Soldering AA batteries together .... ? Then what about charging?

[misterg]

[ QUOTE ]
I was just hoping not to have to spend a fortune on the charging kit ...

[/ QUOTE ]

Is £0.82 too much?

Get an LM317T (UF27E) and a 5.6 ohm resistor (M5R6) from Maplin (order codes in brackets).

Connect DC power + (<40V and >7.5V) to pin 2 of the LM317T, resistor between pins 1 and 3, and pin 1 to the + of your battery pack. Connect DC power - to the - of your power pack.

If you use >12V as the supply, you may need to mount the LM317T on a heatsink. Check it anyway, and bolt it to a heatsink if it gets too hot to touch.

Voila! 223ma 'constant current' charger.

The charging current (in mA) is 1250/Resistor - adjust to suit. The max is 1.5A.

Input voltage needs to be at least 1.25V more than the battery pack voltage.

hth.

Andy

P.S. The risk with soldering non tagged cells is that you damage the cell in the process. It can be done, though: File the area as already suggested, and preferably use a very high power (100W) soldering gun. Be as quick as you can.

 

[lw395]

I've soldered to AA's no problem.
File off the plating
Add some flux
Use a big hot iron and do it quickly to minimise heat transfer.
Tagged cells would be better, but cost much more.
Many nimh cells have a quoted charge rate around c/20 or c/25 below which they can be left charging continuously without damage.
hth.

 

[ShipsWoofy]

erm???



Or is this too simple?

 

[fireball]

Excellent! Thankyou!! I didn't think charging batteries would be that difficult - I just don't know electronics in order to do it myself ... /forums/images/graemlins/smile.gif

I'll have to place a maplin order now ! /forums/images/graemlins/smile.gif Cheers!

edit: Oh yer - and I need a new soldering iron anyway ... time for a new one!

 

[fireball]

Re: erm???

I could do 4+1 I suppose ... but it isn't quite the same as a sealed pack.

 

[moody1]

[ QUOTE ]
- normal AA non-recharge are 1.5v x 4 = 6v -which is exactly what the kit is supposed to work off .... go with 4 recharge and you only get 4.8v

[/ QUOTE ]

I showed that to him and he remarked that you are only correct off-load. Once load is on the cells, the rechargeables in fact would show a better voltage and more constant. The dry-cells are falling in voltage from a load 1.2v ~ as soon as connected. Rechargeables would carry a 1.1 - 1.2V right up to very close to discharged condition, when they would have a sudden drop. He was surprised at the Class accepting extra cell in the receiver pack, but then again it's some years since he was in RC competition. Back then you were restricted to stock over counter specifications except in Cars, and then it was only in Transmitters that an extra 9th cell could be added.
He did comment that if you have to add a cell to get the sail winch to work well, then he suspects a fault in the set-up. Rechargeables are well known to provide serious amps to the point of causing fires. He has a burn mark on his leg from a NiCD cell he carried in his pocket one time.
Don't shoot the author, as I'm only passing on what was said.

 

[fireball]

Interesting ... I'm only going off what is given in the Class handbook ... www.rclaser.org.uk ... I'll have to run a test to see about the motor speed for the winch, but it does make a difference if you can get that sail in quickly around the bottom mark ...
They have even created a splitter cable (not got it yet) that delivers the full 6v to the winch servo rather than the limited 5v delivered through the receiver pack.

Perhaps the developers of this didn't fully understand what they were doing and are infact, overloading their kit ... (and mine!)
Right now, there is plenty of localised cooling ... so fire risk is quite low! /forums/images/graemlins/tongue.gif

Oh - the servos are specified in the class rules as well - so no swapping out for a fast motor ... has to be what they specifiy ..