Battery Parallel Wiring Q.

[Magicthyse]

Hiya Folks

A question about battery wiring. I have to get as near to 5V @ 1A as possible out of 8 AA Ni-Mh 1500mah batteries.
I'm vaguely aware that wiring the batteries in Parallel would get 4.8V @ 3000mah.

This would be ideal since it presumably means that I get 3 hours of power from 8 AA batteries?

The next question being how do you wire these batteries in parallel? Are there battery holders / holsters you can get which already do this? (It needs to terminate in a what looks like a standard mini power plug, center +).

Is for example two of the 4xAA holder listed on this page http://www.technologyindex.com/education/store/electron/battery/holders.html usable?

The batteries have to be easily removable in order to charge them...

 

[Evadman]

Wiring 2000 bateries in parallel will stil get ya 1.5v. ( std AA is 1.5v )

Series is when you "stack batteries" end to end. Parallel is when you connect a bunch + to +, and - to -.

Example:


+ ~~~~~ + wire lead
|| <--- one battery (1.5v)-
-
+
||
-
+
||
-
+
||
- ~~~~~~ - wire lead

When you stack like that, in 4 tall, you will get 6v. ( 3 tall would be 4.5v)

Example #2

+ + ~~~~~ +wire lead
|| || <--- 2 batteries in parallel. Will give you the same voltage, but double the amperage available.
- - ~~~~ - wire lead

I don't think you are going to be able to pull 1A from rechargable batteries. Most are rated for about 100ma, which would mean you would need 10 just to get to 1A, and you would need to stack them 3 deep to get 4.5v, meaning you would need 30 batteries to get 1A @ 4.5v

Do not expect 3 hours from them, as @ 1A they will overheat quick. expect more like 30 min per 5 batteries, giving you a total of about 3 hrs with all 30 of them.

 

[Magicthyse]

Bump cuz the 100mah thing isnt right, these batteries are rated for 1500mah. I know that they're pretty much ideal for high-drain applications like this.

And besides, the rated voltage is 5V @ 1A. In reality it's going to be more like 750ma. Maybe I need more than 8 cells - but it must be pretty close so I'm going to try it with 8.

So how would I wire eight 1.2V 1500mah cells in parallel to provide 4.8V power?

Is it

+ + ----->
[ ][ ]
[ ][ ]
[ ][ ]
[ ][ ]
- - ------>

??

Thanx!

 

[Magicthyse]

Errr. or is it

+ + + + --------->
[ ][ ][ ][ ]
[ ][ ][ ][ ]
- - - - --------->

??
This looks more right to me...

Thanks

 

[blahblah99]

Wiring in parallel isn't a good idea since they will drain each other out (remember that each battery has an internal resistance)... it would be better if you wire up those batteries in series and stick a 5V regulator on it (something like an LM7805) would do the trick. You can pull 5V@1A with that regulator and a proper heatsink, but it will last for less than 5 minutes.

 

[ttn1]

Magicthyse - your first configuration post is correct for what you want to do. The best way to test this is wire up
the batteries hook them up to your load and time how long they last. That will give you a "real" estimate of the
average run time.

Re-read Evadman's post one more time. You want to know the difference between parallel and series.

 

[etech]

+ + ----->
[ ][ ]
[ ][ ]
[ ][ ]
[ ][ ]
- - ------>


That is the correct configaration for 4.8v.

I'll have to look up the current draw you can pull. I believe that each stack will only supply the same amount of current as a single battery ie. the 1500 mAH. The addition of the second stack in parallel almost but doesn't quite double the amount of current but it's been awhile since I've done battery calculations.

 

[Magicthyse]

<<I believe that each stack will only supply the same amount of current as a single battery ie. the 1500 mAH>>

That's my belief as well - hopefully therefore it'll supply 3000mah.
I'm actually going to be using 1700mah batteries so hopefully this will be better.

My digital camera runs at about the same wattage - slightly over 5V @ 1A - going by the W=IV calculation (4.3V @ 1.2A = 5.1ish) on 4 Ni-Mh batteries, which last for about an hour's continuous shooting/'display on' time. So if I run 8, I'm presuming I get 2 hours? That's OK - none of my laptops except the ibook go for any longer than that.