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Author Topic: Replacement 24V Alternator for MC5...8V71  (Read 5981 times)
Tom Y
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« Reply #15 on: August 24, 2007, 09:01:46 AM »

Bob, I may have a voltage reg here. If intrested I will take a look, it worked when I removed it.  Tom Y
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Tom Yaegle
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« Reply #16 on: August 24, 2007, 02:51:08 PM »

Y not Tom?  Pun intended with no offense meant. Cheesy  Since we're already trying to do some business...what would be the effect of monkeying around a bit more?

It might mean a separate shipment ...I don't think the regulator and the muffler would get along on the trip here (sort of reminds me of my ex-wife and me)..but let me know the price and the shipping and we'll git 'er done!

And thanks for the reply.....

Bob

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NCbob
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« Reply #17 on: August 24, 2007, 03:00:10 PM »

And I almost forgot...Thanks to Niles I spoke with Gene Rochester in Walhalla, SC today....what a neat guy!

He's a former BusNut who's built more than his share of Eagle's and knows most of you old timers.  He particularly asked me to remember himself to Jack Conrad.  I'm sure that if Jack had known he was this close to us here in Franklin he'd have opted for a quick ride down there to renew an old friendship.

Gene is building 5/8 or 3/4 scale model Mack trucks for a hobby now on Ford and Dodge chassis.  Tom and I are going to take a day and go down and meet him and see how much fun a Busnut can have after he finds something more interesting than buses.

More at another time....

Bob
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Tony LEE
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« Reply #18 on: August 24, 2007, 04:46:17 PM »

"I removed mine by myself, but I'm only 35 years old.  I'm planning to have help to put it back in as getting it back in will be more difficult."
------------------------------------------------------------
So at 62 yo it was only natural that I felt a bit sore after removing it by myself, stripping it and replacing the stator, AND putting it back by myself last week.
Looks like I'm not going down hill quite as fast as I thought.
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belfert
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« Reply #19 on: August 24, 2007, 08:55:02 PM »

"I removed mine by myself, but I'm only 35 years old.  I'm planning to have help to put it back in as getting it back in will be more difficult."
------------------------------------------------------------
So at 62 yo it was only natural that I felt a bit sore after removing it by myself, stripping it and replacing the stator, AND putting it back by myself last week.
Looks like I'm not going down hill quite as fast as I thought.

Well, I wasn't sore after removing the alternator.  It is just difficult because I was lifting a heavy weight from a fairly high and akward position.

I could perhaps get it back on the mount myself, but getting the bolts to line up would be difficult.
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NCbob
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« Reply #20 on: September 08, 2007, 06:41:15 PM »

I'm resurrecting this thread only for the reason that the topic is one we might all encounter at some time or another. And, the fact that my bus is 39 years old and they've made some serious changes in alternators in the interim.

My 50DN (old style) is an AC, 3 Ph, generator (using the term used back then) it has stationary fields and a rotating armature...contrasted to the rotating field (rotor) and stationary field (stator) of the later units. It is NOT oil lubricated and/or cooled (which in itself is a revelation) and has the typical 3 ph bridge rectifier to put it into that, by today's standards, the alternator classification.  It still uses the black (read Big Ugly Black Box) voltage regulator associated with the later style 50DN alternators.  MCI refers to it in 'Da Book' As a generator.

Without the new regulator in the circuit I 'full fielded' the generator with 24VDC (after cutting back the wires and soldering new terminals on them) and got a spark.  "Da Book' says that the field coils have a normal resistance of 3.9- 4.2 Ohms.  OK, that value would cause enough spark that I got....but not the output that I expected....28VDC.

Since this is a rotating armature that tells me it has brushes to collect the AC to send to the 3PH diode trio. Lightbulb!  I might have something simple like worn or broken brushes!

Unfortunately that means I'll have to pull that ratch-a-pratch rascal out of there and put it on the bench for further testing.  Stay tuned for the ongoing saga of NCbob and his project of the moment.

And don't forget to save your cereal boxtops to send in for your magic de-coder ring to find out what the secret message is for next weeks' adventure!

With tongue-in-cheek.....

