How hot does your coil get?

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luftvagon
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How hot does your coil get?

Post by luftvagon » Wed Apr 17, 2013 7:45 pm

How hot does your ignition coil get? I don't remember my coil getting very hot in stock L-Jetronic form triggered by distributor with points. Now I am sporting Pertronix, and different ECU/pickup.
It's hot to the touch in just xx minutes of idling. How cool is that? No pun intended.
1981 Volkswagen Vanagon Westfalia - air-cooled Type4 1970cc CV (hydraulic lifters, 42x36 valves, stock cam, microSquirt FI with wasted spark ignition)
1993 Ford F-250 XL LWB Extended Cab 7.3L IDI

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RSorak 71Westy
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Re: How hot does your coil get?

Post by RSorak 71Westy » Wed Apr 17, 2013 8:22 pm

It's getting too much voltage. Usually a coil only receives full batt voltage during cranking, then after the engine starts, the coil is fed a reduced voltage around 9 volts. The Ballast resistor does this job. This is how most cars work, I think VW's are different.
Most VW coils if I remember correctly have this resistor built in to them. If so I dont see how it can be bypassed or i.e. how you can even feed too much voltage too it ?
Take care,
Rick
Stock 1600 w/dual Solex 34's and header. mildly ported heads and EMPI elephant's feet. SVDA W/pertronix. 73 Thing has been sold. BTW I am a pro wrench have been fixing cars for living for over 30 yrs.

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SlowLane
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Re: How hot does your coil get?

Post by SlowLane » Wed Apr 17, 2013 10:29 pm

First of all, I think it's normal for coils to run warmer than what would be comfortable to hold for any length of time.

Rick is correct, our VW's don't use external ballast resistors like 'Merican cars do ( or rather, did). Instead, the VW coil incorporates an internal ballast resistance (typically 3 ohms). So no, there is no way to provide "full voltage" to the coil during cranking. The ballast resistance is a permanent, inseperable part of the coil.

Luft, check your dwell with the Pertronix. I was shocked to discover that the dwell provided by my cherished Crane XR700 system was running at 71 degrees. I can't say one way or the other whether it made the coil run warmer or not because of this, and frankly I didn't much care: the XR700 worked flawlessly for the 13 years I had it in the van. But if you're really that curious, measure the temperature of your coil with Pertronix, then swap back to points and measure the coil temperature again.

Or better yet, convert to a direct-fire EDIS system that your mega-micro-maxi-squirter system supports. :geek: Ya know ya wanna.
'81 Canadian Westfalia (2.0L, manual), now Californiated

"They say a little knowledge is a dangerous thing, but it is not one half so bad as a lot of ignorance."
- Terry Pratchett

luftvagon
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Re: How hot does your coil get?

Post by luftvagon » Thu Apr 18, 2013 5:47 am

It's coming!
1981 Volkswagen Vanagon Westfalia - air-cooled Type4 1970cc CV (hydraulic lifters, 42x36 valves, stock cam, microSquirt FI with wasted spark ignition)
1993 Ford F-250 XL LWB Extended Cab 7.3L IDI

DugB
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Re: How hot does your coil get?

Post by DugB » Fri Sep 14, 2018 6:41 am

Very timely to find this thread, as I was just wondering the same thing. My '75 bus, running well with a Camper Special 2.0 (stock FI setup for '75), seems to have a warm coil, too. I checked it with an infrared thermometer after my 7 mile commute on local roads this morning and it came in at 130 degrees F. I do have 10V at the coil...I had thought that was an issue but after some of the previous comments in this topic I'm thinking that's normal.

- Doug :-)

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Amskeptic
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Re: How hot does your coil get?

Post by Amskeptic » Fri Sep 14, 2018 8:00 am

DugB wrote:
Fri Sep 14, 2018 6:41 am
Very timely to find this thread, as I was just wondering the same thing. My '75 bus, running well with a Camper Special 2.0 (stock FI setup for '75), seems to have a warm coil, too. I checked it with an infrared thermometer after my 7 mile commute on local roads this morning and it came in at 130 degrees F. I do have 10V at the coil...I had thought that was an issue but after some of the previous comments in this topic I'm thinking that's normal.

