Need Lithium Batt equivalent of 12v 4-9ah SLA

[Flashanator]

I'm a noob with LiPo & Lion. So I need some advice.

I'm looking for somthing thats 12v & with at least 4-5ah rating (if possible up to 9ah)

It has to be small, not concerned about weight.

It can't be any bigger then these dimensions.


L= 7cm (2.73")
W= 4.6cm (1.79")
H= 10cm (3.9")

Is this possible?

Thank you.

 

[TigerhawkT3]

6 18650s, in 3S2P should do it. 11.1V nominal, 4.4Ah, 5.4cmx6.5cmx3.6cm.

Make sure you can disassemble the pack for individual charging, or get a pack with individual charging taps. Maybe LuxLuthor can help you out.

 

[Flashanator]

thanks for that.


I want it for powering a 35w HID. Would 11.1v be ok as its 12v?


How much runtime do you think I would get with this?



ty.

 

[TigerhawkT3]

That's 11.1V nominal, remember. The voltage range will be 10.5V-12.6V. It should work just fine.

For a 35W HID, I'd say the runtime should be about 35-40 minutes or so.

 

[TorchBoy]

It's threads like this that make me think I should get into that chemistry (although I'd be keener on LiFePO4).

 

[Flashanator]

I was looking on a few sites & stuff.


Noob Question. Will I be able to charge the whole pack at once if i get pre-wired tabs?


thanks.

 

[mdocod]

Inside of that space, you could actually fit 9 18650 cells if you wanted, 3S3P for ~11.1V ~6.6AH depending on the cells...

pack size would be roughly 7cm x 4cm x 9cm after shrink-wrap and wire taps and stuff.

Provided you get a balancing charger that can handle the number of cells that need to be balanced you can charge the whole pack up at once, for an 11.1V pack, you will need 3 balance taps, the cells that are in parallel don't need their own individual balance taps, parallel li-ion balances itself out. Just treat each pair of cells in parallel as a single cell in the wiring...

Another thought, if you can come up with ~7cm x 4cm x 11cm you can fit 12 18650 cells, which could be wired as either a 3S4P 11.1V 8.8AH pack, or a 4S3P 14.8V 6.6AH pack. If the application can handle the peak voltage of 4S3P configuration (~16.8V) then that configuration might be preferable, as running higher input voltages can reduce current requirements, which allows cells to deliver closer to their rated capacity, also.. which increases efficiency of the whole system by reducing the effects of resistance.

---------------------------------------------------------------------------------------

just thinking out loud here about some NIMH solutions that would offer slightly simpler charging methods..

10 18650 (A size) NIMH cells would be a nominal 12V with ~4AH depending on cells chosen and would fit in ~7x4x9cm space.

12 Sub-C NIMH cells would be 14.4V as high as 4.5AH depending on cells. and would be a really tight fit at ~7cm x 4.6cm x ~9cm

I think you could fit 30AA cells in that space... In fact, it would be very tight, after shrink wrapping and wiring, it might be too big. Envision cells laid 3x5 configuration, then 2 of those on top of one another, that should be exactly 42mm x 70m x 100mm before shrink-wrapping, a neat tabbed soldering job might keep everything small enough. The pack would need to be wired 10S3P, and would have ~12V 6-7.5AH depending on the cells chosen... The problem with this big of a NIMH pack, is that it's going to be hard to keep all the cells healthy. I think it would require separate charging taps for each section of series wired cells...

ok.... I've had my fun brainstorming..

Eric

 

[Flashanator]

hmmm.

I like the sound of fitting 12 18650 cells (3S4P 11.1v 8.8ah) in 7cm x 4cm x 11cm.

any suggestions were to get a pack like that built? then what charger I would need?

thanks again.

 

[Flashanator]

My mini-HID is ready & now im just waiting for a li-ion battery pack.

Cant wait to feel how lite it is compared to sla.

So what runtime can i expect with 35w from 11.1v Li-Ion 8.8ah?


thx

 

[mdocod]

should be over 2 hours. Figure the ballast probably pulls around 42W (guessing), little over 80% efficient. That's about 3.5-4+ amps range for power draw depending on the state of charge (ballast pulls more amps as the cells drop in voltage through the discharge.) Individually, each cell only has to deliver an amp, which isn't too bad. So I think a 2 hour runtime rating is conservative and realistic. (You might get a little more)..

