DPDT Switch?

goingtoghanagoingtoghana Posts: 34Solar Expert
If I have a positive and negative line from my panel array that I want to switch from going a (charge controller > batteries (when full)) to a grid tie inverter, can I use some sort of DPDT switch? I can't find any products that.

I want to use the panels to charge the batteries first, but when they are full, I want to use them to supplement the house power.

Comments

  • vtmapsvtmaps Posts: 3,717Solar Expert ✭✭✭✭
    Re: DPDT Switch?

    To answer your question we need to know details of your array, combiner, and the inverters. You may need to have the array in a different configuration for each of the inverters. From your question it is not clear to me if you want to sell to the grid or not. Either way, there are inverters on the market that will do what you want, without the need for an external DPDT switch.

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
  • waynefromnscanadawaynefromnscanada Posts: 3,009Solar Expert ✭✭✭✭
    Re: DPDT Switch?

    One of the big issues in my mind is the very real possibility of DC arcing inside that DPDT switch. Depending on the switch design and the DC voltages involved, an arc could easily be initiated between the internal + and - components, destroying the switch and possibly causing a tragic fire.
  • goingtoghanagoingtoghana Posts: 34Solar Expert
    Re: DPDT Switch?

    What I want to do is start with 4 128W/24V/5.33Amp panels in serial. I want to possibly double that in the near future. Because I plan on having up to 8 of the same panels, I am going have the main wires between the panels and the DC kill switch be 4 AWG. Overkill on wire for now, but planning for the future.

    I am going to use a morningstar 45 Amp MPPT charge controller for the batteries. When the batteries are full, I want to use the panel output and feed into the home. Not looking to sell back, just supplement what the home used during the day. Almost every inverter I see uses 12, 24 and/or 48 V input so I configured the panels so I could direct the same voltage to either the charge controller or the inverter.

    The piece I don't get is how to switch the panel output to either the charge controller for the batteires or the inverter when the batteries are full.
  • WindsunWindsun Posts: 1,164Solar Expert admin
    Re: DPDT Switch?

    You may not need to switch at all. Once the batteries are full, they will not be pulling any more power from the array so you might be able to just feed them in parallel.

    However, it depends on whether or not your grid tie system will leave enough to keep the batteries charged.

    Also not sure why you ran such heavy wire for a rather high voltage DC.
  • CariboocootCariboocoot Posts: 17,615Banned ✭✭
    Re: DPDT Switch?
    If I have a positive and negative line from my panel array that I want to switch from going a (charge controller > batteries (when full)) to a grid tie inverter, can I use some sort of DPDT switch? I can't find any products that.

    I want to use the panels to charge the batteries first, but when they are full, I want to use them to supplement the house power.

    This is the second time this question has come up in as many days.
    Don't even bother to try is my advice.
    Grid tie inverters are not designed to be fed the output of a charge controller. They have their own MPPT function on the input, whereas the output of a controller is meant to charge batteries. This will be 'electrically incompatible'.
    If you want to switch the array from the controller input to a GTI that is another matter, also with problems. For one thing the Voltage level will not be right; arrays design to charge batteries are typically much lower than those designed to power GTI's. One exception here would be micro-inverters which are meant to be connected to a single panel. Their you get the reverse problem; the array in total will be too high a Voltage. Another exception would be to use the Xantrex 600 Volt 80 Amp MPPT controller with a high Voltage array.
    This is a no-go idea. Not impossible to get it to work, but costly and more trouble than it's worth.

    What we normally do in the off-grid world is use a controller with an AUX function (Outback, MidNite) that can be programmed to operate an "opportunity load" when the battery charge reaches a certain state (Absorb, Float). This is the safest and most sure-fire method of capturing those Watt hours that would otherwise be lost.
  • goingtoghanagoingtoghana Posts: 34Solar Expert
    Re: DPDT Switch?

