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Why am I not getting more watts with parallel power supply boards?

RyuHimora

I am trying to build a battery power pack for an off the shelf bluetooth speaker board. The goal is to power it at 12 volts with 2 amps available using one lithium ion battery cell, however there doesn't seem to be an easy way to do this with readily available components. 

What I've come up with so far is to use a stack of six of these 3.7v to 12v regulated power supplies: https://www.amazon.com/dp/B09D3G96KZ?psc=1&ref=ppx_yo2_dt_b_product_details since the output voltage won't drop over time like the other boards I've used. They output 12v 0.3a, which is 4 watts, so 6 of them in parallel should give me the 24 watts I'm going for. However, after soldering everything together, I'm struggling to even get 10 watts out of the stack. I have a little 12v dust blower to use as a test load and a bespoke power meter, and the output tops out at about 9v 1.2a, which I assume is the voltage drop from overloading the power supply. But I should have enough of them in parallel to output close to 24 watts. What gives?

  • 0

    It sounds like your are overloading the battery.

    A 3.7V battery may not be able to supply 7Amps, which is what you would need to get close to 24 W.

  • 0

    Neither linear or switching voltage output regulators intrinsically load share. They are programed for a specific set point and provide as much load current as possible to maintain their output at such setpoint. So if one regulator has a slightly lower setpoint voltage it won't attempt provide any load current until one regulator overloads. 

    You can however add a small output ballast resistor to the output of each converter in an attempt to share the load.

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    I must respectfully disagree with the comment that "Neither linear or switching voltage output regulators intrinsically load share."  I think I understood why that was said and in general, it's true. However, it's all about the design and details. Any regulator, linear or switching, can be easily made to load share. And some are intrinsically capable of load sharing. For example, a DC-DC buck converter that uses current-mode control (it can be analog or digital), will intrinsically load share, especially if the output voltages are set fairly close before paralleling them. This is one advantage of current-mode controlled switching regulators. 

    Without current-mode control, any regulator can be made to current share, with from two up to 10 or more, regulators in parallel by using a simple circuit. The circuit works with an extra wire on each paralleled regulator called the current-share signal. Each of the paralleled regulators would have a circuit to monitor it's own average output current. The current-share signal of all paralleled regulators gets connected together. The current sharing is done by changing each regulator's control reference voltage. If the reference voltage is increased, the regulator's output also gets increased.

    We used this technique back in the 1980's at LH Research where I was a design engineer by using multi-kilowatt output SMPS in parallel and could parallel up to 10 or more to get up to 20KW or more, with the current being shared within +/-10% on all SMPS units paralleled.