[xj] ballast resistors was coil

XJ
1

First of all, i’ll say I totally agree with you, the ballast resistor is totally unnneeded on a car with electronic ignition. This is especially obvious if you realize that the system on the XJ6 is simply a dressed up Chevy HEI system. Anyone who has worked with these has read the warnings to NOT use a ballast resistor with the system.

My question though is, why was a ballast resistor used on the series 3 XJ6s that had electronic ignition. If one purchases a replacement Jaguar “Ducellier” coil these days, it includes a new ballast resistor. Just doesn’t make much sense to me. For what it’s worth I removed my ballast resistor a few months ago and noticed no difference either way.

Collin Bissett
1986 XJ6 VDP===================================================
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2

Collin, I suppose the ballast would be needed depending on how the amp works.
If the input from the pickup is simply magnetic and transient, then there will
never be a situation when the ignition is on, the engine isn’t turning, and
the amp is on. In a points system, the points can be closed, driving current
through the coil continuously if the engine is stopped, but ign is on – the
ballast prevents overheating the coil. If the amp in our systems uses
something like a Hall-Effect pickup, then the input to the amp may be able to
turn it on when the distr is stopped in just the right position. But, I
haven’t looked at the circuit closely enough to say how our stuff works.–
Alex
79xj6L SII (BRG + wires)
86xj6 SIII (Black)
61 Sprite MkII (Red)
Menlo Park, Calif.

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3

Hello Colin,

It is entirely possible that Ducellier includes a ballast
resistor with each replacement coil as a matter of policy.
They have no way of knowing if the coil is going to be used
with contact points or electronic module and thus throw it
in for good measure. Jaguar is only one of their many
customers.

Many “failed coils” are in fact misdiagnosed and the
associated ballast resistor (if equipped) actually has failed.
So the supplier can save himself a lot of grief (and make a
lot of extra money) by enticing the mechanic to change both
as a set. If after both coil and resistor are changed and the
car now runs, who will be the wiser as to what the true
problem really was?

Not unlike changing contact points and condenser as a set
at the same time, for pretty much the same reasons…

Dick Vandermeyden
San Carlos, California===================================================
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4

I think you’re on to something there, as the pickup in the distributor is magnetic, and the ignition system is on even with the engine off, so roating the little cog on the distributor shaft by hand will cause a spark plug to fire. Ask me how I know! Anyway I thought the point of the ballast resisitor was because the coil is 6 volts and the ballast resistor is used to step this down. The ballast is bypassed on startup by the second power feed to the positive side of the coil.

Collin===================================================
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5

Just for fun, I went out to our SIII with an oscilloscope & multimeter.
Here’s what we have:

“Lucas Super” coil with about 1.5 Ohms primary resistance. It says on it, in
a couple of languages: “Use only with 1.3-1.8 Ohm ballast resistor”.

A 1-Ohm ballast screwed to one terminal.

The amp wires go to the remaining coil terminal and the remaining ballast
terminal (the wht/blk amp wire and the tach and ECU wires, tan/grn & tan/blk,
go to one coil term, the wht amp wire and yellow ignition wire to the other).

With my scope, I could see that the ballast drops about 1.5V max. Since it’s
a 1 Ohm resistor, this means it’s passing 1.5A max. The average current on
the meter is about 1.2 into the amp. The waveform across amp shows a max of
1.5V, so it too looks like about 1 Ohm when on (charging the coil), which is
analogous to point closure.

So, I agree that we likely need no ballast on EI XJs.–
Alex
79xj6L SII (BRG + wires)
86xj6 SIII (Black)
61 Sprite MkII (Red)
Menlo Park, Calif.

Vand116@aol.com wrote:

Hello Colin,

It is entirely possible that Ducellier includes a ballast
resistor with each replacement coil as a matter of policy.
They have no way of knowing if the coil is going to be used
with contact points or electronic module and thus throw it
in for good measure. Jaguar is only one of their many
customers.

Many “failed coils” are in fact misdiagnosed and the
associated ballast resistor (if equipped) actually has failed.
So the supplier can save himself a lot of grief (and make a
lot of extra money) by enticing the mechanic to change both
as a set. If after both coil and resistor are changed and the
car now runs, who will be the wiser as to what the true
problem really was?

