Battery Isolator-which one!

[Colin Wilks]

To echo Simon's point, I would avoid the cheap jobs. I had a "red key" cut out fail and it caused a little head scratching since the switch still showed electrical continuity when closed and none when open, so appeared to be working, but it had deterorated so that it couldn't handle the high current for the starter. To be fair, it was about fifteen years old.

Colin

[Paul Nott]

Thanks Guy's
Many different opinions on how to wire and what isolator to use.
I have decided to fit a Lucas SSB106 to the negative battery lead, keeping it as short as possible.
The switch will be located to the floor above the battery, exact position to be decided once floor and interior have been fitted, I'm shortly to retrim interior and modify seat position to give more room.
The on /off is a turn switch so hopefully accidental usage will be avoided.
Many thanks.

[jansens]

Chris, it looks like full on racing switches shut off the battery, ignition and short out the alternator via a resistor. Like these ones: https://www.pegasusautoracing.com/produc...RecID=1464

Dave, that makes sense about the cutout. At low revs I guess it is the battery supplying the ignition and it's not until the cutout switches in that the dynamo takes over. I wonder then if the engine is revved and the battery disconnected will it keep running while the revs are high. I guess so but not something I want to try!

Paul, that Lucas one will work fine as a battery isolator. The black switch won't look too out of place on an old car too. I like the red removable key (which looks modern and plastic unfortunately) type because I always have the top down on the MGB so when I park it it is nice to know I can take the key and someone can't come and switch the lights on or something silly (not that anyone ever has).

Simon

[Colin Reed]

Chris, it looks like full on racing switches shut off the battery, ignition and short out the alternator via a resistor. Like these ones: https://www.pegasusautoracing.com/produc...RecID=1464

Dave, that makes sense about the cutout. At low revs I guess it is the battery supplying the ignition and it's not until the cutout switches in that the dynamo takes over. I wonder then if the engine is revved and the battery disconnected will it keep running while the revs are high. I guess so but not something I want to try!

Paul, that Lucas one will work fine as a battery isolator. The black switch won't look too out of place on an old car too. I like the red removable key (which looks modern and plastic unfortunately) type because I always have the top down on the MGB so when I park it it is nice to know I can take the key and someone can't come and switch the lights on or something silly (not that anyone ever has).

Simon

HI Simon,
It was Common practice before alternators  To fit a charged Battery start the engine increase the Revs then change  back over to the flat and away you go

Colin
NZ

[Roland Alcock]

I once had an "incident" where my passenger had somehow pushed hard with his feet and shorted out the live battery feed. When I went to isolate the battery, the green knob type of switch, had melted and welded itself together. Fortunately the right spanners were to hand to disconnect the other battery terminal. A bit of a scare that was.....

I now use. 

Roly

Wouldn't the same thing happen with this switch ?

Na! The green knob switch has a plastic insulator sleeve and this had melted away with the heat of the short. To be fair all the insulation on the battery to starter motor cable had also disintegrated. I was very fortunate that the incident didn’t end up with a fire. The battery didn’t mind the abuse and is still working well two years on. 

The type of switch I now use , like the red handle one has a construction more like the bacon slicer foot switch. 

Roly

[AustinWood]

Disconnecting the battery with the engine running and the dynamo charging is not a good idea.
The three brush dynamo tries always to supply the current for which it is set up and increases the voltage to achieve this.
It happened to me in 1967 when I bump started my 1934 tourer down the drive at 4am in the winter, intending to drive from Cambridge to Dundee. The battery failed and went open circuit. The sidelights were on, they lit up so bright that they illuminated the whole garden then failed. The ignition warning light lit the whole inside of the car then failed.
I shorted out the dead cell and drove to Dundee on 4 volts. An interesting journey, but that's another story.

[Ian McGowan]

To echo Simon's point, I would avoid the cheap jobs. I had a "red key" cut out fail and it caused a little head scratching since the switch still showed electrical continuity when closed and none when open, so appeared to be working, but it had deterorated so that it couldn't handle the high current for the starter. To be fair, it was about fifteen years old.

Colin

As with Colin's experience, I have recently had a "red key" switch fail on starter demand after about 20 years service; I found how to get a good quantity of Servisol switch cleaner into the little devil and, after about 20 "no-current" operations, the approx. 1Ω contact resistance, that was the problem, dropped to a few milli ohms. Problem solved for the time being but, replacement switch on the shelf!!

[Steve Jones]

To echo Simon's point, I would avoid the cheap jobs. I had a "red key" cut out fail and it caused a little head scratching since the switch still showed electrical continuity when closed and none when open, so appeared to be working, but it had deterorated so that it couldn't handle the high current for the starter. To be fair, it was about fifteen years old.

Colin

As with Colin's experience, I have recently had a "red key" switch fail on starter demand after about 20 years service; I found how to get a good quantity of Servisol switch cleaner into the little devil and, after about 20 "no-current" operations, the approx. 1Ω contact resistance, that was the problem, dropped to a few milli ohms. Problem solved for the time being but, replacement switch on the shelf!!

Sorry Ian. Is that the switch I fitted. If so, apologies but the guarantee expired a long time ago.

Steve

[Dave Mann]

I don't normally switch the isolator off with the engine running however, very occasionally a senior moment takes over.

[AustinWood]

Thanks Dave! Your post reminded me that I switched my isolator (On -ve battery post) off while working on the car yesterday.
Senior moment overcame me and I hadn't switched it on again.
Car now ready for Borders Vintage Automobile Club run tomorrow.