High amp alternator wiring idea.

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fj20spl311
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High amp alternator wiring idea.

Post by fj20spl311 » Sat Jun 08, 2019 3:52 pm

Electrical gurus please chime in on this idea.
The problem: Higher amp alternator overloads the amp meter on start-up. Pins the meter if the revs are too high.
The usual solution is to add a wire directly to the battery, but then the amp meter doesn't work on charging.
My understanding is there is a "shunt" resister in the amp meter that determines the range of the current reading. Ideally you could change the shunt resister, maybe from a cheap 50 amp meter. Without a shunt resister in the new wire, the split of current in biased to the new wire.
What about adding a cheap 30 amp meter in the new wire to the battery, would that split the current through both amp meters?
Phil
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Re: High amp alternator wiring idea.

Post by JT68 » Sat Jun 08, 2019 6:09 pm

Yes, this absolutely will work. If you look up Kirchhoff's current law, that will explain exactly how the current will divide (inversely proportional to resistance). In the simplest example, if both paths back to the battery are equal resistance, the current will divide 50/50. Otherwise, the lower resistance path will carry proportionally more.

If you just use a 10ga wire, nearly all the charging current will go through that and the original ammeter will show very little charging, if any. The ammeter will however still show discharge since the accessories still route through it.

That's really the only downside I can think of- your ammeter will only display a fraction of charging if any, but that's OK. If you install a second ammeter, that would certainly indicate charging, but probably isn't necessary- kinda cool though. You could also install the 10ga parallel line and no other ammeter, but an aftermarket volt meter instead-- if it swings up past 12V, i.e 14-17 or so all is well. All these options are fine.

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Re: High amp alternator wiring idea.

Post by Curtis » Sat Jun 08, 2019 9:50 pm

This is handy for wire size. There are other versions out there that give different types of info.

http://www.gtsparkplugs.com/WireSizeCalc.html
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fj20spl311
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Re: High amp alternator wiring idea.

Post by fj20spl311 » Sat Jun 08, 2019 10:06 pm

JT68 wrote:
Sat Jun 08, 2019 6:09 pm

That's really the only downside I can think of- your ammeter will only display a fraction of charging if any, but that's OK. If you install a second ammeter, that would certainly indicate charging, but probably isn't necessary- kinda cool though. You could also install the 10ga parallel line and no other ammeter, but an aftermarket volt meter instead-- if it swings up past 12V, i.e 14-17 or so all is well. All these options are fine.
j
I have always installed a 10 ga wire from the alternator to the battery. Jon made me a 67.5 dual meter with a volt meter instead of a amp meter, but they are a little $$$$.
Just an idea I want to try out.
Phil
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Re: High amp alternator wiring idea.

Post by redroadster » Sun Jun 09, 2019 9:11 am

I might ask , what is the alt your using and what are the readings on a digital meter, amps and voltage
How high for how long
?
The newer designed alternator's field design (square wave )
May and should read high on the guage for the original alt.

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Re: High amp alternator wiring idea.

Post by Curtis » Sun Jun 09, 2019 10:29 am

JT68 wrote:
Sat Jun 08, 2019 6:09 pm
Yes, this absolutely will work. If you look up Kirchhoff's current law, that will explain exactly how the current will divide (inversely proportional to resistance). In the simplest example, if both paths back to the battery are equal resistance, the current will divide 50/50. Otherwise, the lower resistance path will carry proportionally more.

If you just use a 10ga wire, nearly all the charging current will go through that and the original ammeter will show very little charging, if any. The ammeter will however still show discharge since the accessories still route through it.

That's really the only downside I can think of- your ammeter will only display a fraction of charging if any, but that's OK. If you install a second ammeter, that would certainly indicate charging, but probably isn't necessary- kinda cool though. You could also install the 10ga parallel line and no other ammeter, but an aftermarket volt meter instead-- if it swings up past 12V, i.e 14-17 or so all is well. All these options are fine.

j
OMG, Kirchhoff's law, I would have to get out my basic electronics book sitting under my mouse pad. I can't remember any of that stuff beyond IR=E. I'm glad you know it.
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Re: High amp alternator wiring idea.

Post by ppeters914 » Sun Jun 09, 2019 5:49 pm

JT68 wrote:
Sat Jun 08, 2019 6:09 pm
Yes, this absolutely will work. If you look up Kirchhoff's current law, that will explain exactly how the current will divide (inversely proportional to resistance). In the simplest example, if both paths back to the battery are equal resistance, the current will divide 50/50. Otherwise, the lower resistance path will carry proportionally more.

If you just use a 10ga wire, nearly all the charging current will go through that and the original ammeter will show very little charging, if any. The ammeter will however still show discharge since the accessories still route through it.

