www.robowars.org

RoboWars Australia Forum Index -> Technical Chat

Batteries and Packs


Post new topic   Reply to topic
  Author    Thread
Spockie-Tech
Site Admin


Joined: 31 May 2004
Posts: 3160
Location: Melbourne, Australia


 Reply with quote  
Batteries and Packs

Original by Spockie-Tech here http://www.robowars.org/forum/viewtopic.php?p=1948#1948

According to all Nicd/NiMh cell manufactuers, *any* soldering of cells is too hot. They strongly reccomend against any soldering to cells. the top part (+) of the cells have a plastic pressure-seal around the edge that allows the cells to vent if the internal pressure gets too much under heavy charging or discharging. (Thats why they make a mess when abused). Any temperature high enough for soldering is higher than the melting point of this plastic seal according to the specs, thats why all factory-packs have spot-welded tabs, the split-second tiny pulse of heat dissipates before it can warm up the whole cap enough to hurt the seal.

Having said that, a lot of people (and pack manufacturers) do go and solder their packs anyway, and if done by a skilled soldering person with a high-heat-capacity (not temperature, heat storage) iron so it can be done quickly, the seal *should* survive a second or so of heat. then you get the advantages of the lower resistance, mechanically strong solder joint over the small-contact patch spot welds.

If you are getting the whole cells near soldering-hot, chances are good that the seal wont be be very happy with you. it maybe ok, it might have totally melted, most likely it will have deformed somewhat. If it has melted "open", then the gases produced during the cells normal operation will be able to escape (rather than recombining) and the cell will lose capacity after a much shorter period of time than it would have otherwise, so the damage will not be immediately evident.

If the seal has melted-shut, then as long as it doesnt short out the top to the case (which will kill the cell instantly), then the cells will likely be ok for a while, but if worked hard and the gas-pressure builds up in them, they will go bang, rather than just vent as an undamaged cell would.

So how much heat is OK ? Ideally, None, in practise, the less the better.

To solder up battery packs successfully, get a powerful, high wattage, temperature-controlled (so it doesnt get too hot if you leave it without using it for a few minutes) soldering iron, with a good heavy tip (for heat storage, like a heat capcitor), and practise on a bunch of old useless cells until you can make a good solder joint without cooking the whole cell.
_________________
Great minds discuss ideas. Average minds discuss events. Small minds discuss people

Post Wed Sep 01, 2004 11:01 pm 
 View user's profile Send private message Send e-mail Visit poster's website MSN Messenger
Spockie-Tech
Site Admin


Joined: 31 May 2004
Posts: 3160
Location: Melbourne, Australia


 Reply with quote  

Original by Kkeerroo in the same thread as above

Aocording the bloke who wrote this site bellow you may have damaged your cells by charging them at too high a current.

[url]http://www.angelfire.com/electronic/hayles/charge1.html [/url]

for those who don't want to skim through the site to find the relative info here it is:

"Rechargeable battery capacity is rated in mAH (milliampere-hours). The total capacity of a battery is defined as "C", that is it can supply C mA for 1 hour, or 2C for 30 minutes etc. Charge rates can vary from trickle charges to keep the battery 'topped up' of 3.3% of C to 5% of C, a slow current charge of 10% of C to 20% of C or a fast charge of 50% of C to 100% of C. Slow charges are not meant to be continually applied, and since NiCd/NiMH batteries are about 66% efficient, they normally last about 8-15 hours. Fast charges such as 100% of C should be terminated after about 1.5 hours, providing the battery is flat to begin with. Once a battery is fully charged, the battery produces gas creating a high internal pressure, and a sudden rise in temperature. The charge should be switched to a trickle charge at this point or the battery will begin to vent and release its electrolyte. My old battery was rated at C=1300mAH and my old charger was rated 400mA (30% of C) so the charger should have been switched off after about 4 hours, provided that they were almost flat to begin with. However there is no way of knowing if C was actually 1300maH or if it had decreased a bit, and once the a battery starts to deteriorate, I suspect this becomes a vicious cycle and the battery deteriorates rapidly due to more and more overcharging. The manufacturer suggests these cells should be good for 500 to 1000 cycles if properly treated!"

