Holding an AC charge for ridethru

Discussion in 'General Electronics Chat' started by Wolfe, Nov 18, 2010.

  1. Wolfe

    Thread Starter New Member

    Nov 18, 2010
    I have hit a wall in trying to find a solution to a problem...hoping someone can offer some other ideas.

    I have a 120VAC UPS that when it transfers to/from inverter to/from bypass source it does so just slow enough to trip out some 120Vac relays on the circuit. We put a scope on it and found that the UPS is fast (about 1/4 cycle or 10 ms)...which is good. The trip is not consistant, depends on where in the cycle the transfer occurs.

    I was looking for ideas on how to hold an AC voltage from this UPS long enough to rideout this transfer time...say 40-50 ms or so. In this way the relays would be able to see voltage at all times.

    Would some sort of capacitor system work? Then again this is AC, so?
    Maybe an Agastat relay?

    BTW-I have already looked at replacing the relays with TDDO (time delay off), but they don't make these for my relay base.

    UPS AC Out: 120V, 84A, 60 Hz, 1-ph

    If someone needs more info...I have it all.

  2. SgtWookie


    Jul 17, 2007
    You have a standby supply, which is not the same as a true UPS.

    With a true UPS, they're synthesizing the output 120VAC power continuously from the batteries, while the batteries are continually being charged.

    With a standby supply, they don't switch in until after the AC power shows a fault. They're pretty fast, and are normally good enough for a computer supply. However as you've discovered, they're not suitable for all loads.
  3. Wolfe

    Thread Starter New Member

    Nov 18, 2010
    I thought I started a new Thread...hopefully this worked.

    Thx for the input...but yes this is always inverter supply and and the batteries are upstream of this inverter. The switching is done downstream (electronically) to go from inverter to line power via a stepdown xfrmr.

    My next thought is to put a motor on the output to act as a generator if the power stops, (if only for a couple cycles or so).

  4. Kermit2

    AAC Fanatic!

    Feb 5, 2010
    It would help to know what load you are using on this as well. If the load can be given some increased capacity in its power supply, it might be able to carry over long enough for the UPS you are using to fully energize.
  5. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
    I can't think of a way for an AC relay to stay energized unless you are using an online converter.

    Would stepping the input down to 12VDC with an AC detector work for running the relays? Delays could be added easily in that configuration.
  6. Wolfe

    Thread Starter New Member

    Nov 18, 2010
    Firstly, thanks for the input everyone.

    The only loads are all relays and other power supplies. Additional loads could be added (like motor or other inductive loads).

    Another idea is to add to the output a VFD (variable frequency drive), which is essentially an inverter and a DC bus, which may be able to ride through for a couple cycles. Probably not the cleanest method to ridethru.

    I do it because I just want to understand it!