craig1410
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 posted on 17/12/06 at 11:13 PM |
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Polo Rad Thermo Switch - Current rating?
Hi,
Just wiring up my electric fan and wondered if anyone can tell me whether the Polo radiator thermostatic switch is designed to switch the fan or if it
is only designed to switch a relay which in turn controls the fan? I have wired my loom up on the assumption that it can switch the full fan current
but just had a horrible thought that maybe it can't...
Cheers,
Craig.
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RazMan
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| posted on 17/12/06 at 11:35 PM |
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Definitely not a good idea as it will burn out sooner or later. A fan's startup currwnt can often be more than 10 amps 
I would use a relay 
Cheers,
Raz
When thinking outside the box doesn't work any more, it's time to build a new box
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craig1410
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| posted on 18/12/06 at 12:07 AM |
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Razman,
I am using a relay to provide the feed to take the load off the ignition switch but my question is whether or not the polo thermo switch is designed
to handle the full fan current or not. I don't have a Polo haynes manual or I would check how it is wired.
If it is designed for full fan current then it will be no more likely to burn out than the contacts on a relay and will save me having to run another
wire from the thermo switch to the fuse/relay box.
By the way, I know there are pro's and con's of having the fan driven from a permanent supply or via the ignition switch but I have chosen
to have it driven from the ignition switch.
Thanks,
Craig.
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RazMan
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| posted on 18/12/06 at 12:24 AM |
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Craig, when I mention startup current I am referring to the fan motor (not ignition switch or starter motor)
When an electric motor starts to spin up it will initially consume a lot of current for a few milliseconds and then settle down to a
'normal' level. It is this startup current which will burn out the thermo switch very quickly (if it survives at all)
So use a relay in the same way as you have done for the starter solenoid.
Incidentally your starter motor solenoid will probably draw less current than the fan motor
[Edited on 18-12-06 by RazMan]
Cheers,
Raz
When thinking outside the box doesn't work any more, it's time to build a new box
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indykid
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| posted on 18/12/06 at 12:32 AM |
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i've never seen a polo fan switch, so honestly can't say either way, but if you've already run the loom, get a fan switch from a
cavalier.
they're definitely designed to take full fan starting current. about £3 iirc. effort/cost ratio swings that one i think.
for my build, i just looked through the switches at work and picked the one with a nice temperature range and 6.3mm spade connections. they're
all a standard thread afaik.
tom
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craig1410
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| posted on 18/12/06 at 01:31 AM |
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Razman,
Thanks for the electrical theory lesson - reminds me of the 5 years I spent studying for my degree in electronics...
I appreciate your help but only want to know if the Polo thermostatic switch is designed to carry fan current or relay control current.
Tom, thanks - I should have checked this out before I bought a brand new Polo radiator switch. The one I bought is an XEFS16 from a company called
Commercial Ignition. I'll see if I can find a spec sheet. If it doesn't work I'll buy a Cavalier one.
Thanks,
Craig.
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whitestu
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| posted on 18/12/06 at 08:36 AM |
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I've heard people say it is but don't have any evidence.
Mine is just being used to plug the hole in the rad.
Stu
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RazMan
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| posted on 18/12/06 at 08:49 AM |
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Sorry Craig - didn't mean to teach grandma to suck eggs but I thought you had misunderstood my initial answer.
I did a search on the Quinton Hazell website and it just comes back with thread size and temp range, but no contact rating. I dropped them an email
requesting a spec sheet (I use the same switch and you've got me interested now )
If you have already installed the loom, you could minimise any forward current arcing by putting a diode across the contact connections - it might
make it last longer, although it will of course depend on the size of your rad fan.
[Edited on 18-12-06 by RazMan]
Cheers,
Raz
When thinking outside the box doesn't work any more, it's time to build a new box
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craig1410
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| posted on 18/12/06 at 09:43 AM |
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Raz,
No worries and thanks for going to the effort of emailing QH. I found some links last night too but nothing about current rating. Yes my loom is
wrapped up although it wouldn't be a major problem to add a new wire if I really really had to but I've done this a couple of times
already (first time for the horn feed and last time was to add the 30Amp feed wire for the fan...) and don't really want to do it again,
especially if I don't need to.
My reasoning is that the car will only be doing 2-3k miles per year tops so I'm hardly going to be likely to burn out a thermo switch rated for
a production vehicle which might cover 20-30k miles per year. However, this is only true IF the switch is rated for, say, 30A to start with. If it is
rated at 1A then it ain't going to last long switching a 10A fan.
Another reason I want to do it this way is to keep the electrics as simple as possible. I'm using a Rover V8 on carbs so electrically it is very
simple already. Although I used to design engine management systems for Lucas Automotive and am perfectly happy to work with electronics, at the side
of the road in the rain I'd rather be able to debug a problem with nothing more high-tech than a multimeter or a spare bulb. It also makes more
sense to me to have the feed coming straight through the thermo switch and on to the fan - one feed wire, one link wire (fan to switch) and one earth.
Let me know if you get any joy from QH - much appreciated!
Craig.
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tks
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| posted on 18/12/06 at 09:46 AM |
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uhhh
every fan switch can handle the fan motor current..
the standard thread is M22x1,5mm??
