Overheating coil?

[mark10337]

A standard 12V ignition has a standard coil that produces a full power spark at 12v. A ballast ignition has a ballast coil that produces a full power spark at a reduced voltage (via the ballast resistor in the live feed to the coil) - consuming less power (amps) and producing less heat. In our case, this is the feed frorm IGN 2, through the tacho, through the ballast to the coil. The coil has a second feed running from the starter relay which supplies a full 12v when cranking. Once the car is running the 2nd feed is cut and the coil is powered by the reduced voltage.

It also limits the power being fed to the coil when the points are in the closed position. - ignition on with the engine not running.

So if your coil is overheating, it might be due to it being a ballast coil that is designed to operate at a lower voltage being used instead at a higher voltage.



There is no extra relay required in this setup. It is however a different relay. 33231E for cars with the ballast resistor, 33243 for those without.

Ideally you want to be measuring your voltage at the coil + during crank and then when running. That will tell you if the voltages are at the correct levels or not for the type of coil you have.

[mikey1]

If this is any help I have owned a late series 2 for 40 years. It does have ballast resistor and a relay. Whilst restoring the car over the last few years it took me quite a while to find the correct original position for the relay.

It is on the right hand side of the bulkhead in the engine bay to the left of the brake fluid reservoir and under the v-shaped throttle linkage. I seem to remember someone finding this caused a problem when fitting a Mangoletsi throttle linkage. I also seem to remember reading that the relay was sometimes under the dashboard but the engine bay was deemed safer as it minimised the cable run length to the starter.

By the time I had found one of my pre-dismantling photographs showing the original relay position I had mounted it under the dashboard where it seems fine!

Incidentally I fitted a new coil "just as a precaution" and within 40 miles of driving it failed. With the old coil refitted everything is fine. You do need a different coil with a ballast resistor system, something which I had not appreciated and maybe this was the problem. My car is an original right hand drive and the holes to mount the relay are, in retrospect, clearly visible on the bulkhead,

Mike Williamson

[mgcjag]

I think iv got the figures about right....on cranking 12v through a 1.5ohm coil will be 8amps....the starter solonoid has a resistance of between 0.36-0.42ohms.(pre engaged starter)...so this draws about 30amps.....so tbe relay will switch about 38amps....please correct me if wrong becaus it does sound high

[Hugo]

That doesn't sound right - I've always reckoned about an amp and a half for the coil but that's more a guesstimate than anything else. In cars with ammeters the needle hardly moves when you turn the ign on. I'll measure a solenoid if I can find one.

[Hugo]

Hugo

The S1 3.8 and 4.2 do not have the relay so something changed the designers minds!

That would co-incide with the change from a push-button to a key start, wouldn't it? I will look into this in more detail - as you say, there must be a reason for the relay. I am always sceptical of people who come up wiht 'improvements' on the original design - my answer is always the same; if it's that simple, why didn't the manufacturers do it?
Having said that, I have a 1960 Chevy Impala in Florida. They are renowned for 'bump steer'. If you start off with zero toe-in, by the time you have pushed the wheels 2" up into the wheel arch (well within the normal range of travel), you have two whole inches of toe out. So on uneven roads they're all over the place.
Luckily there is a company that produces a re-engineered steering tie rod that puts the linkage in the right place vis-a-vis the suspension pivots and completely eradicates the problem. The question is why didn't GM do that in the first place? It's just as easy to build a car with correct steering geometry as it is to get it wrong

[mark10337]

No, push button to ignition key changed much earlier. The change to the ballast resistor happened in 1970, well over half way into Series 2. The relay is still a starter relay but of a different type to cope with the feeding power from the main circuit for cranking and via the ballast resistor for running. See previous post at the top of this page.

A different coil is indeed required.
For cars without the ballast resistor it is part C30120 Lucas HA12 (45208A). 12 volt coil.
Car with the ballast resistor uses C32579. Superseded by C35812 Lucas 16C6 (45227). This is a 6 volt coil.

