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Author Topic: over heating capacitors  (Read 2085 times)

lozvik

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over heating capacitors
« on: January 01, 2010, 05:23:55 PM »

does anyone know if excessive heat from soldering iron can damage motor capacitors?
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chingdevil

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Re: over heating capacitors
« Reply #1 on: January 01, 2010, 07:12:36 PM »

If they are ceramic capacitors, yes it can. Why do you ask??


Brian
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lozvik

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Re: over heating capacitors
« Reply #2 on: January 01, 2010, 07:29:44 PM »

its a long story, but to give u an idea ive fitted some mtroniks caps to my twin motors due to interference, and they solved the problem, however, since then ive had the motors out and had to unsolder the wires and then resolder which was quite difficult and i seemed to have to hold the iron on the terminals forever, now it seems i have the interference back again so wondered if ive fried the caps?
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chingdevil

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Re: over heating capacitors
« Reply #3 on: January 01, 2010, 08:45:34 PM »

You could have dry solder joints that would give you the interference back, but if you had to hold the soldering iron for a long time on the terminals I would suspect the caps are u/s.
If you are holding your soldering iron on the terminals for a long time, is it powerful enough for the job??


Brian
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lozvik

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Re: over heating capacitors
« Reply #4 on: January 01, 2010, 09:19:50 PM »

I suppose they could be dry joints, not too sure, is that when it looks dull like an aliminium sort of look? my soldering iron is 25w so maybe its not man enough to solder 2  14awg wires together
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malcolmfrary

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Re: over heating capacitors
« Reply #5 on: January 02, 2010, 11:01:41 AM »

The rule for soldering, and unsoldering, is always to be in and out QUICK.
With a modest sized iron, having wet solder on the tip is a good idea, as you get the best possible surface area for heat transfer.  when unsoldering, having the resin smoke a bit is good - it helps cut through the joint surface and melt the solder faster.  This means that the joint gets hot enough to melt before the temperature has time to travel to the delicate bits of the component.
It is at times like this that you begin to appreciate that an immovable mechanical joint before soldering is not such a good idea.
When re-done, the solder should be nice and shiny, with a concave meniscus, rather than looking like a blob.
Fortunately, it just looks like the capacitor has died, but these are generally cheap items.  The worry is when the motor terminal goes all wobbly............
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lozvik

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Re: over heating capacitors
« Reply #6 on: January 02, 2010, 11:48:08 AM »

The rule for soldering, and unsoldering, is always to be in and out QUICK.
With a modest sized iron, having wet solder on the tip is a good idea, as you get the best possible surface area for heat transfer.  when unsoldering, having the resin smoke a bit is good - it helps cut through the joint surface and melt the solder faster.  This means that the joint gets hot enough to melt before the temperature has time to travel to the delicate bits of the component.
It is at times like this that you begin to appreciate that an immovable mechanical joint before soldering is not such a good idea.
When re-done, the solder should be nice and shiny, with a concave meniscus, rather than looking like a blob.
Fortunately, it just looks like the capacitor has died, but these are generally cheap items.  The worry is when the motor terminal goes all wobbly............

how wobbly is allowed and what will happen? ive just checked and one side seems pretty firm but got to admit the other side is a little "wobblier" than the other, it still working though, well at the moment anyway
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wombat

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Re: over heating capacitors
« Reply #7 on: January 02, 2010, 12:22:24 PM »

Hi Lozvik,

You can overcook ceramic capacitors but it does have to be fairly extreme to get them to fail.
I suggest replacing the capacitors - but what I would do is snip the old ones off at the capacitor body and solder the new ones onto the wire stubs of the old ones rather than onto the body of the motor - you already have a joint there.

