Replacement wire type for nichrome wire

david1

New member
Jul 29, 2007
452
0
0
I have to replace the nichrome wire in my wiring harness it melted. I have already installed the APC cable and I have reviewed some information on the
GMC forum & photo site and it indicates to use 10 ohm resistor rated at 20 watts. My question is what type of wire and what gauge should be used?
THANKS

--
'78 Palm Beach car nut & new to RV'ing
26 ft. 403 OEM wheels, 2 ACs, Pod, ladder, macerator
On FaceBook as David Martin
585-953-53OO call or text
 
Well, let's use Ohm's Law to figure tis out. If there were a dead short, then we'd be applying 12 Volts across 20 Ohms.Divide 12 by 20 and we get a
current of 1.667. power is voltage (12) times current (1.667) or just over 20 Watts. Given that the current is less than 2 Amps in a short
condition, 18 gauge is plenty. Actually, I'd probably use a 25 Watt resistor if I were concerned about a dead short. Both for a bit of leeway and
at times the voltage is a bit higher than 12. 18Ga stranded wire will work OK.

--johnny
--
76 26' Eleganza(?) with beaucoup mods and add - ons.
Braselton, Ga.
"I forgive them all, save those who hurt the dogs. They must answer to me in hell" - ol Andy, paraphrased
 
David,

Johnny's calculations are correct, of course, and I agree with his 25 Watt
recommendation. I'd only add that the resistor should be well isolated
from anything heat sensitive -- it WILL get hot. I have mine located with
a metal bracket in the air conditioning blower's direct flow. If you want
to eliminate the extra plug of the APC, you may want to attach the diode
from that device, or an equivalent one, permanently, in series with the
resistor. That's the way I've been wired since before Gene "invented" the
APC.

Ken H.

On Mon, Oct 1, 2018 at 4:42 PM Johnny Bridges via Gmclist <

> Well, let's use Ohm's Law to figure tis out. If there were a dead short,
> then we'd be applying 12 Volts across 20 Ohms.Divide 12 by 20 and we get a
> current of 1.667. power is voltage (12) times current (1.667) or just
> over 20 Watts. Given that the current is less than 2 Amps in a short
> condition, 18 gauge is plenty. Actually, I'd probably use a 25 Watt
> resistor if I were concerned about a dead short. Both for a bit of leeway
> and
> at times the voltage is a bit higher than 12. 18Ga stranded wire will
> work OK.
>
>
 
Why

> David,
>
> Johnny's calculations are correct, of course, and I agree with his 25 Watt
> recommendation. I'd only add that the resistor should be well isolated
> from anything heat sensitive -- it WILL get hot. I have mine located with
> a metal bracket in the air conditioning blower's direct flow. If you want
> to eliminate the extra plug of the APC, you may want to attach the diode
> from that device, or an equivalent one, permanently, in series with the
> resistor. That's the way I've been wired since before Gene "invented" the
> APC.
>
> Ken H.
>
> On Mon, Oct 1, 2018 at 4:42 PM Johnny Bridges via Gmclist <

>
> > Well, let's use Ohm's Law to figure tis out. If there were a dead short,
> > then we'd be applying 12 Volts across 20 Ohms.Divide 12 by 20 and we get
> a
> > current of 1.667. power is voltage (12) times current (1.667) or just
> > over 20 Watts. Given that the current is less than 2 Amps in a short
> > condition, 18 gauge is plenty. Actually, I'd probably use a 25 Watt
> > resistor if I were concerned about a dead short. Both for a bit of
> leeway
> > and
> > at times the voltage is a bit higher than 12. 18Ga stranded wire will
> > work OK.
> >
> >
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>
--
Gene Fisher -- 74-23,77PB/ore/ca
“Give a man a fish; you have fed him for today --- give him a URL and
-------
http://bdub.net/gmcmotorhome.info/
Alternator Protection Cable
http://bdub.net/gmcmotorhome.info/APC.html
 
Wait a second here.. Johnny has mis-read the 10 ohm resistor as 20 ohms, then he reversed Ohms law and actually got close to the correct current.

