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continuous power to mp3 player

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bobdobbs

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Hello,

I am new to electronics but am really enjoying it. I apologise in advance for my idiotic questions, and look forward to any advice you can give...

I am trying to continuously run an 1.5v mp3 player with a tiny speaker connected to the headphone output. I have tested this with a multimeter and it looks to me like it needs 90ma to run.

I have a solar panel I pulled out of an old maplin solar battery charger. I cannot find a datasheet for the panel, but it has #907-150-7v written on it. I am assuming this means it has 7volt and 150 ma output.

I have connected this via a 4001 diode to a 2 x AAA rechargeable battery pack.

This is then connected through a LM317T circuit to give the 1.5v required to the MP3 player.

With freshly charged batteries in the batt pack it runs fine. However I left the MP3 player TURNED OFF for a day to top up the batts before I tried seeing how long it would last playing through the speaker.

It was pretty cloudy for the day so I assumed my batts would be about the same as when I left them , maybe a little bit more charged. But they were flat??

I have checked my circuit. Diode is correct way round...etc.

Does the LM317 drain power through heat like this ??

Is this ever going to work anyway ?

Does anyone have a better way of doing this?

Many Thanks, any help gratefully recieved!!

Bob
 
The LM317 did drain the pack. I wonder, why not just skip the regulator and use a single cell. Then just use boosted Zener regulator to protect the player from over voltage?
 
Many Thanks WildSwan.

This seems like a good simplifying idea. I will try it. Will Look online for 'Boosted Zener Regulator' as I haven't heard of that. As I said I am a novice!

Just wondering though - The reason I was using more than 1 batt and a regulator was to increase the time the MP3 player could run in the 'dark' (at night, cloudy days...etc). Perhaps I have this wrong and actually its the panel that need to be bigger, not the storage ?? any opinions gratefully received!

Many Thanks
Bob
 
An LM317 has a typical dropout voltage of 1.5V from its input to its output when its current is 100mA and its is no longer regulating. Therefore for an output of 1.5V its input must be higher than 3.0V that two rechargeable Ni-Cad or Ni-MH cells do not provide (they are 2.5V and drop to 1.8V)).
 
Thank you very much audioguru that does make sense..

ok so using an LM317 with 2 x NiMH batts is no good. Do you think my best route is too, run the panel in to 3 or perhaps 4 x AAAs before the LM317?

or go down to 1 x AAA and use the boosted zener regulator WildSwan suggests?

To open this out a little here is the background to my needs - I want to make some sound art that I can leave playing permanently in a public space. I want to use old MP3 players which I can get from ebay for £1 to £2. I am going for non LCD display types to keep power needs down. Also using the smallest speaker I can run direct from the headphone socket. ( I tried a piezo disc but didn't get anything out of it, I believe I may need a passive output transformer to do this - would it ultimately use less juice if i did ?).

Do you think I am on the right path to do this, or would wind power, or perhaps just a big car battery steped down to 1.5 volts would last for ages ??

Sorry to be so vague. I have done some reading and researched this prior to this post but any opinions from people who actually know what they are doing could save me from lots of wasted experiments at this stage...

Many thanks again!!
 
Doesn't a little speaker connected to the earphones output of an MP3 player runing from only 1.5V produce the very low sound level of an earphone?
Can a person walking past it hear anything?
 
Good question Audioguru, but actually its surprisingly loud. I can run it at 1/3rd volume and still get enough volume for my needs.

I went to maplin and bought the most efficient 0.5w mylar speaker. I also bought a cheap 'solar rock light' (also because it was on offer and I cant help but leave that shop with various bits of crap like that), which basically is supposed to look like a small rock, but has a solar panel on the top and 3 x white LED's inside which light up after dark. I had some vague notion of using the panel to power my mp3 player. It wasn't powerful enough but the little reflective cone the LEDs sit in has made a great enclosure for the mylar speaker - one of the reasons I think I am getting so much volume from the MP3 player!

Anyway as an update to this project :

I just ran the MP3 player straight off 2 x AAA bats with no regulation and it worked fine! I then blasted my solar panel with a strong lamp to get the output to max 7v. I wanted to see how the MP3 player dealt with it.... But it seems no matter how much the solar panel gives out I get max 2.75v at the MP3 player terminals....

Are the batteries acting as a regulator?
I suppose they are a big capacitor ?
Is this correct ?

I think I have just solved all my problems! Just need to see how long this sucker plays for 'in the wild'!!
:)
 
A solar panel with no load might have an output as high as 7V. But the voltage drops when there is a load because the solar panel has a series resistance.

Rechargeable Ni-Cad or Ni-MH cells will hold the voltage at about 1.0V to 1.5V each while charging. The voltage depends on how much charge they have and how much charging current.
 
ahh, ok thanks again audio guru...Seems I may have celebrated a little early, does this mean the voltage could get dangerously high once the batts are fully charged ?

I don't think I fully understand current and how it affects voltage. Do solar panels 'push' a current or is it just available to be 'pulled' by a circuit ?

I will try to find some electronics basic for dummies type pages but any links or tips or wisdom gratefully recieved...
 
Nah - you don't need to worry about overcharging.

You'll probably never put more than about 100mA into the batteries, and if it is on ocassionally, they will never rise above about 1.5 or 1.6v/cell.

Andrew
 
A circuit uses only as much current as it needs.
Your car has a battery that can supply 500A to start a cold engine but the same battery powers the clock with a current of only mA or less.
Your home has a 200A electrical panel but it also runs a clock that draws only a few mA.

Your solar panel has a low output current. Its voltage drops when it tries to supply as much current as it can to slowly charge your battery.
 
ok, so would it be correct to say that it is a function of the batteries to 'pull' as many amps as they can from the panel.

And I tested my MP3 player and it looks like it uses 90ma (not used a multimeter before this but seems about right?).

So if the player is on permanently pulling 90ma and the solar panel is feeding 100ma, that only leaves 10ma to charge the batts, and that is only for 16 out of 24 hours, doesn't sound like enough?

The batts say 700mah on the side. So does that mean they will give 7hours at 100ma draw ?
 
So if the player is on permanently pulling 90ma and the solar panel is feeding 100ma, that only leaves 10ma to charge the batts, and that is only for 16 out of 24 hours, doesn't sound like enough?
- But the solar pannel is 7v, so should charge the batteries more quickly.

The batts say 700mah on the side. So does that mean they will give 7hours at 100ma draw ?
- Yes.

Best thing to do is try it and see! Either it will work continuously, or it will run down. Dropping the voltage to the MP3 player (back to 1.5v) would probably lower the current draw.

Andrew
 
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