6V Gauges in a 12V world

Dangermouse · Post by **Dangermouse** » Mon Dec 17, 2007 7:22 pm

I’d like to install a couple of electrical gauges in my 6V beetle, maybe cylinder head temp or oil temp and oil pressure. In the absence of 6V gauges, can I use a 6-12V voltage converter to power them?

What about the sender units, do they require their own 12V power supply also?

I like the look of the VDO Series 1 gauges for resemblance to stock, coupled with a dual terminal sender to operate the oil gauges and idiot light, like this arrangement...

https://secure.cbperformance.com/catalo ... ductID=837

Is this at all doable?

Speedy Jim · Post by **Speedy Jim** » Tue Dec 18, 2007 5:52 am

Yes, it's doable.

You will need a (small) 6V to 12V Inverter.

Only the gauge needs 12V, not the sender.

Some possible sources:
http://www.thesamba.com/vw/archives/man ... verter.php
(Don't know if it's still made.)

This is a DIY:
http://www.aaroncake.net/circuits/6-12conv.asp
and:
http://www.elecfree.com/electronic/lm25 ... regulator/

Another approach is to get a very small 12V battery, like motorcycle,
to power the gauges. Recharge when needed.
Also possible to use a small 6V battery, charge from the car and
then series for 12V out. Getting complicated....

Speedy Jim
http://www.nls.net/mp/volks/

Dangermouse · Post by **Dangermouse** » Tue Dec 18, 2007 12:14 pm

Thanks Jim, I was hoping you'd chime in

I was going to use one of these...

http://cgi.ebay.com/ebaymotors/ws/eBayI ... %26fvi%3D1

which gives me 5A to play with.

In a similar vein - if somewhere down the line, just for giggles, I wanted to install an electrical tachometer also, do you think a 6V input signal at the coil would allow the gauge to function properly?[/url]

Speedy Jim · Post by **Speedy Jim** » Tue Dec 18, 2007 12:56 pm

Neato! Great find. Buy it.
Check this Item # too: 290173332418

I should add that some gauges may operate on either 12V or 6V,
but I wouldn't stake my life on it.

The Tach will probably be OK with the signal from the points; if not,
we will construct a simple circuit to deal with that.

Dangermouse · Post by **Dangermouse** » Sun Mar 09, 2008 7:49 pm

This seems to have worked out quite well so I thought I'd report back for other 6V users who might be interested...

The voltage converter seems to be a good little piece of equipment and appears to do its job well...

Here it is mounted on the back of the radio...

The VDO Series 1 gauges came from nhspeedometer.com who provided excellent service. The only modification was that I asked them to replace the gauge bulbs with 6V equivalents so they could be run straight off the light switch as normal.

One small mistake (which may have been a misscommunication on my part); spot the deliberate error...

Oil pressure and temp senders in place. I was mindful not to overtighten the tee fitting into the engine block for fear of cracking the case so I just kept giving it an extra quarter turn until it eventually sealed and stopped leaking.

I did attempt to run the wires up through the roof channel alongside the wiring loom but had to give up. There was no way I could get a fishtape to feed through. I compromised and ran the wires inside the body, under the back seat, along the floor pan and up into the front just forward of the door pillar.

Here's the gauges in place; I'm happy with the finished result.

Hardest part was trying to figure out how the mounting cups go together; still not sure I've got them right...

Oil pressure, temp and CHT are all functioning well. The bulb on the CHT gauge blew straight away which makes me wonder if it was indeed replaced with a 6V one, the others are all holding steady. I guess I'll just have to just replace that bulb, no biggie.

The tach, while it is functioning, is not reading quite accurately just yet. The diagram of the micro-switches included with its instructions seemed to be reversed so that at first it was registering 2,000 rpm at idle. I had heard about the irregularities of the VDO instructions though and was ready for that one. I believe its now set properly for 4 cylinders and I've got it reading about 500 rpm at idle (actual idle speed as measured by my DMM is closer to 850). The potentiometer on the back allows for some degree of fine tuning but not that much. Its quite steady though.

