Hot Rod Forum : Hotrodders Bulletin Board - View Single Post - need help with a 12 v to 6 v reducer
View Single Post
  #7 (permalink)  
Old 06-17-2006, 05:20 PM
docvette's Avatar
docvette docvette is offline
Hotrodders.com Moderator
 
Last wiki edit: Rebuild an alternator Last photo:
Join Date: Mar 2004
Location: Lafayette, california
Age: 62
Posts: 7,362
Wiki Edits: 12

Thanks: 0
Thanked 6 Times in 3 Posts
Doc here,

OK once again..with feeling...

Quote:
1. Didn't expect the sender to work right, but thought it would move in some relationship to reality until I could get the right sender. (the parts guy said all senders work in a "similar range", which I now see is bogus)
For your parts guy to say this , is like an electric an saying your 220 Volt Compressor is in the same "Range" as your 110 Volt outlet..Or a 6 volt lamp will be fine in a 12 volt circuit..The only similarity is they are both capable of power and one is double the other..dude needs to study basic electrical before giving that kind of advice..

As little as 30 ohm mis~match is a world of difference to a sender circuit..and he should know that..

Quote:
Yes, I rechecked the function of the voltage reducer, and when I read it after it passes thru the gauge, (** as measured on ground?? Thats wrong..you can't accuratly series measure it! **) it is about 9 volts. Do I need to do something to get this down to 6?

I also tested the one that supplies the gas gauge, it also reads about 9 volts. If I wire the 2 in series, would that work?
Test your meter on the battery, It should read 12 volts or close about..11.6 to 13.95..Be sure your readings fall within spec..If not REPLACE the battery's..It is in error..or use a better meter..

NEXT scrap the second resistor..Tie ALL your gauge power to the one resistor..not two..you only need one..and it may be the cause of a 3 volt rise (cross feeding)


Your readings will only apply, with the full gauge hooked up, ground the sender wire, and measure the junction of the resistor and the gauge..It will read 6 volts IF your meter isn't in error.


Quote:
3. the test for value. OK there, except for the "reverse" part, (if the sender has less resistance than is required) . the gauge only has 2 wires. the hot lead and the sender.

I think you are saying to put the resistors between the gauge and its ground, which I can't do easily, cause it grounds to the dash. But we can cross that bridge if we come to it.
No, the resistor is installed between the Power and the gauge in order to work..like this:

12 volt POWER------>RESISTOR----->6 volts<---->GAUGE---->SENDER....

Quote:
4. As a starting point - with the 0 meter set at 20k the sender appears to have a resistance of .15 the gauge had a resistance of .06 Neither hooked up to anything, just a "unit" test. Maybe this is irrelevent.
Set your meter for Ohms..R X 1 Scale..measure between the terminal and the sender body..do this while testing in a pail of boiling water..look at the highest reading..It should be around (example)30 ohms at 220 degrees..then cool it off, read it again..It should be around 0 ohms..(This is Example only..could be higher) This is your "SENDER RANGE" 0 to 30..ohms. It can also be reversed..30 (at high temp, 0 at low)


Quote:
It just seems that if the gauge pegs when connected [it starts out on the low side and steadily moves to the high temp side to totally pegged within about *--->10 seconds<---*] would'nt that indicate the sender has less resistance than the gauge ?
This would be indicative of a "Close Value " sender..not a proper value one..like a 0 to 60 where a 0 to 30 should be.. If you ground the sender wire, you will see the gauge will peg right now..this is because there is NO resistance in the line..(no sender and hard ground)..



Quote:
5. The big question. Assuming I can figure all this out, how do i find the right sender? I can only imagine the look I'm going to get when i walk in and ask for a sending unit from 30 to 60 ohms? The usual response is "what make and model car is that for?"

Quote:
docvette
To test for Value, Go to radio shack, get a collection of 1 watt resistors..in the following values..30 ohms, 60 ohms, 90 ohms, 120 ohms, 150 ohms, 180 ohms, 210 ohms, and 240 ohms..

Next , monitoring your gauge, place one resistor in line on the sender wire, to a known good hard ground..as the meter climbs , note the value..keep "Upgrading" the resistors until "It Just Barely Pegs" the gauge..note that value..it is the resistance Value you need to get for your sender..
That should get you straight..

as far as getting a sender..if they are auto zombie idiots..(sir, I need a model and year) just say it's a S/W gauge on a riding lawn mower..no year no modle it's just an SW 0 to 30 (or what ever you find it is..)

Doc
__________________
Aftermarket Solutions
Electronic & Electrical
Innovations
Reply With Quote