SES-II switch diode - placed on wires, not motor terminals?

[Guest]

Instructions with an older SubTech SES II switch say to install a diode (1N4001) across the motor terminals if the switch is being used to turn a motor on and off. Since I am electronically challenged, I wonder if someone can tell me if I would get the desired interference suppression if I placed the diode across the + and - wires leading from the switch, inside the WTC, instead of at the motor terminals? The motor is in the manufacturer's waterproof housing, in the wet hull, and I don't want to disturb the housing.

[wadester13]

The diode is used to

The diode is used to suppress reverse EMF. If the diode is at the switch it will allow the pulse of energy from the field collapsing in the motors windings to discharge through the wire all the way to the switch where your diode is at, which allows for EMI to come from the wire. So the diode should be placed closest to the motor. You could use shielded wire but why? The same thing goes for relays. It is true there is DC on the wires going one way but the spike of EMF from the motor is much higher than the DC used so the polarity will run backwards for a short time and can hurt electronics.

The switch debounce (the making and breaking as the contacts close and open) I do not believe to be a problem that a diode would have much of an effect.

Hope this helps.

[gerwalk]

Just another SES cuestion]

[color=#000000]Just another SES cuestion]

[tabledancer]

I installed diode on the

I installed diode on the pump motor also,as the instructions directed and I have a SES-3,and the same ballast system.
TD

[Guest]

I have had no interference

I have had no interference problems with the RCABS pump motors, with or without the 1N4001 diode installed. I always used the diode recommended when using the SES II. When I used a microswitch for turning the pump on, I didn't use the diode.
I am however, having an interference? problem with my new thruster motors. I have two controlled by forward only speed controllers, and two controlled by an SES II switch. Sometimes the SES II switch stays on (Thruster running) and won't switch off, unless I turn the transmitter off and on again. Sometimes, after switching one of the SES II controlled thrusters on, the speed controlled thrusters stop responding, unless I throw the transmitter switch to low position and start again. Any explanation? If EMI is the reason, will the installation of the diode in the WTC, some distance from the thruster motor terminals, be helpful?

[jsl]

The reverse current diode only

The reverse current diode only works the exact moment current to the motor is cut, and a voltage spike from the collapsing magnetic field generated. Sounds more like you've got an ongoing EMF problem...

I would try and reduce EMF and noise in the supply lines by adding 0,1uF capacitors (or larger) on the motor terminals. They'll suppress a lot of noise both when the motor is running as well as when it is stopping.

Each capacitor is mounted with one lead soldered to a motor terminal and the other end to the motor metal casing. Use ceramic disc capacitors.

[collins class]

Isn't the optimal configuration for

Isn't the optimal configuration for the capacitors one between the terminals and one each from the terminal to the motor casing for a total of 3 capacitors per electric motor?

[skip asay]

Some motors don't need any

Some motors don't need any capacitors at all. Some can be silenced effectively with 1 capacitor on each terminal to the case (or between the terminals). And some need those 2 as well as another between the terminals. And then there's the occasional motor that needs even more....grounding the case back to the battery. Best solution (generally considered bulletproof) is to use all 3 caps AND a wire between the motor case and battery ground.

As JSL stated, the diode works only when current is cut off to the motor (or relay coil) as a spike of reverse voltage is generated at that point. While there are occasions when this is not really necessary, it's absolutely a good idea to use it.

If the motor is sealed precluding installing caps/diodes directly to the terminals, having those items at the switch is fine. The RS-5 switch and ST-10 speed control have those reverse current diodes right on the circuit board.

Hope this helps.

Skip Asay

[Guest]

Thanks everyone. Skip, that was

Thanks everyone. Skip, that was the answer I needed. This board is a great resource.