Using 2 separate alternators to charge the same bank of lead acid batteries.

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timm

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Nov 5, 2019
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South Africa
Good day all.
Is it possible to run 2 seperate 180 amp alternators off an 11 kw diesel engine and charge one bank of batteries?
Just concerned that the alternators and regulators get “confused” with each other.
 
It will work, but don’t expect to get any where near 360 amps.

David
 
As DavidM says, it will work. But not nearly as well as it could. Some options for you to consider are Balmar Duo Charge, Wakespeed WS500, Arco Zues. All will require external regulation. A device I used on the last boat was the Sterling Alternator to Battery Charger which works with internally regulated alternators. It will take some research for you to decide which path is the best option.
 
I agree with DavidM, and note that there are likely a bunch of more detailed considerations. It all sounds like an interesting project.

- Are these internally regulated alternators? If so, they will likely contribute equally through the portion of charging that will accept full output from the alternators (bulk, in the case of a multi-stage regulator) Once beyond that where less than full output can be absorbed by the batteries, their contributions will almost certainly be unbalanced, and at times might be very unbalanced. But it really doesn't matter as far as charging your batteries is concerned.

- Are they externally regulated? If so, I would use a single regulator and have the field output drive both alternators in parallel. That will provide equal (as close as possible) contribution from both alternators, all the time. You will also probably get quicker battery recharge times.

- An 11kw engine is pretty small. Is this a stand-alone engine just for the alternators, or is used for other things too? I ask because most alternators are pulley-driven, and nearly all engines have limits on how much power you can take off of pulleys. You didn't mention the voltage, but even at 12V you talking about more than 50% of the engine's power, and at 24V you will probably be able to fully load the engine. On most engines you can only take full load directly in line with the drive shaft.
 
- Are these internally regulated alternators? If so, they will likely contribute equally through the portion of charging that will accept full output from the alternators (bulk, in the case of a multi-stage regulator) Once beyond that where less than full output can be absorbed by the batteries, their contributions will almost certainly be unbalanced, and at times might be very unbalanced. But it really doesn't matter as far as charging your batteries is concerned.
This. I have two 175A, 24V Leece Neville alternators that are internally regulated (fixed voltage) on the same engine. Output is a little unbalanced at times, but they function just fine.
 
Thanks so much guys
These have external simple 24 v truck voltage controllers.
I’m not good at electronics and need simplicity in my old age.
I have been using both alternators and separate simple 27,5 v regulators but found that after a period both regulators started to slowly increase the voltage right up to 32 bolts.
However I got 5 years out of 4 185amp lead acid batteries.
I have just installed a new set of the same batteries and am only using one of the 2 alternators and so far the new replaced external voltage regulator is doing its job limiting the charge voltage to around 27/28v
This takes longer to charge than before but I don’t want to have regulator problems with over voltage output as happened before
Would you mind drawing a rough circuit diagram using one regulator to control both alternators ?
Would a simple $40 regulator be able to handle the output of 2x 180 amp alternators? Really appreciate your assistance
 

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If you're looking at this as a project, you will need to do some optimizing in the design. An example would be as TT mentioned you're utilizing half to most of the power output of the engine.

So, the engine will need to reach rated output (and be warmed up) before the alternators are engaged. This would most likely require external programmable regulators to delay the activation.

Also, pulley sizing will be quite important as you don't want to over speed the alternator (premature bearing failure). Undersizing the pulley would equally be bad as cooling the alternator is dependent on fan RPM.

Finally, selecting the correct alternators will be critical for longevity. Most alternator aren't rated for continuous output. So you will need to use large frame continuous output alternators if you are expecting full output for more than about 15 minutes.

Ted
 
Back in 2012 I had 2 x 200 amp Leece Neville alternators installed, one on each JD 6068 engine, and controlled by a single Balmar 612 Dual reg. It has worked flawlessly. Right from get go I would see over 360 amp in total charge rate if the house bank was down a bit in the morning when getting underway. We de-rated the output a little using Belt Manager, and of course had temp sensors on the alts. I suspect that we could have got more than 360 amps had we needed to, but the temps would just have climbed a lot sooner and temp-induced de-rating taken place. I was very happy with the 360 amp charge rate. Kudos to Port Townsend Shipwright's CoOp team.

A few years ago I changed to an LFP battery house bank. I de-rated the 612 a bit more and now don't get more than around 325 amp. Still no issues. So i now have 12 years of alternator and regulator performance without issues.

For some reason Balmar these days want you to install two 612's rather than a dual unit unless the alternators are on the same engine. Back in 2012 they were happy for the alts to be on different engines. I almost invariably have both engines running, and both at almost identical rpm so the alternators rpm are going to be very close to each other I think with this usage pattern they basically simulate being on the same engine.
 
I run both my engine's alternators, which are stock 65 amp each to a separate Blue Sea ACR (automatic charger relay). They then are connected together and run to the house battery bank with the correct fuse in between. www.bluesea.com/resources/1366
CAUTION: they do not work with a lithium house bank. Even though they work fine, I am removing mine because of converting to LiPo batteries so have to use a DC to DC charger using the same wiring.
 
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