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solar > 6v battery regulator

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Stuee123

New Member
Hi, im after a schematic for a solar panel 22v/10w to 6v 4.5ah battery.
this is for my weather station to make it wireless.

thanks
 

MikeMl

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TL431 + transistor shunt regulator. I have a circuit. I will post it as soon as I get back from flying...
 

audioguru

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What does the solar regulator regulate? The output voltage? What is it?
Then you need a battery charger circuit for the type of battery you have but you did not say its type.
If the input voltage from the solar regulator is too high for the battery charger circuit then connect a voltage buck circuit in between.
 

MikeMl

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22Voc, 10W panel will put out (@ MPPT), 10W/16V = 0.6A in bright sun.

To "float" a 6V lead-acid battery, the battery voltage should be 6.83V +- a few mV. A shunt regulator will need to dissipate the full available panel power after the battery reaches full charge. At an output voltage of only 6.8V, that panel will deliver about 0.7A, which means that the regulator transistor will need to have a heatsink capable of dissipating 0.7A*6.8V =~5W, i.e. fairly big slab of Aluminum.

Here is a circuit I have used, modified for your panel and battery...

Red trace is battery voltage. Green trace is power dissipation in M1. M1 is almost any power PMOS, source at the top, drain at the bottom.

If you need to adjust the float voltage a bit, tweak R2. The standby current (at night) is only 42uA, which shouldn't discharge the battery much...

sr.png
 
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MikeMl

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...is there a way to get some sort of red and green led so i can see the charge state? then i dont need to open the box to test voltage etc.
What do you expect the LED to tell you?

Any time the sun is not shining, then by definition, the battery has a charge deficit (its terminal voltage is less than the ideal float voltage of 6.83V). You don't need a LED to tell you that...

If the sun is shining, then either it has not been shining long enough to put back the charge consumed during the previous night, and the battery hasn't yet reached 6.83V, OR the sun has been shining long enough, and the battery has reached 6.83V.

I would have no LED if the battery is low, and light a LED if the battery has reached full charge. That way, you are not adding 10 to 20mA of load to the battery when the sun is not shining!

I modified the circuit I posted above to include a LED that indicates that the regulator has begun to shunt some of the panel current away from the battery, meaning that the battery has reached the "float" voltage (not necessarily that the battery has actually reached its full charge state). To determine that requires a hugely more complex circuit...

sr1.png

I sharpened the knee so that the LED turns on more abruptly. R5 now takes some of the heat, so must be rated for 5W. I plot the battery voltage V(bat), the LED current I(D1) to show when it turns on, the power in M1 and R5. Note that the power dissipation is now split roughly 50/50 between M1 and R5.

i did start looking at this, but i dont want 230v and the input voltage isnt high enough
https://www.homemade-circuits.com/6v-solar-battery-charger-circuit/
All of the crap to the right of that schematic is nothing but a four step voltmeter, which crudely measures the battery voltage, but doesn't really tell you any more than the simple one-LED circuit above...
 
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Stuee123

New Member
Hi mike, thanks, and yes you make sense about the led. is was more a charge to see how flat the battery got over night but i might try see if there is any way i can hook some sort of sensor to the battery and a rpi gpio so that can log it.

Now my next mission is to find somewhere that sells the parts, cant find anywhere in Aus, it all seems to be china or usa
 

MikeMl

Well-Known Member
Most Helpful Member
I would use one of these, wired through a push-button, to let you see how much the battery discharged overnight...
 
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