MTFCA Forum

Who is making these? It would be nice to buy them from the source.

All capacitors have a dv/dt rating. what do you want high or low.

LeakyRad wrote: ↑

Fri Sep 24, 2021 12:00 pm

All capacitors have a dv/dt rating. what do you want high or low.

Preferably the "newer" ones that are .47uF, 400WV film foil type construction capacitor with a dV/dT rating of 1700v/uSec that came out on the Model T scene around 2011.

When something goes awry, today's hip, connected consumer checks her/his credit score, and if eligible, orders a new car/toaster/whatever on the spot. Repair shops? Parts suppliers? Extinct, for the most part.

TXGOAT2 wrote: ↑

Fri Sep 24, 2021 12:28 pm

When something goes awry, today's hip, connected consumer checks her/his credit score, and if eligible, orders a new car/toaster/whatever on the spot. Repair shops? Parts suppliers? Extinct, for the most part.

Well that's unfortunate to hear! The suppliers are out of the high dv/dt caps, so I am trying to find another source.

Here you go: https://www.mouser.com/ProductDetail/Co ... 5QAg%3D%3D

0.47uf +/- 5%, 400VDC, dv/dt=740V/us
21 in stock can ship immediately. Only $4.50 each + Shipping

Or slightly smaller size with higher dv/dt rating:
https://www.mouser.com/ProductDetail/Co ... SJRg%3D%3D

0.47uf +/- 10%, 400VDC, dv/dt=900V/us
131 in stock can ship immediately. Only $7.79 each + Shipping

The high dv/dt foil/film capacitors are somewhat of a specialty item not always stocked by distributors. The vendors provide a great service and value but suspect requires them to place special orders in the 1,000 - 5,000 piece quantities in order to offer them for just $2 each. I can understand why they are out of stock.

MKossor wrote: ↑

Fri Sep 24, 2021 1:55 pm

Here you go: https://www.mouser.com/ProductDetail/Co ... 5QAg%3D%3D

0.47uf +/- 5%, 400VDC, dv/dt=740V/us
21 in stock can ship immediately. Only $4.50 each + Shipping

Or slightly smaller size with higher dv/dt rating:
https://www.mouser.com/ProductDetail/Co ... SJRg%3D%3D

0.47uf +/- 10%, 400VDC, dv/dt=900V/us
131 in stock can ship immediately. Only $7.79 each + Shipping

The high dv/dt foil/film capacitors are somewhat of a specialty item not always stocked by distributors. The vendors provide a great service and value but suspect requires them to place special orders in the 1,000 - 5,000 piece quantities in order to offer them for just $2 each. I can understand why they are out of stock.

This is perfect! Thank you!!

You could also try Digikey for the same items.

You could also try Digikey for the same items.

I usually try Mouser first because they typically have a lower price on the same item and offer reasonable USPS shipping.

I’ve gotten some from Antique electronic supply.

John

I bought some on eBay that were the exact same part number the vendors are selling. They are used in guitar amplifiers. Same manufacture and all. If I remember they were dirt cheap. They’ve been working for me quite some time. They still test good. I just can’t remember the sellers name. But I’m sure some searching would end up with multiple sellers.

Looking to save a nickel on capacitors is personally very discouraging to read about. If it is really important to someone, well, go for it. I'm not the guy trying to sell 'em.

Vendors invest in inventory, pay the mortgage, pay the staff, keep the lights and heat on, parts sit on a shelf for who knows how long waiting for an order, and then they sell them for a WHOPPING $2 each. Every square foot of space taken up by inventory has an overhead price. I'm frankly amazed that a $2 item can pay for the space that it occupies even in volume, but then again, holding too much inventory to justify the space, also robs working capital for other things.

And people wonder why the supplier base is shrinking and many products are showing perpetual backorder? As customers go, we are often our own worst enemy.

Please try to spend your $$ with people/suppliers supporting our hobby.

Scott_Conger wrote: ↑

Fri Sep 24, 2021 11:31 pm

Looking to save a nickel on capacitors is personally very discouraging to read about. If it is really important to someone, well, go for it. I'm not the guy trying to sell 'em.

Vendors invest in inventory, pay the mortgage, pay the staff, keep the lights and heat on, parts sit on a shelf for who knows how long waiting for an order, and then they sell them for a WHOPPING $2 each. Every square foot of space taken up by inventory has an overhead price. I'm frankly amazed that a $2 item can pay for the space that it occupies even in volume, but then again, holding too much inventory to justify the space, also robs working capital for other things.

