Weller Iron Saver

[CJay]

I've been given a couple of old Weller PS-3D and associated irons.

One of the irons works but occasionally overheats, the 'stat is sticking.

I know I can clean and if necessary replace the stat (and I have a box of spares) but it occurs to me that it would be possible to monitor the operation of the thermostat and either sound an alarm or just turn off the iron if it sticks because, occasionally, I might leave the iron on for a period of time and only notice it's stuck after it's been overheating for a while.

I'm sure it would be possible with some very simple electronics (bubblegum 555 comes to mind) but a PIC costs way less than a quid and would be a fun thing to do.

So, I'm thinking monitor the power up from cold, reset a timer the first time the current stops flowing or switch off the current if it overflows and signal failure.

Once the initial warmup period has expired, use a shorter interval timer and, again, reset it when current stops flowing or turn off current and indicate failure if it overflows. 

Reset of the alarm would be as simple as power cycling the PS-3D.

other than the obvious 'fit a new stat you tightwad' can you think of any features or snags?

How would you monitor the current drawn? (I'm thinking either one of the dirt cheap eBay current sensor breakouts or a hall effect device with a few turns of wire wrapped around it or an old school sense resistor)

[Gyro]

Not the answer you're looking for but it's definitely worth changing the lead to a 5 core (as used in cheap Chinese irons) and offloading the stat current to a SSR. It depends whether it is the contacts that are sticking or the plunger (weak spring?).

For your original idea, a low value resistor would work for current sensing as the voltage isn't that critical, but you're dealing with AC power so you would need to derive a DC supply for the 555 and deal with the current sense being AC.

[CJay]

No, not what I was looking for but a damn fine idea all the same, thank you, the 'stat would probably last forever

[Gyro]

You're welcome... and yes, I'm certainly hoping it does!   

This thread (and the other threads referenced in reply #14) should help you:

http://www.vintage-radio.net/forum/showthread.php?t=73577

There's another thread in there somewhere with several alternative wiring schemes, but the 'Junk box mod' one in the above reference works with the existing 3 core cable.


P.S. An ideal SSR candidate (12V minimum switching capability and Zero crossing for low noise).  http://www.ebay.co.uk/itm/Solid-State-Relay-4-Amps-MPF240D4-SSR-4A-Crydom-NEW-x-1-pc-Offers-Free-POST-UK-/232242158385?hash=item3612b61b31:m:m9WSfg_UY-jTRv9nBtfqU4Q

I should have given you the junk box mod link directly: http://www.vintage-radio.net/forum/showthread.php?t=67035

[CJay]

Thanks again

I'm going to clean up the contacts on the 'stats before replacing them

I think I've got enough parts to make three full 'PS' soldering stations and I know I have four W60 mains irons (wonder if I can find some suitable flexible mains rated 5 core...) as well as a couple of other non Magnastat Weller Irons so I'm well served for soldering irons.

I think I might code the iron saver idea to have a PIC monitor the iron and control the SSR, it's always a little disconcerting to walk into a darkened room and see the iron glowing dull red...