Battery powered speaker

[vynncentgm]

I have a speaker that I designed to run off an AC adapter. Unfortunately, my Li-Ion battery packs are currently unable to supply the voltage nor the current to power it. The packs consist of two 7.4v 2100mAh batteries along with what I presume to be over-charge/discharge and over-current protection. Both cells are wired in series in each pack.

The speaker itself (has amplifier) is designed to run at 6v 700mA. Could somebody please point me in the right direction as to how to make this work?

[IanB]

It's a reasonable assumption that the speaker is not voltage sensitive and should be able to work satisfactorily at voltages, say, from 6 V to 9 V. If that is the case, then connecting one battery to the speaker should provide it with a voltage in this range and the speaker should work. Furthermore, a 2100 mAh battery should comfortably be able to supply 700 mA.

So, what is the problem? Can you be more precise about what doesn't work?

[vynncentgm]

Everything works fine when operating at the voltage provided by the AC adapter. I just didn't want to see another thing destroyed by one of these battery packs (usb car charger, rated for 12-24 volts, was connected to one and the magic smoke escaped). The speaker itself is a modified Labtec CS-150 computer speaker. I modified it by  putting both speakers in a more portable cabinet and replacing some components, as well as rewiring it. Effectively, this improved audio quality and made it more portable. Not to mention, originally, you could power the speakers off four D size batteries.

[IanB]

OK, so your Li-ion batteries are not "unable to supply" the required voltage or current. It seems, if anything, that they may supply too much rather than too little.

Those speakers say "DC 6 V" on the input jack. Also, 4 D size batteries will supply from 4 - 6 V. One of your Li-ion batteries will supply as much as 8.4 V when fully charged. This is 2.4 V more than the amplifier is asking for.

As I said above, it is possible the amplifier won't mind, and will be quite happy when fed with 8 V or so. On the other hand, it might not. To find out, you will have to examine the circuit. Look at the circuit board, find out what amplifier chip it uses (or does it just use transistors?), look at the data sheets, reverse engineer the schematic. If you don't know how to do this, you could post pictures of both sides of the board. Maybe someone here could help with that.

But unfortunately, unless someone else here also has a Labtec CS-150, it is going to be very hard to say.

[Audioguru]

Did the smoke come from the USB 5V charger? It is designed to feed the charging circuit inside a cell phone, not to charge a Lithium battery that probably tried to draw way too much current.
7.2V/2100mAh Lithium batteries are common for radio controlled model airplanes and their chargers are also available from a hobby store.

[vynncentgm]

Yes it did come from it. I was trying to power it using the battery.

The Amplifier ICs are JRC 2073D. There are two transistors, C308 and C 3G.

EDIT: Also, can somebody tell me why my public IP appears next to an icon at the bottom of my posts? This is replacing the text "Logged".

[IanB]

Yes it did come from it. I was trying to power it using the battery.

Did you get the polarity right? It is hard to understand how a device designed for 12 - 14 V DC would fail when powered with 8 V DC.

The Amplifier ICs are JRC 2073D. There are two transistors, C308 and C 3G.

And the data sheet for that IC says the supply voltage can be up to 15 V. So you are probably safe with 8.4 V. The other thing you would have to do is look at any capacitors on the board and make sure they have suitable voltage ratings. They probably will have, but it is as well to check.

[IanB]

Also, can somebody tell me why my public IP appears next to an icon at the bottom of my posts? This is replacing the text "Logged".

I see that next to my posts, but not anyone else's. I don't think anyone else can see it.

[vynncentgm]

The polarity was correct on the charger, perhaps the surface-mount regulator couldn't handle it.

The capacitors said 25v on them. So, I guess that they'd work.

[Zero999]

The polarity was correct on the charger, perhaps the surface-mount regulator couldn't handle it.

What surface mount regulator?

If it's the USB charger which blew then it's because the batteries drew too much current. If you tried charging the two cells in series, then the USB power supply would have been subjected to overvoltage. If you tried charging one cell or two in parallel, then the current would have been too high. In fact, you're lucky the battery didn't flame or release a toxic gas.

The capacitors said 25v on them. So, I guess that they'd work.

Yes, the speaker will be fine running directly from the battery.

[vynncentgm]

The polarity was correct on the charger, perhaps the surface-mount regulator couldn't handle it.

What surface mount regulator?

If it's the USB charger which blew then it's because the batteries drew too much current. If you tried charging the two cells in series, then the USB power supply would have been subjected to overvoltage. If you tried charging one cell or two in parallel, then the current would have been too high. In fact, you're lucky the battery didn't flame or release a toxic gas.

Perhaps I might've explained it wrong. I wanted to make a battery bank using the pack, so I connected the battery to the input of the charger. The idea was to make something to charge a phone or mp3 player over usb.

I don't have  a clue as to what the part number was, as I threw the charger out over a year ago. I'm sure that the current may have been too much for it to handle, as it was just an off-the-shelf item that was picked up for free at a SANS conference.