Fan earth/current draw

[swindler]

Hi all

Another troubleshoot. When my coolcat fan comes on my car voltage drops to about 11V, to the extent the horn becomes inoperative. I am using a Fosseway dynamite which shows 14.4v charge at 1000rpm.
I think this might be an earthing issue - I have bought a new fan loom and cleaned the contacts where it plugs into. Can anyone advise where that earth wire runs to please? Or any other thoughts

Cheers
Mark

[MarekH]

Since you have aftermarket items from two suppliers, you should get your technical support from them first. Collectively, we have less experience of these products than the suppliers do, so they can advise better than we can. If they can't, you shouldn't be buying from them.

Why do you think it is an earthing issue? The fan runs, so it must be part of a circuit.

When you operate the fan, put a voltmeter from battery positive to fan positive and report the voltage.
Then put the probes from battery negative to fan negative and report the voltage.

They should both be very small numbers. The second one tells you whether its an earthing issue.

kind regards
Marek

[MarekH]

Also, whilst you are at 11v and 1000rpm, rev the engine to 3000rpm and report back whether the voltage still reads 11v or a value closer to 14.4v....

kind regards
Marek

[swindler]

Hi, thanks

Voltage drop on fan negative to battery negative (it’s a positive earth car…) 3.0V
Voltage drop on fan positive to battery ground (positive) 0.1V


Hmm. So i assume I have an issue somewhere between green wire from number 6 fuse to the otter switch and the black/green stripe wire that comes from the otter switch as I don’t seem to have issues other than when the fan is on.
Unless the otter switch is at fault? If I recall it’s a modern one I bought with the fan about 3 years ago

Since you have aftermarket items from two suppliers, you should get your technical support from them first. Collectively, we have less experience of these products than the suppliers do, so they can advise better than we can. If they can't, you shouldn't be buying from them.

Why do you think it is an earthing issue? The fan runs, so it must be part of a circuit.

When you operate the fan, put a voltmeter from battery positive to fan positive and report the voltage.
Then put the probes from battery negative to fan negative and report the voltage.

They should both be very small numbers. The second one tells you whether its an earthing issue.

kind regards
Marek

[MarekH]

You're throwing away 3 volts before you even get to the fan !! That's absolutely pants.

Now break down exactly where the 3volt loss is, by measuring the voltage drop on each individual stage between the battery and the fan and either clean or replace the defective connection or wire. This will solve your problem and also make your fan run properly.

kind regards
Marek

[swindler]

Just a quick update on this in case it's of help to anyone searching in the future.

There were voltage drops at almost every stage of the circuit rather than one thing going wrong..

I replaced the relay, all four fuse boards (they looked clean but there was quite a drop across each bridge and the Lucas brass replacements are cheap) and with some cleaner on the female spade terminals.

This has brought the total drop down to 1.32V and individual drops down to:

0.24V across the ignition switch (googling some MG forums considered in tolerance..??)
0.08V across the ammeter
0.17V across the (brand new board and fuses) fuse bridge
0.04V across the fan relay

I think I'll also replace the bullet connectors between the engine and fan looms as these are hard to clean properly in situ.

Next step is to try it on the road when the weather allows, but I'm thinking this must be easily within what the alternator can cope with now, and based on the MG forum might be close to tolerance levels, even though I know modern cars would be closer to 0.1-0.2V total drop

Lesson = even when aluminium terminals and connectors look clean they can be hiding resistance!
Thanks for the help

[MarekH]

That's substantially better.

You still drop 0.79v somewhere which you haven't identified. I'm not suggesting it "has to be fixed" but I'm sure you'd like to know where it is. An old loom is what it is.

I'm thinking this must be easily within what the alternator can cope with now

I don't really understand this bit. Each component will draw whatever current it does based on how low its resistance is. Similarly, the voltage output at the alternator isn't going to change - that is based on the regulator - it doesn't much care what make up its load is, be that useful components or duff connections. I would have thought that if V=IR and you have made all of the little R's smaller, then the alternator will now try to supply more I, because its V output overall hasn't changed - it merely doesn't get shared with the duff connectors.

You can make all of the white wire, green, red and white/pink circuits 0.2v higher by fitting an ignition switch bypass relay. (New relay drops 0.04v and ignition switch drops 0.24v - although I have assumed the 0.24v drop is the same in all positions.)

You're also telling us the Jaguar fuseboard is pretty naff as a design. I'd investigate a product like DeOxit, clean all of the fuse connections and easily reachable bullets with emery paper and apply cleaner/preserver - it's such an easy gain for brighter lights, faster fan, etc.

It's a great lesson to others who might think "it must be an earthing issue" simply because they've bought something new. I'm pleased this has worked so well for you.

kind regards
Marek

[abowie]

You're also telling us the Jaguar fuseboard is pretty naff as a design. I'd investigate a product like DeOxit, clean all of the fuse connections and easily reachable bullets with emery paper and apply cleaner/preserver - it's such an easy gain for brighter lights, faster fan, etc.

The original units are actually very good and extremely robust. I'm not sure what the plastic is but we routinely bead blast them to clean the contacts and then reuse them. They cope well with this.

The newer units are made of a modern plastic and these tend to melt if they get hot. I'd avoid them if you can reuse your old ones.

[swindler]

A further update. I fitted an ignition relay and it has indeed brought the drop down to 1.13V.

- I did notice two additional things. Firstly the green wire for the fan was attached to fuse 7 not 6, and also I don’t appear to have the 10v voltage regulator for the water and fuel temperature gauges although they both function fine. I wonder if either of these issues has affected things

- the drop across the ammeter appears to be low but between the battery and the white and brown wire into the voltage regulator (dummy) is 0.29V. I can’t see why as I thought the only thing between the solenoid and there is the ammeter and there is close to zero drop between the battery and the solenoid. I wonder if I should I get a new ammeter anyway ?

Happy new year!

Mark

That's substantially better.

You still drop 0.79v somewhere which you haven't identified. I'm not suggesting it "has to be fixed" but I'm sure you'd like to know where it is. An old loom is what it is.

I'm thinking this must be easily within what the alternator can cope with now

I don't really understand this bit. Each component will draw whatever current it does based on how low its resistance is. Similarly, the voltage output at the alternator isn't going to change - that is based on the regulator - it doesn't much care what make up its load is, be that useful components or duff connections. I would have thought that if V=IR and you have made all of the little R's smaller, then the alternator will now try to supply more I, because its V output overall hasn't changed - it merely doesn't get shared with the duff connectors.

You can make all of the white wire, green, red and white/pink circuits 0.2v higher by fitting an ignition switch bypass relay. (New relay drops 0.04v and ignition switch drops 0.24v - although I have assumed the 0.24v drop is the same in all positions.)

You're also telling us the Jaguar fuseboard is pretty naff as a design. I'd investigate a product like DeOxit, clean all of the fuse connections and easily reachable bullets with emery paper and apply cleaner/preserver - it's such an easy gain for brighter lights, faster fan, etc.

It's a great lesson to others who might think "it must be an earthing issue" simply because they've bought something new. I'm pleased this has worked so well for you.

kind regards
Marek