Lehner 1930 De-soldered Itself??

[jhautz]

I bought a 1930/6 motor that I got new for about half price off of ebay just to try it out and see how it would do in my cen matrix conversion. Its not the high amp version so I was able to re-solder the back of the motor to configure it to a star configuration and effectively make it a 1930/10 (2090kv). The can is even marked 6 / 10. Well it took a little doing getting the solder off of the old D connection and to bridge the star connections but I got it and it ran really great for about 20 minutes or so and then everything just quit. I was out bashing and thought I fried the MM, but there was no smoke or anything else. It was just running along (and really ripping I might add, I like the motor allot) and then nothing. It just quit. No smoke, just nothing???:confused: When I got to it I pulled the lid to see if I could find what was wrong and couldn't figure it out. Everything felt cool enough. The motor was warm, but I could easily hold my hand on it as long as I wanted. I never figured it out so I just put it away and ran my revo the rest of the day.

Just now I was goofing around with the motor to try and see if I could figure out whatthe problem was and I plugged in a battery and the MM lit up and went through the start up routine with the LEDs but no sound. When it was done I could pull the throttle and the LEDs would change color just like it would normally do. So I plugged in an old 9L I had sitting around and everything worked perfectly.

So now I have it narrowed down to the motor. I plugged it into the speed control on one of my other trucks and nothing. So now I'm sure its the motor. I started looking at it thinking that I might have put to long of a screw in it and fried the windings or something, or had I a bad solder joint in one of the wires I soldered into the 3mm connectors so I could use 5.5mm connectors on the end of a short wire instead of those useless 3mm connectors. Thats when I noticed it...

All of the solder points on the back of the motor were disconnected. They looked like they had flowed clean. All 3 of the connections that I made were now clean as if I had never soldered them. I cant figure this out. There was nothing hot enough that I felt that would even come close to desoldering a connection like that, let alone 3 of them all at the same time??? I think would have done more damage than that if the motor got that hot. I admit it wasn't the neatest soldering job, but it was solid and plenty of solder was on there.

I'm wondering has anyone ever reconfigured one of the Lehner motors before? Do I need to use some kind of special high temperature solder? Is there a "trick" to it that I'm missing? I re-soldered the connections and the motor works perfectly again.

Freaky problem.... Any ideas???

jhautz, I've never done what you have on a Lehner before, but I do know that it takes heat to desolder; and if your motor got hot enough to desolder the connections that you made, the desoldered connections would be the least of your problems. Obviously this is not what happened.

In what manner did you do the Y connection? Without having seen it, all that I can suppose is that in your effort not to overheat the little 3mm connectors on the motor when soldering, perhaps you made a series of cold solder joints that literally fell off. Or perhaps you used some solder that had a really low melting point. I know that I have some silver bearing solder paste that melts with the heat of a match.

[jhautz]

I just used some solder that I got from the LHS. I use it for everything and never had an issue. The guy at the LHS told me to gt it, that it was "the best" solder they carried. It sure doesn't seem to be a low temp solder. I usually have to run my soldering station all the way up close to 900 degrees to get a good fast solder joint. I don't think the solder is the problem, but if it happens again Ill have to see about finding some "high temp" solder. Anyone know of any?

http://www.lehner-motoren.com/downlo...use_s10-22.doc
This instruction sheet shows a diagram of the traces on the back of the motor. The breaks in the traces marked "D" and "S" are the spots where you bridge the gap with solder to make the connection in either the "D" configuration or the "star" configuration.

I removed the solder from the D connections and bridged the S connections.

I am wondering if maybe its possible that I didn't use enough solder on the bridges and they heated up locally from the resistance and melted themselves. The weird part is that it just stopped. All 3 melted at exactly the same time. Not sure if I can swallow that, but I don't have a better explanation. I used a little extra solder this time so hopefully that fixes it if that indeed was the problem.

I'm hoping that someone around here has some experience doing this. Its the first time I tried it. I think that CHC did it once for his High Voltage project. I'm just hoping this doesn't have the same disastrous ending as his project did.:032:

I had no idea that changing the configuration on a Lehner was so easy. The thing about your problem is that if the traces got hot enough to melt the bridges that you soldered, there would have been some residual heat there when you checked it.

What about using some small strips of copper to bridge the connections rather than just bridging them with solder? It might be better, but on the downside, if that strip desolders and slides, there's no telling where it might end up, and that could be bad. Very bad. LOL

[jhautz]

Originally Posted by AAngel

I had no idea that changing the configuration on a Lehner was so easy. The thing about your problem is that if the traces got hot enough to melt the bridges that you soldered, there would have been some residual heat there when you checked it.