So.. where did you find a pack to use? I looked around online for ya and didn't come up with a pack in that configuration with balance taps... Easiest way to do it it seemed, would be to use 3 separate packs (each a 4 cell parallel pack with cells in a "block" sort of configuration). That way each pack would have it's own connection, then you could build your own balance taps from there..

 

[Flashanator]

Ive asked a few places that custom build. Just waiting for some responses.

 

[Flashanator]

Think I might just buy this pack. Its size is ok.

http://www.batteryspace.com/index.asp?PageAction=VIEWPROD&ProdID=3180

what do you think?

cya.

 

[mdocod]

nope!, lithium polymer isn't something you slap in a flashlight for reliable repeated use, it's usually used in remote control vehicles, the key word here being *remote*.. The results of the key word put distance between you and it when it explodes.... Not to mention, that pack does not have balance taps from what I can tell.

That may be a bit on the extreme side, but in all honesty, I can recommend nothing less than a fully protected, balanced pack made from LiCo02 for use in a "device" that might be in close proximity to people regularly. you might look at harvesting the pack from a laptop and using the built in circuitry and charger....

With LiPoly all it takes is one good drop and you could damage the cells, causing internal shorting... which can lead to explosions and metal fires. I can't in good conscience recommend that.

 

[Flashanator]

Im confused, So Lipoly isnt as safe as Li-Ion? I wish I knew alot more about all this stuff.

When I enquired to battery space, they suggested this pack.

 

[mdocod]

LiPo can be reasonably safe if it is physically and electronically protected, but overall, has a poor track record for safety. At least with the LiCo "can" style cells the cell has it's physical protection "built in" so to speak, (metal can).

 

[TorchBoy]

Re: Need Lithium Batt equivalent of 12 V 4-9 Ah SLA

LiPo can be reasonably safe if it is physically and electronically protected, but overall, has a poor track record for safety.

I'm now thinking millions of cellphone batteries... Which reminds me that the first time I saw LiPo on a phone I thought "lithium polonium".

 

[mdocod]

Re: Need Lithium Batt equivalent of 12 V 4-9 Ah SLA

there have been some recent moves towards LiPo being used in laptops and cell phones, but *most* of the cells out there in cell phones, in my understanding, have been LiCo prismatic cells. I think some of the new slim notebooks are using LiPo, but those cells are installed such that they should not be distorted during a fall or drop, dropping a LiPo pack into a space not intended for that shape, means the pack could jostle around and have points of high presure applied during said jostle. unless securely and evenly held in place. I think it will be interesting to see some track record for LiPo cells develop in these new devices over the next few years, another thing to consider is that all the electronic protection (balancing and proper charge/discharge) is built in to those devices.... If that pack from battery space had balance taps, I'd be a little less concerned about it being used for this. Over time the cells will probably get out of balance, eventually some cells will be overcharged and others undercharged.

 

[TorchBoy]

Re: Need Lithium Batt equivalent of 12 V 4-9 Ah SLA

there have been some recent moves towards LiPo being used in laptops and cell phones,

It would have been maybe ten years ago that I saw it.

 

[mdocod]

Re: Need Lithium Batt equivalent of 12 V 4-9 Ah SLA

learn something new every day I've seen very few LiPo cells in consumer devices.

 

[TorchBoy]

Re: Need Lithium Batt equivalent of 12 V 4-9 Ah SLA

A quick search turned up this article from Dec 2006 which talks about moving to lithium ion polymer batteries to get fewer exploding batteries. So it says they're safer. :thinking:

But, in the last year, several battery makers pushed the limits of energy density in Li-ion batteries too far. Li-ion batteries use organic solvents to suspend the lithium ions. In situations where the structure of the battery is compromised, that solvent can ignite and vent from the pressurized battery. The result is a dangerous and toxic fireworks display you can see in a video at the end of this article.
...
The main advantage of Li-poly batteries that has been discussed in the press recently is their reluctance to explode under duress