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MER Batteries, How long can they last?
MarkL
post Feb 21 2007, 04:31 AM
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The more I think about it the more I'm convinced that the MER batteries are the unsung heroes of the missions. Here's the web page of the folks who made them, Lithion.

There's a reference to 2100 deep discharge cycles. I followed the earlier discussions on available watt hours with fascination, however we've now seen that insolation is sufficient as long as there are no major dust storms.
I am more interested in learning about the likely lifespan of the batteries based on their chemistry and present physical environment.

It is good to keep Li-Ion batteries at 0 Celsius when storing them (you should keep unused laptop batteries and iPods at 40% charge in the freezer according to several wags). So the cold environment on Mars should improve the longevity of the batteries (as long as they don't freeze and no doubt great care is taken to avoid that). Age (not cycles) is often described as the most important determinant of charging capacity of a Lithium-Ion battery. As the MER batteries age, are they holding less charge? Is there a chart showing this and can we project a lifespan based on current information? Has someone done this already? If so, sorry for trying your patience and repeating it. Please just kick me over to the relevant thread.
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djellison
post Feb 21 2007, 08:07 AM
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There are papers on this on the JPL Technical Reports server....but it seems to be very broken at the moment so I can't have a look sad.gif

I do remember a chart showing capacity as a function of cycles - and it drops to about 80% over a few thousand cycles. - I think....can't quite remember.

Doug
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MarkL
post Feb 21 2007, 02:30 PM
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Thanks Doug. If you come across it please post a link. I did some looking myself but found mostly generic information.
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djellison
post Feb 21 2007, 02:32 PM
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Both http://trs.jpl.nasa.gov/ and http://trs-new.jpl.nasa.gov/dspace/handle/2014/6130 appear to be very dead unfortunately sad.gif

Doug
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helvick
post Feb 21 2007, 02:56 PM
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http://ntrs.nasa.gov/search.jsp appears to be working now. This paper - Lithium Ion Rechargeable Batteries on Mars Rovers in particular seems relevant.
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MarkL
post Feb 21 2007, 09:09 PM
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Thanks. Should get to sleep early tonight!
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MarkL
post Feb 22 2007, 08:09 PM
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Based on this search:

http://trs-new.jpl.nasa.gov/dspace/simple-...y&submit=Go

I found and had a look at

http://trs-new.jpl.nasa.gov/dspace/handle/2014/39912

which says the capacity of the batteries will still be over 80% of original even after Launch, cruise and 1400 sols. This amazed me as I've had trouble getting a laptop battery to last more than three Earth years.

The paper is interesting and has lots of pretty graphs so well worth a read.
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tty
post Feb 22 2007, 08:28 PM
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QUOTE (MarkL @ Feb 22 2007, 09:09 PM) *
This amazed me as I've had trouble getting a laptop battery to last more than three Earth years.



Maybe JPL uses a better quality battery than the manufacturer of Your laptop? smile.gif
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djellison
post Feb 22 2007, 09:10 PM
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The Li-Ion on my Dell went from 2 hours life to less than 40 minutes in about 14 months.

Doug
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ElkGroveDan
post Feb 23 2007, 12:05 AM
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QUOTE (djellison @ Feb 22 2007, 01:10 PM) *
The Li-Ion on my Dell went from 2 hours life to less than 40 minutes in about 14 months.


If you purchased an extended warranty that's covered. If it's not, look to pay $100 for a new one.

My wife flies cross country a lot and we were looking to get her a second battery for those 5-6 hour flights. I paid $120 for an Inspiron B-130 laptop battery. But when I complained about the deteriorating original they sent me a refurbished replacement as well.


--------------------
If Occam had heard my theory, things would be very different now.
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helvick
post Feb 23 2007, 02:01 AM
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I think that JPL also manages the battery conditioning substantially better than mere mortals manage the conditioning of their batteries.
For the MER's Temperature is kept near optimum and charge states are managed so that the batteries are not kept at too high a charge state or allowed to deep discharge (apart from the one occassion caused by Spirits Flash anomoly). It appears that if we could manage the same for Laptop batteries we should be able to expect 80% or more charge after 2-3 years of use.

Anyway as a comparison - here's some stats from my current battery (and IBM Thinkpad T43P - Sanyo Battery):
Manufacture Date: 19/09/2005
First used: ~01/01/2006
Design capacity: 77.76 Whr
Current capactiy: 71.14Whr
Cycle count: 101

That's 4.6% capacity loss per annum since manufacture. Not bad considering I generally keep the battery fully charged at ~20C. At that rate I'll be at around 85% when I hit 1000 sols. Right now I register about 4:00 hours battery life from 69 Whr remaining. Personally I'd like more but I can't complain.
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