Protecting Battery From Short Circuit

Re: Protecting Battery From Short Ciscuit

You are right to be concerned. This is why there are fuses and circuit breakers.

There is no chance the charge controller will output too much current; it is limited to its rating. If the output should short most charge controllers will see 'dead battery' and shut down. The current from the array is usually not a problem because its potential is almost always lower than what the controller can handle. But there's always the possibility, especially with less expensive controllers. You could put over-current protection on the array side, but since PV's are 'self limiting' in terms of current it probably won't do any good (the Isc from the array may exceed the maximum the controller can handle under certain conditions). The risk here is small.

On the other hand when the battery is the power source the risk is large. If the wires should touch or the controller itself short out the battery can dump huge amounts of current into the circuit. Just think about a 'big system' with 80 Amps coming from the charge controller to the battery, but then the battery is wired to supply 200 Amps to the inverter. Now imagine that 200 Amp potential (and it's really more) being fed through the wires connecting to the controller. Instant fire.

That's why we put fuses/breakers on the circuits. One of the best ways in my opinion is the Blue Sea battery terminal post fuses. That puts the protection as close to the power source as possible, reducing the unprotected portion of the circuit to just the battery posts. If you have a detached fuse or breaker, the wire from the battery to that point is not protected and may still allow a full-current short between it and the other pole. It is a low risk, however.

Also, make sure your connections are tight. A lose one not only runs the risk of falling out and creating a short, but also of not falling out and creating a high-resistance arcing point which could be even more dangerous. Fuses and breakers do not protect against intermittent arcs.

Re: Protecting Battery From Short Ciscuit

Jayboy wrote: »

Wow thanks so much, The Blue sea looks great. I am in correct in saying if you were to accidental drop a screw driver on your batteries, With these fuses covering the terminals it will give you the best chance of avoiding a short? I like it because it limits the risk down to ground zero (Battery).

The Blue Sea fuses holders attach to the battery post, but they don't cover it; there is still exposed post there unless you put a rubber cover over it. But it's about as safe as you're going to get.

Have a look at the attached, This came with my Battery cabinet. Only the POS wire is meant to run through it. I don't understand its numbers. Can you help? Is this a breaker that pops when too much current is drawn? Attached If not what is its purpose on the battery cabinet?
Thanks!

I just spent an interesting five minutes trying to find info on that Melan Gelan circuit breaker. I didn't find anything. What I see on it is troubling: "240/415V". That would be a number sequence associated with high Voltage AC, not low Voltage DC. It also appears to be a double breaker typical for use with 240 VAC. I suspect this is unsuitable for DC applications. You got the box used, right? Someone thought it should do because it was going to carry "only" 12 Volts and this was rated for 240 - or some other such flawed logic. Don't use it.

P.S.: Tried Merlin Gerin FC45N; bingo. Now part of Schneider Electric (as is Xantrex). Still not suited for DC as far as I can tell.

Re: Protecting Battery From Short Ciscuit

Jayboy wrote: »

Thank you. I will deff look into the blue seas. So the best on the other lines would be Fuses? Any Good DC breakers?
J

MidNite has the best DC breaker equipment: http://www.solar-electric.com/pvaranddcrab.html

In general you use fuses where you will not need disconnection ability (breakers are handy as disconnects as well as over-current protection) or where there is a low likelihood of failure. Or if you're a cheapskate like me.