Switching between solar and mains power for DC lighting

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Switching between solar and mains power for DC lighting

Postby talha » Fri Jun 13, 2014 5:58 am

hello,

i have 205 W solar panel with optimum operating 37.4 V and 5.34 amp i am using tristare charge controller 12v 20A and i have DC load of


3 12 V DC fans = 3x26w= 78 W
5 12V DC lights= 5x7w = 35 W
total= 113 w



i am using battery backup of 50 AH only

my idea is to build a circuit before a charge controller which switch over the solar enegy when it gets low in evening with dc converted supply of same watts coming from grid.

i will simply buy an adopter of 12V and 20 amp and by using circuit i will switch it with solar energy in evening so that very low backup system is required as well as panel requirements will be lowered.


it is just my personal idea please advise my will it work or not.



Thanks
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Re: Switching between solar and mains power for DC lighting

Postby Tracker » Fri Jun 13, 2014 7:54 am

talha wrote:....my idea is to build a circuit before a charge controller which switch over the solar enegy when it gets low in evening with dc converted supply of same watts coming from grid.....


A circuit b4 the charge controller...???
Why can't you use the charge controller itself.. Many such controllers have a relay output that switches under set conditions ... what is the model of the Tristar..

The assumption is that you want power 24/7 and for that power to be there either from solar, or from the mains, should the solar power fail..
So much will depend on just what you are trying to do..

Now there could be another option..

Treat the two supplies as separate devices, both feeding the load circuit.. both with a diode in series..
The mains power supply might be adjusted to say 12.5v knowing that the battery voltage will be higher ie 12.8 plus.. Some experimenting would be needed..
Ie.. the higher voltage will always prevail..

I think that Oatley Electronics had 300w high efficiency 240/12 supplies and they had one that used 70v from two panels in series to 13.8v as a charger..

So there are a few ways of doing it.... others will have different suggestions ..


....i will simply buy an adopter of 12V and 20 amp and by using circuit i will switch it with solar energy in evening so that very low backup system is required as well as panel requirements will be lowered.

Gotta say this is a bit fuzzy.. ;)
..
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Re: Switching between solar and mains power for DC lighting

Postby Gordon-Loomberah » Fri Jun 13, 2014 8:26 am

A 12V 20A transformer is quite a large and heavy adaptor, are such items easily found in Pakistan?

You'd be best just having both charging sources going into the battery, and have the mains adaptor voltage set around 12.5V, as Tracker said above. Perhaps have a timer on it too, to save wasting the transformer energising power when it isn't required during the day.
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Re: Switching between solar and mains power for DC lighting

Postby Tracker » Fri Jun 13, 2014 9:26 am

Gordon-Loomberah wrote:.... are such items easily found in Pakistan?,....

I guess that is telling me something I did not know..

For what it's worth , these little switch mode, high efficiency supplies come from China and so would be accessible directly..

http://www.aliexpress.com/wholesale?SearchText=power+supply+300w&catId=14191104&initiative_id=AS_20140612152900

Just got to pick the right ones..

Again - the MOST important thing is to ask the motive.. Is it to power from the mains at all times and have emergency power during failure... or
Is it to use Solar Power as and when you can and then use mains when you can't

The battery is very small.. 50AH = 600W and if on regular cycle then 30% DOD = about 2hr of "Battery Power" ""TOPS"" :cry:

and my thinking is to stay away from anything with a transformer.. they are always wasteful in power, and the reason why energy-saving regulations almost DEMAND switch-mode supplies, these days.. :)
..
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Re: Switching between solar and mains power for DC lighting

Postby Privatteer » Fri Jun 13, 2014 11:38 am

I agree about using a dc power supply set to 12.5v or there abouts as its exactly what I am already doing. However those cheap power supplies don't last especially in hot conditions. I brought a couple branded "meanwell" "MW" and even at less than 50% loading they lasted about 12 months. Various failures often with the voltage regulator.
Yes. There was a diode to prevent any back feeds.