When soldering onto large terminals or onot motor cans, especially if your iron is not really up to it I suggest the following tactic:
1/. Clean well - this is critical for a good solder joint - use a coarse sandpaper or emery
2/. Well tin the iron so there is a small bead or bulge of solder on the tip - though not a blob - this indicates the iron is dirty and you will not get good heat transfer.
3/. Apply the iron to the motor case or terminal where you have cleaned with the bead touching the point you want to solder at and using a firm pressure.
4/. Apply the solder to the point of contact between the iron, the bead of solder on thew iron and the thing being soldered.
5/. Hold firm until the solder starts to melt and flow on the surface without blobbing.
6/. Allow the solder to cool and see if iti is firmly adhere - if it doesn't pick off then you are OK - if it does repeat until it doesn't
7/. This is where you will need about three pairs of hands - form the wires on the capacitor so it will be in the right place
8/. Tin the wires
9/. Place the wire in place on the solder bead  formed in 5
10/. Tin the iron and apply to the wrie and bead until the surface of the joint melts and flows around the wire.
11/. Allow to cool

I hold that the secret of a good solder joint is a good mechanical joint - it prevents movement which can damage the joint while cooling , particularly as the solder goes through the "pasty" stage. It prevents stresses foroming in the joint because movement during cooling. Sometimes you cannot avoid it but try to minimise it

As for wobbly on the motor terminals - wobbly is not good as the commutator alignment may be off and this could give some problems.

Wom
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lozvik

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Re: over heating capacitors
« Reply #8 on: January 02, 2010, 12:31:01 PM »

cheers for the info, ive ordered some new caps so ill replace and see what happens
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malcolmfrary

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Re: over heating capacitors
« Reply #9 on: January 03, 2010, 11:55:35 AM »

Well explained Wombat.
My point about the immovable mechanical joint was that if you wrap several times and tie a knot before soldering, come unsoldering time there is a much larger job causing potential damage to the surroundings.  A firm joint that will last until the soldering has done its work is another thing again.  This need be nothing more than 1.5 turns of wrap for a tag, or a simple hook through and crimp for one with a hole.  Assuming everything is clean.
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peter.dwight

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Re: over heating capacitors
« Reply #10 on: April 23, 2010, 10:29:47 PM »

Greetings.
 Some thoughts on the comments regarding soldering and mechanical connections. There are 2 schools of thought.
One says that a good mechanical joint will keep the component in place and not allow a short circuit to occour if the joint fails and the component is free to move about. The aircraft manufacturers/RAF tend to follow this line of reasoning which is fair enough as the reasoning makes sense. The big problem is that it can hide the dreaded 'dry joint'. A component may look soldered but inside there is an unreliable connection, but it will not fall off.

The other school of thought is just the opposite, when I worked for the London Underground Signals and Telegraph Dept, mechanical joints were banned. The danger of an unreliable mechanical joint in signaling systems just cannot be tollerated, so all joints were soldered only. The terminal was tinned and the wire was tinned, the wire was laid on to the terminal and the two parts were soldered together. Each joint was inspected by an inspector, pulled to see that it didnt move and them marked with a dye to show that it had been inspected and deemed fit for service. Neither were you allowed to use sleeving over a joint because it could hide a broken wire.

As far as our hobby is concerned we are not going to cause major incidents if our soldering fails but we might well loose our boats/money and time invested etc. Soldering is not a black art it simply requires that you understand how it works and the correct method of applying the iron and the solder to the work.
Basicly, both parts have to be clean, both parts have to be tinned then brought together, the iron applied to the joint firmly and solder fed in untill a clean joint is formed, remove the solder, remove the iron and a good joint will be formed.
I am interested to hear your comments.
Peter.
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awvs

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Re: over heating capacitors
« Reply #11 on: April 24, 2010, 01:19:25 AM »

I always add some extra solder dipped in flux paste in order to unsolder connection or components. Very often there is not enough paste inside the solder string. This way, heat transfer from the iron is guaranteed and unsoldering no problem at all. Do not forget wiping off the extra paste. By the way, I use a temperature regulated solder iron (Weller) with exchangeable tips.

Regards
Wilhelm
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FullLeatherJacket

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Re: over heating capacitors
« Reply #12 on: April 24, 2010, 06:50:03 AM »

Just as an aside for Mayhem UK members, I saw a fairly hefty-looking soldering gun on sale in Lidl yesterday for a tenner. Sure beats Weller's price!
FLJ

http://www.lidl.co.uk/cps/rde/xchg/lidl_uk/hs.xsl/index_9904.htm
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