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MG Midget and Sprite Technical - Ballast resistor - 1500 cars

Hello,

What is the proper method for bypassing the drive resistor to place a sports coil with higher output on the 1500 cars (45D/Opus #41697 type)? Is it a simple removal of the resistor and connecting the two wires together or do I just disconnect the two?

~ Ron.
Ron Koenig

Proper way? didn't know there was a proper way?, simply wire up a feed wire from the ignition switch to the coil positive,
Robert (Bob) Midget Turbo

Ron -

If you mean the resistor located in the positive feed to the coil, it isn't a discrete "resistor" per se - it's a resistance wire that's part of the harness. There should be two wires, both white with a light green tracer, that attach to the coil positive via a common connector. One of those comes from the resistance wire, and supplies a reduced voltage to the coil once the engine's started. The other white/green wire comes from the starter solenoid, and supplies a full 12V, but only while cranking.

Now there WAS a resistor unit in the 1500, but it was located in the supply wire to the distributor, not the coil.

That said, Bob's nailed the solution.

-:G:-
Gryf Ketcherside

Doesn't the resistance serve to keep the coil from overheating at low rpm situations while allowing more voltage at speed, i.e. a variable resistor circuit?

OK< I just checked the voltage at coil positive, it's 10.3V @ idle, 11.6V @ ~3500 RPM. Different, but I would guess that the difference is due to higher alternator output at increased RPM's, not a variance in resistance.

But won't feeding the full 14.4V to the coil all the time would cause overheating and premature failure of the coil, or is the danger of that overstated? and does the extra voltage make an appreciable difference in performance in a more or less stock engine?

How about a gas-pedal actuated switch that only bypasses the resistance wire when floored? Hmm..

R
Richard 79 1500 with a Type 9 in the garage

This isn't my area of expertise, but you can get high performance coils that are designed to run at 12V all the time. But there's more to the story than that, and although I once studied up on such things, I don't recall the details. Hopefully somebody else can weigh in with more info. There's a good reason to run coils at a reduced voltage. I'm using the ballasted lead with my Mallory coil, and the car runs great.

-:G:-
Gryf Ketcherside

Under the product listing for LUCAS SPORTS COIL
VB PART #8-288...

www.victoriabritish.com:

"For cars fitted with a ballasted ignition system, the ballast resistor or resistive cable should be removed."

Ron Koenig

Ron:

I'm not sure your question has been answered yet. Bob is correct in his advice for bypassing the resistor wire that feeds the coil in key-on position. The externally mounted resistor near the coil is the distributor resistor that Gryf mentions. Vic Brit says "ballast resistor or resistive cable ". Well, which one? If you see what I mean... Back to your question, as the distributor resistor feeds power to the distributor, it seems that "simple removal of the resistor and connecting the two wires together" would be correct, again, IF Vic Brit means the distributor ballast, not the coil resistive cable...

FWIW I replaced my 45D distributor for the Moss P# 143-116 ported vacuum advance model and ballast-matched 1.5 ohm coil Moss P# 143-270, works brilliantly.

I think one should take with a grain of salt what one reads in the catalogs, for example Vic Brit lists a 40,000 volt 3 ohm coil (page 25, Cat. SM57) for all Sprite/midget applications, years 1958-1979. Hope this helps.

R
Richard 79 1500 with a Type 9 in the garage

Actually Richard I am afraid your advice only serves to demonstrate some of the myths tht abound with this subject.

There are 2 types of coil for older vehicles

1 Ballasted
2 non Ballasted.

1 A ballasted coil is used as an aid to STARTING in younger cars and needs a lower running voltage to it. This is achieved in 2 different ways, either through a resistive wire within the loom, or an external resistor mounted on or near the coil. It is either not BOTH both do the same job an reduce the voltage at the coil. To help with starting the ballasted coil is supplied with 12 volts direct from the starter circuit and bypasses the resistor wire or external resistor whilst cranking ONLY.

