Battery Isolator Switch

[Guest danny_samb]

hi all i have an isolator switch fiited on the 12v +ve, its worked fine for ages but now if put the plastic key in and turn it i get nothing, but if push the key in and turn slightly it works, its only 1 of these cheap jobbies off ebay, do i need a more manly isolator switch an fia approved one

thanks

[Guest The Modfather]

You are better fitting it to the negative side of the battery to chassis strap. Fitting them to the positive can cause the cheap connections inside to break down due to the high power when cranking, if it's in between the battery and starter, which is possibly what has happened. All I have had, and seen are fitted to the negative side.

Cheap ones are exactly that, and can be overlooked if the car breaks down. Cheap ones are fine if fitted on the negative side. Expensive ones, like the FIA approved that you state, are ok to fit on the positive side as that is what they're real purpose is intended, to isolate power. If you are fitting as a security aid, then do the negative side and cheapo will suffice.

 

Daz

[fry61]

What goes up, must come down,Daz; & it's the same with 'lectric --- the power in the circuit is the same all the way round. Your idea will only work in the positive side IF starter suppy is connected to battery before cut-out switch.

[Guest danny_samb]

So if I get a better isolator switch then all should be ok, it's in the +ve in between the battery and starter

 

[Guest The Modfather]

the power in the circuit is the same all the way round.

 

?????

The OP has the switch in-line between the battery and the starter. These cheapo switches cannot cope with the power used during cranking as I've already said. The components inside (which is cheap thin brass connector/pins) are not man enough. Either that or he has the type of red key which has a plastic "locking pin" rather than a metal pin. The plastic obviously wears, and therefore can cause miss-connections. I'm also assuming he's using it purely as an anti theft device rather than a safety device in the event of a crash? By the sound of it, he gets a connection when he pushes it further in, therefore either he has a worn plastic locking pin, or the locking pocket in the tower has been worn by the metal pin, or the internals are screwed.

These cheap switches are best used purely to to stop the battery earthing therefore not allowing power to supply the ignition. I know that they are sold with the idea that they can be used in the positive side, but not all things are built good enough for the stated purpose. Anyone who fits these cheapos to the positive side are just asking for trouble. If it is meant for anti theft, and if his ignition is cut off when the negative terminal on the battery is taken off, then it's best to fit to the negative side. Easier still (and cheaper and easier to hide) is just to fit a small toggle switch to the power supply to the coil, the ignition switch itself or fuel pump.

The FIA red key switches are slightly better as they come with a resistor that is wired to an earth in order to stop possible damage to the alternator diode (I think?) along with spade terminals for the coil and ignition, and do have better internals.

Have a look on Demon Tweeks for the proper safety battery isolators if you want crash safety, and see what they sell for, against these cheap nasty red key switches.

I understand that battery earth cables can get hot when cranking continuously, but then that can be down to poor earthing from the engine/starter motor to chassis.

I await to be beaten down again.

[Guest danny_samb]

thanks for the help, as you say i get a connection when push the key down, ill have a browse on the demon tweeks sitw see what i can find

[fry61]

These cheap switches are best used purely to to stop the battery earthing therefore not allowing power to supply the ignition. I know that they are sold with the idea that they can be used in the positive side, but not all things are built good enough for the stated purpose. Anyone who fits these cheapos to the positive side are just asking for trouble. If it is meant for anti theft, and if his ignition is cut off when the negative terminal on the battery is taken off, then it's best to fit to the negative side. Easier still (and cheaper and easier to hide) is just to fit a small toggle switch to the power supply to the coil, the ignition switch itself or fuel pump."

 

 

 

Sorry Daz, not trying to yank your chain,but the current is the same thoughout the whole circuit,so if cut-off switch is operating in the earth lead it's breaking supply to all circuits including starter; as I said in previous post if C/O switch isn't man enough for total battery load then it needs to control all loads except starter load --ie -- starter supply to be connected direct to battery then C/O switch to all other feeds.

[Guest dinger]

Daz,

Bob is right, Current is current which ever side of the battery the isolator is connected,

 

The right side to fit these units are on the positive and you are right in that the FIA ones come with a resistor which protects the alternator when the race marshal flicks it off when the engine is running,

If using the switch for security or battery drain purposes then its ok to fit it to the negative side if you think its safer in regards to shorting to earth,

 

I think you have hit the nail on the head regarding the worn key or locating cutout Daz, New FIA isolator switch needed,,, check out local motor factors before paying £40 from tweeks as they sometimes stock them for around £15 quid, Make sure it has the resistor and usually says FIA on the sticker,

When building my race car I remeber buying my FIA rain/fog light and isolator from Maplins

 

HTH

Dave

[Guest danny_samb]

I have purchased a fia switch with resistor and the 4 spade terminals on the bottom for £15 so just hope that solves my problems

[Guest steve775]

As a qualified electrician and former stock car builder / racer i would always fit the isolator switch in the -ve (earth) side. even the ''expensive'' or FIA approved tend to burn out when installed in the +ve lead, simple rule is that no matter where you break the circuit it has the same affect.

[fry61]

Works fine so long as you hold the twisted wires between thumb & forefinger when cranking --- leave a lasting impres sion.

[Guest snotfart]

how does a seal twist wires with flippers ?

[fry61]

how does a seal twist wires with flippers ?

 

Very slowly

[fry61]

Would they be "SNAP-ON" pincers

[fry61]

Stanley Crab??? wasn't he one of the first to swim the English Channel?