A live chassis.

[Black5]

Evening all,

While installing a dcc chip in a loco the other day I noticed that the chassis was live. As the driving wheels are insulated Romfords, could it be that the insulation has broken down ? (if that`s possible ) and is making the chassis live through the axles? If that is the case my other question is , does this affect the use of the decoder at all in any way?

The loco runs fine on DC and has also been running using a basic Hornby decoder on a Portescap motor. The intention is to fit a ZIMO decoder once things are back together.

You might say, if it`s running alright just carry on, but I wondered if there was a problem in the future it might be difficult to decide if it was the decoder or the live chassis.

Changing the wheels will be a thing I will do but I was curious to know the answer to the other questions.

 

Many thanks,

Jim.

[Il Grifone]

It doesn't actually matter if the chassis is live to the wheels as long as the motor brush gear is insulated from the chassis. That is, there must be no contact between the decoder outputs and anything other than the item being controlled:- motor, lights smoke unit etc.

 

If the driving wheels are all insulated they should not be live to chassis however. Check that none of the wheel tyres is touching the chassis. It may need a thin washer on the axle. The insulation could break down but I have never had it happen.

[34theletterbetweenB&D]

Based on experience my opinion is that a live chassis is a hostage to fortune with DCC. The decoder and motor (and any other powered accessories) if properly isolated are not the problem. The potential for occasional momentary shorts on the running gear is the problem. (Also that if the loco is metal bodied and there are any others of the same construction they must be maintained live to the same rail, unless all bufferbeam fittings are insulating.)

[Black5]

II GRIFONE and 34theletterbetweenB&D

 

Many thanks for your replies,

I understand totally the need for insulation on the brushes, having two other metal bodied/brass chassis locos which work fine. Further checking has revealed only one wheel appears to have insulation that is working. all the others are live to the axles. One of the reasons I stripped everything was the fact that I noticed the valve gear was live as well so my feeling was that I was looking at a possible list of problems as you say.

All the axles have washers fitted so I`m pretty certain nothing is in contact with the chassis from that point. The last thing to check is the balance weights , which are etched brass, but are inboard of the insulation band. If that proves ok then a new set of drivers will hopefully put things right.

Like 34, I`ve never come across this problem before but I suppose it can happen.

Best wishes,

Jim.

[JeffP]

Are you certain you don't have UN-insulated wheels on one side?

[Black5]

Hi JeffP,

Thanks for your reply,

I`ve always fitted insulated drivers simply because it hopefully reduces the chance of any problem that might arrive in that area. However, you could be correct and time has dimmed the memory. I will double check though.

 

Jim.

[Black5]

HI JeFFP,

I have to hold my hands up and say, " you were correct " . I have absolutely no idea why but three drivers were un-insulated. I hadn`t checked that thoroughly because  I don`t ever remember buying non insulated. Anyway, your suggestion proved me wrong and I thank you for that and while everything is stripped down I`ll renew all the wheels.

I`ll go and look for the hat with the big D on it!!

Many thanks once again,

Jim.