Hi,


That instability is due to the capacitor as mentioned earlier.
Remove that cap and the problem goes away, but in real life some
filtering is a good idea so maybe just place a small value resistor
in series with the voltage tap and place the cap across the voltage
tap.
Before i could draw up a circuit, i would need to know what the turn on and
turn off points need to be.

Here is a circuit with a quick fix, although the value of the lower resistor
for the voltage divider would have to be adjusted to make up for the
added 10K resistor (which aids the hysteresis).

Attached Thumbnails

 

 

hi Al,

The problem is when the comparator/relay switches the motor load from solar 'SUN' voltage to the 24V external supply, [at the low SUN limit of 4V], the offload voltage of the solar panel jumps up to about 17V.

This 17V jump causes the comp to switch the relay back to the SUN voltage source, as it exceeds the high limit voltage of 14V, which as soon as it goes on onload drops to about 4V! again.

Basically the circuit design is unstable.

I have run a number of sims in LTspice which highlight the problem.

Regards

__________________
Eric " Good enough is Perfect "
I will NOT answer PM's requesting technical help, please use the Forum
PIC tutorials: Nigel's www.winpicprog.co.uk/ Bill's: www.blueroomelectronics.com/

 

I was thinking the same thing, but for some reason, didn't get around to posting.

Eric, you really go above and beyond when it comes to helping

 

Hello there,


Ok, i was assuming all the simple ground work had already been done
and based my assumption partly on your simulation, which shows the
problem with that cap. Note that whatever system is used, if that
circuit is to be used for anything some mods need to be done.

All i can suggest at this point is that the OP post the entire setup
the way it is wired to all the devices in the system. This way we can
make a better assessment of the situation and recommend a good
circuit to achieve the desired goals.

Overall it was an interesting circuit in itself, but i just feel that
another approach altogether would be a good idea anyway.



Here's the sim i based my circuit on:

Attached Thumbnails

 

 

hi Al,

I agree, the circuit needs to be reworked, based on the complete project.

__________________
Eric " Good enough is Perfect "
I will NOT answer PM's requesting technical help, please use the Forum
PIC tutorials: Nigel's www.winpicprog.co.uk/ Bill's: www.blueroomelectronics.com/

 

Hi again,

Any way we can get a schematic of the entire system rather than just the
circuit alone? Would help a lot :-)

 

Why not just switch a dummy load on the sun to hold the voltage down until the sun starts shining again. Just be careful about getting a spike on the input while the load is switching on.

Also, isn't inputting 13V on a comparator powered @12V violating someting?

EDIT: If you do this intelligently, you can use the dummy load switch to drive the motor relay, insuring the load is connected before switching. Then you only have to worry about bounce.

 

The comparator input voltage is from the voltage divider so it is only 6.5V.

Simulated or "dummy" load does work but it requires the simulated load to be held (delay on release) for at least 30ms to prevent the toggling. Is there some component to add to prevent having to add the delay on release relay?

 

hi again,

There isnt 13V on any of the LM393 inputs.?

Two 10K's is series, junction to LM393 and the other input from 220K and 92K junction.

__________________
Eric " Good enough is Perfect "
I will NOT answer PM's requesting technical help, please use the Forum
PIC tutorials: Nigel's www.winpicprog.co.uk/ Bill's: www.blueroomelectronics.com/

 

ericgibbs,
How can I add the LM193 or LM393 to LTSpice. I downloaded LTSpice but can't find that component. Also need the K1 relay component.

Thanks,

 

Cleaning my glasses

 

Don't release the load. If you choose the load carefully, then the "sun" output will overcome it when the sun starts shining again.

 

The load of the motor is greater than the simulated load - have to release the simulated load or motor won't spin.

Question: what is the output of the camparator. It appears to be a low but it isn't a connection to COM, right?

 

When you DISCONNECT the "SUN" from the motor, then CONNECT a dummy load across the "SUN" input to keep it from going overvoltage at the comparator. Leave the motor connected to the 24V input. Then, when the output of the "SUN" raises to the required level, DISCONNECT the dummy load and reconnect the "SUN" to the motors.

It'll work, I gaurentee.

 

Yes, I've already accomplished this. It does require a delay off though. I think maybe C25 may be a problem as it is being charged by the 24V+ and discharges upon switching to the lower voltage SUN. I'm removing it now to see how it affects the performance.