Help running alternator without engine

[redbeard1]

Hello all,


We are trying to diagnose a problem with our combination tachometer/engine-hour device. The LCD engine counter on the tach never worked when we purchased boat last fall. While winterizing boat, the tach also stopped working. We are trying to see if the problem is with the device, the wiring, or the sensor. Tach device gets its data from a sensor on the alternator. Unfortunately, boat is winterized for at least one more month and we cannot run the engine.

It occurred to me that maybe I could spin alternator with a strong drill to send data to tachometer (I realize reading on tachometer will not be accurate. Right now we just want to know if data is getting to tachometer. My first thought is that the connections were loose. I have tightened them and just want to see if the device starts displaying data.)

Has anyone tried using a drill to do this before? Any other thoughts on how to simulate a running alternator or how to test a tachometer? Thanks all.

[Lepke]

You can spin an alternator with anything, but if the charging is energized it can take up to 25hp to run, but at least 5hp. Learned from running engines on a dyno.

[redbeard1]

Thanks for reply. I fear you may be right. My drill only puts out a couple of hp max. So spinning the alternator will not work.

However, I have just found out that the alternator sensor sends an approximately 5v ac current to the tach as the data. So now I will try to find a way of generating 5v ac without the alternator.

[Wotname]

Originally Posted by Lepke

You can spin an alternator with anything, but if the charging is energized it can take up to 25hp to run, but at least 5hp. Learned from running engines on a dyno.

Originally Posted by redbeard1

Thanks for reply. I fear you may be right. My drill only puts out a couple of hp max. So spinning the alternator will not work.

However, I have just found out that the alternator sensor sends an approximately 5v ac current to the tach as the data. So now I will try to find a way of generating 5v ac without the alternator.

Whoa thar....
The amount of power required to spin the alternator depends (to a great part) on the amount of power the alternator is asked to supply (i.e. on it's output load).

Low output load = low input load.

For instance, if the only load on the alternator is a fully charged battery, then the output load is low and thus requires only minimal input load. Additionally the output load the alternator can develop is proportional to it's RPM. At low RPM, the alternator will only require low input power.

I suggest you try it with your drill before discarding the idea.

[Cheechako]

One thing, many tachs sensed off the alternator wire will not come on until you rev the engine up. Not all though. It's a common problem.

[Wotname]

Originally Posted by redbeard1

......
However, I have just found out that the alternator sensor sends an approximately 5v ac current to the tach as the data. .......

Originally Posted by Cheechako

One thing, many tachs sensed off the alternator wire will not come on until you rev the engine up. Not all though. It's a common problem.

If both of these statements are true (and I'm not suggesting they aren't), then measure the ac volts on the sense line as you spin up the alternator with the drill.

[senormechanico]

You could try an accessory wall wart (power brick) that outputs AC.
Take a look at a bin at a thrift store for a dollar or two.
You should be able to find one with an ac output.
I doubt if the tach ac voltage is critical.
My educated guess anywhere between 3 to 12 volts AC out to work.
At 60 hz, theoretically it would read 3600 rpm but that's assuming it's calibrated for a 1:1 ratio with the crank / alternator pulley sizes which isn't likely.

[redbeard1]

Thanks for all for the tips, i will try the drill and if that does not work, I will try to simulate the 5-7 volts. I'll report back with any success.

[Farmer9009]

I have tested mine on a small drill press before. I just used a socket on the pully nut with an extension in the chuck.

[RaymondR]

There are electronic gadgets called function generators which allow you to set the frequency output and voltages to do what you want to do.

[senormechanico]

Originally Posted by Farmer9009

I have tested mine on a small drill press before. I just used a socket on the pully nut with an extension in the chuck.

Good idea !