    Not understanding why you say I don't need a switch. Are you saying grid tie the batteries to the house circuit? (Panels > MPPT charge controller > Batteries > Grid Tie Inverter)? If I did that, would the batteries not be "used" if the main current to the house stays on from the street? In other words, at night when not generating current from the panels, would the house system try to pull current from the street and the batteries thus draining the batteries?
  • goingtoghanagoingtoghana Posts: 34Solar Expert
    Re: DPDT Switch?
    This is the second time this question has come up in as many days.
    What we normally do in the off-grid world is use a controller with an AUX function (Outback, MidNite) that can be programmed to operate an "opportunity load" when the battery charge reaches a certain state (Absorb, Float). This is the safest and most sure-fire method of capturing those Watt hours that would otherwise be lost.

    So, the controller AUX function sends current to a grid tie inverter then?
  • WindsunWindsun Posts: 1,164Solar Expert admin
    Re: DPDT Switch?
    Grid tie inverters are not designed to be fed the output of a charge controller. They have their own MPPT function on the input, whereas the output of a controller is meant to charge batteries. This will be 'electrically incompatible'.

    From what I gather, he does not really have a "grid tie" inverter - he has some inverters that will put out AC that he can somehow tie into the house for power. Apparently he is also not in the US.

    However, details on exactly what he has are lacking.

    Need to know exactly what you mean by "grid tie inverter", and what model/brand.
  • CariboocootCariboocoot Posts: 17,615Banned ✭✭
    Re: DPDT Switch?
    So, the controller AUX function sends current to a grid tie inverter then?

    No. The AUX function merely controls a relay which can be used to switch on/off any number of things. There is no grid tie inverter involved.
    The batteries power an off-grid inverter, correct? Under normal circumstances the loads on that will vary but remain fairly light. What you want to do is use the AUX function to turn on loads (AC or DC) that will make use of the power that is available from the panels but will not draw from the batteries.

    Example (from my own system): batteries full, panels putting out less than 5 Amps @ 27.6 Volts. Panels are capable of 20+ Amps, meaning there are approximately 360 Watts available from the panels that aren't being 'harvested'. Over two hours this ads up to 720 Watt hours that are unrealized. Solution; turn on the water pump. It runs, fills the pressure tank, and I have water for a day without having 'tapped in to' any of the power stored in the batteries. In fact my whole system is balanced (somewhat precariously) this way; the batteries serve mainly as a power source for over night. During daylight hours the panels 'run everything' including charging up the batteries.

    I'm not sure what you mean by Grid Tie inverter either. Here that would mean one that pushes AC to the household wiring and/or to the utility (if allowed and there is surplus). As per my previous post I know of none that would be truly compatible with a standard off-grid array. Not any that would be recommended for use, anyway. The two types of inverters function quite differently: the off-grid supplies steady Voltage against varying load demands, the grid-tie supplies whatever amount of current it can make from the panels. Or OG's output varies according to loads, GT's output varies according to supply.

    I think Windsun is right in that we could use a few more details about what equipment you are using and how it is wired.
  • goingtoghanagoingtoghana Posts: 34Solar Expert
    Re: DPDT Switch?

    Let me start with what exists today in Ghana, Africa at my missionary friends house:

    Batteries: 5, 12 v, 198 amp hours each, parallel connection
    Inverter: AIMS model pwri8k22050 8000 Watt Power Inverter 12Vdc to 220/240Vac 50Hz

    The batteries are currently charge with an A/C to D/C charger.

    There are frequent balckouts that can occur during the day and night. They want to avoid the noise of a generator.

    I am buying 4 Uni-solar 128W/24V flexible panels
    I think I am still buying the Morningstar TS-MPPT-45
    Planning on Serial

    What I am trying to accomplish for them is the following:

    1) Provide a solar system that will charge the batteries during the blackout thus extending the amount of time power is available to them
    2) Provide a solar system that will charge the batteries when A/C is on from the street.
    3) Provide a solar system that can supplement the A/C coming into the house once the batteries are full.

    1 and 2 are easy. 3 is what I am having difficulty with.

    My thoughts were to do this:

    1) Turn the kill switch to the off position from the solar panels
    2) throw a DPDT switch to transfer all the solar power to a (what type of inverter?) to supplement the A/C power coming into the house
    3) Turn the kill switch back to the "on" position

    Is this doable?
  • WindsunWindsun Posts: 1,164Solar Expert admin
    Re: DPDT Switch?

