Circuit / Device to enable Solar DC Priority Input in a Gridtied installation

[digimart]

Hi
I already have and manage 4 grid-tied solar setups.
In all these I have a UPS accepting AC Mains ( 220 V ), and I connect the Cable coming from Solar Charge Controller to the battery bank of the UPS.
Now at day-time, if UPS's AC Mains is switched ON, then the batteries get charged from AC mains, and not from DC incoming current from panels. I guess the reason for this is that AC mains is coming at 220V, whereas the DC Solar is coming at 24VDC or 48VDC.

I am looking for a device or a circuit through which I set DC Solar as First Priority, and AC mains as Second Priority. So in day time, with sun shining the batteries get charged from DC Solar, and in evening when sun goes down, and batteries come to 50% Discharge level, then the battery charging be done through AC Mains.

There are certain Inverters and UPS available in market, which already have the above mentioned DC Priority feature inbuilt into them. But as I already have UPS, so I do not wish to spend money on buying these new UPS. I like to buy a circuit box, to which I give 2 inputs : AC Mains, and DC Solar, and connect the device to UPS as well as batteries. This circuit be able to monitor battery Discharge levels as well, and at time there is no sun, and battery volts drop to 50% then it should start the AC mains current to charge the batteries, not before that. And next day in morning, as sun comes up it should again shift back to DC Solar Charging.

Any ideas about such device or circuits ?

Regards

[billvon]

Hi
I already have and manage 4 grid-tied solar setups.
In all these I have a UPS accepting AC Mains ( 220 V ), and I connect the Cable coming from Solar Charge Controller to the battery bank of the UPS.
Now at day-time, if UPS's AC Mains is switched ON, then the batteries get charged from AC mains, and not from DC incoming current from panels. I guess the reason for this is that AC mains is coming at 220V, whereas the DC Solar is coming at 24VDC or 48VDC.

I am looking for a device or a circuit through which I set DC Solar as First Priority, and AC mains as Second Priority. So in day time, with sun shining the batteries get charged from DC Solar, and in evening when sun goes down, and batteries come to 50% Discharge level, then the battery charging be done through AC Mains.

There are certain Inverters and UPS available in market, which already have the above mentioned DC Priority feature inbuilt into them. But as I already have UPS, so I do not wish to spend money on buying these new UPS. I like to buy a circuit box, to which I give 2 inputs : AC Mains, and DC Solar, and connect the device to UPS as well as batteries. This circuit be able to monitor battery Discharge levels as well, and at time there is no sun, and battery volts drop to 50% then it should start the AC mains current to charge the batteries, not before that. And next day in morning, as sun comes up it should again shift back to DC Solar Charging.

Any ideas about such device or circuits ?

It is in general a bad idea.

The circuit itself is pretty simple. You need three things:

1) A detector to detect low voltage. Plenty of chargers, battery monitors and inverters provide this functionality. If you don't have this already a monitor like the Xantrex Linkpro can provide a contact closure that will close a contact when the battery voltage drops below a certain level (say, 12.5 volts.)

2) A timer to allow the batteries time to charge fully. You don't want the charger cycling on and off once a minute as the battery voltage comes back up. A timer like the Omron PTC-12 will do this for you. It should be set to approx 8 hours (depending on your charger power.)

3) A relay adequate to handle the AC load. There are plenty out there. For a 48 volt system a relay like the Omron MGN2C-DC48 will work.

You could also do this with a handful of parts from Digi-Key - a comparator to detect voltage and a timer to provide an 8 hour delay. The design of such a circuit is beyond the scope of a single post, and should not be attempted without a good understanding of electrical design. An engineer could probably do a design for you for the cost of an hour's work.

If you do this expect to replace your battery bank in about 8 months.

[digimart]

Thanks billvon

i look forward to opinion and views of other forum members too

[Paul301]

using Solar power when available

Hi
I already have and manage 4 grid-tied solar setups.
In all these I have a UPS accepting AC Mains ( 220 V ), and I connect the Cable coming from Solar Charge Controller to the battery bank of the UPS.
Now at day-time, if UPS's AC Mains is switched ON, then the batteries get charged from AC mains, and not from DC incoming current from panels. I guess the reason for this is that AC mains is coming at 220V, whereas the DC Solar is coming at 24VDC or 48VDC.

