Battery charging - Solar Plus DG Set

emcc
emcc Solar Expert Posts: 44 ✭
in Off Grid Solar & Battery Systems #1
I have a small 300Watt Solar Panel, powering my OFfice cabin, mainly lights and a fan.

I have machines working which run on a DG Set. I want to know, is there anyway that while the DG is running, I can charge the batteries from my Inverter which is being powered from DG? Is there any cheapo Automatic Transfer Switch?

Actually I am after this is because I have an Air Conditioner which cannot be run from a 300W PV. So when the machines are working and I need to sit in a cool cabin, I have to use Power from DG Set. One option is to change the wiring, so that only AC works from DG Set and rest from Solar, but thats not I am looking for.

Any suggestions? I also can't replace the Inverter as Hybrid Inverters are way too costly here.
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #2
    Re: Battery charging - Solar Plus DG Set

    Much of the answer depends on what you've already got for equipment. We'll assume that you have an inverter which does not have a built-in charger. (This is not a "hybrid" inverter, btw; that term refers to a grid-tie unit with battery back-up ability).

    So there are two options: an automatic or manual AC transfer switch that will move the loads on the inverter to the generator when it is running, or a battery charger that will supply power to the batteries when the generator is running.

    Examples:
    Manual transfer switch: http://www.solar-electric.com/miso30amp240.html
    Automatic transfer switch: http://www.solar-electric.com/pomaxpmautrs.html
    Battery charger: http://www.solar-electric.com/bach1.html

    Of course any device picked has to be sized correctly for your particular system.
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  • emcc
    emcc Solar Expert Posts: 44 ✭
    #3
    Re: Battery charging - Solar Plus DG Set

    Ok, but my cabin is wired like this

    Genset > Stabilizer > Inverter > Cabin

    Solar PV > CC > Battery ^

    How an Auto Transfer switch will be wired?
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #4
    Re: Battery charging - Solar Plus DG Set
    emcc wrote: »
    Ok, but my cabin is wired like this

    Genset > Stabilizer > Inverter > Cabin

    Solar PV > CC > Battery ^

    How an Auto Transfer switch will be wired?

    What is a "stabilizer"?

    If the inverter has AC IN then it has a transfer switch built-in. If it does not, there is no way the genset connects to the inverter. If it is a DC genset (unlikely) it would connect to the batteries via a charge controller.

    Normally you'd have AC wiring like this:

    Generator --> Transfer Switch --> Loads
    Inverter
    ^

    That way the loads can be connected either to the generator or to the inverter, but never both.
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  • emcc
    emcc Solar Expert Posts: 44 ✭
    #5
    Re: Battery charging - Solar Plus DG Set

    Its Voltage Stabilizer.

    Ok by installing that way, inverter will not get the AC current. Right?
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #6
    Re: Battery charging - Solar Plus DG Set
    emcc wrote: »
    Its Voltage Stabilizer.

    Ok by installing that way, inverter will not get the AC current. Right?

    Correct.

    As I mentioned before you can also have a battery charger connected to the genset which will supply DC to the batteries that power the inverter any time the gen runs. That will supplement PV and/or remove load from the batteries - in effect doing the same thing as running the inverter loads from the gen (providing the charger is large enough). It is not as efficient as switching the AC over, however.

    Why do you need a separate Voltage stabilizer on your generator output? Sounds like it may not be a great generator.
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  • emcc
    emcc Solar Expert Posts: 44 ✭
    #7
    Re: Battery charging - Solar Plus DG Set

    Generator does not generate DC, its 40KVA 3-Phase 415V AC Genset.

    WE have certain machinery being run by Generator which cause it surge which increases or decreases the speed of genset which result in high or very low voltages. Thats why I need a Voltage Stablizer.
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #8
    Re: Battery charging - Solar Plus DG Set
    emcc wrote: »
    Generator does not generate DC, its 40KVA 3-Phase 415V AC Genset.

    WE have certain machinery being run by Generator which cause it surge which increases or decreases the speed of genset which result in high or very low voltages. Thats why I need a Voltage Stablizer.

    Actually that explanation didn't have to go past "40 kVA 3-phase 415 V". :D
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  • emcc
    emcc Solar Expert Posts: 44 ✭
    #9
    Re: Battery charging - Solar Plus DG Set

    Can we use Blocking DIODE as well between Inverter and Battery?
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #10
    Re: Battery charging - Solar Plus DG Set
    emcc wrote: »
    Can we use Blocking DIODE as well between Inverter and Battery?

    There is no point to putting a blocking diode there.
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  • emcc
    emcc Solar Expert Posts: 44 ✭
    #11
    Re: Battery charging - Solar Plus DG Set

    Wont that be a cheap solution to block the charging current from inverter to battery?
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #12
    Re: Battery charging - Solar Plus DG Set
    emcc wrote: »
    Wont that be a cheap solution to block the charging current from inverter to battery?

    If your inverter has no AC applied to it there is no charging current coming from it to the battery.
    Inverter-chargers have AC in and regulated charging of battery so no diode is needed.
    Inverters (some) will only back-feed to batteries if AC is applied to their output. This is avoided by the transfer switch which prevents the generator output from being applied to the inverter.

