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Haltzy
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# Posted: 28 Jul 2013 10:43pm
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Hey Guys;
During the construction phase of our cabins, we will be living out of our RV's.
During this time we will be living off solar power and generators when needed. the solar system that we are using to supply power to two RV's is described in another post.
my questions is this..
just by sheer numbers it seems foolish to maintain our RV battery by running the inverter that is powered by solar to run our convertor to charge the battery.
Going from DC to AC back to DC basically using 50watts of power to charge the rv battery at .5 amps not smart or efficient.
We are exploring options on just tying the 12 rv battery directly into the battery bank that is located about 40' away using 12awg wire.
has anyone had to do this? What size of wire would be best. or is it just a dumb idea?
We need to maintain or RV batteries for the fridge that is running off of propane when we are away from site.
Chris
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MtnDon
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# Posted: 28 Jul 2013 11:24pm
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Quoting: Haltzy We are exploring options on just tying the 12 rv battery directly into the battery bank that is located about 40' away using 12awg wire.
You mean there is a multiple battery, battery bank 40 feet from the RV? And that battery bank has a PV array and CC connected to it? And you want to share that battery bank with two RV's at a 40 foot distance?
12 AWG wire may be too small to effect a useful charge to reach the RV battery. It depends on the amps expected to travel along the 40 ft distance. A 12 VDC battery needs a minimum of 14.4 VDC applied to the battery to get a decent charge rate going.
If we have 40 feet and assume 15 volts and 4 amps the 12 AWG wire will have a voltage drop of 0.62 volts. That would = 14.38 volts at the RV battery. That would work. But 4 amps is a small current; any higher and the voltage drop will climb. 8 amps will end up with just under 13.8 VDC. Workable but slow.
Much better to place the array, CC and bank of batteries much closer to the RV or use much larger wire, like 8 AWG. Depending on amps of course.
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Haltzy
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# Posted: 28 Jul 2013 11:51pm
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Quoting: MtnDon You mean there is a multiple battery, battery bank 40 feet from the RV? And that battery bank has a PV array and CC connected to it? And you want to share that battery bank with two RV's at a 40 foot distance?
That is 100% accurate. Our issue is as you know the wire length from the arrays (on top of a seacan) to the CC, and then from the CC to the batteries. we need to keep this distance short to ensure adequate charging of the main system. When we are at site, the RV can run off the invertor or a generator if need be. Typically solar power is sufficient unless we are running tools and such.
I will have to buy a meter to ensure the voltage coming in from the battery bank is strong enough to charge the battery at the rv. Im hoping that is does not have a negative effect on the battery bank, by adding two more batteries (two RV's) to the overall capacity.
Since a trickle charge is only.5amps/hr. I estimated that 12awg would be plenty, but like you said, as long as we can keep the volts up.
Thanks;
Chris
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Truecabin
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# Posted: 29 Jul 2013 12:43am
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dont bother with awg for this temp setup get two 40ft of 12-2 housewire and use all3 wires for the plus and all 3 for the minus then you are set to get all the amps at midday
and in case you add a 2nd panel you are ready
then use the housewire on the house or whatever
and when you wire the panels to the house then get the proper wire for that job
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Truecabin
Member
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# Posted: 29 Jul 2013 12:51am - Edited by: Truecabin
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temporary solar is a good use for scrap housewire you can use any wire you can find and they dont have to be same size
the more copper you give it the more amps will flow even if you use 1 wire for the plus and 2 wires for the minus
its a good way to learn about solar and learn about electricity
electricity flows like water think of it in a bigger pipe or smaller pipe
try to balance it but remember more copper is more amps dont leave any unused wires
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Haltzy
Member
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# Posted: 29 Jul 2013 12:01pm
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Hmm, Interesting. I would be hesitant to run house wire due to weather/wear/tear resistance of house wire.
That being said, i think i will upgrade my current wire. They have 50' 12/3 extension cords on at crappy tire for $25 right now.
Chris
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