Alt output/circuit protection

I am in the midst of trying to wrap up my system upgrade/install before nationals and have hit a small snag and was looking for some input.
I am running two separate charging systems. See here for details  http://chevyavalanchefanclub.com/cafcna/index.php/topic,145377.0.html
The issue I am having is in regards to the second system (running off the Nations Alt) it was supposedly a 250A alt. but only tested at 207A peak. When I called nations out on it they asked for the serial # off the alt and it turns out they sent me a 220 by mistake. Since it was already installed and my my gorilla math, I was only going to need about 195 I opted for a partial refund.
Here's where I'm at today.  I have a run of 1/0 OFC cable run to the battery, from there to a Stinger 200A breaker and then back to a distribution block supplying 1/2 of the system, a Kicker KX1600.1 for 1 sub and a RF R600-4D for some of the Mids and highs.  The 1/0 run from the battery through the breaker and back to the block is 17'9" total
My RMS total is 2400 watts (1779 from the 1600.1 and 621 from the R600-4D).  They're both putting out slightly above their factory ratings
By my calculations, my total draw should be right at 189A (12.7 watts generated per amp given the length of the cable) 2400 watts/12.7 = 188.9A
Here's the problem. On test hits, I'm popping the breaker on that side of the system. On the other side, there is no issue, but the draw is less, only 161A
Under normal playing conditions this wouldn't be an issue, but at max, I don't want to have to worry about popping the breaker.
I measured the output of the alt at 207.4A today and sure enough, on a test hit @56Hz. the draw soared up over the 199A mark and popped the breaker.

My question is in relation to the safety of swapping out this 200A breaker to a 250A. According to the manufacturer of the cable I am using, at a length of 18 ft. the max allowed amperage should be 238, which my alt is incapable of producing, so I don't think is would be an issue.  But 250 is more than 238 and I don't want to (and not sure if it's even possible) jeopardized the entire system, or AV for that matter by switching to a breaker that is above the specs of the cable.
In all actuality, I should only be able to get about 8 more amps to the back anyway since that's all the generation I have.  But the way it sits right now, I need those 8 amps, as I am clearly drawing over 200A back at the distribution block.

Thoughts?

So you are trying to protect a 220 amp rated alternator with a 250 amp breaker?  Forget the cable specs, it will get hot but even if it fails, you have lost your protection for your most expensive item, the alternator.  That would be of most concern to me. 

Some things to consider....

The power rating on an alternator is a ball park number. If you try to pull more from it then it will try to output it. If you are CLOSE to the rated value it should not be a big deal as long as you are not doing it for long. What I am saying is that alternators are NOT current limited. If you had a current limited alternator you would be looking at a VERY expensive alternator...  Also as it was explained to me by a now defunct alternator engineer most manufacturers rate their alternators "cold" and when actually running their output could be considerably lower so you really need to look at the "hot" rating. With this in mind you very well could have gotten one of their 250 amp rated alternators...

I am curious how you are testing it too because I was under the impression it takes somewhat specialized equipment to test the output of an alternator. I believe you run a bigger and bigger load on it until the wave form starts to change.

To understand a little more you must understand your alternators make AC power and they use Diodes to bring it back to DC but this DC is more of a saw toothed DC instead of a straight line so you absolutely have to use a battery in the line to filter the DC.

That all being said... When you pull more than the amount the alternator can handle you are pulling from the battery you are charging with the alternator. That battery should be able to handle your pounding bass just fine even if you have momentary surges over 250 amps as long as you are well under the 200 amps during the majority of the time.  You need your battery to be mounted as close to the amplifiers as possible. You CAN use capacitors to help out at the amplifiers but all modern good quality amplifiers put capacitors inside their amplifiers so external power capacitors are pretty much worthless.

The reason why you want to run the batteries as close to the amplifiers as possible is because the wire has a resistance which goes up the higher the amperage pull through it and the longer the run of wire. So if you are using on average 160 amps of power when the subs are not hitting hard and 220 when they are at their max for short bursts you should be more than fine with your battery very close to the amplifiers and running the alternator wire to the battery.

Also notice that you will want to run circuit breakers within 18 inches of ANY power source which means you want a breaker at the alternator and another at the battery and one from the battery to the amplifers. You are protecting the wiring from catching fire not the equipment attached to it...  With that in mind your breaker from the battery to the amplifer can be any size you need... If your wiring supports 300 amps you should have no issue with a 300 amp breaker between the battery and your amplifiers. Be aware that some alternators do not like running without a battery connected for long and it could blow the diodes in the regulator if you don't have a battery to smooth out the power source.

I have the factory 105 amp alternator in my truck charging two batteries at this time and powers a 500 watt amplifier just fine running with 8gauge power cable....  I have mine fused at 200 amps because I am protecting the wiring NOT the equipment...
The equipment has its own 30 amp fuses on it...
Rodney

SmokeyJoe said:

So you are trying to protect a 220 amp rated alternator with a 250 amp breaker?  Forget the cable specs, it will get hot but even if it fails, you have lost your protection for your most expensive item, the alternator.  That would be of most concern to me. 

Click to expand...

