G+_Ben Reese Posted October 27, 2017 Share Posted October 27, 2017 Question about UBECs. If you have a 12V, 2A power source and a 5V, 3A UBEC; would you get the full 15W (5V x 3A) out of it or limited to 10W (5V x 2A)? Link to comment Share on other sites More sharing options...
G+_Jim Hofmann Posted October 27, 2017 Share Posted October 27, 2017 You should be good. Probably want to add 20% for efficiency. So total draw would be more like 18W but you have 24W available so you "should" be good. Then it always looks good on paper. :). Link to comment Share on other sites More sharing options...
G+_Black Merc Posted October 27, 2017 Share Posted October 27, 2017 It depends on the frequency of the UBECs switching. The faster the switching function, the less the current will appear to drop-off at higher loads. Link to comment Share on other sites More sharing options...
G+_Ben Reese Posted October 27, 2017 Author Share Posted October 27, 2017 Thanks for the replies. My thought is that a transformer will change voltage, but have little impact on the overall wattage (I could be wrong on this assumption); whereas a voltage divider using resistors would reduce the voltage and available wattage at the same time - possibly even impacting amperage more than voltage. My initial assumption is that the UBEC may not be able to boost the amperage as it reduces the voltage. Reason for the question... I am wanting to install some WS2812 LED strips. Over the years I've collected several old laptop power supplies, so I'm hoping I can use a 5V 3A UBEC coupled with a 19v 2A power supply to power things. For example, here's a 3A that will take up to 26V as the source: https://www.banggood.com/3A5A7A15A-BEC-Brushless-UBEC-For-FPV-Receiver-p-1007444.html Link to comment Share on other sites More sharing options...
G+_Black Merc Posted October 27, 2017 Share Posted October 27, 2017 Ben Reese your thought on the transformer is correct. Watts in equals(as close to perfection it could get) watts out. The wireless charging is basicly an air transformer(no iron core for magnetic consentration). Link to comment Share on other sites More sharing options...
G+_Telford Dorr Posted October 27, 2017 Share Posted October 27, 2017 Haven't used a UBEC module myself, but it is most likely a form of a buck converter. The trick with this is to store pulses of energy in a magnetic field, and feed it slowly to the load. The 12 volt input voltage is fed to a large capacitor. This capacitor allows a high (3+ amps) current to be switched into an inductor. The output of this inductor charges another large capacitor. When the voltage on this capacitor reaches 5 volts, the input current to the inductor is switched off. A diode from ground to the input of the inductor allows it to continue to dump energy into the output capacitor, maintaining the 5 volt output (it's actually a bit more complex than this, but close enough to get an idea of how it works). This switching is a form of Pulse Width Modulation (PWM) and happens at a fairly high frequency. The high frequency allows the use of a smaller inductor, as it doesn't have to store very much energy at any given point in time. So, because of this switching action and the input capacitor, the input current draw of the converter can average around two amps, even though the inductor (and thus the output) current is up around three amps. The inductor is effectively transforming a higher input voltage to a lower output voltage, As a side effect, it is also transforming a lower input current to a higher output current. Pin = Pout + some losses - or - Vin x Iin = Vout x Iout + some losses See https://en.wikipedia.org/wiki/Buck_converter for a painfully detailed explanation. (Note: doesn't show the input capacitor, for some reason.) Link to comment Share on other sites More sharing options...
G+_Ben Reese Posted October 27, 2017 Author Share Posted October 27, 2017 Telford Dorr thanks! That helps and actually makes a lot of sense. Link to comment Share on other sites More sharing options...
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