Heater Resistor

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DazbodS2
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#1 Heater Resistor

Post by DazbodS2 » Sun Aug 28, 2022 7:01 am

Hi All,
The heater resistor on my 1970 S2 has cracked in two. I suspect it is the original ie wide and flat as opposed to the replacement cylindrical types. The resistance wire however still seems in tact, as a consequence I wondered can the ceramic type casing simply be glued back together? Do these resistors get hot? The replacement units from the likes of SNG seem to have a different fixing method with what appears to be two screw fixing mounting lugs. My original is mounted via two small brackets fixed to the motor casing which slot into the ends of the resistor body. Are these original type resistors available from anywhere?
Darren - 1970 S2 FHC Signal Red.

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MarekH
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#2 Re: Heater Resistor

Post by MarekH » Sun Aug 28, 2022 8:12 am

You can glue it back together if you want to, but bear in mind that it'll get VERY HOT and probably come apart again, so it may be difficult to find a high temperature glue that works on ceramic. You also don't want to do it in a way which provides a combustible material for when the next mishap happens.

This is jut a simple wirewound resistor, so measure the ohms and get another one the same value (or the next higher value). The physical size of the resistor and the fact that it is a wirewound type is down to the anticipated heat dissipation, so getting something physically smaller or mounting it in a more confined space is not a good idea.

If you want to improve the heat dissipation capability (so this doesn't happen again), use two wirewound resistors of double the original ohmage but fit them in parallel to each other.

Another improvement would be to ditch it and fit a speed controller (similar to that which people use for radiator fans) as the sole purpose of this resistor is to stand in series with the fan to make it run more more slowly. Alternatively, you can just omit it and run the fan full on or not at all, rather than have the hokey half speed option via the resistor.

EDIT:- Unless this failure was simply age related, you may wish to ask yourself why it was overheating now, i.e. why is it not successfully dissipating heat or why is there too much current flowing through it?

kind regards
Marek

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#3 Re: Heater Resistor

Post by DazbodS2 » Sun Aug 28, 2022 10:09 pm

Many thanks for the response Marek, much appreciated. Actually the reason for the resistor braking was down to my battery effectively “blowing its top” (for reasons that escape me but that’s another story) and breaking the resistor. It wasn’t the resistor itself that failed. As per my original post, the replacements appear to be completely different in size, shape and fixing. I would ideally like a replacement that resembles the original not least due to the fixing. Am I correct in thinking that this resistor effectively drops the voltage across the motor to give the slower speed setting? TBH I never actually use the the heater fan. I assumed by the nature of the resistor type, it is effectively a power resistor and hence would get pretty hot as your post suggests?
Darren - 1970 S2 FHC Signal Red.

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#4 Re: Heater Resistor

Post by grimes6 » Mon Aug 29, 2022 4:02 am

The original was a cylindrical resistor type which was held on by 2 pop rivets. I can photograph my original if you like .

Regards,
Greg

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MarekH
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#5 Re: Heater Resistor

Post by MarekH » Mon Aug 29, 2022 7:03 am

DazbodS2 wrote:
Sun Aug 28, 2022 10:09 pm
Am I correct in thinking that this resistor effectively drops the voltage across the motor to give the slower speed setting?
Yes
DazbodS2 wrote:
Sun Aug 28, 2022 10:09 pm
I assumed by the nature of the resistor type, it is effectively a power resistor and hence would get pretty hot as your post suggests?
Yes

You should consider gluing to be only a stop gap measure to stop it from falling apart. If you use it in the state it is currently in then the heat cycling and vibration will probably make a break in the wiring. You can hide the replacement wirewound resistor anywhere you like, so long as it is adequately insulated from anything metallic and in free air so it can dissipate the heat. Alternative designs like a metal cased resistor (which you should mount to a heatsink) can also be used.

(Batteries don't normally cause physical breakages. Does your alternator overcharge your battery?)

kind regards
Marek

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#6 Re: Heater Resistor

Post by DazbodS2 » Mon Aug 29, 2022 7:50 am

Thanks Guys. I had assumed that my resistor was original due to its age and the dedicated fixing mounts on the motor casing but perhaps not. The battery is another issue and I was going to do a separate post. It’s a Bosch 56 Ahr unit but is now about 6 years old. The car is only occasionally used and when not it is connected to an Accumate trickle charger. I noticed the other day that charger was indicating the battery, despite not being used, had suddenly gone from charged as it had been indicating for several days, to taking charge. The battery felt cool and I swapped the charger for a similar spare unit, my plan being if this continued to investigate further. The next day the battery top had literally blown off revealing the innards and it was that top/lid that had damaged the resistor which was mounted directly above on the fan motor case. This obviously suggests over charging but could it have been a fault with the battery as I said it was 6 years old? Note the battery is disconnected from the car when on trickle charge.
Last edited by DazbodS2 on Mon Aug 29, 2022 7:57 am, edited 4 times in total.
Darren - 1970 S2 FHC Signal Red.

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#7 Re: Heater Resistor

Post by DazbodS2 » Mon Aug 29, 2022 7:53 am

Hi Greg a photo would be great if it’s no problem thanks.
Darren - 1970 S2 FHC Signal Red.

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#8 Re: Heater Resistor

Post by Heuer » Thu Sep 01, 2022 10:49 am

Here is an original S2 motor and ancillaries:
Image
Image
Image
David Jones
S1 OTS OSB; S1 FHC ODB

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#9 Re: Heater Resistor

Post by DazbodS2 » Thu Sep 01, 2022 10:35 pm

Thanks David that looks the same as my damaged resistor so it does look to be the original. Have now purchased the replacement smaller cylindrical type from SNG which has different fixing so need to work out the best way of mounting it.
Darren - 1970 S2 FHC Signal Red.

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