A123 Lithium cell use

[typhoon_driver]

A123 Lithium cell use

My nicads only expel around 1.2Ah during a 3min fight with a mag on 24v and two 18v drills on 24v.

The problem with running a mag is that you need large surge currents which is why I use nicads. I dont think A123s currently have the ability to give out large bursts of current so you will be looking towards 3 packs.

[nick]

A123 Lithium cell use

On a weight for weight basis, A123 is always better than Nicads, unless the ambient temperature is above ~40C.

[geeza]

A123 Lithium cell use

Matt is planning to use the Mag for an axe which would mean large start up currents, having not used such a mag before how many pack would people recommend. (i.e. how many Ah would be needed - I had suggested 4Ah to him for a 3 min fight)

[leorcc]

A123 Lithium cell use

the amount of Ah is really not that important, more the amount of current the cells can take in short burst without degrading.

You will always be better of with 2 or more packs in parralel than 1 high mAh rated pack.

[nick]

A123 Lithium cell use

Soldered 7S4PA123-M1 should reliably be able to burn out a S28-150 magmotor under any conditions before the cells are damaged. With 7S3P the batteries are still likely to outlive the motor. 7S2P, youre quite likely to slowly damage the cells without current limiting unless the magmotor is not working hard enough to get hot. In general, we should be current limiting low resistance motors. A123 wants current limiting more than Nicads, since the stall currents generally work out higher.

[terrorhurtz]

A123 Lithium cell use

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]

A123 Lithium cell use

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]

A123 Lithium cell use

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]

A123 Lithium cell use

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

[terrorhurtz]

A123 Lithium cell use

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=5vQTBoHPBxQhttp://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]

A123 Lithium cell use

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]

A123 Lithium cell use

cant afford em yet

[terrorhurtz]

A123 Lithium cell use

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]

A123 Lithium cell use

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]

A123 Lithium cell use

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.