Getting started, what do I need?

[fwsorg]

You obviously havnt come across the new Sanyo 2600 Nimh that outperform RC2400 cells (traditionally the benchmark of sub-c performance). Wow.

Eh, what, I missed that one. 2.6Ah Nimh sounds good. Ill look into that when I get the chance. Do you know if they are lighter in weight too! After all we are still running 4.8Ah (2x 2.4Ah Sanyo Nicads) for the heavy drive and a little more battery power would allow us to change the gearing and have a faster bot.

[fwsorg]

A 12V stick pack of RC2400 from overlander weight 585g

A 12v pack of the 2600SCU cells in the same configuration from overlander weighs 610g.

Not that you probably would, but dony buy them in stick packs as they are covered in 2 layers of heat shrink (one round each stick and one around the pack as a whole) which gives very poor cooling potential, and the cells are normally attahced via spot welded tags which have a much much higher resistence than soldered joint. Spaced packs are much much better for your batts and they last a lot longer when spaced, even longer with a small fan, or looking at it another way, you can push them much more for the same amount of damage.. Please dont be tempted to stick the cells in cardboard tubes :-) You may as well heat them gently with a blow torch.

My Gp Ni-Hm 3.3A are coated in 2 layers of heat shtrink and they dont get warm, even with the over-volting of a 12v gold to 24v.
Are the RC2400 a different size to the 2600SCUs then, its getting me confused lol, please tell me if it was a stupid question to ask! hehe
I would expect the 2600SCUs to weigh more than the RC 2400s if they have 200 Ah more.
Im confused.
Grant

[stu]

Yo Grant - im getting thos batteries. I spoke to your brother on MSN about those batteries. Nice packs they are, claim to be better than Sanyo Sub C Ni-Mh packs.

The RC2400 NiCad and 2600CU NiMh and GP3300 NiMH are the same size Sub C cells and weigh the same. There might be about 2 or 3g difference between each cell as it might have a bit more acid or whatever inside it.

Mr Stu

[grant_ploughbot]

Yer they give out 5Ah more than standard sanyo Ni-Hm cells i beleive.

Oh hmm, okie wel thats kinda funny coz someone confused me there, so then the higher ampaere batts should be best to buy? am i correct in thinking and should weigh in at slightly more due to the extra stuff inside (im not an expert on what makes upo the weight lol)
Grant

[fwsorg]

Its all to do with the chemistry inside- more electrolyte layers inside and so on. The weight fluctuates a bit but by very little. You can pretty comfortably say that Sub-C cells all weigh pretty much the same, or at least the variations arnt too big.

Its the chemistry that makes the difference. Traditionally Ni-mhs have a larger capacity that Ni-cds, and they dont suffer from memory effect so much. However Nicads can be discharged faster (i.e. you can pull higher currents from them) than Ni-mh. Thats quite a black and white way of looking at it, and thanks to advances in technology we have got to the point that some Nimhs cells are beginiing to outperform similar Nicd cells in terms of discharge rate, thus pushing Nimh into the lead so to speak :-) A case in point are the recently launched 2600SCU nimh cells, which are said to outperform the RC2400 cells (nicd), as well as having the obvious advantage of higher capacity.

As for the Nimh not getting warm, it depends on what youre doing with them. If you start pulling more than about 45A they start to get pretty warm. This is the point where having them spaced pays dividends. General word of mouth rates them at 45A continuous, 60A for a short time. The RC2600 cells, by the same token, are said to be good for 60A continous and 100A for a short time. Its all just a question of looking at whats best for your application.

Have i got this right, do i only need about 2,6 Ah batteries in a FW?

Yes, if theyre Ni-Cd or Ni-Mh cells.

[fwsorg]

You can get away with even less. If its not a particularly current thirsty robot (which would suggest a simple drive and non-electric weapon, ed flipper) then small er batts will do. I know of Feather Flippers that have been running 1300 packs quite happily (although personally I wouldnt want to go beneath 1700)