I have one watt resistor, shrink wrapped near sender unit and no sign of
overheating
By the way, if anybody needs a sender replacement, Autometer part number
2385 seems to have similar, if not identical resistance curve to Tiger OE.
-----Original Message-----
From: tigers-bounces@autox.team.net [mailto:tigers-bounces@autox.team.net]
On Behalf Of Tod Brown
Sent: Friday, October 22, 2010 6:40 AM
To: Stu Brennan
Cc: 'Smit, Theo'; Carmods@aol.com; tigers@autox.team.net
Subject: Re: [Tigers] Engine Temperature
Stu:
You are right, of course. I didn't read your article carefully enough
and took the 24 ohms to be the total resistance. I checked a temp gauge
I have last night and it measured 62 ohms. At room temp the sender was
at about 900 ohms, so I think for the rough kind of analysis needed
here, we can assume we have a fixed resistance (gauge) in series with a
variable resistance (sender). Like you said, it's Lucas.
Tod
On 10/21/2010 8:16 PM, Stu Brennan wrote:
> Lets try this again. The sensor is 24 ohms around the hot end, but it's
> in series with the gage, which is about 60 Ohms cold (it may get a bit
> higher when the heater gets hot, but for this lets call it 60 Ohms).
> That's a total of 84 Ohms, with an average of 10 volts across it.
>
> Do the math, and that's around an average of about 119 mA running
> through the string. So you can calculate the max power dissipated in
> any added series resistor based on this, P = I*I*R. Add 10 ohms, for
> instance, that makes the string 94 Ohms, that gives a current of 106mA
> at 248 degrees. The dissipation works out to about 0.112 watt. As you
> can see from my data, lower tehperatures give higher resistances, and
> therefore lower currents and power dissipations. So in this case, a 1
> watt or even a half watt resistior in series would leave plenty of
> margin.
>
> It was said elsewhere, but this fixes it at one temperature, but throws
> it further off elsewhere.
>
> Think about this: What info are you REALLY looking for from your
> temperature gauge? As your car warms up, the temp gauge comes up to a
> certain point and stabilizes there, for a while anyway. That's the temp
> your thermostat regulates at. As long as your gage is pointing around
> there, all's well. If it goes a little higher, and circumstances
> explain this, stuck in traffic on a hot day, that's ok, but worth
> watching. If it goes way higher, then you have a potential problem. Do
> you really need numbers for this? This is LUCAS stuff, for heavens
> sake, not NIST traceable instrumentation.
>
> Stu
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