Solar PV brake to avoid burning MOSFET

Hi,

I succesfully build an Arduino Uno which measures a lithium battery array which has 28.7V which gets charged with an 7A 24V (4 x 30W solar panels) and a P-mosfet controls the charging from solar panel to the battery array.

BUT when battery is charged , the mosfet stops the charge, the SOLAR PANEL positive gets disconnected. It gets to 44V in open circuit.

So is there a brake, stop, ceiling to test to get to safe voltage value before turning on the charging-P-Mosfet?

Just tried a load (100 ohms 40w resistor) and only get from 44 to 40V ... so I don't want to fry my P_MOSFET GATE

I guess you need to tell us the maximum voltage the MOSFET can handle.
Solar panels are rated in interesting specifications. The current produced is with the leads shorted together. The peak voltage is with the leads connected only to a volt meter. Your panels should have been rated at 44 volts and 7 Amps. Where did the 24 volt rating come from?
Paul

At least in the U.S., solar panels are often specified by the voltage output when charging a lead acid battery.

A "12V" solar panel is intended for charging a 12V lead acid battery and the open circuit voltage will typically be 21 - 22V. That voltage will drop substantially when the panel is loaded.

4 x 30W solar panels work as 4 x 12V solar panels with open circuit the voltage gets to 22V each

so open circuit is 44V without load and I want to control the charge of my 28,7V battery bank ( 7S44P of 18650)

should I better look into a SSR(solid state relay) to avoid the Gate voltage of my P-Mosfet (IRF-4905 / VGs= 20V)????

ARE you telling us you are NOT using a commercial charge controller?
Paul

Exactly!!! commercial charge controller are expensive and could not find a charge controller for 7 x 3,7V ( 7 x 18650 in series) voltage with balancing capabilities

so I was planing on building and control it with Arduino

I am curious, if you begin with 7 new, identical 18650 cells, why do you need to balance?
Paul

The are not new , reclicled from laptop batterys

I will continue the info in this post:

as I forgot I had it waiting for new info