Running Two Alternators

[S&S]

I'll take a look at the Ample Power stuff. I'm not sure that it's adjustable to be within range or if it has a tap to the BMS (Battery Management System)

[s/v Jedi]

A good reason for using two alternators instead of a single bigger one is that with two you partly/mostly/completely cancel out the sideways pull on the power take-off. This means that the bearing will last much longer.

Also, the engine manufacturer will state a maximum sideways pull which limits the max. size of the single alternator you can use.

cheers,
Nick.

[S&S]

The rig has two on opposite sides so that's covered. The issue is mostly electrical at this point. I'd like to charge in parallel and discharge individually.

[donradcliffe]

Originally Posted by S&S

I'd like to charge in parallel and discharge individually.

Why on earth would you want to do a thing like that! Read about Peukert's law Peukert's law - Wikipedia, the free encyclopedia and see why you are going to get more energy out of your batteries (and longer life) if you discharge them in parallel.

[S&S]

Originally Posted by donradcliffe

Why on earth would you want to do a thing like that! Read about Peukert's law Peukert's law - Wikipedia, the free encyclopedia and see why you are going to get more energy out of your batteries (and longer life) if you discharge them in parallel.

LiFe PO4 batteries are not subject to Peukerts. That's for lead acid batteries only- new technology, new issues. I can charge these at 3C (that'd be 1800A for a 600Ah bank )

[GordMay]

Originally Posted by S&S

LiFe PO4 batteries are not subject to Peukerts. That's for lead acid batteries only...

I’m no expert on Li-Fe-PO4 batteries; but I strongly suspect that Peukert’s Law (not suggestion) still applies - and that only the actual exponent (number) changes with chemistry.

[S&S]

Originally Posted by GordMay

I’m no expert on Li-Fe-PO4 batteries; but I strongly suspect that Peukert’s Law (not suggestion) still applies - and that only the actual exponent (number) changes with chemistry.

Nope, Peukerts is chemistry specific. The charge curve is very flat for these except at the very ends (95%+ charge, 80%+ discharge). Very un-lead/acidlike.

Interesting, no?

[witzgall]

Well, Gord May is right, it Perkerts is still alive and well even for LIFEPO4 batteries. THe difference is that for our purposes, you can ignore the effect, as it so slight an effect.

My LIFEPO4 cells for the Torqeedo battery finally arrived last night. Now I need to build it up in a pack, buy a case, and wire up the BMS. I'll post a separate topic showing how this works out.

Chris

[Sailorguy]

I have a 10hp diesel I use for a power plant to drive a refer comp, water maker pump and two alt.s. The alternators are regulated from a single ample power SAR w/ fields connected together. I also use the same regulator to reg the alt on the main prop. engine using a field selector switch (yes I carry a spare...but it has never failed). The alt outputs are routed through a "fail safe" schottky diode (in case one alt shorts out) and then joined together as a single output. This setup has worked flawlessly for over 10 years and many cruising miles.

Steve

[S&S]

Originally Posted by witzgall

Well, Gord May is right, it Perkerts is still alive and well even for LIFEPO4 batteries. THe difference is that for our purposes, you can ignore the effect, as it so slight an effect.

My LIFEPO4 cells for the Torqeedo battery finally arrived last night. Now I need to build it up in a pack, buy a case, and wire up the BMS. I'll post a separate topic showing how this works out.

Chris

There'll be a ramp down at the last few percent on the charge side. The internal resistance, which is wht gives rise to Puerket's, is negligable at the currents you'd want to draw down.

Who's BMS did you pick?

[S&S]

Originally Posted by Sailorguy

I have a 10hp diesel I use for a power plant to drive a refer comp, water maker pump and two alt.s. The alternators are regulated from a single ample power SAR w/ fields connected together. I also use the same regulator to reg the alt on the main prop. engine using a field selector switch (yes I carry a spare...but it has never failed). The alt outputs are routed through a "fail safe" schottky diode (in case one alt shorts out) and then joined together as a single output. This setup has worked flawlessly for over 10 years and many cruising miles.

Steve

That's a great idea, thanks!

[CharlieJ]

I recommend that you also contact Westerbeke and ask for their input on driving three alternators off of the front of their engine. The side loads generated on the fresh water pump bearing may be too high and may cause premature bearing failure.

Charlie

[S&S]

Originally Posted by CharlieJ

I recommend that you also contact Westerbeke and ask for their input on driving three alternators off of the front of their engine. The side loads generated on the fresh water pump bearing may be too high and may cause premature bearing failure.

Charlie

I'd only be running one off the water pump sheave. The other would be off the crank directly.

[David M]

I think its getting unnecessarily complex. The downside to complexity is the increased chance of failure.

[s/v Thea]

I've got two Leece-Neville 160 amp alternators wired in parallel, driven by a single Ample Power SAR V3 regulator (max field on reg is 15A, alternators are 7A each), have had no problems.

Doug