Technical Do you want to run a 12 Volt tachometer on 6 volt positive ground?

I have been disappointed with the availability of tachometers for 6 volt positive ground systems. There is not a good variety, and what's out there are very expensive. I was discussing this with a friend of mine last year and he said that with today's electronic components, it should be doable. It was, but it wasn't as simple as we first thought. We not only had to reverse the polarity and boost the voltage of the tach control logic, but we also found we had to do the same thing to the signal from the ignition system. After a winters work, my friend was able to come up with a neatly packaged solution that is "wire-up and go".

I have one on the '51 Mercury engine on my test stand and we also have two out being field tested on old GM pickups. Everything works like it should with no problems. I have included a video of the unit running on my test stand. I would like to apologize in advance for the quality of the video, but I am not the world's best "one hand" video guy. Here is that video on "YouTube" : .

The video starts with the engine off, then I start it and let it run at idle for a few seconds. After I rev it a couple of times, I pan down to a shot of the driver unit itself (the black box) and then down to the 6 volt Optima battery. You can trace the cables back to see it is positive ground.

I believe that there is a decent demand for a unit like this among old car enthusiasts of all kinds. If there is enough interest, we plan on producing these for general use. Our problem is that since this is quite a complicated device, it must be built on a commercially produced circuit board to allow us to package it properly. This, along with the quantity discounts available on the required components, will cause the price to vary greatly depending on how many we make. We would probably have to make at least 300 of these to get the price down to where it would be reasonable. We would expect this to be between $50 to $100, depending on quantity. So, what do you guys think? Is this something that people want and will buy? Let me know.

By the way, my friend says that we could easily add an option that would allow us to drive old "meter-type" tachs with this. You know, the old Sun and Stewart Warner units that have a separate control box that either missing or not working. I don't have one of these, so we haven't tried it yet. Let me know about this as well.

 

Pretty simple to build, just get a boost converter IC and wire it to invert the power. After that a simple transistor will up the input voltage to the tach. Probably $10 in parts.

 

Really? Have you built one yet? If you haven't, try it and get back to me.

 

Sure will.

 

Nice build!

 

Once upon a time I wanted a tach. Then I got a car with a tach and never looked at it. Ended my wanting a tach. I can tell the rpm with my ear within 10%. Having tossed cold water, I'm sure there will be a few who simply must have one. GL in your enterprise. and STAY Analog.

 

Bump for the weekend crowd.

 

So... I'm one of the test mules with one of the prototypes installed in my '51 GMC.
I was drooling over tachs in the vintage tach thread and lamenting that that all the units I liked were not something I could use in my pickup, being both a 6 volt and positive ground- All that I could find were "condition unknown" and still selling for more than I wanted to spend. Plentiful 12 volt/negative tachs at all price ranges though.
Our friend Denny set me up with the nifty little box- maybe the size of a deck of cards, with connections in/connections out that wound up being easier than hooking a tach up directly because the wires on most tachs are clipped too short. Hooked up in nothing flat and works perfectly with a tach that matches my style rather than the one oddball 6+p that I wanted to afford.
Stumbled on this post where he's asking if anyone would be interested in one and there's 3 responses. One claiming he could do the same and one putting down tachometers in their entirety.
Don't need or want a tach? A Hot Rodder? I notice in his profile that he's 80. I suppose he's probably not banging gears and doesn't care how many rpm he's turning doing 40 in the left lane with his signal flashing for the last 12 miles- so there's his excuse.
I know that Denny has quite a bit of time into perfecting this unit. I'm not surprised that d2_willy hasn't popped back up with a completed one. It's possible he will, he is an engineer- Not for the 10 bucks he suggests though.

How about the rest of us? Anyone else think they could use such a product? Denny said he will make them for us if there's demand but I assume he's not dumb enough to build a closet full of them to give his orphans when he goes.
I was scrambling to figure something out- and if he can sell them for $75 or so that would've been a deal compared to whats available for these.

My 2 shiny pennies worth- Who else has a 6v+p? or did we all go ahead and switch to sbc and or pertronix.

 

Ya know, 6v + ground, probably isn't real popular on the HAMB-just my opinion...but may gander over to FordBarn, older vehicle specific sites, that want to retain most originality.

