tachometer question

Mine is that exact same tach. It's accurate within a hundred or so RPM. The switch is for a two or three blade prop. It's set for two now. The nub on the end is a CdS cell, a photo detector. Try not to get oil on it, and don't poke at it.

If you turn it on near 120v 60Hz house lighting, set for a two blade prop, it will read 3600 RPM because the electric light pulses at 120Hz(one pulse for each half cycle). It is only meant to be used in the Sunlight, but I turn off the lights in the shop and shine a strong beam from a Maglite through the prop directly onto the photo cell. Mine has no red button. That looks like a user mod. If it reads more or less than 3600 under house lighting, that's the amount of error, so you can consider that if you need to be that meticulous.

Rusty

EDIT: I tried it with an LED flashlight once and it didn't work. Apparently the LEDs are strobed.

I forgot something, the red switch is not genuine. I think once you put new batteries in your tachometer you have to switch the black one (on) and when you want to test your engine you press the red.
If you want you can test it with a lamp, neon lamp, you should read 3000 rpm in France and I think 3600 in the USA..

FYI:

CFL (compact flourescent lights) have been known to interfere with tacometer performance.

SD

SuperDave wrote:FYI:

CFL (compact flourescent lights) have been known to interfere with tacometer performance.

SD

Right. All fluorescent lights, compacts included.
But I was surprised that incandescent lights do too. I would never have guessed that the filament could heat and cool fast enough to affect the tach, but they sure as heck do. So pretty much any indoor lighting will read 3600 in the US, or 3000(set for a two blade prop) on 50Hz house current in some other countries.

Rusty

If I had to guess; I'd say that the push/momentary switch (bottom left) on "yours" was wired to the power (sliding) switch above it, to possibly save the tach's battery if the power was inadvertently left on and forgotten about.

I don't believe that my tach has an "auto-off" function... but it's pretty old... still works though.

Any type of light using AC current will affect these tachs, This style of tach has been around a long time and is probably the most common version ever made, it was sold be many different companies with the only diff was the lable. I also would guess the red button is a momentary switch, that was the biggest problem with them, leaving the switch on...which I can personally attest too.

  man that's very interesting stuff , yes the button was a add on the man at the swap meet told me , $5.00 was pretty good I guess, I checked it at the light inside 03.7 so I guess that's 3700 rpms ? no wonder my power bill is ridiculous; lol too damn windy too fly 73 degrees i'll probley run some engines later . THANKS GUYS ! 

Hi roddie,

My tacho is like the model above, on/off on the left and 2/3 blades on the right.

Rémy

getback wrote:15.jpg" /> I know this thing is old got it at a swap meet ,no instruction's  . It doesn't work right I or I don't know how to use it one I no I am not taching 30'000. what is the switch the screw driver is pointing at for? and is something missing were looks like a antenna goes ? thanks again ,and what is a good tachometer for poor man!

               Well can't confirm that it works right yet was all set up , the super bee I was to run was flooding even with the needle on one turn out fuel coming out the exhaust very heavy. the bw  wasn't getting fuel would run the prime out ever time and stop , gives me something else to work on .

getback wrote:Well can't confirm that it works right yet was all set up , the super bee I was to run was flooding even with the needle on one turn out fuel coming out the exhaust very heavy. the bw  wasn't getting fuel would run the prime out ever time and stop , gives me something else to work on .

Yeah but you already confirmed it works; your lights are blinking at 3700 RPMs. Actually most likely 3600 and your tach reads 100 RPMs high like mine.

Rusty