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Electric fan connections


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I really should know better...........

Last week I refitted the electric cooling fan that was fitted to the radiator that came with the car when I bought it many years ago. I got bored on afternoon took it to bits cleaned up the brushes, commutator and stuff put it all back together tested it painted it made up some brackets and bolted the thing back in the car......smashing.

Today I decided to have a go at wiring it up, I printed off a diagram from the interweb, the diagram was for a mini but I assumed it would be much the same as a TR after all a fan is a fan and 60's electrics must all be similar?

To cut a long story sideways despite what I think is following the diagram I keep blowing fuses, the 30 amp fuse at least lasted long enough for me to hear the fan start then blew.

There are two areas I am not too clear about.

Relay connection 86 should go to a + 12v supply that runs when the key is in acc. position but not in start?   any suggestions please?

Trying to run on both a thermo switch and a manual override switch, Two questions here please, does it make any difference which terminal on the thermo switch has live and which goes to earth?

I have fitted a piggyback connector to term.85 and the wires for both the Thermo switch and the manual switch are connected to that, is that okay?

Terminal 30 is wired direct to the starter solenoid via a 30amp fuse.Terminal 87 is wired direct to the fan.

Sorry to witter on but would really appreciate the answer, i'm running out of fuses!

 

Best regards David

 

 

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Your description of the connections sounds to be OK David.  The fuse blowing is probably because the fan motor takes a very large surge current on starting. That could be normal of course or it could be that it is being mechanically impeded in some way. A stalled motor takes a very large current so if there is something stopping it rotating easily, that might be the cause. 

What size fuse does the motor manufacturer recommend?  It may need a surge-resistant fuse rather than a plain one. 

There was some discussion here some time ago about fuses and their ratings. Automotive fuses are sometimes rated for the fusing current while normal fuses are rated for a highest running current. Do you know what running current the motor draws ?  How did you test it after re-assembly?

Edited by RobH
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Hello Rob

Thankyou for your comments, the fan is a rather old warrior and I don't have any documentation for it.

When I reassembled it I tested it in a very crude way simply touched one wire to pos. and the other to neg. of a spare battery, It worked a treat!

I will have a look on the interweb for surge resistant fuses.

Thanks again David

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Hmmm not as easy as I thought, I cant find a "T" type fuse in the bladed format. a little easier to find in the ceramic cartridge "tube" type fuse as Rob has suggested, but I note the one with the link is rated 240 volt is that important or is it just the amps I need to get right?

I expect the motor once had a little silver sticker on it with details of "stuff" but I think that has long gone. As it was once on the car I can only assume it has worked at some time in the past.

Now for a very silly question whats the worst thing that is likely to happen if I don't use a fuse?..............in this instance.

 

David

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No the voltage rating doesn't matter David, provided it's higher than your circuit voltage.

How about this (slow blow, antisurge and time delay are really all a similar thing)

https://uk.farnell.com/littelfuse/0299030-zxnv/fuse-slow-blow-30a-maxi/dp/9943153?gclid=EAIaIQobChMI8Yum2dX74wIVF-DtCh3kzQxeEAQYASABEgL9_vD_BwE&gross_price=true&mckv=D9cWRxXp_dc|pcrid|78108376509|&CAWELAID=120173390001367010&CAGPSPN=pla&CAAGID=14406255429&CMP=KNC-GUK-GEN-SHOPPING-9943153&CATCI=pla-57456859330

note it is bigger than the normal blade fuse

Edited by RobH
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Thanks Rob

I'ts very kind of you to take the time, I'll make a little shopping list and order a couple of those and some normal blade fuses to replace the ones I've blown +a little stock.

Rather more sensible than using the wiring as a fuse. I wish I understood more about electrics.

Kind regards david

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Graham, Tom and Tony thank you all for your wiring diagrams, I am really very grateful for your help and interest. ( I note some disagreement on terminal 85?) I am sure if I knew more about the subject there would be a perfectly rational explanation.

I confess I had the day off today, the sun was shining and I had a good use for all the old cans of used engine oil, the tractor shed now looks a treat. Back on the case tomorrow. I intend to try a simple test first as suggested by Rob.

Thanks again David

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Relay numbering is standard so 85/86 are the coil terminals and it doesn't make any difference which way round they are connected as long as one goes to supply and the other to earth. 30/87 are normally-open contacts and again it really doesn't matter which way round you connect them. 

(Where it DOES make a difference is with changeover contacts on a 5 terminal relay,  in which case 30 is the 'wiper' which is normally-closed to 87a and normally-open to 87).

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Okay that makes sense.......even to me, probably explains why the numbers are printed so small that you can't read them, or is that just me?

As for the 5 pin relay that just makes my brain hurt. 

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Right I have taken Robs advise and tried to run this fan without the relay ie straight from the battery with a 30 amp fuse in the pos. line.

Result just the same, less than a second running and the fuse pops.

Conclusion the fan is useless, I should dump it.

I started this mini project because I had this fan laying about in a box and thought why not, nothing much better to do. Now I have nice shiny new wiring in place and no fan, I think what I'll do is keep an eye open for another more up to date fan.

Can't win 'em all, thanks for all your help.

 

Kind regards David

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