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# Solar battery charger using irf 150 n chanel mosfet

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#### farrukhtalib

##### Junior Member level 3
Hi All, Am trying to charge a battery from solar panel array and for that am using mosfet irf 150. Driving it low side. i.e, load is conected to drain and source is conected to ground and am using a diode between battery (load) and solar panel Array. Now microcontroler will monitor the voltage of both solar panel array and battery (which is being charged) and will adjust the voltage level best for charging the battery by varying gate voltage of irf 150. My question is if i narrrow the gate of irf 150 the voltage at battery terminal will drop but if the ampares will remain the same or they will fall or not

https://obrazki.elektroda.pl/5765510600_1442040919.jpg
This is a hand made rough diagram and I hope you will understand this. Mow assume that I am using a 300 watt solar panel and gate voltage Vgs are 10v at the gate of mosfet. Mean it is fully open and I am getting 15 volts across battery terminals i.e, I am getting 20 amps there (300/15). Now I start narrowing fet gate by reducing gate voltage say at X voltage applied I get 13.5 volts across battery terminals . Now my question is if I will get 22.23 amps there (300/13.5) or not ?

do you want the MOSFET to act as a switch or a current limiting device( in your diagram)?

I do not want to limit the current I want to limit voltage.

A battery is not charged with a voltage, instead it is charged with a current but the voltage must be high enough to produce the current.
A battery limits its own voltage. Your circuit must limit the charging current, but maybe the solar panel will limit the current. The datasheet for the battery should have a curve showing its voltage and amount of charge with different charging currents.

Your solar panel might produce 300W at 12V but much less current at 15V. Its datasheet will show it.

Your battery might need a voltage of 14V when it is nearly fully charged and you want the charging current to be 20A. The Mosfet datasheet shows that its on-resistance when it is cold is 0.055 ohms which might almost double to 0.1 ohms when it gets hot so at 20A its voltage loss is 2V. Then can your solar panel produce 16V at 20A?

Hi,

there are plenty of solar charger schematics and discussions around. Did you look at them?

Also manufacturers have dedicated battery charger ICs, some with solar charging features.

If you really want to build it on your own you fist need to select a battery according it´s chemistry.
Then you have to learn how the battery needs to be charged. Each chemistry has it´s own behaviour.
Then you should know the voltage and current ratings of your solar panel.
Then you can choose the "size" of your charger circuit.

Starting with a MOSFET type makes no sense.

Klaus

Considering PV is a current source (hi Z) and battery is a voltage source ( sink) with low Z, do you think it is a good idea to know the battery ESR.

What range of Rdson/ESR ratio would be best for minimum loss from a 300W source?
Think!

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