I'n my case, the 5 or 6 pos ground vehicles I've had in my life, we're immediately change to 12 - ground,just easier to deal with (again, in my opinion) especially for accessories and the inevitable jump starts.

Good luck.

 

I think most of us that like 6v positive ground would rather have a mechanical tach and drive. Less wire and less draw on the generator. Plus they are way more simple and go with the look of the car and dash/original gauges. If I was building a streetrod I would use a newer drive train like sbc and it would be 12v anyway.

I think there is enough guys with 6v +g that would buy these like 20s-50s car owners that don't care about "traditional" looks, if you can keep the cost down. If you can make these the cheaper alternative to run a cheaper tach it could be alittle gold mine but you would have to advertise like hell to get the word out. Swapmeets, magazines, tv commercials, sema shows, public service announcements, Lars, gnrs, and even a booth at your local donut dorkalicks. I say if you build them you will sell them.

 

Ha, I went the opposite direction, I had a six volt positive ground tach I really liked and when I converted my truck to 12V negative ground, I designed the circuitry to run the tach with a mini HEI on 12V.

I have a video of it when I was checking my oil pressure gauge. The tach is a modern Westach unit and they run about $125 . . . not traditional, but does the job. http://www.westach.com/

 

"PaintSlinger", thanks for your reasoned response; it is a welcome change from the first two "Naysayers". The lack of response puzzles me because of the way I got into this. I was looking for a tach for my '51 Ford, so I Googled "6 volt tachometer". Just about all I got returned were references to threads on old car forums started by people looking for just such an item, and not finding them. There were a lot on the "H.A.M.B.", so since I was a member, I started here. I have since started a thread on the "Stovebolt Forum" and will probably hit the two major vintage Mopar forums and maybe the Studebaker one. The highest level of interest seems to come from old truck owners, which kinda' makes sense to me. Since I already have one for my car and am in this just for a hobby, that's about as far as I'm gonna go. I'm 75 years old and really don't want to put in the time and effort that you suggest, even though I think your thoughts about marketing are "spot on". I guess we'll just have to settle for making them 10 at a time and selling for the higher price to those who really want one.

As to your thoughts on the "Traditional Market", I don't completely agree. While a mechanical tach might be nice, I'll bet they are hard to find and expensive when you do. Most of them I've seen usually have limited range (0-4000 RPM). As to ease of installation, I'd much rather wire up one of mine than find a tach-drive distributor, run the cable, mount the tach, etc. If you want it illuminated, you still have to run some wiring. As to electrical load affecting your generator, you have to realize that our unit uses modern components that impose minimal load on the system. The unit is also internally fused and filtered to allow it to run even with the "dirty power" provided by these old systems. I also think the capability of running the old "meter" style tachs would make it especially appealing to "Traditional Rodders".

Again, thanks for your input. I think we agree on the size of the potential market.. It's just that it doesn't make sense to me to expend the time, money, and effort to pursue it properly. After all, I have accomplished what I originally started out doing, which is getting a tach in my '51.

 

"Motion Guru", while I applaud your effort and appreciate the technical accomplishment, I don't quite understand it. Given their respective values, you probably would have come out way ahead selling the 6 volt unit (which are hard to find and expensive) and buying a 12 volt tachometer. Hey, but good job, anyway.

 

I think it would be interesting to see if you can develop these to drive the old Sun or SW sending unit tachs.

Sent from my Nexus 5X using The H.A.M.B. mobile app

 

Rich,

Unless something comes up, it looks like we will be producing these in batches of 10 to sell for around $120 each. This will also allow us to put out four different versions : one for 6 volt positive ground motor driven (regular) tachs, one for 6 volt negative ground motor driven tachs, a third for 6 volt positive ground meter tachs, and a fourth for 6 volt negative ground meter tachs. The basic design and packaging would be the same and we would customize each unit depending on what the customer wants. Look for these to show up in the swap meet section on a "built to order" basis soon.

I was hoping to be able to mass produce these things to get the price down, but given the tepid demand and the varieties required, that looks like it is not to be.

 

Welll... I have a couple of the old 'red oval' Sun tachs, and some sending units.
Upon asking about getting one of the sending units repaired to run my 8,500 RPM Sun head, I was staggered by the $$ blow in the estimate. (and the 'short life expectancy', i.e. 'No Warranty'. Yeow.
Your venture is sound, please give it a little more time, as there are still some die-hard flatmotor pilots that insist on 6 volt positive ground. Right here on the HAMB.

