Electrical: Gauge resistors

[Jerry Forrester]

A few years ago I bought some resistors to get the temp. and gas gauges to work properly after changing a Stude from a 6 to a 12 volt system. I think I have one left. I'm not sure if this is one of the original resistors I bought and don't know which end goes toward the gauge.
Can one of you electrical engineers look at this pic and tell me what you think?

It looks like a Brown, Blue, Gold, and Gold stripes.
But it may be a Black stripe rather than Blue.

[radiotech]

It doesn't make any difference, Jerry, it'll work either way. A resistor isn't polarity sensitive. The color bands are there to tell you what value and tolerance it is.

[DEEPNHOCK]

http://www.hobby-hour.com/electronics/resistor_color_code.php

If it is blue, then it is a 1.6 ohm resistor
If it is black, then it is a 1.0 ohm resistor

[Jeff_H]

If its Brown Black Gold Gold, then as Jeff says its 1.0 ohms, 5%.

Black = 0
Brown = 1
Red = 2
Orange = 3
yellow = 4
green = 5
blue = 6
purple = 7
grey = 8
white = 9
gold = 1/10 mulitplier or 5% tolerance
silver = 10% tolerance

So Brown Black Gold Gold means 1 0 x1/10 = 10x.1= 1.0 and 5%

I don't think this will work too well for dropping 12v down to 6v for gauges though. A 1.0 ohm resistor with 6v across it would have 36W power and 6A current through it. That looks like a 1/4W or maybe a 1/2W resistor. The gauges don't draw that much current so the drop will be less and through off the calibration. You can't have more than 7/10A in a 1/2W 1 ohm resistor or it will burn up. 7/10A for 1 ohms is less than a volt.

To get the exact correct value of dropping resistor, you need to know either the resistance to ground of the guages (varies with the sender resistance so varies with gas or temp) or know the range of current draw they have on 6v as the sender varies (with gas or temp).

You'd be better off using some of those runtz voltage regulators on the 6v guages. They are just for that use.

HTH

[gordr]

Agreed, Jeff. Voltage dropping resistors are inappropriate for variable loads, and a gas gauge certainly qualifies. And a quarter or half watt resistor would very possibly just make smoke.

[Jerry Forrester]

Thanks guys,I don't know what I was saving this one for. It's going into the round file.

[RadioRoy]

If you buy a 6.3 volt zener diode, and wire it in the correct polarity, your gauge will work just fine. There are also pre-made ones that are cheap, but maybe not CASO cheap.