Any battery experts out there?

[Steve Kirk]

I am working with a friend on developing a new product, and we need to work out how to power some electronic kit on batteries. Needs to power some 12V and 5V kit for up to 24 hours, about 1 kWhr capacity. Weight is a key issue. Cost is less important within reason. I know that a few people have got into researching efficient lightweight batteries - is there anyone out there who knows about this stuff that could help us?

 

Any comments/suggestions would be most gratefully received, or if you were interested in specifying and designing the power supply side of the kit, that's a piece of work we would pay for.

 

Even if someone can just tell us where to go for this type of info, that would be a great start. Thanks.

[Sue Dinnim]

Steve,

 

I don't know if it will help but YHM.

 

Duncan

[Dickie Normuss]

I do a lot of model flying and in recent years the in ones are Lithium polymer, great capacity for minimal weight. You have to be careful how you charge them

 

Seek forgiveness, not permission.

Rules are for the interpretation of wise men and the obedience of fools.

[Steve Kirk]

Thanks guys. Ric, that sounds interesting on weight front but also maybe expensive. Could you give me an idea on weight/capacity cost for the biggest battery you would normally use? Maybe a few of these might do it? The application needs to run as long as possible, so steady current run-flat characteristics much more important than any peak current specs.

 

Any other suggestions gratefully received....

[Colin Mill]

Hi Steve

 

The big push with electric flight is for high discharge rates (like full to flat in 6 minutes) so what you require of the LiPo cells is not cutting edge which could be good for the price. We supply LiPo protection circuits to a company called Flight Power (www.flightpower.co.uk) You could contact Julian there and mention I put you onto him (he'll put the phone down on you 😬)

 

Colin

 

A rough sum suggests it will take about 5kg of LiPos to give you 1kWhr

 

Edited by - Colin Mill on 25 May 2005 18:31:35

[Peter Carmichael]

Can I see if I've got the sums right...?

 

1kwhr capacity, but run flat over 24 hours running.

 

i.e. 1000 (watt.hours)/24(hours) = 41.667 Watts

 

at 12v that is 41.667/12 = 3.5 amps.

 

So we are looking at 3.5 amps for 24 hours. Which is a big battery as long as 1kWh wasn't a typo.

 

Lithium polymer is very good at producing small packaged batteries, but its energy density is nowhere near NiMH. Industrial NiMH densities are reaching 300Wh/litre and is as good a volumetric efficiency as you will find anywhere. You are however looking at a three litre capacity.

 

You could achieve this with an array of 110 Sanyo Twicell D cells or their Yuasa equivalent. Perhaps DMS technology will be able to help you. They will be able to produce custom matched sets with flylead packaging, boxed or whatever.

 

Edited by - Peter Carmichael on 26 May 2005 18:21:38

[Steve Kirk]

Peter, thanks very much, that's extremely helpful. You're right, we are looking for quite a big battery, to run equipment you might normall think of as mains powered, but it's required to meet the product spec. Yes one kilowatt hour is our estimated requirement - not a typo. And yes those sums look right to me.

[Colin Mill]

Hi Steve

Just to give you the comparitive data for a typical LiPo I have just measured up some sample LiPos we have - they are 3.5Ah @3.7v and the volume is 51cc so that's about 250 Whrs/litre - as Peter says a fair bit behind NiMh. I would also say that LiPo is a much more tricky technology than NiMh. To give you an example a LiPo cell will be damaged if it is discharged below 3v per cell. Also on charge they must not be charged above 4.205v/cell while 4.19v/cell will give a significant under charge. There is also the expense. Basically I would only go for LiPo if the weight of NiMh is out of court for your application.

 

Colin

[Steve Kirk]

Excellent stuff guys, thanks both very much. This is exactly the sort of info I was looking for