Not unlike changing contact points and condenser as a set
at the same time, for pretty much the same reasons…

Dick Vandermeyden
San Carlos, California

===================================================
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6

Collin, I think a problem with understanding coils & ballasts is that coils
aren’t really voltage devices – no such thing as a 6V coil. They are,
however, current devices, because current is what stores the magnetic field
they’re using to make sparks. So, the maximum current the primary winding can
safely take is what we’re really concerned with, when the ignition is on and
points are closed (or amp is on). Using a coil that’s safe when connected to
a 6V system on a 12V system means its primary current could double, causing
burnout, so an external resistor (ballast) is added. You’re right that the
resistor is needed when moving a coil to a higher-voltage system, but its
function is to limit current. This may sound pedantic, but it’s important
that we distinguish between voltage dropping and current limiting.–
Alex
79xj6L SII (BRG + wires)
86xj6 SIII (Black)
61 Sprite MkII (Red)
Menlo Park, Calif.

Clbgdawg@aol.com wrote:

I think you’re on to something there, as the pickup in the distributor is magnetic, and the ignition system is on even with the engine off, so roating the little cog on the distributor shaft by hand will cause a spark plug to fire. Ask me how I know! Anyway I thought the point of the ballast resisitor was because the coil is 6 volts and the ballast resistor is used to step this down. The ballast is bypassed on startup by the second power feed to the positive side of the coil.

Collin

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7

In reply to a message from Cannara sent Mon 18 Nov 2002:

While the discussion amongst the electrical gurus on the list
continues, I’ll bet there’s a bunch of us electrically challenged
SIII owners out here wondering just what the heck to do with the
ballast resistors on our coils :slight_smile:

Leave 'em alone, pull 'em off, what?

Cheers–
Larry Karpman '87 SIII VDP (US), '79 SIII XJ6 (US)
–Posted using Jag-lovers JagFORUM [forums.jag-lovers.org]–

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8

Clbgdawg@aol.com wrote:

My question though is, why was a ballast resistor used on the series
3 J6s that had electronic ignition. If one purchases a replacement > Jaguar “Ducellier” coil these days, it includes a new ballast > resistor. Just doesn’t make much sense to me. For what it’s worth I > removed my ballast resistor a few months ago and noticed no > difference either way.

The “constant energy” system used on later models is conceptually
different from earlier types, and indeed from old points operated
systems. There is no ground contact for the coil until the amplifier
gets signals from the distributor rotating. And is operating with a
variable, amplifier produced dwell angle.

This is, however, subtly independant of the coil question. But any
system shorts the coil to the ground when the ground path is opened. As
the original Ducellier coil has a low ohmic resitance, this will allow
high current flow which may lead to coil overheat, or damage to the
amplifier. So an external resistor is added, and probably should be
added to this coil type regardless of system?

While the Ducellier has a nominal resistance of 0,8 to 1,0 ohms, the
commonly available “standard” replacement/upgrade has 1,2 - 1,4 ohms.
Adding a resistor to the latter set-up obviously will interfere with
the designed output of the ignition system.

Originally, the coil/resistor was a matched set-up to prevent coil
burn-out in prolonged ground situation associated with the contact
breaker system. Refined by a resistor bypass during cranking. Not
regarded as required in the “constant energy” set-up as no ground is
present in a non-run situation.

All that said, a coil constantly grounded without an external resistor
is likely to burn…

Frank
xj6 85 Sov Europe )UK/NZ)===================================================
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9

Larry Karpman wrote:

In reply to a message from Cannara sent Mon 18 Nov 2002:

While the discussion amongst the electrical gurus on the list
continues, I’ll bet there’s a bunch of us electrically challenged
SIII owners out here wondering just what the heck to do with the
ballast resistors on our coils :slight_smile:

Leave 'em alone, pull 'em off, what?

Fact: Manual show the “constant energy” system on the SIII 4,2 without a
resistor.

Fact: Manual mentions only the Ducellier coil in re resistor, but not
with the identically dataed Lucas 32C5

Fact: The “Opus” system used on SII needs coil external resistors to
protect the power transistors in the amplifier, as the ground path is
open with engine stationary.

Fact: Current flow generates heat in coil and amplifier. Beyond a
certain limit either component will be destroyed. Resistors reduces
current, but limits coil output.

Fact: Lots of us use aftermarket coils with higher resistance than the
Ducellier.

Surmise: A high resistance coil (1,2 - 1,5 ohms) is not meant to be run
with an external resistance in the “constant energy” system.

