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Here's the setup I'm attempting;

Small DC motor -> Turns my generator -> Outputs 0-250V DC -> ((Charges Batteries)) -> 48V Battery Bank -> Inverter -> Load

I have a homemade Permanent Magnet Generator (PMG) using strong N52 neodymium magnets and wound copper coils. I can output plenty of voltage from the generator... 0-250V AC. Using a rectifier I can convert that to DC, but my question is now what is the best way to charge a battery bank?

How can I now convert that DC electricity to a 48V battery charger with plenty of amps for fast charging? Maximum-Power-Point-Tracking (MPPT) solar charge controller? DC->DC charger?

I guess I'm asking how to extract all of the juice without wasting any.

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    \$\begingroup\$ What is powering the "small DC motor" at the beginning of the chain? \$\endgroup\$
    – manassehkatz-Moving 2 Codidact
    Commented Jul 18, 2022 at 23:19
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    \$\begingroup\$ You are using too many acronyms, please revise your question to define what PMG and MPPT mean. This might be a better question for electrical engineering and should probably be migrated. oops saw in your title what PMG means, my bad! Still I think your question should be migrated. \$\endgroup\$
    – George Anderson
    Commented Jul 18, 2022 at 23:21
  • \$\begingroup\$ I think an MPPT won't be the right choice, as it is designed to control drawn current until the solar panel's power 'knee' is found, then wiggle around over time to track the 'knee'. Your PMG will have some kind of input-HP-vs-output-Watts characteristic, but it probably won't be a 'knee'-like curve that wants tracking. Have you tried a basic resistive load to see what volts vs amps you can get, and how much engine power it takes to turn the PMG under that load? \$\endgroup\$
    – Triplefault
    Commented Jul 18, 2022 at 23:36
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    \$\begingroup\$ If you want to waste less power, remove the motor (inherent mechanical and electrical losses) and generator (inherent mechanical and electrical losses) and just use a 48V charger designed to operate from whatever voltage you have to drive the DC motor (a "boost" charger if that's presumably low voltage, though you make it a mystery.) Then you only have the inherent losses in the boost charger magnetics. \$\endgroup\$
    – Ecnerwal
    Commented Jul 19, 2022 at 0:56
  • \$\begingroup\$ @manassehkatz-Moving2Codidact Utility/City power. \$\endgroup\$
    – Paul Evans
    Commented Jul 19, 2022 at 1:44

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Small DC motor < ... > a 48V battery charger with plenty of amps for fast charging?

Magic does not apply to electrical power, so "small DC motor" implies insufficient input DC power at (needlessly mysterious, but probably) lower voltage to provide "plenty of amps for fast charging" of a 48V bank.

To charge from a lower voltage (efficiently), you use a DC-DC boost configuration (which converts to AC to do the boosting in a transformer or inductor, usually at high frequency.) If the input is nominally 12V, you need (more than) 4 times as many amps in as you pull out at (nominally) 48V because nothing is 100% efficient, and magic does not apply. Power = Volts x Amps.

Adding two electromechanical steps to generate high voltage (at proportionally lower amperage, and minus the accrued losses) instead of using a boost converter just wastes more of whatever input power you have.

I you've built a Permanent Magnet Generator, you might be partway to making some home-made DIY wind power, in the non-magical real world, where you take energy from the wind and turn it into electrical power. I haven't looked at the site recently, but these folks were into that a long time ago and seem to be still at it.

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  • \$\begingroup\$ Small DC motor was not implying insufficient DC power in this instance. What I meant by small DC motor was not an energy hog. The input motor uses about 25 watts of power to spin the generator and give an output of about 250 volts. I thought that was pretty incredible. Thank you for your answer, although it's not really along the lines of what I'm wanting to do here. I'm not trying to create magic out of thin air, but my understanding of a PMG is that you can create more output than input by utilizing the magnets - just an increase from the input. \$\endgroup\$
    – Paul Evans
    Commented Jul 19, 2022 at 1:58
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    \$\begingroup\$ You can create higher voltage at lower current or higher current at lower voltage. On an ongoing basis (there can be storage aspects on the very short term) you can't get more power out than you put in. \$\endgroup\$
    – manassehkatz-Moving 2 Codidact
    Commented Jul 19, 2022 at 2:00
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    \$\begingroup\$ 25W input producing 250V is meaningless if the current < 0.1A. If it is more than 0.1A, sign me up. \$\endgroup\$
    – manassehkatz-Moving 2 Codidact
    Commented Jul 19, 2022 at 2:16
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    \$\begingroup\$ 25 watts in means you'll get less than 25 watts out, period, in this universe. You can make 50,000 volts from a 9V battery with no permanent magnet involved. The physics & math does not alter, power in = power out (but some of the electrical power turns into heat and is "wasted" - still the total adds up and has been repeatedly verified.) Your misunderstanding of what happens in a permanent magnet generator would be "magic" if it wasn't a misunderstanding. Hook the output to the input and have a perpetual motion machine... \$\endgroup\$
    – Ecnerwal
    Commented Jul 19, 2022 at 2:54
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    \$\begingroup\$ @Ecnerwal yep. that would be perpetual motion, something snake oil salesman have been selling various devices for many decades, maybe centuries. To an extremely smart friend of mine, I was describing pumped hydro, which uses renewables to pump water into a higher elevation reservoir for later hydro-electric generation. He said why don't they just use the power generated by the hydro to pump it back up? I said, well, that would be perpetual motion. Even though he's extremely bright, I couldn't convince him it was contrary to the laws of physics. sigh \$\endgroup\$
    – George Anderson
    Commented Jul 19, 2022 at 4:13

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