 

I already had the tach, it had a white face which was not very easy to find, and it was small enough that it didn't obstruct the view of my other gauges when mounted next to the column shift . . . so I ran with it.

 

There were more 6V positive grounds than most people realize. Fomoco through 1955, Mopar through 1955 and GMC through 1955 as well as a lot of heavier trucks. Whether or not these guys want to purchase a tach is a difficult question. It would all be a matter of marketing.

 

Did a design that works on both 6V pos or neg ground, and the cost of the components total 16 dollars. Now the good news is that the design is for 5 amps. Can your design tackle 5 amps? (I designed it for running 12 volt fuel pumps in a 6v car. (I have several 6 volt cars, both pos and neg grounds.)

 

Awesome. Love to see the video of it in action. And the receipt. Only missed that estimate by 60%. Government engineer perhaps?

----is that a "design" of one or an actual working unit?
If I send you $160 will you send me 10 please?

I think I'll wander off to some other thread and be an ass over there. Join the crowd as it were.


Sent from my iPhone using H.A.M.B.

 

Actually the 16 dollars was misquoted, it was for my universal voltage regulator for generators. Does 6 or 12 volts, pos or neg ground, type a or b fields.
The tach/fuel pump design is less than 16 dollars, I will quote tomorrow and post. Engineer of 37 years.
As far as selling my design to you guys, well I would be nuts to send you or anybody else a product @ my cost. Shipping and margins probably put it more at 30-40 dollars. Way less than 120 dollars.

 

But you'e doing such a good job here!

 

cool thread - Stude also ran a 6 volt tach in 1955....I'm in...luckily my 56 Fury's factory tach runs on 12 volts....

 

"5 Amps"? "Fuel Pumps"? Are we even talking about the same thing, here? "Design"? Have you built one and tried it yet? The initial prototype we built to prove the concept probably had less than $16 worth of components. Going from something cobbled together on a "breadboard" to something that you can confidently sell to others is a huge step. We have taken that step. I suggest you consider all that is required to get to a product ready to market before making any more ill-considered statements.

BTW, when you looked at my video, did you see the A/F meter? That is a 12 volt unit running on a 6 volt system. It was a snap to get that running; just wire up a voltage booster and go. Figuring out how to drive a tachometer was significantly more difficult. I am still waiting for proof of your running unit.

But hey! Thanks for the thread bump!

 

Thanks for the comment "stillrunners". At this point, I am going to hit a few more "Old Car Forums" (Mopar, Studebaker", and some old truck stuff) and offer these on a semi made to order basis. When you consider my price point and the cost of aftermarket tachs, I think this is a viable alternative to the currently available "Westtach" units. Most of the interest I have been getting is from the old truck guys; I think a tachometer is more than a cosmetic option to them.

 

You really don't know anything about my profession. Being amateurish is only going to get you nowhere! You really think I am prototyping on a breadboard, think twice. I design for a living. Therefore a PCB is all ready to go and will send out the artwork in a few days. When I get the board and components I will be able to test on one of my old cars.

The reasoning on building a 5 amp unit is for use on other 12 volt devices, besides the tachometer. The tachometer portion of the circuit is a 25 cent part, which is part of the board. My board is 1.5 x 2 inches dimensional.

My designs take on an average 2 weeks to design. Yours take over a year! Why so long? I rest my case!
I will provide an accurate cost of the components. And believe me, my designs are for production, not some cobbled up pos. you bring up. We will see whose statements are ill considered! Good luck selling anything for $75 that is perhaps $20 in parts and labor. BTW 37 years designing electronic circuitry, with some boards having more than 4000 nets ( if you understand terminology). This stuff is nothing compared to what I have done.

 

"d2_Willys"; OK, I'll be waiting. BTW, nice avatar!

 

Pricing for parts, minus the PCB is $13.35

 

Still waiting..........

 

Not to change the subject and I'm dumb as a nail when it comes to wiring, I just got a 50 ford that been changed over to a 12 volt system with the coil still 6 volt, so can a 12 volt tach work correctly wired to 6 volt coil? THANKS