Community
Message Forum
Photo Gallery
Event Calendar
Book Reviews
Bronco Wallpaper
Bronco FAQ
Link Back to CB!
Photo Gallery
Event Calendar
Book Reviews
Bronco Wallpaper
Bronco FAQ
Link Back to CB!
Buy / Sell
Bronco Tech
3 Arm Wiper Setup
Fix Motor Mount
Roll Cage Braces
Throttle Body 65mm
Wheel Alignment
Heat Riser Replacement
Vent Window Repair
Center Console Mount
Straighten Bumper
Ford 6R80 6 spd
More Tech...
Fix Motor Mount
Roll Cage Braces
Throttle Body 65mm
Wheel Alignment
Heat Riser Replacement
Vent Window Repair
Center Console Mount
Straighten Bumper
Ford 6R80 6 spd
More Tech...
-
Welcome to ClassicBroncos! - You are currently viewing the forums as a GUEST. To take advantage of all the site features, please take a moment to register. It's fast, simple and absolutely free. So please join our community today!If you have problems registering or can't log into your account, please contact Admin.
One wire 3G alternator
- Thread starter turbotim2
- Start date
Small case 90 amp or large case 130 amp?
2g for 90 or 1g to 1/0g for 130 by the charts. A fuse or circuit breaker is suggested.
Those numbers for wire gauge are a full output, doubtful that you would actually pull that. Aftermarket kits, like WH's, don't appear to use 1g for their 130 amp.
2g for 90 or 1g to 1/0g for 130 by the charts. A fuse or circuit breaker is suggested.
Those numbers for wire gauge are a full output, doubtful that you would actually pull that. Aftermarket kits, like WH's, don't appear to use 1g for their 130 amp.
Last edited:
Jdgephar
Bronco Guru
- Joined
- Sep 25, 2012
- Messages
- 1,331
Since your distances are short, you can use 8 gauge or bigger. The reason for this is that you are not going to be anywhere near 130 amps output for any length of time. Most operation will be under 30 amps. However, if you plan on running winches, welders, or big electric fans for any length of time, then go to a larger wire size. Save the expense of the larger wire to go from your battery to your starter, and your engine ground back to the battery.
- Joined
- Nov 3, 2003
- Messages
- 47,744
904 is correct. We use 6-gauge and 175 amp mega fuses for our charge cable kits.
That is typically more than sufficient for the short run of this cable. Roughly 2 1/2 feet if I were to guess.
And when you say “one wire“ are you referring to a specialty version, such as Wild Horses sells? Or are you talking about a standard 3G?
That is typically more than sufficient for the short run of this cable. Roughly 2 1/2 feet if I were to guess.
And when you say “one wire“ are you referring to a specialty version, such as Wild Horses sells? Or are you talking about a standard 3G?
Steve83
Bronco Guru
The specialty 1-wire 3Gs use at least 2 wires; a heavy output wire and a small turn-on wire. Common reliable 3Gs have 1 additional wire (parallel to the heavy output) and a short jumper wire, so it's really not worth the risk, hassle, or cost. As this page shows, all the wires needed for a common 3G are already in the eB harness, right there, ready to be used.
(click this text)
(click this text)
Broncobowsher
Total hack
- Joined
- Jun 4, 2002
- Messages
- 34,983
Here is the thing about wire gauge, it is about controlling voltage drop. And why it really doesn't matter so much on an alternator.
Lets say you have a 100A alternator with a 14.7V setpoint. You fire up the rig that you have been listening to the radio for a few hours and it is run down to 12.0V. That alternator will be at full output to bring the battery up. Lets say you have a half volt voltage drop at that 100A load. What's really happening? The wire is acting like a resistor. Half volt at 100A is 50 watts of energy being lost. It goes to heat. About what an upgraded highbeam headlight puts out. That amount of heat is spread out across the whole wire, radiated off the surface, conducted through the attachment points.
As the battery is charged the amperage output drops off. While this happens so does the voltage drop. Lets say you take 40A to drive, this is about what EFI with wipers, headlights, and old school A/C will draw. I checked it once. That 40A load will reduce the voltage drop to about 0.2V. Now the lost power, and heat dissipation is down to about 8 watts.
That is the math behind why a wire does what it does and why it needs to be sized. If you can't handle the heat dissipation, either the amperage needs to drop or the wire gauge needs increase. But it isn't a magic it works or it doesn't size for everything.
Go back to original starter motors that can draw 300-400 amps of current, on a dainty little 6-gauge wire or so. It's easy to get a full volt drop in that wire. There is 300-400 watts of heat that wire must handle. But it is only handling it for a few seconds. The starter upgrade of going to 4-gauge or even 2-gauge wire was to cut the voltage drop to the starter. Not really the added amperage capacity, but the reduced voltage drop. More voltage to the starter, it spins faster. If you look at many aftermarket starter motors you will see them rated in kw. FYI, 0.746 kw = 1 HP so you can also do this with starters that have a HP rating with a little conversion). If you drop 200 watts of heat dissipation, that is 200 watts more for the starter (0.2kw).