And people wonder why the supplier base is shrinking and many products are showing perpetual backorder? As customers go, we are often our own worst enemy.

Please try to spend your $$ with people/suppliers supporting our hobby.

JBog wrote: ↑

Fri Sep 24, 2021 12:47 pm

Well that's unfortunate to hear! The suppliers are out of the high dv/dt caps, so I am trying to find another source.

I agree with you Scott. But if one needs a part fairly quickly and the suppliers are out, what should one do? One could wait for the items to return to stock which might means parking one’s T for an indefinite period, or source the item independently, or just do without (not always a practical option). Anybody that is willing to pay 3-4x the regular supplier price is not trying to “save a nickel”.

Eric

If suppliers are out, then I'd put in a request "WTB capacitor" in the parts classified and wait for any 1 of likely several dozen people who have them to respond.

Or go here: https://www.ebay.com/itm/184699353570?c ... hCEALw_wcB

I find it difficult to believe that ALL suppliers are out of stock, though.

EDIT UPDATE: The link above is not a certain source of capacitors. A good choice for T coils is a dv/dt rating or 800 to 1700. Those values are not typically printed on capacitors. It is safest to go to Lang's or others to get the actual part number and thus source it. It seems to me, though, that if the suppliers do not have them, then perhaps they are simply not available right now as seems to be so many things these days.

Scott_Conger wrote: ↑

Sat Sep 25, 2021 8:10 pm

If suppliers are out, then I'd put in a request "WTB capacitor" in the parts classified and wait for any 1 of likely several dozen people who have them to respond.

Or go here: https://www.ebay.com/itm/184699353570?c ... hCEALw_wcB

I find it difficult to believe that ALL suppliers are out of stock, though.

Ill try that next time. All 4 coils in the T I bought this spring have tested as having bad caps. I've been running on loaner coils and the owner needed them back, so I've been dead in the water. I didn't think of the WTB section of the forum.

So what is the minimum aceptable dv/dt value for capicators used in a Model T coil rebuild? I looked up a post from 2011 on this subject and a value of 1700 V/uS was mentioned, along with some photos of 'unacceptable' capacitor types. The tech spec's and sales jargon has gravitated to 'Hi dv/dt' without actual values. Examples given here suggest to me that values of 740 and 900 V/uS are acceptable, tho when compared to the 'high' dv/dt of 1700 suggested in 2011, these numbers come in at 44 and 53% of the previous suggested 'high' dv/dt. Parts availability is deffinitely an issue, but if a cap with dv/dt of 740 only lasts 44% as long as one with 1700, that's a potential problem, isn't it. Conversley, if 740 is good, how low a dv/dt value can you use and still have a reliable rebuild? Thanks, jb

James, I just surfed past this and you ask a good question which did not occur to me the other day. With respect to dv/dt, I cannot tell if the link I provided above would actually net the correct capacitor since that information is typically not printed on the capacitor. I will post a warning as an edit.

Thank you.

Thanks Bob...I did not know that.

This thread is bringing a lot of good info to light...

What is wrong the the previous style round ones? That’s what I use. I’ve used them in 12 coils with no failures. When the suppliers where out before I bought some on eBay.

Any coil rebuilders weigh in here?

So I guess my question is….. Is the one on the left ok or should I expect trouble in the future? I definitely am not an electronics expert by any means. I didn’t see many options at the time when I had all bad coils in the cars I had bought and the vendors were all out.

My apologies for taking away from the original poster with my own questions.

Brian

There is an issue with the electronic type of coil tester and the Model T trembler coil capacitors.
There is a thread on the Forum with the problem explained about a month ago. Maybe a computer expert can locate the thread, or maybe Mr MKosser will chime in...n

Brian/Brad

the one on the left is fine. It was about the only suitable one available 5 or more years ago. I am running those in a car with many thousands of miles on the coils and 12 years of running.

There is an issue with the electronic type of coil tester and the Model T trembler coil capacitors.

I believe this is the thread you are referring to:
https://mtfca.com/phpBB3/viewtopic.php? ... or#p173985

The issue discussed therein pertained to capacitor leakage paths when installed in a Model T coil has nothing to do with the capacitor dv/dt rating.

would someone explain why dv/dt is an important parameter in coils which originaly had caps with high inductance and resistance. it was probably not even a consideration back then. high speed in the caps dont hurt but is it needed in t coils. a high voltage rating is better. distributor ignition caps are cycled much faster and i doubt they are high speed.

