Droid sub goes under Antarctic ice on 5000 D-cells

D from BC wrote in news: snipped-for-privacy@4ax.com:

I wonder what the battery pack architecture is;what is it's output voltage and current?

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Jim Yanik
jyanik
at
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I suppose that depends on the motor and the motor load.

I wonder if there's some clever battery switching.. I haven't investigated but suppose it's better to discharge a bank and then switch to another bank as opposed to having all the batteries connected in some series/parallel combo..

D from BC myrealaddress(at)comic(dot)com BC, Canada Posted to usenet sci.electronics.design

Imagine a kid's face when he gets that for Christmas? Imagine the parent's face when he sees "batteries not included"?

I suspect that a single series/parallel bank might be more efficient, for a couple of reasons.

It would result in a lower level of current being drawn through each individual cell in the battery, which would make the cell's equivalent series resistance less of an issue. Less power would be lost in the cell ESR, resulting in a greater effective utilization of the total amount of charge available.

Also, I believe that many battery chemistries are also more efficient (at turning chemical potential energy into current flow) at low discharge rates than at high rates.

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Dave Platt                                    AE6EO
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You migh use multiple banks if you wanted a backup in case of cell failure. OTOH you have also introduced a switch that could fail. Maybe a diode or if there was no regen.

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Robert

Under Antarctic ice?

Does that mean they've got one that goes through rock?. ;-)

Cheers! Rich

Airplanes that fly in the sky also don't go through rock..

D from BC myrealaddress(at)comic(dot)com BC, Canada Posted to usenet sci.electronics.design

Although Antarctica isn't just an iceberg (like the Arctic cap), around half of its coastline has ice shelves (floating ice, attached to land on the inside).

I've done that kind of thing before for ocean bottom seismic recording gear. We even painted the "battery pack" with a gold top to make it look like a big Duracell copper-top battery :->

Not quite as big as that one, but getting close. Alkaline D cells, many parallel strings of 9 x D cells. We had two versions, the first one used solder tag D cells, but we eventually went with standard D cells in a custom made holder. Smaller "packs" would slide down a central shaft pancake style. Mission duration was in the order of several weeks to a month. The only problem was that 50+ units were deployed at any one time in an array, which leads to many *tons* of dead battery packs to dispose of after each deployment. We also did a rechargeable Lithium Ion version (with matching charger) but the customer liked the lower price, simplicity, and safety of the standard D cells.

Dave.

That's what we found with our big pack design. The series/parallel combination was simpler and had some capacity improvement.

Dave.

I feel sad when cheapo old tech wins over expensive high tech solutions. :)

Probably due to the less development time and therefore less income. However, lowest bid often wins the contract..

D from BC myrealaddress(at)comic(dot)com BC, Canada Posted to usenet sci.electronics.design

I don't mostly, I like it when low tech wins!

In our case we actually did the Lithium Ion version and charger design first, but then the customer wanted to price an Alkaline version.

Price was the main driver, but safety concerns also came into it, tipping then in favor of an Alkaline D cell solution.

Dave.

Oh great. Maybe it will hole a French droid sub? ;-)

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Michael

I actually did the math on price/performance and power density on a bunch of commonly available battery types for a similar project idea. I actually got the same result -- a bunch of D cells are hard to beat. Everything smaller just has more packaging (poorer density and cost/watt hour) and everything bigger (alkaline) is just a funny package around smaller cells. I found that some manufacturers' lantern cells are pretty crummy -- just

4 C-equivalent cells and some wadding inside and very expensive. I can't find my notes on lead acid, but they must have lost on cost.

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Ben Jackson AD7GD

http://www.ben.com/

I know that compared to NiCd cells, alkaline just can't be beat for one- discharge performance.

Do you know how Li-Ion perform (forgetting price for the moment)?

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http://www.wescottdesign.com

Depends on the ion, but the power density looks about the same. Maybe slight edge to the better LiIon chemistries. But my project involved throwing the whole lot in the sea and never seeing it again so the one-shot cost totally ruled out rechargables. I also cared about years of shelf life so alkaline was tops there too.

--
Ben Jackson AD7GD

http://www.ben.com/

Yep! Alkalines are your answer, hands down.

Cheers! Rich

I've used Lithium Primary D cells in single use military sonarbuoys (i.e. sit on shelf for years, then deploy for 4 hours, then scuttle to the bottom). The capacity and shelf life was much better than Alkaline for this app.

Dave.