[Kippei]

Just buy a 9v charger set with 2 8.4v 160mAh for $35

or get a battery holder for 8 + $24 worth of batts(8) and a $27 charger

 

[tangent]

Too many variables left unspecified. Some things for you to consider:

1. How hard will it be to get into the case? In the case of your 8x battery pack, this is likely to mean a case that is screwed shut, instead of having a battery door.

2. How likely are you to strip out the screw threads, if any? Batteries trapped in aluminum cases without brass thread inserts are a bad idea, IMHO.

3. How much supply current will your circuit take, and from that, how much run time will you get from either option?

4. Is money an issue? If so, given all of the above, how much are you willing to pay for the ability to put off battery changes longer?

 

[chaostic]

Buy a 17 dollar charger + 4 battery set at Walmart/Target/K-Mart/etc. Then buy another. Cheaper then a 27 dollar charger plus 24 dollars for 8 batteries.

 

[Kippei]

Acutally it is for my custom cmoy.

My plan is Sanyo 8x 2500mAh to create 9.6 v

How will batteries react when it is left alone sardine packed for a month?

 

[tangent]

You're not supposed to connect NiMHs in parallel.

 

[Kippei]

My oringal idea is to connect them in serial...

1.2v x 8 = 9.6v

Forget to tell you is AA size

 

[Kippei]

It is a overkill for a 20000mAh capacity to power a max 30mA cmoy amp?

 

[skyskraper]

u get a battery with a long life between charges

 

[Kippei]

Quote:

Originally Posted by skyskraper u get a battery with a long life between charges

yea... i think i go for AAA method.... smaller den 2 9 v in parrell

 

[AsuAmo76]

Quote:

My oringal idea is to connect them in serial...

I was using such amp a year or so in dual +-5V. These were able to drive class ab output stage (irf510, 9510 around 20ma per channel) it seems forever. NiMH batteries now are very good, just stay away from the cheapest (silver ones from walmart as example). I believe they have too high internal resistance. Can't remember what exactly happened (oscillation?).

 

[Nospam]

Quote:

Originally Posted by tangent You're not supposed to connect NiMHs in parallel.

Good to know... but why not?

 

[BlazerFRS]

Quote:

Originally Posted by Kippei It is a overkill for a 20000mAh capacity to power a max 30mA cmoy amp?

If you connect 8 2500 mAh 1.2v batteries in series you get 9.6v and 2500mAh, NOT 8x2500 (20,000mAh)

If you connected them in parallel (which it seems you shouldn't) then you'd get 1.2v and 20,000 mAh.

Unfortunatly it don't go both ways

 

[Kippei]

Quote:

Originally Posted by BlazerFRS If you connect 8 2500 mAh 1.2v batteries in series you get 9.6v and 2500mAh, NOT 8x2500 (20,000mAh) If you connected them in parallel (which it seems you shouldn't) then you'd get 1.2v and 20,000 mAh. Unfortunatly it don't go both ways

Oooo i see.... i was wrong all the time

 

[tangent]

Quote:

Originally Posted by Nospam Good to know... but why not?

A couple of bad things can happen. If a cell becomes shorted, the neighboring cells can discharge through that low-impedance path, causing heat buildup and such. Another is cell reversal, where a cell goes through 0V, and flips its poles; havoc ensues.

These problems are a consequence of the low impedance of NiMH cells in general, and the fact that they are reused until damage occurs. Alkalines have higher minimum impedances, and they're only taken through one cycle, so there's far less chance of bad things happening.

 

[Nospam]

Thanks for the detailed and informative answer (as usual).

This does throw a wrench into my plans for the next Mint I'm planning to build, but I'll start a new thread about that, since I don't want to thread-crap here