Ignition switch was also changed at this point, from C.28522 to C.35846

This also coincides with a number of other changes: sump; fuel tank (unvented); heater and choke with illumination.

From http://www.xke-lovers.com/ballast.htm

The purpose of this change, according to service bulletin No. 1 B 11 was to provide maximum spark efficiency at high engine speeds and to facilitate engine starting in very cold conditions.

A new ignition coil is used in ballasted applications, Lucas 16C6. This ignition coil has a primary resistance of 1.43 - 1.58 ohms. It is used with a ballast resistor, part number 3BR, with a resistance of 1.3 - 1.4 ohms. Because the ignition coil and resistor have nearly equal resistance, under normal conditions about one half of the nominally 12 volt battery voltage appears across the ignition coil. During starting, voltage drops, therefore it is necessary to bypass the resistor while the starter is cranking.

To achieve this, the regular starter relay has been replaced by a special relay, part number 33231. This relay has two separate contacts, C1 and C4 that are connected to the armature contact, C2 when power is applied to the relay coil through W1 via ignition switch contact 3. The W2 winding of the relay coil connects to frame ground to complete the circuit. Relay contact C2 is directly connected to the battery side of the key switch circuit, supplying nominal 12 volts at all times.

Contact C4 of the relay connects to the solenoid to provide voltage to operate it when the relay is energized. Contact C1 connects between the ignition coil (+) terminal and the ballast resistor, supplying the nominal 12 volts directly to the ignition coil and effectively bypassing the ballast resistor while the starter is energized. Once the key is moved back to the normal run position, voltage is removed from the relay coil causing contacts C1 and C4 to open which removes voltage from the starter solenoid and the junction of the ignition coil and resistor.

Since the run side of the key switch (terminal 2) is now connected to the tach, ballast resistor, ignition coil and distributor points, the car continues to run although the coil voltage is now approximately 1/2 of what it was during the starting sequence.

Series 2 factory fit...?

[Hugo]

Hug

"Actually I did a write up on using a relay in the ignition switch circuit as some people were concerned about its current carrying abilities and stories of the key getting hot." .

Why would the key be getting hot? We're talking about the starter circuit here, remember. The relay is only deemed (by some) necessary for the starter circuit. It doesn't do anything when the engine is running, the implication being that there is no excessive load on the switch in the 'run' position. Indeed, why would there be?

[mgcjag]

Hugo..your quoting out of context....David was refering to 3.8 and 4.2 not having a relay and keys getting hot...hence his upgrade to add a relay viewtopic.php?f=9&t=6885&p=50290&hilit=Hot+key#p50290

[Hugo]

Sorry - perhaps I didn't explain it very well; the key getting hot has nothing to do with the presence, or absence, of a relay. The relay only operates in 'start' mode. The switch is overheating in 'run' mode. No cars have a relay in the 'run' mode. If the switch can't handle the current when the car is running, that is a completely different problem from the perceived need for a relay in 'start' mode. Well, it's the same problem in that the switch seems to be under-rated, but it is two separate faults with the same switch. The solution to both problems, in my opinion, would be to fit an up-rated switch rather than bugger about with relays. There is nothing unusual about the current draw on an E Type, whether in 'start' or 'run' mode. I plan to fit a push-button start to mine anyway, if only because I am constituionally incapable of hanging onto keys. I always lose them, guaranteed. None of my vehicles needs a key. They all have hidden switches somewhere. I don't even possess a key to my houses either in England or in Florida. Broke a damn window trying to get in last time.

[Hugo]

Incidentally, keys getting hot is usually a symptom of dirty connections inside the switch. Unless you have all sorts of auxilliaries running directly off the ign switch, it shouldn't be a problem at all, but if the contacts do get dirty or pitted, they will get hot, obviously, and that will soften the metal so it looses its 'spring', making the connection even worse and creating even more heat. It is a very aggressive vicious circle. Only to be expected with a 50 year-old switch really.

