Someone recently asked a question in another thread about a circuit for a NE555 based solar/wind charge controller. A little googling turned up this as the source of the circuit. http://mdpub.com/555Controller/

I have become interested in the circuit, and redrew it with no (intentional) changes. My schematic is attached. I am interested in the opinions of the members here as to whether the circuit is effective and efficient, and are there any improvements that should be made.

Thanks for your input.

 

I see one quick problem: Switching a MOSFET with a 5V supply. That MOSFET needs at least 10V on the gate to turn fully on.

 

I see one quick problem: Switching a MOSFET with a 5V supply. That MOSFET needs at least 10V on the gate to turn fully on.

My first thought was that a BJT, a MOSFET, and a relay seemed like one switch too many. Can one of them be eliminated?

 

The relay seems redundant, since the load appears to be DC, and just sizing the MOSFET would do the job.

I'm not sure what this circuit is really doing, or why.

[update] Ah, I read the link and see that the 555 is not being used as a timer. Interesting. It also occurs to me that with the low current needed by the relay, 5V probably IS enough to switch the MOSFET, at least so that it's resistance is much less than the relay coil.

 

As I understand the circuit, when battery voltage goes above a setpoint (14.9 V), pin 3 of the 555 goes low, which turns Q1 off, which turns Q2 on, which operates the relay, which switches the output from the solar panel and/or the wind generator away from the battery, and to a dummy load. When battery voltage goes below a different setpoint (11.9 V), the opposite sequence takes place to charge the battery.

This has the benefit of consuming power through the relay coil only when the battery is topped off, and thus using that power only when it is not needed for charging the battery. This seems to be the reason for Q1's inclusion, i.e., simply as an inverter. The designer of the circuit also builds his own wind generators, which have no provision for spilling wind, and thus rely on electrical loading to keep them from overspeeding, hence the need for the double-throw relay and the dummy load.

I only want to use the circuit for solar power control, and don't need the dummy load. Therefore, I think that the circuit could be simplified for my use by eliminating Q1 and the relay, and using the pin 3 output to switch a high side MOSFET.

Unfortunately, I have never used a P channel MOSFET; is that what I would need, and what would that portion of the circuit look like?

Thanks.

 

This seems to be the reason for Q1's inclusion, i.e., simply as an inverter.

That would do it for me, to allow using a simple N-channel MOSFET instead of a P (which I'd have to order). Another way to get the inversion would be a comparator, which could be handy onboard for other chores such as lighting LEDs to show connection, voltage level, current flow, and so on.

 

All this circuit does is to switch the solar panel between battery and dummy load depending on the preset voltage. This is not much of a charge controller. The charge controller needs to have control of voltage and current levels and also implement algorithms such as MPPT.