Tell me about battery isolators

MikeHunt79 · 4 Jan 2009 at 13:57

Right now it seems my battery is going flat on it's own, so at the moment I have to put it on charge whenever I park... It's like driving a bloody electric car!

As my car is old (Pug 205), I don't actually need anything to be powered when parked, I don't care if my radio forgets it's radio stations, etc...

So, I was thinking a battery isolator would be the answer... The only thing I don't really know where to start.

a) Are they simply a high current relay? If so I'm familiar with how to wire them up...

b) Is a dash mounted switch the best thing to isolate the battery or would it better to do something else for added protection from having my car nicked?

c) Anyone fitted one and had any problem or nasty surprises?

Snaggle · 4 Jan 2009 at 14:40

Its just a passthrough switch where the handle makes the contact . Insert handle and circuit is made .
Not to hard to setup but will have to run some extended battery cables to your preffered mounting point and thats it .
Might be easier to trace the fault though ?

Persil

Overlag · 4 Jan 2009 at 14:50

surely it would be better to get a new battery?

Lopéz · 4 Jan 2009 at 15:22

Overlag said:
surely it would be better to get a new battery?

That won't do a lot of good if something is draining it.

Have you tried finding the cause of the drain? It can be a complete pain to work out.

Battery isolator is very very simple, if you can't be bothered to run it in the cabin (extending the wires) just put it in under the bonnet. Use a battery cut-off switch (about £5) which has a removable plastic key.

NathanE · 4 Jan 2009 at 16:15

One cause is "vampire currents"... i.e. things like your radio and alarm which keep on drawing small amounts of current.

But there is another... called self discharge. This is where lead-acid batteries lose charge over time... and it gets worse when temperatures get cold. That's why sales of jump leads rocket in the winter months.

Self discharge could be a sign that your battery is dying. Does your battery let you refill it with deionised water? Or is it sealed? I just refilled mine today and found that one of the cells was almost completely dry...

Get a reconditioner like http://www.optimate-sp.com/ which will "desulphate" the battery and restore it to a better condition.

Dogbreath · 4 Jan 2009 at 16:41

Could also be a "leaky" diode pack in the alternator.

Finglonga · 4 Jan 2009 at 16:48

Best fix the problem than hide it by putting a switch in IMO.

MikeHunt79 · 4 Jan 2009 at 16:54

Overlag said:
surely it would be better to get a new battery?

My current battery is only a year or so old, they normally last longer than that don't they?

Lopéz said:
Have you tried finding the cause of the drain? It can be a complete pain to work out.

I've tried taking out fuses and measuring current where the fuses were, I've also disconnected my alarm (it's useless anyway), but am none the wiser...

I've added a few extra relays over the years so I guess these can draw a small amount of power... I have a feeling that it's quite a low power draw, as it's fine if I leave it for 1 night, but if I leave it for a whole weekend it barely starts.

Lopéz said:
Battery isolator is very very simple, if you can't be bothered to run it in the cabin (extending the wires) just put it in under the bonnet. Use a battery cut-off switch (about £5) which has a removable plastic key.

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Nice place for the switch.

I've got plenty of thick stranded copper cable, I think running wires to the dash shouldn't be too much of a problem... I'm guessing it would be best to isolate all connections to the battery except the starter motor cable as this draws a lot of current?

NathanE said:
One cause is "vampire currents"... i.e. things like your radio and alarm which keep on drawing small amounts of current.

But there is another... called self discharge. This is where lead-acid batteries lose charge over time... and it gets worse when temperatures get cold. That's why sales of jump leads rocket in the winter months.

Self discharge could be a sign that your battery is dying. Does your battery let you refill it with deionised water? Or is it sealed? I just refilled mine today and found that one of the cells was almost completely dry...

Get a reconditioner like http://www.optimate-sp.com/ which will "desulphate" the battery and restore it to a better condition.

I've always tried to leave my battery on charge when the car isn't being used for a while, but there have been a couple of times I've forgotten and have been lucky to start the car without bump start it!

This is the first time I've heard of reconditioners, sounds like they will do the job, in theory at least... My battery is around 80Ah so I guess I'll have to get a different model however.

I can top up my battery however, I'll check my water level tomorrow when I'll have the benefit of daylight.

Ignore the following:

Shopping list:

Isolator + spare key
Yellow crimps to fit on M8 thread - use 2 wires in each crimp
Lots if wire
Lots of 20 and 30 A fuses
Fuse folder, maybe get one for Farnell's Mini fuses

Max current consumption:

Amp - Class A/B chucking out 200Wrms , 50% efficient, 400W draw. 400/12= 33 amps - 30A fuse will do.
New amp - Class D chucking out 280Wrms, 90% efficient, 311W draw. 25amp - 20A fuse will do.
Headunit: 25w? Need to measure, 5A fuse will work.
Drivers lights: 12A - use 15A or 20A fuse
Dip: 10A? - use 15A fuse
Main: 12A - use 15A fuse
Ice - assume 20A
Lights on full - Assume 50A
Heater, etc... Need to measure... Guessing 30A

100A Isolator could be borderline, perhaps 200A isolator would be better? Either that or bypass lighting relays from isolator... Need to redo lighting loon anyway.

Go for 2nd option... I think.