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Through Board Desoldering High Melting Point Solder

Started by Bret Cahill September 14, 2020
The power wires for a 500 watt ebike motor go through the board.  It there any off the shelf insulator designed to protect the caps and other components only 13 mm away?  This is asking for a torch.

Bret Cahill


Bret Cahill <bretcahill@aol.com> wrote:
> The power wires for a 500 watt ebike motor go through the board. It there any off the shelf insulator designed to protect the caps and other components only 13 mm away? This is asking for a torch. >
Two suggestions: Don't start with a torch! Post a link to a photo (or two) to sci.electronics.repair It would help to explain the reference to "High Melting Point Solder". 500 watts isn't a lot of power. Normal solder and 12 AWG wire is sufficient under most circumstances to carry it. An old Weller WTCP with a blunt 800 degree tip can handle that sort of job. It has to be used quickly, the board material will degrade fast. HTH, bob prohaska
On 2020-09-14 14:08, Bret Cahill wrote:
> The power wires for a 500 watt ebike motor go through the board. It there any off the shelf insulator designed to protect the caps and other components only 13 mm away? This is asking for a torch. > > Bret Cahill > >
Try Chip Quik. It's a bismuth alloy that should make the high-melting solder lower-melting. Cheers Phil Hobbs
> > The power wires for a 500 watt ebike motor go through the board. It there any off the shelf insulator designed to protect the caps and other components only 13 mm away? This is asking for a torch. > > > > Bret Cahill > > > > > Try Chip Quik. It's a bismuth alloy that should make the high-melting > solder lower-melting.
At first hard to believe amalgamin' can do that sort of thing. But then I positively zuck at materials. I'll give it a try. Thanks. Bret
On Sunday, 20 September 2020 05:38:57 UTC+1, Bret Cahill  wrote:

> > > The power wires for a 500 watt ebike motor go through the board. It there any off the shelf insulator designed to protect the caps and other components only 13 mm away? This is asking for a torch. > > > > > > Bret Cahill > > > > > > > > Try Chip Quik. It's a bismuth alloy that should make the high-melting > > solder lower-melting. > > At first hard to believe amalgamin' can do that sort of thing. > > But then I positively zuck at materials. > > I'll give it a try. > > Thanks. > > > Bret
There's a reason they used HMP, so you may want to be thorough about removing the bismuth.
> > The power wires for a 500 watt ebike motor go through the board. It there any off the shelf insulator designed to protect the caps and other components only 13 mm away? This is asking for a torch.
> Try Chip Quik. It's a bismuth alloy that should make the high-melting > solder lower-melting.
I tried some with an 85 watt Weller and it didn't do much. I bought a used 260-200 watt Weller and it worked after multiple applications. I was wondering if this hack is common: Since I didn't want to cut off more than a few millimeters of wire for a nice clean packed end I was stuck getting about 40 kinked strands, bits of solder still clinging to them, 3 mm effective diameter, back into the 2.5 mm hole in the circuit board. I wouldn't be surprised if there was a dedicated tool -- they got a lot of cool time savers in electronics -- for crimping all the wires into a nice tight round bundle. I was going to try an insulation stripper tool but maybe it was in the storage locker. It's really frustrating to have a tool, especially one that probably won't work, and not be able to find it. It's like wasting time^2. I was still feeling unlucky when I got some nylon thread, wrapped it around the frazzled copper about 15 - 20 times for mechanical advantage and pulled, tourniqueting them to hexagonal close packing. _It actually werked_! Anyway gearless high torque hub motors shouldn't be used on hills. When the axle reams out the torque arm it spins, reeling up the wires, yanking them out of the circuit board. I can't read any markings on the wires but I measured a strand at 0.3 mm dia. 40 X 0.07 mm^2 = 2.8 mm^2 for one wire. (This is a 38 volt system.) Ultimate yield strength of copper is 210 MPa or 210 N/mm^2. The force on the board when each power wire ripped out could have been up to 600 Newtons ~ 130 lbs. It's hard to tell what actually happened -- the bike mechanic was trying to resolder the wires in the inlet side next to caps, not through board -- but that's one rugged circuit board! I'll add some safety features: An easy disconnect between the plugs. The wires are two short now anyway. An easy disconnect shear pin for the torque arm on the chain stay to preserve the axle. A lower pedaling gear, 13 t instead of 12t. Bret Cahill
The original torque arm was 11 mm between flat sides.  I've been using a 10 mm open wrench to turn the axle which isn't all that mangled.

The axle was designed for a 10 mm torque arm. 

The slack from the loose torque arm allows the motor to build up momentum before it engages.  The impact destroys the torque arm.

Someone put the wrong torque arm on possibly a lot of GO Swissdrive ebikes. 

In case you are wondering I'm a metrologist and measure stuff.