pmhowe Posted January 22, 2018 Share Posted January 22, 2018 The ammeter on my 1935 Cadillac 355D sedan reads a consistent -6.5 amps when the car is running. I would expect that the ammeter needle would be fluctuating about that value, each time the distributor points open, if the generator were malfunctioning and the car was running on pure batter power. I'm not sure what the best diagnostic approach is. Thanks in advance for your advice. Phil Link to comment Share on other sites More sharing options...
Larry Schramm Posted January 22, 2018 Share Posted January 22, 2018 The first question would be is this a new thing? Second is what is the voltage in the system. If it is more than approx. 6.5 volts I would look at wiring. If less than 6volts would look at the generator or voltage regulation circuit. Next is the amp meter ever been out and out and possible wired backwards? Can you put another amp meter in the circuit to see what it reads? Just some thoughts. 1 Link to comment Share on other sites More sharing options...
Friartuck Posted January 22, 2018 Share Posted January 22, 2018 Larry makes a good point, what is the voltage with the car at fast idle? Should be about about 7.2 or so. If your unit uses a third brush arrangement and cut out relay, check to see if there is voltage going to the armature lead (terminal). Its possible the field coils in the generator's housing have shorted either against each other or against the housing. Another possibility is that the cut out relay is faulty. A 6 Amp reading for ignition alone is about right. PM me for additional thoughts. 1 Link to comment Share on other sites More sharing options...
Alfre Posted January 22, 2018 Share Posted January 22, 2018 You are running on only battery power. The amp meter can not react that quickly to show points opening and closing with the engine running . Al Link to comment Share on other sites More sharing options...
Willie Wurke Posted January 23, 2018 Share Posted January 23, 2018 What is the problem you are trying to diagnose? Link to comment Share on other sites More sharing options...
pmhowe Posted January 23, 2018 Author Share Posted January 23, 2018 The car is new to me. When I took it out for a run, I found the ammeter read a steady - 6.5 amps, indicating to me that the battery is not being charged. The discharge rate was independent of rpm. I'm guessing I have a problem with the generator or the voltage regulator, or both. Unfortunately, I have been called out of town and won't be able to revisit the problem for a couple of weeks. Once I get back and can run some tests, I will post an update. Link to comment Share on other sites More sharing options...
Matt Harwood Posted January 31, 2018 Share Posted January 31, 2018 Is it possible that the battery is in backwards and your ammeter is working correctly but backwards? I bet a 1935 Cadillac is positive ground. Link to comment Share on other sites More sharing options...
Curti Posted January 31, 2018 Share Posted January 31, 2018 If you think the generator is not charging, disconnect the battery when the car is running. It will die immediately. If the cutout is stuck, it is stuck shut. This is a potential for a cooked generator , burn't wiring , fire. I highly suggest a diode in the cutout. This is a potential second problem not related to the amp gauge reading incorrectly. Link to comment Share on other sites More sharing options...
Grimy Posted January 31, 2018 Share Posted January 31, 2018 10 hours ago, Matt Harwood said: I bet a 1935 Cadillac is positive ground. Indeed, it SHOULD be positive ground on Cadillacs through 1942. Link to comment Share on other sites More sharing options...
Friartuck Posted February 1, 2018 Share Posted February 1, 2018 Disconnecting the battery while the engine is running is not a good idea. The battery acts like a load and removing it from a properly working circuit can damage the generator. Check the cutout relay. That's the most common failure item. Use a Volt meter on both sides of the cutout relay to diagnose the generator. Link to comment Share on other sites More sharing options...
Matt Harwood Posted February 1, 2018 Share Posted February 1, 2018 33 minutes ago, Friartuck said: Disconnecting the battery while the engine is running is not a good idea. The battery acts like a load and removing it from a properly working circuit can damage the generator. Check the cutout relay. That's the most common failure item. Use a Volt meter on both sides of the cutout relay to diagnose the generator. Correct--on an unregulated system your battery acts as a voltage regulator and disconnecting it will cause voltage to spike, blowing out bulbs and damaging other electrical components like clocks, radios, and gauges. This happened on my '29 Cadillac. The ground cable's connection at the engine block came loose. The car kept running for a while, but the ammeter went wild and my brake lights were blown badly enough to turn the insides of the bulbs black. If the headlights had been on, they would have blown as well. Fortunately, the rest of the ignition system wasn't harmed since it's pretty robust and I noticed quickly. Don't pull a cable while running. That might work on a regulated system or a car with an alternator, but on a car with a fixed-output generator and no regulation, the battery is a critical component to keeping everything within proper voltage ranges. Link to comment Share on other sites More sharing options...
Curti Posted February 1, 2018 Share Posted February 1, 2018 I have done this quick test on a couple of Auburns just idling in my shop, the engine dies no harm done. Takes about 1 second. Point well taken. Link to comment Share on other sites More sharing options...
