Electrical whiz needed....

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We have an outside woodburning furnace which runs our hot water heating system...our problem is the little pump that keeps the water circulating...does anyone know an EASY way to rig a battery(perhaps?) to keep that going. We have a generator capable of running the farm but only plan on using on a limited basis to pump water for stock and household use a couple hours a day. Do have a wood stove inside but the other is so great and heats all our domestic water for free to boot!! Hot showers may be the new luxary next year.....we contacted the furnace manafactuer and they sent us some grad school electrical diagram...know someone on this forum can come up with a more practical method...or its back to the dirty Ashley for us,I guess.Thanks.

-- MUTTI (windance @train.missouri.org), March 12, 1999


You might try contacting:


They have a large number of Battery and Solar powered pumps, or just look up any Solar Power Company on the Web and give them a call, they can send you the diagrams and sell you the pump (you will have to do the plumbing)

-- helium (helium@avid.com), March 12, 1999.

MUTTI, Know what you mean about that hot water -- and hot water heat. Great stuff. I would assume you have a Taylor, or equivalent. Speaking from the experience of my Tarm (Swedish, can be put indoor as well):

1. You will either be able to use 12 volts dc, directly, or you will need an inverter to convert your 12 volts to 120 volts ac. Probably the last.

2. The power demands from the pump are small. You probably can use a simple 500 watt inverter, available from K-Mart for less than $100. Hook the inverter dc input to the battery and run a plug-in cord from the inverter to the power input to the furnace.

3. You'll need to recharge the battery. Use a battery charger, hooked to the generator and charge it every time you run the generator.

If you want, email me with questions

-- De (dealton@concentric.net), March 12, 1999.

Since you said you will be running your generator an hour or so a day for other uses, what you do is this. You purchase some large deep cycle batteries, these will be inside your nice heated house. You purchase a battery charger. You purchase an inverter that changes low voltage DC to 120VAC, which I assume is what the pump uses. You size everything to the pump. You find out what amount of amperage or wattage the pump uses when it is running. Motors use 2 to 4 times as much power in the first few seconds of start up. If the manufacturer of the pump doesn't state what the start up power needs are with water in the line, get an inverter that is 4 times the running power of the pump. Estimate how many hours of running the pump runs. Figure out how many watts per day you need for the pump. Example if the pump uses 2 amps at 120VAC running, it might pull as much as 960 watts at start up. get a 1,000 watt inverter or an inverter that specifically states can start a 960 watt motor at start up. Some inverters have as much as 100% momentary over capacity, others as little as 10%. One hour of pump time would be .24 kilowatts. So 4 hours would be about 1 kilowatt, 8 hours 2 kw, 12 hours 3 kw, etc. Figure that you are going to lose about 10-30% overall (though your better inverters have less loss) so your batteries would need to put out 3 to 4 kw per day if you were to run the pump 12 hours per day. You'ld have to put in around 4-5 kw per day (of course you could run the pump off the generator while charging the batteries). Now over a 2 hour charge period that would be 150-200 Amps! Since you always want to charge batteries at only about 10% that would require a battery bank of 2000 AH IF you do everything at 12VDC. You can buy inverters that run on 48 VDC which would give you the same power but with 1/4th the amperage. Of course if that pump only uses 1 amp, cut everything in half. You can cut everything down again if youthink you only need to run it on batteries 6 hours a day. You want the inverter and charger as close as possible to the batteries to cut down on loss and oversized wires from the inverter to the pump, again to reduce power loss.

More info on inverters and such is on my webpage http://home.earthlink.net/~kenseger

-- Ken Seger (kenseger@earthlink.net), March 12, 1999.

MUTTI, Ken is right in his figuring and outline. However, he forgot one thing I feel needs to be emphasized. Batteries when charging put off hydrogen gas....just happens to be very explosive. So if you do not wish to end up like the Hindenburg, make sure wherever you store these batteries is well ventilated and away from sparks, flames etc.

(Ken, sorry for butting in but MUTTI seems like a newbie to self reliance. Just thought he/she should be warned).

-- Lobo (Hiding@woods.com), March 12, 1999.

Why is it that people keep talking about watts per hour ? Even some people who sell alternative energy products ! !

I should hope that any pump would take zero watts per hour except on start up ! Am I the only one here who passed high school physics?

-- y2kbiker (y2kbiker@bellatlantic.net), March 12, 1999.

Actually, the correct term is AMPS and AMPS/HR. Calculated by dividing the WATTS by the VOLTS. Batteries deliver in AMPHOURS (or milliamphours depending on the size). The motor DOES have a AMP draw which MUST be considered as you size the battery bank. It does NO GOOD to have a 2kmAHR gell cell on a motor drawing 5 amps at startup. Won't start. Equally, if teh unit draws 2 amps teh gell cell will last about an hour.

All numbers and products for illustration only.


-- Chuck, a night driver (reinzoo@en.com), March 12, 1999.

PS twasn't physics, but JR high industrial arts. cr

-- Chuck, a night driver (reinzoo@en.com), March 12, 1999.

I've got a little 120VAC water pump made to continuously circulate hot water (for "instant" hot water at the tap). I use mine as a recirculating pump for an ornamental fish pond. It is rated at 70 watts on 1120VAC. So, through an inverter, it would draw a little less that 7 amps at 12 volts (90% efficiency inverter). One battery (deep cycle marine type) would run it quite effectively with a top off charge whenever you had to run the genset for other reasons. It would require a 300 watt inverter to start it though.

-- Gerald R. Cox (grcox@internetwork.net), March 13, 1999.

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