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Lumenition power unit temperature query


Waynebaby
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Hi,

 

Can anybody tell me whether it is normal for a Lumention optronic power unit to run hot to the touch? I've been trying to track down the cause of a intermittent miss-fire/conking out at the roadside and noticed that the coil and Lumenition power unit were both getting very hot. It turned out that the 1.5 ohm ballast coil was running without a ballast resistor and so I've changed to a Lumention MeGa spark coil and resistor set up as per Lumenition's recommendation so the combined resistance is now ~3 ohms (I also changed the rotor arm and distributor cap for good measure) The coil is now running cool and can be touched without risking burns! By my reckoning the Lumenition power unit should now be switching half the current previously being demanded of it and so it should be running cooler, but it isn't and the miss-fire/conking out symptoms are still there. I'm now concerned that the power unit has been damaged in some way by it's over exertions. Views anyone?

 

Waynebaby 

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Hi Pete,

 

Thanks for the prompt response. I've concluded that there's nothing for it but to buy another power unit and see if that resolves the problem. If I get a moment I might sit down and calculate how many sets of points I could have bought for the cost of trying to chase down a (putative) fault with a piece of "fit and forget" after-market kit. Ho-hum.

 

Wayne

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With the ballast resistor, the coil is now getting ?9V as it should.

Your Lumenition should be getting the full 12V, and switching that, so some heat might be expected, from a power transistor.  But they loose efficiency if they get hotter than about 25C, so if it's hot in your hand it probably has over cooked.

 

Are you still getting the same fault?

John

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Hi Wayne,

 Can you open the module is it it potted with compound?

 

I guess there would be a power transistor for switching and power resistor to measure the coil current.

Running approximately twice the rated current thru the unit could easy cause the transistor and resistor to dissipate approximately 4 times their normal power. If "the" resistor has been overloaded it will probably be an even higher resistance, and even though its connected correctly now, will be getting much hotter than normal.

 

If you can see inside; it should be easy to see if things have got hot.

 

Good luck.

 

Cheers,

Iain.

 

Edit---- change 4 times their to a correct figure of over two times. (little over 2 to allow for greater volt drop on transistor) OK. 2 times... still double... End edit 23:55Hrs

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Hang on - the ballast resistor is for the coil.

It does not affect the volts to the ignition control unit, or the power transistor, which is designed to run at battery volts, and would have been switching the same volts without the ballast.

So if it's still getting hot, and hot in your hand is too hot for a power transistor, then there is some other fault with the unit.

Do you still have the same fault? It's probably a duff unit.

 

John

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Hi John,

 The system was designed to switch a 3 Ohm load (12 v coil). The coil is the load.

If you run a 1.5 Ohm coil (6 v coil) the transistor and the internal resistor (I'm pretty sure one would be fitted), will be switching a much higher current and the dissipation will be very high.

The 12 volt feed to the unit just powers the electronics.

 

It's late, but i'm pretty sure I am correct?

 

Cheers,

Iain.

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Thanks, Iain!

 

Trying to avoid having to draw my own circuit diagram, here is one off the Net, of "Transistor Assisted Contacts" ignition.

Think, when I speak of horses Lumenition that there is the optical breaker where the points are.

And correct my thinking:

The ballast resistor is between the CB points and earth, while the coil and switching transistor 'sees' the full 12V.

This reduces the stress and wear on the points.

 

So would the ballast be in the circuit to the coil AND points if, originally, the car had a ballasted ignition and a Low resistance, 6V coil?

In that case, should our OP make very sure that, having changed from a low resistance coil and ballast to non-ballast and high resistance,12V coil, he hasn't left so additional ballasting resistance in the system?  That would reduce the volts to the coil and make for poor running.

 

Trying to get my head around this!

John

 

 

post-139-0-69247500-1444287611_thumb.jpg

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Iain/John,

 

The power module is a sealed unit so I can't open it up to see what, if anything, has been going on in there. I have ordered a new unit from Merlin motor sports and will see if the intermittent fault disappears when I've fitted that. At John's suggestion I'll do a double check to make sure there isn't a ballast resistor wire still lurking in the loom - I was pretty sure it had been removed by a previous owner of my Mk3 GT6 but I now have my doubts.

 

Wayne  

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if there is a built in wire in the harness, its  dull white with a pink trace, often runs from a pigtail off the ign switch or connected direct to it

there will also be a white yellow from the solenoid starter side to the coil ,this is the 12v bypass when cranking.

 

the wire has a 1.5 ohm resistance but will only show the dropped voltage when under load from the coil otherwise it shows as open  battery voltage .

 

to make add more strife some 1.5 ohm coils are marked 12v  not 6-8v  

 

best to stick with 1.5ohm for ballasted     3 ohm for 12v then current and HT are all as specified , not too high and not too low.

 

i think its best to run a new 12v ign feed add a 3 ohm coil and feed the lecy unit with the same 12v , keeps it reliable and simple

 

Ive just rewired a failing car which had a ballasted feed with a 3ohm coil , ballasted leccy feed and R suffix spark plugs  so hardly any spark at all.

