Choosing An Omron Timer

[iceblu3710]

I am making a DC injection brake for a saw to add some safety to the unit and require a relay to make the system automatic. Here is a breakdown on how I need it to work:

120V 10A input
Start/Stop maintained switch

Press start button to start motor, when you press stop there will be a 1s delay and then DC will be put into the motor for 8s, then the motor will be isolated from the source until started again.

Essentially I have a rectifier and power resister I am inserting in series with the motor which is turning the 120VAC into DC.

I can not figure out what combination of things I would need as a delay-OFF would give me the 1s dead band and that could turn on a delay-ON for 8s but that would require two timers. I am hoping it can be done with just one. I am also open to using the start/stop button as a simple input and having the timer constantly powered. (I would use an e-stop button on the line voltage for emergencies)

 

[D.A.(Tony)Stewart]

What type of motor? Normally brakes are just transferring motor from input to ground resistor on some motor types to act as generator with heavy load to stop quickly, but winding resistance , arcing and current are factors to be considered. Do you have motor model?

for your method, two cascaded timers are required.

 

[iceblu3710]

It is a universal motor. A resistive brake works great on DC motors but does next to nothing on induction motors unfortunately.

Attached is the original design from a magazine on breaking this kind of saw. I am trying to make it automatic instead of a momentary push button as they have it.

I just came up with an idea of making the whole controls out of 74 series logic. If I put in a cheap current sensor and some logic I think I could easily control two relays. Might be cheaper than two multi function timers.