Thread: How many AMPs does my alternator have to put out?

watts = Amps x Volts
Amps = Watts / Volts
191.666 = 2300 / 12

Yea 12v is the "commonly known value" but vehicle voltage is regulated to 13.8V when the vehicle is running. Actual alternator voltage ranges from 13.6-14.4V depending on RPM and age.
On battery power amp current doesn't really come into play -> but 160Amps will kill a battery in minutes so thats a non-issue.

Originally Posted by HiJackZX1

Its a Duralast battery..... Its about a year old, after my install killed the original.
I basically just added all the watts that the manufateurs of the items have listed. I assume its the max it will need.

Thats probably the safest method although realistically max current draw would be a lot lower. Theres lots of variables that come into play, like initial draw verse continuous draw but i'll spare the technical stuff. Only thing to make sure is that your looking at current used not current produced which can be different based on voltage, efficiency, etc.

Originally Posted by HiJackZX1

With me its the other way around, the belt is the easy thing. It has an auto tensioning pulley that keeps the belt tight. The people in the Dakota-Durango forum said it will not be an issue. Its basically the brackets that will be the issue, because the engine is awkward.
Thanx for correcting me, so that means the 220 amp alternator can provide plenty of power, with alot to spare.
I always thought HIDs use more power?

Well yes with a stock configuration (straight alternator replacement or a/c compressor replacement). For dual alternators with a custom bracket, belt routing can be a little tricky. If I remember correctly durangos use a serpentine belt setup with a spring tensioner. In custom setups you need to swap in a larger belt with possibly different sized idler pulleys and depending on placement the tensioner can actually become a disadvantage. The tensioner applies a varied force depending on position (which is really cool because you can use it to guage belt wear), but if the belt routing changes significantly it can provide the wrong amount of tension causing problems. Just a heads up if you go with completely custom dual alternators (which I don't think you need).

Yup should be more then enough power. Can't comment on the battery without seeing specs but I would recommend not running the system on battery unless its a deep cycle->you'll do permanent damage pretty quick.

Your average cars headlights are 40-50watts with 50-60watt high beams. Most HID kits are 35watts total continuous draw. If you know where to look you can find a 50watt kit but i've never seen more then that. While its true the ignition voltage for the headlights is in the 1000's of volts, this only lasts about a mili-second.

Originally Posted by justchat_1

Yea 12v is the "commonly known value" but vehicle voltage is regulated to 13.8V when the vehicle is running. Actual alternator voltage ranges from 13.6-14.4V depending on RPM and age.
On battery power amp current doesn't really come into play -> but 160Amps will kill a battery in minutes so thats a non-issue.

I have no idea what the new alternator runs at, infact, I have no idea what the factory one puts out either, lol.

Thats probably the safest method although realistically max current draw would be a lot lower. Theres lots of variables that come into play, like initial draw verse continuous draw but i'll spare the technical stuff. Only thing to make sure is that your looking at current used not current produced which can be different based on voltage, efficiency, etc.

I agree with you.

Well yes with a stock configuration (straight alternator replacement or a/c compressor replacement). For dual alternators with a custom bracket, belt routing can be a little tricky. If I remember correctly durangos use a serpentine belt setup with a spring tensioner. In custom setups you need to swap in a larger belt with possibly different sized idler pulleys and depending on placement the tensioner can actually become a disadvantage. The tensioner applies a varied force depending on position (which is really cool because you can use it to guage belt wear), but if the belt routing changes significantly it can provide the wrong amount of tension causing problems. Just a heads up if you go with completely custom dual alternators (which I don't think you need).

Here is the setup I came up with.



I tried to keep it very similar to what I have now. Obviously I will need a longer belt, but not much longer. What do you guys think?

Your average cars headlights are 40-50watts with 50-60watt high beams. Most HID kits are 35watts total continuous draw. If you know where to look you can find a 50watt kit but i've never seen more then that. While its true the ignition voltage for the headlights is in the 1000's of volts, this only lasts about a mili-second.

So why do I always read, that when installing HID lights, you have to upgrade all the electrical wires, because HIDs will fry the stock wires.

I assume the belt tensioner is on the far left? In that case the above setup should work fine. Just make sure the new belt is the same type as the old belt.

Regarding the HID:
For the most part thats not even remotely true->the wires the get replaced go from the ballest controller to the actual lights but for safety reasons on the higher-end units that wire cannot be disconnected. All of the stock wiring can be used right up to the ballest controllers (and most people leave the ballest controllers right behind the headlights-even though I think it looks tacky). HID's draw a lot of current for such a short period of time that it really doesn't cause any problems.

Originally Posted by justchat_1

I assume the belt tensioner is on the far left? In that case the above setup should work fine. Just make sure the new belt is the same type as the old belt.

Regarding the HID:
For the most part thats not even remotely true->the wires the get replaced go from the ballest controller to the actual lights but for safety reasons on the higher-end units that wire cannot be disconnected. All of the stock wiring can be used right up to the ballest controllers (and most people leave the ballest controllers right behind the headlights-even though I think it looks tacky). HID's draw a lot of current for such a short period of time that it really doesn't cause any problems.