I am sure cutting and pasting like that will annoy many people but it is all good info. The above site also has good stuff on "memory effects" as well.
_________________
Great minds discuss ideas. Average minds discuss events. Small minds discuss people

Post Wed Sep 01, 2004 11:03 pm 
 View user's profile Send private message Send e-mail Visit poster's website MSN Messenger
Spockie-Tech
Site Admin


Joined: 31 May 2004
Posts: 3160
Location: Melbourne, Australia


 Reply with quote  

Original by Team Hell Bent here

http://www.robowars.org/forum/viewtopic.php?p=3084#3084

Just a tip for soldering wire or tabs on to batterys use BAKERS SOLDER FLUID it makes it a whole lot easyer just dab a bit on where you want the solder to go and solder "It fizzez a bit then sticks real good it stops the solder going all over the place other then where you want it to go but dont dab too much on as it will rust the battery termanal a bit you can find it in plumbing stores if i remember correctly its about $8 for 250ml it lasts you a very long time.
_________________
Great minds discuss ideas. Average minds discuss events. Small minds discuss people

Post Wed Sep 01, 2004 11:04 pm 
 View user's profile Send private message Send e-mail Visit poster's website MSN Messenger
Spockie-Tech
Site Admin


Joined: 31 May 2004
Posts: 3160
Location: Melbourne, Australia


 Reply with quote  

Originally by Kkeerroo here
http://www.robowars.org/forum/viewtopic.php?p=3094#3094

Bakers Solder Fuid is a type of flux. It is a corrosive that helps soldering by cleaning any oxidents off the metal to be soldered. I use it a lot for soldering larger jobs like heavy guage wire. Do not use it for smaller stuff as it is a corrosive and will damage sensitive componants. Also watch out for the "fizzing" as fluxes are poisions so don't breathe the fumes, get any in your eyes and always wash your hands after use. And as it is a corrosive always clean any excess off or around the solder joint when finnished to prevent "rusting".
Another tip to clean surfaces to be soldered is rub with a pencil eraser. This will remove any oils or dirt, and can be done to copper plated PCBs.
You can also try solder paste. It usually comes in a tub or syringe and looks like a cream. Just apply around the joint to be soldered and touch with a soldering iron. The paste contains both solder and flux and is easy to use but can be a little expensive.
_________________
Great minds discuss ideas. Average minds discuss events. Small minds discuss people

Post Wed Sep 01, 2004 11:06 pm 
 View user's profile Send private message Send e-mail Visit poster's website MSN Messenger
Knightrous
Site Admin


Joined: 15 Jun 2004
Posts: 8492
Location: NSW


 Reply with quote  

Places to buy good quality Robot batteries.

Master Instruments
www.masterinstruments.com.au
Good place to pick up singular NiCD/NiMH/LiPol cells, Australia based.

RobotMarketplace
www.robotmarketplace.com
You will find everything here, US based, all prices in $USD, import taxes may apply to your items.

Technobots
www.technobots.co.uk
The UK one stop robot shop, they are the UK equivilent of Robot Market Place.
_________________
Team Knightrous

Post Wed Jan 05, 2005 8:06 pm 
 View user's profile Send private message
Totaly_Recycled
Experienced Roboteer


Joined: 15 Jun 2004
Posts: 1346


 Reply with quote  

http://www.buchmann.ca/ here is a link to a good artical on rechargable bateries of al types writen with the help of a batery testing company in non technical terms it explains about diferent batery types and how to look after them in real world situations and not just in labority test situations ..

Post Thu May 11, 2006 11:43 am 
 View user's profile Send private message
  Display posts from previous:      

Forum Jump:
Jump to:  

Post new topic   Reply to topic
Page 1 of 1


Forum Rules:
You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot vote in polls in this forum

 

Last Thread | Next Thread  >
Powered by phpBB: © 2001 phpBB Group
millenniumFalcon Template By Vereor.