need help with a 12 v to 6 v reducer
Trying to use the original temp gauge in my 41 pontiac,obviously 6 v. system but converted to 12v. bought a reducer and installed it, worked good on the bench, pegged out once it was installed. After much confustion I checked the output on the reducer, it was a full 12 v. Now I'm told, the reducer has to match the use. The one I bought said 1.5 ohms, 4 amps. counter guy said that was Max. 2nd guy says no, that's exact. If you want to run a 1 amp thing, you need to wire 4 of them in series?????? So the questions are : how do I determine the ohm resistance and amp draw of my gauge? Where do I find one the right size (they carried only the one 4 amp job)? And most puzzling to me, what am I missing? If the reducer cuts the voltage to 6 volts, and the gauge draws less than 4 amps, why does that burn it up? More I can understand, but less?
can someone explain the theory/science behind this? have any other solutions? At $12 each I don't want to run 4 of them, plus I don't know where I would put 4 of them.
Doc here, :pimp:
First off, If you have a gauge drawing 4 amps or above...toss it it's way past shot..more like a few mil-amps would be more like it..
Without a LOAD on a resistor..It will show the same voltage in as it does out..Because it is doing no useful work. It is just a straight wire..Current is used in the resistor and changed to heat when a load (the gauge, a light, ect..) is imposed on the resistor..current goes high..voltage goes low. Tell your Guy..whoever told you you need 4 of them..he needs to study OHMS law..sounds like at 12 bucks a pop..he's studied financial management real well...
Current = 12 volts divided by 1.5 ohms = 8 amps
To determine the resistance of your gauge, get out your DVOM, set it for OHMS scale, R X 1 or autorange, calibrated for 000, disconnect ALL the gauge wires..measure across the power and ground of the gauge..Whatever that reading may be..say 90 ohms..apply a little more ohms law..
Current=6 Volts divided by 90 ohms = 0.666 amps..(about 1/2 an amp)
You say something is burning up ? what is burning up?
Sounds to me like you don't have a drop problem at all..but a sender wire open or shorted to ground Or a bad sender, Or a mis matched sender.
The easiest thing to do (and a heck of a lot cheaper..)get a 6 volt lantern battery, remove power and ground from the gauge, and jump in the lantern battery..If the gauge pegs one way or the other..the sender wire is open or short, Or the sender is wrong for the gauge. Troubleshoot that first , then go back to a dropping resistor from the 12 volt system.
You may have another remote problem..If the car was 6 volt positive ground, and you didn't rewire the gauge..your putting the resistor between the gauge and ground making the gauge a dropping resistor for the resisror..(it's dumping the load on the gauge) ..
You need to strip those wires and rewire it for negative ground with he resistor feeding the + side of the gauge.be sure the - goes to the body (not power) and the + side goes to the resistor.
12v to 6 volt
Thanks for the reply Doc. I'm not sure I understand, but at least you do.
Got the strong feeling the parts guys were winging it. Let me see if I can get this straight.
1. No, I don't have a gauge drawing 4 amps, that was the rating on the voltage reducer, I guess if I did, the parts guy would be happy. .
2. "burned up" was my way of saying, it doesn't do what I think it should do. ( I get so frustrated with electrical issues my common sense dissapears. There was no visibile or olfacotry issue with the reducer at all, it just wasn't "reducing" the voltage.)
3. No reverse polarity problems. It's a Pontiac, negative ground.
4. The lead from the gauge to the sender is a separate, direct wire. I can replace it, but seriously doubt it is broken or grounded, as I looked for that. Which leaves the simplest, most likely, problem. wrong sender.
I'm searching for an original sender, in the meatime I used a generic. Before installing, I hooked it up with the lead and a ground. Took a reading in the open air, about 100 degrees (nice south texas day),
then I held it in a cup of near boiling water, about 200 degrees.
For grins I stuck an ice cube on it and it pegged down. So I figured I was close. Installed it and it went straight to the peg on the hot side.
So, I guess either the sender or the gauge must have had some poor ground until they were properly installed? So, I proceeded, assuming the sender was OK.
How would you go about identifying the proper sending unit?
[If i understand correctly - it is the sender that now has too much resistance, so that must have been the poor ground in my test??
Is that correct? ]
Is there a way to "balance" the sender and gauge, or do I just have to have an original sender? Sorry to be so long winded, but I would rather understand the problem, than just throw parts at it till it works.
Doc here, :pimp:
OK I edited your post for ease of read..hope you don't mind.. :sweat:
OK, let's address each issue as listed then deal with what remains..
Senders, Are Gauge/Circuit Specific..and Visa~Versa..you Can't just toss a sender at the gauge and expect it to operate accurately...If at all..You need to determine the resistance of the sender circuit on the gauge (On yours, that vintage, I'm guessing 0 to 30 ohms..) And MATCH the sender to the gauge resistance..
