Is This Normal? Volts Dropping to about 10V on Dash Gauge

[Ramblin 10+ year member]

I'm new to this game, so I ask for forgiveness in advance if the answer to this question is too obvious.

I'm running a (supposed) 250A alternator on a 2000 Silverado. Big 3 is done in 1/0 gauge and connections are good, i.e. paint removed at attaching points, solder-only ring terminals, etc. Battery is a Red Top, but it has been discharged several times. It still starts the truck and takes a charge, but it's been wounded many times by my 15-year-old.

Amps are Hifonics XX Zeus, and RF P850.4 and both are fed off a 1/0 feed to a distro with 1/0 to the Zeus and 4-gauge to the RF. I'm running the Zeus at 1 ohm into four JL 10W3V3's. The P850.4 is running 2-ohm comps at each corner.

My son gets in the truck this afternoon showing his thump to a few friends. So he has it pegged, and I look at his voltage gauge and it is showing nearly in the red at 9.5-10 volts. I tell him to rev it up to about 3,000 rpms, and the needle does not move up off that 9.5-10 mark. He turns the system off and it goes right back up to 14+V.

So now I'm concerned. I know I need another battery, and I have an HC2400 on the way to partner with the Optima. But is this amount of voltage drop normal if I'm running a high output alternator? When I get to work tomorrow I'll find out if our electrical techs have a meter of appropriate size to check my alternator output. I know volts and amps are different things, but thought the HO alt should manage the load a little better.

Any thoughts? Thanks for your help.

Keith

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[hatedonmostly 5,000+ posts]

Well, no, but the dash voltmeter is not very accurate at all, in regards to how car audio draws.

Get that battery in right away, regardless. The purpose of the alt is to recharge the battery, but when you are drawing that much current, there is not enough current available for the equipment.

 

[Supergumby5000 5,000+ posts]

lol, did you really think running that much power on a single red top was going ot be okay?

you need more battery. A lot more than just a single red top.

rule of thumb: no less than 1amp of battery for every RMS watt of power

 

[outsideshot23 10+ year member]

lol, did you really think running that much power on a single red top was going ot be okay?
you need more battery. A lot more than just a single red top.

rule of thumb: no less than 1amp of battery for every RMS watt of power

or you can do the math all the way.. your alt might be 250 amp but it could be anywhere from 100-160 @ idle.. you need to get it tested so you know exactly.. (never a bad thing to gain knowledge about your own system).. and ya if your batt has been discharged that many times i would not rely on it too heavily and lean toward replacing it.. about the math i was telling you... there is a great tutorial on you tube... search "car audio 101" it should eb at the top and say abttery tutorial and it will give you everything you need to know as far as how many watts your running, effeciency, Alt Amps, and ultimatewly how many Ahs in batts you need.. everyone has their own ways of doing things and im not saying mine is the only way to go but this will get you in the ball park and give you an idea.. hope it helps

 

[audiolife 5,000+ posts]

I would see what rpm that alt is kicking on.

 

[ahole-ic]

Well, no, but the dash voltmeter is not very accurate at all, in regards to how car audio draws.
Get that battery in right away, regardless. The purpose of the alt is to recharge the battery, but when you are drawing that much current, there is not enough current available for the equipment.

False. The purpose of the alt is to run all electronics in the vehicle when the engine is started AND recharge the battery. Current is always drawn from ONLY the highest source of potential. Once the car is started, the alt has the highest voltage in the circuit and thus supplies all current in the system while it's voltage remains the highest.

 

[ahole-ic]

lol, did you really think running that much power on a single red top was going ot be okay?
you need more battery. A lot more than just a single red top.

rule of thumb: no less than 1amp of battery for every RMS watt of power

Wow. I have a 270 amp alt and 1 batt in the back just to make sure I don't drop below 12v. I'm running a saz-3500d. If I rev to 1500rpm, NO voltage drop at full tilt. Also, you didn't specify for your made up rule. What amp rating? There are several. Are we talking about amp hours? That's important but not totally relevant. Are we talking about cranking amps? That is important but not really going to help us in this scenario. Are we talking about short circuit amps? That's not really useful at all. You act like you know a lot, but the more I read your posts I think you just wish you knew something.

 

[Supergumby5000 5,000+ posts]

Wow. I have a 270 amp alt and 1 batt in the back just to make sure I don't drop below 12v. I'm running a saz-3500d. If I rev to 1500rpm, NO voltage drop at full tilt. Also, you didn't specify for your made up rule. What amp rating? There are several. Are we talking about amp hours? That's important but not totally relevant. Are we talking about cranking amps? That is important but not really going to help us in this scenario. Are we talking about short circuit amps? That's not really useful at all. You act like you know a lot, but the more I read your posts I think you just wish you knew something.

like i said. rule. of. thumb. This guy is new, no need to get into the mathematics of it. I've taken circuit theory classes, i know what you are talking about, but the OP wont. I mean cranking amps. If i was talking about amp hours, i would have said the phrase "amp hours". Obviously as separate cases, neither makes much of a difference, but in most cases when you buy a battery, even my 15yo sister knows that a battery with higher CCA's will have a higher AH rating as well.

you're running a saz 3500D on two batteries, with a HO alternator, and im guessing the batteries you are running are much better than what the OP has. This guy is running a f*cking redtop on around the same power you are, and thats it

You can put your e-boner away now.