The Stovebolt Site Forums The Shop Area The Electrical Bay Tach for 216 / 6 volt system

Can a tach be used with a 6 volt system? If so what's a good brand? I would sure like to know the rpms as I'm running a stock 216 and 3 on the tree. THX for your help.

I don't know of an electronic tach that will work on a 6-volt system. You might check with Sunpro, or one of the other electronic instrument manufacturers to see what's available. Some of the older farm tractors used a cable-driven tach like a speedometer, with a drive unit built into the back of the generator. You'd need a correct-sized generator pulley for an accurate reading, which might be pretty dificult to set up.
Jerry

Another way tachs were driven in the old days was a mechanical cable from the distributor. I don't know anything about them, except that they exist, and they were used on Corvettes until 1976.

Volkswagens had 6 volt systems. Check online for a VW after market parts supplier.

You should be able to trigger a 12 volt tach with a six volt ignition system as long as you are supplying the tach power supply with 12 volts. You could run a 12V boost converter, should only need a couple amps. You could convert the back light bulb to a 6v bulb to wire to your instrument panel. The tach should trigger from the points grounding the sensor wire and should not be sensitive to the amplitude on the trigger wire, which is only about 3-4 volts even on a 12V system.

Most modern analog electronics run on 5 volts internally, so some of the newer designs may work ok on 6 volts, it shouldn't hurt them to try. They should have a regulator inside to convert the voltage down, and most off the shelf regulators can work with only 1V of headroom. If I was designing a new tach {I actually design instrumentation for a living, but much more complex stuff than tachometers}, I would design it to have 5 volt supply rails internally and use an LDO (low dropout) regulator to derive the internal voltage from 6-30V dc, so it could be used on 6, 12, and 24V systems.

If you can find the schematic for a tach you are thinking about using I'll be happy to tell you if it can be modified to work on 6V if you can email it to me.

Well I taint Mo from Des Moines, IA Josiah but if that offer goes for me I just might take ya up on it. I just ordered one of those cheapo Sun Super Tach II's from Whitney's and it's 12v obviously and I'm running a 6v system.
If ya know me at all by now ya know I like to tinker and antique radio restoration is my other passion. I can fix 'um but I can't design them.
So when I get the tach are ya willin' to take an online look at it with me and see if the power supply section can be modified for 6v???? Like you were alluding to in one of your replies, these things probably revolve around a 555 timer and operate on 4.5v so in all likelihood they are just stepping the 12v down to that.
Denny Graham
Sandwich, IL

Along these lines, does anyone know where I can get a Sun Tach and dwell meter fixed? The model number says TDT 12 and VDC 6-12-24. This thing gas a 9 Volt battery for the tach and a flashlight battery for the dwell meter.

Westach at 800-400-7024 or www.westach.com has several 6volt tachs available. I have a 55 Ford that is 6volt positive ground and they had one to fit it.

Spent the last twenty minutes at Westach's site and finally gave up trying to find prices and by the way I gave up on Westach also because of that! When are the web designers ever going to learn!
Denny Graham
Sandwich, IL

Denny Graham,

Giant double ditto on your comments. In this day and age of instant gratification, not having prices posted on your web site is a instant 'adios' from this thrifty consumer!

Stuart

I agree with you guys about prices being posted.

Have you recently looked at Jim Carter's on-line "catalog"? Prices are not listed until you put an item in the shopping basket/cart.

My Good God Stu, don't tell me we agree on somethin!!!!
Yep it's a changing world, I accomplish ten times more because of computers and the internet and I simply haven't got the time to wait till a vendor decides to tell me how much he wants for his product.
Anyway they are probably some of those $200 gauges that I didn't need in the first place. Just can’t understand why someone can't produce a cheap (under $50) 6v tach.

By the way, back in the 60’s I was stationed at McClellan AFB in Sacramento and spent quite a bit of my free time up around gold country. We used to fly all around Northern, Calf. in a T-34 that the aero club had for rent. It was sure a beautiful area back then, I’ll bet it’s fallen victim to urban sprawl by now.
Night now!
Denny G

Denny Graham,

I agree with you on many things. When I don't agree with you, I still respect your opinion and your ability to do the things that interest you.

