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Re: Points HEI....10ga. wire and My 81 yr. Uncle?
WHO, ME ? #408466 Wed Apr 30 2008 10:07 PM
Joined: Sep 2002
Posts: 154
F
Shop Shark
HRL,what gauge is the wire feeding the HEI from the ignition switch on a stock GM vehicle? Is it fused on a stock GM vehicle? Is it the 20 amp fuse labelled ignition and ECU,the supply for the HEI on GM vehicle I've seen?
I have a HEI on a 235 in my 53 truck.It's got a 15 amp Buss fuse,been that way for years.
Langdon says the big wire is to limit feedback or harmonics on the circuit.
An Amp meter inline on the HEI shows about 3 amps at idle,rising an amp or two with increase in RPM.I'll check it while cranking too.

Re: Points HEI....10ga. wire and My 81 yr. Uncle?
Fast truck #408485 Wed Apr 30 2008 11:01 PM
Joined: Oct 2006
Posts: 5,029
B
Master Gabster
...as my eyes glaze over...
I wonder why this thread isn't in Electrical. headscratch


Jim

Modern ‘science’: the wonder of a
pre-determined mind…

The ‘baseline belief’ of astronomy:
“Any day now, we’ll pick up a tiny,
coded signal from outer space. Then
we’ll know for certain that there is
intelligence out there, because coded
information does not arise by chance”

The ‘baseline belief’ of biology:
The precisely coded genetic information in
every cell would fill many books…
but we know for certain that no intelligence
could have created life.”


Re: Points HEI....10ga. wire and My 81 yr. Uncle?
Fast truck #408522 Thu May 01 2008 12:58 AM
Joined: Feb 2004
Posts: 21,052
H
Boltergeist
Both the feed wire to the ignition switch, and the HEI hot lead on GM original equipment wiring is 10 gauge. The ignition switch is fed directly from the battery cable terminal at the starter through a fusible link, not a fuse, with a 50 amp rating, IIRC. It must carry the surge current of the starter solenoid pull-in winding (up to 30 amps) plus the load of the ignition system.

"All ignition systens work on 6 volts"- - - - -WRONG! Point-type ignition coils designed for 12 volt ignition systems require a ballast resistor to drop running voltage to approximately 9 volts. Why? Because there's a bypass circuit that delivers straight battery voltage to the coil during cranking, usually about 10 volts, and for the coil to work efficently on a cold start, it must be able to work at full output at 9 or 10 volts. After the engine starts and the charging system kicks in, voltage can be 13 to 15 volts, and a resistor is needed to prevent the coil from overpowering the points and burning them due to high primary current.

Solid-state ignition systems don't use points, so they can use full battery voltage and high current draw coils. That makes over 50,000 volts available to fire the spark plugs, instead of 20,000 volts or less from a point-type system.

If you're going to protect the circuit from the battery to the ignition switch, use a 40 or 50 amp circuit breaker, or a #10 fuse link, not a conventional fuse.
Jerry

Last edited by Hotrod Lincoln; Thu May 01 2008 01:00 AM.

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The coroner blamed the crime on a cereal killer!

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Re: Points HEI....10ga. wire and My 81 yr. Uncle?
Hotrod Lincoln #408526 Thu May 01 2008 01:15 AM
Joined: Dec 2006
Posts: 1,154
W
Shop Shark
Jerry.....my mistake my uncle said that the points only ever take up to 6 - 9 volts as 12 volts will cook them and that 6 volt systems never needed ballast resistors as the points only ever got 6-9 volts....you are most correct thanks for keeping me honest. OK...a number 10 fuse link to the Ign. switch Batt. side of switch?...Have we got it? I guess we can get one at the local Napa store....never seen one...... YES... I guess this is electrical stuff but it all has to do with removal and installation of a distributor so either forum could be right...that's my opinion and therefore it is correct! T/C Steve

Re: Points HEI....10ga. wire and My 81 yr. Uncle?
WHO, ME ? #408929 Fri May 02 2008 03:14 AM
Joined: Dec 2006
Posts: 1,154
W
Shop Shark
HI.....Mr. Langdon responded to us by email is, "Steve no fuse is required, Tom." ......Well I guess the master has spoken. I hope this info. will help other people with the same questions as we had. Thanks to you all! Steve and Unc

Re: Points HEI....10ga. wire and My 81 yr. Uncle?
WHO, ME ? #409031 Fri May 02 2008 01:19 PM
Joined: Jan 2000
Posts: 1,609
T
Extreme Gabster
I don't come by here much anymore but I saw this post and can throw in my two cents based on theory and my real life experience of adapting GM HEI's to at least 5 Chevy and GMC 6's
Being an electrican I can understand all this stuff at least in theory.An HEI coil is usually around .5 Ohms at the vehicle running voltage of a nominal 14 volts.Ohm's law says amps is volts divided by resistence,.5 Ohms in this case.So there's a potential in theory for the HEI coil to draw 28 amps.In reality it's less than 28 amps due to short time period the coil is allowed to "fill" with current between sparks.And I do believe the HEI module limts the current to the coil to prevent overloading.
A short run of #14 wire can conduct a steady flow of 20 amps with acceptable voltage loss,The National Electrical Code amperage flow for wire sizes doesn't apply to automotive use.
But the HEI current flow isn't steady,there's an inrush of current 100's of times a second depending on engine RPM's.Beside the current inrush,electrical flow isn't instantanous,there's a slight lag when more current is called for.A larger wire will help to overcome this.Kinda like a drag car taking off,it takes a brief second for all the forces to react.
So the 10 gauge wire is a safety factor so to speak,covers all bases.The large wire keeps voltage losses acceptable in a worst case senario.
In normal situations,like my low rpm truck engines not needing all there is to fire the plugs,a #14 or 12 wire is adequate from my personal experience .

Re: Points HEI....10ga. wire and My 81 yr. Uncle?
Tony #409101 Fri May 02 2008 04:42 PM
Joined: Dec 2006
Posts: 1,154
W
Shop Shark
Thanks for the help you made the information much more user friendly! T/C Steve

Re: Points HEI....10ga. wire and My 81 yr. Uncle?
WHO, ME ? #409110 Fri May 02 2008 05:24 PM
Joined: Jan 2000
Posts: 1,609
T
Extreme Gabster
One more thing,personally I think it's bad practice not to fuse the feed from the ignition switch to the HEI on an old vehicle you have invested time and money into.In case the wire gets shorted somehow,it'll save your wiring harness.My truck has a 20 amp circuit breaker feeding the ignition switch protecting the whole switch from shorts or overcurrent.I have no ignition switched items other than the HEI and a single small electric wiper motor.And in 10 years the circuit breaker has never tripped from the HEI load and or occasional wiper use.
Use a circuit breaker,the ones that plug into a fuse holder are only a few bucks.A 30 amp one will at least not nuisance trip and will trip from a dead short.
Here's some info off the internet,you be the judge if it's totally accurate,shows amp draw etc.
HEI current draw and rpm

Re: Points HEI....10ga. wire and My 81 yr. Uncle?
WHO, ME ? #465046 Sun Oct 26 2008 03:47 PM
Joined: Aug 2006
Posts: 113
F
Wrench Fetcher
Got the 30 amp info off a website, ANY voltage drop would be bad for a hot spark, so 10ga isp p robablyp advisable, Why do they use 12ga on the stock gm harnesses? Someone with a new aftermarket harness look at theirs so the sharpshooters can be SURE that no one "overwires" anything.


64 & 66 GMC long fleetside 4x4
Cartwright, OK
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