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cottagegoer · Dec 17, 2007, 11:14 PM

Okay, I have a cottage. There isn't electricity where it is yet and I want to have power. I've been doing some research and I would like to use a generator. Preferibly a propane generator so I could use the propane for other uses like cooking or aux heat when wood is low. But there'll be times where my loads will be really small, and having a generator run all the time wouldn't be cost effective or good for the environment among other things. So I've been researching battery banks. Basically I'd like to build a battery bank that'll use an inverter that'll supply X amount of wattage. I haven't figured out what my wattage needs are just yet. When the batteries get low, the generator would either run auto or manual, right now that doesn't matter, and recharge the batteries. If a constant large load was going, I would run off the generator totally. And possibly in the future if they have grid power come, is there a way to charge the batteries with AC mains, in case the power goes out and then if its out for a long period, the generator again would be used to charge the batteries.

My questions are, do you have any advice or suggestions for me in this trek? And, is there a way to calculate how many batteries I'd need for x amount of wattage? For instance, if I say needed 5000 watts, how would you calculate the battery amount. Plus I'd need a sizable inverter to handle these watts. And how would you use a generator which has an inverter on it (which I couldn't use in this case), to charge the batteries? And lastly if they bring grid power, how can I charge the batteries from the grid AND/OR the generator as I need it? Thanks in advance!

labman · Dec 18, 2007, 05:14 AM

Maybe you should look at a large UPS system. They have all the circuitry you would need for now. Maybe connected to the generator side of an automatic transfer switch so when the grid comes, the inverter in the UPS doesn't back feed. You could add more batteries to the UPS as long as the charger and inverter could handle the load.

cottagegoer · Dec 18, 2007, 07:30 AM

Where do I find large UPS's? I've looked for battery bank plans, and large inverters and haven't had much luck.

Cobraguy · Dec 18, 2007, 07:57 AM

I've got a friend who has a cabin in the mountains and has exactly what you're looking for. I believe his even has solar charging capabilities as well as the generator. He has no power other than that and it works flawlessly. When he arrives at the cabin, he has charged batteries from the solar panels. He enables the generator and it auto fires as necessary. Pretty slick set up! Spendy though. I'll see if I can reach him and ask him where he purchased it.

labman · Dec 18, 2007, 08:15 AM

You may need to look more at commercial or industrial suppliers. Circuit City won't have them. See what Cobraguy comes up with. I have a 650 VA one for my computer linked to a group 27 deep cycle battery. Try a net search with something like UPS + 6500VA

tkrussell · Dec 18, 2007, 10:34 AM

The last 20KW UPS I purchased was $40,000.00. I suspect that a 10KW unit would be needed, hard to say at this point as there are no loads to size this system. So, say a 10KW UPS is $20K, plus the cost of a 10KW genset about $5K, plus distribution equipment, wiring, labor, etc, gives a sense of the cost for this system.

There are inverters available that are a lot less than a UPS, as UPS units are built also for filtering the power for data equipment, something that is not necessary for this application.

You can start here, at Inverters are Us, with a 7000 watt unit for $1650.00:
Aims DC to AC Power Inverters

This system really needs to be sized to determine the KW of power needed.

cottagegoer · Dec 18, 2007, 05:56 PM

I think I agree with tk. I don't need a UPS. I do still have to find out what load I will need, which I haven't done yet, but my primary concern right now was to just get an idea of some costs. I have found propane powered portable generators, so that's no problem. I like the idea of the 7000 watt inverter, at least that gives me a starting point.

In regards to the battery bank, what is a good option? Should I do it myself, and how would I charge the batteries with my generator? I wouldn't use an inverter to go from the AC part of the generator back to DC to charge the batteries, to then invert again to AC to power the cottage I assume? That sounds very inefficient to me:) Plus, how many batteries would I need say for a 7000 watt inverter just for argument sake?

Fr_Chuck · Dec 18, 2007, 05:58 PM

Also have you considered running many things on 12V and not converting.
Lights, even some kitchen things like toasters, blenders can all be 12 vt

pelle · Dec 18, 2007, 07:08 PM

I have friends that use solar panels that charge deep cell batteries.. they use tenders so they don't overcharge them.. then use an inverter off the batteries to get to AC voltage.. Also Stoves, frig, hot watertanks, even lights can be bought that run off propane.. Go solar and propane and use a propane generator for emergences.

These setups are all over the internet..

labman · Dec 18, 2007, 08:54 PM

To charge the batteries, you buy a battery charger. Be sure and get one that regulates the charge on the batteries so you don't fry them. Check the specs on deep cycle batteries. I think they include watt hours.

Originally Posted by tkrussell

....

This system really needs to be sized to determine the KW of power needed.

I agree. I think your next step is to sit down and figure out what you need to run overnight with the generator off, and how much power it would take. I think a modern, well insulated fridge would hold overnight with nobody opening the door.

Until grid power comes, the more propane appliances, the better. They may not be cost effective once on the grid. 12 volt DC stuff will mean a smaller inverter, and a little more efficient use of the batteries, but still need the batteries and charger. It will be more efficient to be using AC when the generator is running.

KISS · Dec 18, 2007, 09:05 PM

Look here:

Xantrex Technology Inc. - Residential Solar

cottagegoer · Dec 18, 2007, 09:15 PM

Ya, I never thought about turning the fridge off at night etc. I'll have to figure out loads that I'll need. The reason for the batteries in the first place was if I was using only a fraction of my generator power, I'd be wasting energy. But maybe I should try to calculate how much wattage I'd need more or less continuously, and make sure the generator can handle peak and just run off the generator 100% and forget the batteries? But then again noise will get on my nerves while trying to relax at the cottage!

Cobraguy · Dec 19, 2007, 06:44 AM

I called my friend and got his wife. He's at his cabin spending the Holidays and riding snowmobiles. She's going to join him this weekend and said she would have him call me after the first of the year. Sorry...

As to running things like the refrigerator while he's not there, he doesn't. He brings back anything that will spoil and shuts down the entire cabin. It's even plumbed so he shuts off the water, then opens a valve and the entire plumbing system drains. Then he just flushes the toilets and adds RV antifreeze to all the P traps. He's never frozen a thing. This is all pretty common stuff for cabins in this area.

cottagegoer · Dec 19, 2007, 10:19 PM

I calculated how long a single deep cell battery would last if the battery had 100 amp hours, and I was drawing 2000 watt hours. It was about a half hour. Not a lot of time. If I need more than 2000 watts, a battery wouldn't last minutes. Obviously I would have more than 1 battery, but at what point would it make sense to just match the generator power to my use amount, and just go 100% generator. Again, noise is an issue... well I got some thinking to do.