izzyz28

2004 E55 W211

So I recently installed a couple of 12" subs driven by 2-300 watt RMS amps. It's not the ideal setup but it sounds decent, was cheap, and made use of the stuff I had laying around from other projects.

The power and ground for both amps are connected directly to the battery(tell me if this is an issue and where to move the power/ground). At moderate volume levels it works great. However, after ~1/2 hour of listening at a decent volume(driving down the freeway) and then cranking it up I received the "Electrical consumers are reduced" message that you usually get when the alternator dies. I immediately shut off the stereo and within a minute I got the A-ok message telling me everything was good.

I have a hard time believing the alternator can't keep up, but then again I guess 600 watts RMS would mean a draw of at least ~50 continuous amps at 12V. Maybe it is too much or my wiring method is not allowing the car to measure all of the current that's consumed, which pops the message when it gets too high. I know these cars can be picky. I tested the battery when I got the car 3 months ago and it tested better than new. Never tested the alternator, but I've never had any issues otherwise. Any ideas?

BennyzGirl

Did you relocate your battery to the trunk? if not I would try a new ground. Its recommended that you keep your ground within 18 inches of the amp. Dont know if that will make any difference since its working but it would be worth a shot.

izzyz28

The battery is in the trunk from the factory, the positive and ground wires are both 3 feet long and plenty big for the power I'm pulling. It seems to me that either the alternator can't keep up under high demand, or the car is sensing something it doesn't like. Keep the ideas coming though, I appreciate all input.

amdeutsch

Try caps. The car by itself will draw a bit. Plus keep in mind that 600 Wrms does not equate to 50 A @ 12 V. There are loses in the amp within the electronics. The amp most likely takes the 12V input and converts it to 60 V, or there abouts, prior to sending it to the output stage. Keep in mind that 4 Ohm subs running at 300 Wrms means a voltage swing of about 35 Vrms across the sub coil. 300 Wrms ~ 600 Wpeak. That in turn means the voltagge swing is now 49 Vpeak. I would really be surprised if the efficiency of your amp is better than 80%. Class D probably having the best efficiency and the others are lower than that. BTW, that heat you feel on your amp is the losses.

izzyz28

That's why I said "at least 50 Amps", though I'm sure it is more than that when you take efficiency into account. Even at 75% efficient we're still looking at 65+ Amps(okay, maybe a bit less @ 14V). Maybe 600W RMS without a cap is too much for the car to handle, though 600W really doesn't sound like "that" much. Maybe I'm just out of touch with reality? I'm sure there are people running much more than that in their W211's.

Thanks for the advice about the cap. I did notice my lights barely dimming in time with the music when I first installed it, but I got away without a cap in all my other cars so I didn't think much of it. Of course they won't tell you there is an issue with current/voltage until the alternator fries or the battery is junk.

jbondox

could be a whole list of stuff, but adding another load on your battery with a cap isn't going to do much.

weak battery is another, weak alternator, installation, etc

izzyz28

Next time I go to the shop I'll do another load test and a charging system test. I don't know what the alternator is rated at, but I'm guessing the car puts quite a load on it even during normal operation, and askign for another 60+ amps may make the voltage drop to a level that triggers the warning(or whatever triggers it).

jbondox

Good idea. also there is a sensor, that senses the drain and triggers the convenience function, I forget actually what i did to fix it, but will look into it later.

izzyz28

Great, thanks!

nJuDunno

I have about 900 watts RMS from 2 amps that run off the battery in my trunk with no issues, so I would think your setup should also be fine. A healthy electrical system should be able to handle this power so I would think something else is causing the issue

JonMBZ

Im no expert in car audio equipment, but I do know that sometimes people use the wrong battery in their cars. Do you have the high output black non-spillable battery in the car?