Upgraded alternator requires upgraded wiring?

[Ed_Flecko]

I often hear of people who upgrade their alternators to higher amperage models. I've always wondered if doing this type of upgrade has any benefit to the average car/truck, or is it only something you need to do if you have the additional power needs (stereo, winch, etc., etc.) on your vehicle?

If you do install a higher amperage alternator, do you have to upgrade any of your existing stock wiring, or will the stock wiring harness be just fine?

Ed

 

[michaelluscher]

Some of us have to do upgrades just to bring performance up to normal standards.

 

[Lubener]

Only if you increase the load, otherwise the new alternator will loaf along until the demand is needed.

 

[eljefino]

It's worthwhile even on stock alternators. They know they lose a few percent in the wiring (10 gauge for 100 amps!) and use a 2nd wire from the ignition switch back so the alt can sense how much system voltage there is. It'll then overdrive itself so the heart of the car winds up with the right voltage, and is cheaper than putting more copper in the harness.

OTOH a car loafing along at 20-30 amps with normal loads won't have much drop on the wiring. Add a rear defroster, AC, and rad fan and you start noticing.

 

[qdeezie]

I can't speak for all alternator designs, but on the alternators I've upgraded; whether it be the alternator or the wiring (or both) it was well worth it and the wire that goes back to the battery always seemed to be on the smallish side. I always upgraded them to 4 gauge from what appeared to be either 8 gauge or 10 gauge.

In the instance of my 1990 F150, calling the factory alternator junk would be an insult to real junk. The upgraded alternator was leaps and bounds better than the factory less than junk alternator.

On my Focus, I upgraded the wiring when I installed a brand new aftermarket alternator because I felt that the wiring was rather puny and there was a flickering light issue that I sought to get rid of (which I attributed to old and inadequate wiring - and it was).

 

[HerrStig]

I've seen many alternators where the ground return was through the bracket, into the block, and back to the battery through the existing wire. A wire from the alternator body right to the battery negative diesn't hurt. You can measure the drop by turning everything on and putting one DVM lead on the alternator body and the other on the negative terminal of th ebattery. Works for the positive drop as well but you need to go from hot terminal to hot terminal,

 

[Ed_Flecko]

Originally Posted By: Lubener
Only if you increase the load, otherwise the new alternator will loaf along until the demand is needed.


If you do increase the load, what wires (theoretically) need to be upgraded?

Ed

 

[Johnny2Bad]

Generally speaking, an Automotive OEM is going to use the minimum wire gauge, but there are certainly exceptions. The reason is copper is expensive, relatively, and copper is heavy, relatively. Keeping manufacturing cost down and keeping weight down are objectives of the OEM.

If an upgrade alternator was available as an option on the vehicle, the wire gauge *may* be adequate for the higher amperage charging system. Similarly, there may be economies of scale to use the same wire gauges across a platform.

What is needed is to assess the needs, and then assess what you have installed.

To assess the needs, determine the amperage rating of the upgraded alternator, multiply by a safety factor (+25% - Minimum Recommended, up to +100%); and then measure the total length of the circuit (eg from battery to connection point and back to battery, ground point, etc).

The length is quite important as you can use a surprisingly small gauge of wire for very short lengths and carry a large amount of current (which is the basis for automotive fusible links).

You then check a chart to determine the recommended wire gauge. Be sure the chart is for DC current, preferably 12V, and not AC. AC is only at 100% flow twice per cycle, DC is at 100% flow all the time; thus going by AC will result in under-sized recommendations.

You are looking for a maximum voltage drop of 10% for any automotive circuit and I would recommend less in a battery/charging circuit. Do the calculation and use what you are comfortable with. Consider alternator output of 14.4V less 10% = 13.0V available to charge your battery. Not enough.

Please note the following:
Automotive wire gauge is not equal to American Wire Gauge (AWG); the Automotive stuff is smaller / lighter (added weight of vehicle rears it head again), so either use the correct chart or go up one gauge for proper Automotive-rated wire vs AWG

I recommend you use proper Automotive-rated wire (meets SAE J-1127, covering battery and ground connections), and you have a choice of PVC-Jacketed (type SGT) or Cross-Linked Poly Jacket.

Battery-rated Automotive wire in Cross-Linked Poly (XLPE) Jacket rated for -40C to +40C /-40°F to 257°F. You have a choice of type SGX and STX, with the latter having the lighter jacket.

Many people use welding cable, which will be AWG but note the jacket is not as durable which can lead to high current shorts, which is A Bad Thing. If you go this way, route with good practice (proper strain relief, consider motion such as engine block under load, interference with other components, etc) and be careful not to nick the jacket in installation.

Use one of the following charts:

SAE Automotive Wire:
http://news.waytekwire.com/automotive-wire-gauge-guide/

AWG:
http://www.supercircuits.com/resources/tools/voltage-drop-calculator

 

[Johnny2Bad]

Originally Posted By: Ed_Flecko
Originally Posted By: Lubener
Only if you increase the load, otherwise the new alternator will loaf along until the demand is needed.