Suggestion: If you are in this situation, remove the external resistor.
If you are running the original Ducellier, you are on your own… :slight_smile:

Frank
xj6 85 Sov Europe (UK/NZ)>

Cheers

Larry Karpman '87 SIII VDP (US), '79 SIII XJ6 (US)
–Posted using Jag-lovers JagFORUM [forums.jag-lovers.org]–

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10

Cannara wrote:

Just for fun, I went out to our SIII with an oscilloscope & multimeter.
Here’s what we have:

“Lucas Super” coil with about 1.5 Ohms primary resistance. It says on it, in
a couple of languages: “Use only with 1.3-1.8 Ohm ballast resistor”.

A 1-Ohm ballast screwed to one terminal.

The amp wires go to the remaining coil terminal and the remaining ballast
terminal (the wht/blk amp wire and the tach and ECU wires, tan/grn & tan/blk,
go to one coil term, the wht amp wire and yellow ignition wire to the other).

> With my scope, I could see that the ballast drops about 1.5V max. Since it's > a 1 Ohm resistor, this means it's passing 1.5A max. The average current on > the meter is about 1.2 into the amp. The waveform across amp shows a max of > 1.5V, so it too looks like about 1 Ohm when on (charging the coil), which is > analogous to point closure. > > So, I agree that we likely need no ballast on EI XJs.

And I do so agree with you, Alex!

However, just to be pedantic, too! You measured the system dynamically,
where most of the systems resistance comes from the coil’s impedance.
While irrelevant for the “constant energy” system, but relevant for
“Opus” and straight points systems: On a stationary engine current is
primarily limited by the coil-and-resistor ohmic resistance. With your
data to some 5 amps. Increasing to 8 amps if you remove the resistor.

As some of us may run aftermarket ignition systems with unknown
characteristics some care must be taken, even if, as I agree, this is
immaterial to the 4,2 SIII’s normal system.

Incidentally, removing your external resistor will naturally increase
current flow, and thus ign “power”. Probably to some 2+ amps dynamic,
which can easily be checked with an amp meter. And still is well within
the capacity of the coil and amplifier.

Which is a test anybody can do, static or dynamic if in doubt?

Frank
xj6 85 Sov Europe (UK/NZ) - without external resistor :-)===================================================
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11

Frank, tripling the pedantry here, the reason for using the scope was to see
the “on” resistance of the amp, so I could estimate the current through it,
should the system actually be capable of having it on when the engine isn’t
turning. Yes, the DC (static) current will be about 4-6 Amps (12V divided by
2 to 3 Ohms) if that situation can occur. But, I don’t believe our EI systems
will turn the amp on when the engine is stationary.–
Alex
79xj6L SII (BRG + wires)
86xj6 SIII (Black)
61 Sprite MkII (Red)
Menlo Park, Calif.

Frank Andersen wrote:

[clip]

And I do so agree with you, Alex!

However, just to be pedantic, too! You measured the system dynamically,
where most of the systems resistance comes from the coil’s impedance.
While irrelevant for the “constant energy” system, but relevant for
“Opus” and straight points systems: On a stationary engine current is
primarily limited by the coil-and-resistor ohmic resistance. With your
data to some 5 amps. Increasing to 8 amps if you remove the resistor.

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12

Cannara wrote:

Frank, tripling the pedantry here, the reason for using the scope was to see
the “on” resistance of the amp, so I could estimate the current through it,
should the system actually be capable of having it on when the engine isn’t
turning. Yes, the DC (static) current will be about 4-6 Amps (12V divided by
2 to 3 Ohms) if that situation can occur. But, I don’t believe our EI systems
will turn the amp on when the engine is stationary.

The “constant energy” system definitely should not, Alex. And I believe
it to be foolproof in that respect. My pedantic note was more directed
at older or aftermarket systems that hasn’t got that feature. (The GM
has it, supposedly).

However, I wish someone out there has the correct current specification
for the c-e system. Current drain/power should be constant throughout
the rev range as the name implies, and can be easily verified with an
ammeter in series with the coil/resistor. Maybe putting the Ducellier
question to rest…

Frank
xj6 85 Sov Europe (UK/NZ)===================================================
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13

In reply to a message from Cannara sent Mon 18 Nov 2002:

Some of the discussion to date is way beyond me, but surely if you
are using a coil that is supposed to have an external ballast
resistor then removing the resistor is going to cause the coil to
overheat and ultimately fail. Diagnosis of a blown ballast resistor
is simple - if the engine fires with the key on ‘‘start’’ but stops
immediately you release the key, odds on its the resistor. You can
get home simply by joining the wires feeding into and out of the
resistor but remember to replace resistor or replace the coil which
is sure to kark it if you don’t.

