HEI power supply.

General engine tech -- Drag Racing to Circle Track

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Tuner
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Re: HEI power supply.

Post by Tuner » Tue Mar 19, 2019 4:24 am

The module limits the steady state amperage after the coil inductance is saturated. The coil resistance is .4 (four tenths) Ohm. Ohm's law tell us Amperage is Voltage divided by resistance, so 12V/.4 = 30 Amps inrush current when the transistor closes to ground the coil. 14V/.4 = 35A This high amperage surge is why the GM wiring is 10 or 12 gauge.


https://en.wikipedia.org/wiki/Inrush_current
Last edited by Tuner on Tue Mar 19, 2019 4:27 am, edited 1 time in total.

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Re: HEI power supply.

Post by Tuner » Tue Mar 19, 2019 4:25 am

double opst
Last edited by Tuner on Tue Mar 19, 2019 4:29 am, edited 1 time in total.

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Re: HEI power supply.

Post by Schurkey » Tue Mar 19, 2019 4:28 am

Woof. I knew that the HEI drew pulses of current, but I didn't realize they were that great.

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Re: HEI power supply.

Post by Tuner » Tue Mar 19, 2019 4:36 am

The inductor has "back EMF" opposing and reducing the inrush current some, but alas, I know not how to calculate. Bucket list includes oscilloscope games to ponder this, perhaps the next HEI setup in the distributor machine I will get the scope out and hack around with it.

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Re: HEI power supply.

Post by Geoff2 » Tue Mar 19, 2019 4:48 am

The stock HEI current is around 5.5 amp. I have measured it with a scope. NOT 30 amps. I have retro fitted dozens of HEIs & used 10 amp fuses, have yet to blow one. The module has internal current limiting. There is no inrush current with a coil, exact opposite; current starts at zero & ramps up. My understanding of using the low pri resistance with HEI coils is to reduce coil heating & subsequent loss in the secondary winding.
More on HEI & the current limiting cct:

www.worldphaco.net

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Re: HEI power supply.

Post by mag2555 » Tue Mar 19, 2019 7:03 am

While on the discussion of 12 source's and if you will power supply's , noise hash and voltage spikes out of the Alt is a big reason for electronic ignition module parts failure that it seems no one talks about !

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Re: HEI power supply.

Post by Truckedup » Tue Mar 19, 2019 7:51 am

GM did use a 10 gauge wire on many original HEI applications...GM is not known to overbuild on wiring....I have heard from a GM powertrain engineer that it's for a reduction in harmonics...I also heard the original HEI modules had poor dwell control so the amps at low RPM were high....However..I have used 12 and 14 gauge wire with apparently no problems..I don't fuse ignitions for over current protection but use a higher amp fuse/breaker for short circuit protection of the wiring..I don't believe GM fused ignition systems before the use of ECM's ?
Motorcycle land speed racing... wearing animal hides and clinging to vibrating oily machines propelled by fire

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Re: HEI power supply.

Post by novadude » Tue Mar 19, 2019 10:07 am

Tuner wrote:
Mon Mar 18, 2019 1:07 pm
novadude wrote:
Mon Mar 18, 2019 8:47 am
On my '65 Nova, I used removed the resistor wire from the firewall plug and replaced with another wire that I used to switch on a relay. The relay pulls the power for the ignition (10g wire to "BATT" terminal) from the horn relay bus. Works fine.
Relays like the 30~40 Amp Bosch cubes draw so little Amperage It isn't necessary to eliminate or replace the resistor wire If the resistor wire is only used to switch a relay.
I only eliminated the resistance wire because I didn't want to disturb the factory harness. Easier to just pull it out of the firewall plug and insert another connector with a non-resistor wire. That way I was not cutting the harness, or letting resistor wire length dictate relay mounting location. The resistor wire hangs there, still taped in the harness, but disconnected at both ends.

My set-up is a bit unique anyway. I am running a '70s Chrysler inductive pickup and reluctor wheel in an early 327 cast iron points distributor. The Chrysler parts trigger a '990' Declo HEI module that is mounted to a heat sink and tucked away in a cool, hidden part of the engine compartment. This way, I get the benefit of the HEI module, and the appearance of a stock breaker point distributor.

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Re: HEI power supply.

Post by rfoll » Tue Mar 19, 2019 10:38 am

I found a pair of 40 amp relays that I will use on this setup. The choke has a fused supply, and the HEI will be operated by the resistor wire. Curiously, when I tested the resistor wire a few months ago it seemed to give me 12 volts. It's a really long wire, it will reach the passenger fender.
So much to do, so little time...

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Re: HEI power supply.

Post by Schurkey » Tue Mar 19, 2019 1:28 pm

rfoll wrote:
Tue Mar 19, 2019 10:38 am
Curiously, when I tested the resistor wire a few months ago it seemed to give me 12 volts.
No voltage reduction if there's no current flowing. You check voltage at the end of the wire with no load on it, you'll get system voltage.

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Re: HEI power supply.

Post by F-BIRD'88 » Tue Mar 19, 2019 2:00 pm

You're thinking of impedance of a reactive circuit as. Opposed to simple dc resistance . Both are measured in Ohms.
Why not just find the ignition "run" resistance wire on the firewall bulkhead wiring harness pass thru connector. Remove the conector (a bolt in the center holds it in) and push the lil brass clip end connector push it out. Keep that lil clip connector. Solder a new wire onto that lil clip connector. Push it back in so it locks in again . Run the new wire from that bulkhead connector to the hei diz . Now you have a switched on run (12v) and crank (12v) without the inline resistance in the "run" position.

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Re: HEI power supply.

Post by ClassAct » Tue Mar 19, 2019 4:08 pm

F-BIRD'88 wrote:
Tue Mar 19, 2019 2:00 pm
You're thinking of impedance of a reactive circuit as. Opposed to simple dc resistance . Both are measured in Ohms.
Why not just find the ignition "run" resistance wire on the firewall bulkhead wiring harness pass thru connector. Remove the conector (a bolt in the center holds it in) and push the lil brass clip end connector push it out. Keep that lil clip connector. Solder a new wire onto that lil clip connector. Push it back in so it locks in again . Run the new wire from that bulkhead connector to the hei diz . Now you have a switched on run (12v) and crank (12v) without the inline resistance in the "run" position.
I keep those little wire ends on the shelf and just crimp a new wire to the new end and I'm done with it. I haven't soldered a connection in better than 20 years. I had issues with soldered ends. Never with a crimped end. It could be that I'm not smart enough to solder but that's another discussion.

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Re: HEI power supply.

Post by rfoll » Tue Mar 19, 2019 4:57 pm

I'm not brave enough to pull the 55 year old bulkhead plug on someone else's car. I don't disturb ancient wiring unless something doesn't work.
So much to do, so little time...

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Re: HEI power supply.

Post by In-Tech » Tue Mar 19, 2019 7:40 pm

Is this a comedy? It's pretty funny.
Heat is energy, energy is horsepower...but you gotta control the heat.
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Re: HEI power supply.

Post by rfoll » Tue Mar 19, 2019 9:56 pm

In-Tech wrote:
Tue Mar 19, 2019 7:40 pm
Is this a comedy? It's pretty funny.
Does this mean you have all of the answers?
So much to do, so little time...

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