What about using some small strips of copper to bridge the connections rather than just bridging them with solder? It might be better, but on the downside, if that strip desolders and slides, there's no telling where it might end up, and that could be bad. Very bad. LOL

I had both of these thoughts on the copper wire already... Great minds think alike.:D

I agree on the residual heat stament also. Also, if ithe whole motor got hot enough to melt solder I would think that I would have done some other damage somewhere else.

Hey, I'd just run it the way it is and forget that this ever happened.

Is it possible that you had a short in the motor leads someplace and they got so hot so fast that it didn't have time to heat up the whole motor? I'm guessing that your bridges were the weak point in the traces and they were just the first to go.

Another unsolved mystery.

[BrianG]

I'm thinking the heat of the motor didn't desolder it, it was the heat of the bridge itself that did it. Essentially, they acted like a fuse. Fuses use a small piece of metal that can only accept so much current before it heats up and eventually blows. I'm thinking this same thing happened to your LMT. If the solder bridges were too thin, or the solder had a higher resistance. Higher solder resistance means more voltage will be dropped across the bridge for a given current, which produces power (heat) to the point where it melts. You might want to try a better quality solder - maybe something with silver in it instead.

[pb4ugo]

Were there any impacts involved? My first thought was that the joints were cold ones and the solder bridge vibrated off as opposed to melting off. Possibility?

[Finnster]

I was thinking what Brian (basically) said. Your solder joints were crappy. :P

Too much resist thru the joint and melted it. Rest of motor could stay cool tho. Its a bit strange more than one did it. I would think one would go and thats the end, but I don't see any other likely explaination.

[BrianG]

Lol, yeah I maybe got a little "wordy" when "bad solder joint" would have sufficed. :)

I doubt the joints were that bad that they simply fell off. I suppose it is possible if the joints were VERY cold and did not bond to the existing solder.

When you resolder them, I would use solder containing silver for a lower resistance connection, and make sure you get the existing solder hot enough to bond well. That may be difficult since the motor acts like a large heatsink. I have a 250W iron that I use for large jobs like that (and things like soldering 2GA wires together :)).

[rchippie]

I had a a motor desolder once but it was a brushed 17t motor in my emaxx.

[What's_nitro?]

If your using end-to-end joints, you need to make sure BOTH sides of the joint get soldered. I had some problems with the solder not flowing around the whole wire, even with both sides tinned. In that case only half of the joint's cross-section would be soldered at most. Most likely this would cause localized heating and the joint would fail. The one thing that gets me is that they ALL failed, at the exact same time, too, because otherwise not all of them would have failed.

Edit: LOL. This took a while to write but BrianG has the same idea.

[jhautz]

I didnt think I had any issue with the solder joint. I had the sloder flowing very well on the surface of the trace. It was one continuous bead. I wish I would have taken a picture of it after it quit on me. It looked like it flowed perfectly to break the connection on the trace. It was claner than the ones I broke on purpose. I just resoldered it and this time used alot more solder. Its just a taller bead that I used this time. It must be that there just wasnt enough cross section to handle the current and it heated locally. Its the only thing I can think of.

Edit: It wasnt a cold solder joint. If you saw it in person you would understand. I dont think it wouldbe possible to get it to bridge the gap and be a cold solder joint. Its not like a little bead sitting on there. The entire trace on the back of the motor is completely covered in a heavy bead of sloder. I can tak a picture of it later tonight if you want to see what it looks like now.

Brian. I was able to heat the solder to the point here it flowed on the trace when I tipped the motor side to side. Getting it hot ebought wasnt really a problem. I used a 50W Hakko soldering station jacked up all the way to 900 degrees.

[BrianG]

I wasn't questioning your solder abilities, just thinking of the possible causes. I too think the bridge wasn't thick enough, or maybe the solder itself has more resistance due to the metal composition (tin/lead vs tin/silver).

You might want to temp the bridges after a couple minues of running to see if there are any hot spots.

Also, if the solder simply melted off, you'd think there would be some visible evidence of "dripping", or some solder splats on the chassis...

OK, if you're using a Hakko, heat isn't a problem while soldering. The silver solder idea sounds good to me. When I was into my other hobby, I used to mess with electronics where .01 ohms of resistance would make a difference. I started using silver bearing solder and there was never any measureable increase in resistance through a well soldered joint.

Lately, I've been using the roisin core silver bearing solder from Radio Shack and it's been working well. Doesn't add any (measureable) resistance and makes for a heck of a mechanical bond too.