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

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fireball

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I have a nice little 1/4 size RC Laser ... superb boat to sail - rigged in 5 minutes!
The winches and RC receiver are powered by a battery pack - the standard rig has a 4xAA pack for the non-rechargables (1.5v) ..
To get the same power with rechargables (1.2v) you need 5 cells ... which is fine, except you can't get holders for 5 cells ..
I've knocked up a temporary fix with an 8 cell holder attaching the power cable in the right places for just 5 cells .. However, it isn't ideal and is too big really ...
What I'd like to do is to make up a 6v battery by soldiering the 5 cells in series - just short cables between them then seal with shrinkwrap ...
I assume it IS possible to solder a cell in this way?

Once I've got my 6v cell I need to be able to charge it .. at the moment I only have standard AA chargers, they only take 2 or 4 cells at a time, so I've one spare to charge each time - PITA! IIRC, you need to supply 1.4 x voltage to charge the cells - so 8.4v, and that should charge fully flat to full in 15 hours ...
I have a 12v supply - could I use that to charge in less than that time?

Oh - the cells are 2300mAhs ...

ta /forums/images/graemlins/smile.gif
 
Take a look at Maplin (www.maplin.co.uk) They do quite a range of rechargeable cells <u> including cells with soldering tags.</u> There are also cells of sizes other than the AAA, AA C and D with which you are familiar. For example for one application I bought some 2/3AA size NiMH cells.

Maplin I know about but there are probably other better sources if you look around.
 
I've got the cells - that isn't the problem ... I have use AA cells if I want to race in class rules - though doesn't matter if I'm just pottering ..
What is the difference between solder tags and just soldering straight on the terminals? The amount of heat exchange will be pretty much the same I would've thought ... ??
 
model hobby shops will have fast chargers.. 30 mins should be possible. I dont think you need 5 batteries.. Rc models use 1.2v as the norm.
Its a bugr trying to solder the batteries.. you could try the spring boxes, or get a pack ready made up.. have a look at somewhere like AlsHobbies, BRCHobbies for sensible prices (and chargers)
 
I do need 5 batteries otherwise the winch runs slowly ... can't be having that!

The spring boxes already showed their weakness - during a heavy collision one of the batteries was knocked out the holder - which meant no power and lost race ... /forums/images/graemlins/frown.gif

I'll have a look at the hobbies sites - but as I said, I've already got the cells - so don't really want to go spending on another set ..
I'll probably end up getting a better charger, but wanted to understand what the tech was behind charging a standard battery .. eg - could I just take 12v out of the boat battery and plop across the pack?
 
[ QUOTE ]
What is the difference between solder tags and just soldering straight on the terminals

[/ QUOTE ] I think you'll find it difficult to solder directly onto the batteries especially without getting the batteries hot. With soldertags youll find it easy and you won't get the batteries hot at all. Been there, done it, got the Tee shirt
 
Ok ... I might have a go on some old recharges then ... /forums/images/graemlins/smile.gif

know anything about recharging batteries?
 
[ QUOTE ]
know anything about recharging batteries

[/ QUOTE ] Not much, buy a chager and stick em in. You'll need special batteries for the very fast chargers so if thats the route you want to go everything said about solder tags etc may not apply unless you go to a spcialist supplier rather than Maplin.

I had trouble with a Uniross charger (4 hours, not fast) or more likely the set of batteries that came with it.

Nice little unit with separate mains unit and a lead that plugged into a cigar lighter. I got it for my camera and chose it so that I could use it on the boat.

It was "negative delta V" controlled but for some reason cut out after about 20mins. Changed it for another identical pack. Thats OK

Maplins do a range of chargers incl. ones that will work on mains or 12V

The person on here who was the expert on R/C stuff was Nigel Luther, aka SBC. It might be worth tracking him down on the "Small Boat Club" http://smallboatclub.org.uk/ forum.
 
Ah ... old Nige ... didn't realise he was into green power as well as the dirty stuff!! /forums/images/graemlins/grin.gif I'll see if I can find him - thanks!
 
re charging-it depends on what type of battery you have. Nicads are the good old workhorse that take lots of abuse. Fast Chargers usually use delta-peak (the voltage spikes just before full charge) as the cut off. Hydrides are now popular, but cost a bit more and are supposed to be a little less abuse friendly.
I m not sure how you winch works.. is it a servo or a motor? Otherwise get a faster servo !
If you want to go really loopy you can get into lypo batteries, but then you are talking rather alot of money for the batteries and chargers (and voltage supplies). And they might set fire to your model boat (and house). Still, plenty of poke!!
Just thought, maybe Overlander can make up battery packs for you; I ve never managed to get a proper solder on any battery.
 
