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Spockie-Tech
Site Admin
Joined: 31 May 2004
Posts: 3160
Location: Melbourne, Australia
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Most of gary's bots were running on Drill Nicads at the annihlator event.. from being very unimpressed with them originally, we've gone to learning that they can actually be useful and in many cases, even better than SLA's if you work within their limitations..
Their main drawback compared to quality nicads (or SLA's) is that they cant deliver as high a peak-current, or even a sustained high current without cooking.
I did some testing on the bench here with a current-shunt and my scope and found that they will put out 40-50 amps for a half second or so, which quickly drops off to about 20-30 amps and they then warm up *really* quickly. After 5 or 10 seconds of delivering this sort of power, they were uncomfortably hot.
Testing of the Jaycar high-discharge cells shows 60-80 amp peaks with a sustained 40-50 amp discharge. I believe some of the sanyo cells (used in BattlePacks) are capable of 100+amp peaks with sustained discharges of over 60 amps !
So if you are using the drill nicads in a situation that doesnt require too much sustained or peak power then you should be ok.
They actually do *better* than the SLA's do in many cases, since most of the 2.3ah SLA's actually put out less than 1.0 amp hour (about 40% of their capacity) worth of power when discharged in 5 minutes, whereas the 1.1 to 1.3ah drill Nicads will supply 80-90% of their rated capacity in a 5 minute discharge, which gives you about the same amp-hours as a 2.3 SLA, but in about half the weight..
There are a couple of catches though.. apart from the limited power peaks
You either need to be very careful in frequently putting a hand on them when charging them and stopping the charge as soon as they start to get warm, or else invest in a good quality delta-peak charger (like the Tritons or Astroflights) to make sure you dont overcharge them, since that will kill them very quickly.
Secondly, you really need to be able to discharge-test the cells individually prior to combat, since of the many hundreds that gary has been testing and assembling into packs, a fair percentage of them showed pretty low capacity, and it only takes a single dud cell in a pack to really spoil the performance of the whole pack.. so unless you just want to take your chances in combat, breaking the factory packs up, testing the cells and reassembling them into new packs is necessary for guaranteed full capacity.
A lot of work, and you need an expensive charger/discharger to do it properly, but if you can handle that, then they're worth a second look..
Last edited by Spockie-Tech on Fri Jul 30, 2004 12:22 pm; edited 1 time in total
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Thu Jul 29, 2004 3:09 pm |
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Spockie-Tech
Site Admin
Joined: 31 May 2004
Posts: 3160
Location: Melbourne, Australia
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ahem.. paragraphs, tim - paragraphs !!
They make multiple questions much easier to read and more likely to get an answer, but I'll be nice and answer you anyway..
Dont overcharge - correct, worst thing you can do to a nicd/nimh battery. they will heat up and heat is bad.
Dont store at full-charge - for long periods of time, emptier is better for nicd/nimh's. opposite to SLA's where storing them empty for even a short period of time will kill them dead.
discharge-before-recharge - not always - if you have a good sensing charger.. just every now and then, in fact too often will wear them out faster. its perfectly acceptable to even use a little bit of it then top it up, as long as you give them a full cycle every now and then.
of course if I wanted to be an annoying shit, i would have answered like this.
Dont overcharge - correct, worst thing you can do to a nicd/nimh battery. they will heat up and heat is bad. Dont store at full-charge - for long periods of time, emptier is better for nicd/nimh's. opposite to SLA's where storing them empty for even a short period of time will kill them dead. discharge-before-recharge - not always - if you have a good sensing charger.. just every now and then, in fact too often will wear them out faster. its perfectly acceptable to even use a little bit of it then top it up, as long as you give them a full cycle every now and then.
pressing enter every now and then isnt that hard..
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Thu Jul 29, 2004 11:04 pm |
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Spockie-Tech
Site Admin
Joined: 31 May 2004
Posts: 3160
Location: Melbourne, Australia
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Ok, I'll try to be a little calmer about it.. I dont expect spaces after every sentence, just between un-related concepts or questions
Books dont have many spaces, because they arent interactive.. you read them continuously from start to finish without asking questions.. and even then they still have paragraph spaces between jumps in the story. in fact the book I'm looking at here has around 3-5 paragraph breaks per page.