Anyway...
quote:
Incidentally your starter motor solenoid will probably draw less current than the fan motor
a starter solenoid is a coil. mine measures
1 Ohm resistance thats at 12volts 12 AMPS and at 14volts 14Amps..
my fan motor is running on a 10Amp fuse.
and its fine. i gues mine uses approx. 5 amps.. anyway i will depend on the size and quantity of fans that you have.
i would just hook up the amp meter and read what it says..
but i´m 100% sure that in 98% of the cases no relay is needed.
Tks
The above comments are always meant to be from the above persons perspective.
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craig1410
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| posted on 18/12/06 at 09:53 AM |
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Tks,
Thanks for your reply.
I only questioned the current rating because, of the two haynes manuals currently on my garage shelf, one delivers the fan current through the switch
directly (Sierra) and one does it indirectly (Rover 800). I don't have a Polo manual so I wasn't sure how it delivered the fan current.
In the absence of definitive evidence I will take the chance and just carry a small jumper wire with me in the car to short out the fan switch if and
when necessary.
Thanks,
Craig.
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martyn_16v
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| posted on 18/12/06 at 11:09 AM |
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Every other vw i've poked about in switches fan current directly in the switch, and vw certainly like using the same part in every car...
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BenB
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| posted on 18/12/06 at 11:21 AM |
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I asked this question a few months back and the answer came back a resounding no problems (with a few people quite rightly saying "but why not
fit a relay or overide switch anyway"...
I'm using a Polo switch direct to a Honda blackbird fan and it seems to be working after 4-5 hours total (most stuck in traffic due to where I
live!!)....
Battery hates it due to the crappy ST1100 alternator but the thermo switch doesn't seem to care!!!
Fitting an override switch isn't a bad idea. Even if its slightly hidden out of place. If the thermo switch did burn out (open) then you'd
just have to lean forward and flick the override. If the switch arc'd closed the fan being on all the time would obviously just put up the
current drain on the alternator and run down the battery if you've got a BEC and the headlights on!!! 
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NS Dev
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| posted on 18/12/06 at 11:47 AM |
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quote:
Originally posted by indykid
i've never seen a polo fan switch, so honestly can't say either way, but if you've already run the loom, get a fan switch from a
cavalier.
they're definitely designed to take full fan starting current. about £3 iirc. effort/cost ratio swings that one i think.
for my build, i just looked through the switches at work and picked the one with a nice temperature range and 6.3mm spade connections. they're
all a standard thread afaik.
tom
Yep, I've done exactly the same, Cavvy fan switch has no relay in the cavvy and the fuse on the circuit is 20 amp or 25 amp can't remember
which.
edit - obviously it also screws straight into the polo rad hole!
[Edited on 18/12/06 by NS Dev]
Retro RWD is the way forward...........automotive fabrication, car restoration, sheetmetal work, engine conversion
retro car restoration and tuning
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RazMan
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| posted on 3/1/07 at 04:55 PM |
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Update:- I got a reply from QH
------------------------------------------------------
"We don`t have any current ratings for these as it is a characteristic that is never measured, the switches we supply are to OE standard so
there is never any need to test how much
current a fan switch can handle.
The only thing I can suggest is to use a relay between the switch and fan to take the extra load.
If you need further information please let me know.
Mit freundlichen Grüßen
Kind Regards
i.A. Olaf Dallmann
Produktmanagement
Quinton Hazell Deutschland GmbH
Dreherstraße 11
59425 Unna
Fon ++49 (0) 02303 - 673-644
Fax ++49 (0) 02303 - 673-902
E-Mail olaf.dallmann@affiniagroup.com
------------------------------------------------------
So it would appear that even QH don't know the current rating of their own switches
Cheers,
Raz
When thinking outside the box doesn't work any more, it's time to build a new box
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craig1410
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| posted on 3/1/07 at 05:04 PM |
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Well that's comforting to know...
I suppose that takes me back to my original question which was whether the Polo uses a relay to switch the fan or whether it switches the fan current
directly via the thermo switch. If anyone has a Polo Haynes manual could they please have a quick look? I might pop in to Halfords to see if they have
any Polo manuals which are not still covered in cellophane.
Thanks for chasing this up with QH.
Craig.
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caber
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| posted on 3/1/07 at 08:22 PM |
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OK I have a polo rad with switch and fan still installed (scrappy!) shame the rad leaks :-( however i can confirm that the switch is wired direct to
the fan!
I will try and slavage the switch to put on the fan i will be using, just trying to figure how to fix it into the water circuit!
Caber
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flak monkey
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| posted on 3/1/07 at 08:32 PM |
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Its a doddle to wire in a relay, but if the wiring is already in your loom, and depending on the cost of the switches, it might just be easier to keep
a spare one.
David
Sera
http://www.motosera.com
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craig1410
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| posted on 4/1/07 at 01:21 AM |
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I'm just going to keep a bit of wire in the "emergency toolkit" which can bypass the thermo switch. It will have male blade
connectors on it so that it will just plug in.
Caber,
Thanks, that was exactly the information I was needing. So if QH manufacture their switches to OE specs then it should be fine without the relay. In
fact I wouldn't be surprised if the contacts on the thermo switch, now that we have determined it is designed for switching fan current, are
actually larger than the contacts in a typical relay. That could well mean that it is actually more reliable without a relay especially as there are
less electrical connections.
Sometimes less IS more!
Thanks to all,
Craig.
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