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NiCd/Nimh Battery Tech Info
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Spockie-Tech
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Joined: 31 May 2004
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NiCd/Nimh Battery Tech Info

Some very useful information on up-to-date battery tech is here. Good to see someone who isnt perpetuating the "memory effect" myth. Well worth a read for anyone running or considering running Nicads or NiMh's

http://www.camlight.com/techinfo/camlight_whydischarge.pdf
http://www.camlight.com/techinfo/camlight_techtips.pdf


Last edited by Spockie-Tech on Wed Aug 25, 2004 9:56 pm; edited 1 time in total

Post Thu Jul 29, 2004 12:09 am 
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andrew



Joined: 16 Jun 2004
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also something i doscovered yesterday, drill nicads arent bad. I charged up a simple 12 volt xu1 pack and had scrap driving round on pretty much full power for 3 mins. which is as long as a match. Going to do more tests and see if they handle 24 volts for weopon and if i can use them for teh weopon batts.
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Post Thu Jul 29, 2004 6:38 am 
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Spockie-Tech
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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

Post Thu Jul 29, 2004 3:09 pm 
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Glen
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interesting read there.

well as you said those drill nicads arent as bad as we all thought given that plan b was running both a spinner and two big drive motors of, of them.

i think really that garys robots go so long on a single charge of nicads because he has done such a good job of balancing them. same for arachnophobia. they easily ran the 3 minutes whereas cobra however dies in the butt after about 1.5 minutes running the SLAs (12v @24v..).

just a brief OT note - well it seems we can now officially use *EVERY* part of the drill. case as a motor tester/flashlight, chuck as a screwdriver, motor gearbox as drive, trigger as speed controller, and battery as...... battery Very Happy
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Post Thu Jul 29, 2004 6:30 pm 
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timmeh
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hi just read spockie tech's pdf files about nicad and nimh's batterys can some one put in in a simply
is this right dont overcharge\dont store your packs at full charge\discharge your packs before recharge dont let em get hot when charging or discharging and only put em on a cycle every now and then to keep them healthy.
is that basicly all you need to know too keep em healthy without going overboard? and dose it hurt to say if i had a full pack and used 3 1/4s of it in battle and didnt have time to fully discharge and fully recharge it but i had to have a full pack to get threw the next battle can i just charge it with a 1/4 capacity still left in it
dose it hurt to do that on desprite ocasions?
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Post Thu Jul 29, 2004 9:53 pm 
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Spockie-Tech
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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.. Razz

Post Thu Jul 29, 2004 11:04 pm 
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andrew



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ALright Brett all u have to do is state it. Was a bit rude with name calling and such.
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Post Fri Jul 30, 2004 8:05 am 
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Spockie-Tech
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I didnt actually call tim an annoying shit andrew (and hope he didnt take it that way), I meant that if I had answered in a similair fashion then *I* would have been being one, since it would have been deliberate .. I dont think that Tim (or yourself) *deliberately* type hard-to-read messages, its more likely just laziness in my opinion.

It might seem like pettishness, but it can be very annoying when people who have actually put in some effort to understand something are asked questions about it by those who are too lazy to take an extra minute to edit and make sure their query's are vaguely legible.

I know I'm not the only one who finds this irritating.. most literate people do..

Post Fri Jul 30, 2004 11:58 am 
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andrew



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Well different people have diferent methods of typing and expressing themselves through text. Its all water under the bridge anyway's. Ill try to use paragraphs more then in future.
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Post Fri Jul 30, 2004 3:59 pm 
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timmeh
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i agree that using enter makes it easyer to read what people have typed but i think that if you have good reading skills it would be no problem to read the sentence without them. 90% of books dont have spaces on every sentence only little kids books.Yes i know i should probbebly typ better in your opinion but it dosent help when you have people poking shit At you before you get the answer to your question.
If you realy dont understand what im typing just say so.
What if you have a big message to write you dont want it to be 30 times its size just because of all the enters.
But i will try to type a litlte bit easyer to read now you have pointed it out. Laughing
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Post Fri Jul 30, 2004 7:15 pm 
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Spockie-Tech
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Ok, I'll try to be a little calmer about it.. Wink 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.. Wink

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.

Post Fri Jul 30, 2004 11:37 pm 
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timmeh
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How hot is too hot when your soldering cells together as when i was soldering some old nicads they were getn pretty hot!
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Post Mon Aug 02, 2004 10:45 pm 
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ffej
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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.
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Post Mon Aug 02, 2004 11:23 pm 
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Spockie-Tech
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Gee I'm in a lecturish mood tonight (no-one say "when am I ever not !" Rolling Eyes ).

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.
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Post Mon Aug 02, 2004 11:26 pm 
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andrew



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I have a huge problem and am clueless as to why. I tested scraps drive train using the xu1 charger and such and it ran scrap for a full 3 mins with most power. I bought a gws charger for 75 and charged them with it and for some reason it does really bad. lasts about 30 secods then slows down to dragging point. I charged them at what i am certain is 2 amp then tried 1 amp. Its being powered by a 7 amp sla for now for nothing in power supply stuff.

I am just really confused and frustrated at to why its being stupid and such and i need help fast or else scrap wont come to next event.
thanks in advance.
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Post Sun Aug 15, 2004 6:10 pm 
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