Fuel Gauge Vibrator got ya down? FAQ

[Air_Cooled_Nut]

Okay, thanks to Timo78's investigation this fix seems to be a winner I finally got the parts together, tested it, and finalized on 17-ohms of resistance. Here's a pictorial of putting it together:
http://www.aircoolednut.com/cmgallery/index.php?cat=16
Click on the album titled "Bus fuel gauge vibrator replacement". It'll be the last album of the page in the lower right corner. Read the album description first before clicking it.

I'm not an electronics person so how I wired it all up and the exact resistors I used may not be electronically PC but since there wasn't much help, well, this is what you get until someone who knows more actually steps up and does it better. Assuming you already have wire and spade connectors then the total cost would be LESS THAN $6! That's pretty damn good in my book AND there are no moving parts.

<edit>BTW, if you click on the picture a window will open of just the picture and it will be much larger so you can see the details better. Click on the picture again to close the window and return to the album.
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Toby http://www.aircoolednut.com/
Did I mention that I'm an original Darksider?
'72 VW Squareback, 2007cc, GB 5-speed, rag top; '76 VW Riviera Penthouse Sundowner 2.0L; 2015 Audi S5 Cabby w/Stage II APR; '06 Ducati Sport Classic 1000; '14 Ducati Diavel Strada
The First Invasion

[timo78]

I like it! No moving parts is optimal. As a side note, I ran my tank into the reserve zone, and then filled up [yeah I'm chicken and, don't carry my plastic red can except on road trips ]. I put in 12.2g's, which means about 2g's reserve. Seems logical then that there's a direct correlation between visible Full and an accurate empty. If someone was inclined to add a pot/rheostat/ they would not need to empty the tank in order to set the adjustment and get accurate readings. Instead set the ohms at physical full and adjust to a visible full on the gauge. Or do the right thing and add the optimal AirCooledNut-resistor-pack, and adjust nothing. I may have to add one of those
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> 78Grµn Westfalia `Donkey`
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It may be bigger than you and it may be bigger than me, but it’s not bigger than you AND me; can you dig it?

[SGKent]

Really nice job.

There are many different kinds of these boxes but you might find a cheap small one that everything will fit in. That way you can build a box that is quickly and easily replaceable if the diode ever fails and keep a spare. All that would come out of the box would be three wires or connectors - in, out and ground. If one is small enough you could solder a tab on it and mount it in the same place as the original one.

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"Most people don't know what they're doing, and a lot of them are really good at it." - George Carlin

[telford dorr]

Here's an adjustable regulator regulator circuit to replace the vibrator. You can adjust the output voltage from around 7.5 vdc to around 10 vdc. Should make the gas gauge calibration easier.

If nowhere else, you can get all the parts from Mouser ( http://www.mouser.com ). The circuit's a little more complex than the fixed voltage regulator previously described, but flexibility costs a few more parts.

I used a 20 turn trimpot for the adjustable element, which makes setting the output voltage trivial. Tweek the adjustment until the gas gauge reads correctly.

The regulator chip (LM317T) will adjust its output to maintain 1.25 volts between the 'vout' pin and the 'adj' pin. Thus, the more resistance from 'adj' to ground, the higher the output voltage will be. If you want to tweek the design, remember that the output voltage = 1.25 volts x (total resistance / 240 ohms). The chip need about 2 volts drop across itself to function properly, so you can't get more than battery voltage - 2 volts out of it.

All resistors are 5% 1/4 watt; the bypass capacitor is a 50 volt ceramic (disc ceramic works fine.) All parts are non-critical, so use what you have. Build it in the nice box, shown above. Mount the regulator to the box using an insulating TO-220 mounting kit, and a little silicone grease, to keep the regulator cool (not that the gas gauge pulls much current...)

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'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)

[Air_Cooled_Nut]

Nice work, telford! Though I already did the leg work for the calibration
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Toby http://www.aircoolednut.com/
Did I mention that I'm an original Darksider?
'72 VW Squareback, 2007cc, GB 5-speed, rag top; '76 VW Riviera Penthouse Sundowner 2.0L; 2015 Audi S5 Cabby w/Stage II APR; '06 Ducati Sport Classic 1000; '14 Ducati Diavel Strada
The First Invasion

[Air_Cooled_Nut]

Okay, it's official, this mod works great! At a full tank my gauge needle rests on the Full mark. When the needle is on the left white mark on the Reserve marking there is roughly just over 1 gallon of fuel left. Purposely ran out of gas and then filled up (without topping it off) and she holds 14.4 gallons.

I'm now back to driving with confidence with my gas gauge
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Toby http://www.aircoolednut.com/
Did I mention that I'm an original Darksider?
'72 VW Squareback, 2007cc, GB 5-speed, rag top; '76 VW Riviera Penthouse Sundowner 2.0L; 2015 Audi S5 Cabby w/Stage II APR; '06 Ducati Sport Classic 1000; '14 Ducati Diavel Strada
The First Invasion

[vwwestyman]

Telford Dorr,

Could you please write out the hookups "verbally" like someone did with the non-adjustable voltage regulator?

