running a generator in paralell with an inverter

smithy123October 20, 2010

does anybody know a way to safely run a generator in paralell with an inverter? i have the cpi 1575 inverter. the problem is, the battery doesnt last long, even with the engine running. it is not my truck, i am using this at a parade and use it supported by t&b ty rap cablt ties. i do not want a transfer switch, nor do i want them wired with 2 male plgs in paralell.

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Ron Natalie

If the inverter was up to it, you could. The cheapo car ones like you have are NOT up to that. Moer expensive ones as used with solar systems can match the frequency of the incoming line or generator.

Congratulations on not making the suicide double male plug.

The only kludge I can imagine was to take the generator out to make 12V to feed the inverter.

Of course, if you just had a square D QO panel, all would be solved.

    Bookmark   October 20, 2010 at 8:21PM
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smithy123

i know if i switched the power to dc using bridge rectifiers i could run them in paralell, but then i would not be able to run a motor or transformer supplied appliance.

9

    Bookmark   October 20, 2010 at 8:27PM
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Ron Natalie

It would work fine as long as you connected it to a QO panel and made sure you used a GreenLee screwdriver to make the connections.

If your concern is that the battery goes dead, runt he generator into a DC supply that you can parallel with the battery and plug everything into the inverter's DC input. This is exactly how commercial UPS systems work.

    Bookmark   October 21, 2010 at 8:17AM
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smithy123

the dc power supply's output power fluctuates too much, but i can try it next year.
btw, where did the screwdriver thing come from?

    Bookmark   October 21, 2010 at 3:52PM
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DavidR

" run the generator into a DC supply that you can parallel with the battery ..."

I'd suggest using either a battery charger or a well-regulated power supply, set to the battery's float voltage or a bit above (around 13.8v for a 12v battery).

The main downside of such a lashup is that it's not very efficient; there are losses in both charger and inverter. In general, the cheaper they are, the higher the losses. But it will work.

    Bookmark   October 21, 2010 at 11:51PM
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joed

If your running the generator why not just plug everything directly into that?

    Bookmark   October 22, 2010 at 8:42AM
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smithy123

i planned on running most of the lights off of the inverter/genset while running the generator only for the fog macine (500w) and 50 c9's @10w each and to take the load off of the inverter because with just the lights including the c9's, the alternator cannot keep up with the load. we woldd apperciate to run the generaytor only when we are moving.

    Bookmark   October 22, 2010 at 5:10PM
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smithy123

i could make an automatic transfer switch, so when the generator is running, i use the generator, but when the generator shuts off, i use the inverter. i am powering the 500w fogger, 3200w of c9s, a radio at times, 2 100w spotlights,and 100 mini lights. the battery only lasts 15-20 minutes even with the engine running the 100a alternator. i do not mind the gas consumption because the one paying for it owns a gas station, anyway, but i do not like the noise the whole time of a running generator.

    Bookmark   October 23, 2010 at 1:01PM
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brickeyee

"i do not like the noise the whole time of a running generator."

That is what extension cords are for.

A couple 50 foot #10s will get the generator 100 feet away with minimal voltage loss.

    Bookmark   October 23, 2010 at 2:21PM
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smithy123

it is on a parade float.

    Bookmark   October 23, 2010 at 3:04PM
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smithy123

btw, i plan building an extension cord with a 2 space qo panel in it, with an afci breaker.

    Bookmark   October 23, 2010 at 3:31PM
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joed

Add more batteries in parallel to be used during the parade. Recharge them after the parade is over.

    Bookmark   October 23, 2010 at 11:48PM
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smithy123

it would take alot of batteries to feed a 150a load. the auto transfer switch would be cheaper.

    Bookmark   October 24, 2010 at 7:47AM
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pharkus

... something I've often thought of doing, but never have...

and it's probably too late to propose such a kludge...

take the generating part of a genset, shove it under the hood somewhere with a belt to the car engine...

my original purpose for doing this was to run home audio gear (actually concert/pa stuff) in a van. :)

    Bookmark   October 29, 2010 at 12:52AM
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joed

150 amp generator is not going to fit under the hood.

