Overdrive Electric Shock!

[Dicky]

In the last month I've had an electric shock from my overdrive switch on the gear stick, it's not every time and it's not too painful but it's a shock none the less! Just wondered if anybody had heard of this problem or knew what it might be? Could it be moisture getting into the unit?

I've got a Spitfire 1500 1976 MkIV which has now done almost 4000 miles  :) in the last 5 months since I purchased it but this problem has only just occurred in the last month.

Thanks
Dicky

[GT6 M]

:) :), it happens to most at some time ,

put some loot on, that it is where the gear lever, and the wire go thru, up to the switch,

it will have shortet oot,

or, one of the terminals inside the knob/switch have come of, thus shorting,


you will be able to get to the top bit easy, but no the bottom bit,!!!!!

may be tunnel out,

if it is, cut it where the console is, and put little brackets onto both sides, so you can hold them together,

will be easier the next time some thing goes wrang

regards  Marcus

[ghr630]

The only component in a Triumph's electrics that produces enough voltage to give you a shock is the coil. It is not possible to get a real shock at 12V you need 70-80 volts minimum. The coil produces extremely high voltages but at proportiionately low amperages so is fairly harmless.

[Deleted User]

ghr630 wrote:

The only component in a Triumph's electrics that produces enough voltage to give you a shock is the coil.

George !

You should know better - back EMF from the collapsing field of a relay or solenoid coil.

[lordleonusa]

Yes you certainly can get a nasty jolt from the aluminium gear knob, it's usually caused by the thin cable going up the hollow gearlever, becoming overloaded and the internal PVC insulation melting. They can also catch fire!

One of Triumph's mistakes, they did away with the Lucas relay on the late overdrives.

I suggested retrofitting the relay, a Lucas 6RA I believe from Canley Classics plus replace that gearlever cable with a new one from rarebits.

L  

[ghr630]

Ah should have read more carefully, he has the J type without a relay to insulate him from the solenoid. Either way, hardly a "shock" really?

[junkuser]

You can also get a pretty good boot from a starter solenoid as discovered when a metal switch was used temporarily in lieu of a starter button on an old Riley 9.

Needed to slip the finger off when releasing.

[cook1e]

Whenever the cable that runs through the gear lever chaffs through (something which happens every couple of years or so) One of the tell tell signs before the overdrive stops woprking is that I get a shock through the rivets on the back of my mountney steering wheel if I happen to be touching them when I switch the overdrive in.

So yes getting a belt from a Triumph overdrive is pretty common, but it's onlty a little shock, not going to give you any lasting damage but as Marcus says, you may have to take the tunnel out to fix it...

[andy thompson]

856 wrote:

In the last month I've had an electric shock from my overdrive switch on the gear stick, it's not every time and it's not too painful but it's a shock none the less! Just wondered if anybody had heard of this problem or knew what it might be? Could it be moisture getting into the unit?

I've got a Spitfire 1500 1976 MkIV which has now done almost 4000 miles  :) in the last 5 months since I purchased it but this problem has only just occurred in the last month.

Thanks
Dicky

I had this on my 2500 (J Type) and it was certainly a decent shock... electric fence style... no one believe me but my economy suffered until I fixed it LOL LOL ... I added more insulation between the gearknob switch wiring and the the actual metal... shrink wrap and some foam rubber did it for me

[ghr630]

I wish I could learn to keep my big mouth shut until I know what I'm talking about! I had no idea it was such a common phenomenon.

I can accept that a soleniod could  act as a step-up coil when shorted as decribed Kevin, but a relay?

[Nick Moore]

I've had this with a relayed D-type overdrive. I'd just fitted a new column switch, was holding it in one hand and flicked it with the other. Click - overdrive solenoid goes 'clunk', indicator lamp (fitted because I'm forgetful) lit up. Switched it off again - WOW! Having a bare leg languidly draped over the sill provided the perfect earth and conduit for strong language.

No idea what the voltage was - somewhere between sticking your tongue on a car battery and finger in a light socket.

[Deleted User]

ghr630 wrote:

I can accept that a soleniod could  act as a step-up coil when shorted as decribed Kevin, but a relay?

George,

Think Ohms Law.

When the steady state curent is flowing in the coil of the solenoid or relay it has a nominal 12V across it, and will be pulling some current (say 100mA for a relay coil) and will be generating a magnetic field around the coil.  

When you disconnect the supply to the coil, the magnetic field collapses and induces a voltage in the coil.  As there is no load on the coil (apart from a meg ohm or two caused by you touching it) the resultant voltage that will be momentarilly generated is much greater than 12V as the current flowing will be tiny in comparison to when it was being powered, hence the shock.  

The voltages can spike at seveal hundred volts, but you need a very good oscilloscope to capture the waveform properly.

With some coils the voltage spike has such a high rise time that it can defeat the earth bonding and you can get a shock off something that is earthed - this was not uncommon with LOPT coils in CRT's if the service engineer was touching the earthed chassis when turning the thing off.

[Dicky]

Thanks for all the advice, gonna have to wait til the new year to get it fixed now but at least I know it's not major.  :)

[GT6 M]

Dicky, two things to do in the meantime,

1,  wear gloves,

2, put a ..Jonny.. or the like over the gear knob,   ;) ;)

Marucs

[don cook1]

Quote:

but you need a very good oscilloscope to capture the waveform properly

Quote:

put a ..Jonny.. or the like over the gear knob

Don't you just love the diversity of forum members?

[jonnyk5614]

I still do a paper round and every morning, I get 8 hours of static acumilation from the badly earthed lift switch. Can be seriously painful!

Also, try putting your palm on scaelextric track when the controller is full throttle.

You'll just have a worn and shorting cable mate.