Peter–
The original message included these comments:

It is entirely possible that Ducellier includes a ballast
resistor with each replacement coil as a matter of policy.
They have no way of knowing if the coil is going to be used
with contact points or electronic module and thus throw it
in for good measure. Jaguar is only one of their many
customers.
Many ‘‘failed coils’’ are in fact misdiagnosed and the
associated ballast resistor (if equipped) actually has failed.
So the supplier can save himself a lot of grief (and make a
lot of extra money) by enticing the mechanic to change both
as a set. If after both coil and resistor are changed and the

–
MARK IX, E type, SI XJ Manual, MARK II
newcastle new south wales, Australia
–Posted using Jag-lovers JagFORUM [forums.jag-lovers.org]–

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14

In reply to a message from Frank Andersen sent Mon 18 Nov 2002:

Bloody hell, after reading all this electrical guff I wish someone
could come up with a definitive and plain English explanation. Now
I’m starting to panic as I have a ‘‘constant energy’’ electronic
system (Series III) in both my Series I XJ and E type. I wonder
which one is going to fail first ? - or maybe I just won’t worry at
all.

Hooroo

Peter–
MARK IX, E type, SI XJ Manual, MARK II
newcastle new south wales, Australia
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15

paithre wrote:

In reply to a message from Cannara sent Mon 18 Nov 2002:

Some of the discussion to date is way beyond me, but surely if you
are using a coil that is supposed to have an external ballast
resistor then removing the resistor is going to cause the coil to
overheat and ultimately fail. Diagnosis of a blown ballast resistor
is simple - if the engine fires with the key on ‘‘start’’ but stops
immediately you release the key, odds on its the resistor. You can
get home simply by joining the wires feeding into and out of the
resistor but remember to replace resistor or replace the coil which
is sure to kark it if you don’t.

Bypassing the resistor is what it is about, Peter…:-).

Remember on the c-e system an eventual resistor is in series with the
coil, and is “active” both in crank and run. On the other systems the
resistor may or may not be critical while engine is running, but may
certainly blow the coil if the engine is stopped with key on…

Frank
xj6 85 Sov Europe (UK/NZ)===================================================
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16

paithre wrote:

In reply to a message from Frank Andersen sent Mon 18 Nov 2002:

Bloody hell, after reading all this electrical guff I wish someone
could come up with a definitive and plain English explanation. Now
I’m starting to panic as I have a ‘‘constant energy’’ electronic
system (Series III) in both my Series I XJ and E type. I wonder
which one is going to fail first ? - or maybe I just won’t worry at
all.

Stop worrying, Peter! If they haven’t failed by now this discussion
isn’t going to blow them…:slight_smile:

And, BTW, do you have the resistor(s)…:-))

Frank
xj6 85 Sov Europe (UK/NZ)===================================================
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17

Peter, I guess you’re thinking of systems in which the coil is connected
directly to +12 when cranking, but via the ballast after releasing the key and
running. I haven’t checked to see if ours work that way, but the point for us
with EFI and no points is that there’s always the resistance of the amp
transistor in series, which is roughly equivalent to a ballast. So, there’s
likely never a need for the ballast in our EFI cars.–
Alex
79xj6L SII (BRG + wires)
86xj6 SIII (Black)
61 Sprite MkII (Red)
Menlo Park, Calif.

paithre wrote:

In reply to a message from Cannara sent Mon 18 Nov 2002:

Some of the discussion to date is way beyond me, but surely if you
are using a coil that is supposed to have an external ballast
resistor then removing the resistor is going to cause the coil to
overheat and ultimately fail. Diagnosis of a blown ballast resistor
is simple - if the engine fires with the key on ‘‘start’’ but stops
immediately you release the key, odds on its the resistor. You can
get home simply by joining the wires feeding into and out of the
resistor but remember to replace resistor or replace the coil which
is sure to kark it if you don’t.

Peter

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18

I’d recommend use a 123 red coil system it rated 2.1 ohms 8,23 secondary resistances I had big issues with a red Bosch coil been worldwide shortage…… she was 1.8 omhs not sure what the secondary resistance was…. It cured my stalling problem……