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Author Topic: DN50 Alternator  (Read 5725 times)
gus
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« on: December 10, 2010, 10:08:38 PM »

I'm the proud new owner of a DN50 Alternator alternator attached to a 4107 but I need some expert advice.

The volt meter and lights flicker when the engine is running, not much but I know this shouldn't be happening..

I think I remember sometime back someone said this is caused by failed or failing diodes. Is this correct? I hope that is the only problem since it appears to be a straightforward replacement job.

I'm amazed that the diodes are  encased in alt cooling oil!! This 8V71 and DN50 Alternator is a total experience to me after owning a 4104 for five years.
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« Reply #1 on: December 11, 2010, 05:32:56 AM »

If the batteries are fully charged and there is no load on the system a typical DN50 and it's regulator will switch in and out, and the no-gen light will flicker on MCI's, so something like that might be happening on your bus.  You can take the back off the alternator and test the diodes with a good  digital volt meter.  The voltage is regulated by an external regulator, so if the voltage is truly varying I would suspect that as well.  Also, I might not rely on testing at idle speed, high idle would get the alternator spinning up and producing electricity in it's designed speed range.  There are good manuals on line at the delco remy site.

Brian
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gus
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« Reply #2 on: December 11, 2010, 06:26:12 AM »

Brian,

Thanks, that's just the kind of info I need. Doesn't look as if I have a problem after all - very good. I noticed the headlights flickering while at idle.

The bus has been sitting for over a year so I kind of expected some things not to work.

I think the regulator is relatively new.

I just bought the bus and haven't driven it over 50 mph yet but the voltmeter seems to flicker no matter what the engine  speed. I'm about to drive it 500 mi home so didn't want to start out with electrical problems.

Any other ideas or thoughts will be appreciated.
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Rick59-4104
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« Reply #3 on: December 11, 2010, 06:30:02 AM »

 My 4104 has the DN50, at an idle or low RPM's I get some flickering of the gauge, at highway speeds it stops...
Rick
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« Reply #4 on: December 11, 2010, 06:32:50 AM »

possible corroded ground connections on battery or where ground from battery attaches to coach.Simple minor tighten might correct but should be eventually cleaned . wires on voltage regulator slightly loose or corroded
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« Reply #5 on: December 11, 2010, 10:43:57 AM »

Brian is right on.  Increase the RPM and put a load on the alternator (lights, A/C, etc.) and the problem should cease.
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« Reply #6 on: December 14, 2010, 06:47:19 PM »

I just got the bus home after three days on the road. Funny thing, the flickering stopped for two days then today, the last day, it started again. I'm sure the batteries are pretty well charged by now but road speed or load didn't seem to make much difference.

I did notice that the battery grounds to body are pretty corroded, that could be the whole problem right there. Now that I'm back to my shop I'll now be able to get at some of those problems. The drivers elect panel also has some pretty badly corroded terminals just like my 4104. Deja vue all over again!!

Thanks again to all. Just about the time I think I know the 4104 along comes a 4107!!
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gus
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« Reply #7 on: December 27, 2010, 04:26:24 PM »

I cleaned up all the battery grounds (they were pretty rusty) but now there is a new situation.

When I first got the bus the three batteries were not well charged. Now, after much converter and engine charging they are very well charged.

So, now the (New) generator solenoid at the driver's electric panel clicks on and off at a pretty high rate, especially at low speeds. However, when I load the electrics with the big bus heat fan motor or the marker lights the clicking stops.

Am I on the right track thinking the batteries are so well charged that the 300 amp DN50 is cutting out because it has nothing to do?

I'm used to a 100 amp truck alternator, all this extra power is new to me.
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Gary '79 5C
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« Reply #8 on: December 28, 2010, 01:19:32 AM »

Gus,
I had the DD50 for four years and never had a flickering no gen lite or voltmeter fluctuation. The voltage did dip to a low of 24.5V when idling(non fast). Back to 27.5V when driving. Just my experience, not to contradict Brian.

I have since changed this unit out for a J180 truck mounted 24V alternator. Smaller, lighter, all that I need.

