Instrument Voltage Regulator upgrade: why 5V instead of 6V?

Will be redoing the Dash on a 68 Barracuda and will be converting the Instrument Voltage Regulator to Solid State per the November 1992 Mopar Muscle Article.

Most of these conversions use a "7805" voltage regulator which supplies a constant 5V to the gauges. My question is WHY 5V? These gauges are meant to run on 6V so why not get a "7806" voltage regulator instead?

I have heard that people using the 7805 dont get full gauge travel and accuracy. Wouldnt a 7806 therefore be the answer?

Also I have seen some people soldering the additional Capacitor (which is meant to protect the Voltage regulator from spikes) to the 12V input side of the Regulator, and other people soldering it to the 5V output side of the Regulator.

The Mopar Muscle article shows it soldered to the Output side and to ground. This doesnt make sense since it will have no way of protecting the Voltage Regulator since they mounted it "downstream" of the current.

THANK YOU

Here are two links showing different Capacitor configuration:

http://1962to1965mopar.ornocar.org/ml-instrument-voltage-regulator64.html

http://www.jefframin.org/library/IVR.2.jpg

Not sure what the original gauges were designed for, but I could never get the 5v regulator to read full scale, so you might be right on the need for 6V.
You do need to consider the current rating of the regulator, some are too low.

Protection cap at input makes sense, wouldn't hurt to have another on the output as well, for ripple suppression.

I figure by using a 6 V Regulator, I can calibrate the needles at the half way point with 2 AA batteries (3V)

when I test the gauges with 3V they go to half way (give or take 1/16") I can bend the needles as needed so that they all go to precisely half travel at 3 Volts.

I know the parts aren’t that expensive, I’ve built a few to the specs in that article. Would be interesting to see the results of both 5 and 6 volt.

Does anybody know what voltage the Real Time Engineering regulator run at?

why not 6v

Check what .5 volt diff makes

http://www.dodgecharger.com/forum/index.php/topic,37999.0.html

FWIW when I bench checked mine they were exactly halfway with 3 volts.

Just an FYI.
Some years back I bench checked a few factory IVR's using my Fluke 179. It has a ability to average readings over time.
The voltage output of the "point style" IVR will start at 12 volts when first powered up then it will go to 0 volts when the points open. The points close again and the it's output goes back to 12 volts. With in a second or two the points will be opening and closing at a very rapid pace. Way too fast for the meter to read in real time.
I switched the meter setting to average reading over time and found that the IVR was outputting and average voltage of around 4 volts. I was a little surprised that it was not closer to 6 volts. I tested the other IVR's using the same method and found the same results.

The factory IVR s a thermal resistor, it won't work well with the minimal load of the Fluke.

The factory IVR is not a thermal resistor, it is a bimetallic strip that heats and cools cycling the output on and off causing a chopped DC output that averages somewhere around 5V.

I guess if you looked at the output on a oscilloscope you would see a square wave form.

How many gauges are you powering, Temp, Fuel, and oil?

The reason I ask, is if all three, the linear IVR (7805) can go into thermal shutdown unless it had a good heat sink.

The 7805 regulator circuit should have both input and output capacitors.

Is there a picture of one of these electronic conversions completed? My dash does not work and I am pretty sure this is the reason. I would like to replace the old point type with a newer electronic version.
OOPS!
Never Mind. I just found th elink already posted back a few pages.

Why doesn't anybody say anything about Real Time Engineering plug, and play regulator, instead of having to rig something up?

Could it have anything to do with the high price maybe.

I'm wondering what's wrong with the factory regulators.
Has anyone ever really had 1 go bad AND destroy the gauges?
Not really seeing the benefit of paying so much for the solid state version.

While my dash is out, I figured now is the time to do it. It cost $10 (CDN) to make it myself.
Also the A body rally dash doesnt use a seperate plug and play regulator. Its integral to the fuel gauge. I ended up clipping out the regulator parts inside the Gas gauge and rigging it up externally. I ended up using the 5V instead of 6V per Nacho's link. I will test it at school next week and see if I can use their fancy equipment to calibrate them.

$50 is a cheaper than getting the gauges fixed, and they are designed so that if it fails, the power to the gauges are shut down.

Not me, but yes know some and have dissasembled many other clusters damaged because that. Any fail able to keep stuck the points burn the gauges. Even a missed ground which still with a good conditions VL will make the bimetall never to open and feed straight 12v

Dunno if this could be "promotional" to their product, but seems to be kinda logic

I like the RTE setup. Really a better design, but $50.

The linear regulator I pictured, is mounted inside the original IVR case, and the heat sink bolted to the outside of the case, with heat sink grease between the regulator, case, and heat sink. Not the ideal configuration, but with the stock case it plugs in like the original IVR (no soldering to the instrument panel.)
The regulator I pictured is a slightly better 1.5 Amp 7805 regulator, but that was many years ago. I haven't looked recently if there are even better versions now?

I think on my '69 rallye dash, each gauge pulled about 1/4 amp at full scale. Without the heat sink, at 3/4 amps (worst case - full tank of fuel, maxed oil pressure and water temps), the regulator will start to go into thermal shutdown (reduced voltage output) after about 10-minutes (depends on ambient temp.)
At 1/2 amp, I did not see any voltage drop without the heat sink, even after several hours. I think if you just have fuel and water gauges, just using the stock IVR case as a heat sink should be OK, but with all three gauges, the additional heat sink may be needed? I did not have a way to increase the ambient air temps when testing, and I din't know how hot it gets under the dash in the summer time?

On the other hand I almost never have a full tank of fuel, 100 psi oil pressure and 260 F water temps, so the real load is much less than the 3/4 Amp max, but the regulator needs to handle that situation to make sure the gauges don't read low when they should be reading high.

Really, if you have the money, just get the RTE regulator. If on a budget, the 7805 setup works OK but know its limitations.

If you need the 7805 regulator and caps, I still have some extras.

Tech archives

http://www.moparts.org/Tech/Archive/elec/11.html

Man I forgot about this as I read it back then. So I went looking through my stuff this morning and found a pair of NTE960. Yep they are 7805 with new heat sinks. Boy do I love free upgrades.

One of the reasons for the 5vDC regulators was that they are used in computer power supplies and are available cheap.

What's interesting to me is the idea that when car manufacturers switched to 12 volt systems they threw a voltage "regulator" at the dash instead of changing the gauges.

R.

Given a set resistance of the gauges, using 12V instead of 5V would almost triple the current drain.

Not to mention the reason it was done. System voltage varies alot. By using a regulated 5V which is well below any normal system voltage variance you can make sure the gauges read correctly regardless.

Actually the 5 volt IVR the factory uses came out way before any computers were on cars. Unless you mean any computers other then on cars ? Ford also used this setup as I don't know why they decided on 5 volts other then that's the best for the type of factory gauges that use a bi-metal strip that bends to move the needle. The voltage on them gauges has to be steady or the voltage changes just from the charging system with the car running would make the gauges move around. Now GM used magnetic type gauges that uses 12 volts to them and they use to wound coils to move the gauge as one coil is grounded and the other goes to the sending unit so it varies how strong it is to pull on the needle and move the gauge. I don't know which are better but you can tell when cars had the GM type magnetic gauges as they usually will stay where they are when the key is turned off and of course the Mopar and Ford type bi-metal gauges go back to zero or empty when the key is turned off. Ron