I am looking for a device or a circuit through which I set DC Solar as First Priority, and AC mains as Second Priority. So in day time, with sun shining the batteries get charged from DC Solar, and in evening when sun goes down, and batteries come to 50% Discharge level, then the battery charging be done through AC Mains.

There are certain Inverters and UPS available in market, which already have the above mentioned DC Priority feature inbuilt into them. But as I already have UPS, so I do not wish to spend money on buying these new UPS. I like to buy a circuit box, to which I give 2 inputs : AC Mains, and DC Solar, and connect the device to UPS as well as batteries. This circuit be able to monitor battery Discharge levels as well, and at time there is no sun, and battery volts drop to 50% then it should start the AC mains current to charge the batteries, not before that. And next day in morning, as sun comes up it should again shift back to DC Solar Charging.

Any ideas about such device or circuits ?

Regards

I have made such a device and been using it for about a month now. What is becoming obvious is that the solar panels I have are only just enough to run my load during the day. You can test this by manually turning off the mains on a sunny day and watch what happens to your battery voltage. If you can maintain your "float" voltage all is well and you can think about automation. As I say, mine will switch back to mains supply with clouds going passed or a extra load being applied.
I do not think 50% discharge is a good idea because if you have a power failure just at the end of this discharge then you will have nothing much left to use. I have set my switch back to mains at about 5% discharge for this very reason.
Not wishing to modify the inverter too much my solar charge system runs in parallel with the inverter's charging system and the batteries. The only mod to the inverter was to break the feed to the mains sense transformer so as to be able to start up the inverter as required.
Hope this helps your thinking. If you would like more details of what I have done, let me know.
Regards
Paul

[digimart]

Hi Paul , I like your idea and working. Pls send me further details here or on my email, as you prefer. Email is omar@digimart.com.pk

Thanks
Omar

I have made such a device and been using it for about a month now. What is becoming obvious is that the solar panels I have are only just enough to run my load during the day. You can test this by manually turning off the mains on a sunny day and watch what happens to your battery voltage. If you can maintain your "float" voltage all is well and you can think about automation. As I say, mine will switch back to mains supply with clouds going passed or a extra load being applied.
I do not think 50% discharge is a good idea because if you have a power failure just at the end of this discharge then you will have nothing much left to use. I have set my switch back to mains at about 5% discharge for this very reason.
Not wishing to modify the inverter too much my solar charge system runs in parallel with the inverter's charging system and the batteries. The only mod to the inverter was to break the feed to the mains sense transformer so as to be able to start up the inverter as required.
Hope this helps your thinking. If you would like more details of what I have done, let me know.
Regards
Paul

[jimpoe]

Hey, I use 30A transfer switch, made from sho0re power to inverter-works for me!!!

Hi
I already have and manage 4 grid-tied solar setups.
In all these I have a UPS accepting AC Mains ( 220 V ), and I connect the Cable coming from Solar Charge Controller to the battery bank of the UPS.
Now at day-time, if UPS's AC Mains is switched ON, then the batteries get charged from AC mains, and not from DC incoming current from panels. I guess the reason for this is that AC mains is coming at 220V, whereas the DC Solar is coming at 24VDC or 48VDC.

I am looking for a device or a circuit through which I set DC Solar as First Priority, and AC mains as Second Priority. So in day time, with sun shining the batteries get charged from DC Solar, and in evening when sun goes down, and batteries come to 50% Discharge level, then the battery charging be done through AC Mains.

There are certain Inverters and UPS available in market, which already have the above mentioned DC Priority feature inbuilt into them. But as I already have UPS, so I do not wish to spend money on buying these new UPS. I like to buy a circuit box, to which I give 2 inputs : AC Mains, and DC Solar, and connect the device to UPS as well as batteries. This circuit be able to monitor battery Discharge levels as well, and at time there is no sun, and battery volts drop to 50% then it should start the AC mains current to charge the batteries, not before that. And next day in morning, as sun comes up it should again shift back to DC Solar Charging.

Any ideas about such device or circuits ?

Regards