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@autox.team.net [tigers-bounces@autox.team.net] On Behalf
>Of Carmods@aol.com [Carmods@aol.com]
> Sent: Thursday, October 21, 2010 7:06 AM
> To: todbrown@roadrunner.com; tigers@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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