fix a coil, buzz box

[andy2794]

I just purchased a 1916 model T. With the purchase I received 8 buzz boxes, only 3 will buzz. I understand you can purchase new and rebuilt boxes, but I want to try and fix some of the ones I have. I watched many of the videos on YOUTUBE and learned a lot about a buzz box, but I have a lot to learn. I checked the secondary windings and set aside the ones that were not between 30,000 and 40,000 OHMS. I checked the primary windings and did the same if they were less than 1 OHM. That left me with 7 boxes, I checked the capacitors in the those boxes and found they have 0 OHMS and not .47K. I purchased the capacitors from Snyders to be sure I have the correct ones. I pulled the bad capacitors out of 2 of the boxes and the others I just tried to connect with the old capacitors still in the box and cannot get a buzz from any of the boxes. I took the boxes and capacitors to a local electrical shop that rebuilds generators and starters and they could not figure out why they were not buzzing. What am I over looking?

[Steve Jelf]

I would refer to the MTFCA Electrical System book.
I believe you need a reliable tester to do a proper job.
Maye someone with actual experience can confirm or correct that.

[Rich Eagle]

New points would help. If the gap is correct you need to measure how many amps it draws with a tester or at least an amp gage. This can tell you more than I know.
http://www.mtfca.com/discus/messages/82 ... 1535118640
https://th.bing.com/th/id/R.95ad4b99777 ... ImgRaw&r=0
Rich

[Charlie B in N.J.]

Points most likely. Do more research it's the easiest way to learn this stuff.

[jab35]

First step, buy the book and while waiting for it to arrive, verify resistance/continuity of primary and secondary windings. Corroded/burnt/dirty points will often cause open primary circuit. If you test a good coil by applying battery voltage to the primary to make it buzz, be sure to have a spark gap (old sparkplug) in the secondary circuit to dissipate the high voltage spark so you don't burn up the secondary winding circuit. A 9V dry cell smoke detector battery will buzz a good coil, battery polarity is unimportant in this test, but protect the secondary as described. Once you verify function you can move on to getting the 'good' coils rebuilt with new capacitor and points and set to specifications for use in the car. Best, jb.

[andy2794]

When you say "buy the book" which book are you referring to?

[Jerry VanOoteghem]

I checked the capacitors in the those boxes and found they have 0 OHMS and not .47K.

Capacitors are rated in microfarads, (.47 mfd), not ohms. Unless you have a meter that's meant to check capacitors, you have no way of testing them. Even if the MFD reading is correct, you're still not sure if the internal insulation will be good at the operating voltage. (BTW, 0 ohms on a capacitor is actually a good thing. Means it's not internally shorted.)

It's great that you want to repair/rebuild your own coils, and I hope you continue to pursue that. However, my best advice to you, is to have 4 or 5 of your coils professionally rebuilt, then continue in your desire to someday rebuild your own. This way, you eliminate the coils as a possible source of trouble as you continue to sort out your car. Removing even one variable from the equation makes life a whole lot simpler. It's the best way to begin to appreciate your T as soon as possible.

[Quickm007]

I checked the capacitors in the those boxes and found they have 0 OHMS and not .47K.

Capacitors are rated in microfarads, (mfd), not ohms. Unless you have a meter that's meant to check capacitors, you have no way of testing them. Even if the MFD reading is correct, you're still not sure if the internal insulation will be good at the operating voltage.

Agree with Jerry, you have to check capacitors. I do with Mike Kossor ECCT coils tester and work really well. https://modeltecct.com/

[jab35]

Andy, Sorry, the book Steve mentioned, "I would refer to the MTFCA Electrical System book". Available from mtfca museum bookstore and most vendors, third book down on page: https://modeltstore.myshopify.com/colle ... nt=9276612

Actually you can investigate capacitor presence and function but not Farad value nor leakage with a simple vom test (an analog meter works better than digital). First open the points and place a piece of paper between them to insulate contacts. The capacitor is across the points in the circuit, and maybe you have already checked that and read infinite resistance. If this is the case, you know the Cap is not shorted so proceed.

With the meter in resistance mode, Ohms setting, hold the probes on the points briefly, resistance should be infinite if capacitor is not shorted.
Next, quickly switch your meter to the most sensitive DC voltage setting and do the same thing, you will see a brief rise/fall of the needle followed by gradual return of the needle to 0 VDC. That confirms that the capacitor held some 'charge' from your resistance measurement which was dissipated in the voltmeter during the volts measurement. You might see some meter deflection using the Ohms setting by reversing the leads during an 'ohms' measurement. The battery in the Ohm meter charges the capacitor and reversing the leads discharges and recharges in reverse polarity causing a very brief blip in the needle when you switch leads. Not a quantification of capacitor values in Farads, but it confirms it is there, not shorted, not open, and holds some charge. Hope this helps, good luck, jb

[Matt in California]

Andy,
You like to do things the hard way, so do I! The Model T coil has fascinated me most of my life. When I was young I used it to shock my brother! From this experiment I was fascinated with electricity and spent many years earning degrees related to the subject. For the last few years I started learning about how to rebuild and tune these coils gathering info from various sources.

