Fusing Questions

mjp24coho

I'm hoping for a bit of direction here regarding fusing. I'm completing the install of a minor solar system for my offgrid cabin. I use the system to run a few DC booster pumps and DC lights. I currently have a 205 W Kyocera panel with (2) 78 amp-hour 12V AGM batteries. It's currently wired to be just a 12V battery bank. I have a 15 amp fuse between the panel and the charger. I assume I also need an additional fuse between the charger and the battery bank - how do I figure out what size fuse that should be? I then run the batteries to a negative and positive bus bar fuse bock distribution. There are fuses on the fuse block system for each of the loads that are attached to the positive side. Are there any other fuses I should consider?

I'm considering down the road adding a VFX3524 24 V inverter and wiring the batteries to be a 24 V bank. The purpose for this will be so that I can occasionally operate an AC submersible well pump. If I end up going that route, what fusing would you suggest between the battery bank and inverter?

Thanks!

Cariboocoot

Re: Fusing Questions

If you have a fuse between each 12V device and the bus bar, you don't need an additional fuse between the batteries and the bus bar. So long as the cumulative load doesn't exceed the rating for the wire to the battery.

If you're thinking about going to a 24V system to run a FX 3524, you will probably have to replace everything except the one panel, and that will need more. The charge controller could be '12 V only'. Your batteries are only 156 Amp/hrs. Roughly speaking at 12V that's 1872 Watt hours if fully depleted. At the recommended 50% maximum discharge it's half that. Not a lot of power, really. (The same batteries in 24V configuration yield the same total power measured in Watt hours.)

AC motors tend to be power hogs, especially on things like water pumps. There are innumerable such pumps out there, so I don't know what kind you're talking about and can't give you an idea of what it will take. You could be looking at a 1/4 HP 'pond' pump or a 2 HP 'deep well'. Big difference between them.

crewzer

Re: Fusing Questions

I'm considering down the road adding a VFX3524 24 V inverter and wiring the batteries to be a 24 V bank. The purpose for this will be so that I can occasionally operate an AC submersible well pump. If I end up going that route, what fusing would you suggest between the battery bank and inverter?

OutBack recommends a 250 A DC-rated circuit breaker with a high interrupt current rating (AIR) like this one: http://store.solar-electric.com/obdc-250.html

HTH,
Jim / crewzer

westbranch

Re: Fusing Questions

Better safe than sorry, I would place a large Fuse/CB, suitable to the total of all loads expected, in line close to the Batt bank as a fail-safe in case of a short or ? ...

If you wire it so that you have only one cable connected to the batt. + terminal and a "T" in the line from the CC to the load panel, it will handle all incoming/outgoing power to/from the batt., but you are unlikely to exceed Crewzers 250A, based on your current system.

HTH
Eric