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Rethinking an off grid cabin system. Advice Wanted
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Author:  TheWire [ Wed Aug 06, 2008 11:08 pm GMT EthGMT ]
Post subject:  Rethinking an off grid cabin system. Advice Wanted
I’ve been learning a lot on the forums. I was looking to power my off grid cabin with a 2000W inverter system and a set of golf cart batteries. I wanted to be able to run a couple of small kitchen appliances, along with CFL lighting. At this point the appliances were a 1000W microwave and 800W toaster (Only 1 on at a time)

I bought a remanufactured Xantrex Prosine 2000W Inverter/Charger. I liked it because it has a built in charger, pure sine output, and a sophisticated remote display with a lot of monitoring functions and settings. However, I underestimated the cost, wiring size and battery bank to provide this inverter with 200 to 400 AMPS of 12VDC. 1500+ Watt loads would be short term, but still the system needs to be sized to handle what the inverter can pull.

When looking at my other AC loads, they are 165W of CFL (Assuming all the lights are on) and maybe a small TV or a Fan. I’m now rethinking my approach and considering a smaller inverter with the bigger loads run by the generator if needed. The generator would also charge the batteries whenever it’s running.

With taking the big loads out of the equation, I now estimate 450 watt hours per day. At 20% DOD, my battery capacity should be 222 A/H which can be met by a set of 6 Volt GC2(T-105) in series.

I’m looking for feedback on this new design and suggestions for the equipment. (My initial selections are in parens)

Inverter, pure sine. (300W MorningStar SureSine)

Battery Monitor (MorningStar Remote Meter connected to Inverter)

Charger, Could I use a solar charge controller and feed it with a DC power supply or unregulated battery charger run by the generator? When I add PV panels I could use a relay or diodes to allow either the generator DC power or PV panels to feed the controller? (Xantrex C35)

If I use a pair of T-105 225Ah Batteries in series, is 30A bulk charging current to much?

I know I need to fully charge the batteries on a regular basis, but do deep cycle batteries mind getting intermittent bulk charging as the generator is started and stopped for other uses?

Thank you,

Jerry
Author:  Solar Guppy [ Mon Aug 11, 2008 9:41 am GMT EthGMT ]
Post subject:  Re: Rethinking an off grid cabin system. Advice Wanted
With small systems the options are close to limitless, hence I don't see many people respond to the help me design a cabin system posts

The one thing I can add to you thoughts is unless you have a true Mppt Solar Charger, connecting a DC generator is NOT recommended. All solar chargers are designed for solar panels, which have limited DC power on the input. A Generator, when overloaded can easly produce many times its rated output and would damage a solar charge controller. When a Solar panel gets over loaded, its output drops to near zero volts and no damage

The MorningStar Sure Sine is a solid unit ... you should bee happy with its performance
Author:  mike90045 [ Mon Aug 11, 2008 10:16 am GMT EthGMT ]
Post subject:  Re: Rethinking an off grid cabin system. Advice Wanted
TheWire wrote:
However, I underestimated the cost, wiring size and battery bank to provide this inverter with 200 to 400 AMPS of 12VDC.


Ready. Fire. Aim !

You could size your wires to provide for the microwave only. You don't NEED to support maximum capacity. And then some new gadget will come along in 2 years, that you JUST have to have, and you'd wish you had the 2KW of AC.
Locate the inverter close to the batteries, the included charger will nicely charge from your generator. A local battery shop should be able to make up cables for you.

Or consider re-wireing for 24 or 48V, much easier to wire batteries in series, than in parallel, and shop for new inverter/charger.

Personally, 30A into T-105's would work, as the current is likely to drop down quickly as the battery charges up, and I'm likely to monitor it closely. For un-attended charging, I'd limit it to 20A. The battery Mfg likely has a spec for long life.
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