Stuart

Mornin guys, if we didn't have different opinions about how the world should run then there wouldn't be any reason for these discussion groups now would there.

Haven't noticed that yet Toolman Tim. I'm at that one-and-one-half year stage where I've bought most everything that I needed to get her safely and reliably back on the road. So I'm not spending much time looking through the vendor’s catalogs on line or on the throne.

I'm focusing more on her cosmetics now days and looking to places like Eastwood and other body repair sites and forums. I will have to rebuild her bottom-end eventually but for now she runs purty dern good, just uses a bit of oil and I think we can make it through the summer with out any problems.

I'm sure that the merchants are skipping the pricing because of the rapid changes we are seeing over the last ten years. All of the metal prices are skyrocketing. Energy costs in the last few years have done the same because of our dwindling fossil fuel supplies. With the third world countries moving into the machine age that is only going to be more of a problem. I saw the other day where they are banning bicycles in many parts of China because the auto traffic was getting to heavy. Pretty soon they will all be driving like Americans and then we’ll see the price of a gallon go to ten bucks. Now they want to take the food off our table to make fuel so just watch the price of food take off now.
So why bother putting prices up when they will just have to change them the next day. But I would still like to have a rough estimate of how much an item might sell for.

Rant over! Now back to the tachometers! Here is just a little heads up for anyone thinking of buying one of those cheapo Sun Super Tach II for their 12v project. I’m into J.C. Whitney for almost sixty bucks with the shipping and tax and it’s in the mail, should be here today. I was at Blain’s Farm & Fleet yesterday and found the exact same package on their shelves for $29.99 (no shipping either). So shop around a little before you buy.
I’m gonna tear into this one and with a little help from my friends, see it it’s possible to inexpensively convert one to 6v. I may just end up using my voltage booster to power it up.

Gotta go now and get my “big old wife” in harness and out to the fields.
Talk at ya later.
Denny Graham
Sandwich, IL

I myself hate when they don't list the price but saying that I was curious and phoned westach the 6volt 6cyl. Tach is $111.00 plus shipping not a bad price as long as it works

I looked at J.C. Whitney's site they have some nice looking Tach.If they could only come up with a nice 6volt one they could make a bit of money on them... I know there's a demand for them.. So how does one do the conversion???? Peter

Don’t know yet if it can be done Peter, still looking into it.
Thanks for contacting Westech, looks like they are about the cheapest 6v units around at $100. From what I’ve found so far the next step up are the $170 units that ATP Instruments sell out of Bloomington, MN. Tim contributed this link; http://www.gaugeguys.com/Other%20Sales/sales6v&12.htm

Once again, I don't see why you couldn't use any of the cheap 12v units with a voltage booster, as our compadre 4ontheFloor pointed out in another thread.
The problem with using the booster is that it’s gonna run ya another $70 so that bumps ya right back up to that $100 mark and ya still have a cheap plastic tachometer. I would expect the unit Westech sells for $100 to be a much better product and ya won’t have to wire in the extra hardware. They have been around for years I believe that I've seen their gauges as standard equipment in lift trucks.
Anyway ya look at it right now, it’s gonna cost ya a hundred bucks to put a tach of any sort in your Six-Volt-Bolt.
Denny Graham
Sandwich, IL

I had a gauge guys tach but it wouldn't work right...they returned it with out a problem... Peter

I can't remember where I saw it and a quick look at my favorites didn't find it but somewhere I ran across a company that could cut the center out of the cluster with the ammeter, fuel, temp, and gas gauges and mount a six volt tach.

Maybe someone else has seen it and has a link?

