Thread: Electronics O/T

Just use a 12v high wattage zener diode

look up shunt regulators.

Gidday Russell,
Have sent you a PM - saves me the embarrassment of showing up my ignorance on this thread.

Originally Posted by DavidG

Just use a 12v high wattage zener diode

look up shunt regulators.

OO dont like shunts, first problem is you are wasting the power you have produced and second, using a zener the time its liable to fail is on a hot sunny day where the panels are at maximum output. If the thing fails its liable to crack in two and go open circuit. At that stage your motor would get maximum power. I would drive it via transistors (2N3055) and a 555 chip acting as a flip flop. There are protectors but I have never seen one as low as 12 or 15V. They go short and blow the fuse. Thinking of it again, fit two zeners in series on the base of a 2N3055 one 5.6Vor below one above 5.6V (Zener and Avalanche) and feed your input voltage to the base via a resistor network. Transistor is now locked to a maximum by the diodes, but below zener conduction the base is still biased by the voltage of the panels. 2N3055 takes 15A if you need more use 2. The 2 zeners gives heat stability.

All these things sound like excellent suggestions, but without some sort of a diagram to show how the different parts are fitted together it is impossible to judge what is the easiest.

I myself have enough knowledge of electronics to fill several matchboxes and enough misplaced self confidence to say "Of course I can fix it", just before I let all the smoke out.

SawDustSniffer did a couple of schematics and that is all that is required to envisage the making of the items. Plus a parts list wouldn't go astray either.

This is a very interesting thread that has many other applications apart from the waterwheel that Rodney wants to power and I too could use some information on this subject.

Keep the ideas and drawings coming please.

Bob Willson

Now this is my simple regulator using a cheap 2N3055 which handles 15A it needs an insulator and to be bolted onto a heatsink. If you require more power, add a very low value resistor in its collector and parallel it with another exactly the same.
Function/ Power comes in and the base is regulated by the zeners, if the power drops below zener function the transistor is still biased on by the variable resistor setting.
To set up, turn the variable resistor to the earth end when you have maximum power input,
now monitor the output. Turn the variable up till you reach a point just above where the voltage stopped rising.

i did leave out 2 capacitors for each voltage regulator on the first drawing , ??? just figgered you need them to make the LM7812's work , so redrew it

comment on above > a 1000 ohm resistor on the "bypass circuit" will drop the low voltage , voltage , a lot ?


have no idea of the size of the motor , sounds like a real small 12 volt , hope 1.5 amps is enough , would help if we can get a voltage rating of the pump and the ohms across the pump , is the solar panel 20 watts ?

and once again if the resistance on the relay coil is higher than the motor it wont work , without adding a resister to the motor ,

Just throwing this out there and not sure if it would work but is it possible to rewire the solar panel to output a higher voltage then use a voltage regulator?

Originally Posted by Ch4iS

Just throwing this out there and not sure if it would work but is it possible to rewire the solar panel to output a higher voltage then use a voltage regulator?

he wants it to run at low light levels , so just before sunset when the panels are producing 4 volts ,
with a voltage regulator once the panel voltage gets to 1.2volts above the regulators voltage ( 13.2 volts ) it cuts out and no power flows , so say 4pm the pump stops

Hi Sawdust

So, just to make sure that I understand your circuit. The first 7812 regulates the power to 12 volts and doesn't allow anything greater through. The relay will only cut in if the power is above 12 volts and if it isn't, then the final 7812 re-regulates to 12 volts until the amps are too low to drive the motor.

I dunno, I get a bit lost in these things.

PS Sawdust, would you mind signing your name to your posts as I would much rather call you by your proper name than your nom-de-plume.

Bob Willson

So Rodney ...

What is the size of the motor and its voltage?

A bit difficult for Mr SawDust and others to design circuits if you don't give them the info reqd.

Bob Willson

Originally Posted by Bob Willson

Hi Sawdust

So, just to make sure that I understand your circuit. The first 7812 regulates the power to 12 volts and doesn't allow anything greater through. The relay will only cut in if the power is above 12 volts and if it isn't, then the final 7812 re-regulates to 12 volts until the amps are too low to drive the motor.

I dunno, I get a bit lost in these things.

PS Sawdust, would you mind signing your name to your posts as I would much rather call you by your proper name than your nom-de-plume.

Bob Willson

yes
the first 12 volt voltage regulator is only to turn the relay on ,
below 13.2volts ( because of diode junctions , a 12 volt regulator needs an extra 1.2 volts to work ) , the relay is in its NC( normally closed ) position , when the voltage is above 13.2 volts the first voltage regulator turns on and flips the relay to NO ( normally open ) position , directing the power through another voltage regulator to hold the volts at 12volts , when the panel is producing more than 13.2 volts


#there is some question about the coil resistance on the relay , might have to drop to a 5volt coil and put some current limiting resisters in there#
it will properly oscillate at the change over voltage of 13.2 , when the relay coil turns off the line voltage will jump from 13.2 to 13.6 volts , the 1st voltage regulator will turn back on , and voltage will drop to below 13.2 turning it off again , and keep doing it until the voltage drops below 12.5 volts ???? no real harm

cheers Ken

Your circuit is OK Ken but I see 2 problems. You would need some form of control on the first regulator to stop issues when the voltage reached a point where it was just on conduction. When that happened current would flow into the relay coil, cause a load which drops the voltage and it turns off again. So it is possible there is a point where your relay will chatter.
Next is the action of the relay switching the power off then on again. Will this not cause a fairly large spike out of the motor coil.
For the sake of non electronics guys LM7812 the LM does not matter it can be LA and several other things dependant on the maker. From memory 7 is current 8 is polarity 12 is voltage

bit of noise on the line , ??? only a pump on it , shouldn't cause to much problem apart from noise ( chatter ) wear the relay out 10x as fast ? that's about all , i said it would oscillate at junction ,

i deleted a post were i went way to far,posted a TTL controlled circuit that would expect him to make a custom PCB and a lot of testing ??? put it off as wrong ( had a resister across the low voltage line ) and deleted it

after deleting my post i posted a more mechanical solution to the problem

to control the circuit with out a battery back up and not allowed to lower the low voltage line , is a challenge , this question should be used in tests i think , its almost impossible

I have attached a voltmeter to it last night and watched it today to see what is happening. Under 5 volts the flow is not worth worrying about. It stops under 4 volts.
Does that help or is it the same problem with different figures?
Make some suggestions if there is a simpler easier way to do it even if i don't achieve exactly what i am chasing.
Thanks for all the thought you guys have given to it.