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  #1  
Old 06-06-2021, 06:55 AM
BH1166 BH1166 is offline
 
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Location: Eatonton Georgia
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Default Resistor Rating

Need to reduce the voltage of 4.8v by using, per GRand Rapids documentation, a 200 ohm resistor. They call this a red black black black band resistor. Since my fuel pressure is wonky, thought I’d look to see what I have installed ( did not build) . Pictured is what is installed….not red black black black. Anyone electronically knowledgeable to say what I have installed? Looking on line on how to read is confusing, and doesn’t fit anything. Also, do you happen to know what 4.8v will be reduced to by use of my installed resistor?

Blue is 4.8 voltage pin/line, Gray/black is the wire going to VDO fuel pressure sender ( carb engine) .

Yes, I see what appears to be a burned, scraped, damaged gray/black wire, but not cut, appears to be solid.

Thanks
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  #2  
Old 06-06-2021, 07:22 AM
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vlittle vlittle is offline
 
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From the photo, the resistor looks like a 201 ohm or a 301 ohm resistor (the first band looks red or orange). The confusion is that is a 1% resistor, not the normal 5%. That is fine.

The voltage at the sensor depends on the measured pressure. These sensors go bad all the time. I have replaced the fuel pressure senders on both my airplanes because thy got ‘stuck’

V
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  #3  
Old 06-06-2021, 08:16 AM
BH1166 BH1166 is offline
 
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Default Colors

In person , orange black brown black. What makes it a 1% vs 5% ? I have replaced 3 times in three years. Seems to be the one thing I dislike about my GRT panel….. measuring fuel pressure 🤬
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  #4  
Old 06-06-2021, 08:24 AM
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Plummit Plummit is offline
 
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Well that takes me back to high school electronics class: Bad Boys Rape Our Young Girls But Violet Goes Willingly was the mnemonic I was taught and yes it does appear that you may have 301 ohm resister there now.
https://hyperelectronic.net/wiki/res...or-color-code/

-Marc
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  #5  
Old 06-06-2021, 09:41 AM
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n82rb n82rb is offline
 
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the percent is how much it varies from the given value. a 1% has a tighter tolerance. the question is why are you replacing them? most of the time a resistor goes bad due to heat. heat can come from a couple of places, first, to much current for the rating. second, the surrounding area. I would replace it with a 1/4 or 1/2 watt rated resistor. I really don't want to do the math to find out what the wattage through that circuit is, but a higher wattage rating will give you a better margin for heat from the surrounding area.

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  #6  
Old 06-06-2021, 09:42 AM
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GalinHdz GalinHdz is offline
 
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Quote:
Originally Posted by Plummit View Post
Well that takes me back to high school electronics class: Bad Boys Rape Our Young Girls But Violet Goes Willingly was the mnemonic I was taught and yes it does appear that you may have 301 ohm resister there now.
-Marc
Or how about: "Bad Beer Rots Our Young Guts But Vodka Goes Well.. Get Some Now"

But this color code chart should help.

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  #7  
Old 06-06-2021, 11:44 AM
BobTurner BobTurner is offline
 
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Resistors are not physically strong, and should be mechanically supported. Compare your photo (poor) to the sketch (good) on the instructions.
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  #8  
Old 06-06-2021, 09:31 PM
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vlittle vlittle is offline
 
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Quote:
Originally Posted by n82rb View Post
the percent is how much it varies from the given value. a 1% has a tighter tolerance. the question is why are you replacing them? most of the time a resistor goes bad due to heat. heat can come from a couple of places, first, to much current for the rating. second, the surrounding area. I would replace it with a 1/4 or 1/2 watt rated resistor. I really don't want to do the math to find out what the wattage through that circuit is, but a higher wattage rating will give you a better margin for heat from the surrounding area.

bob burns
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The resistor will dissipate a maximum of 0.072 Watts (72 milliWatts) with that sensor. I would recommend at least a 250 milliWatt rated (1/4 watt) resistor or larger.

VV
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  #9  
Old 06-07-2021, 06:25 AM
BH1166 BH1166 is offline
 
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….seems to me there is more to a resistor than just a ohm rating. Wattage, tolerances, etc. Grand Rapids only gives a ohm rating and color bands to choose from. I’m only inquiring due to wonky readings and it seems I replace fuel pressure sensor often/annually. They recommend putting resistor in-line via solder and shrink tubing or using a terminal block, my installation ( not by me) appears sufficient and not subject to any derogatory forces.

Since resistor reduces voltage on the 4.8v line, and per doc, 4.8v will damage sender. I’ve inquired with GRT what voltage should read at wire end with 200 ohm resistor ….. is my resistor bad, allowing 4.8v to get to sender, killing it, having to replace often? Basically what I’m trying to determine. Per vlittle math, not reducing the voltage that much with 200 ohm inline. I do have these handy, if suitable replacement. Thanks for the input/help.
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  #10  
Old 06-07-2021, 07:22 AM
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vlittle vlittle is offline
 
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With a 200 ohm resistor, you will see between 0.229 and 2.27 volts, depending on the pressure being measured.

A resistor is one of the most reliable electronic components, as long as it is properly selected and installed. It's highly unlikely that it is the problem. The VDO pressure sender fails often in our application, and it is one of the reason that Dynon eliminated them from their engine install kit and went with Kavlico, which fail for other reasons (dang).

VV
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