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Simple voltage cutoff schematic for solar charger, any tips?
Psi:
Hi,
I'm building a simple circuit to disconnect a 18V solar panel from a 12V SLA once the SLA is charged.
The main requirement is that it has to go into a very small plastic case and may receive quite hot ambient temps. 50C etc.
So burning off excess solar panel power isn't really an option.
eg I tested a simple zener (18V-12V = 4V @ 350mA = 1.4W of heat) and it started to melt the plastic.
So I created this circuit to have the panel connected across the SLA only until the voltage hits 14V at which point the pfet opens and disconnects the panel.
I would appreciate and tips or bugs you can see with it.
-I'm aware I wont get the full power from the panel due to no MPTT, doesn't matter for this. Just needs to be as simple as possible.
-I'm aware there will be some slow SLA discharge through R3, R2 if the panel is producing enough voltage to turn on M3 and M1 but not enough voltage to charge the SLA. But that's only 200K across a 30Ah SLA so not of any concern.
-D2 zener obviously sets the cut-off point. D3,4,5 are just to protect the fet gates.
-The exact part numbers used in the LTSpice schematic are not what i will actually intend to use, just examples for testing.
Thanks.
LTSpice file attached below if anyone wants it.
Green= Current into battery
Blue = power in PFET
Aqua = Voltage across panel
Red = Voltage across battery
Zero999:
Why not use the TL431, or TLVH431, for lower current consumption?
Psi:
--- Quote from: Zero999 on April 18, 2022, 07:45:20 am ---Why not use the TL431, or TLVH431, for lower current consumption?
--- End quote ---
Any solution using a regulator/zener is going to burn off excess energy as heat once the SLA is charged. The tight design constraints wont handle that much heat dissipation.
I don't want to go down the DCDC route at this stage, need to get something out quickly to fix a problem.
Zero999:
--- Quote from: Psi on April 18, 2022, 08:23:56 am ---
--- Quote from: Zero999 on April 18, 2022, 07:45:20 am ---Why not use the TL431, or TLVH431, for lower current consumption?
--- End quote ---
Any solution using a regulator/zener is going to burn off excess energy as heat once the SLA is charged. The tight design constraints wont handle that much heat dissipation.
I don't want to go down the DCDC route at this stage, need to get something out quickly to fix a problem.
--- End quote ---
The TL431 can be used as a comparator, which turns off a transistor, thus disconnecting the battery from the solar cell.
mikerj:
Why not use a basic PWM solar regulator which is designed for this purpose? The lower current (5-10A) devices are very inexpensive, maybe $5.
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