Manual or Automatic Transfer switch

mryimmers
mryimmers Solar Expert Posts: 117 ✭✭✭
in General Solar Power Topics #1
Hi All,
I have been thinking about installing a transfer switch on my small off grid system to go from battery to generator. I am wondering if anyone has experience and/ or opinions regarding manual or automatic? Does the manual switch also provide a seamless power transition? NAWS has both types on the web site, a manual switch from midnite, and an automatic from powermax. The midnite switch is 240 volt, I only use 120volt, does that matter? Thanks
510 watt pv, TS-MPPT 60, Exeltech XP1100, XP600 & XP250 @ 24V, 4x Trojan 105RE, Trimetric 2030, Yamaha EF2400i gen.
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Comments

  • Thom
    Thom Solar Expert Posts: 196 ✭✭✭
    #2
    Re: Manual or Automatic Transfer switch

    I use a 3 way wall switch .

    Thom
    Off grid since 1984. 430w of panel, 300w suresine , 4 gc batteries 12v system, Rogue mpt3024 charge controller , air breeze windmill, Mikita 2400w generator . Added 2@ 100w panel with a midnight brat 
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  • inetdog
    inetdog Solar Expert Posts: 3,123 ✭✭✭✭
    #3
    Re: Manual or Automatic Transfer switch
    mryimmers wrote: »
    The midnite switch is 240 volt, I only use 120volt, does that matter? Thanks
    No, it does not matter. You can always use a switch rated for a higher voltage in place of a switch rated at a lower voltage. Just stay within the rated current and do not confuse AC (appropriate in your case) and DC (needed for panel combiner, etc.) ratings.
    SMA SB 3000, old BP panels.
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  • inetdog
    inetdog Solar Expert Posts: 3,123 ✭✭✭✭
    #4
    Re: Manual or Automatic Transfer switch
    Thom wrote: »
    I use a 3 way wall switch .

    Thom
    That is, as a practical matter, good enough, but does not necessarily meet the NEC requirements for a transfer switch. The latter needs specific design features to prevent simultaneous connection of both switch poles during the switching process.
    SMA SB 3000, old BP panels.
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  • mryimmers
    mryimmers Solar Expert Posts: 117 ✭✭✭
    #5
    Re: Manual or Automatic Transfer switch

    OK thanks guys, but does anyone actually use one of these?
    510 watt pv, TS-MPPT 60, Exeltech XP1100, XP600 & XP250 @ 24V, 4x Trojan 105RE, Trimetric 2030, Yamaha EF2400i gen.
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  • Thom
    Thom Solar Expert Posts: 196 ✭✭✭
    #6
    Re: Manual or Automatic Transfer switch
    mryimmers wrote: »
    OK thanks guys, but does anyone actually use one of these?

    The 3 way wall switch ? I guess it's not NEC approved . On the 2 systems I use both have a 3 way wall switch.

    Thom
    Off grid since 1984. 430w of panel, 300w suresine , 4 gc batteries 12v system, Rogue mpt3024 charge controller , air breeze windmill, Mikita 2400w generator . Added 2@ 100w panel with a midnight brat 
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #7
    Re: Manual or Automatic Transfer switch
    Thom wrote: »
    The 3 way wall switch ? I guess it's not NEC approved . On the 2 systems I use both have a 3 way wall switch.

    Thom

    It is not NEC approved for use as a transfer switch.
    However in this case where the inverter is only 300 Watts a 15 Amp switch is not going to be stressed at all. The only issue is whether it truly breaks contact on one side before making it on the other. If not there can be some internal arcing between the two power sources which will eventually destroy the switch.

    A manual transfer switch will not be seamless in change-over. An automatic switch should be or fairly close (depending on the design). The ones built-in to inverters are usually the best because the inverter can actually match frequency with the external AC signal before the change.
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,613 admin
    #8
    Re: Manual or Automatic Transfer switch

    A three way wall switch is "cheap".

    Buy two, and take one apart (carefully break apart). And look at the switching mechanism. Ideally, you want the switch to "ALWAYS" break the connection first, before making the second connection.

    The simple three way switches I have seen use one arm to "throw" between 1 and 2 position--So there is no chance that you can have both 1+2 connected at the same time (look at a relay with NC and NO contacts and one moving arm between the two).

    Obviously, what you NEVER want is to have 1+2 connected at the same time--That would be your inverter + other AC power source connected together and effectively shorting each other out (unsynchronized AC power sources tied together).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • 2twisty
    2twisty Solar Expert Posts: 199 ✭✭✭
    #9
    Re: Manual or Automatic Transfer switch

    I'm using an automatic 30a transfer switch that I harvested from an RV. I love it. I've got it wired so that if the generator comes on, it switches the entire house to the generator and fires up my battery charger. Turn off the genny and it flops right back to the inverter.
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  • 66ChevellePost
    66ChevellePost Registered Users Posts: 2
    #10
    Re: Manual or Automatic Transfer switch

    Hi,

    Here's one you might want to consider. I built one myself for about $30.00 and it works well.
    http://2manytoyz.com/ats.html
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  • inetdog
    inetdog Solar Expert Posts: 3,123 ✭✭✭✭
    #11
    Re: Manual or Automatic Transfer switch
    66ChevellePost wrote: »
    Hi,

    Here's one you might want to consider. I built one myself for about $30.00 and it works well.
    http://2manytoyz.com/ats.html

    Nice build description. But our members should be aware that the result is not a UL Listed ATS, and if the work involved getting a permit and an inspection it would not have passed.

    Among other things, there is a property of the utility service called Available Short Circuit Amps or available fault current. This tells you how much instantaneous current the service can deliver into a wiring or equipment fault that produces a short circuit.
    Anything which is connected directly or indirectly to the POwer COmpany (POCO) power must be able to either safely interrupt that current level if it is a breaker or fuse or safely carry that level of current until the actual overcurrent protection device kicks in. The relay you chose is far from capable of either. As a result the relay could fuse, melt or blow up in the event of a short circuit anywhere in your wiring downstream from it. Even if you put it on a 15A or 20A breaker in your main panel.
    You can choose to ignore that as unlikely, but that is a large part of the difference between a $30 ATS and a real $300+ ATS.
    SMA SB 3000, old BP panels.
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  • 66ChevellePost
    66ChevellePost Registered Users Posts: 2
    #12
    Re: Manual or Automatic Transfer switch

    inetdog,

    I only use the one I built when I am at home. I like projects and this was a good experiment to see if a transfer switch would meet my needs. I did not integrate mine into my electrical panel box the way I think he did. I plug mine into a power strip. I appreciate guys like you on these forums who try to keep our families and homes safe. I am doing some research of transfer switches and I will definitely make sure the one I buy a UL listed device.

    Thanks,
    Kenny
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  • vcallaway
    vcallaway Solar Expert Posts: 157 ✭✭✭✭✭
    #13
    Re: Manual or Automatic Transfer switch

    I've used both automatic and manual switches. I much prefer automatic.

    I have the powermax 50A in my RV. Great unit. Mine is about 3 years old. I bought it from our sponsor and have no complaints.

    I used some IOTA 30A ones on my battery backup project in my house. They work the same way with relays and a control board. They switch so fast that things like my computers and TV don't even glitch. In my case I am going from grid to inverter.

    When I wired the IOTA switches for the battery backup I have them set to switch to grid when power is available with the delay active. That means the relays are always energized when the power is on. I contacted IOTA to make sure that the relays would handle the constant on state before I did so. They told me that was the recommended method for my application and to not worry about the duty cycle. The Powermax switch is using the same relays.
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