Question for everybody using a 5v chip to power your gauges.

[Plumcrazy]

Do your gauges all read a little low?  Mine do.

Several years ago I converted the voltage limiter to a 5v chip to power my gauges. I checked to output voltage, 5.01 v.

Since then I notice if I fill my tank at the 1/4 mark I can only get about 11 gallons in the tank, It should be closer to 15.
My oil pressure gauge reads about 40 psi at idle, my mechanical test gauges read about 60 psi.
And my temp gauge only goes to about 170 even though I have a new 180 thermostat.

So i bought one of these to do some testing.
http://www.amazon.com/DROK-Voltage-Converter-Regulator-Waterproof/dp/B00CEP3A0Q/ref=sr_1_8?ie=UTF8&qid=1390528775&sr=8-8&keywords=drok+voltage+regulator
I also have the C-3826 gauge tester from Chrysler.

The fsm says the oil pressure and fuel gauge should read at the 1/2 mark with the tester set to the middle position.
I checked the oil pressure gauge in my car and also my spare oil pressure and fuel gauges. All read noticable below where they should be when supplied with 5v.

So I hooked the voltage regulator up to my spare gauges and started at 5v.  Then I raised the voltage to get the gauges to read right.  With the regulator set to 5.3v the gauges read perfect. 

Maybe somebody will find this info usefull. 

[cdr]

thanx for sharing this info.

[Pete in NH]

Very interesting! I wondered about the voltage tolerances on the 7805 regulators and how it would effect gauge readings. The 7805 regulator is specified to have an output voltage of 5 volts plus or minus 5%. That would give you a range of 4.75 to 5.25 volts. The average output of the original electro mechanical regulator is "around" 5 volts but the actual voltage can't be measured with an ordinary voltmeter, so its actual value is a guess at best. Perhaps a better choice for the "chip" regulator conversion would be the LM-317 which is an adjustable type of 3 pin regulator very much like the 7805. You could also use the 7805 and place a diode like a 1N4001 in series with the center pin on the 7805 to raise its output voltage by .6 volts if you get a low end one. The banded end of the diode would go to ground and the other end to the center pin of the 7805. The metal tab of the 7805 can not be grounded if you use the diode.

[shorty442]

Ditto cdr - thanks to both parties for the info!  will be approaching this very topic on our '67 this Spring!

[Cooter]

Has anybody given thought to the fact that dead nuts empty, these tanks are rated at a certain amount of gallons.
there is a reserve even when empty by the guage, of about 3 gallons.

I put a new tank in a customers Charger and dumped 5 gallons in and the gauge didn't move...
dumped another 5 gallons and shoulda seen about 5/8 tank, but only showed 3/8.

[Ghoste]

I've always wondred about the amount left when empty, is the 3 gallons standard?  I've always thought it was somewhat random?

[Back N Black]

Has anybody given thought to the fact that dead nuts empty, these tanks are rated at a certain amount of gallons.
there is a reserve even when empty by the guage, of about 3 gallons.

I put a new tank in a customers Charger and dumped 5 gallons in and the gauge didn't move...
dumped another 5 gallons and shoulda seen about 5/8 tank, but only showed 3/8.

When you installed the new tank, did you install a new sending unit? If so, the reading is off at least 1/4 tank. The new sending units need adjustment for correct reading.