Ignition coil ballast resistor

[MikeNash]

Greetings Comrades!
Much trouble in the rain yesterday on the A331 when the coil died. Its decided that when we do more than 20 miles it overheats and retires. Cool off for 5 minutes and off we go again. (But 5 minutes was a long time in the rush hour stuck the Dennis roundabout in Guildford last night.)
Got the only coil in Halfords Andover today, a Lucas Type DLB198 (for £6.36) which I find has a primary winding resistance of only 0.6/1ohm. So assume its meant to be used with a ballast resistor. But none for sale around here and it'll have to be ordered.
At the moment I'm using a 40watt headlight bulb in series with the coil to bring the total resistance up to about 4ohms and with which it starts and seems to run OK. (Tried a 21watt bulb and no start.)
So please could you advise please on the appropriate resistance I should go for. Thanks in advance, MikeN.

[Matt]

Do you know if the coil is full of oil or if it has an air gap? if its the latter mount it it facing upwards or it might burn out fairly quickly....

[Cam]

Is that the 'on-load' resistance? When dealing with low values, the heating effect can alter things! Best to measure voltage & current and calculate the on-load resistance.

A lot of cars (Mini for one) had a pink wire which itself acted as a ballast resistor to feed the 9 volt coil.

Best bet is to replace it with the proper 12 volt coil available from virtually all Minor specialists. Usually next day delivery too.

See ESM, Bull Motif, Birmingham MMC, Bath, Charles Ware, etc, etc.

[MikeNash]

Thanks for quick replies.

Re Matt - who can tell if its oil filled and whether there's an air gap? So the answer is I neither know nor how to find out! Any ideas? So far am just trusting to the Prince of Darkness to be making a decent product!
[Just realised that if I shake it can hear the oil shoshing around! So there must be an air gap - but I'd expect one for expansion.]

Re Mr Cam - the resistance was measured straight across the contacts off on the bench. (Surely there's only one figure?) But measurement such very low resistances with home equipment is a bit unreliable.

Other coils I've got are around 3ohms except one Lucas of 1.4ohms which states on its side that it should operate with a ballast of 1.3-1.8 ohms.
Looks like I'll have to order a replacement from Bull Motif to be safe. But the meantime I'm guessing I should be OK. Am I wrong? Regards, MikeN.

[Matt]

Mike, coils that are designed to be mounted sideways are full of oil, so that oil covers all the windings inside when mounted sideways. Apparently there has been an issue getting them lately, but I can't remember what source i got that from (either on here or a spridget forum)

[MikeNash]

Ah! just realised that Mr Cam was refering to the resistance when hot. Good point! Will get it tomorrow and review the bulb wattage!
Just remembered that on the box it says Aston Martin and Jaguar as applications (as well as boring Fiat and Citroen). Suppose they all have ballasts bypassed on start up.
And perhaps I should mount it upright. Being mean, I don't like to give up! Regards, MikeN.

[bigginger]

but I can't remember what source i got that from (either on here or a spridget forum)

Was it not JLH on here? It was definitely this forum

[Matt]

If you say so, I can't remember!

[bigginger]

[Willie]

NO, the theory about coils burning out if mounted sideways because there
is not enough oil in them to cool all of the windings in that position came from
our excellent Technical Advisor,..... Rob Thomasson. My spare coil,which is
oil-filled, reads 3ohms primary,and 5.54K ohms secondary. There is certainly
air space in there as I can hear the oil when I shake the coil. Mounting the
coil upright and away from the engine has surely got to improve its chances
of a long and trouble free life? It is easy to unpick the wrapping on the loom
where the coil leads are and re-site the coil to an upright position. Indeed, I
assume that most people with an Alternator fitted have moved the coil, so it
would be interesting to hear if they have had problems with it in the upright
position?

[lowedb]

With a winding resistance as low as that, it might be they are not meant for points ignition at all. With electronic ignition you can control the 'on' time of the coil and prevent it burning out but with points, if the engine stops with the points closed, the coil (or coil with ballast) has to have enough resistance to stop it ooverheating.

[Willie]

Unless the engine has dropped a valve or holed a piston I doubt that an 'A'
series engine will EVER stop with the points open due to compression values
deciding its stop position. This means that If you switch on the ignition without the engine running then the coil will DEFINITELY burn out reasonably
quickly so if you are doing any sort of electrical testing which requires ignition
ON but engine not running you should disconnect either of the low tension leads on the coil or remove the black/white lead on the side of the dizzy.

[MikeNash]

Can confirm Willies point. Whenever I start or stop the engine my ballast light is on showing the points are closed and the coil passing current. Nice to know my troubles have added to the sunm of human knowledge! Also noticed that at night little spots of light appear thro' the radiator! I'm beginning to like this.
Seen on Aldron site that these low resistance coils are associated with wizzo modern electronic ignition systems. So its onto the garage shelf with it till the day I do something about that sort of thing.
Hey ho, must my order into Bull Motif and get an ordinary coil. Thanks for all your help, MikeN.

[MikeNash]

Alas alack folks!
Problem remains and I'd your further advice. Do about 18 miles and we get "cut, drive, cut, drive" with the car getting slower all the time. Now I've experienced it a few times I keep the speed down < 50mph and then it can be persuaded to level out at about 20mph, cool off, (I presume) and nursed up to about 40mph and kept going.
No trouble with the fuel pump so its all ignition. The symptoms don't suggest to me plugs, suppressors or the leads from the distributor - they don't cut out all together or in groups. Rather I think its the singularly vulnerable items like the coil and capacitor. But I've replaced both those with new items. So I'm left with the dizzy cap, the lead between the coil and dizzy, the rotor arm and the points, none of which show visible signs of trouble. So when it cools down, in we go. If its not te likely things its got to be the unlikely ones. But I find its style of failure baffling.
Any advice? Anything I've missed? Regards, MikeN.

[Nigel2]

Change the rotor arm, look at my post. One friend that had a CI one fail had exactly these symptons, this was on a Healy 3000 (he is a lot richer than me).

[MikeNash]

Thanks for the pointer, Nigel. Mine's got no CI mark but it'll the first thing I change. The brand new one is ex-Bull Motif without a maker's mark. Hoping for the best. MikeN.

[MikeNash]

Got it sorted!
Changing every item in the ignition circuit made no improvement! What to do? Drove around with bulb across coil and it had electrical power at times including stoppages.
Only the fuel system left. But the SU petrol pump is only 8 months old and only done 10k miles and still bright and shiney. Made it pump into a jar (with a bulb across to be sure of power) and lo! and behold! it stops after a pint but restarts with a slight tap!
Never opened it up before but find that the points are knackered. The reason is that the two screws that hold the contact housing to the body are not fully done up so the points gap can be anything it likes. Corr!
Another example for Mr Cam and his rage against modern carelessness in manufacture.
Is SU another name that's been sold on to goodness knows who, and therefore a misleading guide to quality and reliability?
Yours in exasperation, MikeN.

[Cam]

Glad you got it sorted in the end Mike. Annoying as it was finding it!

[Nigel2]

Glad it's all sorted out. As you say more rubbish. The originals go for years & years, why not the replacements!

[bmcecosse]

Mike - sure it's not a vacuum in the fuel tank causing your problems? Typically shows after a few miles driving. And the car getting slower would be right too. Next time it happens - nip out and remove the filler cap - if there is an inrush of air with frantic pump ticking - there's the problem. But I like your thinking with the low resistance coil and the flashing light under the bonnet must be interesting - make the car look like Kit at night !