FWIW, Mine did not have the orfice to reduce oil flow thru the alternator and upon changing to the smaller, non oil cooled, my engine oil pressure increased.


Gus, also start eating your Wheaties if you plan to extract that DD50 any time soon, heavy.
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« Reply #9 on: December 28, 2010, 05:27:47 AM »

Blanchard Electric has a aftermarket regulator that will stop the flickering on a 50D cost around 250 bucks fwiw


good luck
« Last Edit: December 28, 2010, 06:31:35 AM by luvrbus » Logged

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« Reply #10 on: December 28, 2010, 06:27:56 AM »

Gus,
I have seen the same problem over and over on the older buses with the 50 DN. Almost all our all older MCI's used to do the same thing. My dad & uncle just told all the drivers to run the lights all the time #1 for safety by making it easier to be seen (ah yeah like if they have problems seeing a bus, the lights are gonna help!) # 2 to "load" the altenator.
Always worked for us.
Grin  BK  Grin
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« Reply #11 on: December 28, 2010, 07:00:39 AM »

I agree with BK.  And, yes, this is the symptom of fully charged batteries with no load.

We are adamant about running with the lights on all the time anyway, for safety.  I put a big red warning lamp on my dash, which is lit if the engine is running but the lights are off or vice-versa.  This way I can choose to have lights on or off regardless, but the light reminds me in case I just forget.

-Sean
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« Reply #12 on: December 28, 2010, 03:37:04 PM »

Thanks guys, I'm learning more all the time.

Maybe the problem exists mostly with 12v versions?

Since I'm a cheapskate I don't know if it is worth $250 to me to stop the flickering!!

One other thought I had is that the new solenoid might be a momentary starting solenoid instead of the constant type. An easy mistake to make since they look so much alike. I need to check that out.

In my opinion daylight lights were once probably a safety factor but now that most vehicles have them the advantage is lost.

I've learned to be very wary of auto drivers when driving my bus even though it is this tall, solid white monster which should be super easy to see.

One of the shocks to me when I first started driving a big truck was that it seemed as if more people pulled out in front of me than when I was driving a small vehicle?? I finally decided it was because a large vehicle appears to be moving much slower than a small one and drivers think they have move time.

This is a lot more obvious when you compare small airliners landing at the same speed as very large ones, the really big ones seem to be floating in even though they are landing at the same speeds!
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« Reply #13 on: December 28, 2010, 04:03:01 PM »

Yes, I also get the occasional chattering of a relay somewhere in the bowels of the dash - when idling after a long run. Switching the low beam headlights on fixes the "problem".

24V system with the oil cooled alternator.
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« Reply #14 on: December 29, 2010, 02:14:27 PM »

Tony,

Thanks. Forgot to mention that mine is oil cooled also and 12v.

My solenoid is right next to the driver at the left wall where the major electrical panel is located.

The clicking is annoying, but from all these posts, not a real problem - much to my relief!
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« Reply #15 on: December 29, 2010, 02:22:32 PM »

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.
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« Reply #16 on: December 30, 2010, 05:44:27 AM »

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
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« Reply #17 on: December 30, 2010, 07:13:09 AM »

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


good luck
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« Reply #18 on: December 30, 2010, 07:34:04 AM »

Clifford,

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

Brandon
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« Reply #19 on: December 30, 2010, 11:25:18 AM »

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?
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« Reply #20 on: December 30, 2010, 11:32:18 AM »

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
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« Reply #21 on: December 30, 2010, 11:43:48 AM »

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
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« Reply #22 on: September 07, 2011, 08:01:25 PM »

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.
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gus
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« Reply #23 on: June 01, 2012, 07:34:23 PM »

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??
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« Reply #24 on: June 01, 2012, 08:07:52 PM »

 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
« Last Edit: June 02, 2012, 05:32:57 AM by luvrbus » Logged

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« Reply #25 on: June 02, 2012, 02:20:47 PM »

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.
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« Reply #26 on: June 06, 2012, 06:22:38 PM »

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.
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gus
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« Reply #27 on: June 08, 2012, 08:11:48 PM »

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.
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« Reply #28 on: June 21, 2012, 07:26:49 PM »

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.
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