Motorized Hand Crank Coil Tester Speed

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Model T Ford Forum: Forum 2015: Motorized Hand Crank Coil Tester Speed
Top of pagePrevious messageNext messageBottom of page Link to this message  By James A. Golden on Wednesday, November 25, 2015 - 01:54 pm:

I have an original Lyre Shaped Hand Crank Coil Tester that I have restored with Ron Patterson's and Bob Casico's help.

It has a 5 inch pulley attached to the flywheel shaft, but the motor and that pulley were not available.

Last year, I was told the motor turns at 1,750 RPM and should have a 2 inch pulley, if I recall correctly.

That would make the flywheel turn at 700 RPM, if my math is still good.

Do these pulley sizes and numbers sound right?

Does anyone know for sure about the HCCT preferred RPM?

This unit is functionally the same as mine, but is of a different manufacture.

HCCT


Top of pagePrevious messageNext messageBottom of page Link to this message  By Bob Cascisa - Poulsbo, Washington on Wednesday, November 25, 2015 - 02:16 pm:

James,
700 RPM is 11.67 revolutions per second over about 87.5 Hz. Two to three revolutions per second is a typical hand crank
Speed for my HCCT to operate a coil. That's about 120 to 180 RPM. 700 RPM is a fast idle on a Model T. I would tend to want a slightly slower speed.

Be_Zero_Be


Top of pagePrevious messageNext messageBottom of page Link to this message  By Dan Treace, North FL on Wednesday, November 25, 2015 - 02:27 pm:

James

Here is an older post on the subject. Original motorized coil testers ran at 60 RPM's.

http://www.mtfca.com/discus/messages/411944/440096.html?1398612659


Top of pagePrevious messageNext messageBottom of page Link to this message  By Andre Valkenaers on Friday, November 27, 2015 - 09:21 am:

Thanks for this posting.
I saved all the links to earlier threads but this give me an other question.
In one of the threads there is a photo from an instruction shield that say: "and Crank. While voltmeter is reading 6 volts, ... ."
On my home build tester I could only reach about 3Vac. Now I am wondering if my tester is working well??

Thanks
Andre
belgium


Top of pagePrevious messageNext messageBottom of page Link to this message  By keith g barrier Savannah Tn. on Saturday, November 28, 2015 - 08:20 pm:

Andre, I can barely get 3 volt on hand cranking mine and can't hold out at that. I think 6 is out of the question. KGB


Top of pagePrevious messageNext messageBottom of page Link to this message  By Bob Cascisa - Poulsbo, Washington on Saturday, November 28, 2015 - 09:44 pm:

Three volts is typical per an experienced HCCT Person.

Be_Zero_Be


Top of pagePrevious messageNext messageBottom of page Link to this message  By Verne Shirk on Saturday, November 28, 2015 - 10:04 pm:

This may be slightly off thread but these motor driven testers can be turned on and they soon are at operating rpm. A coil can be switched out without turning the switch off. Obviously, the one you crank by hand take a few cranks to come up to speed. I guess you could switch out coils while still cranking at a constant speed if you wanted to. I can turn my hand crank type at a more or less constant speed and the coil will spark. I've noticed that some will start sparking very soon after the hand-crank is starting to turn. Others (actually, it seems like most) will not start sparking until the crank reaches "operating speed". I select the coils that will spark at any speed and, of course, have the proper amp rating. They seem to run better in the car.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Andre Valkenaers on Sunday, November 29, 2015 - 04:17 am:

Verne,
I will try to explain how I understood your coil question. But I will be walking on melting Ice and I hope some of the more experience coil rebuilders will help and make the corrections needed to get the hole story. ( Help Ron, Brent, Toon and John !!! )
To start the coil points to open you need to build up a magnetic field. As the points opens the field will drop and the points will close again and so on till you stop cranking the tester or there is an open (switch) in your electric circuit. (buzzing noise)
To open the points the first time you need to produce a current a little higher as the working current of the coil, due to the working resistance of the coil. My experience 1.5 to 1.8 Amp to start and 1.3Amp as working current .
(The same happens when you start up your starting motor to crank the engine in your car. As you push down the starting button the motor will take about 400Amp and this will drop to about 250Amp when the starter motor is running and cranking the engine.
You can also compare it with you when you need to get out your lazy chair to start a job. Much more energy is needed to get up as to do the job. )
By reading the links above in this thread I understood (and this is new to me) that the delay in the coils starting to open the points has to do with the gap of the cushion spring but... I am not sure how to set this gap right.
I there a tool or a way to do this right and what is the right gap??