Yes the tensioner is to the left. Thankfully all American cars seem to use the same 6 ribbed belt. I have been having a discussion in the Dakota-durango forums and some said, "Why not just add a pulley to the 1st alternator and add a second small belt. I actually thought it was a cool idea, but spacing may be an issue. Also trying to find a belt that small is an issue too. I think it would just be better to go the route I pictured above. It requires more design work, but will be easier to maintain in the future.

Thats good to know about the HID lights.

Originally Posted by soundman98

just wanted to comment on the HID's: i have a set in my car-- i have not replaced any of the factory wiring-it was all plug and play. for the other people that i have talked to with hids, and similar cars, they swear that using one of those hid power kits make the lights turn on faster, and are slightly brighter. though my cars lighting power wires are kind of known to burn up with higher power lights/dirty sockets...

so, it is best to upgrade the wires, and you might get better performance, but it is not required.

i occasionally have issues with the headlights not turning on with the car--my car keeps the last position the lights were and turns them on after the car is started (technically, as the car is starting, they flicker on and off and back on as i cycle the key to start the motor). usually my left light will turn on, but not the right light-- but only when set to automaticly turn on(probably beccause of the current draw from the starter-- there is not enough left over to start the hids.).

if i manually turn them on after the car is started, i usually have no issues with both coming on.

My friend has all the same problems you describe. Infact for his to work properly, he has to leave the high beam setting turned on, otherwise the HIDs will turn off. I think that was the other reason I thought they used more power. He does tend to do things half @$$ed, so it could just be they were installed wrong.

Originally Posted by HiJackZX1

My friend has all the same problems you describe. Infact for his to work properly, he has to leave the high beam setting turned on, otherwise the HIDs will turn off. I think that was the other reason I thought they used more power. He does tend to do things half @$$ed, so it could just be they were installed wrong.

Yea I would bet on a half assed setup...or in used car terms "a giant hack job". Although it could also be he cheaped out and got a single phase HID kit (only low beam no high beam) and hooked it up wrong. Any decent HID kit is incredibly simple to setup->for most its 3 steps (same thing on each side).
1) Remove factory bulb from headlight housing and unplug the bulb from the wire.
2) Plug that wire into the matching connector on the ballast controller.
3) Take the new hid bulb (which should be attached to the ballast controller with a very thick cable) and insert it into the headlight assembly. Done.
Some kits have two extra steps:
4) Connect the very long red wire to the vehicle battery
5) Connect the black wire to an exposed bolt

Originally Posted by HiJackZX1

Yes the tensioner is to the left. Thankfully all American cars seem to use the same 6 ribbed belt. I have been having a discussion in the Dakota-durango forums and some said, "Why not just add a pulley to the 1st alternator and add a second small belt. I actually thought it was a cool idea, but spacing may be an issue. Also trying to find a belt that small is an issue too. I think it would just be better to go the route I pictured above. It requires more design work, but will be easier to maintain in the future.

Yea the dual pulley setup is one i've seen quite a bit. The cool thing about it is if your not going to be blasting your system at 100%, grab a wrench and you can remove the extra belt and save some gas.

You seem like you got everything planned out then. Just make sure you use fusible links on the power wires coming out of the amp. I would also recommend either a dual battery setup or at least running each line all the way to the battery instead of daisy chaining. It's probably overkill but I have seen a few people that will never use a single battery with dual alternators. The theory being that since each alternator is producing a rectified sine wave output, if the waves aren't in phase you can get spikes/sags due to interference. How true this is with modern alternators I couldn't tell you though.

Originally Posted by HiJackZX1

Thats good to know about the HID lights.

Upgrading wiring is not gonna change the voltage sag when the starter motor is cranking-all that does is give people a warm fuzzy feeling inside. I would also bet that in upgrading the wiring these users didn't change the circuit breakers or source wiring for those circuits either. It would be like hooking up a fire house to a regular garden hose spigot->it won't change the flow at all.

Cheaper HID units fire ignition as soon as they receive power and then thats it. If voltage is too low to ignite, then one or both bulbs may fail to light. The more expensive HID units measure current draw and will keep retrying to ignite if power isn't being drawn for up to a few seconds.

Theres a few ways to fix this. The easy one, like soundman said would be to turn the lights on after the engine starts. You could also use a larger battery to prevent the voltage sag or a capacitor on your big draw items (like the amplifier) to minimize the voltage drop.

Oh and that reminds me->if you do any SPL contests or similar where you'll be squeezing every ounce of power out of the system, you'll want to up your idle speed. Alternators produce only a portion of their rated power at idle. I think the sweet spot is somewhere around 1100-1500rpm.

How about using a capacitor for the audio system...
this not only will make it sound better, it will stabilize the electrical system of the vehicle.

check: http://www.crutchfield.com/p_120PP10...apacitor&ssi=0