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Re: Switching between solar and mains power for DC lighting

Postby Gordon-Loomberah » Fri Jun 13, 2014 12:46 pm

The MW power supplies have 2 or 3 years warranty on them,depending on model, so you could get replacements. MTBF is supposedly in the hundreds of thousands of hours for a most of them.
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Re: Switching between solar and mains power for DC lighting

Postby talha » Fri Jun 13, 2014 4:44 pm

Hello every one,

Thanks for your ideas,

i just want to reduce my dependence on (backup) batteries as they are very expensive. 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.

so that my batteries are not used that why i am using very small battery backup.

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. i have batteries just to prevent shutdown during switching or in case of both power fails.


yes, i beleave transformers do consume a lot of power, please suggest me minimum volt adopter should i buy. i want adopter which can only take my load in evening and night which is 113 W, battery will always be charged during day from solar energy.


and is their any charge controller model which has this function build-in.
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Re: Switching between solar and mains power for DC lighting

Postby Tracker » Fri Jun 13, 2014 5:57 pm

talha wrote:....i have batteries just to prevent shutdown during switching or in case of both power fails..

OK so the picture is emerging, that you ONLY want the battery for an emergency.. That is important, because as I said, there is only enough capacity to rune things for two or three hours and even then you would be pushing it..

Others will have other ideas, but my thinking is still, that basically EVERYTHING connects to the battery..

A typical battery will have a FLOAT voltage of 13.8 (ABOUT)
Now you know that the solar charger will hold the battery at that voltage in FLOAT and if there is insufficient sunlight, then the charging will drop and the voltage will settle back to 12.8 to 13V and thus without load, it will remain there..
Now - you take a voltage ADAPTER, or power supply, and connect it via a diode to the battery, fine adjust it's voltage to about 13.4V before the DIODE or 12.9V after the diode (depending on diode)

What now happens, is the when the sun shines, the battery charges, and you things run essentially from the SUN.
When the sun sets, the charging stops and the battery voltage quickly drops to 13v and then to 12.9, which is when the current from the MAINS ADAPTER starts to supply the current and will continue to do so, essentially leaving the battery fully charged.
Now if the mains power fails, then the battery continues to provide current, until YOU decide that you need to shut it down, to prevent over-discharging the battery..

All these voltages would need to be adjusted to suit the battery and other parts..

Now, you may have read about how much better, is an MPPT charge controller.. These ensure that as much of the available Solar Power, gets to the battery..

http://www.ebay.com/itm/LCD-30A-MPPT-Solar-Panel-Regulator-Charge-Controller-12V-24V-With-USB-KJ-/181202497533?pt=LH_DefaultDomain_0&hash=item2a3082affd

http://www.aliexpress.com/item/MPPT-30A-mppt-30-solar-charge-controller-12V-24V-auto-work-with-lcd-display/954287618.html

Here is a typical MPPT charger and it also has a LIGHT function, which I think , turn on the LIGHT or load, when solar power is lost..

There could be few different ways in which you could use this controller..

http://www.aliexpress.com/wholesale?SearchText=mppt+charge+controller&catId=100703&initiative_id=AS_20140613000543

( something that we should add, is that we have no idea how well these things work , but there are so many of them, that they should be likely OK..)
..
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Re: Switching between solar and mains power for DC lighting

Postby davidg » Fri Jun 13, 2014 8:30 pm

Tracker wrote:Here is a typical MPPT charger and it also has a LIGHT function, which I think , turn on the LIGHT or load, when solar power is lost..

( something that we should add, is that we have no idea how well these things work , but there are so many of them, that they should be likely OK..)

Tracker I really sorry to say, there really only a PWM controller, not MPPT :cry:
There is no way of getting a true MPPT controller that cheap, it's the typical misleading promo stuff thats been around forever, unfortunately.
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Re: Switching between solar and mains power for DC lighting

Postby Tracker » Fri Jun 13, 2014 8:43 pm

..
Only PWM... how do you know that... :cry:

Btw... at least with aliexpress they have a complaint come points system... I wonder how they can have good scores and poor history...
..
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