Can a bad/failing battery cause an alternator not to keep up?

[mclerico83 5,000+ posts]

2004 2005 2006 2007 MAZDA 3 & 5 HIGH OUTPUT ALTERNATOR | eBay

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[Sephious 10+ year member]

i would say alternator is junk, send it back, i went with powermax on ebay. i couldn't be happier with my alternator does rated or super close, case is way bigger and heavier, unless you wanna run duals with your stock and this HO(so called HO) contact the seller and if he gives you ****, call paypal and say it was falsely advertised as a 200 amp alternator and it putting out less than 150 and isn't of any use to you.
what kind of car is it?

It's a 2007 Mazda 3.

your running 4 guage to your amp, thats a problem 2, it needs 0 guage required

I'm not so sure about that. My 4 gauge is capable of 200 amps up to 20 feet, and 200 amps is more than the amp can possibly output, and I'm running nowhere near 200 amps to the amp.

EDIT: The eBay alternator you linked above is the one I have in my car right now.

EDIT2: I'm on crack, as that's from PowermaxUSA. Not sure where I got California Alternator and Starter from. That's definitely the alternator I have.

 

[grandam888 10+ year member]

it would be a wise idea to do big three in 0 gauge wire, lets say the cadence amp is pulling 65 amps, hifonics is pulling 25 amps, all other stuff 80 amps?, so we are looking @ 165 amps at most. you really need to be running 0 gauge (bigthree) and all the way to the amp. if your not running 0 gauge to amp in back, you will see a drop in voltage.

upgrade to 0 gauge big three before doing anything else.

 

[grandam888 10+ year member]

well your also forgetting, the wire MAY be able to handle the given amperage @ 20 ft, but your not accounting for voltage drop, the voltage drop @ 20 ft with a 1/0 gauge wire will be HALF of what it would be with a 4 gauge wire. your voltage drop with the 4 gauge going 20 ft pulling 165 amps should be roughly 17% (.175x13.5volts= 2.3 volts) so your @ 10.5-11v.

now look under the hood, you have 130-180 degrees the electricity has to fight against. heat is electricity's enemy, and heat can also affect voltage drop also.

personally i went with 3/0 under my hood, i would go with 1/0 big three, and 1/0 to rear.

 

[Sephious 10+ year member]

it would be a wise idea to do big three in 0 gauge wire, lets say the cadence amp is pulling 65 amps, hifonics is pulling 25 amps, all other stuff 80 amps?, so we are looking @ 165 amps at most. you really need to be running 0 gauge (bigthree) and all the way to the amp. if your not running 0 gauge to amp in back, you will see a drop in voltage.
upgrade to 0 gauge big three before doing anything else.

I may be interpreting it wrong, but assuming I'm at 150 amps for the sake of easily going with the chart, the power run from the alt to the battery is 7 feet and would be equivalent to almost 2 gauge due to running a 4 and an 8 gauge wire. The grounds are 4 gauge and both significantly less than 7 feet. One is probably about 1 foot and the other about 5. The power run to the amp is about 15 feet, and is 2 gauge.

All of that seems well within the realms of that chart. Plus, the voltage drop at the amp terminals compared to the battery terminals is extremely small. Not enough to affect anything. A couple tenths of a volt, even. The voltage drop happens at the battery just as it does at the amp.

 

[GAMEOVERCCA 10+ year member]

Big 3 has been done. This is a new alt. It's a 200 amp alternator from eBay from California Alternator and Starter.

theres your problem, cheap ebay alt saying 200amp but giving 125 probably, change your big 3 leads to 0 gauge, upgrade your battery, bring it somewhere and get a amp draw test, i guarantee that alt is a slouch.. a 5 year old battery will already be weak, get a good battery im sure alot of your problem will be solved, i had this same issue, now i got a optima redtop under hood and a kinetik HC800 in rear = no more problems...

 

[grandam888 10+ year member]

okay, well the chart only gives amperage ratings of wire, the reason this is so meticulous is were nearing the capacity of the 4 gauge wire, try this calculator, and account for temperature etc. and see what you get. also where are you pulling your voltages from. dash gauge? voltage meter wired to amp, wired to front battery? wired to back battery?

