Make an Interval Timer for my Harbor Freight 220 Volt Spot Welder?

[vtsteam]

I'd like to make an interval timer for my Harbor Freight 220 volt spot welder.  I have a couple of timers coming in the mail. They use mechanical relays. Here's a pic:

  [ You are not allowed to view attachments ]  

Specifications:
 Operating voltage: DC 6V - 30V, supporting micro USB 5V power supply
 Operating current: 50mA, static current: 20mA
 Working temperature: -20—60℃
 NO maximum load: < AC 250V/10A, < DC 30V/10A
 Size: 6.4*3.8*1.7cm

HOWEVER:

I'm guessing that triggering the inductive load of the 220V line of the spot welder might be too much for the relay, so I was going to add a second solid state relay, which would be triggered from the timer's relay. Maybe this one....

  [ You are not allowed to view attachments ]  

Twidec/Output Single Phase SSR Solid State Relay
100A
3-32V DC to
24-480V AC
SSR-100DA

BUT, I was wondering if I could eliminate the middle man (the timer's mechanical relay) maybe desolder it and then just hard wire the relay coil's lines to the inputs of the 100 amp solid state relay?

Thanks

[awemawson]

Input to most ssr's is just turning on an opto-coupler in series with a suitable resistor to limit the current so driving them is not usually much of a problem.

[vtsteam]

Thanks Andrew! 

Guess I'll try it on a lightbulb load, at first.


If it checks out, I think I'm going to completely remove the switch wiring in my HF spot welder, which is a little, um, what's the expression..sketchy? Also some additional sketchyness in the fact that you have to squeeze your hand hard on the metal handles while twiddling the sort of homemade looking unencased 220 V switch at the front -- with its paper insulation. I can imagine several non-pretty failure modes ....involving an unreleasable handshake. 

It does make me wonder about the expression "lifetime guarantee."  How exactly does that work?

[WeldingRod]

Oddly enough, I JUST re-did this on my HF 240VAC spot welder!
I bought a 240V powered timing relay with push buttons and a 240VAC to 240 VAC (control side) SSR. 
I recommend buying a 240 VAC rated MOV to put across the contacts!
Pretty sure its this one:  https://store.ametekiscd.com/ncc-time-delay-relay-function-multi-time-range-multi-input-voltage-240-vac/
I used to have a nice spot welder timer off the 'zon, but the darn thing just didn't actually time...  scream.  Picture attached.  This one needed a little step down transformer to run the brain.

I'd actually leave the switch, as sometimes you just wanna zap something but good...

The re-build I did was SUPER valuable!  Took it from maybe-sorta-ok to "whoa nellie!".  Serious kilo-Amps  :-)

[vtsteam]

Thanks WeldingRod  Do you have a larger pic? I can't really see that one.

Wow that's a pricey unit you have ($236.33?). I'm sure it's nice!

The timer I just bought is ummm, a little on the cheaper side..... two for $13.99. 

I'm going to remove the HF Welder's switch and switch wires for sure. Not safe IMO. I can have a switch -- maybe a foot switch off the unit anyway if I want to human-time it.

Update: I just got my little timer(s) and after deciphering the instructions for about the better part a half hour, I finally got the little booger figured out.

For those interested in this timer, I chose Mode p1.2, and as a test time 0.6 seconds.

I hooked up my multimeter to the NO contact and the Common contact of the relay, with the low ohms beep function selected on my meter. Then hooked a 9 volt battery negative to the trigger ground terminal, and a lead to the trigger terminal.

  [ You are not allowed to view attachments ]  

I Touched the lead to the positive side of the battery, and voila, it beeped for 0.6 seconds. Nice countdown display, too on the little board's LED. All is well.

Next the 100 amp solid state relay.....

Sooooo.

(for kicks and giggles, I'm attaching the instructions for the timer. Enjoy)

[vtsteam]

I went at the bottom of the circuit board with the multimeter, and this is what the relay pads test out to be on mine. Don't take this as written in stone for these timers as there are often variations in circuit boards and circuitry.

Since I have two timers for my $14, I'm going to just jump right in and de-solder the existing relay in order to substitute the 100A SSR. If I kill the first timer, I have a spare.

  [ You are not allowed to view attachments ]  

[vtsteam]

And yup, Bob's yer uncle, it works! 

  [ You are not allowed to view attachments ]  

Thanks Andrew! WeldingRod! 

[vtsteam]

I've ordered a a set of 6 20mm 275VAC MOVs. : $9.19.

Adding up the costs

The 100A SS Relay cost $19
Timer (1/2 x 13.99) cost $7
MOV (1/6 x 9.19) cost $1.50

Total $27.50 for electronics.

I'll need a utility box, and I want to add a foot pedal and a couple switches. I have most of that stuff, anyway, but that might add to the cost for someone else.