Battery pack design?
Battery pack design?
(OP)
Hi all,
I need help putting together a battery pack and charger set up for a medical laser. The device is pretty small but currently has no internal power source. I want to couple it with a battery pack to make it portable.
I am a dentist, a hobbyist, and an obsessive DIY'er, but not an electrical engineer. So I thought somebody on this forum might be able to help me determine what components I need to put together a battery pack.
The laser runs on 9 volts DC and draws 5.5 amps. I need it to have enough power to run for 2 hours, be roughly 3x4x1.5 inches, and be easily portable, hence the thought of lithium ion batteries.
Any and all contributions would be appreciated!
I need help putting together a battery pack and charger set up for a medical laser. The device is pretty small but currently has no internal power source. I want to couple it with a battery pack to make it portable.
I am a dentist, a hobbyist, and an obsessive DIY'er, but not an electrical engineer. So I thought somebody on this forum might be able to help me determine what components I need to put together a battery pack.
The laser runs on 9 volts DC and draws 5.5 amps. I need it to have enough power to run for 2 hours, be roughly 3x4x1.5 inches, and be easily portable, hence the thought of lithium ion batteries.
Any and all contributions would be appreciated!





RE: Battery pack design?
Keith Cress
kcress - http://www.flaminsystems.com
RE: Battery pack design?
Also, I'm not really conversant in figuring the needed capacity, so please excuse my ignorance. I figure the battery pack should be about 11,500mAh. Does that sound right?
Thanks!
RE: Battery pack design?
You stated 5.5A for 2 hrs, which is indeed 11Ah, but generally, you need to have a regulator, so you should assume a worst-case of 80% efficiency, and allow another 80% for battery variability and end-of-life. This would put you at 17.2Ah
LiPO batteries potentially offer a reasonable solution:
http://www.ebay.com/itm/MAXAMPS-LiPo-22-000-5-cell... is probably a bit of an overkill, but you can look around for other choices. Note that these batteries probably exceed your dimensional requirements.
TTFN

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RE: Battery pack design?
RE: Battery pack design?
For instance, if the LiPO battery suggested above is the right size but still too heavy, (since it's almost 5 pounds), meaning your laser must be 'cord powered' to it then this may mean the battery's weight has less importance after all. Switching to a 22AHr lead-acid (LA) battery would change the price from $630 down to $50. Weight goes up to 13 lbs. You cannot ship large LiPO batteries on passenger aircraft. Does this affect you? They typically have to be shipped as hazardous materials. Sealed LA batteries can be passenger plane shipped. LA batteries can also be purchased anywhere so if another country was involved you could skip shipping all together and pick one up locally. Chargers for LA batteries cost 1/4 what LiPO chargers do. Easy solar charging of LA batteries is also available.
Lots to think about.
Keith Cress
kcress - http://www.flaminsystems.com
RE: Battery pack design?
IRstuff: I have no idea what the instantaneous requirement would be. However, when the laser device is in use it’s powered up for about 15 minutes total, and of that the actual laser emission can vary from 30 seconds to 2 or 3 minutes total. After that the device would go back to the charger until needed for another patient.
Size is a consideration. If it gets too big or heavy I’d rather go wires and 110 AC. So I was hoping to stay within 3-4 lbs if possible. But $$$ is a real consideration. I was hoping to keep this project under $200. The LIPO would break the bank.
VEBLL: I think the above addresses your question too. I thought 2 hours would be a sufficient buffer.
Itsmoked: You’re right. As I learn about all this, it seems there will be some tradeoffs.
RE: Battery pack design?
The link above is to a photo of the laser. It's small, light, and portable. So a lead acid or LIPO battery may be too big or heavy. That's why I was interested in LI batteries.
Of course the more I learn the more I don't know. Like how to I get a 9 volt pack of batteries. I can't find that voltage in any available pack of LI's. Do I need a PCB and a dc/dc converter? If so which ones do I use? Ahhhh! My poor head is splitting!!!
Thanks to all for the help so far!!
RE: Battery pack design?
Any batteries are going to have end-of-life issues which aggravate users and sully product reputations.
I try to keep batteries out of products I design unless they're actually a fundamental functional requirement like a flashlight would require. I would not include them just because it would be "more convenient" if you see what I mean.
Your product would demand the user continually plug-in to recharge which perhaps is less convenient than; paying less, having no O-o-L problems, and never having a "dead battery".
Keith Cress
kcress - http://www.flaminsystems.com
RE: Battery pack design?
Or, you could go for a smaller LiPO:http://www.ebay.com/itm/FLOUREON-11-1V-5500mAh-3S-... This one would certainly do the job for most short usages, and LiPOs can allow for rapid charging.
Or lithium batteries:http://www.ebay.com/itm/1x-3-7V-6000mAh-18650-Li-i... 3 of these provides 11.1 V like the LiPO, but the weight appears to be only about 1/4 lb, which seems to be the lightest option. 6 Ah seems to be pretty reasonable.
TTFN

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RE: Battery pack design?
Almost certainly.
If this can be an integrated design, then you might be able to use a laser diode current driver that can run directly from the battery pack. But more likely you'll need a DC-DC converter to provide the specified voltage to the laser subassembly.
eBay has plenty on offer, but not for serious medical use (obviously). But you can tour what's available and what the boards look like.
RE: Battery pack design?
Cheers
Greg Locock
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RE: Battery pack design?
My assumption was of a higher voltage pack, converted down to a stable 9.0 volts. If you go the other way the current goes up. Either would work, choose your poison.
RE: Battery pack design?
TTFN

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