JackFlorey said:
SolarSail said:
2) A non-isolating switch mode charger (i.e. CCCV function) does not generate heat.
You have a 100% efficient DC-DC? You're a shoe-in for a Nobel prize, then, since that's never been accomplished before.
Don't have to be insulting or pedantic, if you have a point. Are you trying to make up for Flippy's gaffs?
"Does not generate heat" is not the same as 0%. Any reading of the 2nd law will tell you that 0% is impossible. What I said obviously means that relative to the object at hand, the heat is negligible.
Tell me, how much will the temperature of a 20 kg metal box of volume 12 liters rise due to a 5A switching mosfet, where the 60V DC supplied power is rectified, DC-DC converted and conditioned OUTSIDE the box? Numbers please. Have you built such a circuit? I have.
The CCCV function has conceptually nothing to do with a DC-DC switching power supply. It is an entirely different function that only applies to a li-ion pack. A li-ion charger has three parts -- AC power rectification, conversion and conditioning, DC to DC stepdown conversion and isolation, and CCCV function. You have a benchtop power supply in mind that is CV, and also has a current limiter knob to drop the voltage. Off-the-shelf power supplies generally do not have current regulation that can be controlled. Just think about this: Why would I want to bring AC line power and a 7 kW power supply into each of my nine modules?
Take any standard cheap 24V switching power supply. It does not allow for current regulation and current limitation except for short and exceptional conditions. It consists of AC to DC rectification and filtration, then a switching DC to DC step-down converter/isolater both of which generate heat. There is no CCCV function. The supplied voltage will stay approximately constant 24V and the current will vary according to ohm's law (unless the rating is exceeded). So it has a CV function but not a CC function or the ability to drop the voltage. In addition, the CV function lacks tolerance and may not be suitable for a li-ion pack in CV mode even if your cells add up exactly to 24V at 100% SoC.
In order to charge a li-ion pack, you need a CC function (and better CV regulation) which will drop the supply voltage depending on the SoC, and keep the current constant. A switching mode DC to DC step-down regulator with a low Rds at 5A and associated circuitry generates negligible heat. A IRFZ44 at 100% duty cycle will generate .0175 * 25 = 0.43 W of thermal energy. The rest of the circuit even less. Please let me know when you have calculated the temperature rise.
Cheap off the shelf power supplies are not suitable for charging li-ion packs without a CCCV function. In fact they are unable to drop the voltage.
How do you suggest simultaneously charging 18 modules each 14s11p, with the modules hard wired as 3p6s, and with no internal contactors, with just one charger? There is no common mode. Even if all 18 were in parallel, you still could not do that without each module having its own CCCV regulator. Are you suggesting we carry 18 power supplies around? Maybe you know how Tesla does this, and I am all ears. I would like to avoid timesharing the single charger and multiplexing the power.