Amperage through a circuit doesn't change regardless of the length of the wire. Very large buildings with a central HVAC system will often have thermostats that measure temperature and will output in mA current. The length of the wire, less than perfect splices in the wire, etc. won't matter. Amperage through a circuit doesn't change regardless of voltage drop.
To that there is still a case where wire can be too small for a charge circuit. The stock 10 gauge charge wire, inside a harness, with a splice at the ampmeter. Try running 130A through that and you will have a lot of heat. Being inside a bundled harness the heat can't escape. That is where you melt a wiring harness. Drop 2V, you have 260 watts of heating element and no place to let that heat out.
If you are running a charge wire from the alternator straight to the battery, 90A and 8 gauge is probably fine if left out in the open to stay cool. Want to bundle that into a harness, not let heat escape, you are going to have to go larger. Heat managment, don't let the wire generate as much heat with you have it in a bundle that can't get rid of heat. Running a lot of high amp sustained loads, where the alternator won't be backing off to a lower output level, go a little larger again. How far to go? I want to say an OEM 200A alternator with the charge wire in a harness, as bad as it gets, is about a 2 gauge wire. There is no reason a 90 or even 130A load will need 2-gauge. That is "I don't understand wiring, go bigger, and bigger, and someone else told me that it should be bigger" internet wire sizing. No engineering went into it. Go to a worst case possible generic wire size chart.
OK, enough rant. What is the OEM wire size for that size alternator? Probably don't need 5 sizes larger.
Lets say you have a 100A alternator with a 14.7V setpoint. You fire up the rig that you have been listening to the radio for a few hours and it is run down to 12.0V. That alternator will be at full output to bring the battery up. Lets say you have a half volt voltage drop at that 100A load. What's really happening? The wire is acting like a resistor. Half volt at 100A is 50 watts of energy being lost. It goes to heat. About what an upgraded highbeam headlight puts out. That amount of heat is spread out across the whole wire, radiated off the surface, conducted through the attachment points.
As the battery is charged the amperage output drops off. While this happens so does the voltage drop. Lets say you take 40A to drive, this is about what EFI with wipers, headlights, and old school A/C will draw. I checked it once. That 40A load will reduce the voltage drop to about 0.2V. Now the lost power, and heat dissipation is down to about 8 watts.
That is the math behind why a wire does what it does and why it needs to be sized. If you can't handle the heat dissipation, either the amperage needs to drop or the wire gauge needs increase. But it isn't a magic it works or it doesn't size for everything.
Go back to original starter motors that can draw 300-400 amps of current, on a dainty little 6-gauge wire or so. It's easy to get a full volt drop in that wire. There is 300-400 watts of heat that wire must handle. But it is only handling it for a few seconds. The starter upgrade of going to 4-gauge or even 2-gauge wire was to cut the voltage drop to the starter. Not really the added amperage capacity, but the reduced voltage drop. More voltage to the starter, it spins faster. If you look at many aftermarket starter motors you will see them rated in kw. FYI, 0.746 kw = 1 HP so you can also do this with starters that have a HP rating with a little conversion). If you drop 200 watts of heat dissipation, that is 200 watts more for the starter (0.2kw).
Amperage through a circuit doesn't change regardless of the length of the wire. Very large buildings with a central HVAC system will often have thermostats that measure temperature and will output in mA current. The length of the wire, less than perfect splices in the wire, etc. won't matter. Amperage through a circuit doesn't change regardless of voltage drop.
To that there is still a case where wire can be too small for a charge circuit. The stock 10 gauge charge wire, inside a harness, with a splice at the ampmeter. Try running 130A through that and you will have a lot of heat. Being inside a bundled harness the heat can't escape. That is where you melt a wiring harness. Drop 2V, you have 260 watts of heating element and no place to let that heat out.
If you are running a charge wire from the alternator straight to the battery, 90A and 8 gauge is probably fine if left out in the open to stay cool. Want to bundle that into a harness, not let heat escape, you are going to have to go larger. Heat managment, don't let the wire generate as much heat with you have it in a bundle that can't get rid of heat. Running a lot of high amp sustained loads, where the alternator won't be backing off to a lower output level, go a little larger again. How far to go? I want to say an OEM 200A alternator with the charge wire in a harness, as bad as it gets, is about a 2 gauge wire. There is no reason a 90 or even 130A load will need 2-gauge. That is "I don't understand wiring, go bigger, and bigger, and someone else told me that it should be bigger" internet wire sizing. No engineering went into it. Go to a worst case possible generic wire size chart.