A temperature Sender can not read "AIR" It must be immersed in the flow of the media in which it is being tested..(I.E. in the water or stream)
To accurately test, you must boil a pot of water, (212 degrees) and place the sender fully wired AND a lab or other accurate thermometer in the water..
As the water Temps decline , Note the readings on both..If you have a portable hot plate..you can heat it back up, then note the differences as it rises..
Make a list as you do, and you will find the accuracy and linearity of the gauge..and know at a certain temp, it's 5 degrees off for example..
The sender IS probably OK, Just wrong value for the system to be accurate..
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..
Say that value is 30 ohms..then remove YOUR sender and go to the parts house, and get a value sender that will be 0 to 30 ohms..AND have the same thread pattern as yours AND the same depth..and that will fix that.
BE ADVISED..Some senders work in reverse..It may be that it needs a 30 to 0 to be right..The test still applies, except for the meter drive will be backward, AND when you go to get a sender..be sure it's 30 to 0 not 0 to 30..
If your sender has Less resistance than is required , you can add a resistor on the sender line to bring it within spec, (I.E. a 0 to 30 sender needs to be a 0 to 60 sender..add a 1 watt, 30 ohm resistor) The reverse will apply if the sender is too high, but you need to do a little Math to figure the value, and make that value resistor, go between the sender line and Ground..
The best thing is GET the RIGHT sender..ton's of them in different values out there..
12 v to 6 v reducer.
Doc. I need to chew on this a little, but i think I get it.
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)
Yes, I rechecked the function of the voltage reducer, and when I read it after it passes thru the gauge, 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?
2. not sure I can run the first test, because it just pegs at all temps. Or maybe you didn't intend for me to do that test until I had a gauge that worked.
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.
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.
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 ?
Which is opposite those "unit test" numbers. Or I'm thinking *** backwards. Likewise, if I ground the sending unit wire, it pegs the needle. that is 0 resistance right?
So more resistance in the sender line seems to be the answer, except for that "unit" test. So tell me that was a BS test and to ignore that, and I think I have my mind right.
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?"
Doc, I sure appreciate this help. Getting the original gauges to work properly just seems like the right thing to do. don
12v to 6 v
Doc, I just read my post, and it seems confusing. I used the term sender once, meaning the gauge, not the sending unit in the engine. Might have been confused in your answer also. Your last sentence said "the reverse will apply if the sender is Too high... and make that value resistor, go between the sender line and Ground" ... I read that as gauge and ground. don
Doc here, :pimp:
OK once again..with feeling... :D
As little as 30 ohm mis~match is a world of difference to a sender circuit..and he should know that..
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.
12 volt POWER------>RESISTOR----->6 volts<---->GAUGE---->SENDER....
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..)
12v to 6 v temp sending unit
OK Doc. i think I got it.
When the sending unit lead is grounded ( 0 resistance) it pegs the needle. Takes 30 ohms to get it to read about 220 degrees - as high as it goes.
More resistance, lower temp. 47 ohms - 170 degrees / 68 ohms - 130 degrees and at 100 ohms about 100 degrees, as low as it goes. I noticed it is not a smooth curve. 15 ohms on one end of the scale is about 50 degrees, but 30 ohms difference on the other end is only about 30 degrees. is that normal? big question is - do I ask for a 100 to 30 sender (cold to hot) or the opposite? Turns out the local hot rod shop has many senders, by value, so I'm headed there tomorrow. Thanks, don
Doc here, :pimp:
100 to 30 should be fine..If they don't have that you could go 100 to 0 , just remember it"s high on the "Hot" side a little bit..In fact I'd get a couple around that value if they are cheap enough..you can "Fine tune It " a little bit..
When you get it, boil a pan of water 212 Degrees, and hook the sender up , you need to jump the ground to complete the circuit..get an accurate lab or Kitchen thermometer, and submerse them carefully in the water..
Get a Note pad , and note any variances throughout the range as the temperature declnes..(so you know , for instance the gauge is 6 high through , say , 150 to 165..) and keep the list for future referance..If you have a hot plate..that you can bring to the car..you can do it in both directions.
