P38A ALTERNATOR FAULT

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If you find that any of the cables aren't within spec or you want any replaced, then if you get the actual bare battery cable and lugs, then I have a hydraulic crimper for the terminals at the workshop - so can make them to length for you if you are still coming to the weekend meet on the Sunday? I think I have a few bits of spare cable of various lengths and some crimp lugs, but can't guarantee how long the bits are!

Yes, still in China - flew to Beijing this morning (5:15am bus call after finishing load out at 1am... ) and now here for the next couple of weeks before finally coming home!!

Edit... will be interesting to see if my P38 starts straight up... it won't have been started/driven in 8/9 weeks by the time I get home! Don't get me started on drummer jokes either...
 
martyuk said:
It's definitely worth having a look at the alternator and checking the voltage drop on both the +ve and ground cables from the battery.

I didn't know the Diesel alternators were set at a lower voltage - but if you have something like a MF31-1000 battery, which is great for the p38 power wise - they are a calcium battery and will need a higher charge voltage than what the set point sounds like it is on the Diesel Alternator.

I get 14.1V from memory at idle on my Thor 4.6 - and have had a MF31 battery in there the last 4 years with no problems.

The only not I can find in one of the BECM documents I have regarding the alternator charging signal is that it the BECM is expecting Ground/0V when not charging and Vbatt when it is charging. I haven't had an alternator apart to see where this feed comes from internally, but I would assume it's just a piggyback off the main +ve power stud.
Click to expand...

Early diesels were 13.8 as standard for low antimony low maintenance batteries, maybe later ones 14.2 for half calcium. THOR from XA410482 should be 150 amp unit with a 14.5 volt set point.
 
Good to know about the earlier Diesels... I know I've still got the original 150A Bosch alternator on mine - I don't think I've ever seen it at 14.5V though - it is on the list to check over summer, and hopefully replace/rebuild as there's been a bit of bearing whine in it since I've owned the RR - it hasn't got worse over the years - but it hasn't magically fixed itself either!
 
wammers said:
Early diesels were 13.8 as standard for low antimony low maintenance batteries, maybe later ones 14.2 for half calcium. THOR from XA410482 should be 150 amp unit with a 14.5 volt set point.
Click to expand...

I'll check before I modify it but sure it was 13.6V from new. It was put on the week after I bought the car. Failed before I even got if home.

if you remember you helped diagnose it. The lift pump was running with the key removed and the car locked! I heard the humming and was worried.
 
martyuk said:
If you find that any of the cables aren't within spec or you want any replaced, then if you get the actual bare battery cable and lugs, then I have a hydraulic crimper for the terminals at the workshop - so can make them to length for you if you are still coming to the weekend meet on the Sunday? I think I have a few bits of spare cable of various lengths and some crimp lugs, but can't guarantee how long the bits are!

Yes, still in China - flew to Beijing this morning (5:15am bus call after finishing load out at 1am... ) and now here for the next couple of weeks before finally coming home!!

Edit... will be interesting to see if my P38 starts straight up... it won't have been started/driven in 8/9 weeks by the time I get home! Don't get me started on drummer jokes either...
Click to expand...

Yes, looking forward to it. Was going to see how everyone else was getting on and if no-one needed help maybe swap the logic board over in my BECMs.
 
Grrrrrr said:
I'll check before I modify it but sure it was 13.6V from new. It was put on the week after I bought the car. Failed before I even got if home.

if you remember you helped diagnose it. The lift pump was running with the key removed and the car locked! I heard the humming and was worried.
Click to expand...

Should be 13.8. Should show that at 2000 RPM with everything switched on. Headlamps, heater blowers Etc.
 
Grrrrrr said:
Yes, looking forward to it. Was going to see how everyone else was getting on and if no-one needed help maybe swap the logic board over in my BECMs.
Click to expand...

There's a fair few bits to get done - but enough hands to work on things aswell. I think we are going to try and get most of the heavy stuff done on Saturday as people will obviously be starting to think about heading back on Sunday afternoon! Swapping boards over won't take long though... probably take longer to remove/refit the drivers seat and trim that actually do the board swap!!
 
Grrrrrr said:
I'll check before I modify it but sure it was 13.6V from new. It was put on the week after I bought the car. Failed before I even got if home.

if you remember you helped diagnose it. The lift pump was running with the key removed and the car locked! I heard the humming and was worried.
Click to expand...
I fitted that voltage regulator in Feb 2015, never had a problem since.;)
 
Grrrrrr said:
He's a busy man! He's a rock star! And drummers have a reputation to uphold. I am still expecting a call from the police (or possibly the Police) saying there has been a bizarre gardening accident.
Click to expand...
LOL....

At least his fate will (hopefully) not be the same as the multiple drummers from Spinal Tap.....and yes, 11 is louder than 10!
 
martyuk said:
It's definitely worth having a look at the alternator and checking the voltage drop on both the +ve and ground cables from the battery.

I didn't know the Diesel alternators were set at a lower voltage - but if you have something like a MF31-1000 battery, which is great for the p38 power wise - they are a calcium battery and will need a higher charge voltage than what the set point sounds like it is on the Diesel Alternator.

I get 14.1V from memory at idle on my Thor 4.6 - and have had a MF31 battery in there the last 4 years with no problems.

The only not I can find in one of the BECM documents I have regarding the alternator charging signal is that it the BECM is expecting Ground/0V when not charging and Vbatt when it is charging. I haven't had an alternator apart to see where this feed comes from internally, but I would assume it's just a piggyback off the main +ve power stud.

I think the fuse box will be fine with the higher voltage too. Higher voltage actually means less current flowing (ohm's law). I wouldn't worry about other electronics either - most of the ECU's have their own internal voltage regulators to get the voltages they require to run, and I think from looking at a few of them, the inputs on most of the regulators are good for up to at least 30V - so a difference between 13.6 and 14.x shouldn't affect them too much.
Click to expand...
Higher voltage means less current flowing.......... Really.
If you're going to quote ohms law, at least understand how it works!!!
 
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