Calling All DN 50 Gurus

[gus]

I just returned from a 5000 mi + trip to the NW and found some interesting DN 50 12V gear driven alternator operation on my 8V71 with V730.

Three days from Seattle in remote WY the voltmeter dropped to 13.5v (in the red) after never leaving the 14-15v stage (moving back and forth the whole time as it has since I got the bus in Dec '10) for about 3000 mi.

After another hour or running to civilization I stopped and checked everything out with my VOM - all was well. Started the engine and VM was back to normal. Stayed that way the rest of the day.

The next two days the same thing happened except I just kept on truckin' and it eventually came back to normal after a couple of.

The last day it went off line after only a couple of hours and settled on 12.5V. After stopping for lunch it came back on at normal voltage. An hour later it went off and stayed that way the rest of the day.

I have two 8D starters and one Gp 31 house, my electric load is very modest. When it goes off I turn on all lights but this fails to bring it back on line.

I'm assuming the batteries are so fully charged the alt is cutting out but I didn't know it did this?? The bus manual is no help whatsoever and I've spent the past three hours googling with no useful info.

Anyone else have this happen or know what causes it?

[bevans6]

The classic test for the batteries are charged and I'm takin' a rest for the DN50 is put a load on it and see what it does.  Mine does this at idle after a long run if there is no load on.  Otherwise my suggestion is voltage regulator rather than alternator if it can charge at full rate when needed.

Brian

[gus]

Brian,

Thanks, it charges just fine even with all the lights on. Charging has not been a problem, ever.

Once it shuts down even turning on all the lights doesn't bring it back. But, since the battery voltage stays strong when shut down I don't worry about it. My real concern was that this may be a sign of future problems.

In my case, 300 amps is way more than I will ever need.

When this first happened I load tested my two Gp 31 house batts and found one bad so I disconnected it thinking it was the problem. However, it made no difference but I left it disconnected anyway knowing it might short out at any time.

I also load tested the two 8Ds and found them good.

[luvrbus]

You need to replace the diodes Gus not a major surgery

good luck

[gus]

Well, today I fired it up, batteries weak and no charge. Turned on all lights, nothing.

So, it appears either diodes or regulator so out comes the VOM and some head scratching.

I read the diode test procedure in the book and it seems fairly straightforward. Famous last words!!

I'll probably be back begging for help very soon!

[gus]

Problem solved.

I ran the manual generator test and it produced 15-16v, no problem there.

After a lot of circuit tracing I homed in on the generator sensing magnetic switch in the battery compartment. The activating terminal and connections were corroded enough that the switch wouldn't stay closed. After cleaning up the connections and terminal all is well once again.

Now the voltage is too high so I need to adjust the regulator. I'm not really sure I won't have to replace the mag switch anyway but at least I know the source of the problem. In an emergency I can even jump the switch to keep the gen on line.

This switch shows as a relay in the manual photo but it is not, it is a "magnetic switch" better know as a solenoid, round just like old time starter solenoids on cars.

Now if I could only get rid of that irritating voltage needle fluctuation.