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svsonora 28-02-2019 23:49

Alternator pulley question
Newbie question here. I'm trying to get more juice out of my alternator at low RPMs and idle. I am running a Mando / ARCO 60055 alternator on an Atomic 4. I'm trying to figure out how to change the pulley ratio of the alternator. Do I change the alternator side, or the pulley side? If I'm switching out the alternator pulley, how do I go about looking for a pulley that fits?

Pauls 01-03-2019 00:31

Re: Alternator pulley question
A smaller pulley on the alternator will spin it faster. This can be done, with the provision that you can only go so small on the pulley before the small diameter causes problems by bending the belt into too small of a radius. Assuming you are running an "A" size belt (1/2" wide) the smallest pulley available is 2.5" OD. I'd advise running a bit larger diameter than that. Measure the diameter of the alternator shaft and buy a pulley that matches that diameter. The pulley should be a press fit on the alternator shaft.

coopec43 01-03-2019 00:34

Re: Alternator pulley question
I've just been through this exercise but mine was more complicated as I went from a single groove to a double groove pulley and I had to get it machined.

You could change the size of either pulley on the engine or the alternator but my preference would be for the alternator. There are a number of ways you could go about it but my advice is that you take the pulley off the alternator and take it to a pulley specialist in your area.

Maybe one of these?

You may well have to modify the tensioning arrangement.

(I found the pulley specialists incredibly helpful back here in Perth West Australia)

Dave_S 01-03-2019 00:41

Re: Alternator pulley question
My 0.02c

Alternators can electronically tap out at a preset output so no matter how fast you spin it it won't make more current except when engine revs are low.

Hesti 01-03-2019 02:09

Re: Alternator pulley question
Take care that the alternator does not exceed its max. RPM at max. engine revs. Actually, it is a good idea if it always stays somewhat below these max. RPM - alternators do not like being overspun, either the bearings will give in pretty soon or the rotor may open up and touch the stator. A next size up alternator - if available - might be a solution.

In case you change the pulley: Make sure it is torqued to the manufacturer recommendation. Just saying. Speaking about car style alternators - pulleys flying of at high rpm or shafts breaking are not a joke. About press fit - on the alternators I know, the pulley is not a press fit on the shaft, torquing the pulley nut to manufacturer recommendation is the key.

coopec43 01-03-2019 14:45

Re: Alternator pulley question
I did find in Perth (West Australia) there are pulley distributors who stock pulleys for particular make/model of cars/boats. If you can't provide that detail they don't want to know you.

But there are other pulley distributors who can supply to a particular requirement: diameter, number of grooves, shaft diameter etc: they are not interested in make/model.

a64pilot 03-03-2019 05:10

Re: Alternator pulley question
Average marine motor doesnít even come close to spinning an alternator at optimum RPM, not even close.
A lot of this is due to the size of engine pulley required to gear the alternator correctly would make it harder to fit into a boat.
One of the biggest reasons to spin one faster is to improve cooling, they are fan cooled and the faster fan cools better.

Average alternator is capable of 12,000 RPM and some can go to 18,000.
Measure your pulleys to determine the ratio and determine RPM.

RaymondR 03-03-2019 22:55

Re: Alternator pulley question
Be mindful that the smaller the pulley you put on the alternator the greater the lateral load on the shaft and bearing becomes.

a64pilot 04-03-2019 04:31

Alternator pulley question

Originally Posted by RaymondR (Post 2839225)
Be mindful that the smaller the pulley you put on the alternator the greater the lateral load on the shaft and bearing becomes.

Yes, but there is even more to it than that, the smaller pulley will stress the belt more, and as itís smaller there will be less contact area, and I can almost guarantee slippage and belt dust, plus slippage due to friction overheats the input shaft of the alternator and may burn out bearings, beside adding heat to something your trying to cool down by spinning it faster.
Unless you have some kind of unusual oversized pulley to start with, going smaller really isnít an option, they are about as small as you can get away with to start.

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