This will give you an accurate idea of your "Linearity" of the gauge.
need help 6v to 12 volt
Well Doc, here's an update. Turns out the Hot Rod shop did not have senders listed by resistance. (they seem to know less about this than I do, now). So back to the parts store to browse the Standard catalog. found one that was listed as 24.7 ohms at 220 degrees and 152 ohms at 100 degrees (I figured I needed 33 at 220 and 105 at 100 degrees, but this was as close as I could get). Went home to try the "heating water Test". The gauge pegged before the water got to 100 degrees. (It would start out slowly and about halfway up the gauge just swing over to the peg, as the water got hotter it pegged faster). Almost seems like i have a ground at the gauge or in the wire (I've checked this several times) but when i disconnect the ground from the sender, the gauge doesn't move,(seems if I had a short to ground it would read all the time) Also the resistors placed in the ground wire did make the gauge work properly. Does this make any sense to you? Can you guess what I am doing wrong? Also, I appear to have another problem. My battery went dead after sitting for 4 days (second time), so I put the voltmeter between the negative terminal and the negative cable, I read 10.2 volts. (I expected 0) I get the same reading if I put it between the positive post and positive cable. From reading other posts, I disconnected the alternator completely, but got the same reading. Next I will start pulling fuses to try and isolate this problem. Could this problem be affecting my sender testing?
Lastly, do you have a simple schematic for a mid 80's gm wiring harness with the 3 wire alternator and built in regulator? This one is wired with both leads from the alternator connected together and then runs everywhere. that doesn't seem right to me, and I can't seem to isolate anything cause it just feeds in a circle. Sorry to be so long winded, but most of my hair is on the shop floor. Don
need help 12 v to 6 v
follow up to the above. I have now pulled the starter lead, the horn lead, all the fuses and flashers. my 10.2 volts is now around 9. Is it possible to have a short in the battery itself, even though it tests at 12v from terminal to terminal and it was OK'd at Auto Zombie?
Footnote - I have new ground straps from the engine to the frame, frame to the body and body to the engine and all ohms tests from dash grounds/headlight grounds/etc. all read no resistance.
Doc here, :pimp:
YOU can not take a useful reading on VOLTS DC In SERIES with the load...(as outline two posts back) The only thing you will see is buss voltage and the fact that somewhere in the system , there exists a proper ground through a device..
If you place a DC VOLT meter between the ground on the lamp and hard ground..then turn the lamp on..your meter will read 12 volts, but the lamp won't light..Leave it on for a month..will the battery go dead? ..No..No load..or useful work is implied on the battery..(lamp is not lit EVEN though it says 12 volts in series..)
DC VOLTAGE READINGS are always taken in PARALLEL , Or across the LOAD..or the battery..+ and -..To check your state of charge..put the meter ACROSS the battery, engine at rest..it should read around 12 volts if it is charged..much below , could indicate a bad cell..
NOW, Start the car..let it warm and the high current surface discharge about 5 minutes to recover..then measure AGAIN, ACROSS the battery..It should read between 13.95 and 14.4 VOLTS DC...If the alternator has an output.
NEXT, to measure AMPS..ALL READINGS are taken in SERIES with the circuit..To Do that, remove all load sources..(Domes, hood lamps trunk lamps, anything that will draw power while you test) Remove the battery cable from the battery, CONFIGURE your DVOM for AMPS, and set it for the HIGHEST scale, (usually 10 amps).
Place one Probe on the battery terminal, the other on the Battery CABLE, note your reading as you do..If it pegs you have a major problem that your meter will not be able to handle..stop immediately , or you'll destroy the meter..get a higher AMP Capable meter..or seek help from a local auto electrical shop..If it reads low on the scale..reduce the scale until it "Just" tops out..That will be your actual reading..
On a modern vehicle with Computer, CD player with memory presets, Alarm systems, and the like, it should read between 0.3 and 0.8 (less than 1 AMP) to be good..any higher..you have a problem.
If that's the case..The first logical step , because it is the most common offender, Is disconnect the Alternator complete from the system, and recheck the AMPS reading in SERIES with the battery..If it falls back into Spec, replace the Alternator, OR you can get a diode/Regulator and rebuild kit, for around $15..and an hour or so of your time..
If no change, on the readings, If your Fuse buss is Well marked, pull ALL the fuses and relays from it and recheck the AMP draw again..If it is within spec, or lower, one of the branch circuits are the culprit..
While you have them out check ALL your fuses for CONTINUITY across the fuse, (it is not your cause of the problem, but you'd be surprised how many are found bad..and how much "stuff" begins working after) ..replace any bad ones..Don't eyeball them, the filament can open at or near an end or "blade foot" and you'll never spot it..use a test lamp or DVOM set for Continuity, or Ohms R X 1, calibrated 000.
Replace the fuses back in the buss one by one, watching your Current draw in AMPS..when it jumps up (above an amp) that is your offender..Troubleshoot that branch circuit. Repair or disable as needed. Continue until all are back in the fuse buss.
