I’d like to use my D050S to take 12V from my van’s battery (switched with ignition) to provide 48V charging to my AC200MAX. The only issue is, I need to run a 3m (10’) extension cable.
I’d like to do this in the most efficient way so that the most watts are available to the AC200MAX, whilst minimising watts drawn from the alternator.
So, I can either extend the 12V input side to the D050S or extend the 48V output side from the D050S.
Which would be the best solution?
Thanks
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I would extend the 48V line.
The higher the voltage, the higher the efficiency.
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When considering efficiency and power loss in electrical systems, one of the primary factors is the current (amperes) flowing through the wires. Power loss (or resistance heating) in a wire is directly proportional to the square of the current (I^2R, where I is current and R is resistance).
with this in mind, it’s better to have higher voltages and lower currents when extending cables to minimize power loss.
Steps I follow to justify this:

12V Side: If you extend the 12V input side to the D050S, the current will be relatively high. For instance, to get 500W of power from a 12V source, the current would be 500 / 12 = 41.7A

48V Side: If you extend the 48V output side from the D050S, the current will be much lower. For the same 500W, the current would be 500 / 48 = 10.42A.
Given the formula for power loss, the 12V side would experience a power loss which is (in simple terms, without considering the specifics of the wire resistance) roughly 16 times greater than the 48V side, because (41.7/10.42)^2 is roughly 16.
Therefore, the most efficient solution in terms of minimizing power loss would be to extend the 48V output side from the D050S. Make sure you use appropriatelyrated cables for the current they’ll carry
I keep these figures close by when extending wires:
 1.5mm2 : up to 15amps
 2.5mm2 : up to 20amps
 4mm2: up to 25amps
 6mm2 : up to 32amps
 10mm2: up to 40amps
 16mm2 : up to 50amps
So cleary, go for 48volts so you can stick to 1.5mm2
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Thank you, that makers perfect sense. However having now tried I only get around 110W s into the BLUETTI with a longer 48V lead, and around 140W with a longer 12V lead! 12 lead was 8AWG, 48V lead was 16AWG. The difference is (apart from the wrong way round, huge) Does perhaps the control logic in the D050S have an issue with the output side extension?
Well indeed, 16AWG (1.5mm²) is enough for the 10.5 amps that’d flow in 48V. And that thick 8AWG (10mm²) is enough for 40amps. Sitting 2.5% above that figure in 12V shouldn’t be the cause.
I don’t know the internals of D050S, so I can’t make a proper guess of the potential impact of voltage drop over that 3m wire in terms of D050’s voltage setup. Some DC sources (happens in laptop power bricks) limit the output if the connected devices isn’t “recognized” (I have a dell operating at 10% of its CPU power when using an intermediate, third party DC plug to convert from another Dell power brick…).
Oh and about connector/contact resistance: is that plug reliable? Soldering quality might impact the throughput.