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Question on small off grid system Options
#1 Posted : Thursday, April 09, 2009 2:57:01 AM
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Posts: 134,494

 Okay,think I can help out a bit here,I'm an electrician by trade.Your problem lies in a set of mathematic formulas electricians use called Ohm's Law.You are blowing the fuses on the battery side because at 12 volts the dehydrator will be drawing 42 amps from the batteries.Thats 42 amps on the + AND the - side not the addition of 20 on the + and 20 on the -. Heres how it works: At 120 volts from the inverter 500 watts is equal to 4.2 amperes (500/120 = 4.1667 amperes)or I(amps)= P(power consumed)/E(voltage or pressure impressed on the circuit).Now at the batteries that 500 watts consumed is equal to 42 amps or (500/12 = 41.6667 amps),and hence the reason your fuses blew on your batteries.You need to up the size of your fuses at the batteries to 45 amperes,unfortunately you may need to change your fuseholders to do so because FRN style fuses(small cartridge fuses)are sized only to 30 amps.You will also need to change the wire size from the batteries to the inverter(not the solar panel wiring though)to AWG #8 wire also.This is because the amps flowing from the panel to the charge controller/batteries will never go over the output rating of the charge controller but it will from the batteries to the inverter.The household breaker box is fine because coming out of the inverter the circuit voltage is 120 volts.Other than that the deep cycle marine batteries are well sized;you should be able to store plenty of power.Hope I helped out..

#2 Posted : Thursday, April 09, 2009 1:19:31 PM
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Posts: 134,494

Thank you very much. I understand. I had calculated the amperage on the inverter side, but did not know I must also calculate on the battery side too. Big difference!

As a side note, since installing my system I've lost power company supplied electricity to my house several times. It's really cool knowing if I needed to I could go out to my workshop and have electricity there regardless of what's going on with the house. I love this solar stuff, and hope to be able to take my house off grid next year.

#3 Posted : Thursday, April 09, 2009 1:19:31 PM
Rank: Guest

Posts: 134,494

I've watched a lot of YouTube instructions, and read a lot of sites before setting up my solar powered workshop. The basics are a 130 Watt panel, two large marine batteries from Walmart.

The panel feeds into a fuse box where I have a 20 amp auto fuse. From that I go out to a charge controller which feeds my batteries. To get to the batteries, power goes through another fuse box with a 20 amp auto fuse. From this same box wires run to my inverter. Out of the inverter I sent A/C power to a household type breaker box and distribute power through my workshop.

Everything works fine, unless I plug in something that pulls a lot of amps (I guess it's amps). I plugged in a 500 watt dehydrator and I blow the fuse in my battery fuse box. I saw on one instruction that batteries should be fused with an auto fuse, but either I'm not doing it right, or the instructions I saw were not meant to be used with a 500 watt dehydrator.


You can see a video of it here.




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