MTFCA Forum

With the Holidays over and the bitter cold days of Winter dragging along, time to start thinking about Model T activities again. I've been told the Ol Model T Coil Beepers are in short supply and folks wanting one can't get one. If your not familiar with it, the Coil Beeper is a handy little device popular at swap meets to test Model T coil secondary windings are within the normal range (~3200 Ohms) and worth a try at rebuilding or Open and better off passing.

So I've been working on a worthy replacement that does a little more and a little easier to tote around. The Prototype tests the secondary winding resistance AND capacitor to see if they are within a reasonable range and is very portable; about the size of a Business Card. Just ordered a few boards to build and try out and see how it works. Comments and suggestions welcome and appreciated.

Mike,
A much missed and needed item!
Glad you’re doing these.
Put me down for one!
Brent
The Coil Doctor

Looks swell Mike.

The coin battery is good idea, the original unit used bulky 9v.

So with the small battery you will have indicator lamps to lite if coil meets specs, instead of beeper?

The breast pocket size is amazing. Great to see you make these.

Put me down for 1 will be great for flea market season

We'll be looking for follow-ups on your progress

Mike,
I'm glad to see this coming back for so many who need one. I got mind shortly after John went into production and love it!

I wonder about the usefulness of testing the capacitor. For me, replacing a hundred year old capacitor is standard operating procedure and a no-brainer.

Keith

Great comments and questions. Right now, the intent is to provide both visual (Green LED) and audible (Beep) indication when the test passes. Same pass/fail indicators are used for Secondary winding resistance and capacitor value range tests. I figured the operator will know what test they are performing by what coil terminals they are contacting. The points have to be opened manually to expose the capacitor for measurement.

There sure are a lot of variables for such a simple tool. For example, what are the secondary resistances limits for a "Good" coil? Several knowledgeable and experienced folks have provided data for Ford, KW, Bittner, KoKoMo and Kingston coils with resistance ranging from 2736 Ohms to 3450 Ohms. Newer coil secondary coil windings, I'm told, can be up to 7800 Ohms. I'm inclined to set the secondary winding resistance limits of 2700 to 3500 Ohms in preparation for Beta testing and revisit the limits after feedback from testers.

Keith's comment regarding capacitor test capability is certainly valid, however, there is always the possibility the coils on the table of unknown status may already have had the capacitor replaced and thus good to have that indication when negotiating a price for the coil. That got me thinking, in such a scenario, would a quiet stealth mode with just a recessed visual Green LED "OK" be more desirable for those shrewd Swap Meet browsers? You know who I mean...

The added bonus of the Capacitor test will be a great feature.
It is rare to find an old coil that the Cap passes the specs on the ECCT. I assume all coils will require a Cap replacement during rebuild.
Every now and then, it might be nice to find one not requiring cap replacement before purchase or rebuild. As usual, great work Mike.

Mike, maybe have a silent pass signal (lights only) but have a loud audible failure notification. Upon failure, the device could go "Wah, Wah, Wah"

Mike

The Beeper tester has prongs to stick into the coil solder pads. What type of contact will your card size have? Will the contacts have points to meet a crusted solder pad to be sure of good contact?

On the Beeper, found that it will beep if the contacts can both meet any metal surface, so when carried about, have to keep plastic caps on the pointed contacts. That helps prevent beep and battery drain, and protect the pocket or bag the Beeper is carried in to prevent sticks from the sharp contacts.

And have to wrap tape around the board to keep the 9v battery from escaping, it is held only with the battery contacts and can fly apart from the board easy. So your contained coin battery will be a great improvement.

My Fun Project beeper had a wire tie wrap holding the battery in. Never had a problem with it trying to fall out.

Dan Hatch wrote: ↑

Wed Feb 05, 2025 1:09 pm

My Fun Project beeper had a wire tie wrap holding the battery in. Never had a problem with it trying to fall out.

Mine didn't have that accessory

But the friction tape works, and just peeled away more for the photo, and I used the black friction tape to 'disguise' the device. Lots of sellers of old coils kinda looked at the little black box in my hand that made their coils either beep or not.

Some would ask ‘'what is that thing? I would just say it reads left over voltage so I don't get shocked

I would like one.

