[Gmecm] Heated O2 Current Draw

[Peter Gargano]

mark krawczuk wrote:
> hi, cant u use   ohms law to find current draw, then just add a a couple 
> amps, 2 or so extra ?

Even at sub zero temperatures, a sensor's heater should not be less 
than 1 Ohm. Assume that it is 1 ohm, and assuming a 14 Volt 
battery/alternator, then you may draw up to 14 Amps for the fraction 
of a second it takes the heater to heat from sub zero to room 
temperature where the sensor's resistance will be several ohms and the 
current draw will reduce to a few Amps for several more seconds. Most 
10 Amp fuses will handle higher than rated currents for very short 
periods - in fact all incandescent lights have similar high "starting 
current" characteristics.

A good idea of the operating heater current can be determined by the 
claimed heater power. I have not seen a sensor's heater rated at more 
than 20 watts, so expect less than 2 Amps operating current with a 14 
Volt system.

I'd be happy to recommend a 10A fuse for any system, but expect the 
operating current to be under 2 Amps. A 5 Amp fuse is cutting it finer 
but offers more protection at the expense of blowing in cooler 
climates - but remember battery terminal voltages are usually lower 
when it's cooler too!

Peter




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