    Bookmark   October 29, 2010 at 8:13AM
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Ron Natalie

150A at 12V can be done on an truck engine if you are clever enough. I've seen some 4WD RV things done that way.

150A at 120V is going to take something the size of a car engine just to drive the generator.

    Bookmark   October 29, 2010 at 9:05AM
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brickeyee

You can get 120 V output alternators for vehicles.

Creating very large low voltage currents is always a chore, and results in larger pieces of equipment.

The typical car alternator is just below 100 amps at 12 V.

It is actually a 3-phase AC alternator with a rectifier bridge to produce the DC.
The battery takes car of filtering off the ripple.

    Bookmark   October 29, 2010 at 9:32AM
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DavidR

Probably 40-50 years ago I used to see magazine ads for kits to convert vehicle alternators to produce 120v. The illustration showed a guy with a power drill plugged into his car.

Presumably they tweaked the field regulation (not so tough to do when regulators were external and mechanical) and bypassed the internal rectifiers. I'll bet the frequency was somewhere in close to the moon, though. Certainly it'd be tough to maintain 60 Hz. Universal-motor tools (most or all drills are) wouldn't care, but I suspect induction motor tools such as circular saws would throw fits.

So I'd expect a similar problem with a modern alternator belted to your car or truck engine. You'd have to find some way to keep the RPM steady so the frequency would be correct, unless you borrowed the guts of an inverter-type genset.

A plain, low-cost 12v inverter would be much easier to use - just connect (solidly) to the battery. Just be aware that if you exceed the alternator's capacity (~1000 watts or so unless you have a heavy duty vehicle), you'll drain the starting battery, so you can't do it for too long.

It'll also really send your MPG into the cellar. Hmm, modern computer-controlled vehicle engines are generally more efficient than those relatively crude genset engines, but they're way oversized for the application. I wonder if an inverter setup would burn more or less fuel per kWh than a genset would.

    Bookmark   October 29, 2010 at 11:51AM
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pharkus

? I know a 150A 120V generator won't fit under the hood...

I also know the OP doesn't need 150A at 120V. In fact, I'm not sure where that idea even hatched from.

I also know (relatively) the guts of an alternator. This video is one of my friends messing around with a "welder" we hacked up using one from a Toyota 22RE, belted to a motor scrapped from a mangled tablesaw. Removed the internal regulator and provided external excitation using the AC adapter from a cable modem. I'm the midget in the corner.

Regarding frequency... our OP is running a bunch of lights (don't care about freq), a 'fogger' (if it's like the ones I've had, it's a heat load, which also doesn't care about freq), and a "radio"... the latter is really a question mark, since a small transformer-powered unit will care but not enough to matter, a larger transformer-powered one will definitely care, but some of the newer stuff is switchmode anyway. A device whose first step is to rectify to DC won't much care about the input frequency unless you're getting close to the switching speed limits of the rectifier diodes, which you are probably NOT going to do by driving a genset generator from a car engine at ANY realistic RPM... so really the detail of this "radio" is the only missing information to determine whether or not this hack would work.

And I wasn't suggesting it as an actual solution anyway, merely stating, as a related sidenote, that I've always wanted to try it.

    Bookmark   October 29, 2010 at 2:14PM
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brickeyee

"So I'd expect a similar problem with a modern alternator belted to your car or truck engine. You'd have to find some way to keep the RPM steady so the frequency would be correct, unless you borrowed the guts of an inverter-type genset. "

There are actually ways of controlling the field windings to maintain frequency.
It is effective for slow variation, not as effective for quick speed changes.

    Bookmark   October 29, 2010 at 4:25PM
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pharkus

Wow, I never thought of that! (I do see how it would work though...)

    Bookmark   October 29, 2010 at 8:17PM
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smithy123

it's not my parents or family member's truck. it is the owner of a local gas station's, and he doesnt want to add a second alternator, etc. there is a 100a alternator, so it is 1,000 watts out of the inverter. the headlighrts do not turn off and the fogger also has an electric pump.

    Bookmark   October 29, 2010 at 9:47PM
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brickeyee

18,000 watts of lighting seems a little excessive.

    Bookmark   October 30, 2010 at 5:22PM
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pharkus

A little?

    Bookmark   October 30, 2010 at 6:39PM
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