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I am trying to restore and electronic braking system on a 1950s Dewalt radial arm saw. The circuit had been disconnected (bypassed) from
the saw at one time and I would like to return it to operational condition.
The saw has a 3/4HP single phase induction motor. The components of the electonic brake include:
1. A DPDT toggle switch to control the motor and brake.
2. A large transformer using a 120VAC input with a 20VAC output split to 10VDC.
3. The 20VAC output of the transformer connects directly to the two outer connectors of a large Selenium Rectifier. A third connection on
the rectifier goes to a contact on the DPDT toggle switch.
4. There is also a 9-pin 7 second normaly open delay relay vacume tube in the circuit. This relay uses 120VAC heater coil to heat a
bimetalic strip make and brake the contact. When the contacts "make", 120VAC is applied to the transformer input. I assume this is used to
time how long the brake is applied.
5. And there is a .25uf capacitor which is connected across the contacts of the time delay relay. (arc prevention?)
An inital test of the transformer, selenium rectifier, and delay relay parts look good. The original toggle switch was not working reliably
and may have been why the whole circuit had been bypassed.
I am not sure how to reconnect this circuit to the AC source and saw motor. It looks like to AC source and motor had been connected to the
DPTH toggle switch at one time. But I am not sure which goes where. Does this circuit sound familiar to anyone? I have drawn a rough
diagram which I can attach to an email message for more details.
I understand that it is very difficult to understand a circuit just by a description. And advice or leads would be truly appreciated.
Thank you
Dave Bacon
the saw at one time and I would like to return it to operational condition.
The saw has a 3/4HP single phase induction motor. The components of the electonic brake include:
1. A DPDT toggle switch to control the motor and brake.
2. A large transformer using a 120VAC input with a 20VAC output split to 10VDC.
3. The 20VAC output of the transformer connects directly to the two outer connectors of a large Selenium Rectifier. A third connection on
the rectifier goes to a contact on the DPDT toggle switch.
4. There is also a 9-pin 7 second normaly open delay relay vacume tube in the circuit. This relay uses 120VAC heater coil to heat a
bimetalic strip make and brake the contact. When the contacts "make", 120VAC is applied to the transformer input. I assume this is used to
time how long the brake is applied.
5. And there is a .25uf capacitor which is connected across the contacts of the time delay relay. (arc prevention?)
An inital test of the transformer, selenium rectifier, and delay relay parts look good. The original toggle switch was not working reliably
and may have been why the whole circuit had been bypassed.
I am not sure how to reconnect this circuit to the AC source and saw motor. It looks like to AC source and motor had been connected to the
DPTH toggle switch at one time. But I am not sure which goes where. Does this circuit sound familiar to anyone? I have drawn a rough
diagram which I can attach to an email message for more details.
I understand that it is very difficult to understand a circuit just by a description. And advice or leads would be truly appreciated.
Thank you
Dave Bacon