Soldering RF interference motor capacitors.

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8 January 2010 at 06:26 #24905
Rick Devonshire
Participant
@rickdevonshire
We all find it necessary to solder these capacitors across the electric motor terminals form time to time. Very often there are two capacitor leads togther with a much thicker power lead which need securing with solder at one go. Then two more capacitor leads require soldering to the motor case.

I am always concerned in case the heat from my iron travels up the wires and damages the capcacitors. Is this likely to happen or are my concerns unjustified?

If so how best do I guard against damage?

Rick.
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8 January 2010 at 06:26 #5062
Rick Devonshire
Participant
@rickdevonshire
Just how vulnerable to heat damage are they?
8 January 2010 at 09:08 #24907
Bob Abell 2
Participant
@bobabell2
I also find this job rather tricky, Ricky…… and awkward

I use a biggish solderering iron and tin the motor casing first, making sure the casing is quite hot, then blob the wire on quickly

Make sure the casing is clean and fluxed before you start the job

Bob
8 January 2010 at 12:44 #24913
Telstar
Participant
@telstar
Hi Rick When soldering heat sensetive components I always clamp the component lead with forceps they act as a heat shunt. Also as Bob says clean the motor case well, and ‘Tin’ the motor first ie coat the area for the connection with solder, Before attaching the component.

Happy New Year Tom
8 January 2010 at 13:54 #24914
Dave Milbourn
Participant
@davemilbourn48782
Here’s some very useful stuff from Dr Tim Fawcett, who designs most of our gizmos and who posted this recently on Mayhem:

“When soldering onto large terminals or onto 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 it is firmly adhered – 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 wire 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 forming in the joint because movement during cooling.
Sometimes you cannot avoid it but try to minimise it”

I find that many of the motors I use have a small hole through the terminal posts; this is great as you can then thread the lead from the capacitor through it and wind the lead around the terminal so that it holds firm without solder. Then simply solder up the thin lead at the same time as you fit the thick power lead.

Dave M
8 January 2010 at 17:13 #24916
Colin Bishop
Moderator
@colinbishop34627
A lot of motors have screw mounting threads on the front of the case. Whether or not you are using them, they can come in handy for making an electrical connection to the case using a solder tag and suitably sized screw. No need to make a direct solder connection to the case then.

Colin
8 January 2010 at 18:25 #24917
ashley needham
Participant
@ashleyneedham69188
The question regarding harming capacitors is a good one….after all, its difficult to solder to a motor casing, and then, having achieved that…do you know that the capacitors are working well or not???

Some Graupner small cans come pre suppressed and its a shame they dont ALL come with this as standard.

Taking Colins suggestion a step further, most mounting includes some clampy arrangement and this could be used to hold a wire on to the can surface,,

I see a project here for someone with a meter and some spare capacitors to test them first and then torture the ends with a soldering iron for varying lengths of time, and then test them again to see how they have degraded, or not.. assuming you dont use a pair of thin nosed pliers to act as a heat block on the capacitor leg.

It makes you wonder really.. how many chaps have been busy soldering away to no avail as they have b#####d up their capacitors??? all those forum questions regarding interference !!

Ashley
9 January 2010 at 11:18 #24930
Dave Milbourn
Participant
@davemilbourn48782
You really have to go some to damage a ceramic capacitor. I personally never bother with heat-sinks when soldering them to motor cans. FYI I use a 48W 24v solder station with a 3.2mm screwdriver-tip. Use old-fashioned resin-cored lead-based solder if you can; we only have to use lead-free for production units.

DM
9 January 2010 at 18:44 #24935
60watt
Participant
@60watt
1/32 plywood makes a great prototype circuit board for wire ended components, you know.

Punch or drill a piece of card which you can both insert component leads and also hold those cap leads in place against the motor terminals.In this particular case you want to chop or snip the card or ply off when finished.

Conveniently forget the two capacitors that are sometimes wired from motor terminals to the case.

Edited By 60watt on 09/01/2010 18:46:23
22 April 2010 at 09:11 #26515
HvyCGN-9
Participant
@hvycgn-9
I have a pair of the big Graupner 900’s in my USS Long Beach they R also pre-fitted with suppression cap’s. They R Beautiful motor’s !!

Cheers Bruce
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