What voltage

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Model T Ford Forum: Forum 2013: What voltage
Top of pagePrevious messageNext messageBottom of page Link to this message  By Shawn Hayward on Monday, July 01, 2013 - 06:12 pm:

what voltage do you get from the mag post
when you
removing the spark plugs
set it in neutral
and hand crank it
I am getting between 5 and 7 V AC

I am not sure if my mag ring is any good after the loose bolt incident ,
engine is out off the car


Top of pagePrevious messageNext messageBottom of page Link to this message  By Bud Holzschuh - Panama City, FL on Monday, July 01, 2013 - 06:38 pm:

Shawn

Sounds like the mag coils are OK but the magnets are weak.

Unless your planning on removing the tranny to replace the coil ring, why not try a "in place" recharging of the magnets first? (assuming an inspection of the magnets show everything to be ok)

Lots of instructions on the forum.

It would be helpful if someone could post the resistance of the coil ring (magpost to ground).

If i can get to the garage later I'll see what mine reads.


Top of pagePrevious messageNext messageBottom of page Link to this message  By John F. Regan on Monday, July 01, 2013 - 07:04 pm:

HUH??? He is hand cranking the motor in neutral with the plugs out. 5-7VAC is actually a bit above normal assuming he is not using a digital meter which would make any reading suspect to me.

Those who think he needs to do an in-the-car recharge should try hand cranking an HCCT and measure the voltage and you will have to really whip it to get it that high.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Royce in Dallas TX on Monday, July 01, 2013 - 07:08 pm:

5 - 7 volts while hand cranking is awesome. I am jealous!


Top of pagePrevious messageNext messageBottom of page Link to this message  By Peter Borland. Bathurst. NSW. Australia. on Monday, July 01, 2013 - 07:22 pm:

Don't play with it. Just enjoy it as is.

Peter


Top of pagePrevious messageNext messageBottom of page Link to this message  By Norman T. Kling on Monday, July 01, 2013 - 07:25 pm:

If the car will start, try measuring it when running at various speeds. Then report.
If you get that much when hand cranking in neutral, it sounds pretty good to me.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Hal Schedler, Sacramento on Monday, July 01, 2013 - 08:03 pm:

A good coil will fire at far less. That's a pretty good mag. If the meter on my HCCT is right, I get good spark at around 2V.

John R... does this sound about right?


Top of pagePrevious messageNext messageBottom of page Link to this message  By Jim Thode Chehalis Washington on Monday, July 01, 2013 - 08:08 pm:

John,
Actually, checking the mag out put voltage with a digital meter works just fine as long as the ignition switch is off. It is just AC voltage. A digital meter will go crazy if the ignition switch is on and the coils are firing.

Try it on a HCCT, it is not as hard to crank over as a motor.

Jim


Top of pagePrevious messageNext messageBottom of page Link to this message  By Garnet on Monday, July 01, 2013 - 08:12 pm:

Coilring resistance has been posted many times over the years Bud - roughly .25 ohms.

Regards all,
Garnet


Top of pagePrevious messageNext messageBottom of page Link to this message  By David Dare - Just a little South West . on Monday, July 01, 2013 - 08:12 pm:

install the light bulb/globe and meter ( easy to make ) and count to ten when revving the engine - "POP" at above 18 volts....... l think a new box of them would be a good idea.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Bud Holzschuh - Panama City, FL on Monday, July 01, 2013 - 10:20 pm:

Thanks Garnet, I couldn't find it!


