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power supply timers

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JEBB

New Member
hello,

I'm trying to build a inverter and thinking of using two power sources: regulated power supply or a battery and a solar power.

I need to connect both power sources using the solar power first and automatically switches to a power supply or a battery when the solar power stops generating the 12vdc that I need for my inverter.
I don't have an idea what kind of timer or switches to build to make this work.
Please give me any thoughts

Thank You
 

kinjalgp

Active Member
Try this circuit: Insted of relay you can also use transistor to save some power that is lost in operating the relay.
 

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JEBB

New Member
hi there,
I'm just wondering where i could find a schematic diagram for relay/timer that uses transistor.

thank you
 

kinjalgp

Active Member
You may try something of this sort:
When Solar Panel is gerenarting power T1 and T2 are on and T3 is off. Whereas when no solar power is available, T1 and T2 are off and T3 turns on thereby supplying power from battery.
 

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Phasor

Member
Personally, I would take the approach of using a comparator to detect when the solar voltage drops below a reference voltage, then switching the MOSFETs in and out, as shown:
(apologies if I've drawn the MOSFETs the wrong way round - I can never remember :oops: )

 

JEBB

New Member
Thank you for all your ideas and I'm hoping to connect my power supply properly.
One last question: What tyoe of transistors specification should I use for the 24 hour relay/timer that could switch my solar power to a back-up battery or power supply

Thank You
 

kinjalgp

Active Member
The transistor type will depend upon how much current your circuit is going to draw from battery and solar panels. Select an appropriate transistor with current capacity higher than your system uses.
 

star882

New Member
kinjalgp said:
You may try something of this sort:
When Solar Panel is gerenarting power T1 and T2 are on and T3 is off. Whereas when no solar power is available, T1 and T2 are off and T3 turns on thereby supplying power from battery.
That won't work!!
The current from the battery will be short-circuited through the transistors.
 

kinjalgp

Active Member
:?: :?: :?:
What do you think the 2 diodes are doing out there star882?
 

star882

New Member
The battery current will flow from the positive terminal of the battery to T3's emitter, go to T3's base, then flow through T2 to ground.
Just think of a PNP transistor as e-->|--b--|<--c
and NPN as e--|<--b-->|--c .
Do you see what I mean?
 

kinjalgp

Active Member
I got your point. See the updated schematic above. This will work ok.
 
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