Subject: Re: [Mgs] Fan Relay fried...

From: Paul Root <[email-masked]>
Date: Tue, 21 May 2013 06:14:06 -0500

The point of the relay is to not pass more power than necessary through the
switch that controls the equipment. It's to save the switch.

You don't say which wire it is.

I'm going to guess that the wire was frayed and came in contact with a
ground.

On May 20, 2013, at 10:48 PM, Andrew B. Lundgren wrote:

> One email per question is a good idea right?  ;)
>
> My '78 has been retro fitted with a single pull electric fan with a temp
sensor against the radiator.
>
> I have discovered that the relay controlling the fan fried.  It still
functions, but the wire coming out of the bottom is nearly burned off.  (Won't
be driving until this is resolved.)
>
> The first symptom of the problem was the engined died when the cooling fan
came on.  While investigating why there was no power going to the coil, I
found that by tugging on the harness the power came back on.  I heard
electrical sparks while tugging and my son noticed smoke coming off of the fan
relay.
>
> It appears to be wired correctly as the fan does come on when the power is
applied.
>
> Any thoughts as to why the relay fried?
>
> Bad ground?
>
> Isn't the point of the relay to pass more power though than would otherwise
be possible?
>
> Thanks!
> --
> Andrew
> _______________________________________________
>
> [email-masked]
> Donate: http://www.team.net/donate.html
> Suggested annual donation  $12.75
> Archive: http://www.team.net/archive
> Forums: http://www.team.net/forums
> Unsubscribe: http://autox.team.net/mailman/options/mgs/[email-masked]
_______________________________________________

[email-masked]
Archive: http://www.team.net/archive
Unsubscribe: http://autox.team.net/mailman/options/mgs/[email-masked]

---

From: "PaulHunt73" <[email-masked]>
Date: Tue, 21 May 2013 12:16:51 +0100

Yes it's a bad connection, but highly unlikely to be a bad ground.

Any bad connection reduces the amount of current that can flow, and in the 
process a voltage is developed across the bad connection, and hence heat is 
developed where heat would not normally exist.  That heat can cause damage, 
but it would have to be in a high-current circuit to do so.  The only earth 
connection in the vicinity of the relay is for its winding, which only takes 
a very small current, so any bad connection in the winding circuit is only 
likely to affect whether the relay operates or not, not cause heat damage.

The bad connection is likely to be in the fan circuit, i.e. the 12v supply 
spade at the relay, the relay contact itself, or the relay spade that then 
supplies the fan motor.  If it is the insulation board that carries the 
spade that shows heat damage then almost certainly it is the relay contact 
that has gone high-resistance, I've replaced one myself (on a UK V8) for 
that reason.  The relay needs to be replaced, but you should check the 
condition of the wiring to the relay spades.  If that is showing heat damage 
it may have been from a bad connection between wiring connector and spade, 
in which case the spade will need to be replaced and maybe the wiring cut 
back and pieced out.

But you have a non-standard setup anyway.  From September 76 North American 
MGBs had twin cooling fans as standard, operated directly from a 
thermostatic switch in the header tank of the radiator and no relay, unlike 
the UK V8 which did use a relay.

PaulH.

----- Original Message ----- 
> functions, but the wire coming out of the bottom is nearly burned off.

[email-masked]

---

From: Andrew Lundgren <[email-masked]>
Date: Wed, 22 May 2013 10:21:05 -0600

I think this matches what I am seeing.

The relay itself is fried and the connection for one of the 12v spades 
is fried.  That spade is toasted all the way up into the relay.

It will actually wiggle around now inside the relay.

Here are some links to the relay.

Here are two bad pictures of the relay:  (one blurry, the other with a 
flash glare...)
http://www.lundgren.us/78/P20May2013Mon_2026-09.jpg
http://www.lundgren.us/78/P22May2013Wed_0841-30.jpg

And the wires on the bottom:
http://www.lundgren.us/78/P22May2013Wed_0841-40.jpg
http://www.lundgren.us/78/P22May2013Wed_0841-48.jpg
http://www.lundgren.us/78/P22May2013Wed_0842-07.jpg 
<http://www.lundgren.us/78/P22May2013Wed_0842-01.jpg>

I am concerned that the wire connected to the fried spade has already 
been replaced once...  It is either the initial connection, or this has 
fried a relay before.

--
Andrew

On 05/21/2013 05:16 AM, PaulHunt73 wrote:
> Any bad connection reduces the amount of current that can flow, and in 
> the process a voltage is developed across the bad connection, and 
> hence heat is developed where heat would not normally exist.  That 
> heat can cause damage, but it would have to be in a high-current 
> circuit to do so.  The only earth connection in the vicinity of the 
> relay is for its winding, which only takes a very small current, so 
> any bad connection in the winding circuit is only likely to affect 
> whether the relay operates or not, not cause heat damage.
>
> The bad connection is likely to be in the fan circuit, i.e. the 12v 
> supply spade at the relay, the relay contact itself, or the relay 
> spade that then supplies the fan motor.  If it is the insulation board 
> that carries the spade that shows heat damage then almost certainly it 
> is the relay contact that has gone high-resistance, I've replaced one 
> myself (on a UK V8) for that reason.  The relay needs to be replaced, 
> but you should check the condition of the wiring to the relay spades.  
> If that is showing heat damage it may have been from a bad connection 
> between wiring connector and spade, in which case the spade will need 
> to be replaced and maybe the wiring cut back and pieced out.
>
> But you have a non-standard setup anyway.  From September 76 North 
> American MGBs had twin cooling fans as standard, operated directly 
> from a thermostatic switch in the header tank of the radiator and no 
> relay, unlike the UK V8 which did use a relay.
>
> PaulH.
>

