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I have been looking into Lithium Ion batteries, things such as the 18650 lithium ion battery; however, the details are confusing me.

I am attempting to extract 5V 4.4 Amps (Peltier element powered runs at 5V4A, Fan at 5V .4 Amps) from the smallest Lithium-Ion battery (or batteries) possible.

Before I go into Parallel, I was wondering if someone could help me out on how to find a battery with these specifications, either a single battery, or putting 2 smaller batteries in Parallel.

What I know:

  • Parallel is less than desireable
  • You can discharge batteries at whatever rate you want, but it becomes more efficient to draw 4A from different batteries, say, not 18650s.
  • Different temperatures affect discharge.
  • Nominal voltages don't come at 5V, so getting to 5V is a challenge.

Follow Up:

  • Is it better to try to find a battery whose nominal voltage is at 12V, so that I can discharge at a lower amperage? Where would I find a 12v/7.6V battery that's small as a 18650 but can kick out the power needed? Thank you

Time to Run: I would hope that the setup lasts for around 1.5 hours of run time, and 1 hour is fine but no less. I am willing to run the batteries in parallel, but i'm trying to keep costs down and size small.

If the 18650 battery a must? Are there other batteries that may be better suited?

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  • \$\begingroup\$ 5V * 4.4A = 22 Watts. How long do you need the battery to last? A single 18650 might have 9 or 10 Wh of energy in it. If your load needs 22 Watts, and allowing for losses in the DC-DC converter, you will be lucky to get 20 minutes of operation out of an 18650. Lithium ion batteries are definitely the best choice if you are trying to keep the battery small. But you are probably going to need more than one 18650. \$\endgroup\$ – mkeith Jun 27 '18 at 5:40
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    \$\begingroup\$ A battery powered Peltier element sounds like a real bad idea. \$\endgroup\$ – Misunderstood Jun 27 '18 at 5:54
  • \$\begingroup\$ "You can discharge batteries at whatever rate you want" is the most dangerous assumption you have, and it seems that the rest of your questions are shaped by it. \$\endgroup\$ – Maple Jun 27 '18 at 10:28
  • \$\begingroup\$ @mkeith I think I am understanding that I can't use an 18650 due to power constraints, so what other batteries might I look into that are small and can provide the power I need? \$\endgroup\$ – Omar Sumadi Jun 27 '18 at 11:59
  • \$\begingroup\$ @omarsumadi the problem is less the power but the capacity, how long shall your system run? 18650 batteries are happily giving you 22W or quite a bit more, but if you expect it to run 24h then there is just not enough capacity in a single one. \$\endgroup\$ – Arsenal Jun 27 '18 at 12:07
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If you want a battery-powered 5v, then your best bet is to get a 5v 'power pack', which contains both a built-in conversion to 5v, and a charger for the internal batteries.

Make sure its capacity is rated at the 5v output, when deciding whether it will power your load for sufficient time. Some naughty ones rate the charge capacity of their internal 3.7v battery, which will be less by the time it's been converted to 5v.

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If you are looking for a low cost solution, then I would suggest that you look on places such as Ebay, Banggood, etc, and get a small DC to DC inverter. One that takes the voltage from the battery and converts it to the 5V that you require. I have seen many types of batteries, but none of them will provide exactly 5 volts. Also the batteries are large compared to a small inverter board that will provide 5 amps at 5 volts. Also worth looking at is do you want the voltage to be constant and the current to be limited? That is what I would use in such an application. Also with peltier devices they just as with all solid state devices are easily damaged by too much heat, so you will need to provide proper cooling. Also make sure the hot end is not the smaller end or it will be destroyed in a few seconds. That is done by applying a small voltage with limited current such as with the inverter that I previously mentioned, and starting the current at a low setting and slowly increasing it while monitoring the temperature. If the wrong end is getting hot, disconnect the power quickly.

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    \$\begingroup\$ I think you mean converter. Not inverter. \$\endgroup\$ – mkeith Jun 27 '18 at 5:36
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You will require a generously rated power supply for a Peltier element. Drawing 4A from any lithium ion battery is a very bad idea.

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  • \$\begingroup\$ There are enough lithium ion batteries out there which support 4A or more current during discharge. \$\endgroup\$ – Arsenal Jun 27 '18 at 11:02
  • \$\begingroup\$ But continually from a Peltier element isn't a good idea? \$\endgroup\$ – TestDeviant Jun 27 '18 at 12:44
  • \$\begingroup\$ You can't draw current from a battery continually, regardless of the amount of current, at some point the battery is empty. \$\endgroup\$ – Arsenal Jun 27 '18 at 13:51
  • \$\begingroup\$ I know the obvious. I thought suggesting a power supply was constructive and pragmatic for the question, but I get downvoted because in some applications 4A is viable. Perhaps vaping devices I guess. But you wouldn't run a Peltier off a battery for any decent length of time. \$\endgroup\$ – TestDeviant Jun 27 '18 at 16:32
  • \$\begingroup\$ Well if the question is specifically asking for a battery solution, telling them to use a power supply is not really helpful and stating that "drawing 4A from any lithium ion battery is a very bad idea" is just wrong. \$\endgroup\$ – Arsenal Jun 28 '18 at 11:17

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