pmhowe Posted February 23, 2018 Author Share Posted February 23, 2018 I finally had a chance to get back to addressing my car’s charging problem. The car has a 6V positive ground system. The symptoms are as follows: When running, the ammeter shows a constant 14 - 15 amp discharge. This is more than expected from the ignition circuit (previously when I stated the problem, the discharge was about 6.5 amp. However, I found that the brake lights are on, indicating that I need to deal with a faulty brake light switch, as well.) There is no fluctuation of the ammeter needle. I’m used to seeing a little wiggle as points open and close. I did the following: 1. Checked all connections (except the brake light switch -I'll get to that after sorting this problem.). 2. Polarized the system by briefly connecting the armature terminal to battery. 3. With the engine running at high idle, I connected the field terminal to ground. The ammeter showed the system to be charging at approximately 15 amps. (Recall, brake lights are on.) This indicated to me that the generator is working. 4. I removed the regulator, inspected it and cleaned the points and terminals and reinstalled it. I attached a ground wire from regulator attachment bolts to ground strap. This was overkill; I had established continuity previously. 5. Started the car. At high idle, ammeter still indicates a 14 amp discharge. 6. With engine at high idle, I touched a wire to the battery and armature terminals. The ammeter reading varied from minus 10 to about zero. It never went positive. (The variability was probably a result of my inability to maintain a solid connection between the two terminals.) I’m guessing I have a bad regulator. It is a replacement regulator, with no brand or model markings. Any thoughts? Phil Link to comment Share on other sites More sharing options...
Friartuck Posted February 24, 2018 Share Posted February 24, 2018 Phil, 1. Can you post some pics? Tell us make and model number of the generator. 2. You mention regulator. Did you mean to say Cut-Out Relay? These are two very different methods for controlling generator output. 3. I'm not sure your touching the armature terminal to battery polarizes the unit. I thought polarizing involved field coils, not armature. 4. Does the generator have separate terminals on it for field coils and armature? Can you disconnect the field coil connection and measure the resistance of the field coils? if you have a four pole unit (four field coils) typical field coil resistance should be about two ohms each or between 8-10 total. Measurements of five or less ohms indicates partial shorting and near zero ohms is likely short against the case. 5. How hard is it to remove and service the generator? 6. Does this generator have an adjustable third brush? 7. Given age, I suspect shorted field coil winding to either each other or against the case (grounding). This would result in weak output. The good news is the armature may not be damaged which costly to rewind. Link to comment Share on other sites More sharing options...
Larry Schramm Posted February 24, 2018 Share Posted February 24, 2018 What is the voltage of the battery while the car is running and what is the voltage of the battery before you start the car? Link to comment Share on other sites More sharing options...
pmhowe Posted February 26, 2018 Author Share Posted February 26, 2018 I wasn’t able to get a good picture of the generator. However, it is a Delco-Remy Model 933B. According to the Cadillac literature, it is “…of the shunt wound current control type. It has no third brush, and no adjustment is provided except by the lamp load through a current regulator”. Since briefly grounding the generator field wire while the car was at high idle caused the system to charge at roughly 15 amps, I believe the problem lies with the control box. Pictures of the control box are attached. It looks to be in good shape. I guess my next step will be to take it to a starter/generator/alternator place and have them check it out. Link to comment Share on other sites More sharing options...
Friartuck Posted February 27, 2018 Share Posted February 27, 2018 (edited) This link offers a DELCO service bulletin which may help: https://drive.google.com/file/d/0BwSJ083sGeDtc1NIVHRneTQyQmM/view The inside of this regulator appears squeaky clean, but nonetheless could be the source of problems. Looking at a recent Ebay posting for a 933B generator (with guts shown and refurnished), this is a two pole unit, meaning it has two field coils. Suggest measuring the resistance between the field wire extended from the case and ground. I would expect it to be about 4-5 ohms (about 2 ohms each). If near zero or very low, likely to be shorted field coils. The above Service Bulletin describes polarizing a unit after service. Given this is only a two pole generator, maybe 15 amps is the maximum it can deliver. The BAT terminal connects to the battery, ARM connects to the armature wire from the generator and FLD connect to the field coil wire from the generator. Regulation is controlled by the amount of current supplied to the field. When enough voltage develops from the armature lead, the cut out relay engages and sends it to the battery. Edited February 28, 2018 by Friartuck (see edit history) Link to comment Share on other sites More sharing options...
pmhowe Posted March 18, 2018 Author Share Posted March 18, 2018 After a mess of bad weather, I finally found an opportunity to work on the Cadillac again. I re-cleaned all the connections between the ammeter and the battery, removed, cleaned, checked, and reinstalled the regulator, and topped off the battery with distilled water. Now, the charging system is working perfectly: At idle, there is only a very slight discharge and, at running speed, the generator charges nicely. While waiting for an opportunity to work on the car, I ran across the attached training brochure from Delco. It is an interesting read. Thank you for all your help. Delco Remy Generator:Regulators.pdf 1 Link to comment Share on other sites More sharing options...
Friartuck Posted March 20, 2018 Share Posted March 20, 2018 Glad to hear you got the generating circuit operating properly. The Delco Remy reference is a valuable document. Thanks for posting it. I'm trying to understand what you did to solve this problem. Did you clean the contacts inside the regulator? Link to comment Share on other sites More sharing options...
pmhowe Posted March 20, 2018 Author Share Posted March 20, 2018 I was more interested in getting the car to behave properly than I was in identifying the specific problem. Hence, I took a shotgun approach: I cleaned all the connections - wire to ammeter, wire to regulator, wire to generator. I removed the regulator and cleaned the contacts and measured the gaps. They were fine. I cleaned the base of the regulator and made sure it had a good contact with its mounting bracket. I cleaned the battery terminals. I added a good bit of distilled water to the battery. The upside is now everything is working properly. The downside is I don't know for sure which particular item was the cause of the problem. I suspect that there were several contributing factors that, taken together, added up to bad behavior. 2 Link to comment Share on other sites More sharing options...
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