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302 electrical/alternator problems

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Cement102

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Hello all, thanks in advance for taking a look.

We have a Chris Craft with a 1994 omc cobra 302. We have a standard 55A alternator that keeps squealing and tearing through belts. The alternator is brand new. The old one did the same thing. We thought it had gone out, so replaced it...same issue. Engine starts fine, and alternator squeaks, making me think its overloaded. If I turn the battery switch off, engine revs up and runs perfect. When I switch back to the battery, it bogs back down and squeals. Batter is new and we've tried a couple. I figured we had a short, but the current draw from the battery when the engine is running is about 17 amps, which seems reasonable. Maybe I have a short somewhere engine side? I have pulled every fuse in the panel, no change.

Wondering if anyone has a thought on where to looks. Got a DC clamp meter coming this weekend to help out too.

Thanks!
 
By any chance is the ignition switch sticking in the start position? Try turning the ignition on and then use a jumper or remote start switch to start the engine. Thats the only thing i can think that draws that much power without lighting up a wire. When you turn the battery off the starter will stop spinning. Just a thought!
 
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Cement102 said:
Hello all, thanks in advance for taking a look.

We have a Chris Craft with a 1994 omc cobra 302.
If this is truly a 1994 engine/stern drive, it is most likely Volvo Penta.
By '94, Volvo Penta had purchased OMC and had begun introducing their gimbal suspension Cone Clutch drive.


We have a standard 55A alternator that keeps squealing and tearing through belts. The alternator is brand new. The old one did the same thing. We thought it had gone out, so replaced it...same issue. Engine starts fine, and alternator squeaks, making me think its overloaded.
Over-loading can or may cause a squealing sound. This may also cause the charge lead to heat up.

If I turn the battery switch off, engine revs up and runs perfect.
Unless your MBSS is field circuit protected, DO NOT switch through or turn it to the OFF position while the engine is running! This will interrupt the alternator's field circuit, and may damage the alternator.

When I switch back to the battery, it bogs back down and squeals. Batter is new and we've tried a couple. I figured we had a short, but the current draw from the battery when the engine is running is about 17 amps, which seems reasonable. Maybe I have a short somewhere engine side? I have pulled every fuse in the panel, no change.
Tell us more about the brand and type of alternator!
Click to expand...
 
Like Rick said, DONT turn the battery switch to OFF while the engine is running....

the starter is a good candidate to start with.....

Did you check the water pump bearing when the initial alternator change was done? is the alternator mounting bracket(s) still lined up correctly? Is the belt worn?

17 amps after starting is very reasonable so I doubt the current draw is inducing the noise....was it measured at the alternator ouput terminal or another location in the harness?
 
I figured we had a short, but the current draw from the battery when the engine is running is about 17 amps, which seems reasonable. Maybe I have a short somewhere

If your "drawing power" from the battery ,your not charging . and 17 amp draw is WWAAAYY to much anyway.Suspect blown diodes in the alt or regulator from switching the battery switch to "off" . Alt are capable of putting out 40 amps to charge with good clean pullys and belts of the correct width
 
Thanks all, I will check the starter and starter solinoid when the weather clears up. Also, when I get the DC clamp meter I will get the actual draw from the alternator. The 17 amp draw while running was from battery negative terminal to negative cable. Voltage across batter is 14.3 volts at 2000 rpm, so alternator is good. Same with the previous. The fact that I came jump the solinoid with the Battery off and no issues tells less it has to be accessory side. What is strange is only 5 amp draw with the accessory on (not started). Draw just doesnt align it an overload.

We took the boat to a mechanic when we thought the belts were being chewed up by alignment. He said all was good. Still chewing a belt writhing 20 minutes. Hopefully clamp will help me chase it.
 
Try this turn the battery off and then try to start it normally just leave the switch on then turn on the battery. If the engine starts you need a new ignition switch!
 
kimcrwbr1 said:
Try this turn the battery off and then try to start it normally just leave the switch on then turn on the battery. If the engine starts you need a new ignition switch!
Click to expand...


Gave it shot. No cranking or anything after switching the power back on.

Tomorrow I should have dc clamp meter, so will be able to trace a lot better.
 
Cement102 said:
We took the boat to a mechanic when we thought the belts were being chewed up by alignment. He said all was good. Still chewing a belt writhing 20 minutes.
Click to expand...

Correct pulley alignment is only part of this.
Look at the pulley sheaves for rust or corrosion.
If severe enough, it can eat away at a V-belt eventually ruining it.
 
To the OP, is your OMC EFI or carbed?

I've got a 1993 5.8/351 EFI doing that same thing... squealing and chewing through alternator belts. I've been through three alternators now where they run fine for 5-10 hours; cool as a cucumber, putting out 13.6 volts. Then they squeal and burn up the belts but also don't put out voltage. It's like something in my boat is burning up the voltage regulators.
 
Bt Doctur said:
What is the output rating of the alt?
Click to expand...

