Magnetic pickups for tacks
Printed From: Unofficial Allis
Category: Allis Chalmers
Forum Name: Farm Equipment
Forum Description: everything about Allis-Chalmers farm equipment
URL: https://www.allischalmers.com/forum/forum_posts.asp?TID=130442
Printed Date: 30 May 2025 at 8:58am
Software Version: Web Wiz Forums 11.10 - http://www.webwizforums.com
Topic: Magnetic pickups for tacks
Posted By: Burl
Subject: Magnetic pickups for tacks
Date Posted: 25 Oct 2016 at 6:36pm
| Have a few questions for the pro mechanics. How do one wire mag. sensors for (engine flywheel) tacks really work? I put an OHM meter to one to find out what it does when flywheel lugs pass by magnetic strip. I dont detect a thing. Maybe the sensor is weak , it is a used one. The mag. field will hold a paper clip to itself but,nothen much larger. Is it just a series of quick grounds? I dont have a clue ! Can someone please explain it in dummy terms for me? thanks |
Replies:
Posted By: j.w.freck
Date Posted: 25 Oct 2016 at 7:27pm
| all it is is a phonic wheel.picks up magnetic impulses generated by the flywheel magnets,and induced into a coil pickup,impulses are read in I computer box and converted to rpm..... |
Posted By: Burl
Date Posted: 25 Oct 2016 at 7:42pm
| Well,thats got me lined out ! thanks |
Posted By: Burl
Date Posted: 25 Oct 2016 at 8:20pm
| Can the pickup sensor itself be tested for good or bad? |
Posted By: Gerald J.
Date Posted: 25 Oct 2016 at 8:39pm
|
A sensitive volt meter might show a varying voltage with engine speed, but a digital may not show anything consistently. An oscilloscope may show pulses for each time the flywheel magnet passes the magnetic pickup which is probably a coil a lot like a field coil in an alternator but with fewer magnets than the alternator. Gerald J. |
Posted By: Burl
Date Posted: 25 Oct 2016 at 8:50pm
| Thanks Gerald . Could this style TACK be connected to the distributor (TACK) term or would that be to much pulse?? |
Posted By: HudCo
Date Posted: 25 Oct 2016 at 9:33pm
| a led will change fast enough to show pulse's |
Posted By: Gerald J.
Date Posted: 26 Oct 2016 at 3:28am
|
The pulse from the distributor coil primary would be too much pulse I think and would happen more often like for a four cylinder engine twice per revolution. There have been test tachometers made to operate on the ignition coil connection to the points, same meters often could also show dwell (fraction of the time the points are closed) needed for some GM engines to set the point gap. I have a meter like that somewhere, but haven't used it in a long time. Gerald J. |
Posted By: SteveM C/IL
Date Posted: 26 Oct 2016 at 8:16am
| There aren't any magnets involved other that the one in the end of the sensor.The tack sensor on my 8070 reads the starter ring teeth from the front face of flywheel.My Cat truck engine reads ring teeth from the outer dia. My trucks speed is from reluctor ring on trans output shaft.Ground speed on my F2 Gleaner works same way.A magnetic pulse that has to be dicifered. |
Posted By: gcnoyes
Date Posted: 26 Oct 2016 at 8:38am
| Its measured in hertz. there is an online calculator that converts hertz to rpm. if you buy a tach that measures rpm from a magnetic pick up you will have to input the number of teeth for it to read correct rpm. We use them in all of our oil field compression. |
Posted By: Burl
Date Posted: 26 Oct 2016 at 8:51am
| So , the works inside the tack converts the magnetic pulse to RPMs ? The sensor wire only goes thru a selector switch (under tack) before connecting to tack. What I am up to is putting a tack out of a F2 in a K2 that had NO tack or pickups. All I need or want is engine RPMS. I mounted tack ,bypassed selector sw. Put factory sensor on flywheel and direct wire to tack and hope it will give reading !! |
Posted By: TramwayGuy
Date Posted: 26 Oct 2016 at 10:55am
| If all you need or want is engine speed, get a regular add-on tach made to read the ignition pulses. Unless it is diesel. Otherwise you will need a tach that you can calibrate for number of ring gear teeth. |
Posted By: Burl
Date Posted: 26 Oct 2016 at 11:29am
|
What ever mojo magic go on, it now works fine as a Rolex watch !! Only had to run 1 wire from 4 pin and hot wire from floor console to overhead panel. |
Posted By: gcnoyes
Date Posted: 26 Oct 2016 at 3:03pm
| When the tooth on the flywheel passes the magnet it's converted to a electric pulse. the tach counts the pulses and converts that to a digital signal for the readout. tacks you get will be a tach/ hour meter. They are accurate and trouble free. If the tach ever goes on my 190 I will add the mag pick up and put a digital tach in there. Im sure its better than the factory tack. Thats assuming you aren't a die hard purest. I have already put a timed relay on my manifold heater and it is much better than holding the key backwards and counting. |
Posted By: TramwayGuy
Date Posted: 26 Oct 2016 at 5:25pm
| I know that some alternators had a pulse sensor output built into them; to drive a tach. |
Posted By: Gerald J.
Date Posted: 26 Oct 2016 at 8:00pm
|
The alternator generates alternating current with the frequency proportional to the shaft speed so a sample of that is given to the tachometer designed to use that. No pulse sensor. The alternator then uses silicon rectifiers to make DC for charging the battery. Long ago some Leece-Neville alternators used external rectifiers so put out three phase AC. Gerald J. |
Posted By: gcnoyes
Date Posted: 26 Oct 2016 at 8:12pm
| Gerald just beat me to it. We converted all of our compressors that used alternators to run the tacks to Leece-Nevil alternators we still had problems with the AC signal so we went to different tacks on the panel and converted them to mag pickut types. Pulley size has to be right and still wont be as accurate as the mag pick up type. |
Posted By: SteveM C/IL
Date Posted: 26 Oct 2016 at 8:40pm
Just curious,why the interest in eng rpm? Almost never check mine but I live by ground speed and that cyl rpm is mighty handy when needing an adjustment. |
Burl wrote:Posted By: rw
Date Posted: 27 Oct 2016 at 8:23pm
| I have had some issues getting fertilizer dealers spreaders to cover supposed width properly. Really shows up on grass hay fields that have kind of poor fertility in general. Using a light bar GPS and measuring width of pass and still wind up with overlap strips about 12 to 15 feet wide. I think my fan/alt belt slips on my 7045. Flywheel sensor tach would be something I would like to add for that purpose.rw |