The alternator is the least of my concern, and actually the cheapest (outside of the battery) component connected to that charging system.  The breaker is to protect my AV from burning down in the freak event of a dead short. My main concern is that if by some freak chance a dead short occurs that the cable could be overloaded and cause extensive damage before the breaker trips.

redheadedrod said:

Some things to consider....

The power rating on an alternator is a ball park number. If you try to pull more from it then it will try to output it. If you are CLOSE to the rated value it should not be a big deal as long as you are not doing it for long. What I am saying is that alternators are NOT current limited. If you had a current limited alternator you would be looking at a VERY expensive alternator...  Also as it was explained to me by a now defunct alternator engineer most manufacturers rate their alternators "cold" and when actually running their output could be considerably lower so you really need to look at the "hot" rating. With this in mind you very well could have gotten one of their 250 amp rated alternators...

Click to expand...

Agreed, I considered the "cold" rating and wasn't expecting a true output of 250, but 207 seemed low to me and they confirmed when I gave them the serial that is was only a 220A

redheadedrod said:

I am curious how you are testing it too because I was under the impression it takes somewhat specialized equipment to test the output of an alternator. I believe you run a bigger and bigger load on it until the wave form starts to change. 

Click to expand...

One of my good friends works at NAPA and they have a test cart that has necessary electronics to test. Both times we tested it he did it at idle, at high RPM, and with load controlled by their eqiupment.

redheadedrod said:

To understand a little more you must understand your alternators make AC power and they use Diodes to bring it back to DC but this DC is more of a saw toothed DC instead of a straight line so you absolutely have to use a battery in the line to filter the DC.

That all being said... When you pull more than the amount the alternator can handle you are pulling from the battery you are charging with the alternator. That battery should be able to handle your pounding bass just fine even if you have momentary surges over 250 amps as long as you are well under the 200 amps during the majority of the time.  You need your battery to be mounted as close to the amplifiers as possible. You CAN use capacitors to help out at the amplifiers but all modern good quality amplifiers put capacitors inside their amplifiers so external power capacitors are pretty much worthless.

The reason why you want to run the batteries as close to the amplifiers as possible is because the wire has a resistance which goes up the higher the amperage pull through it and the longer the run of wire. So if you are using on average 160 amps of power when the subs are not hitting hard and 220 when they are at their max for short bursts you should be more than fine with your battery very close to the amplifiers and running the alternator wire to the battery.

Also notice that you will want to run circuit breakers within 18 inches of ANY power source which means you want a breaker at the alternator and another at the battery and one from the battery to the amplifers. You are protecting the wiring from catching fire not the equipment attached to it...  With that in mind your breaker from the battery to the amplifer can be any size you need... If your wiring supports 300 amps you should have no issue with a 300 amp breaker between the battery and your amplifiers. Be aware that some alternators do not like running without a battery connected for long and it could blow the diodes in the regulator if you don't have a battery to smooth out the power source.

I have the factory 105 amp alternator in my truck charging two batteries at this time and powers a 500 watt amplifier just fine running with 8gauge power cable....  I have mine fused at 200 amps because I am protecting the wiring NOT the equipment...
The equipment has its own 30 amp fuses on it...
Rodney

Click to expand...

Thanks, that is what I was thinking, but wasn't totally sure.
I was toying the idea of adding a cap at the distribution block since I have a 4 farad cap in my loft not being used, but didn't think it would help much if at all.
I do have a 200A Mega between the Alt and battery , about 20 inches before the Battery and then the 200A breaker just after the battery, about 16".
I was just uncertain as to weather or not going up to the 250 could possibly be dangerous in the event of a dead short. I think changing the Mega Fuse and the Breaker to 250 shouldn't be an issue then.

The question here should be if the wiring you are using will support 250 amps.

Per this chart you should be fine...

http://www.offroaders.com/tech/12-volt-wire-gauge-amps.htm

12 volts is much different than household current. If we look at a household chart then you are only half way there. But 12 volts 100 amps is only 1200 watts of power... Household amperage would carry 10 times that wattage. They also suggest you need to consider the length of your ground cable as part of the length of your wire.  (Wattage = volts times amperage)

In the past I was trained to use the amperage of the fuse on the amps as an indication of what power to run through the cables. That would be worst case scenario but if your wiring was sufficient for the combined fuses run off that line then you were fine. In Tech school we were told to size your fuses about 50% up to 100% of the expected need to give a little wiggle room. The idea is that fuses do wear out and you don't want to blow the fuse prematurely but you also want to protect your circuit. So you plan the hardware accordingly.  Thus the reason why I was trained to always add up the amperage of the fuses in the circuit to insure your wire can handle the worst case.

Hope that helps.

If you look at the competition rules for sound competitions they require fusing to be no more than 18" from a power source. I would think 20" would be fine.

In my truck I have a 200 amp fuse on the battery line to my accessories but I am running a stud through the fire wall. On the inside of the firewall I currently have 2 wires running. One to my computer and one to the sound system. I have a fuse on the stud to amplifier line as well. I will likely add one to the stud to the computer line and reconfigure my wiring a little. I have some 1/0 gauge wiring I will likely tie from the battery to the stud at the fire wall and leave the 8 gauge wiring inside the truck. 8 gauge is way over kill for the computer since they only have 12 gauge wiring running to the power supply but overkill is always better than not big enough...

Rodney