Voltage drop with good electrical. What am I doing wrong?

[sexy 10+ year member]

Setup in sig. I have:-Two MB Quart DSC1500.1Ds strapped at 1.2 ohm (0.6 ohm each amp)

-Two Sprinter 100Ah batteries in the rear

-Crappy stock battery up front (for now)

-136A alternator

-Big three done in 1/0 (positive to alternator positive, chassis ground to the driver's side fender, engine ground to the top of the engine block)

-Wiring is done as follows: Amps to distribution block (one for + and -), two runs of wire from distribution block to rear batteries (one for + and -), two runs of wire from rear batteries to front battery (one for + and -). No interaction with the chassis or frame of the vehicle, everything is directly connected.

I realize two 1500W amps strapped at 0.6 is going to be hard on an electrical no matter what, but a buddy of mine ran one of these amps at 0.5 with only a stock front battery, 80A alt, and a Deka in the rear and only dropped 0.4.

No clue what I am doing wrong, all of my connections are soldered, each run of wire from front batt to rear is about 20 ft long and each run from rear batt bank to cabin, where the distros/amps are, is 10 ft long. All batteries and alt are working properly

Each battery you have hooked up takes about an additional 10 amps from the alternator to keep up this is common knowledge among guys that build H/O alts but no so much on the people in forums they still think adding batteries without any electrical knowledge is the magic answer. As for what happened in your buddies car with these amps has a lot more to do with box rise than anything else. What ohms your coils are wired to is only ½ of the equation the other half is what determines how much power is needed to the amplifier. Box rise is the other half that people always miss but it is the most important part of why your voltage drops or stays good.

 

[bubbagumper6 5,000+ posts]

That's not "good" electrical, that's piss poor. Your alternator isn't cutting it. I've run 3kw off one of those sprinter batteries & a yellowtop with no voltage drop, but that's because I'm also running a 230A alternator. You need a bigger alt, period.

 

[ahole-ic]

Here is a little electronics lesson for everyone but bubba and sexy(you guys have it dead on)... A voltage (aka difference of potential) is required to make current flow. If a battery is at 12.6v and an alternator is in parallel with it at 14.4v, there is a 1.8v difference of potential between the alt and the batt and so the current can ONLY flow out of the alt to the batt. Once another device is connected in parallel, ALL CURRENT flows out of the alternator, because it is the highest source of potential in the circuit. The battery remains charging from the alt and not discharging. Once the current drawn causes the alternator to drop its voltage, and that voltage gets to the battery voltage, the battery will begin discharging.

Unless the battery is discharging, IT IS ALWAYS CHARGING(aka drawing current from the alternator)

This is BASIC electronics and it is not disputable. Take it to heart. Stop recommending batteries to "stop voltage drop". It cannot and never has done that. The ONLY thing batteries help with is keeping the voltage above 12v so the amps don't blow. That's it. They don't "stop dimming" etc.

 

[ahole-ic]

Here is a little electronics lesson for everyone but bubba and sexy(you guys have it dead on)... A voltage (aka difference of potential) is required to make current flow. If a battery is at 12.6v and an alternator is in parallel with it at 14.4v, there is a 1.8v difference of potential between the alt and the batt and so the current can ONLY flow out of the alt to the batt. Once another device is connected in parallel, ALL CURRENT flows out of the alternator, because it is the highest source of potential in the circuit. The battery remains charging from the alt and not discharging. Once the current drawn causes the alternator to drop its voltage, and that voltage gets to the battery voltage, the battery will begin discharging.

Unless the battery is discharging, IT IS ALWAYS CHARGING(aka drawing current from the alternator)

This is BASIC electronics and it is not disputable. Take it to heart. Stop recommending batteries to "stop voltage drop". It cannot and never has done that. The ONLY thing batteries help with is keeping the voltage above 12v so the amps don't blow. That's it. They don't "stop dimming" etc.

