75ZT Community

When the car electrics play up in various ways from parasitic drain to water ingress we face needing to disconnect the battery often while risking the bonnet opening release going wrong. If the alarm, wipers or whatever will not switch off at the same time the bonnet release plays up it all may feel a bit of an unwelcome challenge. So I am wondering about a battery isolator located hidden on the exterior or the car but now find remote isolators are common. Any thoughts on these:-

https://www.ebay.co.uk/itm/406733515560

https://www.ebay.co.uk/itm/306343796544 ... 9AWY4SEE42

https://www.ebay.co.uk/itm/297874160126 ... H1MF77QZ9A

Not sure of the benefit of fitting outside of the engine bay and would be mindful of any possible insurance implications in its use.

To properly isolate, it would need to be next to the battery. Running battery cables into the car and back out is a challenge.
EDIT: to add. All of those need to be fitted near the battery, which in itself is right. But there's not a lot of space. I'd also be concerned about the current carrying capacity of any of the relays. They will be fine for the car, but could be very underrated when starting. For example one says rated at 200A. A starter will pull twice that, at least until it starts moving, and then on a cold morning will still be high. All the relays I've seen as part of cars, are MUCH meatier when on the battery circuit. Final point, the relay consumes power when switched on, and that in itself would be a problem drain. So for the most part you would switch it off every time. In which case, why not opt for a manual switch under the bonnet, but switch it off before a problem occurs? There also appear to be cable operated ones, for track cars etc. So a switch under the bonnet, to a pull knob inside the cabin. Just a small bowden cable to route. Something like this:

https://www.demon-tweeks.com/uk/automot ... cable-akn/

A cable operated switch is fine when turning off, but you would still need to open the bonnet to turn it back on.

Seems better used as anti theft to me

daveo138 wrote:A cable operated switch is fine when turning off, but you would still need to open the bonnet to turn it back on.

That's a good point I hadn't thought of. But I do think it might still work for what the OP was proposing. A way to quickly disconnect the battery in case of problems if the bonnet also won't open.

Duncan, did you see my email

Devilish wrote:Duncan, did you see my email

Yes, replied.

Thank you all for the discussion. I am now wondering about these sorts of things
https://www.ebay.co.uk/itm/397064550839
https://www.ebay.co.uk/itm/295608277990 ... 3676062063
I am too aware how alive the car still is when we lock it and walk away. Rover 75s are getting older now and more will go wrong. Not only can a battery isolator switch prevent a fire when parked but in the coldest times of winter if we find something drains the battery when parked, having an isolator switch means we simply switch it all off when parked and deal with the problem when the weather gets warmer and drier. In due course I may see what I can do.

Would two switches in the one negative lead extension circuit work? Giving a choice of whether to use an internal switch or external switch that is hidden and so takes a bit of a stretch to reach?

Would anyone know what thickness of negative earth cable to order for this type of switch https://www.ebay.co.uk/itm/397064550839 Some say 110a while a google search suggests 25mm or 35mm.

Well I've looked at the circuits on RAVE, and it seems the main battery earth is 25mm sq. But that's a really short cable. So if you are adding any length you would want to upgrade from that. The current rating is kind of irrelevant as its volt drop that matters (which comes from cable resistance, and connection resistance). To be clear, a cable mm rating is the cross sectional area, in square mm. So your 25mm or 35mm, is actually 25mmsquare, not 25mm radius or diameter.