Relays switch on or off based on AH, Battery voltage or time

miikeemikemiikeemike Registered Users Posts: 3
in Advanced Solar Electric Technical Forum #1
Hi

Just wanted to share some work I did using an arduino to switch latching relays on or off.
Some people might find it useful.

http://www.youtube.com/watch?v=TunjEe3Z3eM

Regards,
Mike
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  • VicVic Solar Expert Posts: 3,185 ✭✭✭✭
    #2
    Re: Relays switch on or off based on AH, Battery voltage or time

    Hi Mike,

    Looks like a fun and useful project.

    I do have one concern, about the Latching Relay shown in the pic. It appears to be an AC relay. Some AC relays DO have a rating for DC as well, which may be the case for the relay that you are using. But, as you may know, DC currents are wicked things to interrupt. There can be large, damaging arcs generated when breaking DC current flow, and some pitting of relay contacts (or, even contact welding) when DC currents begin to flow as the relay contacts "make".

    Again, this relay may well have DC ratings. Often AC/DC relays have a much lower voltage rating for DC circuits, and may have fewer number of rated cycles when dealing with DC.

    Thank you very much for documenting your project. I, also would like to make a controller to automate some of the tasks that are done manually, here. Many of these things involve switching DC. Have considered using DC Solid State Relays, altho, those do have some voltage drop, which translates into lost power. Good Luck, Thanks again, Vic
    Off Grid - Two systems -- 4 SW+ 5548 Inverters, Surrette 4KS25 1280 AH [email protected], 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.
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  • miikeemikemiikeemike Registered Users Posts: 3
    #3
    Re: Relays switch on or off based on AH, Battery voltage or time

    Well spotted. I have the same concern. Did not see a DC rating on the specs for the relay. Figured I would just try them and see how they go. If they don't last very long I'll checking around for an alternative.

    Thanks Vic

    Mike
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  • BB.BB. Super Moderators, Administrators Posts: 33,085 admin
    #4
    Re: Relays switch on or off based on AH, Battery voltage or time

    You can use capacitors or clamping diodes across the contacts to reduce arcing (PDF on snubbing diodes). The snubbing diode supplies current to the inductive load while the switch/transistor is opening (turning off). This prevents harmful voltage spikes and arcs (in DC circuits).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • inetdoginetdog Solar Expert Posts: 3,123 ✭✭✭✭
    #5
    Re: Relays switch on or off based on AH, Battery voltage or time
    BB. wrote: »
    The snubbing diode supplies current to the inductive load while the switch/transistor is opening (turning off).
    -Bill

    And usually for some significant time after it has opened/turned off fully. That dissipates the energy stored in the magnetic field of the inductor over a longer time, so that the instantaneous power dissipation is not as large, and happens mainly in the internal resistance of the inductive load where it (should) do no harm.
    SMA SB 3000, old BP panels.
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  • miikeemikemiikeemike Registered Users Posts: 3
    #6
    Re: Relays switch on or off based on AH, Battery voltage or time

    Great information guys. Thanks.
    I will add the snubber diodes and caps. Makes sense.

    -Mike
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