Series 3 - Battery Isolator

Jacksprat · Dec 13, 2017

Hi all,

Help please..

The plan:
I am planning to install an isolator switch in my series 3. The battery is located in the engine bay. I am planning to install it on the negative (earth side), not as a kill switch but to prevent the battery draining and also for security. I don't have any electrics that will need to be kept running whilst the car is parked. I want to operate the switch from the cab so am planning to put it through the bulkhead, this means running the earth the length of the engine bay from the battery to the switch and then from the switch to a suitable place on the body or chassis.

The Question:
Will it be ok to have such a long earth cable? Does it matter what thickness of cable I use or is it a case of the thicker the better? Are there any other flaws in my plan?!

Thanks

Jam1 · Dec 13, 2017

Why not use a heavy relay close to the battery and a thin guage wire running to a small switch in the cab?
Yes that means you would need a permanent circuit of pos and neg to the switch but it's a lot easier and cheaper

blue beasty · Dec 13, 2017

Why not fit to the seat box then you can just loop under the bulkhead instead of going through?

Length doesn't make a lot of difference but needs to be as thick as the original as a minimum.

Edlandy · Dec 13, 2017

I'm far being an expert but Shirley it should be on the positive side?

rob1miles · Dec 13, 2017

Agreed, I don't think you can do it on the earth side as you can't isolate the starter earth unless its full current and there are lots of earths on the harness and the body is earthed to teh chassis and engine/starter. You put the isolator in the main live feed to the fuse box, mine is on the batt postive but the starter feed is not isolated so the isoltaor is only taking (say) 30 A not 100s. I also don't isolate the main alternator feed as it can be a bad idea to disconnect the alterntor from the batt when its running. Obviouly that would be an error but mistakes happen. The running current on my 2hp starter is 120A.

oxides · Dec 13, 2017

You can put the isolator in either cable - as long as it isn't bypassed in any way. On the other hand, as there is no drain on the battery on a series it won't go flat anyway so you don't need one! If you're getting battery drain and you haven't fitted anything that uses current with the ignition off then you have an alternator fault.

Jacksprat · Dec 14, 2017

Jam1 said:
Why not use a heavy relay close to the battery and a thin guage wire running to a small switch in the cab?
Yes that means you would need a permanent circuit of pos and neg to the switch but it's a lot easier and cheaper

Hi Jam1, I think that this is a great idea. I had thought about it but i was worried about the reliability of the relay switch. Can you recommend a good one? Thanks for your help.

Jacksprat · Dec 14, 2017

oxides said:
You can put the isolator in either cable - as long as it isn't bypassed in any way. On the other hand, as there is no drain on the battery on a series it won't go flat anyway so you don't need one! If you're getting battery drain and you haven't fitted anything that uses current with the ignition off then you have an alternator fault.

Oxides, this is a good point and I have yet to test the alternator with my new multimeter but I want an isolator anyway as an extra level of security..

cornish rattler · Dec 14, 2017

If your using the vehicle off road make sure the switch is up high and out of the way from mud and water as not all isolator switches are waterproof

rob1miles · Dec 14, 2017

Mine came with an isolator fitted on bat positive in parallel with the starter cable - it fixes to the terminal bolt and switches everyting except the cable to the starter and the alternator output. As its under the bonnet that has been modified to be lockable - a padlock. Not elegant but it came that way and now the hole is there it may as well get used. I normally drive withthe padlock off but its handy to be able to fit it when I'm leaving it overnight.

Jacksprat · Dec 14, 2017

cornish rattler said:
If your using the vehicle off road make sure the switch is up high and out of the way from mud and water as not all isolator switches are waterproof

That is a good point.. anyone know of a good one preferably water resistant if cost not too much!

samc88 · Dec 14, 2017

I have a marine isolator switch (the one with a big red key) on the positive wire and is located in the seatbox. Annoying thing with it I forgot to put a permanent live to my radio so it has no memory of stations. Other than that it works perfectly

rob1miles · Dec 14, 2017

I made the same mistake with the radio, should have kept the one with the mechanical presets (doh). It didn't matter when I couldn't hear the radio but since the engine rebuild I can.

samc88 · Dec 14, 2017

Jacksprat said:
That is a good point.. anyone know of a good one preferably water resistant if cost not too much!

Not much, look at marine ones

suburban · Dec 14, 2017

I did mine on the negative battery terminal purely because it was easiest, just as an additional security measure, there was no drain prior to fitting it you could leave the battery for months and the car would still start

Flossie · Dec 14, 2017

samc88 said:
I have a marine isolator switch (the one with a big red key) on the positive wire and is located in the seatbox. Annoying thing with it I forgot to put a permanent live to my radio so it has no memory of stations. Other than that it works perfectly

Just link across the isolator with a 3amp inline fuse holder.

neilly · Dec 14, 2017

Flossie said:
Just link across the isolator with a 3amp inline fuse holder.

This is similar to what I have on my 90 for when I want to leave it for a while. On the bay.

261105200197

Cheers

Flossie · Dec 14, 2017

Yarp, I had similar and it was all inside the seatbox, however, I kept forgetting to insert the big red isolator key and the fuse would blow meaning kicking the Doris out of her seat so I could replace the fuse. I thought I would learn to remember the key after a while but I didn't

so I fitted a bulkhead fuse holder on the front of the seatbox so I could change the fuse easier.
I still kept forgetting

so I replaced the fuse with a resettable one so if I forget it's just a case of pressing a little button in to reset it.

samc88 · Dec 14, 2017

Flossie said:
Just link across the isolator with a 3amp inline fuse holder.

Even easier to go off my common live
Easier still is to use the aux and my phone

Bobsticle · Dec 22, 2017

Even easier............................Take the distributor cap with you.

I know I know, no help at all. I just felt a bit left out.

Series 3 - Battery Isolator

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