Okey dokey, here’s the results! Took the old gal out for some exercise after finishing up the 12v Sunpro Super Tach II installation. I put the little 2 5/8” face model in, so it would fit in between the instrument clusters on the AD and not block out the view.
I made up a plate that bolts to a spare hole in the dash bracket above the mast jacket. Mounted on the plate is a 6v to 12v, 6amp booster cube, a four position terminal strip and a on/off spst toggle switch. I picked up 6v to the toggle off the rear Bat. buss on the light switch. From the toggle switch I’m wired to the booster through a fuse. Out of the booster comes my 12v to feed the terminal strip buss. I wired the power for the tack and its light to the 12v buss so the light is on all of the time. Signal wire goes directly to the distributor side terminal, which is the negative terminal of the coil. And that’s all there is to it.

I had already bought the booster cube because I am sliding a CD player under the dash that can be quickly remove when I want. The CD player will be wired to the remaining slots on the terminal strip and the booster will supply 12v to the Tach and the CD player.

Before I installed the tach I just had to see what made it tick so I opened it up for a look-see. With 12v applied I found a 1w resistor right off the power lead that was dropping a little over 7v, which tells me that the SS circuit probably runs off of 4.5 or 5volts. So, it is possible to change one of them into a 6v tach simply by changing a ten-cent resistor or two. Now what the value of the new resistor should be and how to recalibrate the unit, well, that’s going to take an engineer, I’m just a mechanic.

So for now, I have a Tach or Tunes at the flick of a switch and when she’s gonna have to sit a spell I’ll just flick the power supply to off.

Happy motoring
Denny Graham
Sandwich, IL

Sooooo, did I miss where you said it works as expected! I had no doubt that you could modify the voltage to work approprietly, my question was the trigger deal on the coil wire! Is this a dumb input and not to sensitive to voltage.

Did it work?

Stuart

Well Stu, you know how long winded I am, I figured I'd written enough last night. I mean I could go on forever but I do gotta sleep once in a while! But now that ya woke me up here goes.

Yep, the trigger signal doesn't seem to make a whole bunch of difference. 4ontheFloor predicted the results and pretty much the direction that I took earlier on page one. I’m not gonna repeat all of it again here. I already mentioned that rather than mess with trying to find a 6v bulb so I could control it with the dash lights that I just wired it in with the 12v hot wire that drives the tach so it’s on whenever I have the tach switched on. Oh and I believe that it wants about 500ma to power this up.

So how do you check the calibration of your new tach??? Well just off hand I figured about all I could do was go to a calculator (this is one of the best I’ve found) http://www.angelfire.com/fl/procrastination/rear.html and using the rolling rear tire diameter I discussed a few weeks ago, (that be 29.68”) make a prediction chart up.

I started at 20mph in high gear with five mph graduations up to 55mph. The tach seems fairly close all the way up. One thing that you have to conceder is that we’re working with a cheap ($30) plastic tach. It may say SunPro on the face but this isn’t a Sun instrument by any means. Also this is a tiny tach, and where the ads may say 2 5/8” however that’s to the outside of the bezel. The face is actually 1 7/8” across so the resolution is not really high enough to give terribly accurate readings. That’s one of the reasons that you always see those 3 1/2” dials on most real tachometers, the larger circumference gives you a higher resolution. Since I’m not going to leave this in permanently I probably should have spent the extra $10 and gone with the larger face even though it would have blocked out some of the instruments.

As I’ve been doing for 50 years I’ve just been shifting by sound and feel. In this truck that equates to 15mph for number two gear, 30mph in number three and I try to hold her down to 45 or 50 in fourth. According to the tach the shift points correspond to roughly around 2500rpm and I’m running about 2400 to 2600 in high. My idle reads right around 500rpm. I did take it up to 3000 in second and third and that seemed to sound right. Where my predicted rpm was 2850 at 55mph when I ran her up there (and shes a screamin’ at 55) my tach reading was low by a couple of hundred rpm, again this may just be the low resolution of the small dial face. Something else to consider is the update time on a cheap tach, which can affect the readings.
All in all it was an interesting little experiment, and in retrospect I should have bought the bigger face if I wanted more accurate readings.
Denny Graham
Sandwich, IL