So 12 volts / by 10 ohms = 1.2 Amps

12 volts x 1.2 amps = 14.4 watts

So a 16 or 18 gauge wire is fine.

Ken can be forgiven for rubeer stamping Johnny's calculations because he's an Engineer! :lol:

--
Bruce Hislop
ON Canada
77PB, 455 Dick P. rebuilt, DynamicEFI EBL EFI & ESC.1 ton front end
http://www.gmcmhphotos.com/photos/showphoto.php?photo=29001
My Staff says I never listen to them, or something like that
 
Bruce, HA! Your staff says you "never listen"; I guess they'd say I
"never read". :-(

I did, indeed, only look at the final result and agreed with it! Most
embarrassing!

Gene, I like to have as few connections in any circuit as possible to
avoid corroded ones. That's the only reason I suggest that one may want to
permanently connect the diode.

Ken Red-Faced H.

> Wait a second here.. Johnny has mis-read the 10 ohm resistor as 20 ohms,
> then he reversed Ohms law and actually got close to the correct current.
>
> So 12 volts / by 10 ohms = 1.2 Amps
>
> 12 volts x 1.2 amps = 14.4 watts
>
> So a 16 or 18 gauge wire is fine.
>
> Ken can be forgiven for rubeer stamping Johnny's calculations because he's
> an Engineer! :lol:
>
> --
>
 
Thanks everybody so it looks like 16 or 18 gauge wire ... would you recommend a fuse in line between the resistor and the fuse panel? And if so 5 amp
sorry I'm not all that great with Ohm's law and calculations
--
'78 Palm Beach car nut & new to RV'ing
26 ft. 403 OEM wheels, 2 ACs, Pod, ladder, macerator
On FaceBook as David Martin
585-953-53OO call or text
 
David,
You can add a fuse if you like. Since glass fuses are notorious for poor connections, I would suggest an ATO style fuse. 5 Amp is fine, but since max
normal current is 1.2Amp, you could go as low as 2 Amp.

The resistor should protect the fuse. The fuse will be there in-case you get a short before the resistor.

--
Bruce Hislop
ON Canada
77PB, 455 Dick P. rebuilt, DynamicEFI EBL EFI & ESC.1 ton front end
http://www.gmcmhphotos.com/photos/showphoto.php?photo=29001
My Staff says I never listen to them, or something like that
 
Before I retired that would of been embarrassing. Any more it's just a Senior Moment. One bit which might be of interest elsewhere but doesn't seem
to matter here. As nichrome heats its resistance increases, while a fixed resistor doesn't. I go away thinking somebody had a mile or two of it and
figured to save a nickle.

--johnny
--
76 26' Eleganza(?) with beaucoup mods and add - ons.
Braselton, Ga.
"I forgive them all, save those who hurt the dogs. They must answer to me in hell" - ol Andy, paraphrased
 
I disagree with the calculations
First you should use 15v not 12, actual voltage will be 13.8 minimum to 14.2+ so round UP
This means dissipated power is 15v * 1.5A = 22.5 watts

a 20w resistor will not last long at 23 watts. you want at least double or triple the wattage for long reliable life.
Thats the beauty of the resistance wire solution, it spreads the heat out over 2 feet rather than 1 inch. more area, more power dissipation.
________________________________
From: Gmclist on behalf of Johnny Bridges via Gmclist
Sent: Tuesday, October 2, 2018 8:02 AM
To: gmclist
Cc: Johnny Bridges
Subject: Re: [GMCnet] Replacement wire type for nichrome wire

Before I retired that would of been embarrassing. Any more it's just a Senior Moment. One bit which might be of interest elsewhere but doesn't seem
to matter here. As nichrome heats its resistance increases, while a fixed resistor doesn't. I go away thinking somebody had a mile or two of it and
figured to save a nickle.

