Hi guys, just thought you might be interested in a video of a lipo fire. http://rchomepage.com/~dna/LipoFire.wmv I have seen what happens when a plastic propellor goes through one of these things. Also you might be interested to know that Lipo cells will not take a charge once their voltage drops below roughly 2.9v per cell, cells tend to discharge at different rates and a charger that is chargingmultiple cells can over charge individual cells and the result is not pretty.
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Regards,
Marshal J.

yeah generally any li-ion type batteries are charged as a single cell if possible, because they're so sensitive to voltage changes between cells.

Multi cell packs tend to have a small controller board in them that monitors the cells individually.
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The Engine Whisperer - fixer of things

Good to hear from you, Marshal.
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So even the rain that falls isn't actually going to fill our dams and our river systems

crap.
After much looking and comparing Li-Poly to gel cell, nimh and nicad... Li-Poly don't look so great for feathers...
Besides the cost, I've found some great Li-Poly packs (approx. 12V, 2000mAH) but they have a device on them to limit the power draw... to below usefull levels for this fine sport. They also have heat issues that corrode the chemical in the cells.

BUT

I've found a gel cell ("Genesis", 12V, 2AH, 700grams) for approx $28 AUS.
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There is no such thing as excessive carnage.

WHOA $30 is alot of money to be paying for a 2ah sla,

i get the diamec ones from jaycar for about $25 and brett gets the doss ones significantly cheaper as well. there both 2.2ah.

one question though, why didnt you go for nicads or nimhs?
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www.demon50s.com - Minimoto parts
http://www.youtube.com/user/HyzerGlen - Videoooozzz

You will get some nicads with your drill. Marauder uses drill nicad packs.
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So even the rain that falls isn't actually going to fill our dams and our river systems

quote:

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WHOA $30 is alot of money to be paying for a 2ah sla,

i get the diamec ones from jaycar for about $25 and brett gets the doss ones significantly cheaper as well. there both 2.2ah.

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I don't think everyone has really read what Nick has found. 700g for a 2AH gel cell ir rather light. The 2.2AH SLA's I have here are 1.2kg. Those batteries he found sound good.
They are also Genesis batteries. As in Hawker Genesis, the second best SLA's you could buy after the Hawker Odyssey batteries. Your trying to say your Volkswagons are better then his Ferrari's.
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Get Some!!!

Secretary of the Queensland Robotics Sports Club inc.

The 700 grams is why I'm using them.

From Master Instruments, Genesis SLA NP2-12, 12V 2000mAH, 48mm wide 97mm long and 54.5mm height, 700 grams....approx $28, it kind of jumped off the page compared to the Li-Poly packs I had in mind.

[Edit- they aren't on the M.I. site -I think- I've only seen them in the January 2005 M.I. hardcopy catalogue]

The reason for a weight preference in my selection is that I'd rather build the weight into weapons, mobility and armour instead of on the power to make it go.
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There is no such thing as excessive carnage.

Last edited by original_carnage on Fri Feb 18, 2005 10:28 am; edited 1 time in total

a 650g 2400mah nicad pack thats more energy dense wouldnt be more appropriate?
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www.demon50s.com - Minimoto parts
http://www.youtube.com/user/HyzerGlen - Videoooozzz

You can't determine the charge density by the overall weight of the battery. You must look at the batteries datasheet for that sort of info. Also, you must know the difference in discharge characteristics between lead acid batteries and NiCads (and li-polys) by now so comparing weight is only one factor in choosing batteries.

And can anyone give me more info on these Doss batteries as I can't find anything on the internet.

My opinion on Li-Poly batteries is that they are only suitable for low current applications, but remember that 5 years ago NiMH batteries wern't too crash hot either. Give them time.
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Get Some!!!

Secretary of the Queensland Robotics Sports Club inc.

quote:

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a 650g 2400mah nicad pack thats more energy dense wouldnt be more appropriate?

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quote:

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Li-Poly batteries is that they are only suitable for low current applications, but remember that 5 years ago NiMH batteries wern't too crash hot either. Give them time.

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note that the prevalence of NiCd cell threads is mainly because SLA's suck so nobody uses them anymore
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Mechanical engineers build weapons, civil engineers build targets

"suck" = not suited for rapid discharge applications..

In more detail, the thing you need to look at is how much energy you get from the battery when its discharged in 5 minutes (insead of 20 hous, which they are rated at).

When you are discharging a battery, *240* times faster than its amp/hr rating is spec'ed at, you expect to suffer reduced capcity a bit..

With SLA's, you get around 30%-40% of their rated capacity in 5 minutes.. so suddenly, a 2.2ah batt becomes 0.77ah in a bot.

With NiCd's you get around 80%-90% of their rated capacity, so 2.2a/hr pack becomes 1.9ah.

Plus, the packs weigh nearly half an equivalent SLA, and dont lose capacity with repeated cycling anywhere near as much as SLA's do.

Plus, if you leave them flat, they're not stuffed overnight, unlike SLA's.

So all of the above reasons are why SLA's suck for bot use.. and why we put up with soldering packs, cycling and expensive chargers and so on...
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Great minds discuss ideas. Average minds discuss events. Small minds discuss people

i think thats the hardest way of saying "suck" i have seen ;-P
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Mechanical engineers build weapons, civil engineers build targets