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Spockie-Tech
Site Admin
Joined: 31 May 2004
Posts: 3160
Location: Melbourne, Australia
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Nope, Jake summed it up pretty well..
The only thing I would add is that SLA's arent always shitty batteries... in a lot of applications, they are great batteries, but not Robot Wars..
They arent designed to have all their stored power sucked out of them in under 5 minutes and as a result when you try and do so, you only get about 30%-40% of their capacity from them, since their internal chemical reactions cant keep up with the demmand for current.
NiCd's dont particularly like it either, but cope a lot better, delivering 80%-90% of their stored capacity in a 5 minute discharge.
a battery's capacity is rated at a *20 hour* discharge time (ie, you take 20 hours to gradually discharge the battery to flat), so you can guess how much stress you put on them when you flatten them in 5 minutes.
The reason every starts off with SLA's is simply cost.
1 x 12volt 2.2ah SLA (Gives about 1ah of useful capacity in a bot) - $15
~ 1100 grams in weight
Battery Charger capable of charging it in 1hr - $50
Total about $65
1 x 12volt 2.4ah NiCd pack (gives about 2.2ah of useful capacity) - $~80
Approx 650 grams weight per pack
Battery Charger capable of charging in 1hr - $$150-$300
Total about $320
So the Nicad pack has more than double the capacity in nearly half the weight which means about 4x the power-weight of the SLA, but is around 5x as expensive (when the charging system is taken into account)
So if you can afford it, Nicads are definitely the way to go.. _________________ Great minds discuss ideas. Average minds discuss events. Small minds discuss people
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Wed Jan 26, 2005 10:59 am |
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Spockie-Tech
Site Admin
Joined: 31 May 2004
Posts: 3160
Location: Melbourne, Australia
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quote:
Originally posted by Glen:
i wouldnt say $350, an omni charger is $50, and a 12amp PSU is $10 along with the $45 of the single 2.4ah battery pack.
We've had some trouble with the Omni chargers, and I note that none of the larger teams use them.. they're all Triton's, Astroflights or Schulze's. If you're going to spend the $ on good cells, I wouldnt subject them to a cheap charger myself. If you want to be able to reliably crank power back into the pack without hurting it, I'd spend the extra and get a good charger.
Where do you get a 12amp regulated 12v power supply for $10 from ? Modifying PC power supplies and other hacks are fine, but not everyone has the knowledge and skill to do that. I'm comparing off-the-shelf stuff here..
And 12v Sanyo packs might only cost you $45 in cells, IF you buy 100+ of them, and IF you have the skills, time, braid, and heatshrink to make them yourself. But if you want to buy a ready-to-go battery (as the 12v SLA's are) then it will be more like $80 for a pack. You have to compare apples to apples.. comparing a turn-key battery to a pile of loose cells doesnt count.
$320 might seem high, but its a realistic cost if you want quality gear and dont want to fiddle about making packs and things yourself.. _________________ Great minds discuss ideas. Average minds discuss events. Small minds discuss people
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Wed Jan 26, 2005 8:20 pm |
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