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too many amps


4x4junkie

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As long as the alternator is putting out juice, even if the battery has to help it out, it flips something in the regulator and turns the light off. If the alternator is putting out nothing because of a failure or the belt came off, then the light comes on.

If the engine is getting ready to stall, it's turning so slow the alternator is putting out virtual nothing, I have seen the light flicker. But as long as the alternator is trying to keep up and has output, I have never seen the light come on.
This is correct.
The voltage regulator (VR) switches on the battery light when it sees there is no voltage output coming from the stator winding in the alternator.

When the key is first turned on, the VR is initially fed a small current through the battery lamp circuit (bulb & resistor in parallel). This causes the lamp to illuminate, and also activates the VR which in turn applies a current through the alternator's field coil (activating the alt's ability to generate power, so to speak). When the alt (field coil) begins to spin (starting of the engine), the spinning (energized) field coil induces an AC voltage/current in the stator winding, which is then rectified to DC (via six diodes) and fed straight out to the battery for charging and running of electrical loads. It is this voltage from the stator winding that, if present, will cause the VR to switch off all current going through the battery lamp circuit (causing the light to go off).

If you pull so many amps that the alternator can't keep up and you're now also drawing off the battery, the light still does not come on because there will still be ~12.5-13V at the stator since the alt is still putting out current, it's just not enough to overcome whatever electrical loads you have added and to be able to charge the battery.

At no point should the battery ever be at a higher voltage than that of a properly-functioning alternator (your accessory loads should be connected to your battery, not the back of your alt).


To the OP,
One or two LED lightbars, an E-fan, and two stereo amps the size you mentioned should be fine with a 130A alt. Most "500 watt" car amps for example are in reality closer to around 80-100 actual (or RMS) watts, since watt ratings on 12V car amps are not regulated the way home stereo equipment ratings are (you'll often see things like "Max watts" or "P.M.P.O." (Peak Maximum Power Output) touted prominently, which are nothing more than instantaneous power measurements taken at a specific point such as at the very peak of a sinusoidal waveform, which results in a highly-inflated number relative to the amp's actual power output capability before distortion (clipping) occurs).
If you do find that your truck's voltage fluctuates with the beat of the music (which is not unusual to have happen), like said above, adding a capacitor across the power leads to the amps should solve the issue (a one or two farad cap should do it). Capacitors are available at most places that specialize in mobile audio.
 


BiggSherm1988

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Yall have provided more than enough information to satisfy my question and it shows how well the TRS community is to one another. I actually learned some stuff from something on the internet for once lol.

I just ordered the rest of the wire that I needed to set all this stuff up. Has anyone ever heard of the big 3 upgrade, in reference to the alternator wiring? basically you replace the charging lead, bat ground and engine ground with a larger gauge wire like 1 or 0.
 

lil_Blue_Ford

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Ok, so…

130 amp alternator should be adequate. My first Ranger had a 95 amp alt and I was running a 915 watt RMS amp back then. It worked, but I was close to maxing out I think.

My F-150 has no amp, but a snow plow. The 95 amp alternator did not like the plow at all. Headlights would be glow worms when you cycled the plow. Put in a 130 amp alternator and added a piece of 4 gauge welding cable from the alt to the battery. Made everything much happier. Actually I replaced all the battery cables with 4 gauge welding cable on that.

My green Ranger has been an experiment, I’ve had a few different amps and subs in, mostly testing purposes, sometimes it doesn’t have anything. Working on lights and I’m trying to do an E-fan and electric power steering pump to it. I have 1/0 welding cable off the battery and split down to 4 gauge welding cable as needed. Without the E-fan and PS, the stock 130 (I believe) amp did everything well.

I don’t like the capacitor solution for stereos, if you hit a long base line, you can easily empty the cap and now it’s just another draw on the system, better off upgrading.
 

4x4junkie

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The capacitor is not really there to store a long charge, it's more to stabilize the voltage by smoothing out the large fluctuations (a.k.a. ripples) in amplifier current (such as from bass drum beats played at high volume) so that the alternator VR can manage the system voltage better (it only takes a change of about 20-30 amps to create a significant voltage ripple).

If the capacitor is actually discharging during a long bass note, that just means you're exceeding your alternator's capacity to keep up during said note (915 watts RMS is a quite very large amplifier... To express that as "Max watts" or PMPO, it would likely be a figure around 4000).
 

ericbphoto

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In theory, theory and practice are the same. In practice, they are different.
RMS is a weighted average number, usually around 0.707 X peak. So, I would expect 915 RMS to be around 1294 peak watts, roughly, which puts current in the 100amps range.
 

lil_Blue_Ford

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RMS is a weighted average number, usually around 0.707 X peak. So, I would expect 915 RMS to be around 1294 peak watts, roughly, which puts current in the 100amps range.
It’s been awhile since I had that all set up and I have no idea where the sheet with all the numbers ended up, but that sounds pretty much spot on. Since the truck was power nothing and the subs at the time couldn’t handle anywhere near RMS, much less peak (want to say they were 400 watt peak subs), that explains why it worked. It sticks in my mind that I think I was running an 80 amp fuse on the amplifier.
 

4x4junkie

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4WD
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35x12.50R15
RMS is a weighted average number, usually around 0.707 X peak. So, I would expect 915 RMS to be around 1294 peak watts, roughly, which puts current in the 100amps range.
You're correct, I should've said "peak-to-peak" voltage, which is a number that really doesn't factor into an actual measurement, since "peak" voltage is half of what "peak-to-peak" is, just the polarity is different (in other words, an amp that outputs 25V max and -25V max is 50V peak-to-peak, but at any given instant, the actual peak power can never be more than 156.25 watts into a 4-ohm speaker. Such an amp would be just over 78 watts RMS, but would rate 625 watts if a peak-to-peak number were used).

Because of a lack of regulation of power ratings for car amps, manufacturers can pretty much say anything they want and get away with it.

Probably a good way to figure roughly how much current the amp draws (failing to find actual RMS output ratings for it) would be to look at the fuse it came with, and then derate about 25-30% from that (if it has a 40A fuse, the amp will probably draw around 28-30A under normal operating conditions at the lowest speaker impedance it's rated for (most often 4 ohm, but some are also rated for 2 ohms).
If it has a 30A fuse, then figure around 21-23 amps, and so on.
 

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