--johnny
--
76 26' Eleganza(?) with beaucoup mods and add - ons.
Braselton, Ga.
"I forgive them all, save those who hurt the dogs. They must answer to me in hell" - ol Andy, paraphrased

_______________________________________________
GMCnet mailing list
Unsubscribe or Change List Options:
http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
 
Ideally, circuits should be robust enough that a toaster element should not
have to be bundled in the wire harness where it can do a whole bunch of
damage if "stufffff happens"!
I much prefer fuses or circuit breakers or visible fail safes that
are accessible to look at and test, than hidden fusible links.
Manufacturers use them for only one reason. They are cheaper than the
alternative.
But, you and i are not bound by bean counters, and are free to use the
best stuff out there. Just overbuild the snot out of it, and worry about
something else going haywire. (Grin)
Jim Hupy

> I disagree with the calculations
> First you should use 15v not 12, actual voltage will be 13.8 minimum to
> 14.2+ so round UP
> This means dissipated power is 15v * 1.5A = 22.5 watts
>
> a 20w resistor will not last long at 23 watts. you want at least double or
> triple the wattage for long reliable life.
> Thats the beauty of the resistance wire solution, it spreads the heat out
> over 2 feet rather than 1 inch. more area, more power dissipation.
> ________________________________
> From: Gmclist on behalf of Johnny
> Bridges via Gmclist
> Sent: Tuesday, October 2, 2018 8:02 AM
> To: gmclist
> Cc: Johnny Bridges
> Subject: Re: [GMCnet] Replacement wire type for nichrome wire
>
> Before I retired that would of been embarrassing. Any more it's just a
> Senior Moment. One bit which might be of interest elsewhere but doesn't
> seem
> to matter here. As nichrome heats its resistance increases, while a fixed
> resistor doesn't. I go away thinking somebody had a mile or two of it and
> figured to save a nickle.
>
> --johnny
> --
> 76 26' Eleganza(?) with beaucoup mods and add - ons.
> Braselton, Ga.
> "I forgive them all, save those who hurt the dogs. They must answer to me
> in hell" - ol Andy, paraphrased
>
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>
 
It would be a concern if the circuit >always< had 15 volts applied, which it doesn't. The resistance, pretty much regardless how one obtains it,
seems to be a current limiter in case of failure. In which case I'm with Hupy - I'd rather fail a resistor put in the open than a piece of heater
wire in a bundle of other (meltable) wires.

--johnny
--
76 26' Eleganza(?) with beaucoup mods and add - ons.
Braselton, Ga.
"I forgive them all, save those who hurt the dogs. They must answer to me in hell" - ol Andy, paraphrased
 
I’ll throw something decidedly non-technical into the fray:

A few years ago st Bean Station, When Ken and I had to bypass my nichrome
wire (not because it melted, but while troubleshooting damage from having
reversed battery polarity—another story), we used what was handy: a 12-volt
light bulb holder, with a standard 1156 tail-light bulb in it. At 27 watts
nominal (but variable with heat, like the nichrome wire), it will draw a
little over 2 amps when lit. Any automotive wire will work. It serves to
pull enough current to excite the alternator field wiring, which is the
purpose of that wire. It lights when the ignition is turned on until the
motor is turning fast enough to so that the alternator is balancing the
voltage from the other side. The only time it’s on, therefore, is for about
a second or two after starting the engine, and when the alternator fails.

I just let it hang in the space behind the glove box. It’s easy to test,
cheap to replace, and does the job. If it fails, it fails open. It also
limits current right at the fuse block, so I can’t see much value in also
installing a fuse. I actually bought a resistor to replace it, but have
never gotten around to it.