    If the batteries are fed by a separate charger powered from the gen, the inverter does not care.

    The only thing putting a diode between batteries and inverter does is drop the Voltage to the inverter when it's trying to run. And probably burn out the diode because inverters tend to draw quite heavy current that diodes are not designed to handle.
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  • emcc
    emcc Solar Expert Posts: 44 ✭
    #13
    Re: Battery charging - Solar Plus DG Set

    What about a relay?
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #14
    Re: Battery charging - Solar Plus DG Set
    emcc wrote: »
    What about a relay?

    For what purpose?
    Sorry but I'm having trouble understanding what it is you're trying to accomplish.
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  • emcc
    emcc Solar Expert Posts: 44 ✭
    #15
    Re: Battery charging - Solar Plus DG Set

    Want to avoid double charging. Because when DG is running, Inverter tries to charge battery and solar too already charging the battery. Which cause the terminals to get too hot.
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #16
    Re: Battery charging - Solar Plus DG Set
    emcc wrote: »
    Want to avoid double charging. Because when DG is running, Inverter tries to charge battery and solar too already charging the battery. Which cause the terminals to get too hot.

    In order for this to occur you would have to have an inverter-charger with its AC IN connected to the generator, or a standard inverter with its AC OUT connected to the generator. The later should never be allowed.

    In the case of multiple charge sources to the same battery bank there is usually no trouble except during Bulk when it is possible for all sources to give their maximum current (as charge is regulated by Voltage along; measuring and controlling total current is more complicated).

    So what do you have for an inverter? What do you have for panels & charge controller? What do you have for a battery bank? All essential information in working out any problems.
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  • emcc
    emcc Solar Expert Posts: 44 ✭
    #17
    Re: Battery charging - Solar Plus DG Set
    Cariboocoot wrote: »
    In order for this to occur you would have to have an inverter-charger with its AC IN connected to the generator, or a standard inverter with its AC OUT connected to the generator. The later should never be allowed.

    In the case of multiple charge sources to the same battery bank there is usually no trouble except during Bulk when it is possible for all sources to give their maximum current (as charge is regulated by Voltage along; measuring and controlling total current is more complicated).

    So what do you have for an inverter? What do you have for panels & charge controller? What do you have for a battery bank? All essential information in working out any problems.

    I have 860VA MSW Inverter, two 150W 22VOC Panel connected in Parallel, 20A PWM CC, 12V Battery.
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #18
    Re: Battery charging - Solar Plus DG Set
    emcc wrote: »
    I have 860VA MSW Inverter, two 150W 22VOC Panel connected in Parallel, 20A PWM CC, 12V Battery.

    Not quite enough details.
    For example: does the inverter have a built-in charger? If not, no problem. If so, it can be dealt with.
    The two panels likely produce a total of 17 Amps (8.5 Amps each * 17.5 Vmp). This can charge anywhere from 130 Amp hours to 340 Amp hours. But we don't know how big the battery bank is (other than Voltage).
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  • emcc
    emcc Solar Expert Posts: 44 ✭
    #19
    Re: Battery charging - Solar Plus DG Set
    Cariboocoot wrote: »
    Not quite enough details.
    For example: does the inverter have a built-in charger? If not, no problem. If so, it can be dealt with.
    The two panels likely produce a total of 17 Amps (8.5 Amps each * 17.5 Vmp). This can charge anywhere from 130 Amp hours to 340 Amp hours. But we don't know how big the battery bank is (other than Voltage).

    Ahem, if you are asking about solar charger, then no. But the other charger to charge battery from Grid, yes.
    Battery is 150Ah 12V.
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #20
    Re: Battery charging - Solar Plus DG Set
    emcc wrote: »
    Ahem, if you are asking about solar charger, then no. But the other charger to charge battery from Grid, yes.
    Battery is 150Ah 12V.

    You are still not answering the question.
    Some inverters have built-in battery chargers. Some do not.

    If you plan to use a stand-alone battery charger the easiest way to prevent too much current going to your batteries when solar is available is to not turn the thing on. This is more difficult to do with an inverter-charger.

    A 150 Amp hour battery bank is not very large. The 17 Amps potential panel current will be more than enough unless the sun does not shine. If I were you I would not use any additional charging source unless that was the case (no sunshine). As far as stand-alone chargers go you would only need one of these http://www.solar-electric.com/ioen12vo15am.html and only use it if the weather fails to co-operate.
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  • emcc
    emcc Solar Expert Posts: 44 ✭
    #21
    Re: Battery charging - Solar Plus DG Set

    It has built in charger.Thats why I am looking for something which prevent the charging from Inverter, but allows Inverter to draw the current from Battery
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #22
    Re: Battery charging - Solar Plus DG Set
    emcc wrote: »
    It has built in charger.Thats why I am looking for something which prevent the charging from Inverter, but allows Inverter to draw the current from Battery

    That makes sense.
    In this case you have to get into the specifics of how the built-in charger works; what kind of programming is available? If there's not much choice to the user you are right to disable one charge source or the other when the gen is running to prevent this problem.

