Ignition coils: Ohms and Volts

[JohnA]

I've got two Bosch coils here, both in perfect condition

I've got some Ohm measurements across their terminals
Low voltage terminals:
Coil A:0.9Ohm Coil B:1.6

HT to low voltage
Coil A: 7.21 KOhms CoilB: 14.1KOhms

Does anybody know if this alone can indicate a stronger HT voltage on any of the two? Or is the Ohm ratio irrelevant as their windings can be of different diameter/whatever?

[Dom]

At a "guess" I'd say that the coil with the 0.9 ohm coil would give out a higher energy spark than the one with the 1.6 ohm coil.

Go for the good old formula I=V/R and P=IV

With the first coil, the input power would be 12/0.9= 13 amps approx = 160 watts.

This power has to go somewhere

The HT to low voltage is a different kettle of fish - it sould have twice as many windings on CoilB but it could also have the secondary winding made up of cable with half the resistance lmao

Best thing to do is to build a simple spark gap generator out of the two and see which one throws the longer spark when powered by the same power supply.

Dead easy to do - just wire the primary of the coil to a 12 volt battery, flick the live briefly to generate the spark (dont keep the coil wired permanently to the battery - you only need a momentary contact).

[JohnA]

well, yeah, Ohm's law would apply if we assume that their windings use the exact same kind of wire. I just don't know if that assumption is correct (hence the post! lmao)
Won't be cutting the coils up either (easiest way to check it out)

The funny thing is that the 'performance' item is Coil B. weird, huh?

[Brian_S]

I would say the magnetic properties are more important in coils, if one saturates earlier than the other, then it won't matter how much extra 'power' it consumes, it'll just get a bit hotter.

You don't really have a way of testing the magnetics, so it's touch and go really. You can test the spark gap, like Dom has suggested, that's about the best you can do really.

So long as you don't get misfires with either, I'm sure both will be fine.

[JohnA]

..You don't really have a way of testing the magnetics, so it's touch and go really.

You touch and I go.
With several KiloVolts involved I'm not touching anything matelmao

You can test the spark gap, like Dom has suggested, that's about the best you can do really.

I can do this, even on the car, but it won't be under load (where it matters)

So long as you don't get misfires with either, I'm sure both will be fine.

I don't get misfires, but the 'performance' one felt a bit sluggish, that's why I'm investigating further.

[Brian_S]

You touch and I go.

I've gone!

I can do this, even on the car, but it won't be under load (where it matters)

A longer spark generated by one indicates that it has more energy to dissipate, as it can raise the voltage higher to break over a larger air gap ( higher resistance ) So it is relevant, but not entirely brilliant IMO. It is however, about the best comparison you can do.

I don't get misfires, but the 'performance' one felt a bit sluggish, that's why I'm investigating further.

Uh, oh, lol. I see this one coming to a fore again. In theory ( I express it as a theory ) all performance books I've read on ignition suggest that it's impossible to have a bad spark and no misfires. Thus if something feels sluggish, it must have misfired. Either the mixture is ignited, or it isn't. There's nothing else for the spark to do. It can, however mean that if you only drop one or two sparks every 3-4 seconds, you really won't feel it. You only feel misfiring when you miss multiple times in succsession.

Anyway, what coil is the 'performance' one out of interest?

[JohnA]

Maybe 'performance' is a bit optimistic lmao
It's a Bosch coil, externally identical to the stock one. NOS people use it, so I thought 'wot the heck', I'm a sucker for experimentations anyway...
If it's worth a try I'll put it on my site next week.

The thing is that my car went like a rocket for the last few days - never-ever had it been so quick. So losing some of that edge is not appreciated he he...
Anyway, I'll also double-check the king lead (which had to be adapted) and check for grease or other contaminants (they use grease to push the leads through the boots the monkeys, not soapy water as they should...)

[Gary]

oh the joy of turbos - I found my vectra had a completely open circuit plug lead the other day - not even intermittent contact - which explained the very occasional misfire I was getting.. on a turbo lump it would've run like a bag of poo...

mind you, at least it would've been fixed quickly, and not slowly poisoned the darn o2 sensor, which I've also replaced now and miraculously gained 10mpg, doh.

[JohnA]

Even if there is no contact, the engine may run (the spark can jump a bit like skippy)
Of course on-boost it will be cheaty-shoity-bang-bang

[Gary]

John, do you have a catering size bag of half sucked eggs to mail out to peoples Grandmas lmao

[DOUGAL]

they use grease to push the leads through the boots the monkeys, not soapy water as they should...)

Silicon grease, with high breakdown voltage, or general purpose

Soap or more specifically washing up liquid would be very bad due to corrosive nature

Check internal resistance of each plug, if you lose a spark try and find where it is escaping, side of porceline or valve cover best bets apart from already mentioned "KING LEAD". Mine run in silicon coated glass braid under valve cover to prevent chaffing and add another 14Kv insulation

DOUGAL

[JohnA]

mild soapy water is far better than any grease, Dougal, at least in high-voltage situations. We're talking silicon to rubber friction here, not metals.

Grease carbonises quickly and you get sparks dancing the samba.

My king lead is 2 inches long, by the way. Looks quite funny, but it's very efficient.

[Gary]

My king lead is 2 inches long, by the way. Looks quite funny, but it's very efficient.

nnggmm....mmmm.. mmpphhh.

[Brian_S]

nnggmm....mmmm.. mmpphhh.

lmao

[JohnA]

It's not how long it is, it's what you do with it

[JohnA]

a quick search revealed that the stock XE/LET coil, Bosch 0 221 600 060, has the following:

Primary resistance: 0.20-0.34 Ohms
Secondary resistance: 7200-8200 Ohms

Mine had primary resistance 0.9 Ohms, almost 3 times as much.
I wonder what that means.
Secondary resistance is spot on.

Did anybody else ever had the chance to measure their stock coil?

[Gary]

have you got a decent multimeter John ? - quite often they're not so good at accurately measuring low resistances, where the effect of leads/surface resistance etc will have a much bigger effect on the accuracy.

[JohnA]

It measures even smaller fractions of an Ohm quite successfully. Most digital multimeters can do it nowadays, it's no big deal.

[Coolmist]

hi

yes, that was my reading for my previous coil
the same coil manages to fire 22psi and 140bhp of n20 on my car which is far more than the std coil can cope with

i still think your spark is getting out somewhere under load...

regards, brian

[Kieran]

a quick search revealed that the stock XE/LET coil, Bosch 0 221 600 060, has the following:

Primary resistance: 0.20-0.34 Ohms
Secondary resistance: 7200-8200 Ohms

Did the XE ever use a different coil to this one, as mine has a different part number on it (1 220 522 00 14) and it's having trouble in the spark department somewhere as seen here: Faulty 20XE ignition module??

PS: sorry for pimping threads lmao