I've got the NiMH batteries ... so I guess that's the new ones ...

Can't just go changing the winch servo ... it's all in the class rules don't ya know ... along with the battery type - must be AA cells ...

I'll probably end up spending another small fortune on a battery pack that someone else has brought together from the same cells as I've already got ... and another one on a charger /forums/images/graemlins/frown.gif
 
If you are not too worried about the life of the battery pack you could recharge it just using a series current limiting resistor.

Assuming that the capacity is about 2500mAh (the ones I have at hand), they can be charged at 500mA for 7 hours but obviously check what yours can be charged at. Using a 12 volt supply the resistor needs to drop 6 volts which means that a 12 ohm resistor ((12-6)V/0.5A) is required. The resistor will have to dissipate 3 watts so will get quite warm but a 10 watt resistor should not get too hot.

The problem with this approach is that the battery can be overcharged if left charging for too long especially if you have not used most of its capacity before recharging (or you forget about it).

Maxim make a number of chips that do the job properly (eg MAX712) but then you are into a much more complex circuit.

Hope this helps

John
 
HWMBO used to play with models and RC gear and I showed him your post.
He first of all said that you do not need to make a pack with 5 cells as the voltage under load is better with rechargeables than dry-cells. He illustrated this by showing a radio that had a dummy cell in to replace the extra dry-cell when rechargeables are used.
But his advise actually was to tell you to find a local Radio Control model shop and buy ready made packs. It may be a pound or two more than doing it yourself, but they are proper tagged cells and designed for the job.
As to charging, the same shop will supply suitable charger that will also cater for the Transmitter with probably 8 cells in.
You can also buy all online.
 
I've only read through quickly, so not sure if anyone else has mentioned the difficulty in soldering the end caps of batteries? Before you start, gently file off a small area of the plating on each end of the battery, you will find with cored solder it will "take" very much easier - without the need for too much heating.
 
[ QUOTE ]
Ok ... I might have a go on some old recharges then ... /forums/images/graemlins/smile.gif

know anything about recharging batteries?

[/ QUOTE ]

Ignoring fast and fancy chargers, what you need for nicad / NiMH is to charge at a constant current of about the C/10 rate (i.e. capacity in mAh /10) for ~14 hours. This allows the cells to be charged up "over night", without the risk of damage by over charging.

You can build a simple circuit to give you this from (e.g.) a 12v supply.

If you go for a faster charge, the charger has to monitor the cell voltage, and shut off when charging is complete - a more complicated circuit, but still do-able if you're keen. Cheaper to buy one of these.

Your local model shop will have something that will do the job.

Andy
 
get the ones with tags, it is a bit of a bugger to solder batteries, big heat sink effect so tags make it easier, i revived an obsolete radio doing this, i must say that usually peeps just replace like number with like number and i think you are making it more difficult for yourself using five cells but hey your choice.
to charge you need to be careful, 12v battery across them will make them burn or explode if you are not careful, i had to rig up a small charger for my radio as well, i am lucky in having a computer w/shop with loads of different chargers kicking around, i experimented and found one that was a couple of volts above the nominal voltage that worked ok, i found that if it got them warm then they were charging ok, you can buy variable voltage charger from maplins etc and you would have to experiment.
stu
 
Ta ..

There is no mystery behind the number of cells - 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 which will mean a slower wind in on your mainsheet ... now, tell a trimmer on a big boat that he doesn't have to wind quickly and he'll be laughing ...

It is standard in the RC Laser class - they tell you to use 5 AA recharge cells... I was just hoping not to have to spend a fortune on the charging kit ...
 
Firstly you should be able to find a single AA battery holder at your radio supply shop. If not cut down a double.

To solder on to rechargeable batteries you need a big powerful soldering iron. The heat just disappears if you use a small iron. Clean the area with sand paper and use a resin cored solder.

I agree that the voltage of the rechargables should be similar to that of the non rechargables when under load and a little way into the life of the nonrechargables. good luck olewill
 
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