 

[Tone415 10+ year member]

Here is a little electronics lesson for everyone but bubba and sexy(you guys have it dead on)... A voltage (aka difference of potential) is required to make current flow. If a battery is at 12.6v and an alternator is in parallel with it at 14.4v, there is a 1.8v difference of potential between the alt and the batt and so the current can ONLY flow out of the alt to the batt. Once another device is connected in parallel, ALL CURRENT flows out of the alternator, because it is the highest source of potential in the circuit. The battery remains charging from the alt and not discharging. Once the current drawn causes the alternator to drop its voltage, and that voltage gets to the battery voltage, the battery will begin discharging. Unless the battery is discharging, IT IS ALWAYS CHARGING(aka drawing current from the alternator)

This is BASIC electronics and it is not disputable. Take it to heart. Stop recommending batteries to "stop voltage drop". It cannot and never has done that. The ONLY thing batteries help with is keeping the voltage above 12v so the amps don't blow. That's it. They don't "stop dimming" etc.

Learned something new! Thanks bro

 

[ahole-ic]

Learned something new! Thanks bro

You're welcome man.

 

[SicAudio 5,000+ posts]

The AH of your batteries dont mean much when the car is running, CCA and resistance are the most important numbers

alt amperage and battery Ah matter not cca cca= cold cranking amp... for when you are cranking the starter...

 

[Slayerx 10+ year member]

alt amperage and battery Ah matter not cca cca= cold cranking amp... for when you are cranking the starter...

Cold cranking amps (CCA) is a measurement of the number of amps a battery can deliver at 0° F for 30 seconds and not drop below 7.2 volts.

So ya, I'd say it's fairly irrelevant

 

[SicAudio 5,000+ posts]

Cold cranking amps (CCA) is a measurement of the number of amps a battery can deliver at 0° F for 30 seconds and not drop below 7.2 volts.So ya, I'd say it's fairly irrelevant

quote all of it next time brah...

4. CCA, CA, AH and RC. What are these all about? These are the standards that most battery companies use to rate the output and capacity of a battery.

Cold cranking amps (CCA) is a measurement of the number of amps a battery can deliver at 0 ° F for 30 seconds and not drop below 7.2 volts. So a high CCA battery rating is especially important in starting battery applications, and in cold weather.This measurement is not particularly important in Deep cycle batteries, though it is the most commonly 'known' battery measurement.

CA is cranking amps measured at 32 degrees F. This rating is also called marine cranking amps (MCA). Hot cranking amps (HCA) is seldom used any longer but is measured at 80 ° F.

Reserve Capacity (RC) is a very important rating. This is the number of minutes a fully charged battery at 80 ° F will discharge 25 amps until the battery drops below 10.5 volts.

An amp hour (AH) is a rating usually found on deep cycle batteries. If a battery is rated at 100 amp hours it should deliver 5 amps for 20 hours, 20 amps for 5 hours, etc.

like i said it is pertaining to starting the car... hence the name "COLD CRANKING AMPS"

 

[ahole-ic]

Oh lawd!!! Just refer to my previous post to end all dispute. The battery is not really relevant with the car started until you exceed the limits of the alt.

 

[hatedonmostly 5,000+ posts]

Here is a little electronics lesson for everyone but bubba and sexy(you guys have it dead on)... A voltage (aka difference of potential) is required to make current flow. If a battery is at 12.6v and an alternator is in parallel with it at 14.4v, there is a 1.8v difference of potential between the alt and the batt and so the current can ONLY flow out of the alt to the batt. Once another device is connected in parallel, ALL CURRENT flows out of the alternator, because it is the highest source of potential in the circuit. The battery remains charging from the alt and not discharging. Once the current drawn causes the alternator to drop its voltage, and that voltage gets to the battery voltage, the battery will begin discharging. Unless the battery is discharging, IT IS ALWAYS CHARGING(aka drawing current from the alternator)

This is BASIC electronics and it is not disputable. Take it to heart. Stop recommending batteries to "stop voltage drop". It cannot and never has done that. The ONLY thing batteries help with is keeping the voltage above 12v so the amps don't blow. That's it. They don't "stop dimming" etc.

The way I always understood it was that the alt acts as a tender to keep the voltage at 14.4. If voltage lowers, the alt will restore it to 14.4. Batteries also have a discharge voltage, which is usually 12.8-13v. Anything above the battery's discharge voltage is entirely handled by the alternator.

So in theory, if the amps are drawing enough current to reach the battery discharge voltage, shouldn't the batteries:

1. take the burden off of the alternator; which means that if you have a large battery bank, the voltage should stay around 13v and slowly drop, as the batteries are discharging to power the amps?

