Rad Fan Relay

[2052006 10]

This could be a silly question, but is the fan relay located under the slam panel meant to get extremely hot?

 

Just wondering if it is working properly because of this. I have checked the fan works on both slow and fast speeds using the diagnostic plug.

 

What temp is the fast speed meant to come on? The slow speed comes on about 90.

[M@tt 77]

i assume you mean the cylinder type effort the size of an A duracell battery? and its actually a resistor not a relay.

 

In which case yep its supposed to, just be careful you don't have it touching any other wires as it will easily melt them

[Anthony 1,000]

What temp is the fast speed meant to come on? The slow speed comes on about 90.

Depends on which thermoswitch you have fitted - there's various ones available, distinguished by a coloured band around the body of the thermoswitch, each with slightly different termperatures for the slow and fast speed fans to come on at. Slow speed on at 90 degrees sounds about normal though.

[2052006 10]

In which case yep its supposed to, just be careful you don't have it touching any other wires as it will easily melt them

 

melts fingers too

 

Ok thanks - I'll assume it's ok then. I'm asking as I'm keeping a close eye on the temp now with the gti6 engine in. It copes fine just idling - with the bonnet open - but having done a few test drives now, it does get very hot. How much hotter than the 8v, I'm not sure.

 

I'm pretty sure it's been suggested before, but is it ok to remove the resistor and just connect the two wires, so that the high speed only comes on?

[shalmaneser 26]

melts fingers too

 

Ok thanks - I'll assume it's ok then. I'm asking as I'm keeping a close eye on the temp now with the gti6 engine in. It copes fine just idling - with the bonnet open - but having done a few test drives now, it does get very hot. How much hotter than the 8v, I'm not sure.

 

I'm pretty sure it's been suggested before, but is it ok to remove the resistor and just connect the two wires, so that the high speed only comes on?

 

Yeah that's fine.

[DrSarty 90 1 Cars]

Yeah that's fine.

 

BUT...when you do it, you'd be well advised to disconnect the earth from the battery as these are permanently live wires. One slip meaning you or one of the wires touches the body and you'll get a light, sound and pain show!

[Daviewonder 533 3 Cars]

BUT...when you do it, you'd be well advised to disconnect the earth from the battery as these are permanently live wires. One slip meaning you or one of the wires touches the body and you'll get a light, sound and pain show!

 

Pain?

[DrSarty 90 1 Cars]

Pain?

 

Why has that confused you?

 

[Daviewonder 533 3 Cars]

Im confused about what would cause the pain.

[GLPoomobile 958]

Pain?

 

Go and touch one of the wires to your testicles. That should clear up the confusion

[DrSarty 90 1 Cars]

Nice reply Steve.

 

Im confused about what would cause the pain.

 

Maybe I should write more clearly next time...

BUT...when you do it, you'd be well advised to disconnect the earth from the battery as these are permanently live wires.

 

[Daviewonder 533 3 Cars]

I didnt realise you could get a shock from car electrics (well nothing apart from the HT system). Maybe ive just been lucky

[2052006 10]

Cheers all Battery will be disconnected! I will run it for a few days and see how it copes before removing the resistor...hopefully it will pass it's MOT tomorrow and I can start giving it some proper runs

[DrSarty 90 1 Cars]

Seriously Davey:

If you really didn't know this, i.e. you are NOT winding us up, then you genuinely have been that lucky up 'til now. I hope you see the safety tip as that, because a car battery is a potentially lethal bit of kit.

 

0.5 amps can kill someone, and a car battery regularly wangs out 300-600 amps. I seriously do not advise fiddling with live, battery fed wires with the earth cable still connected. Any chance the battery gets it will try and ground, through a spanner misplaced or through you, and you really DO NOT want a jolt from a battery.

 

A quick zap from an HT lead will only tingle your muscles, but a big jolt from a car battery could stick you on your arse!

[Daviewonder 533 3 Cars]

Seriously Davey:

If you really didn't know this, i.e. you are NOT winding us up, then you genuinely have been that lucky up 'til now. I hope you see the safety tip as that, because a car battery is a potentially lethal bit of kit.

 

0.5 amps can kill someone, and a car battery regularly wangs out 300-600 amps. I seriously do not advise fiddling with live, battery fed wires with the earth cable still connected. Any chance the battery gets it will try and ground, through a spanner misplaced or through you, and you really DO NOT want a jolt from a battery.

 

A quick zap from an HT lead will only tingle your muscles, but a big jolt from a car battery could stick you on your arse!

 

Hi DrSarty, Ive not really had any experence with car electrics, Ive always just thought "12v? pfft" never really considered ampage (think i heard somewhere that its amps that kill you not volts?) i joined this forum to learn and to help me gather information on my engine conversion and so far it seems to be going ok, i wouldnt wind you up im sorry if it appeared this way, i maybe should have put more effort into my question. I apperciate you taking the time to give me a detailed answer. Cheers, Dave.

[jackherer 543]

Seriously Davey:

If you really didn't know this, i.e. you are NOT winding us up, then you genuinely have been that lucky up 'til now. I hope you see the safety tip as that, because a car battery is a potentially lethal bit of kit.

 

0.5 amps can kill someone, and a car battery regularly wangs out 300-600 amps. I seriously do not advise fiddling with live, battery fed wires with the earth cable still connected. Any chance the battery gets it will try and ground, through a spanner misplaced or through you, and you really DO NOT want a jolt from a battery.

