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Circuit for Auto Transfer ( ATS ) of Inverter in between AC Mains and DC Solar

Discussion in 'Renewable Energy' started by digimart, Jul 23, 2012.

  1. digimart

    digimart New Member

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    Hi,
    Am looking for a circuit / device box, which I could attach to Incoming AC Mains (220V ), Incoming DC Solar ( 24/48V DC), AC battery Charger of the Inverter, and the battery bank. Purpose of this would be (1) Monitor Battery bank DC Volts and (2) Switching the AC Mains On/Off.
    I'll explain the above in detail below:
    My objective is to have DC as first priority for charging batteries, and AC mains to have second priority.
    The device to keep eye over the DC Volts of battery bank. For 24VDC system if battery bank drops to 23.5 VDC ( and for 48VDC system if battery bank drops below 47 VDC), the AC Mains battery charger be connected, and batteries be charged through Incoming AC Mains.
    But till the time battery bank has adequate volts, the battery charging be done through Incoming DC Solar Energy through Solar charge controller.


    At number of times, , people require that as at day-time Solar Energy is available, so their battery bank be charged ONLY through DC Solar coming through Solar Charge Controllers. This will save them on AC mains costs.

    In the evening / night after sun has set, then as soon as the battery bank volts drop below the defined limit, the AC charging of battery to be started so that energy could be used for the home appliances. Before that point the AC mains to remain cut-off, and save on the Electricity costs.
    Though in the market such Solar Hybrid Inverters are available, but as most of our clients already have an inverter with AC Battery charger ( they usually call it UPS ), so we like to have a special circuit which we can connect to existing inverters / chargers of the client. In such desired circuits we will give 2 inputs (a) Solar DC , (b) AC Mains. And further that circuit would be connected to battery bank as well, for monitoring battery volts..
    For a 24VDC system, till the time battery bank has 23.5 VDC output, this circuit must keep the AC Mains to battery charger cut-off. And as soon as battery volts drop below 23.5VDC it connects the AC Mains. This scenario will reman in place for whole night, till next morning sun comes up. and Solar DC is available, then at that point again the AC mains is cut-off, and battery be charged through Solar DC only.
    We would like to configure these circuits for 24VDC, as well as 48VDC systems. The AC mains are at 220V. In most of the cases the Inv erters are of 1000 Watts, 1500 Watts and 2000 Watts.

    Please advise.

    Regards.

    Omar
     
    Last edited: Jul 23, 2012
  2. digimart

    digimart New Member

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    I wish someone has time to reply back or guide me how to execute the above stated work
     
  3. Inquisitive

    Inquisitive Super Moderator

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    General electric (GE), Eaton Corporation, Generac are just a few manufactures of Automatic Transfer switches (ATS)., there may be more. I believe theses are governed in North America by strict manufacturing codes such as NEC (National Electrical Code), NEMA (National Electrical Manufactures Association) standards for safety and liability reasons. You might find something made by some of these companies. But, I don't think the average person has access to the type of components needed to make one from scratch. This may be the reason nobody has replied, as it it not common knowledge amongst the masses. This would be known only by a very few people. Some companies protect their patented knowledge/methods very dearly.

    This device may need to be custom made by some of these manufactures to meet your specifications. Just a thought.

    In addition to the above regulation requirements there may be additional rules and regulations that must be met by the hundreds of utility companies that provide the power from the grid. The possibility of back feeding from the solar supply into the grid must be prevented. This also has regulations and standards that must be met in North America. Your mileage may vary.
     
    Last edited: Jul 26, 2012
  4. dave

    Dave New Member

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  5. Jules_Theone

    Jules_Theone Member

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    Am I thinking of a too simple solution -

    (Question to anyone else): Is there a problem with connecting batteries to both a UPS and a solar regulator at the same time?

    If not a problem, measure battery voltage, if above a certain level, disconnect mains to UPS, if below a certain level, connect mains to UPS.


    Jules
     
  6. Zerotolerance

    Zerotolerance Member

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    ATS's are more for instantaneous transfers without any power loss during the switchover and are very $$$$$. Is this what you are looking for or can there be a delay? We have an older ATS laying in the shop that's not being used :D
     
    Last edited: Jul 26, 2012
  7. bryan1

    bryan1 Well-Known Member

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    Well yesterday I went and got those Anderson connectors and hooked up that 1000AH bank properly and while I was there I did ask about high current transfer switchs. The reply I got is it for switching the mains to DC then the girl said expect to pay $$$$$$ for an automatic one. Now for a manual high current DC to DC 300 amp switch they are about $70 but there wasn't any in stock.

