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Old 07-10-2012, 10:51 AM   #1
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Re: using the engine as a generator

why not just get an extra 12v rv pump for fresh water and use that? or get a small gas generator...
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Old 07-10-2012, 02:36 PM   #2
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Re: using the engine as a generator

Where are you getting potable water from that's not under pressure?

I agree with chev49, get a 12vDC pump. Easiest & cheapest solution.
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Old 07-12-2012, 08:49 AM   #3
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Re: using the engine as a generator

What Rich said.

Most North American gensets are set to either run at 3600 rpm (60 r/second) or are double-wound to run at 1800 rpm for longer life. I've worked on fire support apparatus with a Power Take-Off generator that used the "cruise control" circuits to monitor the 60 Hz AC and adjust engine speed while generating in neutral. PTO generators aren't as common as they were 60 years ago, as newer electronics really need stable frequency

[EDIT} Those RPM figures are for direct-drive. Belt-drive gensets, and gear-driven PTO generators may have alternate RPM settings.


Concerning using the inverter: The maximum output will be about 12.5 amps, or 2 horsepower. If the jet pump draws more than that, it won't work. Also check the inverter maximum versus continuous rating. You want the pump to draw less than the continuous rating when it is sitting and pumping. Usually inverters are rated something like 1500/950 watts. The 1500 would provide the starting surge, but the 950 would do the running.

If the ratings are within range, the next thing to consider in your application is the length of any extension cord. If the jet pump is pushing the water from a couple of hundred feet away at the stream, the voltage drop of "normal" extension cords may be too much at that distance to provide a full 110 volts at the end. Test your extension cords by trying to run the pump from commercial AC through the whole length of them. Any warm spot(s) on the cord(s) will be a clue to high resistance points. Measure the voltage at the pump while it is running if you can to see how much voltage you are losing.

The next consideration is whether your battery-to-inverter wiring is too small or too long, or has rusty terminals or a rusty ground. The voltage drop in insufficient DC wiring may be limiting what the inverter can put out. Or perhaps a rusty ground. The inverter needs 125 amps at 12 volts to produce 1500 watts. (I would run the engine to charge the batteries while pumping!)

Is the inverter input wiring less than 6 feet, direct to the battery? Are the wires as thick as your thumb, with metal roughly the size of your pinky? Test the inverter output without any extension cord by running (or trying to run) the pump plugged directly into the inverter. Again, measure the inverter voltage while the pump is running if you can, to see whether it can keep up. Check for hot spots on the battery cable and ground to locate poor connections. At 125 amps DC, a bad connection will probably be too hot to touch. Measuring the battery connections at the inverter while running under full load will also point out any DC drop. Measuring the battery voltage at the inverter when it is off tells you almost nothing, as the rustiest vehicle wires will power a meter, but not an inverter.
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Old 07-12-2012, 11:38 AM   #4
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Re: using the engine as a generator

does your bus have air brakes?
If so a pump like this would probably work
a Air-Powered Diaphragm Pumps

could be plumbed in w/a quick disconnect fitting
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Old 07-12-2012, 04:10 PM   #5
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Re: using the engine as a generator

Have you looked at the marine bilge/wash down pumps? They pump a fair amount of water (up to 7 gpm) on 12vDC.

David doesn't like it when I go cruising thru the marine sites... Too much temptation!
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Old 07-13-2012, 06:30 AM   #6
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Re: using the engine as a generator

you should have twice the capacity of what you want to run in with an inverter. actually you need a real inverter, the $3000 ones. the discussion about wire size, length was good, to go with that, one needs an adquate battery bank, normally something like 400 amp hrs or more.. 8-1200 is way better.

water pumps can be made to run on 12 v motors... course the wire size would be a huge consideration..

just get a 4000w onan gen set.. that will run your pump...
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Old 07-13-2012, 10:52 PM   #7
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Re: using the engine as a generator

Before you jump on that 4K Onan generator you migjht want to talk to Lorna S. Just my 2 cents worth.
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Old 07-13-2012, 11:24 PM   #8
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Re: using the engine as a generator

If you're using a jet pump that would mean you are trying to lift water at 20 plus foot elevation. If you put a portable pump closer to the source of water you could use a pump that would draw less current than a jet pump. Then you'd need to size the power cord to the pump. It then becomes more of a question of how much water you want to lift in a given time, and, of course, the total lift.
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Old 07-14-2012, 09:18 AM   #9
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Re: using the engine as a generator

Quote:
Originally Posted by ol trunt
Before you jump on that 4K Onan generator you migjht want to talk to Lorna S. Just my 2 cents worth.
We used the Onan two cylinder generators when I was in the military to power portable lighting units. They are VERY dependable. I have an Onan 4K generator in my bus.

Just because "someone" doesn't like them, it does not make them bad. Onan generators are GREAT.

And just because "someone (me)" loves them, it does not necessarily make them perfect.

Having worked with them in the Air Force, I saw, first hand, how marvelous the Onan engine is.
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Old 07-14-2012, 09:40 AM   #10
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Re: using the engine as a generator

first, last night, i found in the camping world magazine a 110v/12 v water pump with long hoses for 80 bucks on sale. in the write up, one person says that they use it to fill their fresh water tank.. i think the hoses look like they are at least one inch inside diameter, and it is listed as a sump pump, but clearly can be used to pump in water like from barrels to the fresh water tanks.

second, an onan gen set is very good. i prefer the older non electronic ones as those replacement parts cost as much as an older non electronic gen set...
i run my onan with straight synthetic 15/40 oil with 4 oz of z-max in it. it runs extremely smooth, and is totally clean inside the engine. uses around 1/2 gal of gas per hour,, mostly a bit less than that, and will run all day and night, and there is 4 quarts between the low and high oil marks on the dip stick, so it pretty much is set and forget. i am running it off a 25 gallon tank... these engines are easy to disassemble for inspection, heads only have 7 or so bolts, etc..and online manuals are available from the guys who have a stationary engine bbs.
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