Monarch 10EE Fwd/Rev DC Contactor Operation and Construction Questions

I have a 1942 Round Dial MG + Piggyback with the Reliance large frame 3hp spindle motor and my DC control panel looks much like this one, but mine is missing the Fwd/Rev contactors entirely. In looking for a replacement I am trying to better understand the OEM function and construction. Reading the schematics and other forum posts I believe the labeled contactor functions are as follows (please correct me if I have it wrong).

Looking at just the forward contactor:

A = A1 armature contact
B = A2 armature contact
C = F1 field contact
D = F2 field contact
E = A1 armature connection to the dynamic braking resistor

A,B,C,D are normally open and E is normally closed. When the contactor is closed those are then reversed.

Assuming that's all correct, I have some questions that maybe you can help me with.

1. Why do A,B,C have arc chutes under the contacts and D & E do not?
2. Why is there no barrier between the contacts of C & D like there is between A,B,C?
3. What is the function of the coils of wire under the contacts of A,B,C and why no coils under D & E?
4. Why is the wire diameter of the coil under contact C so much thinner than the coils under A & B?
5. During operation, how much voltage and current can be expected across each contactor when making or breaking the connection?

Any insights will be helpful.

Hobby Racer said:

1. Why do A,B,C have arc chutes under the contacts and D & E do not?
2. Why is there no barrier between the contacts of C & D like there is between A,B,C?
3. What is the function of the coils of wire under the contacts of A,B,C and why no coils under D & E?
4. Why is the wire diameter of the coil under contact C so much thinner than the coils under A & B?
5. During operation, how much voltage and current can be expected across each contactor when making or breaking the connection?

Click to expand...

I found some really good information about the 10ee contactors constructions and operation in this thread.

10ee DC contactors arcing

I will give some short answers here for future readers, but you should read the above thread for more details.

1. Contactors D & E do not carry high voltage/currents compared to A & B and therefor do not need the arc chutes.
2. Since D does not have the side contacts for the blow out coils (since there is no blowout coil on D) there is not a concern for an arc jumping between them like you might have between say A & B
3. The coils under the arc chutes serv to move the arc up and away from the contact points and allow it to cool and break easier. This is also why the contactors need to be mounted vertically.
4. Again, A & B carry high voltage/current and need larger gauge wire in their blow out coils as they are wired in series with the armature circuit.
5. Not sure on this one beyond knowing the armature and field voltages and max current ratings.

Well that is my current understanding of the contactor construction at the moment. Don't take this as gospel as I am NOT an EE, just a guy trying to fix his machine

D is the 'hold' contact and doesn't carry any real power. It's just there to be mechanically connected when the contactor closes. I've stolen the point and hammer from the hold on my lathe when needed over a weekend to replace the main forward point and hammer.

Hobby Racer said:

I have a 1942 Round Dial MG + Piggyback with the Reliance large frame 3hp spindle motor and my DC control panel looks much like this one, but mine is missing the Fwd/Rev contactors entirely. In looking for a replacement I am trying to better understand the OEM function and construction. Reading the schematics and other forum posts I believe the labeled contactor functions are as follows (please correct me if I have it wrong).

Looking at just the forward contactor:

A = A1 armature contact
B = A2 armature contact
C = F1 field contact
D = F2 field contact
E = A1 armature connection to the dynamic braking resistor

A,B,C,D are normally open and E is normally closed. When the contactor is closed those are then reversed.

Assuming that's all correct, I have some questions that maybe you can help me with.

1. Why do A,B,C have arc chutes under the contacts and D & E do not?
2. Why is there no barrier between the contacts of C & D like there is between A,B,C?
3. What is the function of the coils of wire under the contacts of A,B,C and why no coils under D & E?
4. Why is the wire diameter of the coil under contact C so much thinner than the coils under A & B?
5. During operation, how much voltage and current can be expected across each contactor when making or breaking the connection?

Any insights will be helpful.

Click to expand...

Keith Rucker said in his vid that he is donating his panel to some museum as spare parts. You might be able to barter with them to get the parts to fix yours.

Hobby Racer said:

I have a 1942 Round Dial MG + Piggyback with the Reliance large frame 3hp spindle motor and my DC control panel looks much like this one, but mine is missing the Fwd/Rev contactors entirely. In looking for a replacement I am trying to better understand the OEM function and construction. Reading the schematics and other forum posts I believe the labeled contactor functions are as follows (please correct me if I have it wrong).

Looking at just the forward contactor:

A = A1 armature contact
B = A2 armature contact
C = F1 field contact
D = F2 field contact
E = A1 armature connection to the dynamic braking resistor

A,B,C,D are normally open and E is normally closed. When the contactor is closed those are then reversed.

Assuming that's all correct, I have some questions that maybe you can help me with.

1. Why do A,B,C have arc chutes under the contacts and D & E do not?
2. Why is there no barrier between the contacts of C & D like there is between A,B,C?
3. What is the function of the coils of wire under the contacts of A,B,C and why no coils under D & E?
4. Why is the wire diameter of the coil under contact C so much thinner than the coils under A & B?
5. During operation, how much voltage and current can be expected across each contactor when making or breaking the connection?

Any insights will be helpful.

Click to expand...

A & B are armature contacts. C and D are not field contacts. C controls power to the generator rheostat and thus the generator's field windings. D keeps the main contactor coils energized when the anti-plugging relay opens, as Russ stated.

The coils under A, B and C are called "blow-out coils" and the U-shaped, white ceramic pieces are called "arc chutes". The blow-out coils are there to help extinguish the arc when the contacts open, bending the arc into a loop to increase it's length; the arc chutes work to protect the surrounding equipment from the arc. A and B operate at a higher voltage and higher current than C, so need larger blow-out coils.

Cal

So I got half of it right . Thanks for the clarification!