Hi and back again,

The battery will be size 31 deep cycle marine. It is generously rated at 100ah, but wouldn't bet on it. The shape of the battery is questionable, we'll see.

The solar and battery connections will either be by 10A rated pcb screw terminals (current setup) or equally rated polarized pcb header/socket combo. The idea of fool proofing the connections or protection scheme is attractive, because I'm always scratching a loose wire where it shouldn't

Good points about the SFP9540. It was the last type of power PFET in the bin, because I sent two of the IRLR5305's to the graveyard. The Microchip Buck demo board uses the 5305's with an 18volt zener from the gate to the source to clamp any spikes I guess. Did not have a 18V zener, and paid the price.

The SFP9540 is very sturdy with Vds of -100V, Vgs of 30V, Id of -17A and a lousy Rdson of 0.2Ω. The IRLR5305 has o.k Vds of -55V, lousy Vgs of 20V, Id of -31A, and a good Rdson of 0.065Ω. Will make another stab with the IRLR5305, this time with the 18V gate zener, when the parts order comes in. So would rather change chips on the high side switch, than say double or triple up the SFP9540.

Have a new schematic, with the low side power on/off switch suggestion, rather than the schottky diode. Thanks, this will help out a lot. I see running this off a micro or LM339 comparator, with the reference dialed into a low dropout input voltage of say 15-16V? The other half of the LM339 could be run as a low dropout current (say a few hundred milliamps) based off the hall effect sensor reading. The two comparators could be OR'd together with some signal diodes to the on/off power switch driver.

The on/off power switch could be a IRLR7807Z or other low Rdson nfet. The Vds of 30V doesn't look so good. The other specs are Vgs of 20V, Id of 43, and a nice low Rdson of 0.014Ω. The Microchip TC4428A is a dual pfet/nfet driver.

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The divider for AIN3 needs to be to the right of the IRLR7807Z because yout panel (-) is no longer circuit GND. If the IRLR7807Z is turned on, these points are essentially the same.

I wouldn't worry too much about the 30V IRLR7807Z, it would only have (Vin + Vbatt) if you actually hook it up wrong.

You don't need to be exactly 18V on the zener. It needs to be less than Vgs.max and higher than Vgs where you've achieved adequately low Rds-on. I can't seem to find IRLR5305; who makes it?

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de KI6RWX

 

Huh, you are right about AN3 and the voltage divider. That's a challenge, since I was hoping to use an analog comparator (LM393) as a go-no-go, based on the panel voltage, and independent of the micro. Could blip the low side switch on with the micro, take an a-d reading, then decide. That sort of defeats the purpose of the comparator though. I could be barking up the wrong tree; how to reconcile the two different potentials?

Still working on the schematic. It will show how the comparators are worked in to share the voltage divider and current sensor.

Arrgghhh, my mistake, it's an irfr5305 by International Rectifier. Irlr7807z and Irfr5305 datasheets.

Smaller zeners would do, but the only ones I had were like 5.1V, not gonna work. The 18V zeners should be here any minute.

 

Would the open-circuit voltage of the panel give you useful information?

You could put the divider across the IRLR7807Z. It shouldn't upset anything if the value is high enough, and it gives (Vpanel - Vbat). Your controller should be able to do the math. You'll want a protection diode on AIN3 to block negative inputs when Vpanel < Vbat.

__________________
de KI6RWX

 

Was thinking that the open circuit voltage could be an indicator of when to wake up the circuit in the morning, and shut down during the evening. Sort of like an LDR circuit.

Well with the LM393 comparator (that's to be added), you only get Vdd-2V on the output, so it looks like a LM317 enters the mix to power it, as the mosfet driver needs minimum 2.4V. Could run the LM317 and LM393 combo off the solar panel side of the switch. The logic would be if the panel isn't hooked up, or very low light level then no circuit activation. If circuit activated, and not enough current flowing after micro starts PWM: shutdown micro, wait a bit, then try again.

The AN3 input may not provide any useful info, other than debugging a good startup voltage.