question

janvi avatar image
janvi asked

various PWM Charge Controller input sources

Instruction manual for Manual for BlueSolar PWM Charge Controller – LCD - USB shows on page 2 the warning:

BlueSolar Charge Controller is only suitable for regulating solar modules.
Never connect another charging source to the charge BlueSolar Charge
Controller.

while the user manual Manual BlueSolar PWM-Light 48V Charge Controller does not contain this warning.

What happens if we connect a 80V battery instead of solar panels to the input ? Possibly the reverse polarity protection will blow in case of accidental wrong connection but shouldnt it start charging any battery with voltages 24/48V ?



BlueSolar PWM
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3 Answers
johanndo avatar image
johanndo answered ·

You will toast it, please make a YT video of it.

You do have a rough idea what PWM means, I hope. It is basically a switch that turns on and off quickly. An 80V battery connected to a 24 or 48V battery will produce a propper spark.

A MPPT Controller is different, it will transform and regulate the voltage, but still the possible current from the source would be not good / way too high for the controller. Use a DC to DC charger instead, they are designed for this use case.

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janvi avatar image
janvi answered ·

Every PWM regulator contains a inductor what is matched to the PWM frequency and what delays the current after Mosfet switches on. Its the basic task of any pwm regulator to switch off when the required charging current has been reached. Otherwhile it also wouldnt work with any solar panels for source.

The MPPT feature would be useless as the voltage of a source battery hardly drops with its load. Anyway it should work as well but MPPT is only useful for for low iluminated panels.

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janvi avatar image
janvi answered ·

Probably we should ask our friend Johannes Boonstra to make a YT video “inside PWM“ like there is one with „Inside Multiplus“. Anyway I bought a BlueSolarPWM 48-30 to disasemble myself and see how the things work.


Instead of an inductor for current regulation I found many N-channel Hexfets and no inductor for the PV charge current. The regulator considers the PV module as a current source rather than a voltage source. As a current source is short circuit proof by design, it can be connected directly to the battery. The charge current starts and battery voltage increases. This is equivalent to the current what would go up e-curved inside a regulator design using inductors. To switch off, the Mosfets interrupt the battery connection and short circuit the solar panel. The battery voltage goes back e-curved like the currents in inductors do. PWM frequency and pulse width is not like expected in khz range for ferrite magnetics but determined very slow by the battery chemistry. Using a shunt, the uC is able to calculate the battery resistance and exact charge state.


For the reason that PV modules are considered as a current source what is switched off with a short circuit, all solar regulators seems to have a maximum allowed short circuit current in the data sheet. User should avoid connecting other sources than PV modules according to the manuals. Johannes Boonstra: Pls make a YT video to shed some light on this.


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