| Author |
Message |
gerald lancaster (216.236.160.8)
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Votes: 0 (Vote!) | | Posted on Thursday, December 12, 2002 - 9:01 am: | |
I understand that a gauge may not be accurate because of the length of wire involved, so what size wire should be used for a temp gauge that has to run from the back of the bus to the front?
Gerald |
Gary Stadler (Boogiethecat) (68.7.217.217)
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Votes: 0 (Vote!) | | Posted on Thursday, December 12, 2002 - 11:11 am: | |
HI gerald,
In general, temp gauges have a resistance range in the neighborhood of around 200 ohms. (I've seen a few that are around 30-40 ohms but those are fairly old and not common.) This means that they will draw very little current thru the wire, and so the resistance of the wire will not add much error even if it is small in gauge. I would use 20 gauge at minimum, but if you can use heavier, it might make you feel more comfortable. I use 16-18 and have had no accuracy problems.
A good way to rest your concern would be to simply stick the thermometer in a pot of boiling water and hook the gauge up with a battery "right there" and note what it says. Then hook 50 foot coil of your proposed wire between the gauge and sender and see if it reads the same thing. Then you could try it with 50' of really skinney wire and get a feel for how gauge affects error. My guess is that even 22ga wouldn't make much difference.
One big source of error that's sometimes overlooked is on motors that have starters with two wires (+) and (ground) wired directly to the battery, and then have a crummy or even non-existant ground strap from the block to the chassis. In a case like this, the starter may not provide a ground to the engine at all, and the lack of an engine-to-frame ground strap means that the temp gauge's ground return connection is going to be thru linkages and other intermittent or resistave paths that will cause error. Make sure there's a good ground strap that electrically bonds the engine to the frame!
Cheers!
Gary |
George Myers (12.85.14.9)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Friday, December 13, 2002 - 6:55 pm: | |
The electrical gauges are notoriously inaccurate. It should be calibrated. To do this, install the gauge and wire to the engine. Connect the sender to the wire in the coach, but do not install the sender yet. Use a clamp and a wire to ground the sender's case. A battery jumper cable works well for this. Put the sensor part in water that can be heated, but don't let the wire or terminal get wet. I had my wife call out when the needle in the coach hit each mark as I slowly heated the water. I wrote down the corresponding actual temperature from a reasonably reliable thermometer. This is my calibration curve. I used coolant (antifreeze and water) so that I could heat it above 212. While the data is kept in my three ring binder for the coach, I remember the two important points. One is the normal operating temperature and the other critical point is where it is getting too hot. In my coach, the 212 point is just above the line below 220 degrees. I do not let it pass this. That means that I shift down before I get there, or stop |
Henry R. Bergman, Jr. (Henryofcj) (63.224.197.10)
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Votes: 0 (Vote!) | | Posted on Friday, December 13, 2002 - 8:51 pm: | |
Would the same concept work with a volt gage also? The dash voltage gage on my Crown reads as low as around 12.0 volts dc on a very cold day, but the actual battery voltage is more like 12.6 vdc at the battery. Thanks and CROWNS FOREVER!!! |
Gary Stadler (Boogiethecat) (68.7.217.217)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Friday, December 13, 2002 - 9:00 pm: | |
Henry, volt gauges draw extremely low amounts of current, so it almost doesn't matter what wire size you use, it shouldn't affect the calibration unless something else is hooked to the same circuit, loading it down. I'd put a digital voltmeter right across the rear of the gauge and see if they both agree. If not, then you will at least know how far off your gauge is. And measure it at the battery too... the DVM should read the same at both places...
Cheers
Gary |
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