Contact US

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Issue with Magneto

Issue with Magneto

Issue with Magneto

The magneto we are using on our 12 cylinder Waukesha engine needs a voltage of 150-190 to enable the start-up. This mangeto was functioning properly until we had to shut down the compressor station for a period of 4 months. Now the voltage we are getting is 35V on the 12 cylinders which is not adequate to cause ignition. The G-leed is giving 160v. Can a magneto go bad if left for some time and what could be the cause??

RE: Issue with Magneto

They usually have points in them. When running lots of chemistry occurs to the points due to the arcing and ozone around them. If they then sit unused for an extended period they can often fail due to oxidation or them being coated with some sort of poor conducting layer. I'd move the engine until the points are closed then run some emerycloth between them as the first step.

Keith Cress
kcress - http://www.flaminsystems.com

RE: Issue with Magneto

Just an update, we cranked the compressor 5 times and got a higher voltage of 80v though not adequate to start the unit. We had to stop cranking so as not to damage components in the engine.

RE: Issue with Magneto

Some magnetos have a mechanical impulse generator to increase the voltage at cranking speeds.
There is a spring connection between the input shaft and the rotor.
The rotor is held by a stop for a few degrees and then released.
This loads up the spring and then gives a snap action and a retarded spark for starting.
The action is disabled by centrifugal action at higher speeds.
If the mag has a centrifugal advance it may have this feature included.
Look for a stiff linkage or hard grease.

Ohm's law
Not just a good idea;
It's the LAW!

RE: Issue with Magneto

Altronic III magneto's don't have points or an impulse coupling, an Altronic Manual for the type magneto shown in the picture is attached.

I think you posted this in multiple areas, I answered somewhere else, please post your questions in a single area. It is also appreciated if you would provide feedback as to what you find.

Bill/Keith, I have been working on industrial gas engines for over 40 years, impulse couplings and point style magneto's haven't been in production since before I started working on them. The Fairbanks magneto's used both, and have worked on older units with them, but they usually got replaced with a newer magneto instead of repaired, at least in my experience. The Altronic and newer electronic Fairbanks magnetos were far superior in performance and reliability.

Last point style magneto with an impulse coupling I worked on was about 10 years ago on a 1950's vintage unit, was replaced with a digital ignition system.

To the OP, hope this helps.


RE: Issue with Magneto

Thank you for your patience with our obsolete knowledge, and thank you for the up to date information.

Ohm's law
Not just a good idea;
It's the LAW!

RE: Issue with Magneto

Indeed! I've carefully updated my mememeoray blank. I have a single magneto around here and it has both! LOL

It's out of a helicopter. By connecting all the metal chips together it easily set a greasy crowded workbench on fire.

Keith Cress
kcress - http://www.flaminsystems.com

RE: Issue with Magneto


Thanks for the response to this thread, please also see the mail below as response from Altronic.

G-Lead that has 160v seems to be adequate, and depending on how it is measured may be normal. If it is 160V on the G-lead, I am not sure how you think it has 35v on the 12 cylinders as the output to the cylinders comes from the G-lead. The pulse to the cylinders cannot be measured unless an oscilloscope is used as the pulse to the coil is only about 40uS, and cannot be measured with a digital meter.

The best way to test for firing is to use an inductive timing light on the primary going to a coil. If it triggers the timing light then the Altronic III is firing into the coil.

RE: Issue with Magneto

If you look at pg 16 of the manual I sent you, you'll see a schematic diagram for the magneto. The "G" pin is used to shutoff the magneto output, note that it connects directly to the rectified alternator output, and does not go to the circuit board or distribution coils. So if you have 160 volts on the "G" pin, the alternator and rectifier are ok, but doesn't tell you what the distribution part of the magneto is doing. Since you have a box of "spare" magneto's, try swapping the end plate assembly from the best looking one to your magneto on engine. Just make sure you get the timing right.

A timing light on the primary leads to the coil is a good way to check, but not all timing lights work on magneto systems, here is the one i use, http://bgservice.com/59.html

If you want to use a scope to diagnose your problem, I use a Fluke Scopemeter with an 80i-110s current probe, works more reliably and gives a better signal than trying to use an inductive voltage probe. The autoset feature will usually give you a pretty good reading of the primary pulse to the coil.


Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members! Already a Member? Login


Low-Volume Rapid Injection Molding With 3D Printed Molds
Learn methods and guidelines for using stereolithography (SLA) 3D printed molds in the injection molding process to lower costs and lead time. Discover how this hybrid manufacturing process enables on-demand mold fabrication to quickly produce small batches of thermoplastic parts. Download Now
Design for Additive Manufacturing (DfAM)
Examine how the principles of DfAM upend many of the long-standing rules around manufacturability - allowing engineers and designers to place a part’s function at the center of their design considerations. Download Now
Taking Control of Engineering Documents
This ebook covers tips for creating and managing workflows, security best practices and protection of intellectual property, Cloud vs. on-premise software solutions, CAD file management, compliance, and more. Download Now

Close Box

Join Eng-Tips® Today!

Join your peers on the Internet's largest technical engineering professional community.
It's easy to join and it's free.

Here's Why Members Love Eng-Tips Forums:

Register now while it's still free!

Already a member? Close this window and log in.

Join Us             Close