 

12v all round and  Va va Room.!!

 

Pete

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Thanks Pete,

 

The wrinkle about testing for an in-line ballast only when under load from the coil had passed me by. I tested the switched supply side of the coil to earth and got battery volts, so mistakenly assumed I didn't have a ballast resistor in the circuit. I've just repeated the test but with the negative side of the coil earthed and hey presto - 6-7 volts! It seems there was a ballast in the circuit after all so I'll be running my nice new Lumenition MS4 coil without the accompanying ceramic resistor in series (because 3-4 volts in the primary windings might just take the edge off performance)

 

This discovery of course blows out of the water my original theory that running a 1.5 ohm coil without a ballast has done for my electronic ignition and was the cause of a scorchingly hot coil and intermittent engine dying. I'm going to push ahead with replacing the lumenition power unit since it's now in the post and see if that helps things.

 

Wayne 

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Hi John and Wayne,

 If you connected the unit across the coil (Now shown to be a 6V coil supplied from a ballast wire/resistor) the module would be getting near 12 volts when the "points" were open and around 7v when the points were closed. The module electronics would not be happy. I guess your car was not driving nice and was worse at higher revs? EDIT: This is only valid if you connected the module power wire to the +ve coil terminal

 

I assume the module has dwell control so that the coil would only be charged prior to the "points" opening. I know you have no points, but you know what I mean.

 

Feed an ignition wire to the plus of the coil. Connect the power supply in to the same terminal and:

Module gets its 12v for its electronics. The coil gets a nice 12v and the module will switch the coil on and off as intended. 

 

Cheers,

Iain.

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Thanks, Iain!

 

Trying to avoid having to draw my own circuit diagram, here is one off the Net, of "Transistor Assisted Contacts" ignition.

Think, when I speak of horses Lumenition that there is the optical breaker where the points are.

And correct my thinking:

The ballast resistor is between the CB points and earth, while the coil and switching transistor 'sees' the full 12V.

This reduces the stress and wear on the points.

 

So would the ballast be in the circuit to the coil AND points if, originally, the car had a ballasted ignition and a Low resistance, 6V coil?

In that case, should our OP make very sure that, having changed from a low resistance coil and ballast to non-ballast and high resistance,12V coil, he hasn't left so additional ballasting resistance in the system?  That would reduce the volts to the coil and make for poor running.

 

Trying to get my head around this!

John

 

John,

 The circuit you have shown will confuse you. It shows the points triggered from +12V. All negative earth cars are triggered from ground/earth/ zero. This circuit would need a PNP transistor to connect to the grounded points.

Throw the drawing in the bin.  :)

The way the coil is switched is correct.

 

A real circuit would have additional components across the transistor  and such to stop it blowing up.

 

You could make a points triggered transistorized module quite easy yourself. but still left with "the points". If I had to keep the points as the triggering part, I would use  Cap-discharged. CD. Buy a dwell IC so that the coil was charged only prior to discharge.

 

Bigger spark means more power innit. :D

 

Cheers,

Iain.

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Thanks Pete,

 

The wrinkle about testing for an in-line ballast only when under load from the coil had passed me by. I tested the switched supply side of the coil to earth and got battery volts, so mistakenly assumed I didn't have a ballast resistor in the circuit. I've just repeated the test but with the negative side of the coil earthed and hey presto - 6-7 volts! It seems there was a ballast in the circuit after all so I'll be running my nice new Lumenition MS4 coil without the accompanying ceramic resistor in series (because 3-4 volts in the primary windings might just take the edge off performance)

 

This discovery of course blows out of the water my original theory that running a 1.5 ohm coil without a ballast has done for my electronic ignition and was the cause of a scorchingly hot coil and intermittent engine dying. I'm going to push ahead with replacing the lumenition power unit since it's now in the post and see if that helps things.

 

Wayne 

But SHAZAM!!!!!!!!!!!!  I was right!

 

I thang yew!

 

John

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Hi All,

 

The replacement Lumenition power module arrived in less than 24 hours from Merlin Motorsports at Castle Coombe despite me ordering it after their 15:00 next day delivery cut off time. For future reference the module when bought stand- alone has the parts identifier of LUM-PMAZ and when bought with the optical switch has an ID of LUM-PMA50.

 

The good news is that having fitted the new power module the intermittent misfire/engine dying has gone away (at least it didn't show itself during a 50 mile test drive) and so I hope that the fault was simply down to a sickly power module, although now I know that the original coil was correctly matched with a "hidden" ballast resistor (and therefore not producing a primary winding current of 8 amps - higher than the Lumention module specification), I'm not sure what it was that made it sick.  Various web searches under "Lumenition Optronic Problems" suggest that this isn't an uncommon fault which may yet return so although I'm no longer pensively scanning the road ahead for emergency pulling in places, I'm not uncrossing my fingers yet!

 

The bad news is that the test drive has convinced me that the tell-tale sound of a knocking off-side UJ isn't my imagination! There's always something isn't there?

 

Wayne 

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