NCbob
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Stan
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« Reply #21 on: September 08, 2007, 07:13:37 PM »

NCbob: Don't get too involved with nomenclature in the book. Remember that the maintenance manual was written for bus mechanics who had been working on generators on all the previous models and may have never seen an alternator. They provided step by step instructions on how to test it. Your experience with gen sets may be making it appear more complicated than it really is.
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Tony LEE
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« Reply #22 on: September 08, 2007, 07:17:21 PM »

Unless it is completely different to my 50DN, it has a fixed field and a fixed stator winding with a rotor rotating between  and is brushless.

If you were running the alternator without a load (not a good idea anyway) and without a regulator I would have expected a higher output voltage, but maybe not.

If you dismantle it, just unbolt the drive endshield and withdraw the stator. To get the other end off requires the diode assembly to be dismantled first.
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« Reply #23 on: September 08, 2007, 09:55:40 PM »

Bob, it sounds to me like the alternator behaved exactly as it should for the way you tested it; and it doesn't use brushes, so you don't have to worry about that.

Our manual gives a good, detailed instruction on servicing the alternator. It was very enlightening reading for me!

For what it's worth.

Tom Caffrey

I'm resurrecting this thread only for the reason that the topic is one we might all encounter at some time or another. And, the fact that my bus is 39 years old and they've made some serious changes in alternators in the interim.

My 50DN (old style) is an AC, 3 Ph, generator (using the term used back then) it has stationary fields and a rotating armature...contrasted to the rotating field (rotor) and stationary field (stator) of the later units. It is NOT oil lubricated and/or cooled (which in itself is a revelation) and has the typical 3 ph bridge rectifier to put it into that, by today's standards, the alternator classification.  It still uses the black (read Big Ugly Black Box) voltage regulator associated with the later style 50DN alternators.  MCI refers to it in 'Da Book' As a generator.

Without the new regulator in the circuit I 'full fielded' the generator with 24VDC (after cutting back the wires and soldering new terminals on them) and got a spark.  "Da Book' says that the field coils have a normal resistance of 3.9- 4.2 Ohms.  OK, that value would cause enough spark that I got....but not the output that I expected....28VDC.

Since this is a rotating armature that tells me it has brushes to collect the AC to send to the 3PH diode trio. Lightbulb!  I might have something simple like worn or broken brushes!

Unfortunately that means I'll have to pull that ratch-a-pratch rascal out of there and put it on the bench for further testing.  Stay tuned for the ongoing saga of NCbob and his project of the moment.

And don't forget to save your cereal boxtops to send in for your magic de-coder ring to find out what the secret message is for next weeks' adventure!

With tongue-in-cheek.....

NCbob
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Tom Caffrey PD4106-2576
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« Reply #24 on: September 09, 2007, 04:21:37 AM »

Well, boys and girls, this old fart has no choice but to offer an opinion. With the understanding that opinions are like a part of the bodily anatomy that everyone has.

The first and main clue is that Bob indicates that it has a three phase diode bridge rectifier. That simple fact identifies it as an alternator as opposed to a generator and it is a revolving field design for the following reasons.

Therefore, it has two light duty type brushes connecting the DC field control voltage from the voltage regulator, thru a set of slip rings, to the revolving field. The main AC power output (at high frequency) is taken from the stationary windings and routed thru the bridge rectifier to convert the AC power to DC.

I do not believe it has three sets of brushes for the main AC power for two reasons. That design (generator) used commutator bars, instead of slip rings, to collect the output power and the commutator bars actually had the purpose of converting the generated power directly to DC. Therefore the three phase full wave bridge would not be required.

It absolutely will not harm an alternator to operate it with no load forever. The output voltage is controlled by the field voltage which comes from the voltage regulator. The voltage regulator senses the battery voltage and controls the output voltage accordingly. At full forcing voltage from the field the output voltage should be in the 30+ voltage range for a 24 volt rated alternator. With no load on the alternator, there is no current flowing in the output circuit, so therefore the alternator can not be harmed.

