Author Topic: Mystery resistor from a Ferrari 308  (Read 6819 times)

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Offline borud

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Mystery resistor from a Ferrari 308
« on: August 06, 2015, 09:16:12 am »
A friend of mine is fixing the heater on a Ferrari 308.  There is a power resistor that has disintegrated and which will need to be replaced, but I am having trouble finding any information on how much juice the resistor is supposed to be able to handle.  My friend sent me an image of the resistor, but sadly he didn't include a size reference so I have no idea how big the part actually is.  However, there are still some markings on it, so on the off chance that any of you are able to make sense of it, I'm posting it here.

It looks like a 1.5k resistor.  But how many watts?

(I'm stopping by the garage later today to have a look.  I can take a picture with a size reference then)

-Bjørn
 

Offline Wh1sper

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Re: Mystery resistor from a Ferrari 308
« Reply #1 on: August 06, 2015, 09:19:02 am »
1.5 Ohms
I guess
and somewhat in the 7W - 11 Watts Area
 

Online firewalker

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Re: Mystery resistor from a Ferrari 308
« Reply #2 on: August 06, 2015, 09:20:39 am »
I guess 1.5 Ohm at about 10 watts.

Alexander.
Become a realist, stay a dreamer.

 

Offline borud

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Re: Mystery resistor from a Ferrari 308
« Reply #3 on: August 06, 2015, 09:23:18 am »
I guess 1.5 Ohm at about 10 watts.

What do you base the 10 watt guess on?  The design?  The markings?

-Bjørn
 

Online firewalker

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Re: Mystery resistor from a Ferrari 308
« Reply #4 on: August 06, 2015, 09:27:58 am »
I guess that the width of the resistor is the standard width of those kind of resistors. I am holding a 1 Ohm 5 watts resistor now and it seems to be smaller than the half of the image posted.

Alexander.
Become a realist, stay a dreamer.

 

Offline Deathwish

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Re: Mystery resistor from a Ferrari 308
« Reply #5 on: August 06, 2015, 09:30:30 am »
RYK11 gives it away as 11 watts
Electrons are typically male, always looking for any hole to get into.
trying to strangle someone who talks out of their rectal cavity will fail, they can still breath.
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Offline rickselectricalprojects

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Re: Mystery resistor from a Ferrari 308
« Reply #6 on: August 06, 2015, 09:33:40 am »
It is also a 1.5 ohm 11w resistor. Got any pics of the 308? The 308 is a very Beautiful car(-;
 

Offline McBryce

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Re: Mystery resistor from a Ferrari 308
« Reply #7 on: August 06, 2015, 09:34:31 am »
That looks like one of the resistors for controlling the fan speed (1.5ohm). Does the fan only work on one of the three positions at the moment? Can't remember what wattage they were, but you can work it out as you (12V supply / 30A fuse - I think). Unfortunately, if this is burnt, there's probably a short in one of the windings of the blower motor. Also, there was an updated, much more reliable fan released later, so if the car is stripped down for restoration anyway, he should consider looking for the newer as a replacement.

McBryce.
 

Offline tec5c

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Re: Mystery resistor from a Ferrari 308
« Reply #8 on: August 06, 2015, 09:46:56 am »
RYK11 gives it away as 11 watts

+1  :-+
 

Offline borud

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Re: Mystery resistor from a Ferrari 308
« Reply #9 on: August 06, 2015, 09:53:37 am »
That looks like one of the resistors for controlling the fan speed (1.5ohm). Does the fan only work on one of the three positions at the moment? Can't remember what wattage they were, but you can work it out as you (12V supply / 30A fuse - I think). Unfortunately, if this is burnt, there's probably a short in one of the windings of the blower motor. Also, there was an updated, much more reliable fan released later, so if the car is stripped down for restoration anyway, he should consider looking for the newer as a replacement.

