Lithium Polymer Battery?

MooEy · Post by **MooEy** » Sat Feb 02, 2008 7:47 pm

Just curious. Have any of you considered the use of lithium polymer batteries for astronomical use, ie. powering of goto. It seems that the weight of these lithium polymer batteries are very light for their rated capacity. a single 6400mah 3.7v batt only weights 122grams. putting 3 of them together would give a total 6.4ah at 11.1v at under 400 grams.

http://www.batteryspace.com/index.asp?P ... rodID=2169

tempting tempting. of course, all these are mostly based on theory. would be interested in whether anyone have attempted to use them out in the field.

of course, u can see from my link that these batt ain't cheap. considering that you can get a nice 7ah SLA batt at merely 25-30 SGD, and chargers are in the 30 bucks range. A similar set of lipo batt would prolly run into 120-130 usd range, not even including the lithium batt charger and balancers. it seems that these batts are not very popular due to their cost, and weight is of no issue to people who drive. but since i'm going to backpack everything, a 3kg sla vs a 400-600gram lipo batt makes a big diff.

Of course, my main concern now is how much power does my upcoming goto drives require. Somewhere in the manual it states that 11-15v is required. a 3 cell delivers only 11.1v while hooking up 4 cells would deliver 14.8v. still trying to find data on these batts, esp their voltage curves from full capacity to almost empty. somehow i have a strong feeling that a 4 cell pack might work better, since most gotos work pretty well with those 12v sla with their 14.4v.

will appreciate any form of help and comments.

~MooEy~

Post by **weixing** » Sat Feb 02, 2008 9:54 pm

Hi,
Lithium polymer batteries are very dangerous if packed without the protection circuit or carelessly. Most commercial packed lithium polymer battery pack have built in protection circuit.

Anyway, I did ask the battery manufacturer about it in the past. I was advice not to pack it myself as it is not safe to do that. So I don't think it's wise not to pack it yourself.

Just my S$0.02.

Have a nice day.

MooEy · Post by **MooEy** » Sat Feb 02, 2008 10:27 pm

oo, not la, not intending to pack it myself. that webby sells complete battery packs. i saw the 5700mah 11.1v pack for 70 usd. also got 5700mah 14.8v for 90 usd.

still unsure of the voltage requirement, if the goto controller would survive with as low as 10.5v then problem settled liao. somehow the lipo batt are 4.23v when fully charged, can drop to as low as 3v depleted. i wonder how many % charge can it hold while still delivering at least 11v.

~MooEy~

swimaniac · Post by **swimaniac** » Sun Feb 03, 2008 1:07 pm

The LiPo batterries are widely used by the Remote control community. The batteries are rather volatile and must be charged with Lipo chargers. Also the cells must be balanced otherwise the batteries will bloat and may even catch fire.

Read about it in the RC forums - www.daddyhobby.com. There are many threads concerning Lipo batteries and its care.

MooEy · Post by **MooEy** » Tue Feb 19, 2008 9:11 pm

hmm..after some researching, i came across those voltage regulators. thinking of building this one. suppose to input 8-40v and give 12v at 3a. more than enough for my drive. or is there any better options? the drive needs 2a at 12v. i saw a lm2678 version, that would give 5a, way more than wat is required.

http://www.elecfree.com/circuit/power-s ... th-LM2596/

anyone have any idea on how to build it? need help from those who are gd with electronics.

vincent=> yes, i saw alot of exploding lipo on the net, esp youtube. but i dun think my rig would be that dangerous, drawing less than 1c wor, most likely 0.5c only.

~MooEy~

Clifford60 · Post by **Clifford60** » Tue Feb 19, 2008 9:49 pm

Where are you going to find the 8~40V source? for 12V output, you will need 18~24V unregulated input

MooEy · Post by **MooEy** » Tue Feb 19, 2008 10:09 pm

ahh, i just realise the 8v input thing is only when u use it for 3.3v or 5v output. sad. anyway to build a regulator from roughly 9-15v input to 12v output?

~MooEy~

Post by **weixing** » Wed Feb 20, 2008 10:44 am

Hi,

anyway to build a regulator from roughly 9-15v input to 12v output?

You can try the this fixed voltage regulator 78T12 -> Vo=12V, Imax=3A. Input voltage requirement is at least 15V.

Have a nice day.

Post by **rcj** » Wed Feb 20, 2008 1:31 pm

how is the stability of the current draw from these batteries? i understand that for telescope motor drives, the current need to be stable, and not in bursts.

Tachyon · Post by **Tachyon** » Wed Feb 20, 2008 3:06 pm

Talking about Lithium Ion batteries, my laptop battery died last week suddenly, without any warning. Dell tech support said the lifespan of such batteries is only one year or 300 cycles. I have a spare battery which I hardly use and it also went 'weak' at the same time! Either they have a self-destruct mechanism in them, or such batteries have limited lifespans, whether you use them or not.

Just a warning...