Is there a simple breaker solution between the battery and inverter?

TucsonAZ

I know there's the $200 plus disconnect boxes but what were people doing a decade ago? Is there a simple breaker solution to put between the inverter and the batteries for a low budge throw your codes out the window application?

Also, with a 1,500 watt Cotek pure sine 24v inverter, how big of a DC breaker do I actually need?

Cariboocoot

Re: Is there a simple breaker solution between the battery and inverter?

To answer the second question first, 1500 Watts @ 24 Volts is 62.5 Amps. Depending on how low a Voltage the inverter allows (could be 21) this may be as much as 72 Amps. Apply the NEC derating (avoids nuisance trips) and you basically get a 100 Amp breaker. For best results consult the instructions for the inverter regarding sizing of DC wiring and over-current protection.

To answer the first question second, cheap and easy ain't in it. You can get an appropriate size DC breaker for <$50 http://www.solar-electric.com/stfubr1.html but you may need to be handy at fabricating to come up with a mount for it.

TucsonAZ

Re: Is there a simple breaker solution between the battery and inverter?

Cariboocoot wrote: »

To answer the second question first, 1500 Watts @ 24 Volts is 62.5 Amps. Depending on how low a Voltage the inverter allows (could be 21) this may be as much as 72 Amps. Apply the NEC derating (avoids nuisance trips) and you basically get a 100 Amp breaker. For best results consult the instructions for the inverter regarding sizing of DC wiring and over-current protection.

To answer the first question second, cheap and easy ain't in it. You can get an appropriate size DC breaker for <$50 http://www.solar-electric.com/stfubr1.html but you may need to be handy at fabricating to come up with a mount for it.

Awesome, thank you! I came up with this after I typed my post:

http://www.amazon.com/STINGER-SCBM150-Marine-Circuit-Breaker/dp/B002LARRTO/ref=pd_sim_sbs_e_10?ie=UTF8&refRID=1XK7QBN8XXJJ4KV1TR06

I like the MidNite 100a more and if I can use a 100a (I will check specs) that would be my first choice so I will do a little more research, fabricating is what I live for (:

stephendv

Re: Is there a simple breaker solution between the battery and inverter?

You should size the breaker for the surge current not the rated current. Your inverter also has a 3000W surge rating, so I'd say you need at least a 150A breaker.

BTW, Off-topic:
The cotek 1500W/24V inverter and the Victron 1600W/24V have almost identical specs, yet the cotek weighs 5.3kg, and the Victron 10kg, guessing that's because of a bigger transformer.

TucsonAZ

Re: Is there a simple breaker solution between the battery and inverter?

That's a nice inverter for sure, I'm sure the components are substantially better and I would have liked to get a higher quality unit but the Cotek and 1kw of solar panels cost me what that Victron costs so I will have to stick with the Cotek as my backup inverter bought before the inverter it's meant to back up (:

I will disagree on the 150a breaker but I have read this:

http://www.midnitesolar.com/pdfs/Carling_A-DTime-Delays.pdf

As such, I'm fairly certain even with a 3,000 watt surge which is right at 125% of the breakers rated amps that the breaker won't trip for what the inverter is rated to do. I'm not factoring in the 91% efficiency but with that said, I'm not looking to run my inverter at surge capacity beyond a few seconds at a time (which the breaker can handle) and in all honesty would have been fine with a 700watt inverter for my needs I just wanted to be on the safer side. My way of saying that I would rather the breaker trip if I'm pushing the inverter over the 3,000 watt surge it's intended for.

stephendv

Re: Is there a simple breaker solution between the battery and inverter?

TucsonAZ wrote: »

I will disagree on the 150a breaker but I have read this:

http://www.midnitesolar.com/pdfs/Carling_A-DTime-Delays.pdf

Aha, good data that. I'd rather err on the side of a too-big breaker than too small, since the currents generated by a short circuit will be much larger than the normal operating currents. I guess with those numbers and your planned usage you should be OK.

Cariboocoot

Re: Is there a simple breaker solution between the battery and inverter?

stephendv wrote: »

You should size the breaker for the surge current not the rated current. Your inverter also has a 3000W surge rating, so I'd say you need at least a 150A breaker.

Actually, no. Most 'surge' ratings are for such a brief time that a breaker rated for the continuous current will hold for that period. Breakers actually need more than their rated current for a certain period of time before they trip so momentary surges should not cause nuisance trips. Plus most people do not run their inverters anywhere near capacity (which is a good thing).

BTW, Off-topic:
The cotek 1500W/24V inverter and the Victron 1600W/24V have almost identical specs, yet the cotek weighs 5.3kg, and the Victron 10kg, guessing that's because of a bigger transformer.

Quite probably. The small Cotek/Samlex inverters have notoriously poor surge duration (less than 1 second), and a tiny transformer is one reason for this.