Weller D550 Low Power On High Setting. Suspicious of Transformer

Thread Starter

ftm1776

Joined Oct 30, 2020
5
My new "old" D550 (235/325watts) puts out good wattage on low (230 watts) but only about 200 watts on the high (325 watts). I've cleaned and tightened the tip. I took the switch apart and cleaned it with brake cleaner (very greasy). (May add grease back to prevent oxidation) No increase in high wattage. I checked the power by bypassing the switch and jumping from hot wire to each side of the switch; low setting good (230 watts) ; high still 200, nowhere near 325 watts. So now what ??? My only thought is that low power only uses a part of the winding, the high winding may be shorted and is also using only a portion of the winding. Any advice? This is my first, used soldering gun so I am new to this game. Any references to check the functionality of the transformer would be appreciated. Electrical is a weak point.
PS: My gun is in pretty good conditon. It doesn't look like it has been abused in any way .
See a similar gun repair here:
 
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Thread Starter

ftm1776

Joined Oct 30, 2020
5
My new "old" D550 (235/325watts) puts out good wattage on low (230 watts) but only about 200 watts on the high (325 watts). I've cleaned and tightened the tip. I took the switch apart and cleaned it with brake cleaner (very greasy). (May add grease back to prevent oxidation) No increase in high wattage. I checked the power by bypassing the switch and jumping from hot wire to each side of the switch; low setting good (230 watts) ; high still 200, nowhere near 325 watts. So now what ??? My only thought is that low power only uses a part of the winding, the high winding may be shorted and is also using only a portion of the winding. Any advice? This is my first, used soldering gun so I am new to this game. Any references to check the functionality of the transformer would be appreciated. Electrical is a weak point.
PS: My gun is in pretty good conditon. It doesn't look like it has been abused in any way .
See a similar gun repair here:
I want to edit my post. However, for the life of me, cannot find a place to "Log In". I'm running in circles. Where is the log in window??? Yes, this is my first post.
My new "old" D550 (235/325watts) puts out good wattage on low (230 watts) but only about 200 watts on the high (325 watts). I've cleaned and tightened the tip. I took the switch apart and cleaned it with brake cleaner (very greasy). (May add grease back to prevent oxidation) No increase in high wattage. I checked the power by bypassing the switch and jumping from hot wire to each side of the switch; low setting good (230 watts) ; high, not good, still 200, nowhere near 325 watts. Low power current is 2 amps; high power current is 1.5 amps. Current marked on the logo is 2.5 amps.
So now what ??? My only thought is that low power only uses a part of the winding, the high winding may be shorted and is also using only a portion of the winding. Any advice? This is my first, used soldering gun so I am new to this game. Any references to check the functionality of the transformer would be appreciated. Electrical is a weak point.
PS: My gun is in pretty good conditon. It doesn't look like it has been abused in any way .
See a similar gun repair here:
 
It's almost always a poor connection to the tip.
You have to loosen/tighten the nuts several times back and forth, to cut through the copper oxide. This is a regular ritual with soldering guns.
Just measure the secondary voltage and you can see it jump around with the bad connection, or the #222 lamp brightness will surge up and down as well. Last resort, the tip is just plain worn out, they do not last forever, the copper cracks.

Also- note soldering guns make a very high voltage spike at the tip, several kV when switching on/low/high and I have destroyed electronics using them. There are no arc suppression caps across the switch and the solenoid-style transformer just couples the HV to the tip, they are not earth-grounded. For these reasons don't use them on a car/vehicle either.
 

Thread Starter

ftm1776

Joined Oct 30, 2020
5
It's almost always a poor connection to the tip.
Thanks for your comments.
I wire brushed, sanded, filed, basically cleaned the contact area to shiny copper.
Are you saying, that in general, that, even with perfect contact, the tip could be bad
other than at the contact area? You said, "cracked"???
Why, then, does the tip perform at the 230 watt low setting if, as suspected, the tip is the problem??
 