I stopped by Radio Shack this afternoon and picked up the capacitor, the adjustable regulator, and a 10k-Ohm 15-turn Cermet Potentiometer. I noticed that the potentiometer had three legs, one was the "wiper" leg. I measured the resistance between the wiper and each of the other two legs. I also measured the resistance between the two other legs. As I turned the dial, the resistance changed between the center and each of the two outer legs, and the total resistance was always the same. (So, if between the middle leg and the right leg was 4 ohms, then the left leg would be 6 ohms.)

Anyway, I figured that it didn't really matter which of the outside legs on the potentiometer I used.

So, here is how I hooked it up:

12V > capacitor > voltage in leg

ground > potentiometer > adjust leg

Gauge > voltage out let

However, when I hooked it up, I hooked up the new sender to the wires and expected to see the needle somewhere in the middle of the gauge.

Nope. Not even with the sender wires connected. No movement.

So I decided to try to hook the gauge to the 12v to see if the needle would do anything. It went up a bit then dropped and did this a couple times...

Did I wreck the gauge?

What did I do wrong hooking the VR up and such?

[vwwestyman]

Another Q:

I was looking around on other forums and found this:
http://www.thesamba.com/vw/forum/viewtopic.php?t=400870&highlight=vibrator

which indicates that the vibrator is supposed to output 5v, not 10.

I wonder if all the resistors being used in this thread are, in effect, turning 10v into 5...

Anyone have thoughts on this?

[Air_Cooled_Nut]

Well, we already worked out the kinks for a 10v VR, now it's your turn to do the same with a 5v VR...git!
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Toby http://www.aircoolednut.com/
Did I mention that I'm an original Darksider?
'72 VW Squareback, 2007cc, GB 5-speed, rag top; '76 VW Riviera Penthouse Sundowner 2.0L; 2015 Audi S5 Cabby w/Stage II APR; '06 Ducati Sport Classic 1000; '14 Ducati Diavel Strada
The First Invasion

[telford dorr]

[telford dorr]

[vwwestyman]

Telford,

Thank you for the details. I had run into the Radio Shack actually after they closed. (The owner answered when I called yesterday to see when they closed, and he said "I'm just here doing paperwork, come on in.")

Anyway, he admitted that he wasn't real great with interpreting circuit drawings and such.

We ended up surmising that the adjuster is what determined the output of the VR, and it did so by the resistance to ground. We kinda thought that the resisters shown in the drawing were in lieu of the potentiometer.

So I guess I need to head back and get a couple resisters, and a different pot. They had a 10k and 1k ohm potentiometers.

I might also get a 5v VR just to see what happens. I know that it is no guarantee that VW used the same circuitry on other cars, but the rabbits and cabriolets used a 5v VR, and seeing the thread in the beetle forum makes me wonder...

[vwwestyman]

[Air_Cooled_Nut]

[vwwestyman]

I have no real proof that the vibrator in a late bay bus is supposed to be 5v instead of 10v. But my theory is based on some evidence.

First, this thread (which I posted earlier). Several people, including the last two, say that the vibrator in a Super Beetle is supposed to be 5v and is easily replaced with a 5v VR.

Of course, VW could have put a 10v in buses and 5v in beetles, but we all know that they always used the same parts in more than one car when possible. So if in fact it is true that beetles had 5v VRs, then probably buses did too. Newer watercooled cars used the exact 5v VR like from radio shack. Again, not proof but but evidence.

The fact that the gauge stayed too high when a 10v VR was installed (with no resister) makes me think that 10v is probably too much. Another piece of evidence.

This is the basis of my theory that the 10v VR with resistors is simply allowing you some adjust-ability of the current in the system through changing the resistance. I can't think of anywhere I've seen 10v shown as the proper voltage for this circuit other than here. The original idea was based off of a MGB's fuel gauge.

I'm not trying to be a punk or anything, just trying to contribute to the overall availability of information.

[Air_Cooled_Nut]

True and good observations. Sounds okay to me. But ya still gotta try it out
_________________
Toby http://www.aircoolednut.com/
Did I mention that I'm an original Darksider?
'72 VW Squareback, 2007cc, GB 5-speed, rag top; '76 VW Riviera Penthouse Sundowner 2.0L; 2015 Audi S5 Cabby w/Stage II APR; '06 Ducati Sport Classic 1000; '14 Ducati Diavel Strada
The First Invasion

[vwwestyman]

Yeah, I'm pretty sure the stock setup from the factory was 5v, but the really good part about using the 10v regulator or adjustable regulator is that it allows you to compensate for whatever amount of resistance is in the system. One poster said that he used 17 ohms to make his gauge work right, but someone else may have more or less resistance in the system so 17 may not be anywhere close to the necessary amount.

