Lithium cell tests

**terrorhurtz** · 24th February 2008, 00:38

P.S. ThunderPower do a neat little 10 cell stand-alone balancer - the TP-210V http://www.westlondonmodels.com/product1098/ThunderPower-TP-210V/http://www.westlondonmodels.com/prod...Power-TP-210V/

The technique I would recommend for achieving a good result with such a balancer is:

1) If the pack is badly out-of balance, connect the balancer to the pack (without charger) and leave to balance for a few hours.
2) Charge normally (1 to 5 amps) with balancer still connected. Cut-off at 3.6 to 3.7V per cell.
3) Switch to trickle charge of around 30 mAmps and leave to balance for as long as necessary, but check regularly that the pack voltage does not exceed 3.7 Volts per cell. Switch off the trickle charge if it does.

This ensures that the balancing occurs when they are fully charged - the only place where it matters. You cannot accurately tell if a pack is balanced by looking at the votages when the pack is only partly charged.

The most common out-of-balance situation with these cells is one or two low cells in a pack. This quite often happens if you leave the packs for a few weeks. This takes quite a long time to rectify with most balancers, because they have to disharge all the other cells down to the voltage of the lowest one.

John

**terrorhurtz** · 24th February 2008, 00:50

Hah! Just read Jonnos post about using only two NiCad pack in Ripper. Trust you to push it...
Ill bet theyre quite warm after a long fight.

I would agree that three packs of 8 A123 cells should be sufficent, if you needed to save max weight by staying at 24V. I wouldnt recommend less than four packs at 36V.

John

**terrorhurtz** · 24th February 2008, 01:00

@ Little John Lear
The reason it has been suggested that you dont leave a machine powered by A123s in for a second fight is that running them flat damages the cells. It would be OK if you had some sort of low-voltage cut out to protect the cells.

Not a big problem going flat with NiCads, but with A123s you really need to make sure youre fully charged before every fight.

John

**robotwars** · 24th February 2008, 09:08

who me.... pushing things nah !!!!

Surely I am not the only one who only uses 2 packs?

They dont appear to be too warm, and I can get one and a half fights out of them.

When I used to run at 36v they were a lot warmer, Hot even!

So for me, i dont think it would be worth it as i have a relatively light version in comparison and i am happy with the performance!

Plus I never wait for them to be fully charged at an event as im always raring to get back in the arena. Especially when ive driven down the pit after 12 seconds in a fight !! Grrrrrr

I will see how others perfrom though, as the upgrade to 30v is appealing.

John

**john** · 24th February 2008, 09:58

Thanks john

answers what i wanted to know

think we would only get these if it was back on TV as thats when we wont have as many fights close together like we do atm

would save abit of weight and i could put the moving wings that i want for our winning pose :P

**leorcc** · 24th February 2008, 13:12

quote:

I for one will be moving to have the battery rules rewritten soon. Especially as the UK championships are looming.Thank you Kane, much appriciated. When can we expect a final decision on this?

And also a big thank you to John for the great work he has done testing these cells.

**kane** · 24th February 2008, 14:08

I think really, the wording needs to be written, agreed and put into the rules. This needs to happen by the end of March really.

**grant_ploughbot** · 24th February 2008, 16:13

the thunder power balancer john shows is the one ive been using for the last 2 years. Also wherei get them from (only a few miles from me). They can balance upto 10cells in series, but will also balance 2 packs at the same time to be of identical voltages so it is safe to run them in parrallel.