It was mentioned that there are no brushes in an alternator, and this is correct for an industrial stationary alternator. These brushless devices have an additional rotating component. These devices have a rotating exciter with a DC control voltage connected to the stationary windings. This causes an AC voltage to be generated in the rotating component. This AC is then rectified by a revolving three phase diode bridge whose output is connected, along the rotating shaft, to the rotating field windings of the main alternator. This voltage then controls the output of the alternator (AC) stationery windings which is then rectified by the bridge rectifier to provide the main DC output.

The main difference between a generator and an alternator is that a generator produces a DC voltage directly, via the action of the commutator bars whereas the alternator produces an AC voltage which is converted to DC by the three phase diode bridge.

This is only an opinionated opinion and should be taken for what it is worth. I am more than willing to listen to other opinions but I can assure you that it will be very difficult for you to change mine. LOL

Richard

PS: As an afterthought, and if anyone is interested, all rotating devices produce an AC output initially. The primary difference is that a generator produces this AC on the rotating armature and converts this AC to DC by use of the commutator bars on the rotating armature and the brushes on the fixed portion of the device.

The alternator produces this AC voltage on the fixed (non rotating) armature  and converts it to DC by use of the three phase bridge diode assembly.


« Last Edit: September 09, 2007, 05:14:14 AM by DrivingMissLazy » Logged

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belfert
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« Reply #25 on: September 09, 2007, 07:54:26 AM »

Delco Remy's website says the 50DN has no brushes.  This is not to say the design may not have changed over the years.
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Sammy
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« Reply #26 on: September 09, 2007, 08:54:51 AM »

The oil cooled 50 DN alternator does not have brushes.
It does have a fixed field coil, fixed stator, a spinning rotor and a diode bridge rectifier.
It does weigh approx 85lbs.
When testing any charging system you must make sure the batterys good first - charged,load tested,specific gravity,cables and connections,etc.

The "full field" test should not be performed for more than 3 seconds in my opinion.
It can create an output of up to 32 volts with almost 300 amps.
You MUST be extra careful if you have to perform this test.



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DrivingMissLazy
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« Reply #27 on: September 09, 2007, 09:19:00 AM »

The oil cooled 50 DN alternator does not have brushes.
It does have a fixed field coil, fixed stator, a spinning rotor and a diode bridge rectifier.
It does weigh approx 85lbs.
When testing any charging system you must make sure the batterys good first - charged,load tested,specific gravity,cables and connections,etc.

The "full field" test should not be performed for more than 3 seconds in my opinion.
It can create an output of up to 32 volts with almost 300 amps.
You MUST be extra careful if you have to perform this test.




Thanks, Sammy. It must have a separate rotating exciter also, as I mentioned in my writeup.

Also the output of the alternator should generally be disconnected before a full field test is conducted, although as you indicate, 300 amps for a few seconds would not do any damage. Does anyone have an electrical diagram of this device?
Richard
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« Reply #28 on: September 09, 2007, 10:16:06 AM »

Richard, I'll check my library to see if I might have something on the 50 DN for you.
I don't know about a separate rotating exciter - I have never seen one on the oil cooled units i have rebuilt.
They normally don't charge unless the field coil is energized.
The field coil will have different terminal lead configurations, depending on the application.
One example: one lead of field coil is your F1 terminal, other is the F2 terminal.
Second example: one lead of field coil is your F1 terminal, no external,visible F2 - usually grounded to unit inside.
Some have jumper straps from F2 to ground (unit housing).
Some have buss bar from BAT post to F1.
The control circuit to the field coil can be many different configurations also.
Some control a positive voltage to the alternator field coil, some voltage regulators control the ground side of the coil.
Just showing different types of configurations you might come across, no disrespect intended.
Regards,
Sammy  Cool
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NCbob
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« Reply #29 on: September 09, 2007, 10:33:49 AM »

No, Richard, there's no outboard exciter on this alternator.  Too, something I not only didn't mention nor did I test, is that there is another relay in the circuit, a load relay I believe, but that shouldn't come into the picture...yet.  The alternator relay closes with the closing of the master switch so I then have power to the + terminal for the regulator.

I guess it boils down to whether or not there are brushes in this old alternator and I suspect there are not as the cross section of the MC5A Repair Manual shows none.

I will read the field resistance today (guests coming for supper) and that should throw more light on the mystery.

Bob
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