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Efficiency comparison question between PWM and MPPT and a simple relay LifePO4

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Siwastaja:

--- Quote from: Seekonk on December 02, 2022, 02:24:45 pm ---All you need is a simple circuit to keep the panels at a constant voltage.  A little improvement is adding a few extra components to provide temperature tracking. That gives you 95% of the performance of a full MPPT.

--- End quote ---

This is true of course, but then again designing "full" MPPT does not, in my opinion, add any cost or complexity, but that could be just me, because I would have no problem doing it; I would use a microcontroller anyway and can design reliable electronics around it.

The benefit of your temperature-compensated constant voltage switch mode converter is, one can do it with analog components if they are more "fluent" in analog electronics, and as you say, it's really good enough. So I'd recommend that too if MPPT seems like a struggle.

But mostly it's the same. Same power stage (usually buck, can be boost of course, or any topology), with a way to regulate input voltage.

Faringdon:
Your relays will be breaking and opening often, and will wear out.
You should use MPPT...because it draws current out of the panel without overheating the panel with the current, which is a waste of energy....(MPPT reduces the current to the right level)
Eg if the panel has a 12v o/c voltage...then typically you need to draw current out of it, at that exact  rate, which keeps the panel voltage at 12v minus about  10% (ie 10.8v)
If you dont do this, then you waste your precious solar energy.

Siwastaja:

--- Quote from: bigfoot22 on December 03, 2022, 04:06:55 pm ---I'm going to continue to research the MPPT route.

--- End quote ---

This is the route I would go:
* pick a microcontroller. If unfamiliar with micros, do some led blinkers, hello worlds etc. first.
* wire a topology such as synchronous buck with bootstrap fet gate driver, current sense resistor and current sense amplifier
* make the microcontroller Analog Comparator (etc.) generate interrupts when you discharge a capacitor on the current sense resistor
* make the microcontroller generate PWM signals
* combine the two, make it stop the PWM on overcurrent signal
* now you have a DC/DC which does not blow up on every experiment - apply Vin
* make it output fixed duty cycle, which is Vout/Vmp from the solar panel datasheet (compensate to the expected temperature)
* now it's already 1000x better than the 555
* if still interested, go for MPPT:
* wire input voltage measurement (voltage divider + capacitor)
* add a control loop (PI loop works fine) to adjust PWM duty to regulate that voltage.
* replace fixed duty with this regulation loop.
* now it's 2000x better than the 555.
* wire that current sense not only to analog comparator, but ADC as well.
* calculate power (voltage * current)
* add perturb&observe algorithm: make changes to the voltage setpoint, recalculate power to see if it gets better or worse

Geoff-AU:

--- Quote from: bigfoot22 on December 02, 2022, 09:48:40 am ---Only problem with that is that I cannot afford the inefficiencies of a direct connect charge controller AND I cannot afford the possible unreliability of a MPPT/PWM charge controller
--- End quote ---

So..  you can't hack simple and you can't hack complex?

OK good luck.   :-DD

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