What needs isolating?

I have a very old (30+ years) Hornby A4 tender-drive loco into which I'm considering installing a decoder. It has a Ringfield-type motor.

The loco body is connected electrically to the tender by a metal pin and a sort of 'pronged' metal clip. This means that one brush is supplied from the loco wheels and the other is supplied from the tender wheels.

There is loads of room in the tender for a decoder, and I would be quite happy to change the connection between the tender and the loco body to a hard-wired one if that would be better electrically.

What, if anything, needs to electrically isolated when I install a decoder?

Perry

Hi Perry

Three things are important.

Make sure the motor brushes are isolated from everything.

Make sure that the pickup wheels are isolated from each other.  It sounds obvious, but sometimes the body can cause short circuits on these old locos.

Cut the capacitors off the motor.

Thanks, Max. I'll check and alter as necessary.

:cheers

Perry

I have converted a few Hornby ringfield mechs, diesel or electric bogies very similar to the tender drives. As Max said, make sure the brushes are isolated. Some, but not all, of these mechanisms have the brushes already isolated, others, like the ones I did, have a metal screw going through one of the brush retainers and right through to the other side of the metal frame. My way of isolating this was to replace the screw with a plastic 8BA screw from an old K's kit - this was a perfect fit and completely isolated the brush. It was then a simple matter to solder the orange and grey wires to each of the brush retainers. The red and black wires went to the track, one via the now isolated frame using a spade connector attached to one of the cast on tabs on the frame.

I hope this helps a bit and is not too confusing.

I hope you don,t mind me asking a question on your thread Perry, Converting old Hornby loco,s. Changing the wheels to Romfords, Would it be best to use all insulated wheels rather than the old live one side, and insulated on the other, with DCC operation?

Derek, that does not matter as long as any lights & motor are completely isolated from the chassis with any wiring for lights & motor only coming from the decoder.

 

[user=95]Sol[/user] wrote:

Derek, that does not matter as long as any lights & motor are completely isolated from the chassis with any wiring for lights & motor only coming from the decoder.

Many thanks Ron, Thats saved me a headache! :thumbs