Voltage reducer, rallye gauges

[MAXcuda]

Hey Chryco, I'm having my rallye cluster redone over at autoinstruments.com right now, and the guy suggests that I replace my voltage reducer.  (12V to 6V for the small gauges).  He says they sometimes go bad and can send 12V to the gauges and blow them.  Supposedly they're available at local parts stores cheap.  Have you heard of this?  I asked if I could just check it with a multimeter by putting 12V to it and looking for 6V out.  He says no, it actually pulses and gives an average of 6V (RMS averaged is what he means I guess) so that wouldnt work.  How would I make sure I'm getting the right thing from the chevy guys behind the counter before I stick it in my way too expen$ive gauge cluster?

Also, as a side question, I'm curious as to how this thing works.  Since DC current cant be transformed, how would you step it down and get a pulsed output?

[Chryco Psycho]

I`m not sure how they work but they do send a pulse out not a steady voltage
 I have heard of them being readily available form local parts stores , they do not seem to fail often & the real ? is , is the replacement beter quality than the original , most often I have seen them not supply any voltage as opposed to sending 12v to the guages . They are probably sold under the Standard name & have a unique pina rrangement so if it fits it should be the correct unit

[MAXcuda]

ok thanks, ill check on that

[MEK-Dangerfield]

MAXcuda,
  I've seen them in Year One's catalog. Twenty some bucks I believe. I'm not sure about local places selling them.

  Mike

[MAXcuda]

For future reference:

GP Sorensen part number IVR3 available at Advance Auto Parts $19.95

Don't let them sell you IVR4, its for later models, different connections and mounting.   

[zstalker]

there's a guy who sells converters that he's made into solid state systems, to eliminate the pulsing...here's his address: http://www.moparmike.com/

[MAXcuda]

Thanks for the link, I already built a solid state one.  All you need is two capicitors and a 7805 chip.  There are scans from mopar muscle/action about the conversion on http://www.robdiesel.com under techinical info.   :thumbs:

[Katfish]

MAX,

What caps did you use?  I looked at the Mopar article and it didn't mention these.  It only showed regulator and a 270ohm resistor.

Katfish

[MAXcuda]

I used two 10 uF tantalum caps.  It doesn't make a :fire: of a lot of difference.  Input cap protects the chip from voltage spikes and output cap improves transient response.  I tested it today.  It puts out 5.00V and it reads a teeny tiny bit low compared to my stock reducer.  Not enough to worry about.  The stock reducer put the fuel pointer on the end of the lower cross-bar of the F with a full tank, and the solid state one put the pointer on the end of the upper cross-bar.  This is testing it with standard gauges, not rallye.

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[Katfish]

Max,

Did you use the resistor on the output?  I assume this is just to provide a load to keep it in regulation?  5V/270ohm = 18mA.  Maybe the gauges don't draw any real current?


Katfish

[MAXcuda]

I did not use the resistor.  I followed the Mopar action install (which did not use a resistor) instead of the Mopar muscle one, and added an output cap, which was recommended on the data sheet for the chip.  I don't know why you would need a resistor.  If the gauges did draw any current, then there would be voltage drop across the resistor and then the gauges would be getting something less than 5V.  That's what I'm thinking.

[wedge5811]

The gauges do draw current, but varies.  Most chrysler sending units  run from 0 to 180 ohms.  The sending units are just variable resistors. A resistor on the positive side would be used to adjust the range.  They must have used the resistor to calibrate the output so their gauges would read correctly.

[MEK-Dangerfield]

wedge5811,
  I believe what you say, but the resistance readings on the sending units of E-bodies is more like 5 to 70 ohms.

  Mike

[Katfish]

Just a FYI,

I double checked the tech article and the 270ohm resistor is going from the output to ground.  This way it doesn't change the output voltage, just increases the current drain since it's in parallel with the gauges.

I have also measured the resistance of the fuel sending unit in the past when things weren't working, mine went from 10-80ohms.

Katfish

[MAXcuda]

Ok, that makes sense.  I couldnt tell where they had the resistor.  What purpose do you think it serves?  To shunt some of the current away from the gauges?  I figured the gauges would just draw whatever current they needed, no more and no less.   :dontknow:    anyway, I'm taking it for a test drive tomorrow to check the speedometer and tach.