Car Audio on a Cart - Alternatives to Battery Power?

[DanL]

Alright, let it be known that this year, 810 has joined the list of teams who put car stereos onto their carts. Before the flaming comes, I'd just like to say that Joel J. said it best in this thread when he said something to the extent of a sound system on your cart is not a bad/illegal thing until it is being blasted in the pits - something we're not going to be doing. We're building this to increase moral on the team, give the less-advanced kids something to do that they'll enjoy working on while the robot design is being finalized, and lastly, to have something to play music in our work room. With that said, on to my question.

Are there any good ways of powering a car-audio-based system (headunit + 2 20watt 5's + 2 30watt 7x9's, no amp) other than a battery? We plan on having this going during our building phase, so we don't really want to have to charge a battery 3, 4 times a day. We also don't want to dish out $50 or $60 for a car battery. Specifically, we want something that can just plug into an outlet -- like an ac power brick, but can deliver a lot more current. It's a 120watt headunit, so does that mean it needs 10amps? I've heard that ratings for headunits are only peak readings (tricks the manufacterers play to make them seem more powerful than they are), but actual rms power is much much less. Anyone know how much less, and what would be a good current value to shoot for? Finally, does anyone know where to buy an ac adapter that can supply this much current?

Or, for teams that have done this using car batteries, how often do you have to recharge your battery?

[Greg McCoy]

I believe that real car batteries will not survive long if you just take them out of the car and discharge them. They usually can only stand being empty a couple of times before they are shot.

Here's a quick list of power supplies that you could probably use, I'm sure you could find cheaper ones though:

http://www.universal-radio.com/catalog/hamps.html

I think the MFJ ones are probably the most cost-effective. Remember that you can always use a 12V power supply around the shop for other things too, so it's a good idea to have one. If you had a power supply and a battery (like a robot battery), you could rig it up so that you could just switch power sources when you were "mobile." I definitely wouldn't charge the battery with the power supply though

Good Luck

[DanL]

thanks for the link, but those are kinda out of our budget. Is it possible to buy something like a 12v, 10amp power supply for around $50 at most?

Originally Posted by Greg McCoy

If you had a power supply and a battery (like a robot battery), you could rig it up so that you could just switch power sources when you were "mobile."

What about powering the stereo through a battery while the battery is hooked up to a battery charger? My gut instinct tells me thats a really bad idea, but can anyone explain why?

Better yet, if anyone has created such a cart, how did you go about the task of powering your system?

[Andrew Rudolph]

Originally Posted by SuperDanman

thanks for the link, but those are kinda out of our budget. Is it possible to buy something like a 12v, 10amp power supply for around $50 at most?



What about powering the stereo through a battery while the battery is hooked up to a battery charger? My gut instinct tells me thats a really bad idea, but can anyone explain why?

Better yet, if anyone has created such a cart, how did you go about the task of powering your system?

Last year on 212 we had a head unit simmilar to the one you described in power ratings and a 300 watt amp all running off of a lawnmower battery we bought at sears for 20 bux it lasted a whole day. The ratings on head units are peak power, i.e. when bass kicks and the volume is all the way up. We had 2 batteries and made it easy for us to change them, but the die hard battery lasted all friday at nats, so that was alot of play time.

[KevinB]

Why not use a Robot battery?

They're only like $30.

[j_pannell]

You could use a old computer powersupply. Just rip off all of the wires, and solder it to the PCB! I used the sam idea to make a 12v PS for some R/C pit equipment.

-Jon Pannell

[fox46]

I am assuming that your cart has a on-board 12V battery. Just buy a 10 Amp battery charger, and have the battery on-charge while you're listening. Don't use a charger as a powersupply because the quality of power is very poor (lots of noise, and no voltage regulation - could hurt the AMP). By using a battery, it acts sort of like a reservoir in a plumbing system- It takes the erratic power from the charger (pump) and uses it to "fill" the battery (reservoir), and then you can draw as much/as little electricity (water) from the "reservoir" at the same quality as pure DC power. The battery essentially acts as a crude voltage regulator/power stabilizer.