OK, enough rant. What is the OEM wire size for that size alternator? Probably don't need 5 sizes larger.
Steve,The specialty 1-wire 3Gs use at least 2 wires; a heavy output wire and a small turn-on wire. Common reliable 3Gs have 1 additional wire (parallel to the heavy output) and a short jumper wire, so it's really not worth the risk, hassle, or cost. As this page shows, all the wires needed for a common 3G are already in the eB harness, right there, ready to be used.
(click this text)
Your diagram shows that a new 4 gauge wire needs to be added going from the alt to the starter relay. It also says "with factory style voltage regulator" but I assume that is deleted since the alt is internally regulated.
I don't have a lot of high draw accessories but I do have a finicky Holley Sniper that is looking for 14v at idle, that is really the only reason I am looking to upgrade.
Steve83
Bronco Guru
Yes, the output cable has to be large enough to handle the 3G output, of course; and the original cable sized for ~40A won't do it. But that's just from the alt. output stud to the starter relay by the battery. The voltage regulator wires are all there & available when you delete the 1G VR, so it's not like you have to rewire the harness for the common 3G VR to work. And it's more reliable than the "1-wire" version (which has at least 2 wires).
ntsqd
heratic car camper
I use Ancor Marine's resources page for sizing low voltage (<50VDC) DC conductors. When I worked thru sizing the cables to charge our camper's batteries (2X 2GC's) at a max of 80 amps the cable was pretty small until I realized that the voltage drop was too great and such a system would barely supply a high enough voltage to those batteries to charge them. Voltage drop in the conductors when charging a battery has proven to be far more a concern than actual conductor ampacity. Doesn't take much voltage drop to slow the charging to a trickle. When I ran thru the process again using 3% as my max allowable voltage drop with 80 amps the result was 6 gauge cables for both power and ground. Keep in mind that this is for a total circuit length of over 20 feet. I arrived at 80 amps somewhat arbitrarily. The truck's alternator is rated 130A, but I knew that full output would be rare. I did want to be able to pump some reasonably serious current just in case, but full alternator capacity didn't seem likely, so I 'de-rated' the output to 80 amps and based my conducotr sizing and breaker choices on that.
Not a fan of "One Wire" alternators as they do not self-excite at idle unless first rev'd up. The early units had low power delivery at idle, don't know if that has changed. IMHO they give up too much for convenience in wiring that isn't all that big of a deal to start with.
Not a fan of "One Wire" alternators as they do not self-excite at idle unless first rev'd up. The early units had low power delivery at idle, don't know if that has changed. IMHO they give up too much for convenience in wiring that isn't all that big of a deal to start with.
Broncobowsher
Total hack
- Joined
- Jun 4, 2002
- Messages
- 34,983
When I had my Sniper it wasn't happy with the stock charging system. It was a '77 F250, but for all pratical purposes the same charging system as a Bronco. I swapped it out for https://www.amazon.com/gp/product/B007Y87USQ/?tag=classicbroncos-20
Did have to swap the pulley and spacer behind the pulley, and pick up a metric bolt for the adjuster arm. It bolted right in. No belt issues. Wiring was pretty simple.
After that the Sniper rarely threw up any over/under voltage alerts. Headlights no longer dimmed at idle. Everything was happy.
There are 3 wires to hook up (not counting the ground which is hopefully good)
The charge wire,
Turn on wire, tied to the ignition switch, picked up off the old voltage regulator.
Then the one that people put "the little jumper wire" one, but I did it correctly. That is the sense wire. It goes back to the battery, actually the first junction point after the battery at the starter solenoid. It is there to sense the actual battery voltage, not the alternator output voltage. People do the jumper because they are lazy and it is quick and often good enough. The team that developed that alternator knew that they wanted the battery charged, so they put a sense wire on the battery to really know what was happening. Even the original 60's style alternator has a direct to battery sense wire on it. Corrects for voltage drop in the wiring.
Did have to swap the pulley and spacer behind the pulley, and pick up a metric bolt for the adjuster arm. It bolted right in. No belt issues. Wiring was pretty simple.
After that the Sniper rarely threw up any over/under voltage alerts. Headlights no longer dimmed at idle. Everything was happy.
There are 3 wires to hook up (not counting the ground which is hopefully good)
The charge wire,
Turn on wire, tied to the ignition switch, picked up off the old voltage regulator.
Then the one that people put "the little jumper wire" one, but I did it correctly. That is the sense wire. It goes back to the battery, actually the first junction point after the battery at the starter solenoid. It is there to sense the actual battery voltage, not the alternator output voltage. People do the jumper because they are lazy and it is quick and often good enough. The team that developed that alternator knew that they wanted the battery charged, so they put a sense wire on the battery to really know what was happening. Even the original 60's style alternator has a direct to battery sense wire on it. Corrects for voltage drop in the wiring.
