# Alternator too small, what happens?



## criddopher (Apr 3, 2011)

Just like the title says, what happens when you have a system that can pull many more amps than the alternator can produce? Does the system just produce less wattage than it could? Does it effect the equipment? I'd imagine its tough on the alternator but I'm more interested in what effect it has on the sound system.

Anyone has facts?


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## minbari (Mar 3, 2011)

Depends on how much of a deficiency you have. If the system can pull 100A and you have a 90 A alt. Then doubtful you will have any problems unless you listen at 100% all the time. Your will only pull 10-20% of max most of the time.
You also have to consider that the car needs juice too 

To answer your question, 2 things are likely to happen if you do exceed it. 
1)Your battery will go dead, when you turn off the car, it won't start again.
2)you will melt the diodes in the alt and have to replace it

As for the sound gear. It will have a minimal effect. As voltage drops your gears performance will suffer. Shouldn't hurt it though

Sent from my LGLS992 using Tapatalk


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## FordEscape (Nov 23, 2014)

minbari said:


> Depends on how much of a deficiency you have. If the system can pull 100A and you have a 90 A alt. Then doubtful you will have any problems unless you listen at 100% all the time. Your will only pull 10-20% of max most of the time. ....


*Fact*ual (empirical) example of this:

2014 Ford Escape 2.0 EcoBoost
Alternator spec: *100* amps at 650 rpm (min) to *175* amps at 2,200 rpm (max) 
Battery spec: Group 96R Motorcraft; 56 amp/hr rated; 590 Cold Cranking Amps (CCA)
Car has OEM "Smart Charging System" that regulates (minimizes) alternator output for 'fuel efficiency'.

Audio System:
3x JBL MS-A1004 + 2x JBL MS-A5001 = 2,200WRMS _rated_ total output
2,200 W = *157*A @ 14VDC; = *183*A @ 12VDC
Total of 12 tweeter, mids and midbass (front, front center, rear fill) + 2x SI BMmkIV subs
Never put a clamp-meter on the main-feed to check my _actual_ vs _rated theoretical_ current draw

I'm ignoring the JBL MS8 DSP (internal amps not used) and whatever load is presented by the non-audio car systems (ignition, lights, electric fuel pump, electric power steering, etc).

Audio system as above for ~2 years; battery is the 4.5 year-old original equipment; I often listen to music for 5-15 minutes after engine off (gotta finish the 'song in progress' at the end of the drive ). I like to listen loud but the entertainment is for me in the car, not the car next to me :laugh: 

Never used a charger except for extended engine-off tuning sessions, never needed a jump, car always starts with first turn.


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## criddopher (Apr 3, 2011)

Good to know. Ive always been at least a little over the alts power, most of the time way over, and never had anything die. This new system i'm building is using much more high end gear than I have in the past, I wanted to make sure it posed no risk to the amps and such. Thanks!


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## JH1973 (Apr 21, 2017)

FordEscape said:


> minbari said:
> 
> 
> > Depends on how much of a deficiency you have. If the system can pull 100A and you have a 90 A alt. Then doubtful you will have any problems unless you listen at 100% all the time. Your will only pull 10-20% of max most of the time. ....
> ...


Wow,identical power specs I'm installing in a 2011 Terrain.I don't plan on beefing up the electrical,not even the big 3.


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## JH1973 (Apr 21, 2017)

FordEscape said:


> minbari said:
> 
> 
> > Depends on how much of a deficiency you have. If the system can pull 100A and you have a 90 A alt. Then doubtful you will have any problems unless you listen at 100% all the time. Your will only pull 10-20% of max most of the time. ....
> ...


Wow,identical power specs I'm installing in a 2011 Terrain.I don't plan on beefing up the electrical,not even the big 3.


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## minbari (Mar 3, 2011)

I have never bothered with big 3 unless I ran into issues. alot of cars already have sufficiant cable for most systems 1000 watts or less. Contrary to what people seem to think 1000 watts is way more than enough power if smartly used.


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## SPLEclipse (Aug 17, 2012)

criddopher said:


> Good to know. Ive always been at least a little over the alts power, most of the time way over, and never had anything die. This new system i'm building is using much more high end gear than I have in the past, I wanted to make sure it posed no risk to the amps and such. Thanks!


When voltage drops you get a large spike of current through the amp and this can cause problems. The extra current can burn out resistors and fets. But....you have to dip pretty low and for pretty long to do anything. If you're not explicitly playing drawn out bass notes at full volume and dropping below ~11v you don't have to worry.