I'm not sure if it is burnt or if it has just disintegrated due to "environmental factors".  From what I gather the fan has three speeds so there is another resistor I might be able to have a look at.  I think it works at the other two(?) speeds, but I'll check.  In fact I think I'll bring along my own multimeter to have a look.  The measurement values my friend mentioned over the phone didn't make a whole lot of sense to me.  Or him.  For different reasons.

The updated fan is a drop-in replacement?  In order to figure out the specs of the resistor I stumbled across quite a few fan assemblies.  My goodness Ferrari parts are expensive.  You'd think they were made of unicorn tears.

-Bjørn
 

Offline McBryce

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Re: Mystery resistor from a Ferrari 308
« Reply #10 on: August 06, 2015, 10:53:21 am »
I'm not sure if it is burnt or if it has just disintegrated due to "environmental factors".  From what I gather the fan has three speeds so there is another resistor I might be able to have a look at.  I think it works at the other two(?) speeds, but I'll check.  In fact I think I'll bring along my own multimeter to have a look.  The measurement values my friend mentioned over the phone didn't make a whole lot of sense to me.  Or him.  For different reasons.

The updated fan is a drop-in replacement?  In order to figure out the specs of the resistor I stumbled across quite a few fan assemblies.  My goodness Ferrari parts are expensive.  You'd think they were made of unicorn tears.

-Bjørn

Yes, that's why I gave it up as a hobby too. As far as I can remember, it's a drop-in replacement. It's made for that car, it was just a later revision. I was told it's much more efficient too, but I can't vouch for that, it was one of the last repairs I did before selling it on... and buying a 348 which burnt money even faster! (Gearbox failed after 12 months  >:( )

McBryce.
 

Offline borud

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Re: Mystery resistor from a Ferrari 308
« Reply #11 on: August 06, 2015, 11:35:42 am »
Yes, that's why I gave it up as a hobby too. As far as I can remember, it's a drop-in replacement. It's made for that car, it was just a later revision. I was told it's much more efficient too, but I can't vouch for that, it was one of the last repairs I did before selling it on... and buying a 348 which burnt money even faster! (Gearbox failed after 12 months  >:( )

Talked to my friend on the phone and he could confirm that two of the other speeds work, and they have indeed upgraded the fan.  (I was under the impression that there was an entire fan assembly of which the resistor was a part, but I probably didn't pay proper attention since I was only interested in the resistor).

(I have an 1987 Alfa Romeo 75 Turbo Evoluzione.  It is a homologation car so it looks like a teenagers idea of what an Alfa 75 should look like and it is terrifying to drive.  I have taken some steps though.  Like putting in a steering rack with a lower ratio and adding power steering since the car is awfully tail-happy. It involved a lot of flailing about to keep it pointing nose forward when the turbo figured it was time to do its bit).

Okay, so now I'm off to see if I can find a suitable replacement on Farnell.  Any recommendations?

-Bjørn
 

Offline McBryce

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Re: Mystery resistor from a Ferrari 308
« Reply #12 on: August 06, 2015, 11:42:30 am »
From memory it was around a 12W resistor I used (wanted to be on the safe side).

McBryce.
 

Offline amyk

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Re: Mystery resistor from a Ferrari 308
« Reply #13 on: August 06, 2015, 02:22:22 pm »
My first thought was, wouldn't PWM be better for adjusting the fan speed than dropping resistors? But then again, if this is part of a heater, maybe the resistors help...
 

Offline KJDS

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Re: Mystery resistor from a Ferrari 308
« Reply #14 on: August 06, 2015, 03:38:59 pm »
My first thought was, wouldn't PWM be better for adjusting the fan speed than dropping resistors? But then again, if this is part of a heater, maybe the resistors help...

Modern cars certainly use FETs rather than resistors, but I don't know if they use the linear or on/off approach.


Offline c4757p

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Re: Mystery resistor from a Ferrari 308
« Reply #16 on: August 06, 2015, 04:21:18 pm »
My first thought was, wouldn't PWM be better for adjusting the fan speed than dropping resistors? But then again, if this is part of a heater, maybe the resistors help...