Rick “too simple for calculations” Denney

> I have to replace the nichrome wire in my wiring harness it melted. I have
> already installed the APC cable and I have reviewed some information on the
> GMC forum & photo site and it indicates to use 10 ohm resistor rated at 20
> watts. My question is what type of wire and what gauge should be used?
> THANKS
>
>
> --
> '78 Palm Beach car nut & new to RV'ing
> 26 ft. 403 OEM wheels, 2 ACs, Pod, ladder, macerator
> On FaceBook as David Martin
> 585-953-53OO call or text
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>
--
Rick Denney
73 x-Glacier 230 "Jaws"
Off-list email to rick at rickdenney dot com
 
As Rick reminded us, the Initial Excitation terminal on the alternator only
draws current when the alternator is not running. When running, that
terminal is at output voltage. I was reminded of that today in a
discussion with my 50+ year experienced automotive electrician. I took
some CS10 alternators and a GMC starter to him for overhaul in expectation
of offering them at Tallahassee. He convinced me that the 64A CS10's are
not worth rebuilding -- buying's cheaper. While discussing them, I told
him about the GMC's Nichrome wire and related problems. Then I started on
the APC. He went to his parts bin and brought out a 2" long pair of 2-wire
terminals with a diode in one of the wires -- the equivalent of the APC.
"Been selling them for YEARS -- cost $3.81." I didn't get a part number,
but you may want to reconsider fabricating them, Gene.

He also reminded me of the fact that when the alternator's producing power,
ALL THREE of its terminals are at output voltage. I guess I forgot that
when I oversized and air stream located my resistor. :-)

Ken "EE EDUCATED -- NOT experienced" H.

> I’ll throw something decidedly non-technical into the fray:
>
> A few years ago st Bean Station, When Ken and I had to bypass my nichrome
> wire (not because it melted, but while troubleshooting damage from having
> reversed battery polarity—another story), we used what was handy: a 12-volt
> light bulb holder, with a standard 1156 tail-light bulb in it. At 27 watts
> nominal (but variable with heat, like the nichrome wire), it will draw a
> little over 2 amps when lit. Any automotive wire will work. It serves to
> pull enough current to excite the alternator field wiring, which is the
> purpose of that wire. It lights when the ignition is turned on until the
> motor is turning fast enough to so that the alternator is balancing the
> voltage from the other side. The only time it’s on, therefore, is for about
> a second or two after starting the engine, and when the alternator fails.
>
> I just let it hang in the space behind the glove box. It’s easy to test,
> cheap to replace, and does the job. If it fails, it fails open. It also
> limits current right at the fuse block, so I can’t see much value in also
> installing a fuse. I actually bought a resistor to replace it, but have
> never gotten around to it.
>
> Rick “too simple for calculations” Denney
>
>
 
Oh my God now I'm totally confused should I get a 100 watt resistor at 10 ohm I'm crying here
--
'78 Palm Beach car nut & new to RV'ing
26 ft. 403 OEM wheels, 2 ACs, Pod, ladder, macerator
On FaceBook as David Martin
585-953-53OO call or text
 
>
> Then I started on the APC. He went to his parts bin and brought out a 2" long pair of 2-wire terminals with a diode in one of the wires -- the
> equivalent of the APC.
> "Been selling them for YEARS -- cost $3.81." I didn't get a part number, but you may want to reconsider fabricating them, Gene.
>
> He also reminded me of the fact that when the alternator's producing power,
> ALL THREE of its terminals are at output voltage. I guess I forgot that
> when I oversized and air stream located my resistor. :)
>
> Ken "EE EDUCATED -- NOT experienced" H.

Gene should also look on Ebay for anti-feedback for 10, 12, 17 and 27SI.

Matt ONP at the casino in Erie PA.
--
Matt & Mary Colie - '73 Glacier 23 - Members GMCMI, GMCGL, GMCES
Electronically Controlled Quiet Engine Cooling Fan
OE Rear Drum Brakes with Applied Control Arms
SE Michigan - Twixt A2 and Detroit
 
What is this

Gene should also look on Ebay for anti-feedback for 10, 12, 17 and 27SI.