Top of pagePrevious messageNext messageBottom of page Link to this message  By Ron Patterson-Nicholasville, Kentucky on Monday, July 01, 2013 - 10:37 pm:

Jim
The AC magneto output waveform is not "continuous" under all conditions
Digital meters do not deal with that correctly.
Hence the need to use an analog meter when measuring the magneto output.
Ron the Coilman


Top of pagePrevious messageNext messageBottom of page Link to this message  By John F. Regan on Monday, July 01, 2013 - 11:10 pm:

Ron is correct. An expensive digital "true RMS" reading meter will be OK but digital meters are sometimes hard to read on "transient" voltages and the peak AC is going to vary a bit as you crank it. Analog meters are not necessarily "true RMS" type meters either when on AC but they tend to give you more meaningful readings since you can watch the needle move up and down easier than trying to figure out flipping numerals on a digital scale. The digital meter is resolving the reading to at least 3 digits while the analog meter is really not doing that but rather is averaging all of it together when the voltage is changing a lot.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Jim Thode Chehalis Washington on Tuesday, July 02, 2013 - 12:39 am:

Maybe it depends on the digital meter used. At least in my case my digital meter seems to give the same result as my analog meter in the range of about 2V to 6V on my HCCT.


In Shawn's case, the 7V seems a little high for hand cranking the engine but no matter how he measured it, it would give an indication the the mag is working and a more complete test may be warranted with the engine is running.

Shawn,
Do a test with the engine running as outlined in the following links. You have to use an analog meter, a digital will not work when the coils are firing.

Read this thread:
http://www.mtfca.com/discus/messages/257047/282864.html?1334956032

Including this link:
http://coildoctor.com/yahoo_site_admin/assets/docs/MAGNETO_TEST.58163152.pdf

Once you do that you should have a very good idea if the mag is up to snuff or not.

Jim


Top of pagePrevious messageNext messageBottom of page Link to this message  By Shawn Hayward on Tuesday, July 02, 2013 - 05:40 am:

Thanks for all the help guys ,
I am going to try and run it before I put it back in the car ,(it is on an engine stand) and I will post what I find
,I have an analog meter I can check it with tonight , and I will make a test light ,
hoping it works as I don't want to have to take it apart


Top of pagePrevious messageNext messageBottom of page Link to this message  By Bud Holzschuh - Panama City, FL on Tuesday, July 02, 2013 - 08:28 am:

Jim

Your right, it would depend on the digital model used and how that meter integrates (or averages) the readings over time.

In fact its possible to make a digital meter that would reproduce a given analog meters readings exactly.

I've often wondered why meter manufacturers don't offer a switch to select between fast and slow averaging. At least I've never seen one that does.

BTW analog meters average due to the mass of the needle assembly. They can vary in their readings also depending on that mass and the frequency of the AC or pulsating DC they're reading.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Shawn Hayward on Tuesday, July 02, 2013 - 08:25 pm:

Well,
I connected a 12 v bulb to the circuit ,...
and it lights up hand cranking it, 4.8 v ac across it (digital meter) AG meter not the right scale
hoping for the best


Top of pagePrevious messageNext messageBottom of page Link to this message  By John F. Regan on Tuesday, July 02, 2013 - 08:49 pm:

Bud explained it. The term ANALOG VOM is almost a generic term since almost all analog volt meters are simply a current meter movement with a series resistor. The damping of the movements are different but not wildly different since the movements are typically 20uA movement in an expensive meter down to 1mA movement in a cheapo with various others in between. So long as the series resistor and simple diode rectifier (for AC scale) are OK they typically give consistent readings from one meter to another.

The term DIGITAL VOM is not at all generic. There are many sampling rates that might be used. All sorts of input filtering is used to narrow or widen the band widths and even the method of digitizing the readings involves totally different techniques using successive approximations or other techniques to digitally display the Voltage presented to the meter. If the term "digital VOM" defined any group of meters well enough that we could be certain of repeatable AC readings on them at frequencies other than 60 Hz line, I would have no problem with it but even in this thread the first reading sounded very high to me while others were convinced the engine needed a magneto recharge. I don't want to get into a lengthy discussion on analog versus digital meters and which might be better for one thing or another but just want folks to be able to make reasonably accurate readings and report those readings here so that we might be able to help them. If we have doubts about the readings then how do we help? I want to help but I don't want folks to think that they should try an in-the-car recharge of a magneto unless it really needs that because it is risky business. I don't think it helps by telling folks that their digital readings are "probably" OK when the direction of advice then points in the wrong direction because the reading was inaccurate enough to make that happen. To me readings that are "probably correct" are useless. Your mileage may vary.


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