Anyway, sorry to be a bit sarcastic in my original posting, I'll chill and you put *some* spaces in and we can get back to our battery thread..
Back on track, if anyone wants a source of *cheap* drill nicads, without having to buy the whole drill, a friend of mine told me about a surplus place he visited recently in Moorabbin (Vic) that had a 6ft square box full of a huge variety of apparently-new (no guarantees) drill packs.
9.6v to 18v.. all one price. $5 each - but thats a one-off price, He's sure if someone went in there and asked for 10 packs that you would probably get them for $2-$3 each, which is pretty good - especially if you got mostly 14.4 or 18v packs with 12-15 cells per pack.
If anyone is interested, let me know and I'll get the address and details for you.
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Fri Jul 30, 2004 11:37 pm |
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ffej
Experienced Roboteer
Joined: 22 Jun 2004
Posts: 595
Location: Kurrajong, NSW
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The less heat the better. They will heat a bit while you put your iron on them, but I would think you should still be able to touch the cells comfortably while your soldering them.
What size iron did you use? From the info ive seen around, the bigger iron you use, the better, as you dont need to leave it heating the cell long to get a good join between the cell and the bar. On the 24V bodged up drill pack I made, I used my 60W iron, and was heating up the cells a fair bit with that.
It seems that the thing you need to worry about most is stuffing the cell vent at the positive terminal . If it opens and you loose gas from the cell, it will no longer hold its full charge, and will bring down the entire packs performance. if you somehow manage to seal to vent while soldering, and for some reason the pack gets overcharged, pressure inside the cell will build up, and it could explode. _________________ Jeff Ferrara
fb@ffej.net
ffej.net
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Mon Aug 02, 2004 11:23 pm |
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Spockie-Tech
Site Admin
Joined: 31 May 2004
Posts: 3160
Location: Melbourne, Australia
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Gee I'm in a lecturish mood tonight (no-one say "when am I ever not !" ).
According to all Nicd/NiMh cell manufactuers, *any* soldering of cells is too hot. They strongly reccomend against any soldering to cells. the top part (+) of the cells have a plastic pressure-seal around the edge that allows the cells to vent if the internal pressure gets too much under heavy charging or discharging. (Thats why they make a mess when abused). Any temperature high enough for soldering is higher than the melting point of this plastic seal according to the specs, thats why all factory-packs have spot-welded tabs, the split-second tiny pulse of heat dissipates before it can warm up the whole cap enough to hurt the seal.
Having said that, a lot of people (and pack manufacturers) do go and solder their packs anyway, and if done by a skilled soldering person with a high-heat-capacity (not temperature, heat storage) iron so it can be done quickly, the seal *should* survive a second or so of heat. then you get the advantages of the lower resistance, mechanically strong solder joint over the small-contact patch spot welds.
If you are getting the whole cells near soldering-hot, chances are good that the seal wont be be very happy with you. it maybe ok, it might have totally melted, most likely it will have deformed somewhat. If it has melted "open", then the gases produced during the cells normal operation will be able to escape (rather than recombining) and the cell will lose capacity after a much shorter period of time than it would have otherwise, so the damage will not be immediately evident.
If the seal has melted-shut, then as long as it doesnt short out the top to the case (which will kill the cell instantly), then the cells will likely be ok for a while, but if worked hard and the gas-pressure builds up in them, they will go bang, rather than just vent as an undamaged cell would.
So how much heat is OK ? Ideally, None, in practise, the less the better.
To solder up battery packs successfully, get a powerful, high wattage, temperature-controlled (so it doesnt get too hot if you leave it without using it for a few minutes) soldering iron, with a good heavy tip (for heat storage, like a heat capcitor), and practise on a bunch of old useless cells until you can make a good solder joint without cooking the whole cell. _________________ Great minds discuss ideas. Average minds discuss events. Small minds discuss people
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Mon Aug 02, 2004 11:26 pm |
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