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Old 11-12-2014, 15:42   #1
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Alternator squeals when field turned on

I just replaced the belt on one of my alternators, and when the engine is running there is no noise. But I have a switch that means I can turn the field current on or off. With the switch off everything is fine but when I hit the switch to turn on the field I get a loud squeal. What's going on here? Is there a problem with the bearings of the alternator that is caused by an extra load on the bearings when the field is on or is there some drag on the belt that causes this. Can I lubricate the bearings or do they run dry, oh by the way its a Balmar 100Amp job. The other alternator, is running fine no noise from that just when I switch in the balmar. Anybody know whats going on here.
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Old 11-12-2014, 15:46   #2
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Re: Alternator squeals when field turned on

Have you checked the belt tension?
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Old 11-12-2014, 15:59   #3
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Re: Alternator squeals when field turned on

Belt tension is a good start. YOu need to help us understand what the alternator is doing, since the other one you say is OK. Usually belt squeal comes from either an undertensioned belt, or too high a load on the alternator from the eleftrical side. What's it feeding, what kind of regulator (internal or external), what size battery bank, what SOC of the bank?
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Old 11-12-2014, 16:06   #4
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Re: Alternator squeals when field turned on

You may have a high output alternator and a single belt? Not uncommon at all. If it's an external regulator you may be able to adjust the output down. I had one boat with a 100 amp alternator that just wouldnt stop doing this. I had to put the other regulator on and live with less output.
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Old 11-12-2014, 16:27   #5
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Re: Alternator squeals when field turned on

If this is not in an OE location, you may not have enough belt contact on the pulley. Should be approx. 120 degrees of contact for a single belt high output.
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Old 11-12-2014, 17:45   #6
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Re: Alternator squeals when field turned on

Belt isn't too narrow so it's riding too deep in the pulleys and bottoming out it it?
I think we all think it's belt slippage and nothing to do with the Alt.
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Old 11-12-2014, 18:06   #7
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Re: Alternator squeals when field turned on

It stands to reason it's probably a belt problem as the OP just changed the belt and apparently did not have this squealing problem prior to installing the new belt.
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Old 11-12-2014, 18:57   #8
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Re: Alternator squeals when field turned on

As mentioned already assuming the only new piece in this equation is the new belt, it's slipping.

Anything from not enough belt tension, some oil or grease in the pulley(s) added when doing the maintenance, to a different friction coefficient of the new belt.

I would recommend getting a scale to measure the belt tension. Over tightening the belt can lead to premature bearing failure in the alternator. No idea if it can also cause bearing wear in the engine but with the high cost of boat repair why take a chance. If improper maintenance leads to a problem it always seems to fail at the worst possible time too.
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Old 12-12-2014, 05:22   #9
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Re: Alternator squeals when field turned on

Thanks folks, I've inherited a sort of hybrid system here, and so this is what I have. I have a 160A alternator driven by two belts, backward facing, and the 100A Balmar. Both are wired to together in parallel at the main switch. Both field wires go to a Next step regulator and are tied together on the field terminal. To get charge into the engine battery I have to switch on the main switch, if I don't switch it on then both alternators would only feed the house bank. The other switch just switches on the circuit to the starter and the feed to the ignition.
The SOC at the time was very low, below 12v, anyway, on both banks.

I've wondered about this belt on the Balmar sitting too deep in the pulley but I've been replacing it with the same spec as the one I took off. Is there a simple way to calculate the size of belt for a pulley like measuring the pulley width, and the belt width.

I must say as an electrician who has only dealt with AC systems that I find DC confusing. I don't see, for instance how the next step regulator can monitor two batteries and alter the field current for the SOC for two separate battery banks. What if one needs charging but the other doesn't, how can that work. In my mind I think I need two regulators, one for each alternator.

But my OP was sort of about why the Blamar only squeals when I turn the field on. Does this subject the rotor to more torque and hence more resistance on the belt. And if the batteries are particularly low there is more torque.
Hope this ramble makes some sense, thanks guys
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Old 12-12-2014, 05:33   #10
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Re: Alternator squeals when field turned on

Oh forgot to say, House bank is four six volt batteries 200Ah each, and one 12v engine battery. The house bank should be six batteries but only have four wired up as one of the six needs replacing.
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Old 12-12-2014, 05:34   #11
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Re: Alternator squeals when field turned on

Quote:
Originally Posted by shantycrew View Post

But my OP was sort of about why the Blamar only squeals when I turn the field on. Does this subject the rotor to more torque and hence more resistance on the belt. And if the batteries are particularly low there is more torque.
If the field is off there is no load. When you turn it on the load hits with a jolt. Hence a noise if it slips momentarily.
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Old 12-12-2014, 06:06   #12
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Re: Alternator squeals when field turned on

Quote:
You may have a high output alternator and a single belt? Not uncommon at all. If it's an external regulator you may be able to adjust the output down. I had one boat with a 100 amp alternator that just wouldnt stop doing this. I had to put the other regulator on and live with less output.
Used a 150 amp alternator on a single belt for years. No problems.
It had an external regulator and perfect alignment on the pulleys, the most I saw however was 95 amps being delivered, probably because I never took the house bank to less than 70% or becuase the losses in the system, and or the temperature in the engine compartment.

The only squealing I have heard is when the bearings are starting to go.
Always keep a spare, and newly overhauled alternator on the boat so easy to swap when at anchor and no reason to listen to the squeal for days or weeks on end
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Old 12-12-2014, 06:24   #13
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Alternator squeals when field turned on

The new belt is slipping because the torque goes way up when the field is on versus off. How often do you replace the belt? Is the new belt the same brand and type as the one you took off? If not try to find the highest quality belt you can and try that first. Size is not the only difference between belts. Good belt companies will tell you how to measure correct tension in the belt. You may have to retension the belt after it runs for a short time. Belts stretch.

Next, since the alternators are paralleled it's a remote possibility that the other alternator is not working. Does the other alternator charge the batteries if the squealing alternator belt is removed?

I don't think this problem has anything to do with the battery switching.
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Old 12-12-2014, 06:40   #14
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Re: Alternator squeals when field turned on

I've had good luck with Gates Gatorback belts in other applications, new to this sailboat thing, but believe a good belt, is a good belt.
If the belt sits low in the pulley, it may be too narrow, if you have the old belt, the numbers on it I believe are length and width
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Old 12-12-2014, 10:14   #15
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Re: Alternator squeals when field turned on

Sorry, I missed the fact that the belt was just replaced. Evidently with the same type and size of belt... so that's pretty confusing if the old one was OK. I've had good luck with Gates Green Stripe and Dayco "Cog" belts.
I wonder if the Balmar doesn't get enough "belt wrap" around the pulley in this setup... maybe the new belt needs to "burn in" a bit to mate with the pulley groove? grasping at straws.
My HC38 had a 100 amp alternator on it with single belt. It was fine with the old Balmar III regulator that came with the boat, but when I switched that out with a Next Step regulator... it never would stop squealing.... pretty much showing how much better the Next Step was.... I had to put the Balmar back on to sell the boat....
OP: did you buy a matched set of belts?
Have you thought of having a Field switch on both alternators rather than just one? That way you could let one alternator go thru its "hi load" 15 minutes or so before turning the other on... relieving belt tension...
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