Author Topic: Chrome ECU and Ballast Resistor  (Read 8695 times)

Offline mojavered

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Chrome ECU and Ballast Resistor
« on: May 03, 2010 - 04:15:05 PM »
When using the chrome MP ECU box, do you need to use the .25 ohm ballast resistor?  Or is it a matter of what coil is used? 

I have a coil that came with the car, it has the tan/brown cap on it and is chrome.  However, the chrome looks sort of like a piece of polished sheet metal wrapped around a black coil.  Is this the Mopar Blaster Coil? 
Jason




Offline MEK-Dangerfield

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Re: Chrome ECU and Ballast Resistor
« Reply #1 on: May 03, 2010 - 04:45:46 PM »
With a Mopar ignition module, you need a ballast resistor with the coil. Typically they are around 1.2 ohms. It sounds like you might have an aftermarket coil, but it should work fine. 

Mike

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Offline Chryco Psycho

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Re: Chrome ECU and Ballast Resistor
« Reply #2 on: May 03, 2010 - 11:00:53 PM »
the Ballast only has an effect on the coil not the ECU so the coil & ballast need to be matched

Challenger - You`ll wish You Hadn`t

Offline mojavered

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Re: Chrome ECU and Ballast Resistor
« Reply #3 on: May 04, 2010 - 12:25:32 PM »
Is there a way to tell if the coil is good/bad?  If I need to get a new coil, are the Accel super stocks any good?  Will the instructions with it let me know what coil I need?
Jason

Offline shadango

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Re: Chrome ECU and Ballast Resistor
« Reply #4 on: May 04, 2010 - 01:23:40 PM »
I had a round Chrome Accel "super stock" coil and it died (leaked) very shortly after being installed.......got another one under warranty and i started having issues that I am not sure were related to a bad ballast or that the coil was going bad again...its my spare since I know it will at least run the car til it heats up....right now I am using an autozone unit.  So far, so good (knock wood) but would love to get something "better".

I have firecore wires and the crhome box and know that a hotter coild would be cool.....no pun intended.  LOL

Offline UKcuda

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Re: Chrome ECU and Ballast Resistor
« Reply #5 on: May 04, 2010 - 04:47:42 PM »
What will work better and more reliably on a Mopar ECU system is more about the impedence of the coil versus the ballast, not so much about the make and model of the coil.

The coil needs to be about one and a half times the resistance of the ballast and added together they need to be no lower than about 2.5 ohms.

So if your ballast is about 1.2 ohms (which is typical) you need a coil round about the 1.8 ohms mark, giving you 3 ohms overall.

A bit lower value on the ballast and bit higher on the coil will give you a better spark but push that too far (the extreme case being a 3 ohm coil and no ballast) and you will have hard starting.

'72 'cuda

Offline mojavered

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Re: Chrome ECU and Ballast Resistor
« Reply #6 on: May 04, 2010 - 05:15:31 PM »
Thanks for the explanation.  I needed a new ballast as mine was broke.  The coil measured only .5 ohms, I think a little low.  I just bought an MSD vibration blaster and a .7 ohm ballast resistor.   I think that this should work well.
Jason

Offline UKcuda

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Re: Chrome ECU and Ballast Resistor
« Reply #7 on: May 04, 2010 - 06:09:36 PM »
Thanks for the explanation.  I needed a new ballast as mine was broke.  The coil measured only .5 ohms, I think a little low.  I just bought an MSD vibration blaster and a .7 ohm ballast resistor.   I think that this should work well.

Yes, there is nothing wrong with a 0.5 ohm coil as it stands but it is a bit of a no no on a Mopar ECU system.

You now have a 0.7 ohm ballast but you don't say what the impedence of your MSD coil is. 

If your coil is say 1.4 ohms then the ratio stacks up good but you are still running only 2.1 ohms overall which I would say is getting really near the borderline for the ampage the ECU unit can take in ordinary use (not like race use where it is short periods only).

If that's the set-up then I would think it will probably be OK but I would say you are near the borderline so I would not go on any really long drives out in the country.

'72 'cuda

Offline MEK-Dangerfield

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Re: Chrome ECU and Ballast Resistor
« Reply #8 on: May 04, 2010 - 06:50:26 PM »
Just throwing this out there..But how are you mounting the coil? Some only want to be mounted vertically.

Mike

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Offline Aussie Challenger

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Re: Chrome ECU and Ballast Resistor
« Reply #9 on: May 05, 2010 - 06:26:31 AM »
The reason to by-pass the ballast resistor during cranking is there is usually only about 9 volts available at the coil, most coils that use a ballast resistor are rated at 8 - 9 volts therefore the coil is getting full voltage during cranking.   :2thumbs:
Dave

Offline mojavered

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Re: Chrome ECU and Ballast Resistor
« Reply #10 on: May 05, 2010 - 04:42:39 PM »
Yes, there is nothing wrong with a 0.5 ohm coil as it stands but it is a bit of a no no on a Mopar ECU system.

You now have a 0.7 ohm ballast but you don't say what the impedence of your MSD coil is. 

