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What Size Alternator Do I Need?

49K views 46 replies 13 participants last post by  blaqyukon 
#1 · (Edited)
Well Mr. Aukland suggested that I put a couple of my FAQs up here and since the title to this thread question seems to come up a lot I figured it a good start.
Q: What size Alternator do I need?

A: This is a question that seems to be arising more and more these days with the addition of larger (more powerful) amplifiers.

1)First you will need to look at the amplifier(s) themselves and their fuse values (total).
2)Next you will be required to know the amperage rating of your stock alternator

Most typical stock alternators use a value of 70-80%, meaning that the vehicles maximum load is 70-80% used under vehicle usage.
Now we take the alternators amperage rating and multiply an average of 75% (you may use 80% if you wish to allow yourself an added protection of power). Now take that number and add the total fuse values of the amplifier(s) and the final figure will be how much power you will require from an alternator.

Side Note #1: The addition of added aftermarket items that will require power will increase your amperage load and you should judge accordingly. Items such as Video Monitors, On Board Gaming Systems, DVD Players, Lighting, ETC. may not require a huge amount of power alone, but added with together or with an aftermarket audio system may have a larger load than expected. If you are planning (or even thinking about) the additional items afore mentioned then you may wish to just add the total calculated fuse value(s) to the stock 100% value of the alternator.

Side Note #2: If you are currently only adding a single amp for subwoofer(s) and are planning (or even thinking about) the additional amplifier(s) for highs, midrange, components, etc. then please estimate the amount of power required and add to the total fuse value(s) to save yourself the headache, time, and money of having to upgrade your alternator again in the future.

Examples:
Example #1
Adding a single amplifier with (2) 40 amp fuses
Stock alternator rated at 90amps
Fuse values total = 80 amps
90 x 75% = 67.5 (always round up) = 68
68 + 80 = 148
So therefore you will require an alternator with a minimum rating of 150 amps

Example #2
Adding a single amplifier with (2) 40 amp fuses
Stock alternator rated at 105 amps
Fuse values total = 80 amps
105 x nothing as we will (or do) add for additional items (let’s just say Monitor, DVD, HID lighting, & a couple neons)
80 + 105 = 185
So therefore you will require an alternator with a minimum rating of 185 amps

Example #3
Adding multiple amplifiers with (2) 40 amp fuses (amp #1) and (2) 25 amp fuses (amp #2)
Stock alternator rated at 120 amps
Fuse values total = 130 amps
120 x 75% = 90
130 + 90 = 220
So therefore you will require an alternator with a minimum rating of 220 amps

Side Note #3: While other electrical components of your vehicle may help such as the Big 3, Upgraded or Additional Batteries, (Capacitors not suggested) these are not a direct replacement for creating power and are only to assist in transferring and storing power and are Not and should Not be used as a substitute.

Thanks and above all when dealing with electricity of any sort, think smart and safe for yourself and your equipment :thumbsup:
 
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#3 ·
I think you're trying to add up the wrong fuses... you need to add up all the fuses in your amplifiers themselves and not the fuses leading to the amps... In some cases you may have to use an external fuse rating as some amplifiers do not have internal fuses and give you a recommendation of external fuse size and in that case you would you that as your figure added in with any other internal fuses you may have for other amplifiers (if they are present).
 
#8 ·
Okay then... with the 4) T2Ks by calculations you would need over 1250 amps, but I also know that the T2Ks only require about half of their fuse ratings for true power thus for optimum performance about 600 amps would be premium and would probably get you beyond that 150 mark as long as you had the power reserves to hold it (batteries for those of you that didn't understand that last part) ;)

To give a more accurate calculation for most as a reference:
Trailblazer/ Envoy stock alt ='s 150amp 75% is 112.5 amp (so we'll round to 115 amp for safety)
Standard amp of 2000watts rms 2 x 40 (some very but this is a close estimate) ='s 80 amps
So we take those figures and add them together 115 + 80 ='s 195 thus you would need a 200 amp alternator
In addition remember that even with a h/o alt you need to have the reserve to hold the power... battery(s) and proper wiring to handle the current or all is for not.
Hope this helps everyone out a lil bit :)
 
#9 ·
Thanks, but why is this different than what you explained above? First you're saying that 1250 amps is what that fuse rating calls for, but then you're saying that it only needs 600 amps of power?? Thats a huge difference.. Can you explain a little more for those that are going WTF??? :thx
And if by 150 mark, you mean 150DB.:duh: LMAO. I'll be over that with my 2nd T2K and 2nd Kinetik HC2400:thumbsup:
 
