Fuel Gauge Vibrator got ya down? FAQ

[telford dorr]

Don't have any pics of a completed device, but here's a schematic from the gallery:

You used to be able to get the LM-317 regulator device from Radio Shack. Fry's should have all of the parts.
_________________
'71 panel, now with FI
'Experience' is the ability to recognize a mistake when you're making it again - Franklin P. Jones
In theory, theory works in practice; in practice, it doesn't - William T. Harbaugh
When you're dead, you don't know you're dead. The pain is only felt by others.
Same thing happens when you're stupid. - Philippe Geluck
More VW electrical at http://telforddorr.com/ (available 9am to 9pm PST)

[GeorgeO.]

Going to make one as a backup just in case. The original still works but has almost 100,000 miles on the speedo.

[SGKent]

resurrecting an old thread. This is an area I need to cover when the trans is done. I added an amp before our last trip to Yosemite, and it gets noise even when the stereo is off. I suspect it is hearing the instrument regulator cycle because it is the old style.

There are notes somewhere in one of my books where VW indicated that when stereos were installed, the mechanical points style regulator needed to be replaced with the electronic style regulator. I am nervous about that and here is why. When we bought our 1977 bus it had an electronic regulator in it, and the fuel gauge itself was fried - as well as the sender being bad too.

I looked over the wiring and the only place the gauge got electricity from is the instrument voltage regulator. The electronic one in the bus was genuine VW and it still put out a constant voltage so I don't think it was bad. Looking at how things worked - it looks like the gauge system we designed for the older style voltage regulator. In fact it does not look like it is a regulator at all. Both the gauge and the old style regulators are heaters. The current passing thru the windings heats them and causes the needle to move. The "regulator" simple allows the gauge to maintain temperature by turning current on and off to the gauge. It also has windings which drop the voltage.

Here is a typical cycle on the old style. Power runs thru the VR windings dropping the voltage and sending that to the gauge. The gauge windings use heat to drive the needle. When the VR is on for a set period of so many seconds, it warms up, warps and points disconnect. That starts a cool down on the gauge. When the VR cools off enough its points make contact and the cycle begins again. The gauge deflection is not due to current or voltage but rather the max and min temperature during the cycle.

Apparently the noise generated by the VR points opening and closing could be heard in stereos so VW replaced the VR with an electronic one to make it quieter. Problem is that at least on my bus the gauge itself burned up internally - the windings were cooked. That has to make me think that the VW solution is only a temporary one that eventually causes the gauge to burn out.

I am looking for a more permanent solution. I am concerned that the style of gauge in these buses may not fully adapt to an electronic VR due to "the needle heater" being on all the time even if at a reduced voltage. If someone for example measured output on the old style they might see voltage V but it would be a square wave V off V off V off V off. Now we substitute a reduced but constant V. We might be able to get the needle to maintain the same temperature and deflection, but the windings might burn out sooner as there never is a cool down cycle.

So - has anyone with an electronic VR for the instruments on a late bay got 100,000 miles of no problems or are we still experimenting that it will work?
_________________
“Most people don’t know what they’re doing, and a lot of them are really good at it.” - George Carlin

[telford dorr]

Would seem to me that, seeing as how the fuel gauge pointer position is a function of heat, it wouldn't care if the heat source was pulsating or steady (as long as the pulse frequency was much faster than the thermo-mechanical response time of the indicator).

To eliminate the noise of a mechanical regulator, you might try putting a series resistor-capacitor network across the regulator to slow the rise and fall of the current (maybe guessing 22 ohms and 0.47 uf? The capacitor slows the points-open current transition, and the resistor limits the peak capacitor current when the points close again). Taking out the fast current transitions should eliminate the source of the noise.
_________________
'71 panel, now with FI
'Experience' is the ability to recognize a mistake when you're making it again - Franklin P. Jones
In theory, theory works in practice; in practice, it doesn't - William T. Harbaugh
When you're dead, you don't know you're dead. The pain is only felt by others.
Same thing happens when you're stupid. - Philippe Geluck
More VW electrical at http://telforddorr.com/ (available 9am to 9pm PST)

[Wasted youth]

How different is the early Vanagon circuit from the late bay? I see my 1981 Vans have an upgraded VR. Can we use that setup on a late Bay gauge?