The Sender you have (numbers wise) should be the right one..Try your test again with just the sender hooked up to your meter, set it for OHMS , R X 1 Scale, Calibrated to 000, hook one probe to the center terminal and the other to the sender body, and carefully retest your sender..with / against your lab thermo..note the ohm readings as it ascends / declines and be sure it is the sender advertised on the box (they mix them up some times..) If it is..then I'm thinking you have a gauge linearity problem.. If the sender test "True" post back, I can give you a circuit you can build that you add in line to "Gain " linearity over the range..
Also, there may be a problem with draw through the dropping resistor to the gauge, try putting an instrument lamp on the power side of the gauge..this will keep the draw constant through the resistor as the gauge resistance to ground is changing..If that works, you'll need to wire the lamp up to the gauge + and ground , permanently, or install a 6 volt instrument regulator ..
The Alternator sounds like it's wired correct. The main output from it to the battery via Fuse link or maxi fuse, the red terminal jumpered to it, and the brown wire to the Idiot lamp, bypass resistor and fuse into the switch.
6v to 12 v help
OK Doc. Can't say I really understand, but I believe you.
Tonight we did the following. Put a meter between the positive battery post and the positive cable, set to amps. There was no draw at all.
opened the door, the dome light pulled about .6 amps. with the door open and the ignition on we pulled about 1.2 amps.
plugged all the fuses, etc. back in, hooked up the alternator, hooked up the starter, no changes.
With the key off and door closed, we had no draw at all on the battery.
Drove to Auto zombie. they checked the battery at 12.75 volts. did a draw down test, it never got below 11.75 and bouced back to 12.75 when the load came off. With it running the alternator was putting out just over 14 volts, and the battery was taking a charge. There appears to be nothing wrong with the system at all. Guess we'll wait another 3 or 4 days and see if the battery is dead again.
Now for the temp gauge. We repeated the ohms resistance test.
30 ohms resistance the gauge reads about 220 degrees,
at 100 ohms resistance, it reads about 100 degrees.
Same as before. Tested the sending unit with an ohm meter. Cold it was at 170 ohms,
as the water warmed it up the resistance dropped.
at boiling it read about 30 ohms resistance.
Independently they both work and seem to have fairly relative values.
In the car, hooked up, with the temp sender end submerged in cold water, the gauge will climb slowly until it pegs.
As before, if we heat the water, it just pegs faster.
You referenced something I didn't fully understand, but I think
you were reffering to the voltage reducer.
So we put a test light from the power side of the gauge to ground, it lit up, but was pretty weak as it was a12 v light.
As we ran our sending unit tests again we at least got some reading (like 180 degrees on the gauge while the sender was in cold water) but it didn't peg, so I think we are on to something.
you mentioned a 6v instrument regulator. Can you explain?
Also, It may not be relevent, but the gas gauge is hooked up to the same voltage reducer as the temp gauge, and it works fine?
Doc here, :pimp:
OK, I edited your post to make it bit easier to follow..hope that's OK by you.. :sweat:
First, It sounds like your charging and electrical system is functioning fine..and the battery is up to snuff..It may have been a fluke before , something sticking on..running the battery dead..as you said, watch it for a few days and see where it goes..
Something to check, the belt may be "Just" loose enough not to charge under Peak loads .. recheck that and tighten a bit if you think it needs it.
Now about the Instruments, You may not have enough of a load on the dropping resistor to effect enough of a voltage change on the instruments..
A regulator does not depend on the output load to drop voltage..it's 12 volts in a chip, and 5 or 6 volts out , regardless of if it has anything hooked to it or not consuming power..
You can get an instrument regulator at any auto parts store for Dodge or Chrysler in the mid 60's to 80's range of years..If you can't find one I can tell you how to build one from a hand full of parts you can get at rat shak..consists of a 3 terminal regulator chip, a heat-sink, some 18 gauge wire and a bit of your time..wire it power into the chip, ground , and 5 volts regulated out..The only rule is you must keep the draw UNDER 1 amp..(instruments won't draw that much..)
Just had another post on here SAME issue..the guy built one , installed it and was simply amazed how well they worked after all these years.. :D
This is one of the "Little headaches " that crop up on "split buss" systems..(Why I do not like splitting a buss..6 and 12..and advocate all or nothing at all..)
12v to 6v help
Sounds good to me. Need a break from electrical to work on something I understand. Called my local parts store (the one that actually tries to find things they don't stock) and they found several listings for Instrument Cluster Voltage Regualtors, $50. Do you have a particular preference -make/year/model? Or are they all the same? Unless I can build it for less than half of that, I'm better off buying one.
Assume this would replace the voltage reducer I have, and I would run both temp and gas gauge off of it.
Using the schematic you show above, Where would I hook in my amp gauge?
Seems like it would have to be in one of the two red lines, not where the idiot light is. (FYI. My horn relay is a small aftermaket one that is wired thru a fused circuit, powered only when the switch is on, not part of any original harness, so I can't go there, but I get the idea).
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