Monday, January 11, 2016

What is an RSU?


I was asked recently what an "RSU" is. I think I'd mentioned it on the blog somewhere and blithely thrown the term in without thinking about it.

Well, to answer the question, it's the box in the photo. Is that enough?


OK. RSU stands for Resistance Soldering Unit. It's a clever way of soldering two bits of metal together, or at least heating up the solder between two bits of metal so it melts and joins them together.

The box above has a black earth lead and a red positive. The red lead can be plugged into different sockets to vary the voltage coming through it. The unit is switched on with a foot switch.

The main use of the RSU, for me at least, is laminating brass bits on a kit. The part is tinned on the back with solder and then sploshed with some flux.

The earth lead is clipped to the kit. Then the item to be fixed is held in place with the probe. I press the foot switch and power flows and as it passes through the solder, the resistance is higher and causes the solder to heat up and melt. Take the foot off the switch, the power goes off and and the joint cools.

Nowadays this isn't a cheap bit of kit. Even when I bought mine it was over a hundred quid. Now the only UK supplier I know of, London Road Models, charges £190. Still, it's a one-time buy.

1 comment:

Paul B. said...

I have the same unit.
My dog knocked it off its shelf (don't ask...) which knocked out a rivet and bent the lead plugs. Worried that it was broken I handed it over to London Road Models to be checked over.
They looked it over, fixed the broken rivet and used it for a week to check that it worked as it should. It was fine.
After a couple of weeks I had an e-mail telling me the good news and that it was in the post.
I asked how much I owe them.
What about postage?
Nothing, just part of the after-sales service.
Should anyone want one of these (and if you do a lot of etched kit work sooner or later you'll want to investigate RSUs), talk to London Road Models.
And next time I see them at a show I shall take them cake.