Hello All,

I am thinking about setting up a power system for the house and I am wondering what others thing. I am looking to put together a couple of 12V deep cycle batteries that will power a largish power inverter to power the refridge and some lights ect. Maybe a battery like this for example:

http://www.partsamerica.com/ProductDetai...tegoryCode=3583

My refridge is rated at 10 amps.

Then I am planning a home brew generator based off of:

http://www.thefarm.org/charities/i4at/surv/tow02077.htm

to recharge when necessary.

thoughts?

Dave

Your not going to run a fridge off a couple batteries very long. Remember that power into the inverter has to equal power out of the inverter. So your 120v 10A fridge is 1200w, taking 1200w on the input side divided by 12v your drawing 100A. Then if your inverter doesn't have an energy star label its less than 80% efficient so your loosing at least 20% to inversion loss which means 120A draw from the batteries.
Granted that 10A probably isn't the continuous running current but its still a lot.

Your link for the battery only turns up the home page so there is no way to know which battery your considering getting, any deep cycle marine or even a golf cart battery should work.

As far as the home brew generator goes, I used to have one, it worked great, the only reason I parted with it was because it was only a 3000 watt and wouldn't power what I needed it to. If you go to auctions esp farm auctions you should be able to pick up the parts easily, thats the way I did it.

If your building a generator to charge batteries to use a inverter why not just use the generator, I would think you would be farther ahead, you would use just as much gas trying to keep the batteries charged as you would running the generator for short periods of time to keep the frig cold.

So why not set up a solar set up.

Though I don't have any plans on running a fridge off any invertor, one of my projects planned for January is this home built 12 volt setup. .

This along with a 3-4 golf cart batteries will allow the use of a few 12V LED lights, laptop etc in the house.

This setup along with solar is sufficient for basic needs and precludes running a big generator all the time. The fridge and freezer depending on the ambient temps only require periodic runs to keep cold.

Well I called Batteries plus and this is what they said, the inverter will draw 3000 watts + 10-15% for loss in conversion. So that is a 27.5 amp draw on the battery if used full draw. which I will not be doing as the fridge will cycle on and off. It will draw 1200 watts running and I am not sure on start up.

Sorry about the bad link for the battery. Here are the details: Exide Deep Cycle Battery: Orbital Select; 12 Volt; 750 CCA; 950 CA; 100 Minutes Reserve Capacity

So if I am doing my amp hour conversion right it will provide 37.5 amps an hour over 20 hours. I would probably use 2 batteries in parallel to double the amp hours and only run the generator to recharge the batteries as not to draw attention. :-)

Am I wrong with my math?

Dave

The person at batteries plus doesm't have his math right, 3000W / 12v = 250A not 27.5A to start with.

Whatever you do, I recommend PowerPoles for your outlets. For 12V up to 45A use the red/black pairs. You can get a nice panel outlet (and a bunch of other neat doodads) here:

http://www.powerwerx.com/product.asp?ProdID=1783&CtgID=1681

HTH,

A

(For your higher-current lines I recommend you hard-wire them- you're not really going to want to plug and unplug a 250A connector! Oh, and you shouldn't anyway- only unplug and plug high current loads when the supply is off.)

Thanks! Well I guess I would get 2 hours of full out run time then on a single battery. Well maybe I need to get one of these;

http://www.harborfreight.com/cpi/ctaf/displayitem.taf?Itemnumber=93519


to measure how much energy the fridge actually uses. It really doesn't run that much, but maybe I just don't know. I am thinking that I should get some pretty good run time since the refridge will be cycling on and off as needed.

Dave

Thanks Ame, Those are pretty cool.

Dave

I hear ya. Maybe this will only be used until the important stuff in the refridge is consumed or if it is winter, we could move every thing in the fridge out to the breeze way and just used the battery pack to provide a few lights or a few hours of tv a day.

Dave

I'm switching all my gear over to power poles myself. I've ran into the issue with the car cig lighter plugs where you just can't get more than a couple amp through them, ples they are rather large making cords big and bulky.
I've standardized all my electronic gear on being able to run from AA batteries or 12v and have 12v powered AA chargers. This gives me a few advanatges such as 1 being able to use automotive components which are cheap, pleatiful and reliable. Both out vehicles use the newer miniATc fuses so I standardized on those as well so that if/when I do build a cabin or put a rv/trailer on the farm I can follow the same standare and spares for everything will be the same and I could borrow parts from one to fix another. 2. I'm eliminating inversion loss, since inverters are classified as power supplies they fall under the energy star rule of having to be at least 80% efficient and I haven't yet seen a store bought inverter that has the logo so they are all wasting at least 20% of their power.

Something I have seen done on some alt energey web sites/forumsis to take a small top opening freezer and disasseble the thermostat and replace it with a refirgerator thermostat. Freezers have a lot better insulation than refrigerators so that cuts down on run time, the door on the top also helps prevent the cold air from "spilling" and they have better compressors. SO by switching to a refrigerator thermostat the compressor has to run fewer cycles to maintain the less cold that what it was originally designed for making a very efficient refirgerator.
There are also high quality 12v refirigerators, not the cheap crap in the rv stores but the expedition quality stuff. Downside is they cost about as much as a regular refrigerator for a cooler sized space. But if say you have someone that needs medication such as insulin to live then cost isn't as much as a factor. There is a forum called expedition portal where I found some brands and info on those.

