New Alt Still voltage drops!

[Anonymous 10+ year member]

Oh the last question it was at idle with the system on

 

[QtrHorse 10+ year member]

They will put a load on the alternator, to see if it is putting out the stated amperage. If it's a 200 amp alternator, it should put out 200-210 amp at a full load. A good result would be for you alternator to be putting out 200 amps and a bad result would be for your alternator to put out 150 amps if it's rated at 200 amps. They will also be able to tell you exactly what voltage it is putting out at idle. They should also be able to test your batteries under as well.

If all your tests were done at idle, then that is your problem. The alternator will never be able to handle that load at idle, without the problems you stated.

 

[helotaxi 5,000+ posts]

A bad ground for your amp will cause the voltage to drop under load. A bad connection will have the same result. Basically the resistance is high at the bad connection. As the current through the high resistance connection is increased, the voltage drop across is increases as well. With a light current draw, it will pass normal voltage since the voltage drop is dependant on current.

 

[bumpin_blazer 5,000+ posts]

you paid extra for a pulley that should charge more at idle? that sounds like a bit of a rip off IMO. your alt at idle might do 120amps at idle with nothing drawing, you play your music loud you have no power simple as that. before you waste your time getting it tested, REV THE ENGINE. why can't you do that when like 4 people suggested it? the only time i've seen an alternator do a lot at idle was in my car and other SPL vehicles who bought the alts that way. my alt did 180 at idle and 300 at full tilt.

 

[helotaxi 5,000+ posts]

A smaller pulley that spins the alt faster is kinda common. Spinning the alt faster at idle has the same effect as running the engine at a higher RPM. If you spend a lot of time in traffic or low RPM highway cruising, it might well be worth it.

 

[Anonymous 10+ year member]

I have tried revving the engine like when the batt light comes on but it does not help i have to turn the music down

 

[headless 10+ year member]

I have tried revving the engine like when the batt light comes on but it does not help i have to turn the music down

You need a volt meter/DVM/clamp meter to see what is really going on here.

Rev the engine while under that load, and while the system is playing and the engine is revved, test your voltage at the alternator where it runs to the battery.

If the alternator's voltage is still high (13+v), you have a connection problem between the front electrical system and your amp (cap).

If the alternator is reading 10v like your amp's cap does, then your alternator is not putting out it's rated voltage at the load you're providing it, even when revved.

If that's the case, check your amp draw from your batt to amp and see if it's

To see if the alternator is seeing additional load above and beyond your audio system, check current draw from alternator to the battery; if current draw is excessively higher between that connection than the battamp, you know there is additional resistance either inside the batt or connected to the batt that isn't your stereo

 

[helotaxi 5,000+ posts]

If the load is much above 220a, you're probably simply overdrawing your power system and discharging your main batt down. Get a new batt.

That makes no sense whatsoever. You're saying that since the car electrics are drawing more than the alt can provide to replace the battery?!? That's like saying that the tires are worn get a new engine, or the amp isn't big enough get a new headunit. If the problem is that the car and system are drawing more than the alt is putting out, then the alt or the system, not the battery, are what need to be addressed.

To see if the alternator is seeing additional load above and beyond your audio system, check current draw from alternator to the battery; if current draw is excessively higher between that connection than the battamp, you know there is additional resistance either inside the batt or connected to the batt that isn't your stereo

The car draws power from the alt to run everything electrical. There will have to be a load above and beyond what just the stereo is drawing. Depending on what is turned on in the car, it could be pretty significant. It looks like the two most likely problems are that the alt isn't putting out the right power or the battery is bad.

 

[headless 10+ year member]

That makes no sense whatsoever. You're saying that since the car electrics are drawing more than the alt can provide to replace the battery?!? That's like saying that the tires are worn get a new engine, or the amp isn't big enough get a new headunit. If the problem is that the car and system are drawing more than the alt is putting out, then the alt or the system, not the battery, are what need to be addressed.

I've seen a dying battery cause excessive load to be placed on an alternator before; replacing batt solved dimming issues because it removed a massive load (the dying battery) from the load the alternator was seeing. If that's the case, you'd be able to measure the load by checking between the alt and batt. Ya dig? You're taking my words totally out of context.

The car draws power from the alt to run everything electrical. There will have to be a load above and beyond what just the stereo is drawing. Depending on what is turned on in the car, it could be pretty significant. It looks like the two most likely problems are that the alt isn't putting out the right power or the battery is bad.

That's exactly what my post said, man. That load could be a dying batt. You can see the load by checking draw between alt and batt.

 

[knukonceptz 10+ year member]

Like Headless mentioned, get a real voltmeter and measure voltage at the battery, ALT and amp (forget the cap has a voltmeter for the time being) Make SURE ALL places have the same voltage reading with and with out load. Lots of folks jump to conclusions without all the facts and make statements that have no value if the facts are not listed.

If the front battery is reading VERY different, your problem is your installation of the amp, if the voltage is the same, you have issues with the charging system. Also - what is the Battery voltage with car off? if low a good over night trickle charge would be a smart move

some vehicles have voltage regulators that have a delay in them to avoid spikes, I am not sure if that model has it, but it is common on Ford Trucks, that could be something as well, but I would think Dom is aware of this.

 

[helotaxi 5,000+ posts]

That's exactly what my post said, man. That load could be a dying batt. You can see the load by checking draw between alt and batt.

The current between the battery and the alt will be the total current drawn be all loads in the car. That alone doesn't tell you any more than what the alt is putting out at that time. It gives you no indication of WHAT is drawing the current. To check the battery, the easiest thing is just to take it to an autoparts place and get it checked. I'm fully aware that the load could be a dying battery, but what you suggest will not diagnose what the problem is. As knukonceptz said, checking the volts at the alt, the volts at the battery posts and the volts at the amp will give you a far better indication of where the loss is. If that is what your post said, it was worded awkwardly enough that that is in no way what I got from it.

 

[headless 10+ year member]

The current between the battery and the alt will be the total current drawn be all loads in the car. That alone doesn't tell you any more than what the alt is putting out at that time. It gives you no indication of WHAT is drawing the current. To check the battery, the easiest thing is just to take it to an autoparts place and get it checked. I'm fully aware that the load could be a dying battery, but what you suggest will not diagnose what the problem is. As knukonceptz said, checking the volts at the alt, the volts at the battery posts and the volts at the amp will give you a far better indication of where the loss is. If that is what your post said, it was worded awkwardly enough that that is in no way what I got from it.

Please excuse my horrible english skills; that was what my post said.

 

[Anonymous 10+ year member]

I went and had it tested and they told me to the batt was not bad but it had a weak charge, so they said they could not run tests on the alt. So i am going to go have it trickled charged fully for a day and see what happens.

 

[Anonymous 10+ year member]

Could the reason that the batt has a weak charge due to me not really ever driving it or starting it?

 

[headless 10+ year member]

...

Yes

Batteries don't charge themselves; the alternator has to run (engine run) and put out sufficient voltage for it to charge.