 

A quick zap from an HT lead will only tingle your muscles, but a big jolt from a car battery could stick you on your arse!

 

Actually its the other way round, 12V DC is not high enough voltage to give you a shock but the HT from the coil could stop the heart if it grounds through it.

[GLPoomobile 958]

I've had a shock from a 7.2V battery for a remote controlled car. That bloody hurt at the time, although I was only kid so I'm probably hard enough to take it now Actually, I'm probably not

[fast_eddie 0]

As an apprentice I fitted tail lifts to wagons which involved welded, wiring, fitting etc but the first job to do was to disconnect the battery---first day, spanner on the 13mm battery bolt then BAAAANNNNNNGGG!!!!--The end of my spanner was literally missing and I had a huge burn in my hand where I had shorted out the live side of the battery post to the chassis!!

 

Lesson learned until 3 phase power lifted me off my feet and through me 3 feet across the room---went into shock after that one!!

 

BE CAREFUL YOU CAN DIE!

[lagonda 41]

Puzzled...plenty of times I've had hand on live bits whilst other hand on engine or other earth....& noticed.....nothing. Might be different with wet hands, & yes, I realise enough amps are there to melt metal. I speak with experience as I seem to have spent my life collecting electric shocks.

 

When I was a kid I used to put pennies on the Southern Electric railway....the tracks seemed so innocent, one day I connected all three together with a length of bare wire! Nothing happened ....so boring....perhaps a train was on the way using the power. No I'm not immune, had a few shocks from the mains....some of those made me sit down & think for a while. Worst however was after reading a pre-war car manual stating you could check firing by holding ignition lead...so I tried it on my pre-war car. Fortunately I was in the garage so got flung against the wall, otherwise don't know how far I would have flown. Guess that author must have moved onto Haynes!

 

So sorry, Dr Sarty, have to disagree..."tingle" from HT? I wouldn't like to risk it, especially with the power being developed on modern electronic systems.

[DrSarty 90 1 Cars]

So sorry, Dr Sarty, have to disagree..."tingle" from HT? I wouldn't like to risk it, especially with the power being developed on modern electronic systems.

 

OK: 'tingle' was an inappropriate choice of word. I've had plenty of belts off of HT leads and it definitely smarts.

 

My point was in comparison, that the damage done to your flesh etc from the amps and how it could effect your heart is demonstrated by what can happen to a spanner. Touch the spanner to the HT leads and you'll just get a pretty blue spark. Touch the spanner between the battery terminals and the difference and danger is immense, hence the reduction of the HT thing to 'tingle'. It was a comparison.

 

Both are unpleasant, but one is downright nasty.

[lagonda 41]

Yes...not just spanners....friend wore a watch with a metal wristband....somehow rested hand on battery whilst leaning over engine...inadvertently shorted wristband across battery terminal and battery retaining bracket......painful! Didn't do watch any favours either.

[jackherer 543]

OK: 'tingle' was an inappropriate choice of word. I've had plenty of belts off of HT leads and it definitely smarts.

 

My point was in comparison, that the damage done to your flesh etc from the amps and how it could effect your heart is demonstrated by what can happen to a spanner. Touch the spanner to the HT leads and you'll just get a pretty blue spark. Touch the spanner between the battery terminals and the difference and danger is immense, hence the reduction of the HT thing to 'tingle'. It was a comparison.

 

Both are unpleasant, but one is downright nasty.

 

The current from a battery will short circuit through a spanner and if you are close will burn you but that same current wont discharge through the human body due to resistance, 12v will NOT give you an electric shock. The high voltage from the HT leads can however and shouldn't be underestimated.

[Anthony 1,000]

Exactly - by and large, 12v DC is not going to electrocute you, proven by the fact that you can put a hand on each battery terminal and not light yourself up like a Christmas tree. The big danger with working with car electrics is not electrocution, but shorting out a circuit or the battery terminals and the damage (and potential fire) that the resulting current discharge will do.

 

HT on the other hand can very easily give you a nasty belt, and potentially cause you some serious harm.

[welshpug 1,626]

one thing people have forgotten, is that unless the engine is hot when you fiddle with the resistor (i.e 85 degrees +)

 

 

 

 

 

 

is that its not permanently live

 

 

 

 

 

unplug the thermoswitch and the resistor will be isolated totally from the power supply.

[DrSarty 90 1 Cars]

One of the wires going to the thermo switch is permanently live Mei, you know that. That's why the fan can stay on when the ignition's off.

 

Only when the engine reaches certain temps does the wiper switch in effect move round to make the other pins live; first the one going to the resistor and secondly directly to the fan.

 

But the feed wire is permanently live.

 

And on this shock thing, I'm not sure I said anything about the jolt side of things, I said a light, sound and pain display which started this whole thing off. The spark and heat and 'zzzzttt' as you touch a live 12v DC wire whilst making a circuit through you and your spanner to earth is going to give you a nasty surpise which is (as you say) quite different from an HT jolt or shock. This 12v DC thing is a nasty, burny, aggressive thing that burns skin and eats metal rather than shooting you across the room.

 

Both very nasty, but different experiences. I would say that one is no more risky than the other, because ultimately there must be roughly the same potential energy there in the first place surely?

 

So Mei: right back atchya!

Edited July 27, 2009 by DrSarty