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Have a machine in mind which is intended to be portable (hence weight and dimensions is a constraint), has a miniature refrigerant compressor (like those of Aspen) plus a blower of nominal wattage. Furthermore, the machine is desired to run on rechargeable batteries and give a backup of at least 8-10 hrs. Hence the primary power consuming thing is compressor itself. Following are the specs of intended compressor

Capacity: 360W
Input: 12V or 24V or 48V (3 models)
Max. Current: 9.5A, 9.5A or 7A respectively
(Add-on info: Weight: Around 0.5KGs just)
Battery Backup required: 8-10 hrs continuous operation but will have compressor trip-outs in between.
Rechargeable Battery: Yes
Battery Cycles: At least 100 cycles will be good.
Desired cost: Off course minimum
Desired Weight: Max. 4-5 KGs??? or what's the minimum I can get?

I don't know much about batteries, this is my first encounter. Have read quite a lot on net and stack but wanted to have exact and precise information rather than my not-sure-calculations as the whole idea depends on this battery thing.

So considering the current world of batteries, is it even possible to have a practical battery solution for this scenario? Because weight of battery and size is the biggest constraint. It should not be so heavy or bulky that it renders the equipment non-portable. I assume that for very accurate answers, more information on compressor (like current drawn in its tripped condition, if it just slows down instead of stopping etc is required but considering the given data, you can suggest a direction at least and approximate answers)

What can be the optimum battery type which I should search for? Liquid, Gel, Dry or anything else? 12V or 24V? Please suggest any brand or model too if possible so that I can find the supplier and evaluate the cost. What should be the capacity? (I have figured out that it should be around 300Ah, on 400W load (assuming an FOS, correct me if I am utterly wrong.)

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  • \$\begingroup\$ To stop lines wrapping when you do not mean them, to put at least 2 spaces at the end of each line. \$\endgroup\$ – Russell McMahon Apr 4 '15 at 15:19
  • \$\begingroup\$ The lightest battery will be lithium polymer/lithium ion chemistry. According to wikipedia, the maximum energy density is 265 Wh/kg. This means that your 0.5 kg limit will constrain you to around 130 Wh. This is enough energy to supply your 360 W load for roughly 20 minutes. So I think you need to re-think your application. \$\endgroup\$ – mkeith Apr 4 '15 at 15:35
  • \$\begingroup\$ @mkeith The compressor is 0.5 kg. The battery is <= 5 kg givin g about 3 hours using your data. Duty cycle of compressor MAY make an immense difference. \$\endgroup\$ – Russell McMahon Apr 4 '15 at 15:49
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    \$\begingroup\$ @mkeith = his loads vary. The 12V comp is say 120 W. So 5kg at 265 Wh/kg = 1300 Wh or 10+ hours on 12V and "you have a horse race". \$\endgroup\$ – Russell McMahon Apr 4 '15 at 15:51
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    \$\begingroup\$ Immense difference in stated powers. 12V / 114W, 24V 228W, 48V/336W. Knowing % time on utterly crucial, of course. 12V. 8 hours x 114W ~= 900 Watt hours = 900/12 = 75 Ah delivered. For longevity you'd not discharge past 50% so need 150 Ah - but even at 75 AH weight is far above your limit for lead acid batteries. LiIOn/LiPoly may work depending on compressor duty cycle. \$\endgroup\$ – Russell McMahon Apr 4 '15 at 16:07
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You can see from the comments that your only potential option is from the lithium chemistry. The lead acid is just way too heavy and probably too bulky as well.

265Wh/Kg is quoted for lithium. This is correct, but also more of an accepted 'potential' value and not necessarily what you will get given your specific needs. For example your need for a relatively high current might require a lithium battery that is constructed slightly differently giving you a lower capacity per kilogram.

Let's look at what you can get in the real world. The LiMn battery that powers the Nissan Leaf will handle your compressor. With a little rearrangement of the cells you could make it into a 12.6 volt 60 Ah battery that weighs exactly 12 lbs (5.5kg). It would give a nominal 684 Wh and can supply as high as 240 amps! Note that this lithium battery doesn't come close to the example given by Russel McMahon!

Depending on your compressor's duty cycle, this might work for the 10 hours, or it might only give you 3 hours. You will easily get the 100 cycles you asked for even if your depth of discharge is 90%. .

This battery could be purchased for about $160 or so.

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  • \$\begingroup\$ Thank Filek. The duty cycle is 1/3 normally in Ref. and AC devices. So i think the said Li battery will work out. \$\endgroup\$ – Syed Arslan Ali Zaidi Apr 6 '15 at 13:20

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