Hope this helps a little

Andre
Belgium


Top of pagePrevious messageNext messageBottom of page Link to this message  By Anthonie Boer---- Klaaswaal NL on Sunday, November 29, 2015 - 04:46 am:

Andr้ ; Ron Pat. has a modification of a vice grip [griptang] for sale to set the right gap of the cushion spring. I have the same with my HCCT .I have to turn a little faster to start the coil to spark .Hope this help.
Toon


Top of pagePrevious messageNext messageBottom of page Link to this message  By Verne Shirk on Sunday, November 29, 2015 - 11:44 am:

An "old timer" (the late Bud Voth - 2012 Speedster HOF Restoration of the Year winner) told me one of his secrets to getting a coil to throw a good spark is to get the point on the cushion spring to travel a nice distance. He was one of these guys that just knew how to do it by feel, not by a measuring device. I never saw anyone who could pass him in one of his T's. If you examine cushion springs, some were not manufactured properly and drag on the pin. I've not found much you could do about those, short of tearing the point apart and re-riveting it, which is too much work. I'd say the point should travel maybe 0.010" to 0.015". You can change the tension on it too by bending the area where the lower point attaches to the upper point. This will adjust how much pressure is exerted on the point to keep it in contact with the lower point. I used the coils he set "by hand" to verify my HCCT was working properly!

If I can get my daughter to help me, I'd post a video of what I am talking about in the previous posting...and about the cushion spring.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Willie K Cordes on Sunday, November 29, 2015 - 12:29 pm:

I have a speed control on the motor of my "homemade" motorized hand crank coil tester. I mostly run it a speeds below 100 RPM.
It turns great without all that hand cranking, it has a spark rack and amp meter. (built out of T parts)


Top of pagePrevious messageNext messageBottom of page Link to this message  By Mike Kossor - Kenilworth, NJ on Sunday, November 29, 2015 - 09:50 pm:

The thing that makes coil points difficult to adjust for optimal performance is the number of interacting variables. The ones typically adjusted are:
1. Point gap
2. Vibrator spring tension
3. Cushion spring tension
4. Limit rivet height

A common attempt to minimize the number of possible combinations is to specify fixed values for some of them like Point gap = 1/32” and Limit rivet height = 0.005”. I’ve seen other favored values of cushion spring travel cited by folks that feel work best for them but do not cite the basis for their reasoning; perhaps an elevated wet finger. I searched the forum but found little technical basis so decided to take some data of my own to characterize the effect of the limit rivet height without changing any other variables. This would be difficult to do if not for an ingenious arrangement that Garrett Green introduced me to shown below:

Adjustable Revit Travel


The limit rivet on a brand new set of points was drilled out and tapped for a 2-56 screw then a brass machine screw was installed with brass shim washer and lock nut. The cushion spring travel can be adjusted from anywhere between 0 and 0.030” with this arrangement. I used an optical microscope with graduated eyepiece calibrated in thousands of an inch to accurately measure and set the cushion spring travel to specified values. I set the limit rivet for 0.010” and adjusted the point gap to 0.031” then adjusted the vibrator spring tension and cushion spring tension coil for consistent firing as indicated on the ECCT Multi-Spark test. The coil was fired by applying a 12V DC for a brief duration sufficient to fire a single spark (about 4ms) using precisely timed electronic switch. The current ramp up dwell time and peak firing current was measured for a range of limit rivet heights. Here is the data I took in graphical form:

Coil current vs revit travel

The purpose of the cushion spring contact travel is to allow the cushion spring contact to follow the vibrator spring contact as the coil is energized; allowing them to remain in electrical contact, continuing the flow of coil current until it reaches a minimum value (~5.5A) to ensure the energy of the spark produced is sufficient to reliably ignite the fuel/air mixture. Once the coil current has reached this minimum value, the cushion spring of a properly adjusted coil will have reached the limit rivet head to abruptly stop its travel and allow the vibrator spring contact to quickly move away from it before the magnetic field collapses and generates spark. The contacts must move away from each other quickly because the 0.47uf capacitor connected across the points can only delay the magnetic field collapse briefly (just a few microseconds) but is enough time for the contacts to physically move far enough apart to suppress generation of an arc at the coil points. This is important for two reasons, the well known reason of preventing point contact wear and pitting. The second, less known reason is because point arcing allows coil current to continue flowing at a gradually decreasing level. This is bad because, delaying the collapse of the magnetic field (generation of spark) delays (retards) the spark timing and the fact that the current is at a lower value when spark finally occurs means the spark has less energy which is more susceptible to fouling.

It is interesting to note that for the point gap, vibrator spring tension and cushion spring tension of this coil; the effective range of the limit rivet is about 0.006”. This is because adjusting the limit rivet height for less travel decreases the dwell time, peak firing current and spark energy. Beyond 0.006” it does not, however longer travel (up to 0.020" travel on recent points I have measured) permits the opportunity for the vibrator spring contact to slowly pull away from the cushion spring contact and cause arcing and associated performance degradation without the benefit of ever contacting the limit rivet to abruptly open the contacts.

It is possible to adjust coil points with excessive cushion spring travel (0.006" - 0.020") for proper operation but it can be difficult. It is essential to be able to monitor the firing time consistency to strike the correct balance between point gap, cushion spring tension and vibrator spring tension if you really want to achieve best performance on these points in my opinion, based on solid measured data.


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