For a very weight-critical application (model rocket) I need a battery (or batteries) that will deliver 5mA at 5V for about 20 minutes. I don't mind paying $20 or $30, if I can get a really light battery. Can anyone suggest something appropriate?
"ted"
** Look up the CR1216 lithium coin cell. 3 volts at 25 mAh, weighs about 0.7 gmsBuy them at retail stores for watches etc. for about $3 - 4 each.
.... Phil
ted wrote in news:327d3372-546b-4bf9-823d- snipped-for-privacy@a9g2000prl.googlegroups.com:
Two lithium watch batteries should do the job nicely.
--Damon
If you can stand more weight, Digikey will sell you 200 pieces of 2.9g Panasonic CR2032s for $44, but best put them on a separate order as they'll ship via a slow surface method.
5mA is a really a very large current for a button cell, watch the internal resistance specification, especially if the ambient temperature might be low.Best regards, Spehro Pefhany
-- "it\'s the network..." "The Journey is the reward" speff@interlog.com Info for manufacturers: http://www.trexon.com Embedded software/hardware/analog Info for designers: http://www.speff.com
"Spehro Pefhany" "Phil Allison"
** See data sheet:The IR is about 30 ohms pere cell - so 60 ohms in total.
At 5mA this equates to a 0.3 volt drop.
The data suggests that slightly over 5 volts will be available.
I * doubt * the OP's tiny model rocket will reach the upper atmosphere where temps are below zero - particularly as he is scared of a few grams of weight.
...... Phil
That's right at the bitter edge of functional. Maybe something a bit heftier, such as the common button cell used in PC's.
240 ma-hr. 19 ohms infernal resistance.Well, there's another problem which makes button cells rather problematic. If he stuffs two button cells in a typical PC battery holder, the acceleration forces of the rocket launch, chute deployment, and crash landing will tend to unseat the button cells from the holder. Spring loaded anything is a bad idea in a rocket.
Also a sufficiently large motor will rip the leads out of heavy components that aren't glued or screwed down. One rocket I helped build included a cheapo digital camera. When the camera was retreived, there were no photos because several surface mount components had ripped themselves off the flex circuit boards. In addition, the altimiter and apogee detector failed because the inertial load on about 3ft of #20awg stranded wire that wasn't nailed down, was sufficient to rip the leads out of the board.
If you're gonna use button cells, order them with welded contact leads. No battery sockets. Don't try to solder to the button cells. They can be soldered but I've killed a few cells by overheating. Bury the batteries in foam or gel. Keep the interconnect wires short and nailed down.
-- # Jeff Liebermann 150 Felker St #D Santa Cruz CA 95060 # 831-336-2558 jeffl@comix.santa-cruz.ca.us # http://802.11junk.com jeffl@cruzio.com # http://www.LearnByDestroying.com AE6KS
cp. the Panasonic CR1216 data, which is a bit more complete when it comes to high currents and temperature (but only goes to about 2.5mA)
By times it's pretty cold outside right at ground level, but if the OP kept the rocket (or at least the electronics portion, considering safety concerns) warm before launch that might not be a factor.
Best regards, Spehro Pefhany
-- "it\'s the network..." "The Journey is the reward" speff@interlog.com Info for manufacturers: http://www.trexon.com Embedded software/hardware/analog Info for designers: http://www.speff.com
Jeff Liebermann wrote in news: snipped-for-privacy@4ax.com:
some of those coin cell holders really hold the cells tight.I've seen some that had little tabs on the edges that had to be lifted to get the cell out.
(my largest rocket,2.5 lbs,flew on a G motor.everything scratch-built.)
-- Jim Yanik jyanik at kua.net
"Jeff Liebermann" "Phil Allison"
** Sure - but the OP has to try it out since he asked for lightest weight possible." I don't mind paying $20 or $30, if I can get a really light battery. "
** How utterly pathetic !!!I inventing a dopey problem just SOOO you can CRAP ON about it and BIG NOTE your stupid self.
** I expected the OP to realise this and carefully solder wires to the cells.PCB mount ( with solder) versions on the CR1216 are available too.
** Absolute BOLLOCKS !!ROTFLMAO !!!
...... Phil
Thanks, everyone, for your advice. On the one hand I'm encouraged that people are suggesting I could use a couple watch batteries. On the other, I see from the data sheets that batteries like the cr1216 are designed to provide currents in the tenths of a mA, and not the
5mA I need. In fact, as far as I can tell (but please correct me if I'm wrong) the data sheet for the cr1216 doesn't contemplate a current as large as 5mA even in momentary pulses. To the poster who estimated that, while draining 5mA, I'll still be able to get 5V our of two 3V batteries: please explain how you got that result.I know 5mA is a lot. It's all going to go to an accelerometer -- a Freescale MMA2201. I don't know why it sucks up so much power but the data sheet says it does.
