Westach installation

[Speed20]

So i’m out here installing a westach tachometer and installed the requisite inline fuse with a .4 amp fuse . When I test the tach by running a jumper from either fuse connection to ground , the fuse doesn’t blow and engine quits. I have .4 amp fuses from Wicks aircraft, but if it doesn’t specifically say quick blow could I have the wrong fuse? Wiring couldn’t be simpler, but I’m stumped.

 

[eschrom]

I'm unfamiliar with testing a tach with a jumper but in general in an electrical circuit a jumper from the hot side of the fuse to ground should make a lot of sparks and maybe melt the wire and from the instrument side to ground should blow the fuse. Either that or I don't understand the installation. Do you have a wiring diagram?

Ed

 

[Speed20]

I'm unfamiliar with testing a tach with a jumper but in general in an electrical circuit a jumper from the hot side of the fuse to ground should make a lot of sparks and maybe melt the wire and from the instrument side to ground should blow the fuse. Either that or I don't understand the installation. Do you have a wiring diagram?

Ed

 

[Speed20]

They tell you to run a wire from p lead to an in-line fuse then tach itself other wire to ground

 

[soneraifred]

The purpose of the fuse is to prevent grounding of the p-lead if the tach fails to ground. You’ve just proved that the current flow required to short to ground is much less than .4 amps. You’ll need a much smaller fuse, if one exists. I installed an on-off switch in the tach circuit so that I could isolate the tach if should fail. When I installed my T-30 digital tach in place of the Westach, it required a 47k ohm resistor in the p-lead to the tach for isolation and signal cleanup. I still kept the tach switch.

 

[Speed20]

The purpose of the fuse is to prevent grounding of the p-lead if the tach fails to ground. You’ve just proved that the current flow required to short to ground is much less than .4 amps. You’ll need a much smaller fuse, if one exists. I installed an on-off switch in the tach circuit so that I could isolate the tach if should fail. When I installed my T-30 digital tach in place of the Westach, it required a 47k ohm resistor in the p-lead to the tach for isolation and signal cleanup. I still kept the tach switch.

Thank you Fred, I also wondered about that .4 amp fuse being too much despite the fact it’s what’s recommended

 

[Steve Stephenson]

If the jumper was placed from the "hot" side of the fuse to the frame then you grounded the magneto and it would shut the engine off.

 

[DeadRinger]

Did you test it at idle? Maybe it will blow at higher rpm. Amps go up as rpm goes up in a mag.

 

[Speed20]

If the jumper was placed from the "hot" side of the fuse to the frame then you grounded the magneto and it would shut the engine off.

Tried both connections on fuse same result

Did you test it at idle? Maybe it will blow at higher rpm. Amps go up as rpm goes up in a mag.

. Did it at around 1500-1800 rpm

 

[Steve Stephenson]

Okay, so the Westach is protected from current above .4A, which seems about right. If the instrument draws any more than that, the fuse pops. As I look at the wiring diagram, either side of the fuse could be grounded and therefor ground the magneto. If your aircraft was not running and you had a battery (and alternator) you could use the the jump wire to cause a short and thereby test the fuse. If you don't have an electrical system and the tach is working, don't worry about it too much. Fred's switch idea for the tach is a good one.

 

[Speed20]

Okay, so the Westach is protected from current above .4A, which seems about right. If the instrument draws any more than that, the fuse pops. As I look at the wiring diagram, either side of the fuse could be grounded and therefor ground the magneto. If your aircraft was not running and you had a battery (and alternator) you could use the the jump wire to cause a short and thereby test the fuse. If you don't have an electrical system and the tach is working, don't worry about it too much. Fred's switch idea for the tach is a good one.

Thanks, having an electrical system with alternator, I’ll test as you suggested. Also a tach switch is going to be installed in a easy to reach location

 

[DeadRinger]

I still want to see if the fuse pops at higher rpm just for my log of info I retain for the future but I think Fred is right you need a smaller fuze for isolating the P lead on short of your idle on decent for landing and it shorts engine off no go around.

 

[Speed20]

I still want to see if the fuse pops at higher rpm just for my log of info I retain for the future but I think Fred is right you need a smaller fuze for isolating the P lead on short of your idle on decent for landing and it shorts engine off no go around.

This week when I go out to the airport I’ll, try at a higher rpm, but I found a place online , Elliot electronics in Tucson, that carries fuses lower than .4 amp. I ordered an assortment and will see which one works, but I’m also installing a tach switch per Fred, as a backup. I really like the tach though, very steady indication and easy to read

 

[Speed20]

Went out to the hangar today and replaced the .4 amp fuse with a.3 amp fuse. With engine running about 1500 rpm , used test lead and grounded the tach. The fuse blew as it’s supposed to and the engine never skipped a beat. I also installed switch for the tach. All is normal.

 

[DeadRinger]

Nice!!