[Tigers] Engine Temperature

[Tod Brown]

Looking at Stu's data, the temp gauge reads 248 F at 24 ohms, so we can 
calculate the power consumed from P = V*V/R = (12 v)*(12v)/24 ohms = 6 
watts, so a 10 watt resistor should do the job.  I mounted the resistor 
under the bonnet, near the sender.  I have not had any melting of the 
plastic coating.  Using a resistor with a low power rating risks 
overheating it and frying it, just like a fuse.

Tod

On 10/21/2010 9:17 AM, Smit, Theo wrote:
> Hi all,
> As Tod noted, resistors used in the temperature sender or fuel tank sender circuit can pull quite a bit of current and they should be appropriately rated or else they'll get too hot.
>
> I forget offhand what the minimum resistance in the gauge circuits is, but I think that the maximum current can be on the order of 1/4 to half an amp. In that case, a 4 ohm resistor would dissipate one watt (1/2 x 1/2 x 4 = 1). That doesn't mean that a one-watt resistor is sufficient power rating, since that power rating is typically obtained when the case temperature of the resistor is 75 degrees C or higher (that's like 160 F or something). You should probably use a 2, 5, or 10 watt resistor to keep the temperature rise under control and prevent inadvertent burns or melting of other underdash parts.
>
> Cheers,
> Theo
> ________________________________________
> From: tigers-bounces at autox.team.net [tigers-bounces at autox.team.net] On Behalf Of Carmods at aol.com [Carmods at aol.com]
> Sent: Thursday, October 21, 2010 7:06 AM
> To: todbrown at roadrunner.com; tigers at autox.team.net
> Subject: Re: [Tigers] Engine Temperature
>
> Tod,
> I have used a resister approach to calibrate the temperature gauge like you
>   did but I found that if I put shrink wrap on resistors it may burn off so
> now I leave resistors exposed to air.
>
> John Logan
>
>
>
>
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> Thank you for your cooperation.