The equation dV/dT is used to express the capability of capacitor's dielectric to withstand high current pulses.
These current pulses naturally occur in all trembler type ignition coils (invented in the late 19th century) because of the nature of the coils internal circuit design.

The Model T Ford ignition coil is a Trembler Coil. Because of these naturally occurring electrically current pulses, when purchasing replacement capacitors the dV/dT capability must be taken into consideration.

When solved, the above equation (dV/dT), is expressed in Volts per Microseconds where "d" is rate of change, "V" is Voltage and "T" is Time.
Capacitors come in varying types of internal construction. If you carefully study a capacitors electrical specifications you will notice some types have high dv/dT ratings and others are lower because their of there intended use in circuit design applications. Capacitors not intended for high current applications usually do not even mention dV/dT specifications. This is usually the case with metalized Mylar capacitors, commonly and mistakenly installed in Model T coils, but well known to work for only a short time.

The original Ford coil capacitors are of the film/foil type internal construction which generally have higher dV/dT ratings because of the type dielectric used. The film is the waxed paper dielectric and the foil is Tin foil, the electrically conductive element.

The two capacitors shown in the photo above were specifically selected or developed (physical size and capability ) to be recommended to Model T Ford parts suppliers to sell for use in Model T Ford ignition coil repair. Many thousands have been installed in Model T coils and are known to work well and will last another 100 years.

There are several commonly available capacitors that will reliably work in the Model T coil, but you have to be careful and know exactly what you are doing. The world is just a little too simple and can be a trap for logical people.

Hope this helps.

There is also no shortage of these. The main people have 1000's in stock and the suppliers who sell the correct ones do as well.

Andy,

Are you suggesting a conspiracy among distributors to report a shortage of these capacitors, possibly to increase the sales of their own rebuilt coils at $100 each? I admit that if they were buying 10,000 caps at a time to get the low price, it does seem odd they all “ran out” of these caps at the same time. But I’m suspicious by nature.

Phil

besides suspicious by nature, you perhaps are prone to exaggeration? The average coil rebuild goes for under $60 a pop. Not $100.

Considering the standard parts set of points, capacitor and top fittings will set you back around $17, there ain't much meat on the bone for the rebuilder. It's a filthy job and frankly, even in volume and using a system, it is a hard way to make a buck. $100 a coil? I wish! I'd still be doing them, but you can count me as one more guy who no longer serves the community in that capacity.

All I can say about the folks who still do this, is this: God Bless you.

BTW, "ModelTCoils.com" is for sale and if you wish to produce $100 coils, that could be your chance! Either that or there's one less vendor for them...

All thatr is mentioned above of pro & cons of the two capacitors are correct (and nice to see "The Coilman" is back sharing his knowledge) but one thing is omitted:
The physical difference in geometry:

The left one do not fit right into the void from the original condenser and require some more digging out tar and rearranging the glassplate insulator.
The right one fits just in: And sorry Ron - my workbench is not as clean as yours use to be

So all four of my "new" coils tested as having bad capacitors on two different ECCTs. That's what motivated me to start this thread. I got four new caps from a generous member of the forum. I opened the coils last weekend, and this is what I found. I unsoldered these capacitors and replaced them with the four I got in the mail, which are the high dV/dT kind. I need to schedule a time with one of our club members who owns an ECCT to readjust them, but I am planning on dropping them in the car this weekend (pending a possible snowstorm) to see how they do.

Jason

Snow should not stop you. T's are fun to drive in the snow. Bring your coils here to Milwaukee and we can test on my ECCT. Then you can take them back to Wyoming and the snow should have melted by then.

David

the problem for Jason is that the snow falls in Montana, and lands in Colorado...it just spends a little time in WY carried gently by 80 MPH winds.

I bet Milwaukee sees some good snow! Scott's right, Wyoming snow can be a nightmare. I'm hoping I can get it out of my garage for a little bit next week. At least with the wind, I get really good gas mileage.

Jason

regarding your caps registering as bad...you did separate the points and block them with card-stock before you measured them, right?