That's really the only downside I can think of- your ammeter will only display a fraction of charging if any, but that's OK. If you install a second ammeter, that would certainly indicate charging, but probably isn't necessary- kinda cool though. You could also install the 10ga parallel line and no other ammeter, but an aftermarket volt meter instead-- if it swings up past 12V, i.e 14-17 or so all is well. All these options are fine.

j
Curtis wrote:
Sun Jun 09, 2019 10:29 am
OMG, Kirchhoff's law, I would have to get out my basic electronics book sitting under my mouse pad. I can't remember any of that stuff beyond IR=E. I'm glad you know it.
Can't find that stupid rear brake line ferrule (actually, both the original and the one from my parts car :roll: ), but I can remember the mnemonics for resistor color codes! Oh, and P=IE.
redroadster wrote:
Sun Jun 09, 2019 9:11 am
I might ask, what is the alt your using, and what are the readings on a digital meter, amps and voltage?
How high for how long?
The newer designed alternator's field design (square wave ) may and should read high on the gauge for the original alt.
Yes, please. What alt are you using, Phil?
Pete
-------------------------------------
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Re: High amp alternator wiring idea.

Post by fj20spl311 » Mon Jun 10, 2019 1:46 am

I have used lots of them from IR B210 on the right side of a U20, Stock FJ20, IR circa 1984 ~ 65 amps, I am now using the mini single wire alternator on my U20, also 65 amps I think. The car with an Amp meter SRL311 00148. It has the mini single wire alternator on the right with a modified smog pump bracket. When you first start it, I need to keep the RPM under 2000 or it pegs the amp meter. The needle goes to about 10 degrees past 30 amps. The battery is good, so it takes a surface charge pretty fast and the charging is under control after 1 -2 minutes. I don't care about the actual charging rate, voltage is 13.2Volts. I just don't want to "burn" the meter and would like it to look like its working correctly.
Phil
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Re: High amp alternator wiring idea.

Post by spyder » Wed Jun 12, 2019 1:21 am

I replaced the ammeter with a voltmeter and ran a heavy wire from the alt to the battery.

viewtopic.php?f=3&t=15556#p122713

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Re: High amp alternator wiring idea.

Post by Curtis » Wed Jun 12, 2019 9:10 am

spyder wrote:
Wed Jun 12, 2019 1:21 am
I replaced the ammeter with a voltmeter and ran a heavy wire from the alt to the battery.

viewtopic.php?f=3&t=15556#p122713
Yup, did the same. Works great. 50 amps is plenty.
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Re: High amp alternator wiring idea.

Post by ppeters914 » Wed Jun 12, 2019 9:38 am

fj20spl311 wrote:
Mon Jun 10, 2019 1:46 am

[snip]

I have used lots of them from IR B210 on the right side of a U20, Stock FJ20, IR circa 1984 ~ 65 amps, I am now using the mini single wire alternator on my U20, also 65 amps I think. The car with an Amp meter SRL311 00148. It has the mini single wire alternator on the right with a modified smog pump bracket.
What specifically is the mini single wire alternator? TechWiki only mentions 3-wire.
Pete
-------------------------------------
'67 1600 - frame off in progress. What a stupid idea. :smt021
'66 1600 - parts car
'66 WPL411 - no engine or trans. If I was smart, I would sell it.
A couple of Porsches, a pickup, and a motorcycle

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Re: High amp alternator wiring idea.

Post by greydog » Wed Jun 12, 2019 10:21 am

Mine is 35 amp rated but tested to produce 45 amps peak.
Amazon....New Mini Alternator 1 wire install 100211-1660.
Comes with v-groove pulley. Truly simple 1 wire connection. I wired in a fuse, then directly to the white power wire.
Ammeter works as it should. Provides enough power to run the radiator cooling fan wiht the lights on ans still not show discharge (all lights but the headlights are led now tho).
When the car starts, you have to blip the throttle (maybe 1500 or so) to start it charging.
Dan
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Re: High amp alternator wiring idea.

Post by redroadster » Wed Jun 12, 2019 3:58 pm

The 3 wire , one for the field , 1 to the fuel pump relay/ cnt. Unit if the engine should get killed but fuel still pumping in a wreck
1 for volt meter etc.
The crank sensor and pcm did away with the need for them

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Re: High amp alternator wiring idea.

Post by Curtis » Wed Jun 12, 2019 4:01 pm

redroadster wrote:
Wed Jun 12, 2019 3:58 pm
The 3 wire , one for the field , 1 to the fuel pump relay/ cnt. Unit if the engine should get killed but fuel still pumping in a wreck
1 for volt meter etc.
The crank sensor and pcm did away with the need for them
Photo?
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Re: High amp alternator wiring idea.

Post by Toptech360 » Wed Jun 12, 2019 6:52 pm

ppeters914 wrote:
Wed Jun 12, 2019 9:38 am
fj20spl311 wrote:
Mon Jun 10, 2019 1:46 am

[snip]

I have used lots of them from IR B210 on the right side of a U20, Stock FJ20, IR circa 1984 ~ 65 amps, I am now using the mini single wire alternator on my U20, also 65 amps I think. The car with an Amp meter SRL311 00148. It has the mini single wire alternator on the right with a modified smog pump bracket.
What specifically is the mini single wire alternator? TechWiki only mentions 3-wire.
Ive often seen 3wire alternator s (a stud for one wire and 2 wires to a plug) marketed as one wire alternators. It's kinda confusing. The tech wiki has info on the denso alternator I used. My application was with a charge light (1964 spl310) not an ammeter.
Dan
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