- Doug :-)

Coils are resistance devices, and therefore do create some heat. They will overheat if you leave the ignition on AND the points happen to be closed. This is true for Pertronix, too. If you happen to leave the ignition on and the Pertronix is parked at "ground" position, it will fry in minutes.

As for the resistance that American cars used to call "ballast resistors", VW relied on twenty feet of wire from the battery to the fuse box to the ignition switch to the fuse box again and back to the coil. As a general rule, anything over 10 will give a sufficient spark, measured under starter draw.
Colin
BobD - 1978 Bus . . . . . . . . . . . 111,155 miles
Chloe - 1970 bus . . . . . . . . . . . 206,820 miles
Naranja - 1977 Westfalia . . . . . 108,000 miles
Pluck - 1973 Squareback . . . . . . 55,570 miles
Alexus - 1991 Lexus LS400 . . . 78,885 miles

kreemoweet
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Re: How hot does your coil get?

Post by kreemoweet » Fri Sep 14, 2018 7:35 pm

The good thing about having an external ballast resistor, instead of built-in coil resistance, is that it
can be bypassed during cranking, in order to counteract the inherently lowered voltage that the coil
gets during cranking. It's pretty common with the weak stock VW ignition system for the engine to refuse
to fire until the instant the key is released and starter current is cut off, letting the ignition voltage
bounce back up to normal.

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whc03grady
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Re: How hot does your coil get?

Post by whc03grady » Fri Dec 07, 2018 1:39 pm

Amskeptic wrote:
Fri Sep 14, 2018 8:00 am
If you happen to leave the ignition on and the Pertronix is parked at "ground" position, it will fry in minutes.
Colin
Not that I doubt this, but how is it that ignitions aren't burning up every day? Points (and their Petronix equivalent) are closed almost as often, relative to a circle, that they're open, right?

Lemme see, four cylinders x ~50deg dwell=200deg of open, 360-200=160deg of closed, so 44% of the time?

Shouldn't that mean that points/Petronixes park at "ground" position nearly half the time, and therefore burn up on those of us who do lots of work with the key on much more often than they seem to? Is my math wrong?
Ludwig--1974 Westfalia, 2.0L (GD035193), Solex 34PDSIT-2/3 carburetors.
Gertie--1971 Squareback, 1600cc with Bosch D-Jetronic fuel injection from a '72 (E brain).
Read about their adventures:
http://www.ludwigandgertie.blogspot.com

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Amskeptic
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Re: How hot does your coil get?

Post by Amskeptic » Sat Dec 08, 2018 10:54 am

whc03grady wrote:
Fri Dec 07, 2018 1:39 pm
Amskeptic wrote:
Fri Sep 14, 2018 8:00 am
If you happen to leave the ignition on and the Pertronix is parked at "ground" position, it will fry in minutes.
Colin
Not that I doubt this, but how is it that ignitions aren't burning up every day? Points (and their Petronix equivalent) are closed almost as often, relative to a circle, that they're open, right?

Lemme see, four cylinders x ~50deg dwell=200deg of *open, 360-200=160deg of *closed, so 44% of the time?

Shouldn't that mean that points/Petronixes park at "ground" position nearly half the time, and therefore burn up on those of us who do lots of work with the key on much more often than they seem to? Is my math wrong?

Here's a fun fact. At shut off, most engines stop rotating on a compression stroke. Tired engines are more likely to end up with open points/un-signalled Pertronix. Fresh engines are more likely to kick backwards to a closed point position/signalled Pertronix. Brand-new rebuilds just stop HERE, NOW.

Most points and coils can sit at closed position with ignition on for an easy 10 minutes. You'll have a hot-to-the-touch coil, but the points really don't care. They do not burn up due to ignition current in a closed state. They burn up in operation when the faulty condensor sends a 250 volt surge + inductive coil winding backwash through the points just opening/closing, spark city!