2 The non ballasted coil is simply a direct feed from the ignition circuit with no resistor in circuit of any kind. The non ballasted sports coil (lucas gold) requires 12 volts from the inition circuit direct and NOT through eith the resistor wire or resistor

Here is a simple eplanation from our website
http://www.mgcars.org.uk/mgcc/midgetreg/Ballastedcoil.shtml
Robert (Bob) Midget Turbo

Bob: My point was that there are 2 resistors in the ignition circuit (North American cars, 1975 and up), and the externally mounted one is not the coil resistor, but rather the distributor resistor, as evidenced by the wire coloring. Ron's second post seemed to indicate some confusion on the subject which I was attempting to help with. After re-reading my post it does appear I was suggesting the bypassing of the distributor resistor, not my intent. Your advice stands on the bypassing of the resistive wire for the sport coil.

R
Richard 79 1500 with a Type 9 in the garage

I never knew there were two resistors in the system. I always thought the one mounted on the pedal box (for distributor) was the only one. I always thought that was the ballast.

Looking at my Workshop Manual AKM 4071, it shows a second resistor on the white w/light-green tracer wire from the ignition to the coil on all of the North American spec and UK spec cars' wiring diagrams from 75-79. I did some additional research and it appears that the ballast resistor terminal is located within the housing (casing) of the LUCAS starter solenoid #33114 which is fitted to the 1500 cars. Please verify my findings, I uploaded a diagram for viewing.

So if this is correct... to install higher output coils, such as the Lucas sport coil, on a ballasted Midget, you simply unplug the white/light-green wires from the solenoid and attach them together to by-pass the resistor?


http://www.classicpartsworld.co.uk/product_details.php?item_id=172



Ron Koenig

>>> I did some additional research and it appears that the ballast resistor terminal is located within the housing (casing) of the LUCAS starter solenoid #33114 which is fitted to the 1500 cars. <<<

I just had a look at that listing, and I think they mean that the solenoid has a TERMINAL for the ballasted lead, and not that the resistor is located in the solenoid itself. If I understand correctly, the resistance is actually provided by the wire itself, but since I've never been that deeply into the wiring loom, I can't say for sure where it is or what it looks like.

To reiterate, the only visible resistor you'll see in the 1500 - at least, in the US-spec 1500 - is the distributor resistor as stated. To supply full-time +12V to a Lucas Sport Coil (for example), you'd need to fit a switched +12V line in place of the ballasted lead.

Cheers,

-:G:-
Gryf Ketcherside

I am not aware of 2 resistors fitted to any cars.

The starter solenoid terminal as shown in the part by Ron is the direct 12 volt feed that is given to the coil ONLY when cranking. Thus when the engine has started and key released this terminal become dead. The only way to wire the 12 volt coil is as Gryf states and requires a wire fitting to the ignition switch and to the coil positive. Therefore bypassing the resistive wire.

If the car has a seperate resistor and does not have a resistive wire (white/green) (this can be easily checked with a voltmeter. with the ignition on remove the wire from the external resistor and measure between it and earth, if you read 12.5 volts then it is direct supply and can be connected directly to the new coil. If it is 8 volts then it is a resistor wire and needs bypassing.
Robert (Bob) Midget Turbo

< to install higher output coils, such as the Lucas sport coil, on a ballasted Midget, you simply unplug the white/light-green wires from the solenoid and attach them together to by-pass the resistor? >

No. There are 2 W/LG wires in the system that terminate at the coil, but only one of them originates at the solenoid. The solenoid-to-coil wire must remain in place as this is the (full voltage) power to the coil with the key in start position.

The other W/LG wire is the resistive wire that powers the coil with the key in the on position. This is the one that needs to be removed (simply disconnect at the coil) and replaced with a wire that is hot with the key in the on position.

R
Richard 79 1500 with a Type 9 in the garage

Back when I was playing around with coils, I found that there was an unused switched +12V lead hanging out of the loom near the coil and doing nothing. I eventually figured out that it was originally the power supply to the distributor resistor. My car's original distributor had been replaced by a PO with a different Lucas unit when I bought it, and the wire was no longer needed. (FYI, the lead has a white elbow-type female blade connector on it.) So I used that to power the coil for a while, but finally changed things around and am back with the ballasted setup.

Just wanted to mention that, since you've got a 1500. If you're running a distributor that's different from the original, you may have that extra lead available.

Cheers,

-:G:-
Gryf Ketcherside

This thread was discussed between 30/06/2009 and 03/07/2009

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