Mag problems

Topics Last Day Last Week Tree View    Getting Started Formatting Troubleshooting Program Credits    New Messages Keyword Search Contact Moderators Edit Profile Administration
Model T Ford Forum: Forum 2016: Mag problems
Top of pagePrevious messageNext messageBottom of page Link to this message  By Tim Eyssen - Abilene TX on Tuesday, November 01, 2016 - 03:41 pm:

Decided to try and charge the mag in my 14. Have about a half Ohm drop from mag post to ground. Did the Tom Carnegie in car charge with 36 volts. Put an 1156 bulb from post to ground and it burns with engine running, but will not burn brighter when engine is speeded. Installed a John Regan mag battery charger using a 5402 diode and an 1156 bulb, but it will not even glow, at any speed and cannot get any dc voltage reading from the diode to positive battery post.Setting the analog meter on 10 I get about 6 volts when I go to ground.The charger lights hooked up to 6 volt battery and diode is good. I have hooked and un-hooked so may connections so many different ways that I finally gave up and here I am. Is it me or my mag? Ideas appreciated, and thanks in advance.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Roger Karlsson, southern Sweden on Tuesday, November 01, 2016 - 03:47 pm:

Maybe the coils has a short to ground somewhere, leaving only a few working - then only a few of the magnets would have been charged, unfortunately..


Top of pagePrevious messageNext messageBottom of page Link to this message  By Tim Eyssen - Abilene TX on Tuesday, November 01, 2016 - 04:19 pm:

Roger: If that were the case, would't the Ohms be almost zero, showing a direct short? Just asking, because I really have trouble understanding some of this electrical stuff. Thanks for your idea.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Norman T. Kling on Tuesday, November 01, 2016 - 04:34 pm:

Are you reading volts AC or ohms? The resistance of the mag coils is very low. That seems normal, but the AC volts should be close to 6 volts AC at idle.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Norman T. Kling on Tuesday, November 01, 2016 - 04:37 pm:

With the magneto battery charger disconnected, check the AC output from the magneto If around 6 volts at idle and nearly 30 volts at high speed, your magneto is good. So maybe the problem is in the charger.
Norm


Top of pagePrevious messageNext messageBottom of page Link to this message  By Roger Karlsson, southern Sweden on Tuesday, November 01, 2016 - 04:40 pm:

I don't know about exact ohm values, maybe they can vary a little?
But I know that if in car recharging doesn't work, then it's unfortunately time to pull the engine and rebuild the coils and magnets if you really want a reliable magneto..


Top of pagePrevious messageNext messageBottom of page Link to this message  By Tim Eyssen - Abilene TX on Tuesday, November 01, 2016 - 05:33 pm:

Norm: AC is about 6 volts and will not increase with motor speed. Charger works in only one direction as it should with a diode in line when I test on 6 volt battery. Just do not understand that I can get some bulb light but will not get brighter with speed.
Ohms read about one half, so maybe like Roger says, some of my coils are shorted. But: if that were the case, would not the Ohms be almost zero since many would be a direct short?
Roger, you are probably right, but am just trying everything short of pulling engine. So far, I have run all my tours and parades on battery only with no problems (except those sticking valves at the T Party this year)
Thanks again for ideas.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Tim on Tuesday, November 01, 2016 - 06:05 pm:

Get a real mag tester and see what's going on. I see no way for the voltage to stay the same as the engine accelerates - that's the nature of the beast. I would expect zero volts or normal behaviour from any magneto.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Ted Dumas on Tuesday, November 01, 2016 - 06:13 pm:

Remove your mag post and measure the volts directly from the solder pad on the mag coil. Your mag post could have a poor connection or a leakage resistance to ground.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Tim Eyssen - Abilene TX on Tuesday, November 01, 2016 - 07:52 pm:

Ted: I have measured the Ohms from both the mag solder pad and the top of the post, and they are the same. Will try the volts directly next time in shop.
Tim: I would expect the same thing. Maybe I am measuring everything wrong, but that still does not explain why the 1156 from mag post to ground does not get brighter, nor why the Regan battery charger will not even glimmer.
Thanks to all for you input.


Top of pagePrevious messageNext messageBottom of page Link to this message  By John F. Regan on Tuesday, November 01, 2016 - 09:46 pm:

Typically an analog meter when switched to AC just puts a diode in series and then reads the voltage using the same range multiplier resistors so if you happen to have DC voltage of 6V connected to anything that is not grounded and touch it with your meter probe AND the diode inside just happens to be measuring on the positive half peaks when on AC then you will see a steady 6V reading coming from the Battery through the diode in the meter and giving you that reading that is fooling you. Check that out by placing your meter on AC volts and then connect the probes to your 6V battery directly and then reverse the meter lead connections at the battery and you will probably get a 6V reading in one direction and NOTHING in the other.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Royce in Dallas TX on Wednesday, November 02, 2016 - 06:41 am:

A regular ohm meter can be misleading when measuring a magneto. A better choice is a Megger or a DLRO. Either of those are going to apply a load to test the continuity of the low resistance path.

I suspect Tim you will have to take the engine apart to repair or replace the MAG coil. There may not be one in there, are you sure that Pete installed one? Let me know if I can help.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Mike Kossor - Kenilworth, NJ on Wednesday, November 02, 2016 - 12:27 pm:

Knowing the Magneto output voltage under load and no load conditions, you can calculate the Magneto internal resistance, including the magneto post contact resistance, the value is typically around 1 Ohm.

The voltage should be close to the no load voltage. The caveats: Voltage must be measured under resistive load using an instrument that displays the true RMS value of AC voltages with frequencies down to 5Hz. The engine must be run at a very steady RPM between load and no load measurements. Here is an example of the resulting data:

Magneto Test Example


Top of pagePrevious messageNext messageBottom of page Link to this message  By Royce in Dallas TX on Wednesday, November 02, 2016 - 12:29 pm:

Tim I tried to respond to your PM but it bounced back. Apparently you have changed your email.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Thomas Mullin on Wednesday, November 02, 2016 - 12:51 pm:

Remember, when testing the mag ring with an Ohm meter that the sixteen individual coils are connected in series. The firs one is connected to the mag post and the last one (right next to the first) is connected to ground. So you should read a very low resistance. That is good and is normal

Do the light bulb test or use a mag tester to see how well the magnets are working.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Jerry VanOoteghem - SE Michigan on Wednesday, November 02, 2016 - 01:47 pm:

Tim,

I believe that checking a mag coil with an ohmmeter has little value, unless it checks open. I say this because, as Mike indicates, a mag coil offers about 1 ohm resistance. You are getting 1/2 ohm, as you say in your initial message. You also state, "If that were the case, wouldn't the Ohms be almost zero, showing a direct short?" Well, even 1 ohm is essentially zero, given the accuracy of most over-the-counter ohmmeters. Maybe you're using something very accurate but, I know my ohmmeter will show a slight resistance even just touching the two test leads together. It's essentially indicating the resistance of the test lead wires themselves, (or it's a crappy VOM). So, your 1/2 ohm reading may possibly be a dead short or it may actually be 1 ohm...

The EE's may differ... If so, I stand corrected.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Royce in Dallas TX on Wednesday, November 02, 2016 - 07:50 pm:

Tim,

I am getting messages from you but when I send emails to you it bounces back as "undeliverable". Send me your phone number and I will call.


Add a Message


This is a private posting area. Only registered users and moderators may post messages here.
Username:  
Password:

Topics Last Day Last Week Tree View    Getting Started Formatting Troubleshooting Program Credits    New Messages Keyword Search Contact Moderators Edit Profile Administration