Pertronix burns up just from continual 12 volts to ground. Boo. I hear they are getting better.
Colin

( * p.s. wear limit dwell is (think: dwelling, home, closed) 50* X 4 = 200* closed, 160* open.
fresh adjustment is let's say 45* X 4 = 180* closed, 180* open, yay)
BobD - 1978 Bus . . . . . . . . . . . 111,155 miles
Chloe - 1970 bus . . . . . . . . . . . 206,820 miles
Naranja - 1977 Westfalia . . . . . 108,000 miles
Pluck - 1973 Squareback . . . . . . 55,570 miles
Alexus - 1991 Lexus LS400 . . . 78,885 miles

telford dorr
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Re: How hot does your coil get?

Post by telford dorr » Sun May 12, 2019 10:03 am

whc03grady wrote:
Fri Dec 07, 2018 1:39 pm
Not that I doubt this, but how is it that ignitions aren't burning up every day? Points (and their Petronix equivalent) are closed almost as often, relative to a circle, that they're open, right?

Lemme see, four cylinders x ~50deg dwell=200deg of open, 360-200=160deg of closed, so 44% of the time?

Shouldn't that mean that points/Petronixes park at "ground" position nearly half the time, and therefore burn up on those of us who do lots of work with the key on much more often than they seem to? Is my math wrong?
As I recall, dwell is the measure of degrees that the points are closed per 90 degrees of four cylinder distributor rotation. Thus, 50 / 90 = 56% of the time closed. So, if the coil pulls approximately 4 amps with continuous 14 volts applied, then the coil should be dumping 14 volts x 4 amps x 56% = 31 watts of heat (this would be at a slow idle). So yeah, the coil is gonna run a little hot. Now at speed the coil is going to pull less current because coil inductance will limit the rate of rise of the current, so the coil will run a little cooler. On the other hand, with the ignition on but with the engine not running and with the points closed, the coil will be dumping 12.6 volts x 3.6 amps(1) = 45 watts - about 45% more heat! Unhappy coil!

Now with a Pertronix, things are a bit different (and I will confirm this with a 'scope the next time a Pertronix-loaded 009 comes by). From what I can tell, the dwell angle with one of these is much greater than with points because the unit dumps current into the coil continuously except when a little magnet swings by the sensor, causing the unit to interrupt the coil current for an instant and fire the spark plug. Not sure if this "off" time is a fixed duration or not, but I suspect so. Will confirm and report back. If true, then the coil will run a bit hotter with one of these compared to with points.

(1)With a resistive load, current varies proportionally with voltage, and therefore power varies as the square of the voltage.

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Amskeptic
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Re: How hot does your coil get?

Post by Amskeptic » Sun May 12, 2019 11:52 am

telford dorr wrote:
Sun May 12, 2019 10:03 am
whc03grady wrote:
Fri Dec 07, 2018 1:39 pm
Not that I doubt this, but how is it that ignitions aren't burning up every day? Points (and their Petronix equivalent) are closed almost as often, relative to a circle, that they're open, right?

Lemme see, four cylinders x ~50deg dwell=200deg of open, 360-200=160deg of closed, so 44% of the time?

Shouldn't that mean that points/Petronixes park at "ground" position nearly half the time, and therefore burn up on those of us who do lots of work with the key on much more often than they seem to? Is my math wrong?

As I recall, dwell is the measure of degrees that the points are closed per 90 degrees of four cylinder distributor rotation. Thus, 50 / 90 = 56% of the time closed. So, if the coil pulls approximately 4 amps with continuous 14 volts applied, then the coil should be dumping 14 volts x 4 amps x 56% = 31 watts of heat (this would be at a slow idle). So yeah, the coil is gonna run a little hot. Now at speed the coil is going to pull less current because coil inductance will limit the rate of rise of the current, so the coil will run a little cooler. On the other hand, with the ignition on but with the engine not running and with the points closed, the coil will be dumping 12.6 volts x 3.6 amps(1) = 45 watts - about 45% more heat! Unhappy coil!

Now with a Pertronix, things are a bit different (and I will confirm this with a 'scope the next time a Pertronix-loaded 009 comes by). From what I can tell, the dwell angle with one of these is much greater than with points because the unit dumps current into the coil continuously except when a little magnet swings by the sensor, causing the unit to interrupt the coil current for an instant and fire the spark plug. Not sure if this "off" time is a fixed duration or not, but I suspect so. Will confirm and report back. If true, then the coil will run a bit hotter with one of these compared to with points.

(1)With a resistive load, current varies proportionally with voltage, and therefore power varies as the square of the voltage.

