9 volt battery voltage breakdown

[olemacky]

I would like to power an MP3 player that uses a single 1.5 volt AAA battery with a 9 volt battery. I have been using AAA batteries that are rated at 1,100 mA. They only last about 2 hours. Rechargeables last even less. Is it feasable to build a simple circuit that would allow me to use a 9 volt battery to power this thing? It would seem a 9 volt battery would give me power for quite some time. Any help would be much appreciated.

 

[MikeMl]

Wrong! use an AA, C, or D cell

 

[olemacky]

I thought a 9 volt could be used. I once met a fellow that had a handheld computer that used 2 AA cells. He had rigged up a 9 volt battery to run the thing and hadn't replaced the battery in months. I was thinking along the same lines. I just wish I knew more about electronic circuit design. At 62 I'm a bit old for school. Oh well if it can't be done then perhaps I will try the larger 1.5 cell.

 

[vne147]

I would like to power an MP3 player that uses a single 1.5 volt AAA battery with a 9 volt battery. I have been using AAA batteries that are rated at 1,100 mA. They only last about 2 hours. Rechargeables last even less. Is it feasable to build a simple circuit that would allow me to use a 9 volt battery to power this thing? It would seem a 9 volt battery would give me power for quite some time. Any help would be much appreciated.

You could use a 9 volt battery but without opening up your mp3 player and hacking it, you'd have to step the 9V down to 1.5V. There a couple of ways you can do this but not all of them are suitable. A 9 volt battery has only about half the capacity of your AAA. So if you were to draw the same amount of current out of it as you are when using the AAA, it would die in about 1 hour instead of the 2 you're getting with the AAA. That means that you can't use a linear regulator. The other option would be for you to use a switching regulator. Check out these links:

**broken link removed**

Buck converter - Wikipedia, the free encyclopedia

Since power is conserved, the current draw out of the 9V will be less when it's stepped down to 1.5V than it was when directly using the AAA. If we were to assume it was a perfect circuit the current draw out of the 9V would be 1/6 of the current draw out of the AAA. So, your mp3 player would last 6 hours instead of 2. However, the regulator will not be 100% efficient and that will affect the amount of time. Efficiencies of 90% or more are not uncommon, so I'd say that you could significantly increase your battery life by going to a 9V.

 

[MikeMl]

I thought a 9 volt could be used. I once met a fellow that had a handheld computer that used 2 AA cells. He had rigged up a 9 volt battery to run the thing and hadn't replaced the battery in months. I was thinking along the same lines. I just wish I knew more about electronic circuit design. At 62 I'm a bit old for school. Oh well if it can't be done then perhaps I will try the larger 1.5 cell.

Battery capacity chart1: Battery Capacity

Battery capacity chart2: Battery (electricity) - Wikipedia, the free encyclopedia

Besides the device is designed to operate on 1.5V; 9V would likely damage it.

 

[vne147]

Mike is right, a C or D would be the easiest solution and would be the most bang for your buck. But, your idea is not impossible. It would just take a little work.

 

[crutschow]

As the Wikipedia battery chart shows, the "energy" capacity of a C or D cell is much greater than that of a 9V battery. Thus, even if you had a converter for 9V to 1.5V with 100% efficiency, the 9V still won't last as long as a C or D cell. So use a C or D cell in place of the AAA. They will last longer than a 9V and don't require any voltage conversion.

 

[olemacky]

Okay guys. Thanks for the advice. I got some C cells around here somewhere. Sounds like the way to go. Simple and quick fix.

 

[vne147]

As the Wikipedia battery chart shows, the "energy" capacity of a C or D cell is much greater than that of a 9V battery. Thus, even if you had a converter for 9V to 1.5V with 100% efficiency, the 9V still won't last as long as a C or D cell. So use a C or D cell in place of the AAA. They will last longer than a 9V and don't require any voltage conversion.

I agree but then you wouldn't have to lug a C or D cell around.

 

[crutschow]

I agree but then you wouldn't have to lug a C or D cell around.

A C cell is not that much larger than a 9V (50mm x 26.2mm versus 48.5mm x 26.5mm x 17.5mm).

 

[Sceadwian]

And a D cell will provide more running time than you know what to do with. Like 10-20 times what you're getting now.

 

[tylernt]

IThey only last about 2 hours. Rechargeables last even less.

What rechargable? A Low-Self-Discharge (LSD) NiMH, though it only has 800mAh, will usually outlast "traditional" NiMH cells because it will hold a higher voltage during discharge thanks to a lower internal resistance. Depending on the device's current requirements and low-voltage cutoff, an LSD can outlast even an alkaline.

Good LSDs include Sanyo Eneloop, Recyko GP, Duracell pre-charged with WHITE top (NOT black), and RayOVac 4.0.

 

[Sceadwian]

You could just try to give it two AA batteries instead and see what it does with the extra voltage, those kinds of boost circuits can almost completly drain 1.5 volt alkaline cells, two might provide enough of an extra voltage overhead you never have to worry about it, however if the regulation can't handle the extra voltage it might just kill it. It really depends on how the boost circuit in your mp3 player handles all of a sudden having the roll of buck converter placed on it.

 

[mneary]

Two identical AA cells in parallel would give you boosted capacity.

They must be identical, installed new, and always change both (never put a new cell with a used one)