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Alternator issues. Any ideas?


Jak

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Hi all. So i replaced my batteries and alternator a couple of weeks ago. 1.5 BMC, new 55 amp alternator and 3 95ah leisure batteries (the 105s are just too big for the battery box).  All was good once fitted. Seeing 14.5v to the batteries (according to the solar controller). I have renewed exactly the same set-up I had for the last 5+ years as it has worked well. 
 

Yesterday the fan belt was squealing. Fair enough. Loosed off the mountings, gave the alternator a good tug, tightened them up. checked the connectors. No squeal and the charge light gone out. Excellent.  Job done. 
 

But no its not. Now I am only seeing 13.6v. I have double checked everything, always had 14.5v plus - up until today - from this set-up. Fired it up again today. Still 13.6v :(
 

Why?  The connections look good. The belt is definately not slipping now. Where have my volts gone?!  Is it really likely my new alternator has gone duff already or should I be looking elsewhere?


Thanks for any ideas.  Jak. 


 

 

Edited by Jak
Typo
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One suggestion is that when you have the 14.5v showing on your solar controller you had some input from the Solar, now, when you don't, you are getting a different figure.

 

Why would you rely on reading the voltage from the solar controller, you should be reading the voltage coming out of the alternator at the alternator terminals, and the voltage going into the battery at the battery terninals.

 

Who knows what sort of volt drop or dry-joints you have got when you are reading the voltage of another piece of equipment which itself can provide a voltage.

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Hi Alan. Thanks. No the 14.5 has been in the dark too!  Yes, I dont have a tester to hand but agree of course. Its just that the big drop is visible on the solar controller where I am used to seeing the 14.5v plus volts with this set-up. 
 

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Batteries were down to 12.4v with nothing drawing current. Then I fired up the engine to get charged. So cloudy nothing coming in from the solar.  I’d normally see 14.5 straight away. 
 

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1 hour ago, ditchcrawler said:

Any idea of the current being produced

 

This is important information because the alternator will reduce it's charging voltage as the charging current increases. with batteries over 25% (12.4V rested) discharged I would wait a bit with the alternator running at 1200 rpm plus to see if the voltage starts to climb.

 

The squealing alternator belt tends to speak of well discharged batteries.

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2 hours ago, Jak said:

But after charging for and hour and a half still at 13.6v. 

I does sound a bit like a blown diode on the alternator. However to be sure,  first you need to check the charging voltage actually at the alternator (with a multimeter) in case the problem is voltage dropped in bad connections / isolator switches etc.

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8 minutes ago, nicknorman said:

I does sound a bit like a blown diode on the alternator. However to be sure,  first you need to check the charging voltage actually at the alternator (with a multimeter) in case the problem is voltage dropped in bad connections / isolator switches etc.

 

True, but I would still see if running t for longer increased the charging voltage, on the grounds anyone can do it and there is no need for an ammeter or taking the alternator off for testing.

 

Edited to add: or using an oscilloscope to look at the phases

Edited by Tony Brooks
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Nick. Hmmmm. I just checked my multi-meter and is looks like it is only rated for 10amps. If connect it to the 55amp alternator wont that blow the fuse?

 

Tony. I tried almost 2 hours running the engine at more than idle and still max 13.6v. 
 

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7 minutes ago, Jak said:

Nick. Hmmmm. I just checked my multi-meter and is looks like it is only rated for 10amps. If connect it to the 55amp alternator wont that blow the fuse?

 

Tony. I tried almost 2 hours running the engine at more than idle and still max 13.6v. 
 

 

1. Yes, it would but on the 10 amp range it will probably burn the shunt that is inside it. That is why you need a DC clamp meter for that job. The internal fuse is often only used on the 2 amp (or similar) range.

 

2. Then I agree with Nick, probably a blown diode unless there is a wiring or charge splitting issue. What type of charge splitter do you use?

 

I would suggest putting the voltmeter between the alternator positive (B+) and the battery positive and revving the engine. Whatever it rads will be the volt drop on the wiring and charge splitter. Do the same for the negative. I would on;y want to see about 02 to 0..3 volts on either.

 

 

Edited by Tony Brooks
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5 minutes ago, Jak said:

Nick. Hmmmm. I just checked my multi-meter and is looks like it is only rated for 10amps. If connect it to the 55amp alternator wont that blow the fuse?

 

Tony. I tried almost 2 hours running the engine at more than idle and still max 13.6v. 
 

 

Measure the Volts. That'll tell you if the alternator is putting out the same as is getting to the battery terminals.

You will need a DC ammeter to measure the amps (If you buy one make sure is does DC many / most dont)

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48 minutes ago, Jak said:

Nick. Hmmmm. I just checked my multi-meter and is looks like it is only rated for 10amps. If connect it to the 55amp alternator wont that blow the fuse?

 

Tony. I tried almost 2 hours running the engine at more than idle and still max 13.6v. 
 

We are talking about volts here! So you certainly don’t want to measure “amps” across the alternator positive and negative (chassis) as that would create a dead short circuit with added smoke!

So multimeter on volts range, probes on fat B+ terminal and alternator case (or B-). Engine running above tickover (be careful of moving belts, no loose clothing etc) and see if you still only have 13.6v, or whether it is up to 14.5v

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