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Generator/Cutout switch function

Started by hursst, December 05, 2015, 03:48:31 PM

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hursst

Hello,
   I've written here before about this issue, but had some additonal questions:  How is the cut-out switch normally supposed to operate on a stock generator for these cars?  I have a 30-U.  I've been having a lot of problems with my generator recently, but I don't really know what "normal" is anymore, since it's never really worked correctly.  From my understanding, the cutout switch will operate when the battery needs to be charged.  When the cutout is operating, it should read around 0-1 at idle and up to about 18-20 amps at full throttle.  When the battery is fully charged, and the cutout switch is not operating, what should the amperage reading be?  Will the cutout come on when headlights are turned on no matter what, due to the large drain on the battery?  What is the normal reading for amperage at idle and at full throttle if the cutout switch is off?

   I had my generator profressionally rebuilt and tested with a functional cutout switch.  When I got it home, it worked for about 15 minutes, then did not work at all.  I cleaned all the connections to the bracket where the generator attaches, cleaned the attachments to the cutout, and cleaned some residue off the inner rotor where the new brushes are leaving some black residue.  This made it work again for another 20-25 minutes of driving over 2 trips, now it doesn't work again.  When I put the headlights on, the cutout switch does not turn on and amperage drops to around -17 amps.

   Is all of this normal and the cutout switch should turn on again later if I drain the battery further, or is this indicative of a problem?  I'm not an electrical guy, so I don't know if my system is really functioning correctly or not.  Thanks for any further advice.

Old Man

#1
Antique automotive electrical systems do not no run on their battery. They run on their generator all the time. EXCEPT when the engine slows down to idle for a stop and then the cutout relay releases and the car runs on it's battery. The ammeter will then show a discharge equal to all the loads that are on at that time,ignition,lights,heater fan etc. and the headlights will go "dim". At all other times the ammeter shows a slight "charge" of 5 to 10 amps. This isn't really a charge but the output of the generator to run the car. That's it. If the ammeter is going up to it's highest position the battery is taking that in as a charge. It should,and will, go away after a few miles as the battery charges up and the remaining amps showing will once again be what the car needs to run. It's like a "Y". The generator at the one end and the car's running load at one of the other ends and the battery at the remaining end. The cutout is in series with the generator end. If it wasn't there then the generator would just keep pumping current into the other ends,the battery and the car's load, as required and all would be fine. The only problem is when the engine slows down or is stopped altogether, the battery will try to put it's charged current right back into the generator's windings. Hence the full name of the cutout "Reverse Current Cut Out". It performs no other function  but to stop the battery from "seeing" the generator as a dump to ground. I have replaced all mine with a modern 50 amp. diode. No stuck points ,no lazy switching,no reverse current while the cutout is trying to make up it's mind.
So what's wrong with your car? Good question. You should only see a high charge at high rpm after a "hard" start as the battery is recharged. By the way, a 6 volt car runs at 7.5 to 8.0 volts when all the charging has settled down. When the car has been sitting in the garage for awhile the battery should read 6.0 cold. Both readings are determined by the condition of the battery NOT the generator. I have found it always difficult to determine when the battery has reached it's "end of life" (sulphated). I find the only way is to substitute it with a known good battery. (And I'm a retired electronics engineer.) So I suspect you have battery problems. My local tire store has a gizmo that they hook across a battery and load it and also try to charge it. They can determine if the battery has reached it's end of life. You will,I've found out troubleshooting other guy's cars, go nuts trying to fix the generator/cutout circuit when it's been the battery all along. There is no regulator on the these early cars and the makers considered the battery to be the regulator. (God bless them.) So the battery is the heart of the system and it, and it alone, determines what the generator needs to put out at all times and what voltage you will read across any point in the system at any time. Hope this all helps. If not please ask. 

(p.s.; Some after breakfast thoughts. The battery in these old cars is a "brute force" regulator. This is why they heat up and evaporate their water as a natural course of events. If not looked after they will bend their plates and short out a cell. The old books tell of batteries being changed every year(!) and loaner batteries being put in cars while the battery shop tried to "rebuild" theirs. Thankfully our batteries do not even resemble those batteries of long ago. However the battery is still the regulator in your 30U. By 1934/35 Chrysler gave in and put a regulator on the generator housing along with the cutout. However it only regulated voltage and this is why we call the regulator a "voltage regulator" even though by the end of the 30s they installed a 3rd relay to regulate current as well. They also found the heat of the generator and engine to be too much and it changed the operating points of the relays,both cutout and voltage, and they moved it to the firewall to cool it down. They then had to put a fourth wire on it to bring the generator's ground over to the regulator because there was too much resistance in the engine mounts and fenders etc.  And modern cars still run on their generators not their batteries. We forget the correct term for the car's battery is the "Storage battery". It's only there to store current so the car can be restarted. Today,atleast, it serves no other purpose. 
One further note: While troubleshooting these early cars with no regulator, DO NOT disconnect the battery while the engine is running. Since the battery is the regulator,the generator will ramp up to about 24 volts(!) and blow everything on the car from lights to the tubes in the radio. Anything that's "on" at the time. Again, the battery's terminal voltage is what determines the voltage across the car's load. Later cars with regulators could actually have their battery disconnected on a running engine and the voltage would remain at 7.5 v.(or 14.8 for 12 volt systems). I understand this stunt can no longer be done to vehicles from about 2000 onwards because of computerization.     

ski


chetbrz

Hi Old Man,

Great read concerning the battery and cutout switch.  Do you mind if I add your explanation to the Tech Section of this web.