Any suggestions Jim?

Speedy Jim · Post by **Speedy Jim** » Sun Mar 09, 2008 8:02 pm

Nice setup and nice writeup w/pics!

Love the H2O temps gauge. LOL

I wonder if the inverter could be causing the tach to mess up.
Try a 12V battery feeding the gauges, as a test.

If not that, maybe the signal from the coil is deficient as far as
the tach is concerned. Post back if the 12V battery solves it or not.
May have to come up with a circuit to drive the tach (hope not).

Speedy Jim
http://www.nls.net/mp/volks/

MNAirHead · Post by **MNAirHead** » Mon Mar 10, 2008 10:43 am

those are incredibly cool..

Thanks for the write up and help (speedy)

Dangermouse · Post by **Dangermouse** » Mon Mar 10, 2008 1:27 pm

Love the H2O temps gauge. LOL

Yep, I decided to keep it

Try a 12V battery feeding the gauges, as a test.

No change when supplying the gauge with a 12V battery feed unfortunately.

If not that, maybe the signal from the coil is deficient as far as
the tach is concerned

I suppose a very easy test here would be to just hook the tach signal wire to a 12V coil on a donor vehicle and see if that changes the state of the signal? It would rule it in or out at least.

May have to come up with a circuit to drive the tach (hope not).

Sounds ominous...

Speedy Jim · Post by **Speedy Jim** » Mon Mar 10, 2008 2:05 pm

Good idea to hook it up to a 12V coil donor.

Await result with bated breath

Dangermouse · Post by **Dangermouse** » Sat May 24, 2008 5:06 pm

Just to revisit this one briefly...

I did end up trying to connect up the tach on a 12V donor vehicle, I just backed a friend's beetle up beside and ran a wire from their coil to my tach sender; it didn't help (if anything it was worse). I wasn't sure if there needed to be some sort of common ground connection between the two vehicles for this to have worked, I did try connecting the two bodies together with another wire but there was no improvement.

The tach (and the other gauges) continues to function well, if inaccurately, and I has happy to leave it at that and not pester Jim further...

Then the other day I spotted this in an electronics catalogue -

http://www.jaycar.com/productView.asp?I ... &SUBCATID=

Is this the sort of circuit you were thinking about? It reads...

"Speedo Corrector MkII Kit - When you modify your gearbox, diff ratio or change to a large circumference tyre, it may result in an inaccurate speedometer. This kit alters the speedometer signal up or down from 0% to 99% of the original signal. With this improved model, the input setup selection can be automatically selected and it also features an LED indicator to show when the input signal is being received. Kit supplied with PCB with overlay and all electronic components. "

I don't know if there's a difference between the signals for an electronic speedo as compared to a tach; do you think this could be used for my application?

Speedy Jim · Post by **Speedy Jim** » Sat May 24, 2008 5:49 pm

What a nice circuit. And very affordable too!

Technically, it's overkill for your needs, but at that price, what the hell...

If it's able to produce a good signal for the tach, worth a try.

Jim

MNAirHead · Post by **MNAirHead** » Sun May 25, 2008 9:36 am

Theory question.. any guess of how big a voltage converter we'd need to fire guages and a wiper?

Tim

Speedy Jim · Post by **Speedy Jim** » Sun May 25, 2008 12:06 pm

Well, I wouldn't run them off the same inverter; the wiper takes many amps.
It would probably be more practical to substitute a 6V motor (or just the armature).

MNAirHead · Post by **MNAirHead** » Sun May 25, 2008 12:22 pm

What about just the guages?

Speedy Jim · Post by **Speedy Jim** » Sun May 25, 2008 12:29 pm

All the gauges should be OK on the small "booster" inverter at the beginning of the thread.