When is a high output alternator needed?

[James909]

Hi all, quick question. I was just curious when it is necessary to put in a high output alternator? I have a 500 watt RMS amp powering two 12" subs which according to my math should draw about 60 amps. The alternator in my Yukon just died and the regular replacement is a 105 amp alternator. Should I go with say a 140 amp alternator? Also there is a possibility of me adding a 50W x 4 amp for the speakers so please take that into account as well. Thanks for any help anyone can offer.

 

[aznboi3644]

if your voltage is dropping into the battery reserve for long periods than a high output alternator is needed

The cutoff point for me is if the voltage drops below 12.5 volts upgrades are needed. Not necessarily a new alternator but electrical upgrades

 

[specialized7]

by electrical upgrades do you mean the big three?
or is there other things you can do?

 

[BigBoom]

you can add batteries to help supply it. anything over 1000 watts i'd look into alternator upgrades. if you're needing to replace an alternator now, i'd go ahead and get the biggest you can. mine went out today too. drove home on battery reserve gotta get a replacement till i get my high output fixed

 

[aznboi3644]

replace every ground you can find...including underneath the truck

 

[James909]

Thanks for the input guys. I think I'll spend a little extra money for a 140 amp which should be more than enough for my mild system. Also I plan to upgrade the wiring.

 

[jshak07]

you dont need a HO alt for 1000 watts. There are alot more factors that play in there. How much battery bank do you have, what kind of wire do you have, what kind of engine wires do you have upgraded? If you are having electrical problems than upgrade you wire to 1/0 or 2/0 welding cable, add a good battery or two to support your amp(s), upgrade all your grounds to 1/0 or 2/0 cable. Do the Big 3 in 1/0 or 2/0

 

[aznboi3644]

either way...if he can afford it...a bigger alternator will only improve the overall electrical system

 

[jshak07]

ya but for a mild system there should are smaller upgrades that are still necessary that should be done first.

 

[meterman1976]

Ok. What do you mean by the big 3?

 

[ShakesAllDay]

Ok. What do you mean by the big 3?

I believe it's enhancing/adding wiring to these three things

1.) neg. battery post to frame/chassis
2.) pos. battery post to alternator
3.) engine to frame/chassis

Basically, it is creating less resistance in the electrical system.

Do a Google search for "Big 3 electrical". There are many "how-to's" out there.

If you are gonna take the time to do it, I would not use anything less than 4ga. wire. Preferably 1/0.

I only performed #1 on a 2005 Toyota Corolla (OEM looked to be about 10ga.) and used 4ga. I could tell an immediate reduction in headlight dimming. It didn't eliminate it, but it was better. I was only running about 40-45amps, so I chose 4ga (plus I already had the wire).


edit: To the OP: How did you come about your estimation of 60amps? Using the formula A = W/V, I end up with...

A = 500w / 12.6v
A = 40a

 

[James909]

Thanks guys. Let me just clarify a little bit. I don't know if I am actually having voltage problems as I don't actually have the subs installed yet. I'm getting the subs for Christmas, I should have stated that in my original post. Also I plan on upgrading the Big 3 with 1/0 wire when I install the subs. Since the alternator just stopped charging I figured since I was planning on installing the subs I would get a higher output alternator if you guys thought I needed it. But for some reason soon after I made the initial post the alternator started charging again. Probably worn brushes so I would imagine it's going to stop charging again. But now hopefully I will get the subs installed and test it before the alternator stops charging for good. Then I can decide if I want a higher output or not.

ShakesAllDay, I don't know if this is correct or not but since amps only operate at about 60% efficiency I figured that if the amp is outputting 500 watts than it would actually be drawing about 800 watts. Also I used 14 volts since I'm trying to calculate the amperage with the truck running. So 800W/14V = ~60A

 

[ShakesAllDay]

ShakesAllDay, I don't know if this is correct or not but since amps only operate at about 60% efficiency I figured that if the amp is outputting 500 watts than it would actually be drawing about 800 watts. Also I used 14 volts since I'm trying to calculate the amperage with the truck running. So 800W/14V = ~60A

I see. Thanks for the clarification.

I'm not sure how efficiency ratings apply to advertised output. I know there have been voluntary regulations in place that require specific parameters on CEA-2006 compliant equipment. Not sure if efficiency is factored in or not.

Interesting.

BTW, what size of fuse(s) does your amp(s) have?

 

[James909]

The amp (Alpine MRP-M500) has two 30A fuses.

 

[ShakesAllDay]

Nice. I have the previous model, the M450. Not sure why they call it that as it's a 400 watt amp, not 450. I had it on a 12" Infinity Kappa 124.7 in 1cu.ft. sealed... sounded good.

 

[BigBoom]

either way...if he can afford it...a bigger alternator will only improve the overall electrical system

yes indeed. why skimp on such an important part?

ya but for a mild system there should are smaller upgrades that are still necessary that should be done first.

those should be done regardless. then onto more pressing issues...like alternator power. it doesnt necessarily HAVE to be high output, but an upgrade in amperage is a good idea. also depends on how big the stock alt is and how big of a load it has to deal with on a day to day basis

 

[celly]

either way...if he can afford it...a bigger alternator will only improve the overall electrical system

That's kind of my view on the subject and why I'm going back to a HO alternator (mine just crapped out). If anyone's interested, I'm trying to build up a list of good suppliers of these alts here (thanks to Dan W for starting it).

 

[celly]

p.s. I thought this High Output Alternator Myths article was pretty good.

 

[BigBoom]

interesting...except i dont agree with #6

6. Just add a second battery: NO! NO! This is the worst thing you can do unless you are running dual alternators. The only thing a second battery will do is allow you to play the stereo longer with the key off. Otherwise it will make your situation worse. An alternator is “looking” for stability, that is it sees the battery voltage is at X and the output voltage is at Y the difference is the system load. Then the alternator will increase amps output until the system is balanced. If you add a second battery the alternator will have a hard time determining the load and will produce less power.

i agree to an extent...but on some parts i dont

 

[celly]

interesting...except i dont agree with #6

6. Just add a second battery: NO! NO! This is the worst thing you can do unless you are running dual alternators. The only thing a second battery will do is allow you to play the stereo longer with the key off. Otherwise it will make your situation worse. An alternator is “looking” for stability, that is it sees the battery voltage is at X and the output voltage is at Y the difference is the system load. Then the alternator will increase amps output until the system is balanced. If you add a second battery the alternator will have a hard time determining the load and will produce less power.

i agree to an extent...but on some parts i dont

Frankly, I don't know what to agree on and what not to. I'll never use a second battery or caps. I gave up on ultra high-end systems years ago after losing too much money on resale on them. My basic Pioneer/Fosgate/Boston Acoustics/Hertz serves my purpose and didn't break the bank.

Dom Iraggi recommended a 220 amp unit for what I use my electrical system for. I've got an Optima Yellow Top already and am in the process of completing the Big Three shortly. As mentioned to you on the other thread, I may go 260 amp just because the price is right. I actually prefer the idle output of the 220 amp unit over the 260, but the 260 is nothing to shake a stick at either.