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## mitchell0715 (Apr 11, 2015)

Put a voltmeter directly on your amplifier inputs and just watch it, that's really going to give you the best indication of how you're treating it


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## criddopher (Apr 3, 2011)

minbari said:


> I have never bothered with big 3 unless I ran into issues. alot of cars already have sufficiant cable for most systems 1000 watts or less. Contrary to what people seem to think 1000 watts is way more than enough power if smartly used.


I've almost always done mine. It's so easy, I always just did it when I was running the main power. Although, I did skip my g35x that car already had beefy wire. Any other car I have is a cheap compact joint, they have like 18 gauge run lol



SPLEclipse said:


> When voltage drops you get a large spike of current through the amp and this can cause problems. The extra current can burn out resistors and fets. But....you have to dip pretty low and for pretty long to do anything. If you're not explicitly playing drawn out bass notes at full volume and dropping below ~11v you don't have to worry.


Interesting. I'd imagine I would have to be pulling some major power to really dip that low too eh? I'm going to have to check it like mitchell said.


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## mitchell0715 (Apr 11, 2015)

criddopher said:


> Interesting. I'd imagine I would have to be pulling some major power to really dip that low too eh? I'm going to have to check it like mitchell said.


depends on the cars output, I've seen people dip in the 11's because they're on stock electrical (or near stock electrical) with a 1-2k amp, obviously it was a true 1-2k amp not a boss 5k


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## Holmz (Jul 12, 2017)

mitchell0715 said:


> Put a voltmeter directly on your amplifier inputs and just watch it, that's really going to give you the best indication of how you're treating it


*"Treating it"* Meaning treating the amp?

A volt meter and an amperage clamp in the alternator will give some solid factual idea how one is treating the alternator.

(Just because there is a 3000W amp does not mean that it is drawing much current or outputting 3000W)

Turn it up as loud as you can stand it and see what that level is required in terms of current draw by the amplifier, and what the alternator is needing to provide as total current.

Voltage is good to know too - but wires, cables and alternators use amps as the unit of measure.


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## mitchell0715 (Apr 11, 2015)

Holmz said:


> *"Treating it"* Meaning treating the amp?
> 
> A volt meter and an amperage clamp in the alternator will give some solid factual idea how one is treating the alternator.
> 
> ...


both? the only problem is if you have voltage drop on the wiring to the amplifier, which is why i recommend you check the voltage at the alternator output stud references to the case as ground, and ensure under load its the same voltage at the amp

the average person doesn't have a DC Amp clamp, and if they think they do its most likely an AC amp clamp so I almost never mention it because with noobs it just leads to confusion

measuring the voltage under load at multiple points is going to give you all the information you need because as you know, V=IR


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## ckirocz28 (Nov 29, 2017)

criddopher said:


> Just like the title says, what happens when you have a system that can pull many more amps than the alternator can produce? Does the system just produce less wattage than it could? Does it effect the equipment? I'd imagine its tough on the alternator but I'm more interested in what effect it has on the sound system.
> 
> Anyone has facts?


I've never had an aftermarket alternator and never had problems. I'm currently running 2286 watts with 2 subwoofer amps (class D) and less than 300 watts on one class A 4-channel amp, 105 amp alternator and 1 Optima Yellow Top battery (88 Camaro). The headlights dim a bit if I really crank it up, but I only do that occasionally.
Like others have said, if you run it into some serious voltage drop for an extended time (more than a few seconds), you could fry your alternator or amplifiers (amplifiers are much less likely to fry, usually they go into protection mode).

Sent from my SM-G935U using Tapatalk


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## NealfromNZ (Sep 3, 2013)

Had a BMW e36 with a PG xs4600. These amps were rated for 25x4 RMS at 12 volts. They ran unregulated power supplies to take advantage of car stereo comp rules so would produce quiet a bit more power at 13.8 volts

On the winter commute with headlights / wipers / car stereo on in stop go traffic the alternator wasn't producing much with the engine crawling along just of idle.

It use to overwhelm the electrical system and the first you'd notice was a rough idle and some dimming.

One evening I had the system cranked and the voltage collapsed. The amp power supply tries to compensate and pulls more current with the voltage dropping. One channel on the amp goes pop and takes out one of the component speakers and most of the power output mosfets in the amp.

The amp was connected via 4g and an 80anp fuse (far too high in retrospect). Scary thing was the red wire insulation had gone brown over a 2 foot section . 4g at that length should be good for 120 amps so it must have seen a short for the insulation to get hot enough to change colour

Replaced speakers and amp with larger ab amp for comps , but importantly class d on sub. Never had the issues of overwhelming electrical system after. But the lesson was not to push a car electrical system beyond its abilities.

Mind you , that so called 25x4 pg amp could draw 80 amps. Takeabout sandbagging specs !