Has Pertronix actually conducted an improvement of their engineering so that they are not so sensitive to melting with the ignition on/engine off?

I got into a dust-up with Pertronix several years ago (c2008) when I discovered that the magnets were not equidistant 90*. My #3 was a good 3* more advanced than the other three cylinders. Pertronix then technical support suppositioned that the black plastic magnet hole castings were off.
Quick test: put your timing light on the center wire to distributor at idle. Do you see ghost images of your timing marks? Investigate each cylinder's timing. My 2 and 4 were the same against the valve adjustment mark, 1 and 3 were noticeably different at 1* BTDC for #1 and 4* BTDC for #3.
BobD - 1978 Bus . . . . . . . . . . . 111,155 miles
Chloe - 1970 bus . . . . . . . . . . . 206,820 miles
Naranja - 1977 Westfalia . . . . . 108,000 miles
Pluck - 1973 Squareback . . . . . . 55,570 miles
Alexus - 1991 Lexus LS400 . . . 78,885 miles

telford dorr
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Re: How hot does your coil get?

Post by telford dorr » Sun May 12, 2019 1:10 pm

Amskeptic wrote:
Sun May 12, 2019 11:52 am
Has Pertronix actually conducted an improvement of their engineering so that they are not so sensitive to melting with the ignition on/engine off?
No idea. Don't / never have run a Pertronix (which is weird, seeing as most everything on my bus is now electronic..) I've only (generally) removed them for people who have either cooked them (engine off, key on) or hooked them up backwards (instant death). On those who still have them working, I put a little 1/4" green heat shrink on the black wire connector, and a little 1/4" black heat shrink on the red wire connector, so the "color codes" are back to VW stock. Seems to help prevent misconnection.
I got into a dust-up with Pertronix several years ago (c2008) when I discovered that the magnets were not equidistant 90*. My #3 was a good 3* more advanced than the other three cylinders. Pertronix then technical support suppositioned that the black plastic magnet hole castings were off.
Sort of understandable, considering how critical the maching on the rotor would have to be to maintain timing tolerance. Truthfully, I'm impressed that, for the price, it's as good as it is. Then again, I'm impressed that the machining on a stock points cam is as good timing-wise as it is. But then again, it's German, so you sort of expect it...
Quick test: put your timing light on the center wire to distributor at idle. Do you see ghost images of your timing marks? Investigate each cylinder's timing. My 2 and 4 were the same against the valve adjustment mark, 1 and 3 were noticeably different at 1* BTDC for #1 and 4* BTDC for #3.
Next time an Pertronix equipped engine passes through Areomech's shop, I'll do just that. Will also explore the dwell issue touched on in the previous post.

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Re: How hot does your coil get?

Post by Amskeptic » Mon May 13, 2019 5:13 am

telford dorr wrote:
Sun May 12, 2019 1:10 pm
Will also explore the dwell issue touched on in the previous post.
I have a plastic "distance gauge" for the pick up module. The further out the pick up, it seems, the greater the dwell. I generally find 60+ degrees at the plastic width, which doesn't bother me as far as engine function, but as you noted, that is more time for heat generation. I will be interested to read of your investigations.

I have been setting breaker points at 45-47* to give them time to slowly wear towards 50*. With good grease (Valvoline semi-synthetic) and a gorgeously seasoned breaker cam, it is not difficult to get 20K miles per adjustment.
Colin
BobD - 1978 Bus . . . . . . . . . . . 111,155 miles
Chloe - 1970 bus . . . . . . . . . . . 206,820 miles
Naranja - 1977 Westfalia . . . . . 108,000 miles
Pluck - 1973 Squareback . . . . . . 55,570 miles
Alexus - 1991 Lexus LS400 . . . 78,885 miles

telford dorr
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Re: How hot does your coil get?

Post by telford dorr » Mon May 13, 2019 9:52 am

Interesting! If you can affect the dwell angle by tinkering with the sensor spacing, then that implies that the "off" time is not fixed by the internal circuitry as I previously thought, but is a function of the width of the imbedded magnets and the pickup coil design. So a Pertronix circuit is just a magnetically controlled high voltage switch? Will definitely investigate this further...

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