Chet...
http://www.1948Plymouth.info           Web Master - Forum Administrator - AACA member

Old Man

Sure Chet. Do we know if hursst found his problem?

chetbrz

Quote from: Old Man on December 14, 2015, 03:05:55 PM
Sure Chet. Do we know if hursst found his problem?

I am not sure if the problem was resolved.
http://www.1948Plymouth.info           Web Master - Forum Administrator - AACA member

racertb


hursst

Sorry for my being gone for a month and not replying.  I have/am involved in a big move...with double the garage space, but no time for old cars for a while.

Old Man, thank you for the excellent post.  I at least now have a clear understanding of how the system works, and of how simple it really is.  As far as my car, I've been chasing this problem for 6 months now and it still has not been resolved.  Since my last post, I did a few minor tweeks and I've been working with a gentleman from www.aaca.org who's been quite helpful.  Things have gotten a little better, but still not resolved.

So, the battery is less than a year old and there are no problems with it.  I tested my 1930's cutout switch that's on the car as well as a modern backup I have, and both of them appear to work.  I replaced the wire going from the lower brush inside the generator to the "gen" side of the cutout switch, as it was frayed and I suspected grounding.  These minor changes have resulted in the car now running at about    -3 amps at idle, about -12 or so with the headlights on.  At -3 amps with headlights off, revving the engine or increasing the load will not increase the amps above about -2 no matter what.

I still need to test for any electrical drains, test the output, and see if I can test the ammeter.  It's also possible something went wrong inside the generator, but it has a fresh restoration on it.  I should be able to find some time after my move is complete in about 3 weeks to continue working the issue.  It's frustrating when something that should be so simple is so difficult.  Doesn't help that I'm very ignorant with electrical, but learning from you guys.

Thanks again for the posts.

-Chris

Old Man

#8
It's a head scratcher for sure. In any troubleshooting I have to assume your car is wired correctly. If it's polarization you should have more problems than you say you have. Hmmmmm. Just for the heck of it take a jumper wire from the battery over to the wire coming out of the generator. Just touch it for a second no longer. There will be a spark. This will magnetize the generator's pole pieces both in the armature and the field. The polarity of the generator is now set to the same as the car battery, positive ground,negative on the high side. The generator will always 'remember' this through something called 'reminence'. (I hope that's the correct spelling. SPELLCHECK doesn't recognize it.) It a fancy word for remaining magnetism. When the engine turns over the generator will start to ramp up it's voltage in that polarity and and a small current will run down through the cutout's pull-in winding. When the current reaches a set point,built into the winding and point's distance apart, the points close and connect the generator to the battery. The points however are wired in series to heavy copper wire and a heavy charge ,or running, current can then run over to the battery or car's loads. The reason I say all this is if the battery were polarized in the opposite polarity,all hell would break loose the moment the cutout's points closed. However no matter what polarity the generator is polarized to,it will still close it's points when a predetermined point is reached. Unfortunately. So you must NOT have had a reverse polarized generator or you would have mentioned a lot of sparking and noise coming from the generator when the engine runs? And it would seem by now you would have had the generator connect to the battery by happenstance and polarized the generator to the battery anyways. Hmmmmmm. Since the ammeter is showing a discharge in the correct direction,headlights on,I can only presume it's wired correctly. The only thing left is the generator not putting out. And since you've had it rebuilt,the only thing left however is polarization. A last though:once you have the engine running you can take a jumper wire and connect it from the input to the output of the cutout effectively taking it out of the equation. The ammeter should,under normal conditions, now show the charge/running current mentioned in my first post. This will do indicate if the cutout is still the problem. Do not leave the jumper wire on the cutout when you stop the engine. Although not disastrous in the short term, you will see a VERY large current discharge on your ammeter. That's if everything is hooked up correctly. I suppose its a good wiring check. If you do your polarization by jumping across the cutout, someone in the car should see the very large discharge,actually full scale, on the ammeter. I just noticed an error in my post, you can not polarize a generator on a running engine. It must be stopped. (Anybody owning one of these early cars would be wise to look over at the ammeter every time they shut down to make sure the points on the cutout didn't stick and did open when the generator stopped. This fault was how many batteries where ruined over night in those old days.)                         

frankp

Wasn't familiar with remanence, but am now, thank you.  Hysteresis was the word that came to mind for me.

http://www.britannica.com/science/hysteresis
frank p

chetbrz


You guys are dragging me back to my collage days.  I don't think the average Joe thought in these terms back in the day.  Interesting none the less. 

I must admit I never favored DC generators even back in the day when cars came with them.  When they worked they worked fine but when you had a problem it was usually a head scratcher.  I don't think I can add anything new except that there was mention of a frayed wire.., I was wondering if this might have caused some other less noticeable damage to the generator. 

Have you read the following:  Also a good read.

http://www.1948plymouth.info/SupportPages/PNWR_Reprint.pdf

Good luck,  Chet...
http://www.1948Plymouth.info           Web Master - Forum Administrator - AACA member

hursst

Finally completed the move.  I gave up on the generator and sent it back to the rebuilder.  There was an internal problem, so now I don't feel as bad about my lack of electrical diagnostic skills.  Turns out there was a ground wire on the brush holder end plate that was not attached.  The wire was sandwiched in between the end plate and generator case.  It was still grounding but that could have been intermittently due to the primer inside the case.  I also replaced the wire to the relay the field wire (the one that was frayed), but I evidently did not get it tucked back up against the case like it should and was shorting on the armature, to add insult to injury.  Fixed under warranty, but of course had to pay shipping out to the rebuilder.  I should get it back Monday.  Maybe I'll have a working generator again after 9 months of nonsense and frustration.  Thanks again for the great posts, I've really learned a lot so now maybe I can do a better job with testing and diagnostics in the future.