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Originally Posted by coolhandcountry
Is the 31 watts gone to heat? You do have the electronics in the charger to
draw a little. That is some good info.
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Yup, if the charger is drawing 151w, but only delivering 121w of that to the battery, the rest has to go somewhere - the heatsink.
However, when not charging anything, the charger only draws 87mA (0.087A), which equates to a measly 1.1w. That's just with the charger "on".
I just thought it was interesting to test worst-case power draw so people could judge their supplies accordingly. At least it shows that there is in fact losses and about how much, in this case about 20.5% at full capacity, which makes the charger 79.5% efficient. This really isn't bad and much of that high efficiency is attributed to the DC-DC switching supply in the charger.
Once I finish building my linear power supply (just for basic electronics projects), which can hold a steady 11v-16v up to 40A, I'll probably try this again with a higher input voltage (~15v). This will cause the charger to draw less current and also increase its efficiency.