Well, two CR1216 batteries weight 1.2 grams. Two CR2032 cells weigh
6.0 grams. If this is a fly weight rocket, 4.8 grams might make a difference, but I doubt it. It would really be embarrassing to have the battery crap out due to excessive draw. However, there are various other button cells in between marginal and overkill.Sure. I spend my spare time lurking in various newsgroups looking for your postings just so I waste my time crapping on your ideas.
Seems like a worthy cause. Besides, you craft such intelligent retorts when someone suggests your comments might be somewhat lacking.
Assumption, the mother of all screwups. It's not enough to simply suggest a particular component. One should also supply some clue as to why it was selected, what are its merits, what limitations must be accommodated, and what pitfalls might be encountered. This is also why I personally detest one line answers. They usually lack the detail necessary to make the answer useful to the OP.
-- Jeff Liebermann jeffl@cruzio.com 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558
Manufacturers don't like to toss parts that meet specs other than for power supply current, so unless the application requires micropower, the power limit is quite wide. For a one shot deal, you may be able to hand select a Freescale part that meets your needs.
I'd like to see a follow up post with the final results of your project.
Good point. I just happen to have a dead ATX motherboard handy with one of those holders with the difficult to extract button cells. I just beat the board edges and bottom, on the bench, trying to dislodge the batteries. The batteries (2 x CR2032) stayed put. I have no idea how many g's were experienced but I suspect it's more than what a rocket will see (about 20-60 g's). I have an accelerometer in the office and can try it again in a few days. Methinks the holder will work.
Nice. "G" would be the biggest of the "ordinary" rockets (that are not classified a high power). Probably an Aerotech motor. I haven't built much myself. Well, some of my early rockets looked more like flying pipe bombs. Currently, I help design, build, install, test, troubleshoot, and run post mortem autopsies on the radio and instrument packages. Mostly troubleshooting. Also some APRS/GPS tracking.
-- Jeff Liebermann jeffl@cruzio.com 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558
"ted"
** What something is "designed " to do is irrelevant to what it can do, if asked. ** What something is "designed " to do is irrelevant to what it can do, if asked. ** See the graph that shows IR = Internal Resistance.Shows it is around 30 ohms so a 5mA load will cause the voltage to drop only
0.15 volts.** No - it is a tiny current for a battery .
Time you went a bought a sample CR1216 and tested it at 5 mA - ie with a
500 ohm load.See what happens.
Your spec of 5 mA for 1/3 of an hour = only 1.7mAh.
Not that much to ask from a 25 mAh rated cell.
...... Phil
"Jeff Liebermann = posturing f****it "
** Irrelevant drivelWith every response you change context.
Classic symptom of autism.
** Well, you got that right.Snip more spew inducing drivel with another, entirely new context.
** No - a very reasonable expectation about someone familiar with model rocketry.OTHO:
You are nothing but a lying, stupid, bloody fruitcake - Liarmann.
Go and drop dead.
.... Phil
I think the lightest solution might be to use a small alkaline or zinc-air button cell and a small step-up converter. Alkalines can provide a lot more current than lithium coins of similar size. Not sure about zinc-air but they are popular for hearing aids so there must be an advantage.
Do you really need 5V? If you can run on a lower voltage this will help a lot with power budget.
For reliable connections at high G, conductive epoxy may be better than a spring holder.
"Mike Harrison Pommy Fuckwit "
** Purest lunacy.Is there no end to the supply of f****it, pommy ratbags ??
** Post a link that proves that.Cos it is very doubtful.
** A pompous, mid-air argument - if I ever heard one.** Now I know for sure this trolling cretin is total f****it. ** QED.
How boring.
.... Phil
Jeff Liebermann wrote in news: snipped-for-privacy@4ax.com:
Yeah,G-64. I have 29mm and 24mm reloadable casings. The 29mm rocket will take an H or I motor,but I haven't felt like going for Level 1.
I like building the rockets more than finishing or flying them. I have one 3-sided "stealth cruise missile" I made using foamboard,about
30" long,big handcarved balsa NC,that weighs just over 1 Lb.;24mm motor mount.-- Jim Yanik jyanik at kua.net
button cell and a small
of similar size. Not
advantage.
I beg to differ. Lithium cells have a much higher power density (watt-hrs/kg) than Alkaline. Li = 120 watt-hrs/kg Alkaline = 50 watt-hrs/kg The numbers are from some of my scribbled notes with no obvious source. This is all I could find (in a rush):
I dunno about zinc-air.
Most of the rockets I've seen and been involved with use LiPo (Lithium Polymer) batteries from cell phones with leads soldered to the contacts or from electric model airplane parts. Lots of available power for a very short time.
with power budget.
spring holder.
No way. Conductive epoxy isn't really all that conductive. It won't stick too well to the smooth button cell surface. I suspect it may be brittle and crack. Think welded straps or welded contact pins. The better button cell holders seems to have sufficient edge grip to survive a launch (tested by beating a board with holder on the table).
-- Jeff Liebermann jeffl@cruzio.com 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558
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