switch between two power supplies

[talha uzair]

hello,

I have two DC power sources primary and secondary, i need circuit which should simply turn my primary power off when it gets lowere than some given voltage and turn on secondary power, and again turn on primary when it gets higher than same given voltage.
same type of circuit is installed in ups also

please help

i want to install this circuit in my solar system as solar power will be my primary source and dc adopter will be my secondary source.

 

[flatfootskier]

Half post deleted

 

[flatfootskier]

How much current are we talking, or how many watts is your pv and what is your load?
How big is your dc adaptor? Sounds small...
Need an idea of scale?

Simplist system is probably to have the solar holding a relay open. When it runs out of sunlight, the relay closes and connects mains to the adaptor. possibly add a diode between each power source and load, so they never interfere with each other and can both run concurrently.

 

[talha uzair]

Hello,

Thanks for your reply.

i have solar panel of 200W ,28v and 7 amp (optimum operating) which is running: i am using charge controller of 12 v and 20 amp

3 12volts DC fans= 3x26watts = 78 Watts
5 12volts DC lights= 5x7watts = 35 Watts
Total = 135 Watts


i have adopter of 12 v and 20 amp

really speaking i am not good at electronics please help me through any schematic diagram if possible.

Thanks

 

[4pyros]

So you are looking for a charge controller?

 

[talha uzair]

no, i have a charge controller. I need a circuit which can switch the inputs power source to my charge controller form solar to adopter in evening and to solar again in morning, i need to reduce my backup system(batteries) as it is very costly.

thanks

 

[NorthGuy]

no, i have a charge controller. I need a circuit which can switch the inputs power source to my charge controller form solar to adopter in evening and to solar again in morning, i need to reduce my backup system(batteries) as it is very costly.

You need to explain in more details what you want to do.

You said you want to charge your batteries during the night from an "adopter". Why would you want to do that?

 

[flatfootskier]

My understanding is that you want to run the load ( fans and lights ) constantly, preferably from the solar when available? Is that right?

 

[talha uzair]

Hello every one,

Thanks for your ideas,

yes you are right

my idea is when solar energy get fail in evening a circuit should start using supply from DC adopter and in morning again turn solar power on.

and i want to have this circuit before my charge controller. circuit will be supplying one of the two powers available all the time to my charge controller.

my adopter will only take my load in evening and night which is 113 W, battery will always be charged during day from solar energy.

please advise my any circuit which i can use to switch between two power supplies.


Thanks

 

[NorthGuy]

I see. If you charge your battery at night then, obviously, it will be fully charged in the morning. Then, since the battery is already full, you won't be able to charge it with your solar because you cannot charge a battery which is already fully charged. Most people charge battery during the day then discharge it at night. This way, the battery is somehow discharged in the morning and has room to accept new charge from the solar. To accomplish this, you need to install your switcher between the battery and the loads. If battery voltage gets low, it switches your loads to the "adopter". As soon as the battery starts charging from solar and voltage goes higher, it'll switch your loads back to the battery. Is that what you want to accomplish?

 

[flatfootskier]

I think you're saying ignore the batteries and charge controller for this design - they are just 'additional load'
If so then.. When there's solar power, hold a relay open. When solar power can no longer hold relay, relay closes and powers up the mains to the adapter. The relay will have a big difference ( hysteresis) between the voltage at which it turns on vs off. I dont think this will trouble you though if it does, To overcome this a simple Zener and transistor circuit will do that. I'm on an iPad so can't draw it... Hopefully someone will step in.
5-10 components totalling $5.
10 mins with soldering iron and some simple testing.

 

[NorthGuy]

If so then.. When there's solar power, hold a relay open. When solar power can no longer hold relay, relay closes and powers up the mains to the adapter.

This will waste a lot of solar power. The panel produces more than OP consumes. You either store this extra power in the battery or throw it away. But if you want to store, the battery must be somehow discharged, which can be done at night. The "adopter" is only needed to prevent over-discharge.

 

[flatfootskier]

This will waste a lot of solar power. The panel produces more than OP consumes. You either store this extra power in the battery or throw it away. But if you want to store, the battery must be somehow discharged, which can be done at night. The "adopter" is only needed to prevent over-discharge.

My interpretation is...
The excess power is being thrown away ( I prefer 'not used'). I think the OP has realised that storing power when on-grid is often not worthwhile, hence the ask. He says he's fed up with battery cost. I assume the batteries will now sit there as a backup only, no longer cycling. i.e. the batteries are being substituted overnight by the dc adapter.

If so, I think my relay design is what's required, but it really could do with an op amp as comparator with feedback resistor to give known hysteresis to give clean switch over

Or...

**broken link removed**

 

[NorthGuy]

He says he's fed up with battery cost.

Batteries cost the same whether you cycle them or not.

 

[flatfootskier]

Batteries cost the same whether you cycle them or not.

Sort of.
My understanding is that heavily cycled lead acid cells have shortened life

 

[eTech]

Hello,

Thanks for your reply.

i have solar panel of 200W ,28v and 7 amp (optimum operating) which is running: i am using charge controller of 12 v and 20 amp

3 12volts DC fans= 3x26watts = 78 Watts
5 12volts DC lights= 5x7watts = 35 Watts
Total = 135 Watts


i have adopter of 12 v and 20 amp

really speaking i am not good at electronics please help me through any schematic diagram if possible.

Thanks

Hi

So...is this the current architecture?
See attached

Solar Panel output = 28vdc
Charge controller output = 12 VDC

 

[eTech]

My interpretation is...
The excess power is being thrown away ( I prefer 'not used'). I think the OP has realised that storing power when on-grid is often not worthwhile, hence the ask. He says he's fed up with battery cost. I assume the batteries will now sit there as a backup only, no longer cycling. i.e. the batteries are being substituted overnight by the dc adapter.

If so, I think my relay design is what's required, but it really could do with an op amp as comparator with feedback resistor to give known hysteresis to give clean switch over

Or...

**broken link removed**

Probably will need an indicator(s) to show whether the system is on Primary or Secondary power(?)

eT