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## ChaseUTB (Mar 28, 2018)

My 2015 Q40 has 130 amp Alt. Waiting on a singer 240A that will prob do 270 amps hot. Had a 110 Alt for older Altima and one 1.3k rated 1500 @ 1 ohm and they lights would dim with the bass very noticeably. Car would drive kinda weird after listening for awhile in traffic. This car had the big 3 done however it was my first time doing it and it could have been done better. 

I am going to install a 2300 watt system soon, 1500 watt RMS sub amp & 800 watt RMS 4 channel. I upgraded my lead battery to Odyssey AGM under the hood. It had the most bad ass specs out of all group 35 batteries. Even though IDK how the battery CCA/MCA amount affects audio system electrical pull, I figured the more the better. I know RC is about a 25 Amp discharge rate above 10.5 V But not sure how that equates to the electrical whether the car is on or off lol. 

Group 35 
1400 PHCA
820 CCA
850 MCA
RC Min. 125

Going to get some lug style battery terminals and see how the system performs. I don’t want my headlights dancing and don’t want tonto damage my car. I will probably have the big 3 done professionally this time ?


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## Holmz (Jul 12, 2017)

mitchell0715 said:


> both? the only problem is if you have voltage drop on the wiring to the amplifier, which is why i recommend you check the voltage at the alternator output stud references to the case as ground, and ensure under load its the same voltage at the amp
> 
> the average person doesn't have a DC Amp clamp, and if they think they do its most likely an AC amp clamp so I almost never mention it because with noobs it just leads to confusion
> 
> measuring the voltage under load at multiple points is going to give you all the information you need because as you know, V=IR





mitchell0715 said:


> both? the only problem is if you have voltage drop on the wiring to the amplifier, which is why i recommend you check the voltage at the alternator output stud references to the case as ground, and ensure under load its the same voltage at the amp
> 
> the average person doesn't have a DC Amp clamp, and if they think they do its most likely an AC amp clamp so I almost never mention it because with noobs it just leads to confusion
> 
> measuring the voltage under load at multiple points is going to give you all the information you need because as you know, V=IR


^Good pointS^

Basically anyone that says that they have X-Watts usually leaves what they actually use in terms of watts.
And not knowing what the actual amperage that is used makes it hard to say whether a 90-amp alternator is good or not.
But I agree that the voltage is pretty good to know.

I guess if someone preplacing their own alternator themselves, then just do it.

If they are considering having the alternator replaced, the a good clamp meter may be about the same money as an alternator, or they could find a shop or someone to measure the current draw.. in order to know with more certainty whether they need one.


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## mitchell0715 (Apr 11, 2015)

ChaseUTB said:


> My 2015 Q40 has 130 amp Alt. Waiting on a singer 240A that will prob do 270 amps hot. Had a 110 Alt for older Altima and one 1.3k rated 1500 @ 1 ohm and they lights would dim with the bass very noticeably. Car would drive kinda weird after listening for awhile in traffic. This car had the big 3 done however it was my first time doing it and it could have been done better.
> 
> I am going to install a 2300 watt system soon, 1500 watt RMS sub amp & 800 watt RMS 4 channel. I upgraded my lead battery to Odyssey AGM under the hood. It had the most bad ass specs out of all group 35 batteries. Even though IDK how the battery CCA/MCA amount affects audio system electrical pull, I figured the more the better. I know RC is about a 25 Amp discharge rate above 10.5 V But not sure how that equates to the electrical whether the car is on or off lol.
> 
> ...


Generally the ratings given are cold at max output rpm. I highly doubt you'll get 270a hot out of that alternator unless you're at peak rpm's, it's a 6 phase hairpin, and a large case

I'm more than happy to get 210dca out of my DC Power 300XP at idle hot, 270a hot is A LOT to ask

maybe you meant 170a, that makes more sense based on my experience clamping alternators



Holmz said:


> If they are considering having the alternator replaced, the a good clamp meter may be about the same money as an alternator, or they could find a shop or someone to measure the current draw.. in order to know with more certainty whether they need one.


You can get a good DC clamp meter for about $100-200

A HO alternator that actually produces 150a+ at idle (especially in small cases for cars) will run you at least double or triple that

most good alternator shops will have an oldschool load they can put on the alternator which does essentially the same thing but those shops are becoming increasingly harder and harder to find


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## Holmz (Jul 12, 2017)

I suppose if the lights are dimming, like a scene in a ghost movie, then something is not good.
Current draw is a better thing to know, if one wants to know what size alternator to get for the load they need.

Horror stories about uncle Bob's truck, auntie Sally's sedan, burning up the harness don't us tell much.

I just had an alternator replaced because it was bad, and alternators go bad without a radio, or with just a stock radio.


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