Modern cars certainly use FETs rather than resistors, but I don't know if they use the linear or on/off approach.

I can't really imagine why you'd use a FET in linear mode to control fan speed - you want a fixed resistance anyway, and all you're doing is replacing a resistor with a more expensive (yes, power FETs are technically cheaper than power resistors, but require more expensive thermal management) and less reliable substitute.
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Offline borud

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Re: Mystery resistor from a Ferrari 308
« Reply #17 on: August 06, 2015, 05:39:27 pm »
My first thought was, wouldn't PWM be better for adjusting the fan speed than dropping resistors? But then again, if this is part of a heater, maybe the resistors help...

That was my first thought as well. 

Then I pictured myself standing beside the smoking remains of the car with a "uh...sorry?..."-face.  Sure, it's easy to do, but I'm not an electrical engineer so I might screw it up in precisely the way that produces viral videos.  And then I'll be known as the "Ferrari burner" and kids will throw rocks at my house.

If it was my car I'd probably go for that.

-Bjørn
 

Offline KE5FX

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Re: Mystery resistor from a Ferrari 308
« Reply #18 on: August 07, 2015, 08:28:28 am »
Wait'll you see the fuse box.   |O  Believe me, no actual electrical engineers were involved when the 308 was designed.
 

Offline KJDS

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Re: Mystery resistor from a Ferrari 308
« Reply #19 on: August 07, 2015, 08:36:01 am »
Wait'll you see the fuse box.   |O  Believe me, no actual electrical engineers were involved when the 308 was designed.

I was chatting to a friend that owns a Countach last weekend. It just never occurred to the Italian supercar designers of the 70's that electrics on a car had to work reliably.

Offline McBryce

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Re: Mystery resistor from a Ferrari 308
« Reply #20 on: August 07, 2015, 10:40:56 am »
You've got to remember, the design work for this started around 1969. Using resistors for fan speed was normal practice back then. Almost all vehicles use PWM now.

McBryce.
 

Offline vk6zgo

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Re: Mystery resistor from a Ferrari 308
« Reply #21 on: August 07, 2015, 12:51:34 pm »
Ford used resistors wound with Nichrome wire on a mica former in the 1988 Falcon.
Unfortunately it was in the heater/ventilator airflow.
Gum leaves find their way in to that too,so you get the smell of an incipient bushfire coming out of the vent.

The resistors become open circuit very readily,& I was going to replace the circuit with a big fat BJT,but got lazy & bought another resistor.
The later Falcons used solid state devices,so my idea wasn't so far from Ford's thinking.
 

Offline McBryce

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Re: Mystery resistor from a Ferrari 308
« Reply #22 on: August 07, 2015, 12:58:09 pm »
On some Fords you'll also find a resistor hidden inside the wire harness going to both headlamps. This was because the specs for headlamp supply voltage doesn't work well with the newer alternator output voltages they used.

McBryce.
 

Offline mikerj

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Re: Mystery resistor from a Ferrari 308
« Reply #23 on: August 07, 2015, 03:16:20 pm »
You've got to remember, the design work for this started around 1969. Using resistors for fan speed was normal practice back then. Almost all vehicles use PWM now.

McBryce.

Resistors were used to control fans in cars less than 10 years ago, and probably still are in some cases.
 

Offline PChi

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Re: Mystery resistor from a Ferrari 308
« Reply #24 on: August 08, 2015, 03:49:26 pm »
Resistor power rating is so dependant on how they measure it. Just choose one of the same or larger physical size.
It'w worth checking that the fan motor spins freely.
My Vauxhall Astra Mk1 used a series resistor to control the fan speed. One day with the fan on I smelt hot electronics and switched the fan off (though my nose isn't as sensitive as Dave's) before the resistor burnt up. It turns out the fan motor was hard to turn and the excess current taken was too much for the resistor. The motor was exposed to the dirt passing through the ventilation system so inevitably after some years the bearings started to seize up. After taking the motor apart giving it a good clean and lubricating the bearings it gave some more years of service until the car was stolen.
 


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