A123 Lithium cell use

[terrorhurtz]

If you decide to go with less batteries, you would need to be vary carefull that you could never stall the motor e.g. by fitting limit switches or timing it.

[big_nipper]

In the last Little Spinner that used the S28-150 we had 3 sets of 1100mAh NiMh battereis in parrellel and to limit the current we had a magnetic clutch arranged so it would slip if the load on the mag got too high and couldnt stall the motor, we did have to add an acceleration ramp to limit the inrush current so as not to slip the clutch when spinning up the disc.

[terrorhurtz]

Some Mega Power 960SR chargers and LCB-12S balancers available on ebay.
http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&item=380020491998http://cgi.ebay.co.uk/ws/eBayISAPI.d...m=380020491998

Just ordered one of each.

[Mouldy]

John, whats your opinion on the a123 packs sold on robotmarketplace?

[terrorhurtz]

Looks promising, except I cant see any mention of balance wires in the packs. Triple welded tabs sounds good. Youd have to either buy loose cells, or open the pack and add your own balance wires.

BattlePacks do them with balance wires:
http://www.battlepack.com/LiFEPO4.asphttp://www.battlepack.com/LiFEPO4.asp
but it doesnt say how they are connected - soldered or welded?.

Im now thinking that, unless you have very high current needs and are preapred to lose some capacity, it is better to go with spot-welded tabs, rather than soldering.

1) Welded - lower current capability, unless done well with copper tabs. See http://www.youtube.com/watch?v=5vQTBoHPBxQ
2) Soldered - higher current, but probably affects the cells, even if done carefully.

If youre just running drive motors, the standard steel tabs (as found in the DeWalt packs) should be fine.

The question also is: does soldering increase the internal resistance of the cell, as well as reduce the capacity? I shall have to do some tests.

What we really need to find is someone that has a nice little spot-welder...

[leorcc]

quote:

Looks promising, except I cant see any mention of balance wires in the packs Thats why I sent an email to verify. As soon as I get a response I will let you all know.

It is very interesting indeed.

[swanaldo]

cant afford em yet

[terrorhurtz]

Just posted some findings on the MegaPower Infinity 960SR charger with LCB-12S balancer:
http://www.terrorhurtz.com/a123/MegapowerInfinity960SR.aspxhttp://www.terrorhurtz.com/a123/Mega...nity960SR.aspx

[leorcc]

I almost forgot to mention, I never really got a satisfactory answer back from RMP. They said their lipos had balancing wires even though i specificaly asked about their A123 packs. So I replied that I was referring to their A123 packs but I never got an answer back on that email.

[terrorhurtz]

The significant finding on the 960SR is that it does NOT prevent individual cells going over 3.7V, even when using the balancer. It just uses the average cell voltage. No better than a dapter in that respect. On a not too badly balanced pack, this is OK, because the balancer should have got the cells fairly close by the end of charge.

But as I say in the piece, you need to keep an eye on new packs, and if they look badly out of balance, then reduce the current, to give the balancer time to do its work. Fortunately the 960SR makes it easy to see if they are way out.