    Looking at what actually exists, it might be easier to shift some AC loads in the house over to the inverter/battery setup than to make changes in the solar panel wiring.

    You could use a standard AC transfer switch for that and would make the system overall a lot more flexible. That would allow you to just keep the solar panels tied to the battery all of the time.

    Doing that, whenever you see that the batteries are full, just switch some of the AC loads over to inverter power. That setup would also allow you to just leave the AC battery charger connected all the time also for faster charging when needed.
  • CariboocootCariboocoot Posts: 17,615Banned ✭✭
    Re: DPDT Switch?

    It would be safe to say I am somewhat familiar with such system needs. It occurs often: unreliable grid power, needs steady supply.

    Here's how it is normally done: off grid inverter with built-in charger. AC from utility feeds charger and loads when available. When the grid goes down, the inverter immediately takes over loads and batteries are kept charged by solar panels through charge controller.

    The first thing to do is get a handle on the daily load requirement: peak Watt draw and total Watt hours used. That will tell you what you need for inverter capacity, system Voltage, and battery bank size.

    This means the AIMS inverter becomes a doorstop, which is the best use that can be made of one. No one in their right mind designs a 8kW 12 Volt inverter! That can draw over 600 Amps if actually pressed to put out its rating (more if you let the Voltage go too low). It's not a good idea at all, no matter what they say. Also it has no built-in charger which is key to making this system work.

    The second thing that needs changing if at all possible is the five parallel batteries. It is nearly impossible for such an arrangement to share current evenly between the batteries. Some of them will be doing more work than others, resulting in shortened lifespan.

    I know you have limits on what sort of equipment is available and no doubt a budget as well. So here's another solution utilizing the existing equipment: an AC transfer switch. Something like this one: http://www.solar-electric.com/miso60amp240.html It will allow the loads to be run either by the utility (when available) or the inverter, but it will not be automatic. It will also be necessary to keep the battery charger on the utility directly so that it is never powered by the inverter.

    Does any of this make sense?
  • VicVic Posts: 2,589Solar Expert ✭✭✭✭
    Re: DPDT Switch?

    And, the MS MPPT 45, IIRC, includes NO Display, and has NO built-in Aux Control function. The MS products often appear inexpensive, until one realizes that the only thing included, is the CC and a manual. OH, you wanted a RTS (Temp Sensor)?? OK that is extra, OH, you need a Display, OK, that, too, is extra. This is the way things have been with MS in the recent past. Doubt that much has changed. Just Opinions. Vic
    Off Grid - Two systems -- 4 SW+ 5548 Inverters, Surrette 4KS25 1280 AH X2@48V, 11.1 KW STC PV, 4X MidNite Classic 150 w/ WBjrs, Beta KID on S-530s, MX-60s, MN Bkrs/Boxes.  25 KVA Polyphase Kubota diesel,  Honda Eu6500isa,  Eu3000is-es, Eu2000,  Eu1000 gensets.  Thanks Wind-Sun for this great Forum.
  • CariboocootCariboocoot Posts: 17,615Banned ✭✭
    Re: DPDT Switch?
    Vic wrote: »
    And, the MS MPPT 45, IIRC, includes NO Display, and has NO built-in Aux Control function. The MS products often appear inexpensive, until one realizes that the only thing included, is the CC and a manual. OH, you wanted a RTS (Temp Sensor)?? OK that is extra, OH, you need a Display, OK, that, too, is extra. This is the way things have been with MS in the recent past. Doubt that much has changed. Just Opinions. Vic

    Accurate opinion in my opinion. By the time you add on all the "extras" you might as well buy the MidNite Classic in the first place. :D
  • goingtoghanagoingtoghana Posts: 34Solar Expert
    Re: DPDT Switch?
    Here's how it is normally done: off grid inverter with built-in charger. AC from utility feeds charger and loads when available. When the grid goes down, the inverter immediately takes over loads and batteries are kept charged by solar panels through charge controller.

    Does any of this make sense?

    If I understand you correctly then, the panels:
    1) will be used to supplement the batteries when the grid goes down.
    2) will be used in combination with the A/C charger when the grid is up.

