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Why can't I add a bigger battery to a micro usb audio recorder??

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ChristianAnarchist

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I've tried twice now with two usb audio recording thumbdrives to add a larger battery after dissassembly. The little battery in the thumbdrive is a 3.6v and I've tried to solder in a 3.6v cell phone battery for longer record times. The first one got too hot and things melted. The second one will get hot but then I remove the wire before damage can occur. When I put the small battery back in place, the recording feature still works, but each time when I try the larger battery, things get hot right away and I have to remove the wires.

Of course I'm careful to use my meter to make sure that I'm connecting the polarity correctly. If I remove the leads quickly, it does not damage the circuit and I can replace the smaller battery and it's fine. There's a very tiny cb between the battery and the thumbdrive that I'm also careful to include in the circuit.

Thanks ahead of time for any ideas on what I can try...
 

Is the standard power source a lithium coin cell or what?
 

I'm not sure, but I believe it's lithium. It's not a coin, but a rectangle soft wrap battery. It says 3.6v and nothing more.
 

The current rating is something you might want to take a look at. Every battery has a compliance range within which it will easily provide the rated voltage. Say the cell phone circuit has a higher load impedance then the battery will reach 3.6V with lesser output current but if you connect it to a much lesser load the battery will try to reach 3.6V by providing more current and might quite possibly be not within its specification.
 

Can you provide additional info? Nice to have some pictures of the audio device and the batteries. :cool:
 

I'm guessing that the original battery is a lithium ion polymer rechargeable and that you're having trouble with the protection circuit.
 

Not sure why the image only shows as a link, but anyway here is an image of what I have. The top recorder was damaged before I noticed how hot it was getting and no longer works. The bottom one still works, but as soon as I connect the large battery, it starts overheating. The small battery can be connected and the recorder works as designed. I've connected the battery with and without that micro-board and the results are the same.

ImageBam - Fast, Free Image Hosting and Photo Sharing
 

I agree with above.Even i was about to do mistake when i checked on some site that its ok even
if we connect higher amperage source to a lower ampere rated device.But i checked using led to a high ampere 3v battery and to my surprise it went hot in few seconds.

even i`m in search of solution to this now.i`ll let u know soon if i get it.
 

Yep. Most power supplies have this rating of x Voltage at y Current. For a cellphone battery or any dedicated battery for that matter since the expected load and stuff is known they might not be caring about loads outside that range.
These are trade offs they're bound to have since they've to reduce the size of the battery.
 

Even i was about to do mistake when i checked on some site that its ok even if we connect higher amperage source to a lower ampere rated device.But i checked using led to a high ampere 3v battery and to my surprise it went hot in few seconds.
Click to expand...
Most circuits are in fact specified by its supply voltage and current demand. They don't have a problems to work with a voltage source of higher current capability. A LED is very bad example, because it has to be driven basically by a current rather than voltage. There are however some simple LED pocket lamps, that use the internal resistance of the battery as current limiting device. You won't find this specified in a LED data sheet, but it can work though. May be the said audio recorder does something similar, depending somehow on the batteries internal resistance. But I fear, you won't know without analysing device operation with the original battery connected. Maybe adding a series resistor to the oversized battery can help.
 
Then if at all i want to connect any low ampere device to a high amperage source then how can i do that. There must be some way isn`t it.

:)
 

As I explained, it can work without additional means in most cases. In some cases, a current limiting resistor or an active current limiter cicruit may be needed. But you can't design it with knowing the exact properties of the device.
 
And there's no way to "guess" the value of the current limiting resistor? Or is there a way to figure it out by measuring the current draw?
 

i think we do have a way, i`ll first try it out and let u`ll know the results.
 

I really don't understand why this circuit needs any kind of limitation on amps. I'm not that great at electronics but I think of a car battery which is 12 volts and has a huge amperage capacity. You can connect any 12 volt item to it without problem. How are these circuits different? Is it simply because of the leds in the circuit or does it also have to do with the integrated circuits?
 

I really don't understand why this circuit needs any kind of limitation on amps.
Click to expand...
I also don't why. But I think, you have demonstrated impressively, that this is the case.
 

Can you measure the voltage at the two batteries when they are connected to the device?
Perhaps the small battery can't deliver the 3.6V due to high internal impedance.
 

flanello said:
Can you measure the voltage at the two batteries when they are connected to the device?
Perhaps the small battery can't deliver the 3.6V due to high internal impedance.
Click to expand...

Yes, I have measured them both and they are within .1v of each other.
 

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