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Using car alternator for 12 volt generation

Discussion in 'Renewable Energy' started by Bach On, May 5, 2013.

  1. Bach On

    Bach On New Member

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    I've got a power washer where the pump froze. Replacement of the pump is too expensive. In fact, I already bought another.

    I believe the Briggs & Stratton Engine is around 5 hp. The HP is not listed, but the CC is given. From reading elsewhere, it looks like 5 hp is about right.

    Let me say that none of this is carved in stone. I'm open to any and all suggestions. This is the engine I have. And it is now surplus. I want to use it for charging batteries during extended power failures. We are in a hurricane zone (Eastern North Carolina.)

    I can pick up an auto alternator in the 60-80 amp variety. They are all over eBay. It will take same mechanical savvy to get it configured. I figure some sort of belt drive. (The engine shaft goes down like a lawnmower.) I figure to start the engine. Then have a lever that will tighten the belt and get the alternator turning. I suspect starting it with the alternator online could be a challenge. And there are few things more frustrating than a stubborn 4 cycle engine that won't start.

    Many newer alternators are designed to work with the vehicle's onboard computer, I thought I'd buy one for an older vehicle. I'm guessing that the engine might stall if too hard a load is put on it. For that reason I've ruled out an alternator over 80 amps.

    My issue is voltage regulation. Is this going to be such a big challenge as to prevent the juice being worth the squeeze?

    Has anyone here tried this? If so, what approach and what challenges did you experience?

    I'm not into reinventing the wheel.

    Thanks, in advance, to anyone with experience in doing this.

    Bach On
     
  2. MikeMl

    MikeMl Well-Known Member Most Helpful Member

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    Just turn off the field and the alternator will free-wheel during starting.

    14V χ 60A = 840W. 1 HP = 746 W so a 5HP engine will be only ~25% loaded.
     
  3. Nigel Goodwin

    Nigel Goodwin Super Moderator Most Helpful Member

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    You MUST have a car battery for it to charge, and the regulation is internal in most alternators.

    Drive belt to alternator, alternator to battery - as simple as that.
     
  4. dave

    Dave New Member

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  5. Bach On

    Bach On New Member

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    Thanks for the input.

    So I could go with a more robust alternator. I'm guessing that running the engine at a lower speed will reduce the horsepower actually produced. There is probably a limit on how much power for charging I'd need. 100 amps would seem like my top limit. Running the engine at lower speed would consume less fuel and MIGHT be slightly less noisy.

    "Turn off the field" - Would a switch (I'd guess a knife switch) that disconnects the alternator from the charging circuit accomplish this?

    How does one determine (before buying) if an alternator has internal voltage regulation. I don't want to damage batteries because of this thing.

    And I do get that the battery bank is required. Some say it is somewhat like a voltage regulator.

    I don't know what an optimum RPM is for an automotive alternator to be able to produce it's rated current.

    Bach On
     
  6. tcmtech

    tcmtech Well-Known Member Most Helpful Member

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    I would suggest going with a common 1 wire type Delco alternator.

    You only have to have the ground and 12 volt leads to work with plus they don't self excite until around 1800 - 2500 RPM so that give your engine plenty of time to get up to speed before the load comes on.

    Now relating to alternators most Delco 1 wire type are rated for full output at 3600 RPM which is also what most small engines run at which means doing a direct drive setup is not a problem.

    The other option is to run the engine at a lower RPM and gear up the alternator to run faster being you likely have more than enough engine to power it.

    Either way your engine is plenty powerful enough to run any 12 volt alternator rated for under 150 amps.
     
  7. Bach On

    Bach On New Member

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    Thanks for the useful information. So the 1 wire alternators put the positive in that wire and use the metal mounting for the negative. Is that the way it works?

    My limited understanding of small engines is that some run better with a larger pulley to keep the inertia going. It is rather like the blade on a lawnmower. I'll probably use the belt drive method. The washer was on a rolling cart. I figured to use a plate to extend behind the engine. It'll take some measuring and testing.

    Do all the one wire models have internal voltage regulation? Looking at car model years, when did this style become the norm? Versus the external regulator?

    I've also been thinking of some sort of fuse for protection. Seems like a wise idea. Do you have any thoughts or good ideas on this issue?

    Very helpful input. Again, thanks!

    BO
     
  8. tcmtech

    tcmtech Well-Known Member Most Helpful Member

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    Yes a 1 wire is just power out and case ground and all excitation and regulation is done internally.

    If the engine was not on a push mower it has the necessary cast iron flywheel so no extra mass is needed or justified.

    No fuse is needed. If a 1 wire alternator is overloaded it just loses its self excitation and freewheels until the overload or short circuit goes off it or if you have more alternator than engine your engine just lugs down to what ever power balance it can handle.

    If it was me I would go with one like this. http://www.ebay.com/itm/140AMP-CHEV...Parts_Accessories&hash=item3ccb567942&vxp=mtr

    Or just get the conversion kit and pick up a used one at the wrecker for cheap.

    http://www.ebay.com/itm/10SI-DELCO-...Parts_Accessories&hash=item2571256c51&vxp=mtr

    The Delco SI series alternators are very robustly built and take running at full output for extended periods without issue so if you are looking for a reliable unit I would recommend one of those. Its the only type I use on all of our farm equipment conversions.
     
  9. Bach On

    Bach On New Member

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    I hate to be a pest. You've already been very helpful. But I also don't want to overpay. Being frugal is in my genes.

    In searching through the alternators on eBay, I saw that the one you suggested was a 10SI. That one was described as having a top output of 140 amps. There are others listed on eBay, also described as the 10SI, that have lower outputs. Is this just marketing hype? Or are there a variety in the 10SI series rated for different amps?

    The copy for the one you suggested said it only puts out 85 amps at idle. You have to get it above 1200 RPM to get the full 140 amp output. I really don't think I need 140 amps for two deep cycle batteries. I'm pretty certain that 100 amps would be more than enough. And running at a lower speed would be a tiny bit quieter and use less gas.

    And the copy stated that this needed to be run through a fused 4 gauge cable. I'm sure that is more for the battery than the alternator, based on what you've said.

    Does this thing need one of those big capacitors? I saw several of them while doing a 'Delco SI alternator' search.

    Any and all sage advice or suggestions are appreciated. I don't want to reinvent the wheel - or screw up and blow up my batteries.

    BO
     
  10. ozarkshermit

    ozarkshermit New Member

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  11. tcmtech

    tcmtech Well-Known Member Most Helpful Member

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    The difference in output depends on what is done internally to the alternators. The original factory ones were usually in the 63 - 78 amp range but aftermarket designers figured out how to push them way past the original stock capacities using different stator core materials and better components.

    If you don't need all the power then by all means get a lower output one. Or as I mentioned earlier just get the 1 wire conversion kit and rework a stock unit off a vehicle from the salvage yard. Around here a good used Delco alternator off of a older GM vehicle will set you back $15 at most.
     

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