Lotus Elan

Mystery high current device.

PostPost by: billwill » Mon Jun 19, 2017 5:07 pm

While sorting out some speaker wires behind the left hand panel, I noticed after all this time (43 years ? ) that there was a mystery electrical object mounted in the main fat battery cable with the terminals covered with insulation tape.

It didn't seem to be doing anything useful there so (after disconnecting the battery in the boot) I took it out and bolted the resulting two ends of the battery cable together and taped them up.

The operating handle was evidently on a fine stem and has broken off, so I cant really tell if it was a push-pull switch or a rotary one. I tried both actions using an ohm meter and the two fat terminals seem to be always connected and the other terminal never connected.

Has anyone seen one like this before?
It is maybe a relic of when Malcolm Ricketts owned the car for its first year and did some hill climbing events (I think). Perhaps it was a batter isolation switch and the handle broke off.

The small terminal is labelled C-B, the large copper one near it is labelled B and the other fat one is labelled E. It appears to be made by LUCAS, but I cannot make out the part number. There is a number which might be 76605B4482

img_20170607_164528.jpg and
Mystery object


img_20170607_164505.jpg and
Mystery object
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PostPost by: lotusfan » Mon Jun 19, 2017 5:13 pm

Mike
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PostPost by: billwill » Mon Jun 19, 2017 5:15 pm

Aha, I found it.

It is indeed a battery isolator, though not much use now with the knob broken off.

https://www.autoelectricsupplies.co.uk/product/834
Image

The extra contact would be used to short the contact-breaker to earth (i.e. permanently close the distributor points) to abruptly stop the engine.
Last edited by billwill on Mon Jun 19, 2017 5:18 pm, edited 1 time in total.
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PostPost by: billwill » Mon Jun 19, 2017 5:16 pm

lotusfan wrote:Bill

Is this it perhaps?

https://www.holden.co.uk/displayproduct ... de=020.232



Yes, that is the same thing, but a modern replica version.

The original that I have here is a stupid design the bit that broke off with the knob is a mere 2mm diameter at the centre of a 4mm square shaft. It was bound to break.
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PostPost by: Andy8421 » Tue Jun 20, 2017 7:24 am

From a safety perspective, it was important to have the engine cut out circuit included or the engine would continue to run with the switch off and battery disconnected - the dynamo would power the ignition coil.

I recall seeing exactly that switch a long time ago in an Aston Martin DB5 boot next to the battery. I think it was a standard fitting. My father was considering buying the Aston, but at £5000 thought it was too much for an old car that needed some work.
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PostPost by: rgh0 » Wed Jun 21, 2017 11:43 am

With a battery isolator it is also advisable to wire the alternator output to the battery side of the switch. Otherwise if the switch is turned with the engine running not only can the engine keep running due to alternator output power still going to the ignition but you can also cause the alternator controller and rectifiers to fail with over voltage with the sudden loss of load when the battery is disconnected or for other electronics in the car to be damaged. See the attached description of options

http://www.adaptronic.com.au/battery-is ... ge-spikes/

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PostPost by: Craven » Wed Jun 21, 2017 12:50 pm

Clearly then under some conditions problems,
But in the illustration of a single pole switch the alternator always has a load, However in the 4 pole switch solution the alternator has no load AT ALL definitely a No No. Also safety wise, a direct high current route from the battery to engine bay still exits by returning the alternator to the battery, re an Elan.
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PostPost by: rgh0 » Wed Jun 21, 2017 1:29 pm

Yes - no simple complete solution

1. fully disconnect the alternator from both ignition and battery and may blow is internals
2. leave alternator connected to car ignition and may blow alternator and electronics in car and car may keep running
3. leave alternator connected to battery and alternator OK and car stops but still live wires inside engine bay.

I use option 3

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PostPost by: Craven » Wed Jun 21, 2017 2:11 pm

Interesting how people view the battery isolation switch, I think it should be just that, the high power source of a battery being isolated.
I thought most people fit the switch in the Chassis connection ie Battery Negative lead.
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PostPost by: rcraven » Wed Jun 21, 2017 4:28 pm

If your battery cut-off switch is there to comply with MSA or other similar competition regulations you need to take account of what Rohan refers to because it may be someone other than you who turns it off in an emergency when the engine is still running.
You can get isolators with auxiliairy switches for this purpose.
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PostPost by: 1owner69Elan » Wed Jun 21, 2017 6:06 pm

I fitted the following cut-off switch just recently at the tail end (hopefully) of my restoration. Obviously worried about protecting the effort (and money) put into the car over the last 2 years. Not on road yet.

https://www.pegasusautoracing.com/produ ... RecID=1464

I think this switch hopefully covers the bases that Rohan outlined.
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