Bench test a Tach with a Battery Charger?

[64SprintV8]

Has anyone ever bench tested a Tachometer with a battery charger as explained below:
******************************
When hooked it up to a V-8 tach's input (+ve to tach +ve and -ve to gnd), it shows exactly 1800 rpm.

A 120 Vac 60 Hz battery charger puts out an imperfect DC voltage. It is actually a pulsating DC voltage that corresponds to


1800 rpm for an 8 cylinder,
2400 for a 6 cylinder
3600 for a 4 cylinder


I did this with my tach and although it lit up the needle never moved. Suggesting that it is kapput if the above test is valid. :doh:

[BillP 98201]

Is it an original Sprint tach? Read in modified mustangs that Ford had a design flaw....... they hoooked up their tachs different. If the sprint dies..... it could be from the tach being hooked up different. Get scared now every time I look at my tach.....:NERVOUS:

[Luva65wagon]

Yeah, I couldn't answer the original question for sure (other than to say, "why not just use a real motor to test it" :D ) but I do know they ran the ignition circuit through the tach, so it the tach fails, the engine dies. And then you have to bypass the tach to get the car running again.

I don't have one, but if I did I would figure out what that bypass is and wire a switch in to throw to bypass the tach in one second.

[64SprintV8]

It is not an original Sprint tach it's a 2 5/8 Sun mini. I had it hooked up to the car as well and no joy there either. Looks like new/old tach time for me. The Early Bird Swap Meet at the Puyallup Fair is in a few weeks (2/18-2/19) maybe I can pick up something cool there.

[Jeff W]

How does that meet compare in size to the spring meet in Monroe?

[Luva65wagon]

I go every year. It is the big one at that location; about the same size as Monroe, maybe 25% smaller. I like it because it feels a bit less disjointed to maneuver to each booth. I never leave there feeling like I didn't get to see every vendor.

[BillP 98201]

Im going also. Maybe someone could show me how to bypass this later.... Maybe on the tech day. :o

[Luva65wagon]

Maybe someone could show me how to bypass this later.... Maybe on the tech day. :o

Does anyone have a wiring diagram for a 63 Sprint with the tach option? If so, it would be easy to draw up a plan for the bypass.

[64SprintV8]

Will these suffice?

https://skydrive.live.com/redir.aspx?cid=ce56b7799e1791cf&resid=CE56B7799E1791CF!450&parid=CE56B7799E1791CF!103&authkey=!AIJEZGcNSt5Xbv8

[Nathan289]

I'd be very careful testing a sprint tach.. I don't think they are designed to see a full 12v. Kinda like ford points:WHATTHE:

Some of the very old sun pro tachs needed a box to make them work. With out the box you had a cool looking dash orinment (sp?)

Autozone sells the new sunpro II and they are like $30 probably made in china.

Hopefully you'll find some vintage tach at the swap.. I found a cool auto gauge tach that was still in the box.. it had been opened but never installed.. its sitting in the garage still not installed..

Nathan

[Luva65wagon]

Will these suffice?

https://skydrive.live.com/redir.aspx?cid=ce56b7799e1791cf&resid=CE56B7799E1791CF!450&parid=CE56B7799E1791CF!103&authkey=!AIJEZGcNSt5Xbv8

That might help. Pretty fuzzy, but I'll study them closely. Gracias.

[64SprintV8]

******************* U P D A T E ***********************
I verified that the battery charger test does work. :rocker:

Basically, hook all wires to power and the remaining black wire to ground/negative. Attached are some pictures. The new tach is showing 1,800 RPMS as anticipated. The others tested bad and are just there for reference. Oh, and I am not keeping the white face tach, it was just for testing. That is why the wires were carefully removed from the back of the packaging. :)