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Old 07-10-2012, 09:51 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, 01:36 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, 07:49 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, 10:38 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, 03:10 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, 05:30 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, 09:52 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, 10:24 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, 08:18 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, 08:40 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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Old 08-04-2012, 02:55 PM   #11
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Re: using the engine as a generator

Yeah, I think that getting your inverter situation figured out is your best bet. As others have mentioned, getting a stable RPM at 60 hz isn't something that your engine is currently designed to do, and a modification would be a pain in the ass, and you'd probably end up adding extra drag to your engine that would eat up HP when driving around. I know others do, but I'm also not a fan of tapping into the air brakes. Messing with your braking system just seems scary to me.

Going the inverter route, any electric motor takes a little extra juice to get started, so you probably just need a bigger inverter. As a general rule, if you aim for twice the pump's power draw, you should be ok. I'm not sure where the $3000 price tag chev49 mentioned is coming from, that seems way high. I have a 6000 watt Powerbright inverter for around $600 which is way overkill for pretty much anything. (side story: It is not, apparently, overkill for cooking a hot dog with direct AC current through jumper cables, and I am currently awaiting a new inverter from Powerbright covered under my warranty ) You probably need about a 3000 watt inverter, which you can probably find on ebay for ~$100. Depending on how long you need to run your pump to fill your tank, you may or may not need A) a bigger/second alternator, or B) a bigger battery bank. I'd start with a new alternator, and keep an eye on the voltage drop as you fill.
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Old 08-05-2012, 05:40 PM   #12
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Re: using the engine as a generator

Quote:
Originally Posted by bus-bro
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.

THIS!

to move water, it is very very difficult to suck or pull water over a long distance or elevation. As a matter of fact, it is impossible to pull water much over 25 feet elevation.

It is much easier and more efficient to pump or push water. Get a pump you can put near the water source and pump it to the bus. Either 12 volt, 110 volt or an actual gasoline powered pump.

If you want to use your bus engine to pump water, you need attach a pump to the bus engine (think firetruck) But this pump needs to only turn when you want to move water. It cannot spin when there is no water or you will burn it up. But for this to work, you need to park near the water source. Many pumps are not rated for any sort of side loading, so you cannot simply run it off a belt, but requires a drive shaft or similar setup.

The simplest solution is either a larger inverter to run your existing pump, or a smaller pump. 110 volts through your inverter has the advantage that if you are going to run the pump any distance away from the bus you can use an extension cord. You need to carry 10 times the current to run a similar size pump at 12 volts which makes it not practical at any distance because of the size conductors required.

depending on how many gallons per minute you require a small 12 volt pump and a spare bus battery near the water source may be a good solution.

as far as engine powered generator, there are commercial engine driven generators that are hydraulic drive. Your engine turns a hydraulic pump that spins a hydraulic motor that spins a generator head. I imagine these start at about $10K These allow for varying engine speed while keeping volts and hz relatively constant.

One thing i've thought would be fun to play with is a honda inverter type generator coupled to a bus engine. Most generators require constant rpm to make the proper output 110 volts and 60 hz. The honda eu series are different as they make 110 volts and 60 hz at various speeds. (they are actually a complex alternator and an inverter) If only you could find a cheap honda with a damaged motor you could modify to spin off the bus engine with a belt. Then you could make pure 60 hz power at any speed.
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