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Old 01-18-2016, 12:59 PM   #1
bmw325ci2002
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e46 325ci dyi sound system help please?

Hi I have a 2002 325ci. Batteries in the trunk. I haven't been able to afford and legit sound system so last night I hooked up my computer speakers and sub(120v 240watts) to an old power convert that plugs into the cigarette out light (120v(200w) I just wanted to see if it would actually work and not did so I talked to a buddy who knew a little more about electronics and speakers than I did and he told me I should be fine with a a converter that is 120v with 240+ watts. Last night I got the durlast one that's 105-120vollts and 400 Watts. My sub's and sound system is working perfectly and my car seems to be tunning just fine.(114k miles just put in brand new spark plugs and fuel injector cleaner). My question is, will this converter or the sub/speakers end up draining my battery or killing my alternator? My cars cigarette outlet is on 100% of the time since I've owned it for 2 years and haven't had to change the battery yet. I'll leave my phone charging on my car over night plugged into a little USB cigarette outlet. Idk if BMWs have crazy advanced electronics that allow for that or if my cars just weird but if someone could let me know of this ghetto speaker system.is going to blow my battery or alternator please let me know asap (:
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Old 01-18-2016, 01:14 PM   #2
jdstrickland
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What you are doing might work if the car is always running when you are driving the system, but if the car is parked, engine off, then the battery will not last very long.

You report that the cig. lighter is always powered, but you do not seem to realize that it is not actually working and draining the battery. You might be using a USB charger for your phone or tablet, but that is stepping the voltage down from 12 to 5, then drawing an amp, maybe two. This is waaaaay different than inverting the voltage upwards from 12 to 120 and then drawing 3 watts. Watts and amps is a function of the volts, you are pulling 10 times the volts that the battery provides, it stands to reason that this would be 10 times the amps also. You are pulling 30 amps at the voltage of the car battery, this will not last very long if the engine is off.

Your car has an amp in the trunk on the left side behind the liner. It is in the general area of the wheel well. Remove the liner from the inside of the trunk and the amp will be mounted to the side of the car.

For the record, all BMWs have the battery in the trunk. You are using an inverter, it makes 120v AC out of 12v DC.
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Old 01-18-2016, 03:34 PM   #3
bmw325ci2002
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@reply

Sorry I'm a little retarded when it comes to elextrocty and electronics. I'm a profession detailer I can make a car look brand new inside and out, wet sanding buffing and all that, just starting to learn mechanical components and how to work on my own car and street bike. So basically from what I understood, my alternator and battery will be fine as long as I don't use my sub and speakers and converter without the engine running? Because that's perfect. I only use it or listen to music in my car in general of I'm driving. Every time I turn my car off or whatever I make sure to turn off the converter box as well as unplug it just on case.
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Old 01-18-2016, 05:11 PM   #4
jdstrickland
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INVERTER.

You are using an inverter. There is such a thing as a converter but that's not what you have, or are using.

Yes, if you remember to unplug your Dr. Frankenstein project every time you park the car, your battery and alternator will survive the ordeal. I'm not entirely sure if I calculated load correctly, but I think you are pulling about 30 amps through your system, that's going to be very close to the limit of the cigarette lighter fuse.
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Old 01-18-2016, 05:21 PM   #5
bmw325ci2002
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Ok awesome thanks a lot, appreciate it. I remember I tried it a few years ago in my sisters 07 elantra and IDL of the inverter was different without the required volts or watts but he car was running and the lights and the dash start dimming and flickering and ****. I asked a service tech at work today about it and he said it would be bad for my car cause the alternator only pushes out like 10-15 volts or something. Lol like I said I know all about compounds polishes chemicals paint sealants and what not but nothing about electricity i n terms of watts volts and amps lol
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Old 01-18-2016, 05:55 PM   #6
jdstrickland
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The car makes 14.4vDC while running. All cars do this. The tech is right, sorta.

Lots of companies make an inverter to turn 12v into 120v. You can get them in several sizes, where "size" is the number of watts they produce. Motorhomes are a place where these are useful because the coach will have appliances and lighting that may run on 120, but the engine only makes 12. People that use a laptop might want to use an inverter to provide ground power to the power supply so that the computer can be used. There are solutions that are not 120-centric, but an inverter is reasonably cheap and very easy so many people will go that route. I'm not sure how to convert the load calculations from 12v to 120v, I used a simple factor of ten. If you are using 3A at 120, that should be the same as 30A at 12. I'm happy to admit my mistake if I did this wrong, but I am pretty sure I am right. 3.25A x 120 = 390 watts (or 32.5A @ 12v), I thought you said that you have a 400W inverter. You can have more capacity (higher watts) than the load needs, but you cannot have less else the voltage will drop and the load will not operate properly if at all.

Your car will not be harmed by using an inverter. You can read the box that the inverter comes in. An inverter can be connected directly to the battery should you desire to do that, be sure to fuse it sufficiently on the input side. It should have a fuse built into the wire that connects to the + terminal on the battery, if so then there will be an alligator clip to clamp onto the terminal. There can also be a cigarette lighter adaptor that plugs into the cig lighter socket. The cig lighter is protected by a 30A fuse. The load will discharge the battery if there is no charging device (alternator) to replenish the battery -- the battery will drain quickly if the engine is off. It won't drain in minutes, but it will drain in hours.

Cold will play a role in your satisfaction with this solution, or dissatisfaction as the case may be. Cold and batteries are a bad combination, and cold batteries with a heavy load just makes the bad combination worse.
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Old 01-20-2016, 09:49 AM   #7
bmw325ci2002
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Really appreciate the input and feedback. Things have been running smoothly haven't noticed anything except the interverter fan kicking on every 15 seconds of I sit in a lot idling with my engine on for too long. While driving though there's no change I'm engine power or electronics, and the speakers play smoothly without any kinks. It's just a klipesch computer sub / 2 speakers, I'd say its probably an 8-12inch sun. Like I said the speakers run 120volts 240watts and the inverter claims 105-120 volts with a maximum of 400 watts so I feel pretty confident this was the right way to go for the sound i wanted
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