2. the alt should charge the batteries while they are discharging; which means if the voltage should already stay around 13v from the batteries discharging, then alt charging them should increase the voltage a little? Making it a combined effort from the alt and the batteries?

Theory is different from practice, but that seems to be how it should work...

 

[Slayerx 10+ year member]

quote all of it next time brah...

4. CCA, CA, AH and RC. What are these all about? These are the standards that most battery companies use to rate the output and capacity of a battery.

Cold cranking amps (CCA) is a measurement of the number of amps a battery can deliver at 0 ° F for 30 seconds and not drop below 7.2 volts. So a high CCA battery rating is especially important in starting battery applications, and in cold weather.This measurement is not particularly important in Deep cycle batteries, though it is the most commonly 'known' battery measurement.

CA is cranking amps measured at 32 degrees F. This rating is also called marine cranking amps (MCA). Hot cranking amps (HCA) is seldom used any longer but is measured at 80 ° F.

Reserve Capacity (RC) is a very important rating. This is the number of minutes a fully charged battery at 80 ° F will discharge 25 amps until the battery drops below 10.5 volts.

An amp hour (AH) is a rating usually found on deep cycle batteries. If a battery is rated at 100 amp hours it should deliver 5 amps for 20 hours, 20 amps for 5 hours, etc.

like i said it is pertaining to starting the car... hence the name "COLD CRANKING AMPS"

Guess I should have been more clear. I was agreeing with you lol. Saying it was irrelevant to OP's problem

 

[sexy 10+ year member]

Along the same line about temps a 135 amp alternator will only do that 135 amp ratting when cold and at 2000 engine RPM in alternator RPMs it would 6000

 

[SicAudio 5,000+ posts]

I know ya was lol just wanted to make it clear for him why CCA is irrelevant //content.invisioncic.com/y282845/emoticons/wink.gif.608e3ea05f1a9f98611af0861652f8fb.gif

and yes RC on paper that is how it works, but each car is different. And as Ecrack/Sexy both said the box rise is often overlooked..

for daily IMHO you need 3-400Amps of alt/battery power in reserve. if you hammer it all the time you need an H/O alt and 2-300 Ah of battery..

I have built more systems in my profession than I can recall and hardly any of the DD setups "needed" H/O alts... some absolutely did w/o a doubt but not many.

in your case with those amps strapped and drawing close to 400 or more amps.. I would definately agree at least a 200A alt as well as 300 Ah of batts minimum...

the ohm load you have the amps at makes their efficiency go way way down...which requires alot more amps for the same power...

 

[ahole-ic]

Short answer? NO! lol

The way I always understood it was that the alt acts as a tender to keep the voltage at 14.4.

The alt puts out 14.4v. Nothing else does. It puts out a higher voltage than the batts can charge up to, so that there can be a difference of potential and current can flow FROM THE ALT into the batteries to charge them.

If voltage lowers, the alt will restore it to 14.4.

The reason the voltage lowered is because the alternator could not keep up with the current being drawn.

Batteries also have a discharge voltage, which is usually 12.8-13v. Anything above the battery's discharge voltage is entirely handled by the alternator.

Except for the voltages you listed this statement is true.

So in theory, if the amps are drawing enough current to reach the battery discharge voltage, shouldn't the batteries: 1. take the burden off of the alternator; which means that if you have a large battery bank, the voltage should stay around 13v and slowly drop, as the batteries are discharging to power the amps?

So far so good.

2. the alt should charge the batteries while they are discharging

No. How could this happen? IT TAKES A DIFFERENCE OF POTENTIAL TO MAKE CURRENT FLOW!!!!!!! LEARN THAT. A difference of potential is a voltage. If the alternator couldn't keep up and it's voltage dropped and now the batteries are discharging, how the hell is current going to flow from it into the batts? It can't! Furthermore, if the alternator were charging the batts and they were discharging to power the alternators, it would be totally unsustainable. Batteries discharge much faster than they recharge and they waste power when recharging. Something would fail really quickly. If the alternator can raise it's voltage above the battery voltage, all current is being drawn from it, and it is then powering the system as well as recharging the batteries.

which means if the voltage should already stay around 13v from the batteries discharging, then alt charging them should increase the voltage a little? Making it a combined effort from the alt and the batteries?

Nope. Read above. What you're saying is not even close to correct.