Sun tach rebuild

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ElDavo64

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Has anyone had reworking a sun tachometer to eliminate the need for the 2 odd mercury batteries in the control box any help would be appreciated
 
Maybe that is why my Sun tach stopped working. Should open mine up, I take it the batteries are not available?
I think that Bosch acquired them, I bought the look alike Bosch.
 
Maybe that is why my Sun tach stopped working. Should open mine up, I take it the batteries are not available?
I think that Bosch acquired them, I bought the look alike Bosch.
Yes the batteries are no longer available I’m hoping that someone has invented another way to make these vintage tachometers operational and accurate
 
I had my Tach rebuilt and made fully electronic by Williamson's Instruments Inc. Located in Chester Arkansas. Phone 479-369-2551. Sent in the sending unit Eb-9A along with the tach and he made the sender electronic and checked and cleaned the tach. Nice steady needle and no complaints whatsoever. Would use again without hesitation.. No more batteries. Lifetime guarantee on their work.
 
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My tach is a Sun Pro ll, no semding unit. Will give them a call.
Thank you.
 
mercury batteries have silver oxide or manganese replacement part numbers but the voltage is lower. Tachs are minimal by design, a few caps, a few transistors and a movement. The caps can dry out.
 
You'll have to do a Google search. There are numerous tach circuits over the years DIY and otherwise, and there are people making tach replacement boards for such as the old Mopar factory tachs

The "tach head" is simply a meter. I don't remember the "full scale" ma rating. If you can find a tach with a busted meter you might even adapt the guts to your meter. DO NOT however try to use a modern one such as Autometer. The clue here is that some modern tachs the meter movement does not "fall to zero." The needle stops and stays/ floats wherever the key was shut off. These are a different setup
 
A tachometer is a frequency to current converter. There are many ways with electronics to do that. There are circuits with NE555 timer and a few components. The circuit is basically a one shot, that is triggered by ignition pulses, more pulses more on time, hence more drive current, capacitance, and inductance of meter movement filters pulses to average value. Calibration done various ways, series resistance, pulse voltage, pulse width. Pulse width must be short enough to accommodate highest RPM without over run.

Taking signal from coil - can be troublesome if there is point bounce, it will cause over reading of tach. If input circuit loads coil - (too low of input resistance) it degrades spark energy, it also must be capable of handling 300 to 500V transient. Modern tachs get signals from position sensors, measure period between ignition events. Inverse of period is frequency, that number is used to drive display.

The modern tach Del writes about uses a stepper motor to drive needle, it increases needle deflection a specific number of degrees per pulse. Permanent magnets make poles of x degrees, coil drives rotor, to index next step. More complicated smart control electronics, but needle movement more reliable.
 
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