Tach test setup

[Bill Rogers]

Here's the the tach test setup I described in Waterwings' "RPM vs Horsepower" thread. This is a typical Teleflex 8k tach with a calibration adjustment. The fluke meter is set to read frequency. The tach is set for a 12-pole alternator so the conversion is 10 rpm per Hz.

More photos to follow ...

Can you attach mulitple photos in a single posting? I guess I could combine them somehow into a single jpg. Oh well, this will get my post count up - my goal is to achieve Senior Member status by the end of the season:D

[Bill Rogers]

Pretty close @ 2k

[Bill Rogers]

and 4k

[Bill Rogers]

6k not so good

[Bill Rogers]

and look how far off it is @ 7k. Yikes!

[Bill Rogers]

First thing I did was move the pole selector switch through all the settings. Sometimes the switch gets dirty and causes some erratic readings - no change though.

Then I went to the cal. adjustment pot - soon as I touched it the reading changed a little. I worked it back and forth to clean it and set it dead on @ 7k.

[Bill Rogers]

6k looks great now.

[Bill Rogers]

4k is off just a tad more than before, but still acceptable

[Bill Rogers]

and here's 2k after calibration. Still OK in my opinion.

I think the cal adjustment pot was dirty causing most of the error. This tach is ready for prime time!

[Bill Rogers]

Rookieflyer, since you're developing a line of marine tachs, have you thought about building a tach calibrator? It would be nice to have some sort of battery powered device to hook up to the boat's wiring harness that would produce accurate drive signals for 1k, 2k, 3k, etc.

Hope y'all enjoyed this little show ...

[gaineso]

Interesting piece Bill. I don't have the equipment to do that, but maybe you or Rookie or some other Electrical genius will come up with something at least semi affordable that the rest of os can use. 'Preciate it.

[ShorePounder]

Bill you're turning into one of my favorite people. :D

I've never used my Fluke as a freq. counter. There's one on my O-scope. This will sure be better than draggin out my heavy scope.

[mattyc]

Ever since reading this thread my mind has been churning with ideas for putting together a little hand-held battery-powered tach calibrator. If something like this could retail for $30, do you guys think it would work?

I'm always looking to have a little fun trying to develop anything useful and make a buck off of it. My last failure was a fan controller:

http://www.fandaddy.com

Turns out I just can't compete with the labor rates and mass production that comes out of Asia!!!

[gaineso]

Sounds like a great idea if you can do it. $30.00 I'd go for. Much more and I'd try to borrow it from Pounder.

[ShorePounder]

No sweat gaineso, I'll rent it to ya for $35 :D :D

[Techno]

Bill I think you have it closer than it seems. The needle seems to not be on the mark so the digital reading is indicating closer to what the dial is saying.
Unless it's the angle I'm seeing and the needle is on the mark.
A little gizmo to check the tach would be nice. I think it would be great if it only checked say a high reading or only a few.

I'm wondering if it matters how many increments it reads since if you calibrate it for say 7600 or 8400 or whatever you can't fix the others? The rest "should" be correct right?

[Bill Rogers]

Pounder, thanks for the kind words. I'm humbled by your comment. I might can help you guys a little with this electrical stuff, but I want you to teach me how to make horsepower!

Gaines, the investment here is minimal. The Fluke 87 is by far the most expensive piece. I rescued the oscillator from the scrap heap. All it cost was a set of tubes and a few capacitors. And of-course the power supply is optional - you can just use a battery, but it's better to check the tach over a wide voltage range. BTW, the tach I just checked quit working at 10.8 volts - not as good as some.

Mattyc, I'm impressed with your enthusiasm. Go for it man! Let me know how I can help. For a battery powered device, don't worry about 15v rms output. Just go for at least 6v rms.

Here's something else y'all might find interesting. That's a Quicksilver tach on my Moto Guzzi 850T3. It's the LAPD version which came from the factory without a tach. I got to studying the alternator one day and figured out it has 12 poles just like most big outboards. Bingo - tach problem solved! I did the same thing for a friend with a BMW 600/5 - it has the same Bosch alternator as the Guzzi.

[Bill Rogers]

Apparently the photo didn't make it

[Bill Rogers]

I think we were posting at the same time ...

Yep, it's the angle thing. I must have taken a half dozen photos of each reading and I tried to pick the ones that most accurately showed what I was actually seeing.

Thanks for the comment

[ripperd2]

I just did this with my boat, in the backyard. Heres what I did:

1. Connect one end of the meter to ground, underneath dash.
2. Connect other end of meter leads via aligator clip to the signal post on the back of the tach.

3. Set meter to Hz and start motor. Luckily it appears my motor has the correct stator so that it puts out 100 Hz at 1000 rpm.

Your meter will read the frequency coming from the motor, which is your actual rpm (within your gauge error, usually within 5% for even the cheapest)

Here is the meter I use. 49.99 or was it 59.99 at sears one week.

[mattyc]

Hey guys, check out the attachment. It's kind of a hack job at what I'm dreaming up on a little tach calibration tester.

Two buttons -- up and down -- to select # of poles. Another two buttons -- up and down -- to select 1 through 8 thousand RPMs.

Maybe three wires coming out of the thing with insulated color-coded alligator clips... Or maybe just put terminals on the unit itself.

The file is just an executable that anyone running windows should be able to run, just unzip it first.

Let the feedback commence!

[Techno]

If you can only adjust the tach once then I'm thinking a few LEDs that read just a few positions would probably be enough. Adjust the tach with say the 6 grand light. Then run it down to see if the other Idle? one comes on.
If it made it cheaper seems like all you need.

[mattyc]

My thinking is that this setup would give everyone a lot of options. The way I'm thinking about doing it, it's really not that much harder to put all of the options on there.

On that little software app, note that the idea is just layout of the device. And the app lets you click on the "buttons" to change from different pole settings and then set the RPMs. It's just to see what the device would do and look like.

[Bill Rogers]

Techno, I've been thinking about your earlier comment. I probably should have set the oscillator to the target rpm each time and then showed the actual tach reading - might have been better for illustration. My procedure has always been to sweep the osc. freq back and forth until the tach needle is dead-center on the mark - with my eyeball right up close and personal - then read the osc. freq. Taking the photos was a challenge because if I lined up straight ahead on the tach, the flash would was it out.

Far as what rpm to do the calibration - that's up to the owner. There's one guy that wants his calibrated at 1000 rpm. He does a lot of offshore trolling - swears he catches more fish at exactly 1000 rpm!

One thing I've noticed though is the calibration adjustment effects the upper rpm range much more than the lower.