Voltage Drop Calculator Tool

 

[grandam888 10+ year member]

okay, well the chart only gives amperage ratings of wire, the reason this is so meticulous is were nearing the capacity of the 4 gauge wire, try this calculator, and account for temperature etc. and see what you get. also where are you pulling your voltages from. dash gauge? voltage meter wired to amp, wired to front battery? wired to back battery?

Voltage Drop Calculator Tool

 

[grandam888 10+ year member]

theres your problem, cheap ebay alt saying 200amp but giving 125 probably, change your big 3 leads to 0 gauge, upgrade your battery, bring it somewhere and get a amp draw test, i guarantee that alt is a slouch.. a 5 year old battery will already be weak, get a good battery im sure alot of your problem will be solved, i had this same issue, now i got a optima redtop under hood and a kinetik HC800 in rear = no more problems...

i will say, before we can get REAL numbers on the alternators, lets not bash it.

i have an ebay alternator, i a can run 50 amps worth of off road lighting, 20 amps of hid headlights, 2000rms amp(160 amps), 150rms amp(15 amps) a/c, etc. pulling app. 200-230 amps with a small hc800 kinetik battery, i have 2 runs of 1/0 wiring, and my alternator does just fine hovering around 13-13.5 volts. so the eBay factor can be ruled out, but as far as the seller he dealt with, who knows.

but the wiring is a big issue, if he keeps running these voltages, he will fry his amp.

 

[Sephious 10+ year member]

I'm no longer running those voltages. I currently have my subs at 350 watts (as low as I can get them at 1 ohm with this amp) until this is resolved. The voltage drop is far less severe at this wattage.

Also, I'm measuring with a multimeter at the amp's terminals and the battery terminals. At the new 350 watt load, the difference between the battery's terminals and the amp's terminals is .15V, which is not a lot. That's about 1%.

Also: I'm an idiot and have only done 2 of the big 3. I have not done the engine block to chassis. I'll do this as soon as I can find a "y" connector instead of a ring terminal, as I don't want to completely take off any engine block bolts without my mechanic buddy on hand in case I wreck something.

 

[grandam888 10+ year member]

The voltage drop is lower because amperage draw was minimized.

The amont of Amperage running through a wire affects the voltage drop. If you had looked at the voltage drop calculator you would have noticed the little box where you put the amperage.

 

[Sephious 10+ year member]

The voltage drop is lower because amperage draw was minimized.
The amont of Amperage running through a wire affects the voltage drop. If you had looked at the voltage drop calculator you would have noticed the little box where you put the amperage.

Yeah, and the calculator said 0.17 volts, where I measured 0.15. So it's pretty accurate. At the absolute max I'd ever have my subs, and accounting for amp inefficiency, it says 0.48 volts, which is still pretty negligible when we're talking about starting from 13.8 or higher.

The voltage drop from running 4 gauge wire and 8 gauge wire from the alternator to battery at the full 200 amp output would be 0.56 volts according to that calculator. 0.56 volts, even if my max charging is only 13.8 (and I've seen it higher than that), leaves me with 13.24 volts. 13.24 volts - my theoretical maximum voltage drop = 12.76, which doesn't even dip into my battery yet. Yet, calculating for my current tested draw, I should be at at least 13.37 volts at my amp's terminals, yet it is already dipping into my battery so something isn't right.

I'm almost positive at this point that that something is the alternator.

Also, I just did the engine block to chassis wire and it made no difference. Even if you think my wiring is the problem, you have to admit that it would have made some difference, especially since this is supposedly the most important wire, and yet it made absolutely no difference. Revving also makes no difference, and again, there's no way my alternator puts out its full 200 amps at idle when it specifically says it does it at 1200 RPM's. That also makes me think it's the alternator.

 

[Sephious 10+ year member]

Sent a message to PowermaxUSA. We'll see what they say.

 

[Sephious 10+ year member]

So PowermaxUSA replied awhile back and asked if I had used the smaller pulley that came with the alternator. I definitely didn't change the pulley on it, so that's not the problem. I bought a new battery, made no difference, tried temporary larger wire runs, no difference. At this point it's gotta be the alternator being faulty.

 

[BlactimusCrime 10+ year member]

So PowermaxUSA replied awhile back and asked if I had used the smaller pulley that came with the alternator. I definitely didn't change the pulley on it, so that's not the problem. I bought a new battery, made no difference, tried temporary larger wire runs, no difference. At this point it's gotta be the alternator being faulty.

Have you checked all your grounds? made sure all connections were to clean chassis metal?