    There's more than one way to do that too. You could bypass the inverter entirely with a separate transfer switch so that its charger is never active. Or you could install a relay that would switch off the panels when AC IN is present on the inverter.

    But it is essential that you understand just how the inverter-charger works before you choose your option.
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  • inetdog
    inetdog Solar Expert Posts: 3,123 ✭✭✭✭
    #23
    Re: Battery charging - Solar Plus DG Set
    emcc wrote: »
    I have a small 300Watt Solar Panel, powering my OFfice cabin, mainly lights and a fan.

    I have machines working which run on a DG Set. I want to know, is there anyway that while the DG is running, I can charge the batteries from my Inverter which is being powered from DG? Is there any cheapo Automatic Transfer Switch?

    Actually I am after this is because I have an Air Conditioner which cannot be run from a 300W PV. So when the machines are working and I need to sit in a cool cabin, I have to use Power from DG Set. One option is to change the wiring, so that only AC works from DG Set and rest from Solar, but thats not I am looking for.

    Any suggestions? I also can't replace the Inverter as Hybrid Inverters are way too costly here.

    Do you plan to run the generator constantly whenever you will be needing A/C? If so then Coot's suggestion of a transfer switch would be fine.
    If you are able to autostart the generator, set it up to start the generator just before the A/C turns on, and either wire the A/C to generator only or include a transfer switch.
    Take a look at this thread for more on starting an A/C from a generator.
    The office machines are more of a problem, since I imagine you will be using them irregularly for short times and then letting them run in idle mode off the inverter or shut off completely.
    You could set them up with a similar connection to the transfer switch and add them into the generator auto-start sensor circuit (which you may have to build!)
    SMA SB 3000, old BP panels.
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  • emcc
    emcc Solar Expert Posts: 44 ✭
    #24
    Re: Battery charging - Solar Plus DG Set

    I'm planning to use a 5-Pin 30A relay. This will prevent the charging from Inverter. Let's see if it works.
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #25
    Re: Battery charging - Solar Plus DG Set

    If your plan is to interrupt the DC line between batteries and inverter whenever the generator is running be advised that the relay will have to be able to withstand the full current draw of the inverter when not interrupted. Since this is a 12 Volt system that is potentially 200 Amps or maybe more depending on the inverter's rating. That is quite a lot of power, and why I suggested disconnecting the PV instead (about 1/10 the current).
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  • emcc
    emcc Solar Expert Posts: 44 ✭
    #26
    Re: Battery charging - Solar Plus DG Set

    The maximum current I draw is around 20A. Because On inverter, I can only run a fan and 4 CFL of 23W each.
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #27
    Re: Battery charging - Solar Plus DG Set

    What you actually use and what the inverter is capable of supplying are two different things. Checking back I see you have an 860 VA (odd size?) inverter, which would draw about 72 Amps @ 12 Volts if operating at maximum continuous capacity. This should be connected to the batteries with 2 AWG wire. Any relay used to interrupt that line would need to be able to handle 100 Amps.

    It is also more economical to use the inverter-charger for charging while the gen is running. The genset is large and has the capacity; it will be more efficient if you keep it loaded. Not that the charging circuit is going to be much of a load for it. Making it impossible to use the built-in charger is not necessarily a good idea either, as it means you would not be able to charge batteries when the sun doesn't shine.

    On the whole, using a relay activated by the presence of power from the generator to interrupt the PV charging is the better option. It will limit the maximum current to the batteries by eliminating one charge source, still maintain the ability to charge in cases of inclement weather, allow the generator to take all AC loads when running, and remove any risks of improperly sized components on the heavy current DC lines.
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  • emcc
    emcc Solar Expert Posts: 44 ✭
    #28
    Re: Battery charging - Solar Plus DG Set

    I guess interrupting the Solar would be a good choice.
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  • emcc
    emcc Solar Expert Posts: 44 ✭
    #29
    Re: Battery charging - Solar Plus DG Set

    Relay made me confused. I have a 5 PIN Relay. Since this is a DC Relay, how would I trigger the switch to throw the load change?
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #30
    Re: Battery charging - Solar Plus DG Set
    emcc wrote: »
    Relay made me confused. I have a 5 PIN Relay. Since this is a DC Relay, how would I trigger the switch to throw the load change?

    Well you need to have the AC power the DC relay. So you have to get it to match Voltage and current type. So if the relay coil requires 200 mA @ 12 VDC you need a power supply connected to the AC IN that will deliver that to the relay coil.

    Two of the pins on the relay will be the coil. The other three will be Common, Normally Open, and Normally Closed. The PV would go through Common and Normally Closed. When AC is present on the inverter-charger's input (generator running) the power supply will activate the relay and switch the Common from Normally Closed to Normally Open thus cutting the PV to the charge controller.
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  • emcc
    emcc Solar Expert Posts: 44 ✭
    #31
    Re: Battery charging - Solar Plus DG Set

    Yes, I figured that out. Actually I was planning to trigger it with the same power lines, but I realized its not possible. So will be triggering it with a 230V to 12V Transformer connected to main line with fuse.
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