[SGKent]

[telford dorr]

[SGKent]

where in the circuit is this cap and resistor going? Bridging across the points?
_________________
“Most people don’t know what they’re doing, and a lot of them are really good at it.” - George Carlin

[telford dorr]

Exactly.
_________________
'71 panel, now with FI
'Experience' is the ability to recognize a mistake when you're making it again - Franklin P. Jones
In theory, theory works in practice; in practice, it doesn't - William T. Harbaugh
When you're dead, you don't know you're dead. The pain is only felt by others.
Same thing happens when you're stupid. - Philippe Geluck
More VW electrical at http://telforddorr.com/ (available 9am to 9pm PST)

[SGKent]

got it - thank you. So when the points open the current continues to flow then reduces to zero slower reducing the spark. When the points close the energy in the capacitor flows back into the circuit but thru the resistor. 1/2 watt be adequate or would 1 watt be better?
_________________
“Most people don’t know what they’re doing, and a lot of them are really good at it.” - George Carlin

[telford dorr]

Based on the energy storage in the cap, 1/2 watt should be plenty.

---

Details, for those curious

Energy stored in a capacitor, in Joules (AKA, watt-seconds):

E = 0.5 x C X V x V

where: C = farads, V = volts

for C = 0.47uf = 4.7 x 10e-7, V = 14.4

E = 4.87 x 10e-9 watt-seconds

Assume the points open 10 times a second (or 0.1 seconds / pulse), and the capacitor discharges completely:

P = E / 0.1 = 4.87 x 10e-8 = 0.0000000487 watts

Note the value of the resistor doesn't matter, as long as it allows the cap to discharge in the specified time.
_________________
'71 panel, now with FI
'Experience' is the ability to recognize a mistake when you're making it again - Franklin P. Jones
In theory, theory works in practice; in practice, it doesn't - William T. Harbaugh
When you're dead, you don't know you're dead. The pain is only felt by others.
Same thing happens when you're stupid. - Philippe Geluck
More VW electrical at http://telforddorr.com/ (available 9am to 9pm PST)

[sestino]

Bump.

I don't understand all of the discussion of electronics, but I saw above that one of the components is an adjustable voltage regulator.

I just stumbled across this adjustable voltage regulator on DX.com selling for $1.80 plus shipping.

http://www.dx.com/p/20083-adjustable-power-supply-...7PGqCgrI2w

Could this inexpensive piece be used in place of the vibrator? One commenter on DX.com wrote:

Pros:
Simply and sturdy board for DIY aplications, ideal to branch to a 12-24V line and reduce to 5 or 3.3V MCU application. Just branch and adjust the tension using the potentiometer.
Cons:
Limited to 2.5 A, means that you must have that current limitation in your proyect. Not sutable for motors or other stuff, but it can be very useful for install a led bar in a car or add sensors on a industrial installation.

[awreed]

For $1.80 plus S&H, why not give it a shot. Though if it doesn't work, would you risk frying the gauge? Not sure if I'd risk that.

[telford dorr]

It's sort of overkill, but for the price, why not?
_________________
'71 panel, now with FI
'Experience' is the ability to recognize a mistake when you're making it again - Franklin P. Jones
In theory, theory works in practice; in practice, it doesn't - William T. Harbaugh
When you're dead, you don't know you're dead. The pain is only felt by others.
Same thing happens when you're stupid. - Philippe Geluck
More VW electrical at http://telforddorr.com/ (available 9am to 9pm PST)

[sestino]

Thanks everybody. I just ordered 3 for a grand total of $5.40 delivered (free shipping).

If someone wants one of the 2 extras that I purchased, send me a p.m. and I can send it to you gratis - it may take me a while to install mine, so I'd love to see if anyone else gets it done faster.

[SGKent]

wanted to update this thread. The stock original vibrator is an on off bimetallic device. In buses with a radio it was replaced with the electronic regulator 113957099A - same for a bug or bus.

The repop one being sold as genuine in some circles today was unstable and started at 5.34 volts then drifted as it warmed. The genuine factory one was 5.1 V and held solid. Telford was here when we made the measurements. The meter they were checked with was just calibrated less than a month ago with a lab standard voltage generator.

The factory unit is worth the difference in price if you can find one.

http://www.thesamba.com/vw/forum/viewtopic.php?t=6...highlight=
_________________
“Most people don’t know what they’re doing, and a lot of them are really good at it.” - George Carlin

[sestino]

[telford dorr]

[telford dorr]

[SGKent]

I spent about an hour last night looking for any articles from VDO specifying what the voltage should be. The only thing I found of value was a fellow selling dash voltage regulators. He indicated that the value for VDO gauges is 5.10V which matches that factory unit. That said I saw the note from Old DKP Driver. He indicated VW had some issues with the screw coming loose. If so, I suspect that with a loose screw and no ground then the full 12V would reach the gauge and sender - is that correct Telford?
_________________
“Most people don’t know what they’re doing, and a lot of them are really good at it.” - George Carlin