[email-masked]

---

From: "PaulHunt73" <[email-masked]>
Date: Thu, 23 May 2013 08:47:42 +0100

I'd suspect the problem has happened before but only the heat damaged wire 
was pieced out, the real cause of the problem i.e. the relay was left behind 
to damage the new wire.  You need to do both, changing just the relay now 
may result in a reoccurrence if the wire connector is heat damaged and makes 
a bad connection to the new relay spade.  Unless the motor or its wiring has 
a partial short and is drawing too much current I doubt both were replaced 
last time.  And originally the fan was fused, so a partial short should have 
revealed itself ... unless that has been bypassed because it did keep 
blowing because of a partial short!  You need to check that fuse as well, 
indeed that it does have one, as that relay is not standard for a 4-cylinder 
MGB cooling fan.

PaulH.

----- Original Message ----- 

[email-masked]

---

From: "Michael Singleton" <[email-masked]>
Date: Thu, 23 May 2013 07:41:00 -0700

Small addition to your post. The fan in the North American cars I've seen is
protected by a circuit breaker instead of the fuse shown in the wiring
diagrams. This being the case, the breaker could reset itself after tripping
any number of times, possibly eventually damaging the wiring, relay, or
whatever. Of course as you have pointed out, the relay is a non-factory
component, and we do not know how it is wired into the system. If the relay
was installed taking its power directly from the Brown/White wire, it
wouldn't be protected by any fuses and resultant damage could be caused by
any number of issues. Note the factory wiring diagram, 1977 Supplementary
wiring diagram-thermostatically controlled radiator fan (p. Na12  - factory
manual).

Michael Singleton
Sportscars Ltd
10170 Croydon Way
Suite M
Sacramento, CA 95826
(916)366-0330
[email-masked]

-----Original Message-----
From: [email-masked] [mailto:[email-masked]] On
Behalf Of PaulHunt73
Sent: Thursday, May 23, 2013 12:48 AM
To: Andrew Lundgren; [email-masked]
Subject: Re: [Mgs] Fan Relay fried...

PaulH.

----- Original Message ----- 
> been replaced once...  It is either the initial connection, or this 
> has fried a relay before.

[email-masked]
Archive: http://www.team.net/archive
Unsubscribe:
http://autox.team.net/mailman/options/mgs/[email-masked]
_______________________________________________

[email-masked]

---

From: "PaulHunt73" <[email-masked]>
Date: Thu, 23 May 2013 16:58:25 +0100

Yebutt ... North American cars never had the relay from the factory.  They 
did eventually get the circuit breaker, but that should be able to switch on 
and off repeatedly without causing any damage certainly to the wiring. 
Frequent short pulses to the motor such that it never reaches full speed 
could cause that to overheat (it draws more current while accelerating up to 
full speed).  But in that case it would give inadequate cooling which should 
be indicated on the temperature gauge.  I suppose if a relay were fitted (as 
in this case (but see below)) it would eventually shorten the life of that 
by arcing at the contacts eventually burning them and causing them to go 
high-resistance as seems to be the case here.  But there were differently 
rated rectangular relays, and using the wrong one in an application could 
cause either the winding to burn out, or the contacts.  I don't know if the 
same applied to the cylindrical type as here, but as I say from everything I 
have heard, read and seen it shouldn't have a relay there anyway.

It's just occurred to me that this probably isn't a fan relay at all, but 
the ignition relay.  That did supply the fan, as well as everything else.

PaulH.

----- Original Message ----- 
> whatever. 

[email-masked]

---

From: Andrew Lundgren <[email-masked]>
Date: Thu, 23 May 2013 10:23:06 -0600

On 05/23/2013 09:58 AM, PaulHunt73 wrote:
> It's just occurred to me that this probably isn't a fan relay at all, 
> but the ignition relay.  That did supply the fan, as well as 
> everything else. 

I would like to hear more about this...  As I mentioned in the original 
thread, when the fan kicks on the car died.

I assumed that the hot line was grounding out and killing the car, are 
you suggesting that all of the power to the ignition and the fan is 
supplied though this relay?

There is no fuse or breaker in line with the fan (that I saw this 
morning in my quick examination of the wires before work).  The line 
that fried is connected to the hot brown line in the harness, so I guess 
there could be one further up the line, but I haven't gotten that far yet.

I was planning on getting a relay and other bits locally tonight to get 
things running again.  This one is available and appears to match the 
requirements:

http://www.autozone.com/autozone/parts/Duralast-Relay-Radiator-Cooling-Fan-Motor/_/N-9cj89?itemIdentifier=297371_0_8419_

I can later replace it with another mountable UK one.

[email-masked]

---

From: "PaulHunt73" <[email-masked]>
Date: Fri, 24 May 2013 09:02:45 +0100

That is more confirmation that it is the ignition relay then (didn't notice 
that in the original post).  When the fan operates the additional current 
from that causes even more volt-drop through the bad connection at the 
relay, killing the voltage to the ignition and everything else.

That link is for a 'hi/lo blower' relay which looks to me as if it is 
intended for two-speed cooling fan motors as often found on modern cars. 
You just need a basic Bosch 4-terminal 12v/30A relay such as 
http://www.ebay.co.uk/itm/RELAY-0332014125-BY-BOSCH-/380569119474.

The circuit breaker should be below the fusebox, brown/white and green 
wires, as shown here 
https://www.dropbox.com/s/tes6x4hirjoz9gk/DSC00012.JPG?n=117394008

PaulH.

----- Original Message ----- 

[email-masked]