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Cmoy with 2032-type 3V Coin Batteries

post #1 of 4
1/19/11 at 8:11am
Thread Starter 

Hey everyone, I have a quick question on the possibilities of an alternate setup to the cmoy power supply.  I am wondering if it would be possible to take a stack of 2032 type 3 volt coin batteries in series to power the amp.  This would allow me to get greater than 9 volts in a smaller space.  Many of the rechargeable 9v batteries are rated ~200-300 mAh, whereas these are at 235 mAh.  Would this work or am I missing something?

 

I realize that pricing is probably a hold up, but I am able to source these in bulk for $0.66 a piece, which is pretty cost effective.  Thanks!

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post #2 of 4
1/19/11 at 8:59am

You should check the maximum discharge current on those batteries. 

 

On that note, if you look around you can find single use duracell 9V at 580mah or rechargable batteries at the mentioned mah's in the very nearly $2 each range. 

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post #3 of 4
1/19/11 at 9:01am
Thread Starter 

Thanks for the response, I will look in to that.

 

I can actually get 9v Duracell alkaline batteries for $0.74 a piece as well, so only slightly more expensive.  I was mostly just curious on experimenting with the constraints of the coin batteries versus the larger 9v batteries.

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post #4 of 4
1/19/11 at 11:03am

Discharge current isn't a problem with these in a CMoy, but their ESR is awfully high. It starts at 20-30 Ω (yes, ohms, not milliohms!) and rises to about 100 Ω by the time the cell is dead. ESR of a 9 V alkaline starts at more like an ohm or two. I verified this empirically here with resistor loads.

 

This means that if you build the CMoy exactly as originally designed, you can expect to lose nearly a volt at the battery terminals, just in ESR, with a stack of three CR2032s. The 9 V battery sags by only ~40 mV with the same current load. Add to that the inevitable negative effects on sound quality, and you've got a pretty bad situation.

 

Not to mention that it's horribly wasteful.

 

If you want to get clever, buy a lithium 9 V replacement and a charger. It'll have ESR way lower than an alkaline, will last longer per charge than a set of coin cells, and should pay for itself before you have to replace the first battery.

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