> >
> > Then I started on the APC. He went to his parts bin and brought out a
> 2" long pair of 2-wire terminals with a diode in one of the wires -- the
> > equivalent of the APC.
> > "Been selling them for YEARS -- cost $3.81." I didn't get a part
> number, but you may want to reconsider fabricating them, Gene.
> >
> > He also reminded me of the fact that when the alternator's producing
> power,
> > ALL THREE of its terminals are at output voltage. I guess I forgot that
> > when I oversized and air stream located my resistor. :)
> >
> > Ken "EE EDUCATED -- NOT experienced" H.
>
> Gene should also look on Ebay for anti-feedback for 10, 12, 17 and 27SI.
>
> Matt ONP at the casino in Erie PA.
> --
> Matt & Mary Colie - '73 Glacier 23 - Members GMCMI, GMCGL, GMCES
> Electronically Controlled Quiet Engine Cooling Fan
> OE Rear Drum Brakes with Applied Control Arms
> SE Michigan - Twixt A2 and Detroit
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>
--
Gene Fisher -- 74-23,77PB/ore/ca
“Give a man a fish; you have fed him for today --- give him a URL and
-------
http://bdub.net/gmcmotorhome.info/
Alternator Protection Cable
http://bdub.net/gmcmotorhome.info/APC.html
 
Gene,

If you Google "DELCO ALTERNATOR HARNESS ANTI- FEEDBACK DIODE", you'll get
lots of APC equivalent device sources. I don't see one as cheap as the
$3.81 my local guy says he pays, but probably several costing less than
it's costing you to make them. The one he gets is similar to this one:

https://www.ebay.com/itm/Delco-Alternator-Anti-Feed-Back-Diode-Harness-Plug-10SI-12SI-15SI-27SI-Regulator-/192348053201

Well! Looking at that more closely, it's cheaper than his cost: $6.95/2!
(IF you can get the shipping cost down enough on a volume buy.)

HTH,

Ken H.

> What is this
>
> Gene should also look on Ebay for anti-feedback for 10, 12, 17 and 27SI.
>
>
>
>
>

>

> > >
> > > Then I started on the APC. He went to his parts bin and brought out a
> > 2" long pair of 2-wire terminals with a diode in one of the wires -- the
> > > equivalent of the APC.
> > > "Been selling them for YEARS -- cost $3.81." I didn't get a part
> > number, but you may want to reconsider fabricating them, Gene.
> > >
> > > He also reminded me of the fact that when the alternator's producing
> > power,
> > > ALL THREE of its terminals are at output voltage. I guess I forgot
> that
> > > when I oversized and air stream located my resistor. :)
> > >
> > > Ken "EE EDUCATED -- NOT experienced" H.
> >
> > Gene should also look on Ebay for anti-feedback for 10, 12, 17 and 27SI.
> >
> > Matt ONP at the casino in Erie PA.
> > --
> > Matt & Mary Colie - '73 Glacier 23 - Members GMCMI, GMCGL, GMCES
> > Electronically Controlled Quiet Engine Cooling Fan
> > OE Rear Drum Brakes with Applied Control Arms
> > SE Michigan - Twixt A2 and Detroit
> >
> > _______________________________________________
> > GMCnet mailing list
> > Unsubscribe or Change List Options:
> > http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
> >
> --
> Gene Fisher -- 74-23,77PB/ore/ca
> “Give a man a fish; you have fed him for today --- give him a URL and
> -------
> http://bdub.net/gmcmotorhome.info/
> Alternator Protection Cable
> http://bdub.net/gmcmotorhome.info/APC.html
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>
 
> What is this
>
> Gene should also look on Ebay for anti-feedback for 10, 12, 17 and 27SI.
>

Gene should also look on Ebay for anti-feedback for 10, 12, 17 and 27SI
>

>
>
Over the past few months I have been working on alternative ignition
designs for our Onan generators. During my tenure as a GMC owner I have
suffered the failure of two Pertronix 1181 modules mounted in the blower
housing scroll - one due to a fatigue failure of the module’s aluminum
mounting tab due to wind buffeting - and the other due to a flywheel strike
where the flywheel magnet somehow impacted the module’s face for at least
several revolutions. These two events occurred with super-rigid mounting
arrangements that I made myself - I was NOT using the C-channel mounting
kit commonly found in the GMC community. Photo albums of these two:

http://www.jcmco.com/gallery/Pertronix<
http://www.jcmco.com/gallery/Pertronix> and
http://www.jcmco.com/gallery/PertronixModII<
http://www.jcmco.com/gallery/PertronixModII>