If your coil is say 1.4 ohms then the ratio stacks up good but you are still running only 2.1 ohms overall which I would say is getting really near the borderline for the ampage the ECU unit can take in ordinary use (not like race use where it is short periods only).

If that's the set-up then I would think it will probably be OK but I would say you are near the borderline so I would not go on any really long drives out in the country.

Not sure as I have not received it yet.  I ordered on line as the local autoparts store wanted 20 bucks more for the same coil.  I do not see where the impedence info is.  Here is the info for it:
Coil Wire Attachment      Female/Socket
Coil Style      Canister
Primary Resistance      0.700 ohms
Coil Internal Construction      Epoxy
Coil Color      Black
Maximum Voltage      45,000 V
Turns Ratio      100:1
Secondary Resistance      4.70K ohms
Inductance      8.0 mH
Peak Current      140 mA
Spark Duration      350 uS
Mounting Bracket Included      No
Coil Wire Included      No
Ballast Resistor Included      No
Coil Shape      Round
Diameter (in)      2.125 in.
Height (in)      6.000 in.

Just throwing this out there..But how are you mounting the coil? Some only want to be mounted vertically.
Being that it is not oil filled, I do not believe that there will be an issue with it being mounted horizontally.  It is going to go in the stock location.
Jason

Offline mojavered

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Re: Chrome ECU and Ballast Resistor
« Reply #11 on: May 06, 2010 - 07:48:54 PM »
I thought I bought the .7 ohm, but I got the .8 ohm resistor.
When I was looking things up I ran into this.  Why does it always say that when you are using stock points ignition, you need to use the ballast.  Why does it only specify points?  Thanks!
Jason

Offline UKcuda

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Re: Chrome ECU and Ballast Resistor
« Reply #12 on: May 08, 2010 - 09:47:09 AM »
Sorry to question your explanation, but that just doesn't add up to me.  Every Mopar ignition "Bypasses" the ballast resistor completely during start up.  Which according to your theory would result in hard starting.  Why would the factory design it that way?

It's because the stock system doesn't use a 3 ohm coil.  What I was saying was that, in theory, you could reduce the ballast resistance to zero and maintain overall resistance value by using a 3 ohm coil which ought to improve spark output (due to more volts across the coil).  However, that would probably cause hard starting because, as with the stock system, you would be dropping the available voltage due to powering the starter, but, unlike the stock system, you would be also trying to overcome 3 ohms in the primary ignition circuit (rather than about 1.7 ohms on the stock system).  As noted by AussieChallanger, you would be operating at about 9 volts, but you would have a circuit designed to operate at 12 volts.

mojavered, 

So it seems you have a coil rated at 7 ohms and a ballast resistor rated at 8 ohms.  When the engine's running your coil will be operating at less than 6 volts which is not really making the best of that coil, though it will probably still run OK.  Starting should be fine.  The problem is that your total resistance will be only 1.5 ohms.  So at 12 volts that's drawing 8 amps.

When you are driving it's not a constant 8 amps because the system is constantly switching on and off, but I think it is still in excess of the design load for the ECU (although for a chrome box I don't know what that is supposed to be, I doubt it is as high as 8 amps).

If you left the ignition on without the engine running it would be a constant 8 amps.

This is why people often find they cooked their ECU parked up listening to the radio.

So basically it might be OK depending on how tough the chrome box is supposed to be, but I didn't think they were built to handle that sort of current except maybe for short periods (like racing).
'72 'cuda

Offline mojavered

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Re: Chrome ECU and Ballast Resistor
« Reply #13 on: May 08, 2010 - 01:55:23 PM »
I think that I am getting a little confused.  I went with the ballast that MSD recommends for their coil. 
Here is the note from their instructions.
Note: This Blaster Coil Kit is intended to be used with an MSD Ignition. If installing on a stock, points style ignition system, a 0.8 ohm ballast resistor or resistor wiring must be installed. MSD offers this Ballast Resistor as PN 8214 or the Blaster Coil Kits, PN 8200 and 8203 are equipped with one.

I looked around this site for recommendations for a coil and ballast before posting and could not find too much.  It seems that the blaster 2 is recommended often, but needs to be mounted vertically.  It seems that there is not much difference between these other than being epoxy filled instead of oil filled.  Given MSD instructions, what would you do?  Thanks!
Jason

Offline UKcuda

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Re: Chrome ECU and Ballast Resistor
« Reply #14 on: May 08, 2010 - 02:28:34 PM »
I don't know mate  :dunno:

Maybe I am missing something here and it will all work fine.  But I can't see why it can be a good idea to use a ballast resistor rated higher than the coil since it drops the voltage on the coil lower than half.  I guess with it running it is 7/15 x 14 volts (not 7/15 x 12), so that's actually still like 6.5 volts.  It will probably run alright like that but it's hardly what you'd call optimal.

As I say, my main concern would be the current handling capabilities of the ECU.  But again, maybe I'm missing something and the chrome box is up to the job.  I know the orange box is supposed to be OK up to 5 amps (they're normally set up with a coil and ballast that runs at about 4 amps) and I know the chrome box is meant to be better, but 8 amps is still quite a lot of current.

Perhaps someone else can tell us what the chrome box is rated up to ?
'72 'cuda