I can't imagine what that's going to sound like when it's running. I camp at Burning Man for a week, and store-bought generators are noisy. I don't even want to know what a generator made from a lawn mower engine is going to sound like.

For your batteries to run AC appliances, you need to know what wattage the appliances draw, then you need to convert the watts to amps:
Amps = Watts/Volts
Watts = Amps x Volts

DC batteries show amp-hours of power, which is to say the maker assures us that the battery will provide so many amps for so many hours. The problem is that if you run a battery totally flat, you wreck the battery, so you have to know what your voltage is pretty much all the time. See
http://www.cieux.com/bm/batteryWreck.html
for information on trying to keep your battery from being consumed.

My EEE laptop says its 22W. So if I want to run it off my 100 Amp-hour 12VDC battery, I have 100 Amps x 12 Volts = 1200 watts of power. 1200/22 is about 54 hours, not taking into account inverter lossage.

Or 22 Watts divided by 12 Volts = about 1.83 amps draw -- 100 amp-hours divided by 1.83 amps draw is about 54 hours.

Figuring out what your AC equipment draws is simple if you look at the plates on the back of the equipment. Figuring out what amp-hour battery size you need is simple math. Xantrex, for example, has a FAQ that guides you through the calculations in the hopes you'll buy their batteries:
http://www.xantrex.com/web/id/1040/info.asp
I'm sure other manufacturers do, too.

Inverters produce AC from DC in a variety of ways. You need to know if what you power with the inverter _requires_ true sine wave. If so, you need an inverter that puts out true sine wave AC, and those are somewhat more expensive. If your AC equipment doesn't require pure sine wave, you can get square wave or modified sine wave.

If you're pulling lots of power from the battery, you'll need big cables, by the way. I recommend fuses on both positive and negative cables between the battery and the inverter. See here for recommendations on wire size based on draw and length of wire:
http://www.the12volt.com/wiring/recwirsz.asp
If you don't have wire with ample :-> capacity, the current won't reach the fridge and whatever else you're trying to power, and the wire will get hot. The twin concerns are power loss and fire.

I'd suggest lots of research at sites that promote off-grid living, RV and sailing sites, and back-up power sellers (like UPSes).

Thanks Philip. I will be looking for a 12 RV small fridge instead of trying to power my 120V one.

It shouldn't be louder than my lawn mower. :-) Well I will be modifying the exhaust to an car/tractor exhaust to quite things down.

Dave

The kill a watt meters are quite popular, I see them mentioned a lot. Chances are the label on the fridge is the starting current and the running is much less but you'll need to take into account the brief starting current when sizing your power system. I think the kill a watt has a timer so it can measure how much the fridge runs and doesn't run to get a good estimate there.

Thanks Eugene!

Dave

re: Kill-a watt, Mower engines and noise.

The Kill-a-watt does have a timer. It shows voltage, frequency, amps, watts, power factor, KWH, run time ......and probably more. I have two, but both are being used and I can't get to the units to check. You can cut one in half, putting the socket at one place and the display at another. I used a 10' piece of Cat 5e cable (just happened to have it around) but probably any cable with sufficient (don't remember how many circuits/wires are necessary) number of conductors.

Don't expect a lawn mower engine with a large muffler to be quiet. Once you reduce the exhaust noise, you will discover that much of the noise is just mechanical noise. That is why water cooled engines are so much quieter.

My cousin found that out when he attached a small muffler to a Generator. they ended up buying one of those little Honda ones.
I've been looking at doing the same thing though because I have a small pressure washer similar to this one but without the wheels and long handle. It sits unused most of the time so I thought maybe I could make it easy to swap the pump for a pulley and leave the alternator on the front and justswap back and forth as needed.

Hello All,

Today I purchased my small motor and looked at marine deep cycle batteries. (They sale Starting and Deep cycle) The largest ones I could find are rated at 125ah for 69.00. I will be using two or three of these to create a battery bank. I found this site: http://www.xantrex.com/support/howlong.asp that will calculate run times on a bank of batteries. With a 375ah pack I will get 62.5 constant draw hours out of the pack.

I am thinking that I should get a lot more run time as a refrigerator cycles on and off as needed. It looks like it will take quite awhile to re-charge though with my home-brew system.

Is this a reasonable plan?

Dave

I haven't followed this thread, so if this is a repeat, I apologize. Many full time RV'ers use six volt "golf cart" batteries, rather than the usual 12 volt deep cycle batteries. They may take a tad longer to recharge, but they last longer between charges. There are many sources, we got ours from Interstate Batteries...

Oh I should have added that the 12V RV refrigerators that I have seen use about 2.5 amps.

Dave

If you wire two 6v batteries together the right way, they put out 12v. Not sure about the amps...

Thanks OBG!

Dave -> Young Semi-bald