#10 ·
As I said about the 1250/ 600 amp difference... The T2Ks are more efficient than there fuse ratings and for daily 600 would be plenty to power them, but if you were looking to compete in dB Drag on a burp 1250 would be the amount to get to full charge quickly ;)
And yes I did mean 150 dBs and a second T2K may not guarantee a 150+ score as the estimate of +3 dBs for doubling power is only that an estimate.
The 150 mark (dB) is a tough one to break... I speak from experience as we built a Buick with a wall of 4) 15" that ranked #12 in the country with a 153 and we were doing a 149 with Autoteks and 3000w and 3) 2150 batts, 150 with it when it had 4) Elevation Executions with 6000 watts and 4) 2150 batts, when we made some mods to the rear and port, then swapped out for 4 specialty built FSQs and 8000 watts and 5) 2150 batts to finally get to the 153 dB mark. If 150+ dB was easy everyone would be doing it ;)
 
#11 ·
I'm already doing a 48.7 with just 1 T2K at the "C" pillar. That in itself is a pretty badass task @ 45hz.:yes: I have no doubts that I'll break the 50 mark this year when I add the second one. Adam (my friend that helps me) placed 6th last year at world finals. If all else fails, I'll have to resort to plan c, which is taking the rear seats out and putting 4 of those 15's (memphis Mojos) and 4 T4K's with a couple HO alts and several Hc2400's. I don't want to do that, but everyone else may force my hand. I want to be and remain the loudest TB.:duh::weird:
 
#13 ·
At 45hz thats pretty high tuning and you only did 148.7. Its easier to hit higher numbers with higher tuning. I did 146.7 @ 35hz with less than 2k of a modded mtx81000D with only one 18. My new setup is gonna break 150s without a sweat and at low tuning. I predict mid 150s. Doing two 18s in 11cu.ft. encloser and over 4000watts rms. 280amp H/O alt from Mean Green and two g31's in rear.
 
#20 ·
^Exactly... For competitions you will see many that have amps that will far outweigh the alts capabilties and that's why you need to have all of the extra reserve from the batteries... These systems are not for daily purpose and many competitors also use larger wheeled type battery chargers to help recharge the batteries quicker.
Example: The Buick I have mentioned (although fully drivable) was not set up as a daily driver and the 300 amp externally regulated amp would not be able to feed the amps for general purpose... The 5) 2150s in the back though would hold the current in the lanes and the Deka under the hood would allow the car to start up again every time so that the alt could recharge them (15V) while waiting for the next run.
The FAQ formula is for using when applied to daily driving to meet the demands required for a fully operational electrical system with no light dimming ;)
 
#22 ·
You could run one batt to each sub amp and a third smaller battery for the mids n highs. I would go either the kinetik hc2000's, the odyssey 2150's, or the dekka (i dont know their models, but one that can handle 2000 watts ea). This would give you that extra boost you system may need.
 
#24 ·
i have an 800 watt amp with my subs (max power rating) and when the audio shop installed my subs about a week later the car wouldnt start and would not make any noise .. i dsiconnected the subs and the car worked again, the chevy place even gave me a new ignition switch .. if i hook the subs and the leds in my car to a seperate battery do u think this will solve my starting issue?
 
#25 ·
A secondary battery may not be the cure for you... it may very well be the stock battery not holding to it's full capacity... As I said in the pm, you may want to have it checked... If you do go with a new battery (for stock location) get a dry cell and preferably one with secondary terminals as it makes installing accessories much easier and then you know that there isn't a poor connection for the rest of the vehicles electrical system.
 
#27 ·
Yes, but in your case Aukland, We went with a 31 series (big mama jama) and for the replacement of a stock oem battery he could get by with a standard Optima or Orbital with the regular top and side posts... Not everybody goes with the one of the biggest batteries Optima makes for under the hood :p lol
 
#30 ·
Your voltage meter on the dash is only showing you the charging rate of the alternator... and with the vehicle not running (key "On") it will probably still read 12volts too... What I am suggesting is that you take the battery and have it load tested to check and see if it is holding it's reserve potential.
 
#47 ·
what size alternator do i need

well cargodz for examples 1,2,3 you need about 250 amps your count was
was 220, ok most ppl pick alternators and they foget about what we call headroom, laymens terms peak amps, for sound if you have an amp that pumps 150 watts by it self where not counting other devices that use current,
they have rms watts and then theirs peak watts, in audio peak is about 2 to 3 times of what rms is, give or take . so you need an alternator thats going to produce enuff amps so that the amp dont sag.. in order to produce watts its volts x amps=watts ohms law.


sorry admins no disrespect my next thread i will introduce my self to the
community, in the introductions forum...my bad i was reading and just jumped rite in while getting ready for work...
 
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