1926 Dodge Brothers Business 2 unit electrical polarity question

The car is a negative ground 6V 2 unit system.

I connected the battery and went for a drive. The car lost all power. I discovered the negative post cable had disconnected. I re-connected the cable, started the car, noticed the ammeter gauge was pegged to the left, then a wiring burning smell and smoke from the dash happened. I turned it off. The wire insulation from the generator to the ammeter was burned off.

I am thinking the polarity changed. What happened and what has to be done to fix it?

Thanks,

David

It sounds like your have a short somewhere.

1926 DB 6v two unit should be positive ground.

Having the polarity wrong should not cause the problems that you experienced I agree with the chocolate man you have a serious short somewhere

Yes it is positive ground, I had it backwards.

Any ideas what best to test first for a short? Is there possibly a sequence, i.e., ammeter, cutout, start switch, horn, ignition switch, ... ?

Start with the cutout/regulator. That's the part that's most susceptible to failure.

Then again don't overlook a rubbed through wire either.

Thanks for the direction. How can the cutout be tested and what indicates it is good or bad? Or simply replace it? Is there a polarity issue? Any re-install nice to knows?

A faulty cutout will cause the ammeter to show a discharge when the ignition switch is shut off.

Depending on the generator it can be a severe discharge.

Severe enough to burn wires........ :eek:

Disconnect the wire at the cutout and see if you still have something going on under the dash.

A faulty cutout will cause the ammeter to show a discharge when the ignition switch is shut off.

Depending on the generator it can be a severe discharge.

Severe enough to burn wires........ :eek:

Disconnect the wire at the cutout and see if you still have something going on under the dash.

I am following this thread with interest. Can you please elaborate how the duff cutout causes the discharge with the ignition switched off. I have not come across this before.

My first thought regarding the short was that the loose battery wire could have heated enough to melt the insulation. Is this a possibility?

Ray.

Ray if the cut out is faulty and sticks closed the current is drawn from the battery regardless of what position the ignition switch is in If that is the scenario then the generator is acting like a starter motor but because the wiring is to light to carry the required current you end up with lots of smoke and burnt wires

Thanks Ron. I understand now. Because the charging and ignition circuits are separate the cut out contacts need to open be at rest or current will be drawn to the dynamo. Could a fuse in the circuit be fitted and what rating?

Thanks Ron. I understand now. Because the charging and ignition circuits are separate the cut out contacts need to open be at rest or current will be drawn to the dynamo. Could a fuse in the circuit be fitted and what rating?

Ray the cutout is automatic switch between the battery and the generator, as the generator comes up to speed and charge out put the relay closes and connects the battery to the generator,now when the motor stops this relay automaticly disconects the battery from the generator ,if this does not happen than the battery will discharge through the generator ( and could cause damage to the generator ) resulting in a flat battery. If a fuse was in this line and burn out than the generator would have no means of voltage control and could cause a very high voltage to generated and burn out most of the electric circuits of the car(lights ,coil etc). In the third brush generator system the battery acts as voltage regulatorand UNDER NO CONDUITION WHEN THE MOTOR IS RUNNING IS TO BE DISCONEGTED FROM THE GENERATOR. This system is called a constant current charging system . The current is controled by the action of the third brush in the generator to distort the magnet field and as speed incresses the out put decresses. Hope this helps ,more info if needed regards bob

dadsdodge.......getting anywhere?....... :confused:

Not yet. Electrical is challenging. I am learning more about this and will be trying some things in the next few weeks. I will report my findings.

Although I am familiar with how the cut out works what I am uncertain about is the function of the field fuse. Does it blow if the generator (dynamo) voltage becomes too high? or is it also there to protect the dynamo should the cut out fail with the points stuck shut (with or without the ignition on) as discussed earlier?

Ray.

In 1934 Dodge got their first regulator and it was a voltage regulator. (Hence the reason we are stuck with the term 'voltage regulator' even though the later device regulates current and voltage and contains the cutout as well.) The 1934 voltage regulator was mounted on a saddle on the generator. It has a fuse in a holder sticking out the side and it interrupts the field circuit if blown. Why? I assume since they did not want the field to go 'full flux' and overcharge the battery, so they included the fuse to kill the field if it went above a certain current,the current stamped on the fuse body. This would have been caused by the relay points of the new voltage regulator sticking. (The same way wiring would burn if the points of the cutout stuck,as previously mentioned.) Within about 2 years they added another vibrating point relay to control the current during charge. The 2 vibrating point relays,one for voltage and one for current, pretty well stopped the cooking and overcharging of the battery. Prior to these regulators,also as previously mentioned, the battery itself was the regulator. Much water was used by the battery and it had to be refilled virtually every time the car was used. Some of you guys with these older vehicles,prior to 1934, must still have this problem? Although your modern batteries are built much better and out of better materials,they should be still using water. It wasn't until the industry put all 3 relays in under one cover on the firewall that they finally got hold of the charging cycle of the battery. The regulator stayed there for several decades until the transistor era when it went inside the generator. By the way, those of you that have the 1934 era voltage regulator mounted on the generator will experience problems because the heat of the generator threw the settings of the moving points off as the current came out of the generator and it heated up. That's why they moved it to the firewall.(They also had a further problem with grounding. The vehicle would rust with age and the generator would lose it's ground path back over to the firewall. Some were actually mounted on the fender. That didn't help. Finally the regulator was insulated on rubber mountings and a 4th wire was connected from it's chassis over to the generator's body. This was the final version.) I'm not sure why the various versions going back into the 20s. Cost? Or they actually didn't know what they were up against? It took them years to get it right.

DodgeKCL you have an admirable way of explaining the facts and the history associated with them. Thank you.

Ray.

Although I am familiar with how the cut out works what I am uncertain about is the function of the field fuse. Does it blow if the generator (dynamo) voltage becomes too high? or is it also there to protect the dynamo should the cut out fail with the points stuck shut (with or without the ignition on) as discussed earlier?

Ray.

Ray if the conection between the battery and the generator (dyanmo) become seperated by any means the field fuse is there to protect the field coils of the said generator from drawing to much current and will in cause blow the fues to protect the generator field winding from burning out.. As there is there is no other route for the current to flow ( when the battery is disconected )but through the field coils in turn over heating and burning them out . The fuse will blow to protect these coils.

Many thanks Robert. When I got my (1926) car the wiring was a mess. There were so many things which had been done badly I decided the only course of action was to rewire. Starting with a clean sheet made things easier. I was advised to fit a field fuse so I put in a 6 amp to protect my (expensive) newly rebuilt North East generator. I hope it was the right thing to do as there was no evidence that a fuse had been fitted originally.

Incidentally Austin also had a chequered history with various cut outs and voltage regulators which indicates to me that the industry in general must have been unsure as to the best solution to these electrical questions.

One thing that I have picked up on recently is that the temptation to use a later two bobbin voltage regulator and cut out on the two unit 6 volt cars should be resisted because their principle of operation is to mechanically switch the dynamo output on and off giving an average voltage at a pre set level. This loads and unloads the drive to the generator which is fine for later cars where the dynamo is driven by a flexible belt or earlier single unit cars with a chain driven starter/generator which absorbs any variation in the drive load. This is not the case with the gear drive generators and can cause the timing gear train to rattle noisily at certain revs. Apparently.

Ray.