First how to destroy a coil: Do not make a 1/4 inch spark gap from the primary spark terminal. Obviously you don’t want to destroy your coils, so it is absolutely necessary to make a spark gap in testing. If you don’t have a test fixture you could do this with a paper clip attached to the primary coil post and pointed with a gap near the secondary.

I have found that many of the coils that don’t buzz have issues with hardware being dirty/corroded on the top. Yes you can buy new hardware, but that requires understanding how to tune it. For a novice it does take a bit to learn setting new points. I have found that if I can takeoff the nuts on the top, I can usaily get the points/hardware to work. Yes, there are times times when it’s too rusty and they need replaced. Most of the hardware can be cleaned up on a wire wheel. I put the small hardware on a loop of wire so it doesn’t go flying.

Regarding testing a capacitor. If it is shorted when the points are open obviously it’s a bad capacitor. I have followed the role: replace any original capacitor. But lately I’ve been wondering how much life is left in some of the early Ford capacitors. If you’d like to save a dime at the expense of $10, like I do, you could see how much life is left in the original capacitors:-) If your coils are the KW coils made in the 1940s to 1960s consider the capacitor a piece of trash and it needs to be replaced. You can test a capacitor with a Ohm meter if you know what you were doing. This will not give you a accurate measurement, but it will verify that the capacitor is storing energy. You need to set your ohm meter to the highest setting. Make sure the points are open if needed put a piece of paper between them. Then when you connect your ohm meter you will see it charge and then go to infinite reverse leads and you will see this happen again. Again this is not a very good test, but it does demonstrate the capacitor has some capacitance. (Some digital ohm meters have too long of a delay between updates for you to even detect the charge.) I along with a number of other people here in the forum have built a inexpensive coil tester. It includes a capacitor tester. If you are interested I could send you one- just send me a message. All I ask is that you give a full review of your experience here on the forum.

Matt

[andy2794]

Matt, I would be very interested in receiving the coil tester. I have talked to the local parts stores, tire dealers, Snapon dealer, I cannot find anyone local that knows anything about repairing a coil. I want to thank everyone that has replied and I will give a full review of my experience here on the forum. Please advise.

[Matt in California]

Matt, I would be very interested in receiving the coil tester. I have talked to the local parts stores, tire dealers, Snapon dealer, I cannot find anyone local that knows anything about repairing a coil. I want to thank everyone that has replied and I will give a full review of my experience here on the forum. Please advise.

Andy,
The advice that I give anyone starting in the hobby is to get a set of rebuilt coils from one of the recommended rebuilders. It will likely be the best bang for your buck. But if you want to get into this coil madness...

Attached is a document that I put together with suggestions on getting coils working.

Regarding me sending the coil tester, please me an email with your mailing address.

Matt

[Oldav8tor]

In my opinion there are some things better left to the experts, at least initially. I sent my coils to Ron Patterson and received back a set of perfectly functioning and adjusted coils that have powered my T thru more than 5000 miles since Aug 2019. Does that mean I don't want to learn how to rebuild and adjust coils? No, the interest is there but in the meantime I'm enjoying my T, not wondering if I did it right. For someone like me who is new to the hobby there is a lot of information to absorb...better to take it in manageable bits and work your way into the harder stuff as your overall knowledge increases.

[J1MGOLDEN]

That Buzz Box will show you the coil is bad, if there is no spark at all.

It will not show you the random misfires, mostly caused by a bad capacitor.

So, it will fake a good coil for you, if nothing else.

The original capacitor is just about always bad and you can get sparks with it cut out of the circuit, but the points do not last very long.

Later made coils often have a rather small capacitor and some new ones have an extra large capacitor.

That capacitor evident does not have a good ratio for the time required to fully charge and discharge the capacitor in normal operation.

The HCCT will show the misfires, but it will not check or measure the capacitor.

You can buy a separate meter to check the capacitor size for $30 to $50.

Then too, removing a bad capacitor, will often break a wire and result in a coil with no sparks.

Rebuilding those coils for maximum sparks is best left to the experts and their information is always shown in ads in both our popular magazines.

It is really amazing how easy a Model T starts with their rebuild capacitors.

I just got two compression starts from a 1917 engine that had been sitting for two months in the cold, pulled through three times with the coke closes, and when I turned the switch to Bat, the engine was running again.

Then too, it does have a Russ Potter recently rebuilt carburetor.