I find it hard to believe that those new caps measured "bad".

that said, unfortunately those coils do not come with the best reputation. Once repaired, do yourself a favor and secure the caps somehow to keep them from vibrating. DON'T use silicone or any other similar material. I would think that some hot glue sufficient to mechanically nail them down would be fine. I'd normally say "use high-slope tar" but who wants to try to source that for less than a cup-full for the job?

Those Capacitors in Jason's "new" coils are made by Michicon and are metalized Mylar type constructions with a dV/dT rating less than 75 volts/microsecond and are entirely unsuitable for use in a Model T For ignition coil for the reasons I described earlier in this thread.
Ron Patterson

Ron

this response is not in disagreement with you, but to clarify a point: when tested properly with typical test equipment, if the actual capacitor was not able to be seen by the repairman, would that capacitor not test just fine at the proper capacitance? My point is that to the hapless T owner, the existence of the wrong capacitor is normally invisible to the owner until such time as it fails.

Personally, I am unhappy to see these coils still being manufactured and marketed to the hobby. I thought that they had ceased producti

Scott_Conger wrote: ↑

Sat Oct 09, 2021 9:55 am

Jason

regarding your caps registering as bad...you did separate the points and block them with card-stock before you measured them, right?

I find it hard to believe that those new caps measured "bad".

that said, unfortunately those coils do not come with the best reputation. Once repaired, do yourself a favor and secure the caps somehow to keep them from vibrating. DON'T use silicone or any other similar material. I would think that some hot glue sufficient to mechanically nail them down would be fine. I'd normally say "use high-slope tar" but who wants to try to source that for less than a cup-full for the job?

Scott,

The two club guys whose ECCTs my coils were tested on were very protective over them, so I wasn't able to test the coils myself, but I hope that since they owned ECCTs that they knew what they were doing.

Why not use silicone?

Your garden-variety silicone sealant will outgas, which is mildly corrosive within a confined space. Plus it creates a very difficult situation for the next guy to remove the gunk and then afterwards expect to get solder connections clean enough to flow solder.

Expanding foam can be used to re-pot capacitors.

"besides suspicious by nature, you perhaps are prone to exaggeration? The average coil rebuild goes for under $60 a pop. Not $100."

Actually, Macs sells their coils for $100 with no core charge, and Langs sells theirs for $57.95 IF you give them a good core.

One thing that I was thinking about the other day; heat rating. While all is well and good at normal operating temperature, what about when the hot tar gets poured in? Using the capacitors from the suppliers, I have had cases where they showed a reading before potting, but while still warm did not. After they cooled completely they were ok. Left me wondering if I was "cooking" the capacitors from too much heat and if so, when would they give out? Next time I melt the tar, I might do a temperature reading.

regarding your caps registering as bad...you did separate the points and block them with card-stock before you measured them, right?
I find it hard to believe that those new caps measured "bad".

I concur with Scott, coils can develop leakage paths through the coil core and wire insulation that can appear to be capacitors with poor leakage when tested with the vibrator spring held open against the coil core. Placing a piece of card stock between the coil core and the vibrator spring insulates the vibrator spring from touching the coil core and the source of leakage.

Another issue I have come across with these type of coils is conductive black paint which resulted in failing the capacitor leakage test limit (5 Meg Ohms).
For these reasons, folks using the ECCT to test capacitors need to be aware of these issues and judge capacitors by capacitor VALUE NOT leakage resistance as per the previous link I posted: https://mtfca.com/phpBB3/viewtopic.php? ... 4&p=173985 Capacitors that measure within acceptable uF range (0.47uF +/- 20% or >0.33uF but <0.68uF) But test "POOR" for leakage are NOT bad and DO NOT need to be replaced.

Phil

as you noted, my statement

The average coil rebuild goes for under $60 a pop. Not $100

is completely accurate.

If you wish to change your statement to "new plastic-cased coils from Mac's go for $100", well I guess I agree. Why anyone would want a new plastic coil over an original rebuilt coil that has found it's way successfully through history for over 100 years, is beyond me.

If someone thinks they're buying an extra $40 worth of reliability, they will find themselves sadly mistaken. To each their own.

I use a capacitor test meter. I have not seen any non rebuilt coil over 60 years old that had a good capacitor.
The dozen or so that I rebuilt 5 years ago using the slightly flattened style capacitor still tests good at this time.
New capacitor meters are available at a reasonable price on the internet. I highly recommendto all to get one. Mine was a Christmas present from my son.
Art Mirtes