less wire loss) for a given load and better support surge loads, but it really depends on your loads. 2500w is about where it might make sense to go to 48v. If you don't really use 2500w much though, staying at 24v may make more sense.

blue · July 2018

The 60 amp fuse worked we had good direct sunshine today and I didn't have to throw a towel over the panels. My guess is those breakers are not good for 60 amps. I had 2 from asdomo they sure look nice but they don't work. Thanks all. Big problem solved.

blue · July 2018

Had so much more charge in the batteries this am. 24.6. Usually I am around 24.3. Perhaps the asdomo breakers were arcing all the time reducing the flow through till it would cut off at 40 amps instead of the 60amp rating. Question? Can I use the same shutoff switch for the inverter and the controller. Will there be a problem with the flow of electrons? I am a novice at this but it would save switches and wiring.

Estragon · July 2018

You could, for example, have both the inverter and controller (each separately fused/breakered) wired to + and - bussbars, and a single + and - wire to batteries with a single disconnect switch. You would want the switch to be have proper dc ratings, and to avoid opening it under load (turn inverter and controller off first).

BB. · July 2018

Blue,

If I follow your question correctly, the answer is no for several reasons.

First, usually the wiring to the inverter is heavier than the wiring to the charge controller/charge controller connections. The fuse/breaker is used to protect the wiring from overheating/causing a fire. A large enough breaker for the inverter is generally too large for the charge controller.

Second, the battery bank is what "regulates" the DC voltage of your system. If you were to connect the charge controller to the AC inverter, get everything running, and then open the circuit breaker, the output of the charge controller will no longer be (for example) 12-14 volts... It will be all over the place (and could easily be >> 12 volts) and this could damage the AC inverter... Also when you "open" a switch/breaker/fuse, you can get voltage surges/spikes which can damage your equipment. It is best to have separate switches/branch circuits back to the battery bank for each major component.

Another reason is--Sometimes you need to service your components (work on the charge controller or the inverter--Don't want AC power "gone" while working the charge controller...). Also, if you leave the system for a few weeks or want to shut down the system over winter, you generally want to turn off the AC inverter and keep the charge controller running to keep the bank floating/charged.

-Bill

blue · July 2018

Thanks it didn't feel right. I appreciate your help.

BB. · July 2018

You are very welcome Blue.

-Bill

DC circuit breaker

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