Ok, there's been a few posts about getting those old sun tachometers to work (most started by me ) anyway, rather than paying the prices to convert to electronic, which is probably still not a bad idea, I wanted to get mine working on a budget. For whatever reason you arn't supposed to use AA batteries, though I still don't know why you can't. I'll get to the point, duracell PC12A is still an alkaline 1.5v battery, not unlike an AA, but is apparently a DIRECT replacement for the RM12R mercury batteries that the sun transmitter takes. Perhaps it's operating voltage is lower? Who cares, you can buy them online from several places for about $5 each! I know I'll give em a shot! This info was given to me from actron, which is what sun became at some point, and after punching in PC12A on the search I found several sites that sell the batteries and also confirm that they are mercury replacements in duracell's "profesional" line. Only snag, your old beat to hell transmitter needs to still work! But as long as this battery remains to stay available and will last in your car for a year, and you pay $10 for two, you can use your tach for 20 years before you would have paid for the conversion. Hope someone finds this as helpful as I did.
I gave mine to the EE in the office 2 months ago and he doesn't seem to be making much progress. I'll be ordering a few. Thanks for sharing!
The theory behind the sun tach transmitter requires 2.7 to operate (two 1.35 volt cells in series). Mercury batteries were used because of thier long life and stability. A mercury cell has an initial voltage of 1.35 volts which it then holds until the last 5% of its life, when it dies very quickly. Alkaline batteries on the other hand, have an initail voltage of 1.5 volts, which rapidly drops to around 1.4-1.3, then down to nothing. Every alkaline battery has these same characteristics, and because of this, your tach will NEVER be calibrated correctly. People back then were pretty damn smart when it came to building things like this. These days, we can whip up a circuit that will perform the same functions using a CAD program in about 10 minutes, make it into an IC, and make a million of them for about 45 cents each. It wasn't so back then. The transmitter you have is one amazing device, considering that it performs a very complex function with about 4 components, and does a very good job of it. But to perform its function, it requires a stable, tighly regulated power supply of 2.7 volts. Alkaline batterys are not capable of delivering on this constraint. Crease, tell your EE to use a 2.7 volt zener diode a few reisitors and a 9 volt battery. David
David, if what you say is true, then I'm in deep ****, as a few years ago I had a circuit made to use the 14 volt current in the car, reducing it to 1.35 volts at all times. Why 1.35 volts? Well I thought it used 1 battery only. It cost me $100, and fits into a box the size of the transmitter. Can anyone draw me a circuit that will do the correct job, so as I can get one made, please.
Automotive stud, you are the MAN!!!! that's why i love the HAMB so much...one guy busts his *** on finding info that everyone can use and shares it with the world...or shall i say hamb world. THANKS
Well I sure hope it does work for everyone. Four-thirteen and stovebolt have me worried, could you guys shed some more light on your at home conversions? I don't need mine to be dead on, as long as it works and isn't totally off, so they might work for me. I'll give them a shot.
I don't know how large or what capacity the batteries are,but if you need 1.35 volt batteries,I would consider using watch batteries wired in series.I believe most watch batteries are 1.35 volt but I don't know if they would have enough capacity to work.Hell,you could always series pair them and then wire the pairs in parallel.Just a thought.
I stole this drawing from Mr 42 on the other sun tach post: The drawing shows the two 1.35 volt merucry cells wired in series, for 2.7 volts total. If you somehow come up with a 2.7 volt regulated power supply, and install it in the transmitter, that would work just as well. So...... here is is, the simplest, quickest, cheapest circuit imaginable to produce 2.7 volts for use in your sun tach transmitter. Hook the + terminal on the circuit up to the + terminal on the transmitter, on the right side battery, and the - terminal of the circuit up to the - side of the left side battery. Then you are good to go. David
There are about 2 dollars worth of parts in the above circuit, if you bought them individually from radio shack. bought in bulk you could get them all for about 9 cents. a 2.7 volt voltage regulator IC would do the same thing, provided you could find one. It would probably do a better job of it too, that circuit is pretty unrefined, but will get the job done. A voltage regulator in IC form might cost a buck or two, but then you wouldn't have to ***emble it. The biggest problem i can see is battery life with my design. The battery has to be disconnected when the motor isn't running, as it will continue to drain the battery even while not in operation. David
That is interesting. Here is an idea, instead of using an internal battery, could you run a power wire that is hot with the key into the box? That would use 12v into the transmitter, or you could come off of the factory instrument resistor and you'd have about 6v going into the transmitter.
using the car's own 12 volts MIGHT work, but you must make sure the tach drive circuitry is isolated from the other wiring. The EB-9A and RC 5DTA sitting in front of me SEEM to be isolated, with a quick check with the multimeter, but I can't say about every tack and transmitter sun made.
[ QUOTE ] Crease, tell your EE to use a 2.7 volt zener diode a few reisitors and a 9 volt battery. David [/ QUOTE ] He drew up 3 or 4 circuits, he just needs to get off his *** and do it. He's one of those "I could do it this way, but this would be cooler" kinda guys. I just want my Taco Meter back.
[ QUOTE ] I gave mine to the EE in the office 2 months ago and he doesn't seem to be making much progress. [/ QUOTE ] Aw Crease, you know better than to give an engineer a project that actually needs to get built! You'll either never get it back or he'll turn into a lightning generator or some ****.
Yeah, your right I should have known better. Im hoping to get it back in time to be buried with it. I hope he knew I was kidding when I said "It aint countin tacos like it should"
Thanks very much - I'll have to check mine out and see if I stuffed up. Now to find someone to do the circuitery for it.
I didn't even know there were batteries in there, will open ine tomorow and see what's in there. Thanks!! Tom
Whadja expect, a mouse on a wheel? JK Seriously, do you have one in your car or on the shelf? Does it work?
They were probably still available in 2004, which is when the last post on this thread was made (until you woke it up).
An electrical engineer buddy of mine (a true hot rodder type, also) got my early '60's vintage SW tach working after a 40 plus year slumber. He found batteries to replace the originals somewhere on the web. They were pretty expensive. I'll look for the paper work on it and post it when I can.
I just put a AA1.5 in my single battery unit and it showed a little sine of life. Im going to try to adjusting it. When I tried it the tach would move just a little when I revved the motor. Not sure why your not supposed to put AA batteries in it but I figure its worth a shot. I am running it with a Du Coil ignition. The battery I took out actually looked really good, looked way better than any pictures I have looked up. The unit is in a survivor car so I'm sure it worked at one point... I am going to try adjusting it with the adjustment screw and see if I can get something out of it.
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