Darel Leipold

I still have two working Fun Projects Beepers, but I might purchase one, if it has a capacitor test for sure.

When I bought my StroboSpark, I thought I would have to send it back, as I had tested over 40 coils and they all had a bad capacitor.

I was telling Ron Patterson about my capacitor issue.

Ron told me not to worry, as he had tested over 10,000 coils with the StroboSpark, and he helped John in the development, so he got an early unit. In that group, he had only found about 40 coils with a good capacitor.

The StroboSpark is worth bringing back to!

One of my friends paid $650.00 for one last year and he only as one Model T.

Just finished building the prototype Model T Coil RC Tester. First pass success!
The circuit simulation software really is that good in helping to get it right the first time.
Only problem is.... the tiny beeper that fits in the compact case puts out a tiny sound that you can hardly hear.
Question: Do you think the Beep is really necessary?

The Green LED tells you all you need to know and does so without broadcasting what you just learned about a perspective coil.

Coil Secondary Winding Resistance Check: 1850 to 3840 Ohms = OK


Capacitor Value Check: 0.47uF +/- 20% = OK
Inside Voice: "Humm, That's a great coil for $10..." OK, I'll take a chance on it for $10

Mike,
While the beep is handy, it’s not at all necessary.
Just my two cents worth!
So happy you’re working on these for the market again!
Brent

A Model T friend of me ,made a tester with a batterie and a led lamp . Toon

Update: prototype circuit boards are due in this week. I was able to incorporate most of the great suggestions made here.

If all goes well, should have a production run made late May or early April.

Thank you for all the great comments and suggestions.

Thank you for the update Mike

I see that you hope that capacitor is .47uf.
That's right for modern 'orange' ones, but I think that Ford originals are about 1uf.
Now, most of the originals need replacement - they will leak DC, but not all.
Will your beeper tell you if you are lucky enough to have a good original capacitor?

I believe the Capacitor value in original Ford coils was 0.5uF, if so, yes the new Model T coil secondary resistance and capacitor checker will tell you if the capacitor Value is 0.47uF +/- 20% and may not need replacing.

Mike sent me one of his testers. It’s well thought out and very portable.
Thanks to Mike for getting a reliable tester back on the market!
Definitely a welcome addition to the hobby!
Brent Mize
The Coil Doctor

Brent, that is a great improvement if it can test both the capacitor and secondary coil.

If Mike built it, I know it will work!

J1MGOLDEN wrote: ↑

Thu May 01, 2025 11:12 am

Brent, that is a great improvement if it can test both the capacitor and secondary coil.

If Mike built it, I know it will work!

.

"If Mike built it, I know it will work! "…...... Quality indeed ..... Reminds me of a automobile that never needed flashy or extravagant commercial ads.,.... Speaks for itself....". Packard ... Ask the man who owns one..!'

Pocket Coil Checker - Update

Several design revisions were made thanks to great feedback from folks here and the Model T FB groups.
The new Digital Version is the same business card size but has significantly fewer components and more features:

1. Power turns on automatically when secondary resistance measurement is detected
2. Power ON indicator
3. Checks Model T coil secondary resistance is within its nominal range (2200 to 3800 Ohms)
4. Checks Model T capacitor value is within its nominal range ( 0.47uF +/- 20%)
5. The TEST OK beep can easily be turned off (or on) based on user preference
6. Low battery alert is signaled by 4 short beeps at power up and flashing Low Battery LED

Thank you for the helpful suggestions to make a Model T tool with feature folks need and want.
A few more bugs to workout so if there is a feature missing let me know soon! Should have them available by June.

The Pocket Coil Checker instruction manual can be viewed here: https://img1.wsimg.com/blobby/go/f76807 ... 6840302570

Mike... Thanks again for the update .

The one suggestion I don't is to make sure the lights are bright enough to in the bright of day outside. Sometimes you cant see if the light is on or not in the daylight.

Status update - project delays due to unexpected business travel. Great feedback from Beta testers. Still working on perfecting the coil contact interface. Another design iteration is in progress. Want to get it right before doing a production run. Thanks for the feedback and patience.