    Now as far as the OP's question goes what is asked is for a very dangerous operation if done wrong and I'm sure any level headed person wouldn't give advise that could put a persons life at risk. There are plenty of commercial solutions and in my opnion that would be the way to go.

    My 2.2 cents

    Cheers Bryan
     
  8. Jules_Theone

    Jules_Theone Member

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    After reading the OP's question again, he doesn't actually have UPS's. I was thinking he could use the UPS(s) as the instantaneous switch-over, but I don't know what would be more expensive ATS's or swapping inverters for UPS's?

    Jules
     
  9. digimart

    digimart New Member

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    I like to clarify my original query.
    I have UPS. Now these UPS are hooked to AC Mains supply, and it uses the Incoming AC mains to charge the batteries, as well as run the attached load devices too. The incoming AC mains are at 220V
    Further, I have solar panels, and through a Solar Charge Controller, I have connected these to my battery bank of UPS. The battery bank is 48V DC.
    Both the sources, ( i.e. AC Mains as well as Solar DC ) connected simultaneously. But at day time, if AC Mains is coming, then batteries get charged through AC Mains and not through the Solar Panels. Reason I guess it that AC is coming at 220V, where DC is coming at 48V.
    If I switch OFF the AC Mains, then batteries get charged through existing Solar DC current.

    Now my wish is that this switching OFF / ON of AC mains be done automatically by a ATS switch or a circuit. Meaning thereby that in day time if sun is shining brightly, then AC Mains be cut-off, so that I do not have to pay utility bill expense, and my batteries are charged through solar system. However, if there are clouds / rain, etc, then as the batteru bank volts drop to 46V DC, the ATS should automatically activate the AC Mains for batteries charging.
     
  10. Jules_Theone

    Jules_Theone Member

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    Depending how smart your UPSs are, I believe the UPS might output on the serial or USB that the batteries are getting flat (wanting you to safely shut down the servers connected to it before it completely cuts out) You could read both this and the "battery full" indicator from the UPS and just switch the mains on and off with that. I assume you want to just purchase a unit that does that for you and not build something yourself?

    Jules
     
  11. digimart

    digimart New Member

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    My all the UPS ( qty = 4 ) are able to manage the battery charing through AC Mains. So thats not the issue.
    As I have added Solar Power to all 4 different systems, and I like to save on AC mains expense, so wish to use the AC mains only when batteries are down and sunlight is not available.
    You are right, I like to purchase a unit or circuit or box which would automatically shutdown AC mains in presence of sunlight, and switch it ON at time sunlight is not available, and batteries have gone below the safety discharge limits.

    Some of the high priced Inverters available in market, already come with such a ATS included in them ( example Xantrex ). But as I already have these UPS, so I just wish to add the switching device, and not want to bear expense of complete UPS unit.
     
  12. Jules_Theone

    Jules_Theone Member

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    So is it not as simple as a solid state relay controlled by a voltage detecting circuit? That would be a custom build though...

    Jules
     
  13. digimart

    digimart New Member

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    @Jules, why not ?
    if some engineer could design a circuit.. OR it may already be available off-the-shelf
    as per my understanding, the device has to have 2 inputs: one AC Mains, and other DC Solar, the device has to check battery volts.. say for example in a 48V DC system, if battery volts drop below 46V, then it switches on the AC Mains, and then it keeps on re-checking the battery volts after every 30 mins.. at time the battery volts go about 50V or DC solar starts coming in, then it switches OFF the AC Mains.
     
  14. Jules_Theone

    Jules_Theone Member

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    A quick Google search for "voltage controlled relay" yields:

    http://www.solarconverters.com/ss-1.htm

    Is that what you are looking for? It looks like it will switch on and off at two voltage levels. You might need to add a higher power relay if you are running inductive loads.

    You should be able to just have the mains switched and leave the batteries, inverter and solar charger connected together all the time.

    Jules
     
    Last edited: Jul 27, 2012
  15. Jules_Theone

    Jules_Theone Member

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    Had another thought as I'm planning on doing a similar thing -

    Wouldn't it be better to avoid charging the batteries from the mains at all unless there hasn't been much sun for a couple a days? Can the batteries be left flat(ish) every night until the sun comes up in the morning. For instance, in the day, the solar will charge the batteries and power all the AC loads, at night the batteries will power the loads until they are exhausted, then the system switches over to grid mains to power the loads but NOT charge the batteries because come the morning the batteries will already have been charged by the grid over night giving the solar not much to do. This setup means that there wouldn't be any battery backup if the grid mains fails AND the batteries are flat.

    Jules
     

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