DN50 Alternator

[Tony LEE]

One day I'll track it down and see which relay it is, but it happens rarely enough that it will be hard to find. Mine is a RHD bus and the chattering comes from the drivers aircon area. Perhaps a simple series resistor, parallel capacity would vary the timing enough to stop it chattering.
Low beam headlights on (for safety) generally makes it go away.

[brando4905]

Not trying to hijack this thread but, I get the clicking sound in my 4905 also, and sometimes when this starts the tach needle bounces down to zero and back to proper reading(over and over). Turning on the lights used to solve the problem, but on our last trip(5 days of driving), the tach went to zero and stayed there with the lights on. Two months later, drove bus to shop and tach was back to normal. Voltage reg. was replaced three years ago.

Thanks,
Brandon

[luvrbus]

Brandon, alternator driven tachs are famous for that the relay doesn't open or close


good luck

[brando4905]

Clifford,

Thanks for the reply, is there any fix for this problem? Or just something I have to live with?

Brandon

[mcidave]

I am assuming that my 50DN is a 24volt...I am looking to hook it up to an inverter and need to match voltage correctly. The MCI manual does not seem to specifiy.
Does anyone know what is the tell tale sign distinction between 12v and 24volt?

[wildbob24]

Dave,

I've never seen an MCI that wasn't 24volts, but you can look and verify that your 12 volt start batteries are wired in series. Series is 24volt, parallel is 12 volts.

There's usually, but not always, a sticker on the inside of the battery door stating the voltage, as well.

Bob

[luvrbus]

Yours will be a 24v a easy way to tell is check the charging relay a 24v will be 12V and the 12V will be 6V 

good luck

[gus]

I finally had the time and motivation and traced this out.

The "generator" magnetic switch in the driver's electrical panel is there only to provide power to the heating/def/AC blower motors. It won't allow their use unless the generator is charging. There is no purpose for this mag switch unless you need those blowers.

So, what I plan to do is splice a switch into the ground circuit of the mag switch activating circuit and keep it turned off except when I need the blowers.

End of clicking.

[gus]

As a follow up to this old thread I now have a new problem.

I did add the switch to the air system relay and stopped the clicking. After this it worked flawlessly for the next eight months.

Now, right after a 3500 mi three week trip I have a new problem. On the third day of my five day return from NY to AR the alt suddenly decided to charge at 15.5-16.5V!

This would happen only at high rpms when on the road or upon acceleration. At normal street speed or idling it would charge at the normal 14.1V. After an hour of this I disconnected the field at the VR and went on my way for the next three hours with no problem.

The next morning I reconnected the field and ran it another two hours at these high outputs and again disconnected the field for the rest of the day. Measured the batts at the end of the day and they were a perfect 12.85V!! Same thing this morning.

Today I reconnected the field and the output varied between 13 and 14.7. Turned on the big air blower and it dropped down to 14.2. Not long after it again went up to the higher readings. Turned on the lights, turned off the blower and it settled down to around 13V for the rest of the day with an occasional jump to 14.8.

I'll test the batts again tomorrow after they settle down but this is a puzzler. It has sometimes had a low output but never this high before. I don't have the guts to leave the batts charging at these high voltages for very long.

A side note. At first I tried decreasing the output at the VR but it wouldn't turn down below about 15V at high idle. However, once I had turned the adjusting screw CCW  about 160 degrees, which is supposed to decrease output volts, the voltage suddenly jumped to 16-17V?? Interesting. Must be a cam type adjustment.

This one has me baffled??

[luvrbus]

 That is a sign of a bad ground between the regulator and alternator Gus, is the regulator inside the front bay ? those GM buses drive me nuts with grounding problems lol

[gus]

The 4107 VR is inside the rear left bay just above the battery box. It is about 1/4 the size of the one on the 4104 and is solid state. However, the 4104 has a generator, not an alternator.

You're probably right about the grounds. A PO added a ground wire to the body from the VR ground terminal. I'll clean these plus the batt/body grounds (again) to see if that helps.

One thing I forgot to mention. When it went up to 15-16V the last day I connected in the house batts and it settled down to the proper 14.1 for a while, then dropped down to 13.1V again.

The bus batts were 12.71v and house batts were 12.58v? Don't know why they are not the same but I think I may have disconnected the house batts when the dash voltmeter dropped to what I was afraid was too low for charging. Those numbers are not too bad for all the weird stuff that was going on.

I'm going to clean all the grounds tomorrow but they don't seem to be much of a problem from all the continuity checks I took today. Next I'll check out the actual alternator connections and ground.

Since we're leaving for WA in a few weeks I need to get this thing resolved, that will be about a 5000 mi trip.

[gus]

I discovered today that the ground wire between the alternator and VR had been left disconnected, probably when the AT was added. I had seen the large black disconnected wire at the alt before but didn't think much about it since disconnected wires are pretty common on these old buses!

Turns out the wiring diagram in the manual shows a chassis ground for the VR but the diagram I got from one of our board members shows a direct ground wire from the alt to the VR negative terminal.

Evidently the ground path the VR/Alt had been using has corroded and made the VR go crazy.

Hopefully this will solve the problem of the wandering voltmeter needle also! Didn't have time to check it out today but will be eager to see the results tomorrow.

Luverbus was right about GM grounds, seems they discovered the problem after the manual was printed and added the direct wire.

[gus]

Problem solved!

After hooking up the direct ground wire there was no change.

The VR/Alt Positive wire connector at the alt was broken from vibration along with another wire which I think goes to the AT cooling radiator fan. The breaks couldn't be seen until I moved the wires with my hand.

The Pos wire is heavy, 8 gage, and the insulation is rock hard from heat and age so vibration just broke it off after all these years. I installed a short pigtail of new, flexible wire.

Unfortunately the flickering VM needle is still there, I had hoped the ground wire would stop that. Anyway I'm glad the problem was so simple, very hard to access, but I now have electric power again.

[gus]

Problem completely solved.

I replaced the Voltage Regulator Magnetic Switch, the panel VM needle is rock steady and the VR setting stays where it is set. This didn't happen even after I replaced the broken alternator connectors although the VM needle did settle down to about half the amount of oscillation as before.

I replaced the old magnetic switch because it got so hot. Unfortunately the new one is just as hot but now the alternator is stable. I presume the main contacts in the old one were so corroded from opening and closing due to low load that they made the VR go crazy and the arching burned the contacts.

I don't really understand why this switch gets so hot because all it does is connect the alternator to the VR via the engine run switch? I wouldn't think that would involve much current, especially at low loads.

I much earlier put a cut off switch on the heating fan relay circuit to stop the clicking on and off at low load so maybe this new magnetic switch won't be damaged.