65 amp, which I believe matches the OE.

First one:
https://www.westmarine.com/buy/sier...amp-single-groove-pulley--5327309?recordNum=4

Second One:
https://www.amazon.com/gp/product/B...arch_detailpage?ie=UTF8&psc=1#customerReviews

The second one I know is a cheapy but I just needed something over-nighted as a hold-over as we were on vacation with the boat for 4th of July. It doesn't seem coincidental to me that they both failed in such quick succession. And I did wire a sense jumper from B+, because my OE alternator was internally-sensing. The battery was also replaced with a Marine Starting battery from West Marine last season.

I think next year I'll try an ARCO alternator. The boat is already stored for the season.

Is it possible my trim motor could be over-loading the system? The failure mode squeal seems to start when I adjust trim. And then it just squeals all the time.
 
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And I did wire a sense jumper from B+, because my OE alternator was internally-sensing.

Can you elaborate on this internal sensing thing. you either have a "1 wire " with just an output terminal or you have a 3 wire that needs a "sense" and "excite" . Squealing a belt when hitting the trim can be a loose belt, wrong size belt, or slipping belt. You put a heavy load on the system, the alt tries to keep up but cant. belt now slips and squeals
 
A battery is a voltage storage device.
If sized correctly, it will provide the AMPs that are being consumed.
An alternator simply supplies and keeps the battery voltage up where it should be.
The battery also acts as a buffer.
Heavy loads are first derived from the storage device... i.e., the battery.
The battery's cables (both Positive and Negative), the cable terminal connections and the MBSS and it's connections must be capable of the loads.

NOTE: some Perko MBSSs are known to have weak contacts.

So....., when loads are placed on the battery, the battery (and all paths) should be able to serve the load.
The alternator will increase output as required, but should never be expected to take the heavy loads.

I would suggest going through your system and checking all paths!



.
 
Last edited:
Bt Doctur said:
And I did wire a sense jumper from B+, because my OE alternator was internally-sensing.

Can you elaborate on this internal sensing thing. you either have a "1 wire " with just an output terminal or you have a 3 wire that needs a "sense" and "excite" . Squealing a belt when hitting the trim can be a loose belt, wrong size belt, or slipping belt. You put a heavy load on the system, the alt tries to keep up but cant. belt now slips and squeals
Click to expand...

The original Prestolite alternator only had Positive, Excite, and Ground connections. The voltage regulator had an internal circuit for sensing. The replacement alternators I've had don't have that internal circuit, so I added a jump from sense to B+ so the regulator can sense the battery voltage. I've replaced and re-tensioned belts countless times with no change until I replace the whole alternator again. Then it runs perfectly for a few days and does the same exact thing; slipping burning belt and the voltage just reads 12-ish, which I assume is just battery voltage.

RicardoMarine said:
A battery is a voltage storage device.
If sized correctly, it will provide the AMPs that are being consumed.
An alternator simply supplies and keeps the battery voltage up where it should be.
The battery also acts as a buffer.
Heavy loads are first derived from the storage device... i.e., the battery.
The battery's cables (both Positive and Negative), the cable terminal connections and the MBSS and it's connections must be capable of the loads.

NOTE: some Perko MBSSs are known to have weak contacts.

So....., when loads are placed on the battery, the battery (and all paths) should be able to serve the load.
The alternator will increase output as required, but should never be expected to take the heavy loads.

I would suggest going through your system and checking all paths!


.
Click to expand...

No MBSS in our boat; just one starting battery.

Thanks for the clarifications. What should I be checking these paths for? High resistance? I'm slightly mechanically inclined but have a limited understanding of electrical stuff.
 
1096d.jpg
No reason to add and additional wiring, you may actually be causing the alt to go to full output and causing the belt to squeal. might want to try a different type of alt.
 
Really appreciate your help and pointing me toward the Prestolite literature! All of the alternators I've found with part numbers that supersede the original equipment in my boat are the "Mando" style. When I first replaced it I didn't add the sense jumper and the alternator was continuously putting out 14.5+ volts and still burning up the belt. Did some more research and found the jumper suggestion and it brought the voltage down to 13.6 like it usually is and worked perfectly, until it died again. And again.

Wiring diagram for my engine:




How I wired the replacement alternators:



And the later 5.8 wiring diagrams (once Volvo took over) show it this way too:
 
Hi. Do you have all of this wiring diagram?


raquettelaker2 said:
Really appreciate your help and pointing me toward the Prestolite literature! All of the alternators I've found with part numbers that supersede the original equipment in my boat are the "Mando" style. When I first replaced it I didn't add the sense jumper and the alternator was continuously putting out 14.5+ volts and still burning up the belt. Did some more research and found the jumper suggestion and it brought the voltage down to 13.6 like it usually is and worked perfectly, until it died again. And again.

Wiring diagram for my engine:




How I wired the replacement alternators:



And the later 5.8 wiring diagrams (once Volvo took over) show it this way too:
Click to expand...
 
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