# stacking inverters and a home built 12v generator



## Cidney00 (Jul 9, 2013)

I setup my first solar system recently with 400w of renogy panels with a 30amp charge controller and 4 4d batteries and a 2500/5000w unforced inverter. I am looking to.expand the system as funds allow. For the moment the system will be used to power the well/house pump for water supply.

Does anyone have any experience stacking inverters to increase the output. I have seen "stackable" inverters that are tied master and slave with a switch to tell them their role. Has anyone stacked normal inverters such as the sunforce 2500 http://www.amazon.com/gp/product/B0010X5KPG?psc=1&redirect=true&ref_=oh_aui_detailpage_o03_s00 ?

I am also going to repurpose an old lawn mower engine to act as a generator of sorts to charge the battery bank in emergency situations. I plan on back feeding the home with the inverter to run lights/fridge/fans/ect. I am going to.use the mower engine to drive two alternators to keep the battery bank charged during high draw periods or in low light times. Has anyone attempted something similar? I.am a mechanic so I know the system will work but I am looking to see if anyone has any experience input or ideas.


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## LincTex (Apr 1, 2011)

The inverters *must* BOTH be designed to work each other. 
If not - they will kill each other. 
Best case scenario is burned out fuses.... 
worst case scenario is two inverters with all the magic smoke let out of them.

How big is your well pump? It might be the only item you have that an inverter won't run!

How big is your mower engine? It had better be BIG (riding mower type, 10+ HP) to run two car alternators at load. Two small alternators are typically not very efficient as one large one. Small car alternators are cheap and plentiful, but not very efficient (less than 30%). The large 160-200 amp "semi-truck" style Leece-Neville and Nippondenso alternators are closer to 50% efficient. If you can find a Ford ambulance in the wrecking yard with a V8 diesel, grab that alternator! They are some of the best.

You might find that you'll burn a lot of gas with little power out with such a setup. it depends a LOT on what you are piecing together. Please state what you plan to use for parts.


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## Cidney00 (Jul 9, 2013)

My well pump is 3/4 hp. Shallow wells here in fl. The inverter runs it no problem with an average 1000w draw when running. The inverter is pure sine so no issues with the motor running. 

The mower engine is a 12.5hp kohler command out of an 80's john deere 38" that was rebuilt not more than 20 hrs ago before the rest of the mower gave up on me. Its actually a really fuel efficient engine and I was averaging 3-4 hours of mowing time on the small 1.5 gallon tank at high rpm. I was debating between running a big single diesel alternator or a pair of singles. I intend to gear the pulleys to put the alternators at optimum rpm while the engine is working as close to idle as possible. 

If I was to run the inverter back feed to the home durring lets say hurricane aftermath at a full 2500w for whatever reason thats a 209 amp draw in an hour. Obviously things would be prioritized and not run like that but figure worst case highest draw scenario. I would like to be able to maintain the battery banks charge in times of low or no light post power out. Back in 2005/2006 seasons my area did not have power restored for over a month and we were a glancing blow. 

I haven't picked a particular alternator yet. I work at a custom truck shop so I have the option of taking a heavy diesel alternator and having it wound to put out whatever I want at a reasonable price if needed.


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## Marcus (May 13, 2012)

LincTex said:


> If you can find a Ford ambulance in the wrecking yard with a V8 diesel, grab that alternator!


Plus 1 on the ambulance alternator. They are much bigger than a regular alternator just like a diesel starter is much bigger than a gasoline engine starter. It's been years since I've seen the specs on one, but I seem to recall the alternators were roughly 2x the charging capacity of a full size truck alternator.


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## Viking (Mar 16, 2009)

For our solar back up system we bought a Magnum Energy 4024 PAE 4,000 watt pure sine inverter/charger because it can be stacked up to four units. In order to be able to stack them I had to buy a RTR router control so they would all operate at the same sine wave. I may never get additional inverters but at least I'm set up to be able to and the RTR unit works as a controller so I don't have to buy anything extra for that. I have considered building a generator like you have mentioned only I have to get a hold of a heavy duty 24 volt alternator as our inverter runs on 24 volts.


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## Cidney00 (Jul 9, 2013)

Viking. You could run two alternators in series with one charge leg going to each side of 12v with isolated grounds on the charge side. That should provide you with you're 24v. Worst case power down the system and use a throw switch to split the batteries into 12v banks and use an alternator per 12v side to charge in down times. It's a lapse in power but provides a non solar charge capability.


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## Tirediron (Jul 12, 2010)

I don't think that you would have much luck running 2 12v alternators in series, it might work, but I think the voltage regulators would get confused.

running 2 separate alternators feeding the 12 v battery separately while connected in series should work as long as the circuits were fully isolated and the second battery groups (24v side) charging unit was fully electrically isolated. 

Or just get a 24V alternator from a piece of 24 volt construction equipment


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## zombieresponder (Aug 20, 2012)

1 mechanical hp = 760ish watts

I have a number of engines and alternators laying around and have spent a fair bit of time on researching using this combination as a power source and welder. It's pretty easy to accomplish, but the problem is in how an alternator produces power versus how a gasoline engine produces power. Your Kohler is rated at 12.5hp *at 3600 rpm*. Above or below that rpm, it produces less power. Even a 60 amp alternator is going to require a couple of horsepower to drive, which may bog the engine enough(at idle speed) to kill it. I happen to have a 320 amp Leece Neville and an 18hp Briggs sitting around. I have very serious doubts that the engine can actually handle full load _if_ I can get enough tension on an 8 groove serpentine belt to prevent slippage. Most likely I will have to adjust the pulley ratios to far less than ideal to get it to work acceptably well. YMMV.


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