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I have a device that runs at 5v at 1amp. I am looking for a way to increase battery life without modifying the device itself.

I know that some electronics (for instance a 5v wall wart) allows for 2.1amp output at 5 volts and have 100-240v inputs which draw 0.3a. Could I apply a similar concept with a voltage regulator or some other device to work with batteries?

For instance if I was running off 3 lipo cells in series (11.1v), if I ran my device off a 5v regulator from the 11.1v battery source, would I draw less current from the battery source (and thus extending battery life) than if I were to use a 5v battery source directly?

Any explanations or math/logic behind this concept would be appreciated.

Thanks!

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If you use more or bigger batteries, then you can increase the battery life.

The important thing here is the energy of the batteries. Your device uses 5W of power, which means that it uses 5Wh of energy every hour of operation.

If you use a battery that has 10Wh of energy capacity, then in theory, you device would work for two hours (in practice a bit less due to various inefficiencies).

A DC-DC converter can help here, that is, it can help you use more batteries in series to have more total energy. You can also connect the device (using a Dc-DC converter) to a car battery (~840Wh) and have it work for ~168 hours.

The DC-DC converter changes the voltage and current, but laves power constant, so, it can take 12V/!A and produce 1V/12A. In practice, due to inefficiencies, the converter will always take more power than it outputs, the difference being used to heat up the converter itself.

However, you have to use a switching DC-DC converter, and not a linear regulator such as a 7805. The linear regulator takes as much current from the power source as the load needs (it would use 12V 1A (12W) to produce 5V 1A (5W) dissipating the rest (7W)), therefore it dissipates much more power as heat.

A switching converter is usually 70% to 95% efficient.

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  • \$\begingroup\$ For clarification, using a DC-DC switching power converter, I can extend the life of the batteries by converting a higher input voltage to the required voltage the device needs reducing the amp draw on the batteries? \$\endgroup\$ – randy newfield Sep 20 '15 at 0:06
  • \$\begingroup\$ No, the capacity of the batteries determine the life. Watts = Volts*Amps, so raising the volts can reduce the amps, but the watts always stay the same. So more batteries will always yield longer life, since they contain more watt-hours of electricity. 5W is a fairly large amount of power to be running from batteries for a long time. Is there any way to reduce the amount of power the device needs? What kind of device is it? Perhaps there are some efficiencies to be found there. \$\endgroup\$ – rdtsc Sep 20 '15 at 1:56
  • \$\begingroup\$ @rdtsc Unfortiently there is not a way to reduce the power usage of the device. The device is a pocket computer using an ARM cpu, I assume I will just have to look into larger lithium cells instead. Thanks for the clarification. \$\endgroup\$ – randy newfield Sep 20 '15 at 2:20
  • \$\begingroup\$ You may want to look into the many (new) types of rechargeable lithium cells, from lithium-iron-phosphate to lithium-polymer. Some are better optimized for size and weight to capacity, so if either is more important in your application, you can pick a better-suited battery. Some topologies can be quite dangerous however (catch fire and explode, see youtube videos), so make sure they are charged and protected correctly. \$\endgroup\$ – rdtsc Sep 20 '15 at 17:54
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I have been experimenting with MC34063, a neat dc-dc SMPS chip. This would be my choice for your application. (ON Semiconductors published a useful paper AN920/D with examples. TI, Motorola, etc also have good info : just google!)

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