So I decided to experiment with something different…I mounted the module on
the outside of the generator’s bellhousing and have it being triggered by a
magnet embedded in an aluminum tonewheel:

http://www.jcmco.com/gallery/Pertronix-ModIII<
http://www.jcmco.com/gallery/Pertronix-ModIII>

This produced very good results - nearly identical to when the module is
mounted inside the blower scroll and triggered by a flywheel magnet.
However, during testing I made the observation that the ignition coil was
running very hot and was uncomfortable to touch even after very short
amounts of runtime. I determined that the Pertronix 1181 module that people
have recommended for our Onans was keeping the coil energized for about 355
degrees of rotation of the crankshaft - and only dropped its output for a
few milliseconds as the magnet went by the module at which time the spark
plugs fired. This is contrasted with the 140 degrees per revolution which
the OEM breaker points used as a coil dwell time. In other words, the
Pertronix 1181 causes current to flow in the coil primary for almost three
times as long as the original Onan design. No wonder the coil is getting so
hot… once the magnetic field builds up in the core of the coil the
remaining current flow produces nothing but heat. I wrote to Pertronix tech
support for advice and they confirmed that the 1181 is not the right module
for this application. Their words:

"You really should be using what we call a latching Ignitor module. This
module takes two magnets to trigger the unit. One to turn it "ON" then one
to turn it "OFF" to fire. This allows you to control the charge time of the
coil. We use this module on all our applications that have less then 4
cylinders. This is so we don't overheat the coil and don't over heat the
Ignitor module. … The part number I would recommend to modify would be part
number: 1121”

At that point I bought an 1121 and modified my mount and magnet wheel for
it: http://www.jcmco.com/gallery/PertronixModIV <
http://www.jcmco.com/gallery/PertronixModIV>

The 1121 module has been in service on my Onan for 20 hours of runtime so
far and has worked flawlessly. Just as with the 1181 module, the 1121
produces repeatable and precise spark timing but - unlike the 1181 - the
1121 produces no appreciable heating of the ignition coil. Having worked 35
years in an electronics career I know quite

>
>
>

>

>> >
>> > Then I started on the APC. He went to his parts bin and brought out a
>> 2" long pair of 2-wire terminals with a diode in one of the wires -- the
>> > equivalent of the APC.
>> > "Been selling them for YEARS -- cost $3.81." I didn't get a part
>> number, but you may want to reconsider fabricating them, Gene.
>> >
>> > He also reminded me of the fact that when the alternator's producing
>> power,
>> > ALL THREE of its terminals are at output voltage. I guess I forgot
>> that
>> > when I oversized and air stream located my resistor. :)
>> >
>> > Ken "EE EDUCATED -- NOT experienced" H.
>>
>> Gene should also look on Ebay for anti-feedback for 10, 12, 17 and 27SI.
>>
>> Matt ONP at the casino in Erie PA.
>> --
>> Matt & Mary Colie - '73 Glacier 23 - Members GMCMI, GMCGL, GMCES
>> Electronically Controlled Quiet Engine Cooling Fan
>> OE Rear Drum Brakes with Applied Control Arms
>> SE Michigan - Twixt A2 and Detroit
>>
>> _______________________________________________
>> GMCnet mailing list
>> Unsubscribe or Change List Options:
>> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>>
> --
> Gene Fisher -- 74-23,77PB/ore/ca
> “Give a man a fish; you have fed him for today --- give him a URL and
> -------
> http://bdub.net/gmcmotorhome.info/
> Alternator Protection Cable
> http://bdub.net/gmcmotorhome.info/APC.html
>
--
Gene Fisher -- 74-23,77PB/ore/ca
“Give a man a fish; you have fed him for today --- give him a URL and
-------
http://bdub.net/gmcmotorhome.info/
Alternator Protection Cable
http://bdub.net/gmcmotorhome.info/APC.html