4300 Alternator Low Current

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4300 Alternator Low Current

Postby marco on Sun Jan 29, 2012 8:22 am

I have a 4300 Alternator on my Motorhome and I am only getting 150A or so out of it at max RPM. When I installed it I got over 300 at the same RPM several years ago.

The bushes are 20mm long so does not seem likely that is the problem and the regulator is putting almost 12V across the field winding so should be maxed out.

Are the bushes OK? Anything I should look for?

I am off to do some more debug but I think I am missing some diodes. Going to put my oscilloscope on it.
marco
 
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Re: 4300 Alternator Low Current

Postby marco on Sun Jan 29, 2012 9:27 am

Update. Seems the regulator is OK. It is asking for 100% putting the full voltage on the field winding. If I measure the current with my clamp I am getting about 4.5A which seems low. To be sure it is not the regulator I jumped the field widing to the battery through my amp meter and it also read in the 4-4.5A range. This seems low? These measurements were taken at idle since I have no good way to rev the motor and poke around with the meter. I can read the max current from the alternator using my max function on my current clamp.
marco
 
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Re: 4300 Alternator Low Current

Postby marco on Sun Jan 29, 2012 8:18 pm

Fairly sure the diodes are bad. Will not know until I take off the alternator next Saturday. THoughts please? Can I get a new diode pack?
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Re: 4300 Alternator Low Current

Postby Coulomb on Mon Jan 30, 2012 5:35 pm

At idle, little or no current is produced.

Diode assemblies are available, though I'm not convinced that is the problem.
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Re: 4300 Alternator Low Current

Postby marco on Mon Jan 30, 2012 9:49 pm

At idle I see 15-30A. Idle is about 2500RPM at the alternator.
The field current is 4-5A
Jumping past the regulator gives the same field current and the voltage on the other terminal is close to zero.

At 6500RPM I see 157A. I have not tried to measure the field current at higher RPMs

I have a heavy load on the batteries (3kW inverter running the AC and all the lamps on) the battery voltage is about 12.5. Brand new lifeline batteries (new last monday) 3x8d in parallel or about 760Ah worth. The regulator should be asking for maximum amps.

No belt slip since it is a big wide 9 rib multi-v on the cummins ISC and anyway it would not slip at idle.

What else could be wrong? A blown winding? Bushes? It is not the regulator since bypassing it gives the same output current. The cables are very good and I do not see much voltage drop in either the ground or the power. I am running a dedicated ground line as well as the chassis connection.

My plan is to pull off the alternator Saturday and fit a 200A new Bosch alternator which should get me though our next trip. I would like the 300A back though since it lets us run an AC unit as we are driving cross country and it give me a proper 3 stage charger.

For the record I am an analog IC designer with 20+ years of experience in power microelectronics so I understnad wires. Perhaps not alternators specifically.

What do you think could be up?

What should the field current be?

Best regards... Marco.
marco
 
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Re: 4300 Alternator Low Current

Postby marco on Mon Jan 30, 2012 9:53 pm

BTW I will know if the diodes are bad for certain Saturday and I think that may be my best plan of attack and I can measure all the windings etc too. The Bosch Alternator will get me though the next few weeks since I will not likley be running the ac 100% and if I do I can always fire up the genset.

Be good to know what the field current should be... Marco.
marco
 
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Re: 4300 Alternator Low Current

Postby marco on Sat Feb 04, 2012 3:59 pm

The diodes are bad.

At least half of them are actually loose. They are press fitted into the heatsink and half of the ones you can see from the outside are loose. They may in fact be OK but I suspect if I push them back into place I have no reason to beleive they will stay in place.

I must admit this tech support is fairly useless. I figured this out for myself and got told that diodes are not likely the problem.

Can I just buy replacement diode assemblys and if so how much and how to you actually connect them to the stator?
marco
 
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Re: 4300 Alternator Low Current

Postby marco on Sat Feb 04, 2012 4:08 pm

BTW the Bosch ALternator I fitted is awaesome. 180A at idle and 220A at cuise. No three stage regulator but in a motorhome this is not such a big deal since I really want enough amps to keep up with the inverter with the AC running. I am sure it would be fairly easy to hack into and drive the bushes directly with an external regulator. The bosh regulator also cuts back the current if the alternator begins to overheat. Oh and it is smaller and ligher too.

This Bosch Alternator was $278 from Amazon with 2 day free shipping. The ample alternator never gave close to that at idle and at speed fell a little shy of the advertised 310A. Good job Bosch 15% of the price and gives more Amps than advertised. Oh and it comes with a 2 year 200,000mile warrenty. For $278 who cares I just get another....
marco
 
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Re: 4300 Alternator Low Current

Postby marco on Sat Feb 04, 2012 4:09 pm

BTW the Bosch ALternator I fitted is awaesome. 180A at idle and 220A at cuise. No three stage regulator but in a motorhome this is not such a big deal since I really want enough amps to keep up with the inverter with the AC running. I am sure it would be fairly easy to hack into and drive the bushes directly with an external regulator. The bosh regulator also cuts back the current if the alternator begins to overheat. Oh and it is smaller and ligher too.

This Bosch Alternator was $278 from Amazon with 2 day free shipping. The ample alternator never gave close to that at idle and at speed fell a little shy of the advertised 310A. Good job Bosch 15% of the price and gives more Amps than advertised. Oh and it comes with a 2 year 200,000mile warrenty. For $278 who cares I just get another....
marco
 
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Re: 4300 Alternator Low Current

Postby Coulomb on Mon Feb 06, 2012 3:39 pm

You'll want to budget for frequent battery replacement.
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