Author Topic: Using 6HP Briggs w/multiple 12V Alt  (Read 8249 times)

BigGreen

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Using 6HP Briggs w/multiple 12V Alt
« on: October 26, 2009, 03:19:43 PM »
I know this is certainly off-topic to this forum but I trust you guys :)

I have a 6HP vertical shaft lawn mower engine in great shape. I also have a 90A, 12V alternator. The alternator has the built in regulator and externally controlled field, meaning I can place a control switch in line with this circuit to activate, deactivate the output. I have this stuff lying around and of course I want to play and tie them together. My first thought was to use it for a battery charger but then I thought about adding another, larger alternator as well to produce ~2.5KW to operate the A/C on my travel trailer. The big ticket item will be the modified waveform power inverter at about $400. The second 140A alternator is about $100. I know some of you are thinking “why not just go buy a mickey mouse 3600 rpm screamer?” and I have to say “where is the fun in that?”
Questions are:
Will there be a problem paralleling two 12V auto alternators of different capacities?

Has anyone here attempted this and can provide firsthand experience?

Is having a high wattage rheostat in series with the field voltage to control output doable?

Thanks
Dave
« Last Edit: October 26, 2009, 04:07:02 PM by BigGreen »
Dave
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Doug

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Re: Using 6HP Briggs w/multiple 12V Alt
« Reply #1 on: October 26, 2009, 04:29:34 PM »
Run the bigger alternator and set ther speed of the engine for bets fuel ecconomy. Assume you can get 40 amps from the 90 on average spinning around 2500 rpm and the engine running around 3000. Thats a decent number and won;t strain the engine or alternator too badly.

If you found a way to increase the engine speed and decreas it with load you would be very close to building your very own inverter generator with a battery bridge to provide surge energy.

Its not a bad idea and has been kicked around I say go for it if you feel like tinkering.

The answere to your other questions is very complicated, and too much trouble to control it...
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Stan

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Re: Using 6HP Briggs w/multiple 12V Alt
« Reply #2 on: October 27, 2009, 12:41:33 AM »
I agree with Doug.....Since you already have it, why not use it until it breaks.  Automotive generators are not really built for producing lots of power for long periods of time (heat).  But hey, it's free for now anyway.
Stan

BigGreen

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Re: Using 6HP Briggs w/multiple 12V Alt
« Reply #3 on: October 28, 2009, 02:00:31 AM »
Thanks for the replies but I think we may have missed the main question. I will require more power than one alternator can provide. I need to tie two in parallel.
Would that work or would they might fight each other?

Thanks again
Dave
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needenginerunnin

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Re: Using 6HP Briggs w/multiple 12V Alt
« Reply #4 on: October 28, 2009, 07:50:25 AM »
morning
as far as i know'anybody feel free to say different' you can not run two automotive alt's on the same battery bank as the regs fight.
same goes for charge control units with offgrid systems.

needenginerunnin
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SteveU.

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Re: Using 6HP Briggs w/multiple 12V Alt
« Reply #5 on: October 28, 2009, 07:06:38 PM »
Hi BigGreen
Before you run out and get that second alternator best just set up the 90amp you already have and see how well you will do.
My years experience in Auto Electric says with a ~40% efficient 12 volt automotive alternator you are going to use up 5 of those engine horsepower.
Not asking you to trust me - don't.
Just best to try what you have first BEFORE you shell out money.
Easy to 90 degree turn your vertical shaft motor power to horizontal with a long wrapped power drive belt. Look under most riding lawn mower decks.

You puzzle me with this internally regulated alternator with an external "Field" line. I have only ran into powertrain command turn off lines for engine unloading purposes. This ties to the internal regulator, not the actual field circuit.
What make and model is this alternator?

Regards
SteveU.
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BigGreen

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Re: Using 6HP Briggs w/multiple 12V Alt
« Reply #6 on: October 29, 2009, 02:54:18 PM »

You puzzle me with this internally regulated alternator with an external "Field" line. I have only ran into powertrain command turn off lines for engine unloading purposes. This ties to the internal regulator, not the actual field circuit.
What make and model is this alternator?

Regards
SteveU.

Thanks Steve
You may be 100% correct. I do not have the model in front of me but one contact is "R" and the second is "F" therefore I ASSUMED regulator and field. And I ASSUMED that I could control the field current at this contact. There is also the third large post for the regulated voltage output. I had this same alternator connected to a 2-stroke chainsaw engine many years ago used as a stand-alone auto battery charger. It worked great until the clutch finally smoked and I just tossed in the corner with the rest of my junk. I had to pulse it on and off for awhile utlil the battery was partially charged to keep it running but once I got enough charge in it the little engine would stay up with it. It would give me about 2.5A once running unassisted. I was wanting to try to control the output current then by controlling the current through the 'F' connection but didn't get to it before failure. I acquired this briggs as a valid replacement but really don't have a need for a charger anymore. It was one of those things when a friend asks "you want this old engine" and of course I say "YES", then thinking up some justification story for the wife all the way home with it...
 
WOW, 40%? That pretty much kills the whole idea if this proves to be coreect. I will never see the required 2kw from this type of setup with 6HP. I am guessing at 2kw as well. I do not know how much this little A/C actually draws but I do know it will melt the 15A adaptor plug if used for too long but will never trip the 20A breaker. I will do as you suggested and connect the two to get some real numbers. I didn't bother last time. I need to get my hands on a current probe anyway and I can use this as an excuse :)

Thanks
Dave
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listerdiesel

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Re: Using 6HP Briggs w/multiple 12V Alt
« Reply #7 on: May 02, 2010, 12:09:30 PM »
Is the F terminal for the warning light, to provide field flashing at start-up?

Peter