If you do increase the load, what wires (theoretically) need to be upgraded?

Ed


Battery ground to chassis wire;
Chassis to engine block wire;
Alternator positive (+) to battery positive (+) wire

Sometimes the starter (+) needs attention as well, and it's OK to go crazy and do some overkill here, because the current is extremely high ... higher than your alternator current by a long shot ... during starting, and it's usually not a particularly long wire so not much weight penalty.

Also, the reason for the higher output alternator is ... ? Be sure whatever that is, assuming it's some kind of add-on or aftermarket device, has proper rated wire. For example maybe you have switched to electric fan from engine-driven with a 40A startup load. Do the same math for this wire (total circuit including to ground) and size accordingly.

Be sure there are good mechanical grounds at Alternator and Starter, and sometimes body grounds need to be checked. They are a bit tricky but for example the trunk or front clip may have ground connections to chassis ground.

 

[Ed_Flecko]

Originally Posted By: Johnny2Bad
Generally speaking, an Automotive OEM is going to use the minimum wire gauge, but there are certainly exceptions. The reason is copper is expensive, relatively, and copper is heavy, relatively. Keeping manufacturing cost down and keeping weight down are objectives of the OEM.

If an upgrade alternator was available as an option on the vehicle, the wire gauge *may* be adequate for the higher amperage charging system. Similarly, there may be economies of scale to use the same wire gauges across a platform.

What is needed is to assess the needs, and then assess what you have installed.

To assess the needs, determine the amperage rating of the upgraded alternator, multiply by a safety factor (+25% - Minimum Recommended, up to +100%); and then measure the total length of the circuit (eg from battery to connection point and back to battery, ground point, etc).

The length is quite important as you can use a surprisingly small gauge of wire for very short lengths and carry a large amount of current (which is the basis for automotive fusible links).

You then check a chart to determine the recommended wire gauge. Be sure the chart is for DC current, preferably 12V, and not AC. AC is only at 100% flow twice per cycle, DC is at 100% flow all the time; thus going by AC will result in under-sized recommendations.

You are looking for a maximum voltage drop of 10% for any automotive circuit and I would recommend less in a battery/charging circuit. Do the calculation and use what you are comfortable with. Consider alternator output of 14.4V less 10% = 13.0V available to charge your battery. Not enough.

Please note the following:
Automotive wire gauge is not equal to American Wire Gauge (AWG); the Automotive stuff is smaller / lighter (added weight of vehicle rears it head again), so either use the correct chart or go up one gauge for proper Automotive-rated wire vs AWG

I recommend you use proper Automotive-rated wire (meets SAE J-1127, covering battery and ground connections), and you have a choice of PVC-Jacketed (type SGT) or Cross-Linked Poly Jacket.

Battery-rated Automotive wire in Cross-Linked Poly (XLPE) Jacket rated for -40C to +40C /-40°F to 257°F. You have a choice of type SGX and STX, with the latter having the lighter jacket.

Many people use welding cable, which will be AWG but note the jacket is not as durable which can lead to high current shorts, which is A Bad Thing. If you go this way, route with good practice (proper strain relief, consider motion such as engine block under load, interference with other components, etc) and be careful not to nick the jacket in installation.

Use one of the following charts:

SAE Automotive Wire:
http://news.waytekwire.com/automotive-wire-gauge-guide/

AWG:
http://www.supercircuits.com/resources/tools/voltage-drop-calculator





Thank you...this is good information!

Ed

 

[Johnny2Bad]

I should have added that the charts/calculators are based on wire in free air; if you use a jacket or wire loom you need to compensate for the added heat retention. In fact in essence you can say that all the recommendations are based on heat; every wire carrying a current wastes energy by heating up. As it heats up, it's current carrying capacity falls, which causes more wasted heat, which causes more loss of capacity ... well, you get the idea.

 

[Johnny2Bad]

An alternative to running complete wire to replace existing, you may find you can run a wire of identical SAE or AWG gauge alongside existing wire. 2 wires of the same gauge = 3 GA increase; ie 2x 10 AWG = 7AWG.

Brass connectors (such as a lug to connect to a post) are inherently non-corrosive.

Invest in a large-gauge crimp tool the hammer-type is least expensive; Pro-grade is again expensive but Chinese-made copies can be found for about $30.

I am of the solder + crimp school but there are those who crimp only. Care must be taken with solder as it creates a stiff joint but with proper strain relief it's not an issue.

If you want to go that route, heat the stripped wire with a heat gun, apply solder to the wire. Then crimp, then re-heat with the heat gun and add solder as required to fill the lug. Use Eutectic solder which is 37/63 tin/lead. There is no need to use ROHS solder which is much harder to work with (higher melting temp); Automotive applications are exempt from ROHS, even in Europe.