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I would like to build a portable bluetooth speaker and I would like to know how much current I can draw from a battery like this?

The battery is rated on 3.7V and I want to supply this amplifier with a step up dc dc converter. The amplifier suggests 3A 12V power supply.

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    \$\begingroup\$ Please provide proper believable data sheet links and not aliexpress links \$\endgroup\$
    – Andy aka
    Commented Apr 22, 2020 at 9:42
  • \$\begingroup\$ Done Thank you :) \$\endgroup\$
    – matthewg
    Commented Apr 22, 2020 at 9:45
  • \$\begingroup\$ Here is the datasheet of the battery lithium-polymer-battery.net/wp-content/uploads/2019/07/… \$\endgroup\$
    – matthewg
    Commented Apr 22, 2020 at 9:46
  • \$\begingroup\$ So, if you read that data sheet, what does it tell you about the maximum current? \$\endgroup\$
    – Andy aka
    Commented Apr 22, 2020 at 9:48
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    \$\begingroup\$ It depends on what the battery specification says, I would say that you cannot trust a manufacturer if they have not specified what the levels are and at which operation conditions \$\endgroup\$
    – user103776
    Commented Apr 22, 2020 at 9:48

3 Answers 3

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From the battery specification that you posted it says that the maximum continuous discharging current is 1000mA. Or 1A if you convert the units. So for safe use of the battery and safety to yourself you would not want to exceed this amount.

You were asking about using a boost converter to increase the battery voltage to 12V. A well designed boost converter would be able to achieve an efficiency of say 85%. This means that:

Power_Out = 0.85 * Power_In

Power_In = Vbat * 1A max = 3.7V * 1A = 3.7W max.

Power_Out = 0.85 * 3.7W = 3.14W max.

Current_Out = 3.14W max / 12V = 0.26A max.

This means that you must not place a load on the boost converter of more than 260mA in order to stay within the safe operational zone of the battery.

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After commenting about it, I revise my answer. For your battery which is of type LP543450 / 544350, there are different datasheets which state different things. I summurize it to 2 options:

Option 1: Specification1

According to this variant: Standard discharge current: 0.2A Max discharging current: 1.9A(2x charge current) Max impulse discharge current: 4A Max charge current: 950mA

Option 2: Specification2

Max charge current: 500mA Max discharge current: 1000mA.

Result: According to me its safe to assume 500mA of charging current and 950mA of discharge current.

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  • \$\begingroup\$ And what exactly is rapid drain. What is the difference from discharging current? \$\endgroup\$
    – matthewg
    Commented Apr 22, 2020 at 9:47
  • \$\begingroup\$ Rapid drain is draining 1.3A for a short time after which you have to return to the 0.52A maximum. \$\endgroup\$
    – CFCBazar
    Commented Apr 22, 2020 at 9:51
  • \$\begingroup\$ Thank you very much for your help... :) \$\endgroup\$
    – matthewg
    Commented Apr 22, 2020 at 9:53
  • \$\begingroup\$ After you test my answer, please select it as the solution and upvote it. \$\endgroup\$
    – CFCBazar
    Commented Apr 22, 2020 at 9:56
  • \$\begingroup\$ @CFCBazar - Hi, (a) You don't mean "2600A/h" :-) (b) Why are you including (IMHO) potentially confusing details about a 2600 mAh 18650 cell into the answer, when the question is about a totally different cell?! If you really want to include details of that different cell type, I suggest you make it very clear in the text that you are not giving any numbers that apply to the type of cell in the question - but in that case, how do they help the OP? See what I mean? Thanks. \$\endgroup\$
    – SamGibson
    Commented Apr 22, 2020 at 11:08
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Try a LiPo battery as used in Drones & RC cars. They're not the same thing as the batteries used in cellphones & computers. Designed to output MUCH higher currents.
They also have built-in safety circuits, making it much much harder to blow yourself up ;) They're also available in higher output voltages, making your boost-job easier and less taxing.

Example: https://www.ebay.com/itm/Ovonic-50C-7-4V-5200mAh-2S-Lipo-Battery-for-Traxxas-RC-Car-Truck-Boat-Drone-FPV/183819976582?hash=item2acc863f86:g:oEEAAOSwq2heWNGZ

This one has 50C rated output - Meaning it can source 5200mA * 50 = 260A ! Notice how thick the wires are.

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    \$\begingroup\$ Good suggestion on a high power battery, but 'they also have built-in safety circuits' is wrong. In fact the batteries used in RC vehicles generally do not have any protection circuits built in, in order to supply the greatest amount of power with lightest weight. It is the user's responsibility to add safety circuits as needed (charge protection is usually built into the charger, and discharge protection into the speed controller). The only 'internal' protection that most RC car batteries have is a 'hard' case to prevent physical damage. \$\endgroup\$ Commented Apr 23, 2020 at 21:31
  • \$\begingroup\$ ^^^ I don't drive RC vehicles, but last year I was involved in the design of a drone. We used standard LiPo "drone" batteries, modified slightly for our purpose. They were prismatic cells. They 100% absolutely had a small circuit board inside that provides protection circuitry. As part of the design, I actually visited one of the major drone battery manufacturers in Asia, and saw every prismatic cell going down the assembly line had this circuitry in it. I presumed such circuits were in RC car batteries also. I shouldn't presume, you're right. .... \$\endgroup\$
    – Kyle B
    Commented Apr 24, 2020 at 0:14

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