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What wattage 100 ohm resistor?


CageyH

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What wattage 100 ohm resistor should I use for my Innovative LC-1 wideband Lambda sensor to a K3 ECU?

 

I assume a 1/4 Watt will suffice?

If not, how about a 1 Watt?

 

Also, for the rotary switch, the 1K Ohm resistor - again a 1/4 Watt?

 

Only dead fish go with the flow....!

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If your answer to the questions "Do you know the maximum current through it" or "Do you know the maximum voltage across it" would be along the lines of "Oh - for heavens sake - if I knew that I wouldn't be asking the question" then I apologise and I will retreat rapidly. 😳

 

If, on the other hand, the answer is, for example, 10 volts, then the wattage can be calculated simply:-

 

power dissipated = v squared / R

or

power dissipated = i squared x R

 

Farmer Terry (and his car)

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If your answer to the questions "Do you know the maximum current through it" or "Do you know the maximum voltage across it" would be along the lines of "Oh - for heavens sake - if I knew that I wouldn't be asking the question" then I apologise and I will retreat rapidly.

 

I don't know the current draw....

I am guessing .25 Watt will be ok, as we are talking about an ECU, and it is there to cut out noise (found from further reading).

 

Only dead fish go with the flow....!

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CageyH

 

If you fit the 1/4 watt one, you might check the voltage across it once it is installed. Providing it is less than 5 volts then 1/4 watt is OK. (power = volts squared / R = 25/100 = 1/4)

 

If it is 5 volts, then you have little leeway, and you might choose to uprate it for safety.

 

If it is more than 5 volts you will need to increase the power accordingly.

 

Assuming a 12v system, the max should be 12 squared / 100 = 1.5 watts.

 

There are certain assumptions in this regarding the fluctuating nature of the voltage, but the advice should hold.

 

Farmer Terry (and his car)

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As Farmer Terry points out, the max current that a 100 ohm resistor across a 12v supply is around 1.5W. (or 1.9W at 13.8v...)

 

However the lambda sensor is feeding an ECU input, which will be high impedance so as not to affect the output of the sensor. I'd happily assume this input impedance to be of the order of 100K ohms or so, in which case your resistor is going to have less than knack-all current through it.

If it were me I'd use a 1/4 W on the grounds of size & cost. Checking the voltage drop across it when installed is a sensible suggestion.

 

Martin

supersported ex-Roadsports B

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Can someone confirm if this is a 100 ohm resistor?

 

Also, checking the voltage drop across the resistor, what kind of drop should be expected? and what I am failing to understand is how the emerald will cope with this, since if its expecting 1v to = AFR 12 for example, (and it does), but it gets 0.5v because of the voltage drop, it will show AFR of 11.5 (or at least less than 12)

 

Or should the voltage drop be negligible and something like 0.01v for example?

 

Possible 100 Ohm

resistor - Pic 1

Possible 100 Ohm resistor - Pic 2

 

 

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It's 40 years since I last did this - 😳 - but if you are concerned that I might be a little shaky - check the chart here

 

Brown 1, Black 0, brown 1 = 10 x 10^1 = 100 ohms. *thumbup*

 

I was taught a little mnemonic for remembering these codes that would probably get me 5 years in the current PC climate ☹️ - but 40 years on I can still remember them. *smile*

 

Farmer Terry (and his car)

 

Edited by - Farmer_Terry on 2 Jun 2008 17:48:04

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Also, checking the voltage drop across the resistor, what kind of drop should be expected? and what I am failing to understand is how the emerald will cope with this, since if its expecting 1v to = AFR 12 for example, (and it does), but it gets 0.5v because of the voltage drop, it will show AFR of 11.5 (or at least less than 12)
I think you are worrying needlessly. I have no idea what the resistor does, so I have no idea what the voltage drop should be. All I suggested was measuring was it is, as this will indicate the power being dissipated.

 

 

Farmer Terry (and his car)

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What wattage 100 ohm resistor should I use for my Innovative LC-1 wideband Lambda sensor to a K3 ECU?

 

I assume a 1/4 Watt will suffice?

If not, how about a 1 Watt?


 

In a reply from Emerlad, they said the 1/4 watt is fine, but in fact they said the wattage rating isn't important, as the resisitor is only there to buffer the LC-1 from the capacitive load of the line filter in the Emerald.

 

Edited by - viperbl on 3 Jun 2008 09:36:14

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