Batteries

[supernova]

Hi,

I'm sorry if this has already been covered, I'm sure it has but I cant find it!

I'm looking for some batteries (36V) , charger, and PSU. Where do people get this stuff from these days?

Ive been baffled with all the new technologies, preferred the days when it was just SLAs, so simple!

Suren

[terry]

i have 2 complete a123 packs left at 36v, both just been rebalanced and enough brand new cells to make another pack at 36v.
also 5 packs of a123 at 33.3v (9 cell) available. cellar are the chargers we use for a123 and lipo batteries.

[typhoon_driver]

With your FRA membership you get a heavy discount on optipower lipo batteries. They do also sell chargers and psus but you may be cheaper going elsewhere.

Lipo packs come in various cells counts (like the days of nicad/nimh) denoted by the s value (3s, 4s, 5s etc). The C value tells you in multiples of the pack capacity what the discharge rate of the pack is. Generally there is a constant C value and a burst rate which is much higher. For example a 5000mAh pack with a cont. rating of 20C can discharge 100A constantly (5x20). You will generally find a max charge rate in the same units. When charging, you need to make sure that you use a balancing charger to keep the cells voltage close to one another. If one cell goes too far out of range then it can destroy the whole pack.

You must also charge lipo in a lipo sack (find them for a few quid on ebay) as a safety measure. If the pack decides to go up then it keeps the fire damage contained.

I realise this all sounds very nasty and negative but the power available from lipo for the weight is incredible. If you are running any kind of high power motor on a disc for example then you will notice a huge difference when compared to SLA.

[maddox10]

It is covered mainly in the feather topics.

But, a normal setup for a modern machine is with LiPo or LiFePo4 technology.

If it is for Supernova or simular machine. I would go for this setup.

4 packs of these
Giving you 37V 16 Ah (comparable with at least 25Ah SLA), with a burst load of 640A.

If you want more peak load capacity, 6 packs of these wil give you 37V 15Ah and a whopping 1050Ah of burst load.

Charging the packs I suggest. Depends on speed you want to load them.
If money is no objection and you have a powersupply that can handle this monster, go for it.
I'm intending to buy it.

[terry]

forgot I've got 2 packs optipower 6c 5000mah aswell nearly new asking £60 per pack.
now sold.

[supernova]

Thanks folks,

So from the above, I have learnt that for power to weight, the best option is LiPos.
I need a Lipo Sack for every pack charged.
I will need 10s, does it matter if I get two 5s and put them in series? I'm struggling to find 10s?
Top brands seem to be Optipower and Turnigy
Good source of this stuff is Hobbyking or direct from Optipower (with the FRA discount).

Money is always an issue!

Terry let me do some research and i'll get back to you...

Suren

[maddox10]

10S is 2 5S packs in series. That's just wire loom work.


You can avoid LiPo sacks per battery if you use a LiPo bunker. That's a steel box with conduits for all the wires you need.

For each pack, a power lead and a balancing cable. I did build a LiPo bunker from a steel breadbox. Works fine.

[supernova]

To be honest I'd rather get 10s as they will fit well in the robot, and less connections to go wrong, but I cant find any online....

[maddox10]

10S is more expensive, and not a lot of chargers can handle that. Most affordable chargers are up to 6S, and some to 8S.

And EC5 or XT90 connectors ain't self removing Andersons.

Soldering a decent wire loom isn't rocket science. Just needs good solder and soldering station.

[overkill]

An 80 watt iron is just right for soldering large battery connectors; I used to use a giant 175W iron but the 80W has just the right combination of tip size and thermal mass to get the job done neatly. If you are shopping for a soldering iron, try to get one from Weller - the cheaper brands I have tried had absolutely crap plating on the tips.

[terry]

the 6s lipos are gone now.

[supernova]

I went for 6s, 5ah 50C optipacks so 12s 10ah in the robot. Gonna see what the voltage drop is like when I turn the big motor on to see if I need more burst current.

Xt90 connectors

What cable would you recommend I use?

Thanks for the soldering iron advice.

[maddox10]

15a per mm2 max as a guideline . The 2 Bosch 750's are 80a together , the big brute for the disk 80a on its own.
I would use 2x6mm2 at least. Just because I have a supply of 6mm2.

[supernova]

I can see that the battery packaging is getting damaged. What have you guys done to toughen up the packaging? Heat shrink?

[maddox10]

Most of the time I ducttape those in a shockmounted snug fitting selfmade aluminium case.