I like sound systems on carts - post some pictures when you're done

[DanL]

Originally Posted by j_pannell

You could use a old computer powersupply. Just rip off all of the wires, and solder it to the PCB! I used the sam idea to make a 12v PS for some R/C pit equipment.

-Jon Pannell

Well, how much amps can a computer power supply supply? If the rating is say 250watts, does that mean 250/input voltage (250/120), or does that mean 250/output voltage (250/12)? Besides, I was under the impression that each rail in a computer power supply is designed for a different amount of current, and if I were to open one up, I'm not sure where to tap in before the power supply splits up into the individual rails. If you've done it before, I'd appreciate some explanation on what to be looking for and how to find out how much current the power supply can take.

[Kevin Sevcik]

Yes, different rails are rated at different amperages. It would appear that a decent 250W power supply is rated at 13A on the 12V rail. you'd tap into it from the normal molex connectors, I'd think. Not real reason to rip the thing apart that I can think of. 12V would be the yellow wire, BTW. If you need more amperage I suppose you could up the wattage of the PS.

Keep in mind that the computer PS is going to do a poor job of charging a battery since the charge voltage is 13.8V or so. Using a normal battery charger should be fine, since car amps are designed to run off the 13.8V an alternator puts out anyways. I'd say just go with that idea.

[pras870]

Well, with car audio being a specialty of mine, I think I can offer some advice right now. You're not going to be drawing a lot of power, so i'd have to say, the easiest thing to do, would be to buy a simple power supply. Since you're not running an amp, you probably won't exceed anymore then 150 or so watts, so I would use a power supply such as this one (http://www.millionbuy.com/pyrps12k.html). I know it's rated at more then 150, but this is just to be safe. Besides, at that site, the prices only range about $5 an amp above or below. (If that makes no sense, I apoligize, it is 4am here in New York )

And if the deck is rated at 120watts, then that means that each outlet (or speaker connection) is rated at 30watts peak. The RMS power is probably more along the lines of 15-20. The RMS is what you're really concerned about. The peak power is just when say a bass note hits, it jumps to that for a split second (u can also eliminate this if the deck has a high pass filter on it).

[Al Skierkiewicz]

Originally Posted by SuperDanman

thanks for the link, but those are kinda out of our budget. Is it possible to buy something like a 12v, 10amp power supply for around $50 at most?



What about powering the stereo through a battery while the battery is hooked up to a battery charger? My gut instinct tells me thats a really bad idea, but can anyone explain why?

Better yet, if anyone has created such a cart, how did you go about the task of powering your system?

Radio Shack has power supplies for CB radios that are fairly inexpensive.

[DanL]

Originally Posted by pras870

...such as this one (http://www.millionbuy.com/pyrps12k.html).

It says Output: 13.8V DC... a car electrical system is designed for 12v, no? Would the constant 1.8v extra hurt it in any way?

[Andrew Rudolph]

Originally Posted by SuperDanman

It says Output: 13.8V DC... a car electrical system is designed for 12v, no? Would the constant 1.8v extra hurt it in any way?

No they put off more than 12v, if you look at most 12v batteries, like the one that comes with the robot when its fully charged is about 13.5v, a good thing to know if you are in charge of making sure batteries are charged.

[andy]

How bout fuel cells?

Is internal combusion an alternative?

What about propane, like on a forklift?

Seems like a propane "people transporter" would make an excellent robot cart. They use them in airports, to transport the elderly and handicapped...

Just a thought...

Good luck this year!

-Andy

[Al Skierkiewicz]

Originally Posted by SuperDanman

It says Output: 13.8V DC... a car electrical system is designed for 12v, no? Would the constant 1.8v extra hurt it in any way?

The type of battery used in cars has a terminal voltage of 13.8 volts when fully charged. It is generally referred to as a 12 volt system simply to delineate it from 6 volt systems used in some cars or 24 volts used in some trucks. Auto accessories are designed for operation up to 15 or 16 volts so that they will not be damaged should the voltage regulator in your car charging system fail and provide a higher voltage.