    I don't understand what the built-in charger for the off-grid inverter is for.
  • CariboocootCariboocoot Posts: 17,615Banned ✭✭
    Re: DPDT Switch?
    If I understand you correctly then, the panels:
    1) will be used to supplement the batteries when the grid goes down.
    2) will be used in combination with the A/C charger when the grid is up.

    I don't understand what the built-in charger for the off-grid inverter is for.

    The separate AC charger is not used for an inverter with built-in charger.
    Normally the panels would provide all the charging the batteries need.
    If weather does not permit this, power supplied to the inverter's AC IN terminals (either from the utility or a generator) will run the loads and charge the batteries via the built-in charger. The transfer of loads from utility to inverter is automatic and seamless.

    But that arrangement presupposes changing the inverter.
  • goingtoghanagoingtoghana Posts: 34Solar Expert
    Re: DPDT Switch?

    so, When the grid is up, both the panels and the inverter with a built-in charge are charging the batteries. correct?

    1) Could you recommend an inverter of this type? Assume 5000W needed and I can add batteries to confgure to a serial 48V. No clue on current usage. They don't have much other then a refrigerator and 2 window A/C units.

    2) Should I just give up on the notion of switching the panels from battery chargers to Grid-Tie Inverter as I described below? Just seems like I am not maximizing the potential of the panels when the batteries are full.
  • WindsunWindsun Posts: 1,164Solar Expert admin
    Re: DPDT Switch?

    Bear in mind that this guys system is in Ghana, and they are probably not loaded with funds - so ideal setup might have to be reduced to what is practical given the tech, logistics, and money issues.
  • goingtoghanagoingtoghana Posts: 34Solar Expert
    Re: DPDT Switch?

    In this case, I'm the bank. :)

    I'm doing it b/c a) I want to help a friend with his ministry b) I'm learning a a ton about something that is of great interest to me. May do it for my own personal use later.

    I just want to make sure I am doing it correctly.

    So far, you guys have sold me on the midnite MPPT charge controller. Now, I'm just trying to find out the right inverter.
  • CariboocootCariboocoot Posts: 17,615Banned ✭✭
    Re: DPDT Switch?
    so, When the grid is up, both the panels and the inverter with a built-in charge are charging the batteries. correct?

    1) Could you recommend an inverter of this type? Assume 5000W needed and I can add batteries to confgure to a serial 48V. No clue on current usage. They don't have much other then a refrigerator and 2 window A/C units.

    2) Should I just give up on the notion of switching the panels from battery chargers to Grid-Tie Inverter as I described below? Just seems like I am not maximizing the potential of the panels when the batteries are full.

    Egad. A refrigerator and two window A/C units in Ghana. This is definitely a worst-case scenario. That is going to demand a lot of power!
    Typically a good refrigerator uses 1200 Watt hours per day. An A/C unit might run 6 kW hours. It all depends on what unit, how hot it gets, how well-insulated things are, how many times doors are opened ...

    You use "European power" there: 230 VAC 50 Hz. Any chance you could get one of the Europe versions of the Kill-A-Watt meter and send it over, then have them measure actual usage? We are talking about some big money difference between getting it right and getting it wrong.

    At this point I'm going to say the best choice for an inverter would be an Outback FX2348ET http://www.solar-electric.com/fx2348et.html or perhaps a VFX3048E http://www.solar-electric.com/vfx3048e.html
    Both will supply 230 VAC 50 Hz power and the Outback reputation for standing up to harsh conditions. The first one has a 35 Amp charger and the second a 45 Amp. That equates to about 2.4 kW hours difference in power storage (all other factors being equal).

    What you will have is not "grid tie" but "grid interactive" as it will make use of the grid (automatically) for power loads and charging the batteries whenever it is available.
  • waynefromnscanadawaynefromnscanada Posts: 3,009Solar Expert ✭✭✭✭
    Re: DPDT Switch?

    Unfortunately many people have no idea what total energy hogs fridges and AC units are. If you want to run these units, I suggest you'll be looking at having to come up with tens of thousands of dollars for your solar system :(
  • nielniel Posts: 10,311Solar Expert ✭✭✭✭
    Re: DPDT Switch?

    a generator is probably far more economical for backing up these loads even at the present cost of gasoline there.
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