I still need to figure out if I can make my new (used) sender work right. Since the needle goes to 1/1 when the two sender wires are connected, I can only surmise something is wacky to make the needle not go up there when hooked to the sender. If I can get that worked out, then I can see how closely the gauge works with the 5v resistor.

[busman78]

Brought this back to life due to some testing I have been doing.

The bench has 8 gauges, 8 vibrators, 3 senders, one of them new, plus a couple 5V Voltage Regulators, one NTE960 and a LM7805C ready for the fun to begin. First off was testing the senders, then ran voltage tests on all eight vibrators, two of them are extremely low mileage units, the vibrators do not put out 12V, in fact they do not even get to 5V, voltage ranges from 1.5 +/- .1V to a max of 3.8V, occassionaly there would be a spike to 4.2V. The norm was 2V to 3.5V. The vibrator does exactly that, pulses voltage, they are not a constant voltage devise which is what keeps the gauge needle from bouncing when the fuel gets sloshing in the tank.

The higher the voltage from the vibrator the higher the gauge will read at the full mark, the lowest vibrator at 1.5V will push the needle of the gauge even with the full line, the vibrators that has 2V as the lowest voltage will trip the needle 2mm past the full line. Did not matter which sender was hooked up, the two used and the new one gave the same reading. Tried numerous gauges including the two low mileage gauges, one with 54K and the other with 67K original miles, also installed different vibrators for testing with each gauge. Pretty much got the same readings, within 1mm spread across all the gauges and depending on which vibrator the empty was within 1mm and full 2mm max. Now this was all on an bench with good wire and a dedicated battery not powering anything else.

The 5V regulators also worked, slight movements with the sender did not cause the gauge to fluctuate. But have not done over the road thesting.

Now there are two adjuster holes on the gauge, one for empty and one for full, with a small screwdiver the max travel of the neddle can be set, now I have only bench adjusted based on the movement of the sender clamped in the vise. Suspect this would do the same thing as a Pot will do.

Now my bus which has always had goofy fuel readings, never would get to full and be in the red with five gallons still in the tank. For fun I ran a wire from the sender to the gauge, yes I do have a sender access hole and gained 2mm of needle movement up, so there is some resistance in the old sender wire. Something to consider when concerned about low or inaccurate gauge readings.

The above is not all conclusive or absolute, the use of a Voltage Regulator with resistors or a pot is probably a better solution than buying a vibrator, at least cost wise, as for constant 10V hitting the gauge I have no idea what it will do in the long run. Even with the VR/Res/Pot there is still the mechanical sender, gauge and ten to twelve feet of 30+ year old wire.

I do plan on putting the new sender in, best reading vibrator and run a new sender wire to the dash, then fill the tank and perform adjustments to either the gauge or sender to read dead on full, then start draining the tank to verify 1/2 tank, reserve and finally set dead on empty.

[RatCamper]

THANK YOU!

I have been asking around for these numbers for years. because I had no functioning vibrator / zener and light bulb based voltage/current regulator I had to guess. And guess I did. On here or AVD or somewhere else I did a writeup of my findings.
The only info i could find was for a 6v beetle and it wasn't the most relevant.
Now my old calculations have disappeared into the aether and I needed the info again.
The best setup i had was running a truck fuel gauge with a parking light as a current limiter and a resistor between a couple of the terminals. I tried putting a smaller bulb on but the gauge pretty much just reads empty now. I've been hesitant to put the parking light bulb back on because a better solution had to be out there. Thank you

I have to read some of the posts here more closely still, but when the linear regulator is being used (the variable voltage type which is set using a resistor right?) what is being done about current limiting? If nothing, those little regs can push more than an amp if allowed to. Of course they burn up awfully quick that way. If it's a fixed voltage type and it is connected backwards by accident, absolute mayhem ensues. it's hard to explain and took me a lot of probing to figure out what happened on a piece of computer interface hardware i was developing. It seems counter intuitive but it was still trying to regulate the voltage but by dragging the ground plane up. Add to the mix a second regulator trying to do things the right way and things get very ugly very fast.
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Vehicle: 1975 Special order delivery walkthrough panel based pop-top camper (LCA / Sunliner). Motor: Nippon 1.8L Single port Wasserboxer, Transmission: 3 rib 002.

[busman78]

Suspect that the 5V for buses and 6V for bugs is nothing more than factory max volts, cause no vibrator I have tested reaches the 5V range.

Did some more testing with the 5V Regulators today, seems after a minute or so the voltage begins to climb, the LM7805 triped past 10V and the NTE climbed to 9V, so fixed regulators they are not. And with the voltage increase the needle rises on the gauge.