[Series1 Stu]

Hugo

Using relays can mean that you don't NEED to use switches capable of carrying high currents. Therefore the switches can be smaller and easier to operate. Believe me, it can be very difficult finding a switch with a decent current rating at DC voltages.

More to the point, however, is the fact that siting the relay closer to the power source and the load will reduce the losses that would otherwise occur due to the resistance of long runs of cable. This means that there's more energy available to start the car as well as the reduced risk of overheating cables in the looms.

Like others have said, Jaguar wouldn't fit things that aren't necessary.

Regards

[Hugo]

Hugo

Using relays can mean that you don't NEED to use switches capable of carrying high currents. Therefore the switches can be smaller and easier to operate. Believe me, it can be very difficult finding a switch with a decent current rating at DC voltages.

More to the point, however, is the fact that siting the relay closer to the power source and the load will reduce the losses that would otherwise occur due to the resistance of long runs of cable.

Like others have said, Jaguar wouldn't fit things that aren't necessary.

Regards

1) An ign switch has to be designed to cope with the (entirely predictable) loads it will carry.
2) Yes, indeed, putting the relay closer to the coil would reduce current losses. But they haven't done that - it's only a few inches from the switch.
3) That sounds like it ought to be true - Jaguar wouldn't fit things that are unnecessary. But their reasoning ought to be transparent, and it's not. I'll be satisfied when somebody tells my why it's there.

[Series1 Stu]

. I'll be satisfied when somebody tells my why it's there.

Several of us have been trying

[Hugo]

True, lots of theories, but none that stands up to scrutiny.

[64etype]

The explanation in the Jaguar Service bulletin is perfectly clear. They wanted better cold starts and better high RPM performance from the ignition system. Ballasted systems are very common in older American cars equipped with points type distributers for these very reasons. It requires a relay to make it work correctly. And by the way, not all electronic points systems are designed to work without a ballast resister and relay. Allison/Crane make two versions....the XR700 is for ballasted systems and their 300 series is for non-ballasted systems. I had an XR700 on the shelf and elected to install a ballast resister (with relay) to my '64 S1. I had to use the correct S2 coil. Rather than deleting relays, you should be adding them. My car "currently" has ten of them in two banks ...a couple to completely offload the ignition switch.

Fuse panel and relay bank in original V/R location

[Hugo]

[quote="64etype"]The explanation in the Jaguar Service bulletin is perfectly clear. They wanted better cold starts and better high RPM performance from the ignition system. Ballasted systems are very common in older American cars equipped with points type distributers for this very reason. It requires a relay to make it work correctly. ..."

Yes, I think we all understand WHY the resistor is fitted. Whether it is necessary is another matter. But my point is that it does NOT require a relay to make it work, and with respect I fear you have muddied the waters a bit by saying it does. The relay, if fitted, does NOT operate the ballast resistor; it operates the direct feed to the coil which BYPASSES the resistor when the starter is energised. And that is the bit that has me foxed. Just saying that Jaguar must have had a reason to design it that way may satisfy some, but I remain baffled.
My best guess at the moment, in the absence of any better explanation, is that they fitted the relay to cover up for a weakness in the switch. But that's only a guess.

[64etype]

The reason is that the starter circuit has to be isolated/protected from feed back/drain from the ignition circuit. When I say it's necessary to make it work correctly, this is what I'm referring to. If you look carefully at the S2 wiring diagram, this will be apparent. Read the last paragraph of this link.

http://mgaguru.com/mgtech/ignition/ig207.htm

[Hugo]

Of course!!! Thank you so much! The push-buton starter eliminates this problem of course, as would an ign switch with two separate terminals at the 'start' position (one for the starter, one for the coil), which I believe is a more common way of doing it.
Now I can sleep without this thing bugging me!

[64etype]

I believe the feedback issue remains with a pushbutton as coil voltage would still be at the "output" side after the button was released.

[Hugo]

You are quite correct. My apologies for getting it wrong. In both instances it would be 7 volts feeding back into the starter solenoid of course. I believe, if I have read the posts correctly, that the push button cars didn't have ballast resistors anyway.