Car Audio on a Cart - Alternatives to Battery Power?

[DanL]

Originally Posted by Al Skierkiewicz

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.

Ah, alright... many thanks for the explanation and everyone who posted suggestions on power supplies and the like.

[Andrew Rudolph]

You do realize you have to tell us what it finally came out to be, otherwise we will all go craaaaaazy......errrrrrrrrrrrr

[Rickertsen2]

Are you still lookign for a power solution for your robot cart? I designed you a VERY SIMPLE(4 compenents) circuit that wil met your needs. Its costs $28.1(plus parts shiping) and when used with a lawn tractor battery(about $20 from home depot) will give you more power than you will ever need.

Here is what you will need along with part numbers from http://allelectronics.com
TX-12625 $20 power transformer
FWB-352 $2.50 bridge rectifier
EC-648 $0.65ea( you need 2 of them, so $1.30) 680uF capacitors

LCAC-129 $3.00 7.5' power cord
ACS-3 $0.65 plug for power cord


Note: Don't use this with SLA batteries(like the robot battery). The charge curent is way too high and it will signifiganly shorten their lifespan.

Tell me if you(or anyone else) are/is interested and i will post a schematic.

[DanL]

Originally Posted by Rickertsen2

Are you still lookign for a power solution for your robot cart? I designed you a VERY SIMPLE(4 compenents) circuit that wil met your needs. Its costs $28.1(plus parts shiping) and when used with a lawn tractor battery(about $20 from home depot) will give you more power than you will ever need.

Here is what you will need along with part numbers from http://allelectronics.com
TX-12625 $20 power transformer
FWB-352 $2.50 bridge rectifier
EC-648 $0.65ea( you need 2 of them, so $1.30) 680uF capacitors

LCAC-129 $3.00 7.5' power cord
ACS-3 $0.65 plug for power cord


Note: Don't use this with SLA batteries(like the robot battery). The charge curent is way too high and it will signifiganly shorten their lifespan.

Tell me if you(or anyone else) are/is interested and i will post a schematic.

Yes, I would be interested in this... maybe if you have some time, could you also post some of the basic theory behind how it works?

[Rickertsen2]

Originally Posted by SuperDanman

Yes, I would be interested in this... maybe if you have some time, could you also post some of the basic theory behind how it works?

Sure. But that will prolly be tomorrow, bc i'm up pretty late with homework as it is.

[velocipenguin]

I'm guessing that this design uses the transformer to step down 120 volts AC to 12 volts AC, along with a full-wave rectifier to transform 12 volts AC into 12 volts DC and a couple of filter caps to eliminate ripple. Am I right?

[Rickertsen2]

Originally Posted by velocipenguin

I'm guessing that this design uses the transformer to step down 120 volts AC to 12 volts AC, along with a full-wave rectifier to transform 12 volts AC into 12 volts DC and a couple of filter caps to eliminate ripple. Am I right?

you get a cookie. Basically thats it. Its pretty simple, but thats all that is needed for car audio stuff, which generally isn't too picky.

[Kevin A]

Originally Posted by Rickertsen2

you get a cookie. Basically thats it. Its pretty simple, but thats all that is needed for car audio stuff, which generally isn't too picky.

When using a transformer a capicitor will make it sound sooo much better.

[Rickertsen2]

Here is a basic description of the circuit. The fist part of the circuit is the transformer. One side(the primary) is hooked up to the wall plug. The transformer takes the 120V AC from the outlet and steps it down to about 12.6V. Both the input and the output from the transformer will look like the wave shown in fig1, with the difference being that the input will have a magnitude of 120 volts, while the output will have a magnitude of 12.6 volts. The next stage of the circuit is the rectifier, which internally consists of an arrangement of 4 diodes. The the output of the rectifier is the absolute value of the input, and looks like fig B. The purpose of the rectifier is to convert the AC from the transformer to DC. As you can see in fig B, the rectifier output is a series of pulses, which need to be smoothed out into a continous wave to be of use. This is the job of the capacitors. They act sort of like a tank for electricity. when the voltage is on, thye take in electricity. When the voltage drops, they provide power. Finally we end up with soemthign that looks like fig C., a steady relatively clean(ripple free) 12 volts. When plugged in, the circuit will power whatever is hooked up to is, as well as charging the battery(up to 12V). When it is unplugged, power will come from the battery. This circuit is one of the most basic types of power supplies and is a bigger version of what you would find if you cracked open a "wall wart"( the big annoying things that use more plug space than they should). This circuit has only 1 problem, an it is that it will only charge batteries up to 12V. A fully charged battery is normally about 13.8V. This van easily be fixed by replacing the 12.6 volt transformer with a 14-15volt transformer.

[DanL]

Thanks for the info and the explanation... I'll look into this.

One question though - how do you determine how much current this thing can handle?

Off topic, about those pesky "wall-warts," I found this product from CyberGuys to be the solution: Liberator. It's essentially a 1ft extension chord. At first I thought it was a cheap gimmick, but I bought one anyways. I then proceeded to buy about 5 more. These things do wonders for ya!

[velocipenguin]

Originally Posted by SuperDanman

One question though - how do you determine how much current this thing can handle?

The transformer you buy should be rated to pass a certain amount of current. It should be safe to use that value as the theoretical maximum current rating of the circuit.

If you're feeling more adventurous, connect an ammeter in series with the positive supply lead and a variable load, such as a potentiometer. Slowly decrease the resistance of the load and record the ammeter's reading when the magic smoke leaks out of any of the components. (NOTE: This is a BAD IDEA and should not actually be implemented.)

[Rickertsen2]

Originally Posted by velocipenguin

The transformer you buy should be rated to pass a certain amount of current. It should be safe to use that value as the theoretical maximum current rating of the circuit.

If you're feeling more adventurous, connect an ammeter in series with the positive supply lead and a variable load, such as a potentiometer. Slowly decrease the resistance of the load and record the ammeter's reading when the magic smoke leaks out of any of the components. (NOTE: This is a BAD IDEA and should not actually be implemented.)

The rectifier ratings are important too. They should be rated for at least the current of the transformer. Btw if you run this circuit without the battery, then it would be a good idea to up the filterign capacitors to a combined value of 5,000uF to 20,000uF depending on how much you will be stresing it. The battery is actually doing most of the smoothing in the above circuit.

O yea, this circuit it rated for about 25A constant (25X12=300watts!!). Your system will probably never ever reach these current even momenarily, and this thing is way overspecified, but you never know, you might want to put like 50 neon lights on it or something. The reason for the overspecification, is that the only place that i could fond that did not want 2 arms, your soul, and your first born son for high current transformers was All Electronics. And the transformers they carry jump from 5A to 25A.

[Al Skierkiewicz]

James et. al.,
The circuit shown is a fine and simple power supply but...
The output is unregulated so the voltage does vary quite a bit with load changes and with line voltage. (audio produces some wild load changes.) There is no provision for limiting current when charging the battery. A dead battery will take as much current as can be pulled from the transformer. For a fixed current transformer, adding output capacitors will likely draw the output voltage down below 12 volts. There is no protection fuse shown. Be sure to protect the circuit by fusing the input to the transformer. And one thing that hasn't been said yet, a 25 amp transformer weighs a lot!

I still like one of these for your application...
http://www.radioshack.com/product.as...ct%5Fid=22-506
http://www.radioshack.com/product.as...ct%5Fid=22-504
or if you need 25 amps...
http://www.radioshack.com/product.as...ct%5Fid=22-504

[Greg McCoy]

Yeah, I would go with a store-bought power supply for reliability and less headaches