You really should have an on/off switch before the PWM board. If not to keep the PWM from being powered all the time, but for safety reasons. How many machine tools do you see that don't have a switch? Counting on just the plug is not very safe.

Good point Shortbus - that's a definite difference between treadmills and power tools. I'll incorportate a switch to cut the power completely (instead of just relying on the potentiometer to turn the motor on/off).

 

One in particular I looked at is a KBAP-240D "Current Sensing Relay and Overload Protector" (http://www.kbelectronics.com/data_sheets/kbap240d.pdf). My question with it is this: When it trips, is it opening or closing the circuit? It has a 2 amp trip (on up to 20 amps) but I'd need it to close (complete) the circuit - I have a hunch that it's opening the circuit when it trips instead.

Anyone have an opinion or any experience with this board?

 

Here's a basic ("non-technical") summary of the relay specs I need as best I can tell:

• Either need voltage sensing relay or current sensing relay with following specs:

Voltage Sensing:
Load voltage (DC): 12v

Control voltage (DC): 10v (trigger point):
Amp rating: 10 (for extra cushion)

NO/NC: Normally Closed (opens at 10v)

--------------------- Or ----------------------

Current Sensing:
Load current: 900mA

Control current range: 1.5 - 5 (or more) Amps (trigger point=1.5 A)
Amp rating: 10 (for extra cushion)

NO/NC: Normally Open (closes at 1.5 A)

Can anyone please point me to specific relays that match these criteria?

 

It's for opening the circuit when the motor overloads. Used instead of a fuse to protect the motor. Why would you want it to turn on a circuit?

 

It's for opening the circuit when the motor overloads. Used instead of a fuse to protect the motor. Why would you want it to turn on a circuit?

Thank you for clarifying.

For the purposes of triggering the fan, I'd either want a voltage sensing relay to turn on the circuit at 10 volts or less (the voltage decreases as the motor speed increases) or a current sensing relay to turn on the circuit at 1.5 Amps or more (the current increases as the motor speed increases - please see the table I just posted prior to this post for clarification of desired range).

 

I'd just have the fan on when the motor is on. If you wait until the motor is at a certain temperature, then you will have to wait till it cools down to keep running it. Motors that are fan cooled have the fan on at all times, no off/on at a certain temp. By keeping the motor cool the whole time it allows it to live longer. You did say it was a "muffin" fan, like from a computer, right?

As far as overloading the motor, isn't there a fuse on the output? In the leads to the motor?

 

Yes, there is a fuse on the output. I'm not so much concerned with overloading the motor, since the fuse is in place, as I am in triggering the fan to come on while the motor is running.

The fan is a "muffin" type - 80mm pc fan. As you alluded to, I also prefer it being on when the motor is on, instead of using a temperature sensor that was suggested previously. To have the fan run when the motor is on, the relay will have to approximate the specs laid out in the table I posted.

 

No relay needed. Just wire your on/off switch to both the PWM board and the wall wart for the fan, when switch is on both will run. Or to eliminate the wall wart get a fan that runs on 120V. http://www.allelectronics.com/make-a-store/item/CF-117/115-VAC-80-MM-COOLING-FAN/1.html From this page - http://www.allelectronics.com/make-a-store/category/220/Fans/1.html

 

Hi All,

Here's the latest update. Thanks Shortbus for your suggestion about using power switch to turn on/off PWM board and wall wart - that's what I finally ended up doing. So now the fan doesn't start as soon as the power plug is inserted into the wall outlet. Would have liked to find a way to control the fan as previously mentioned but this works to my satisfaction.

Saw is up and running - am loving the variable speed capability. Now just need to learn how to dial in the adjustments better - blade positioning on drive wheels (too far toward front of top drive wheel/too far toward rear, etc - this Skil model seems a little tricky to get used to) and blade tightness. Started cutting crooked on 1/4" steel plate. I'll play around with it & am sure I'll get the hang of it.

Thanks to everyone for their suggestions - really appreciate the help!