Vintage DeWalt RA Saw

[PoTreeBoy]

Got a challenge for the geniuses on here. My BIL has an old (mid-50s) DeWalt 14" Radial Arm Saw they use occasionally in his business. Last time I visited, it had just quit starting, it would just oscillate a small amount. He had the original schematic.

I cleaned the contacts on the start relay and it has worked since then, but I'm not confident that's a long term fix. I'd like to find a replacement.

I've scoured the 'net and found Original Saw Company, who makes new saws and some old DeWalt parts, but they couldn't help.
Q1 - know where I could find one?

I've not seen a setup where the start capacitor switch doesn't have a time or speed function. This one just opens as soon as power is applied. Here's what it looks like

Q2 - Could I just substitute a power relay, 240v coil 20-30A contacts for this? I'm not sure I can find one that will physically fit. All the ones I've seen are DPDT and all I need is SPST NO.

Thanks for any help.

 

[dlsmith]

If it's operating on 115V, then use a 115V 20 amp relay. It doesn't say on the wiring diagram, but the capacitor should be wired through the NC contacts, as the capacitor is only needed on initial startup.

 

[radas]

Finally, an offtopic that can't be turned political looking forward to seeing more of the saw restoration.

 

[North Idaho Wolfman]

If you notice that relay has a thermal breaker in it, so it does have a time function ( break caused by thermal trip time).
You will not be able to just put a standard relay in place of it, as it will not operate the same way.

 

[torch]

Finally, an offtopic that can't be turned political

Wanna bet? Here, hold my beer and watch this...

"That start relay is just part of an Illuminati conspiracy to distract us from the real issue: Capacitors are not really needed at all to start the motor, their function is to generate the weather control rays mandated by the government on the day the saw motor was built. But now that you know the secret, you can figure out the weather by decoding the date of manufacture, adding the number of days the current party has been in power and multiplying by the number of times the saw has been started since the last full moon."

(JUST KIDDING!!!)

 

[Henro]

If you notice that relay has a thermal breaker in it, so it does have a time function ( break caused by thermal trip time).
You will not be able to just put a standard relay in place of it, as it will not operate the same way.

I don’t see any thermal breaker. I do see the relay contacts. Where is the thermal device you are referring to?

I admit sometimes I can’t find my nose either…

 

[PoTreeBoy]

Update: These relays are called potential relays these days. Turns out they are commonly used on residential air conditioner compressors. The relay coil is connected in parallel with the start winding; when the back emf in the start coil builds to a certain voltage the relay contact opens, turning the start capacitor and start coil off.

The pickup voltage spec depends on the motor design, which I have no way of knowing. But I found these universal relays - one is voltage adjustable and the other is timed. I think either would work, but I'm leaning toward the adjustable. I'll just have to accommodate the size.

Any relevant comments appreciated.

This has been a non-political announcement.

 

[ctfjr]

Have you checked / tried another starting cap?

 

[radas]

Wanna bet? Here, hold my beer and watch this...

"That start relay is just part of an Illuminati conspiracy to distract us from the real issue: Capacitors are not really needed at all to start the motor, their function is to generate the weather control rays mandated by the government on the day the saw motor was built. But now that you know the secret, you can figure out the weather by decoding the date of manufacture, adding the number of days the current party has been in power and multiplying by the number of times the saw has been started since the last full moon."

(JUST KIDDING!!!)

Excellent!

 

[PoTreeBoy]

Have you checked / tried another starting cap?

The saw is working since I cleaned the relay contacts. I just don't know how much life they have left.

 

[PoTreeBoy]

If you notice that relay has a thermal breaker in it, so it does have a time function ( break caused by thermal trip time).
You will not be able to just put a standard relay in place of it, as it will not operate the same way.

I think you're looking at the thermal overload in the starter. There is a disconnected wire in the j-box which I suspect took out the overload.

The 110-220 selector switch has also been removed since the saw is permanently on 220. I'm inclined to let sleeping dogs lie on this one.

 

[radas]

Update: These relays are called potential relays these days. Turns out they are commonly used on residential air conditioner compressors. The relay coil is connected in parallel with the start winding; when the back emf in the start coil builds to a certain voltage the relay contact opens, turning the start capacitor and start coil off.

The pickup voltage spec depends on the motor design, which I have no way of knowing. But I found these universal relays - one is voltage adjustable and the other is timed. I think either would work, but I'm leaning toward the adjustable. I'll just have to accommodate the size.

Any relevant comments appreciated.

This has been a non-political announcement.

View attachment 82686

Can you measure the starting/running voltage while the saw is in use with a multimeter? I think you can set a baseline voltage/amperage by running it a few times and taking the average. This is my uneducated electrical advice.

I would also check with someone who is familiar with industrial HVAC/electronics, they may be able to help. Electrician forums are another good option and I'm sure you'll get a reply since your goal is not to rig a house with unpermitted electrical work.

This is my non-political response to your non-political announcement

 

[RCW]

No help with the technical side.

Like you said, looks like a challenge to accommodate the new relay size in a small space......1.75x2.25x1.5" could be tight...

I'm RCW, and I approved this message.....

 

[PoTreeBoy]

And now, the rest of the story . . .

I installed a SUPCO SUPR universal relay on the 50's model DeWalt radial arm saw this weekend. It works like a champ. It fit in the motor box, just had to drill a couple of mounting holes. The 110/220v selector switch had been previously removed and wired permanently for 220v. I gave my BIL the standard repairman's guarantee, "It was working when I left." I suspect the APR5 relay would have also worked, after adjustment.

Maybe this will help SGOTI someday.

 

[PoTreeBoy]

I just thought it was the rest of the story. Mid-May the saw stopped starting (Microsoft problem?) again. So it worked eight months. This time I ordered one of the adjustable relays, with one of the timer ones to have as a known backup.

I've installed the adjustable one and set it at about 280 volts. I didn't bring my clamp-on meter and I'm not sure there's enough room to connect it anyway, but it sure starts and runs smooth. We'll see how long it lasts this time.

I took the old one apart (of course) and the relay contacts had definitely been hot.

 

[BigPoppy]

I just thought it was the rest of the story. Mid-May the saw stopped starting (Microsoft problem?) again. So it worked eight months. This time I ordered one of the adjustable relays, with one of the timer ones to have as a known backup.

I've installed the adjustable one and set it at about 280 volts. I didn't bring my clamp-on meter and I'm not sure there's enough room to connect it anyway, but it sure starts and runs smooth. We'll see how long it lasts this time.

I took the old one apart (of course) and the relay contacts had definitely been hot.

When I installed the apr5 relay the saw starts great but wants to bogg out when cutting. Any help? Please

 

[BigPoppy]

When I installed the apr5 relay the saw starts great but wants to bogg out when cutting. Any help? Please

Also tried the supr and same thing happens

 

[PoTreeBoy]

When I installed the apr5 relay the saw starts great but wants to bogg out when cutting. Any help? Please

I'm not a motor expert at all. But once the motor starts, that relay takes the start circuit out of the picture.

What saw do you have? Did the problem come on gradually or suddenly? Do you have a schematic to check the wiring? I'd check the contacts on any contactor or switch. Are you running a 220 set-up on 110, by chance?

 

[mikester]

Maybe the ball bearings fell out

I've purchased 3 POS dewalt tools in my lifetime and now say never again

 

[PoTreeBoy]

Maybe the ball bearings fell out

I've purchased 3 POS dewalt tools in my lifetime and now say never again

I don't know about BigPoppy's saw, but my BIL's was bought by his father in the mid-50's. "They don't make 'em like they used to".