MaxHeadRoom

Joined Jul 18, 2013
21,958
The Weller gun like you show is just a simple transformer with a 1 turn secondary and over 100amps flow when trigger is pulled.
On the Wellers I have owned, the first pull is the high output primary winding the full pull the low, the switch consists of a couple of spring activated contacts and two small rollers that click over when pressed.
You should hear the first click half way through the pull.
It could be that the pull switch has become corroded on the high switch setting over time?
You can carefully dismantle it and clean it, if necessary as per the video and take good note of the exact construction for reassembling.
It is however as mentioned, imperative to have a good connection all the way through the secondary/tip path.
There is no HV on the secondary.
Max.
 
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Thread Starter

ftm1776

Joined Oct 30, 2020
5
Thanks, Max.
I have dismantled the switch and cleaned all of the grease out of it. The thing that I did not do it scrape the flat contact area that the rollers touch or the rollers themselves. Maybe I'll see what affect that has.

But I have to point out that I completely cut the switch out of the circuit by jumping from the 120 volt hot line to the individual transformer contacts. The results are the same 230 for low(reasonably good) and about 200 for high. So, to me, it doesn't seem to be the switch.
I even jumped across both high and low at the same time....WOW...she put out about 500 watts.

CORRECTION: This particular D550 is labeled for 240/325 watts.
 

prairiemystic

Joined Jun 5, 2018
147
[...] There is no HV on the secondary.
There is HV pulse on the secondary at switch-off. Put a neon lamp or LED from the tip to earth-ground and it will flash. The Weller solenoid-style transformer is notorious for having high capacitance pri-sec. edit: 'leakage inductance' so the primary arc across the switch gets coupled to the tip. All you have to do is check it. It does damage electronics, so I pull the gun away from the connection and then release the switch.

OP, don't short both the high+low transformer taps, that will cook it. It is strange high is lower power than low. I wonder if the taps are mixed up?

I have seen tips go bad, just high resistance but non-linear. I'm not sure if it's the cracks in the copper causing localized hot spots or what. But replacing the tip solved it.
 
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MaxHeadRoom

Joined Jul 18, 2013
21,958
I don't see how a shorted turn is going to impose a pulse for such a low resistance, essentially shorted single turn secondary!
There may "Possibley"? be a pulse if open circuit,
Why tip to earth GND?
Max.
 
OT - The Weller solenoid-style transformers have very high leakage inductance due to their construction. The primary winding flux is poorly coupled to the core, so there is a fast HV spike at the primary when you switch off. They use no capacitor or snubber across the trigger switch contacts.

Because of the transformer's winding capacitance, the HV spike on the primary side, gets coupled over to the core and secondary (tip) in common-mode. The spike does not appear differential-mode i.e. across the one-turn 2VAC secondary and tip. One leg of mains is always connected to the transformer's primary, the other leg is switched. So the HV spike appears between the tip and mains. Since mains neutral is connected to earth-ground, the spike does have bite.

I know this is true after investigating a bunch of gear that got killed or rebooted while soldering with an 8200 N. Put a neon lamp to the tip and it will flash (assuming the neon lamp other end is connected to anything).

I'm just letting people know, these ungrounded-tip soldering guns can damage electronics. If you don't believe me, do the simple test. Car makers also state "do not use a soldering gun" on ECU wiring, I think for this reason.

The fix would be an earth-grounded tip (power cord) or at least a cap or snubber across the switch contacts. For now, I remember to pull the tip away from the soldering joint before I let go of the trigger, so the HV spike doesn't hit the circuit.

pic taken from History of Soldering Guns: https://stevenjohnson.com/soldering/guns.htm

OP, does the #222 lamp work? It should get brighter on high if the transformer is putting out more voltage. It will also flicker brighter and dimmer showing any intermittent poor connection at the tip.

weller-d550-inside.jpg
 
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