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Please help me reduce heavy ripple and HF harmonics at 25-60 amps 24 volts

Discussion in 'Electronic Design' started by [email protected], Feb 16, 2007.

  1. Guest

    Hi everyone,

    Recently I acquired a broken down SOLA 1500 sinewave UPS which I was
    able to repair. Since I already have a UPS for my PC I decided to use
    it solely as an inverter. I replaced the internal 24v battery pack
    with 2 external 65AH deep cycle marine batteries connected to the unit
    with 2 80cm 300A high grade welding cables to minimise losses.
    Problem is; when the unit is running under a light load, it
    immediately sounds the "low battery" alarm. It can run for hours like
    this, but the thing that makes me uncomfortable is when looking at the
    battery voltage on my CRO, I can see very pronounced "dips" approx
    every 9mS; alternating between 2 distinct "dips" of 4-5 volts and 2
    volts with apparent high frequency harmonics. Either my batteries are
    damaged, they were bought as new factory seconds with cosmetic
    defects, or these types of batteries simply cannot supply the heavy
    surges of power needed, fast enough. Under load, they steadily supply
    around 24.6 volts which is probably why the UPS is complaining.
    However, I do not like these dips in voltage since I can hear the unit
    struggle when a large monitor is switched on, which does not happen
    with the internal batteries. I doubt they are defective though, so I'd
    like to build a capacitor and choke filter close to the UPS unit to
    "support" the batteries. An LC filter would help, I suspect, however I
    have never built one even remotely as powerful as this unit needs.
    Could anyone please point me to a schematic or describe a simple
    filter that would be cost-effective? How many turns of what gauge wire
    would I need and would I be able to salvage the inductors found in
    wrecked PC power supplies?
    If you read through all this; thank you. I'd be grateful for your help
    and post an update with any success or failure stories.
     
  2. Tim Williams

    Tim Williams Guest

    It should suffice to use a few large capacitors. Start with perhaps 10 x
    2200uF 35V in parallel, at the inveter, and finish it off with one of those
    1F caps across each battery (or both, if you can find a 25-35V unit). Maybe
    1F is a bit much, even 100,000uF will help. Heck, even just the smaller
    caps will help, since it sounds like the inverter, remarkably, has little or
    no filtering inside it to begin with!

    Tim
     
  3. Guest

    Thank you for your response.
    I was "afraid" of ending up having to use large and expensive
    capacitors to help keep the voltage steady. I assume this UPS has so
    little filtering because the small 7Ah SLA batteries, combined with a
    shorter cable run, are more adept at handling the "surges" of current
    required, without dropping the voltage too much. These high current
    draws from the batteries last only around 1-2mS.
     
  4. Fred Bartoli

    Fred Bartoli Guest

    a écrit :
     
  5. Guest

    So why don't you just keep the internal SLA as a bypass?

    Hi Fred,
    What do you mean by "bypass"? I have replaced these batteries since
    they only give me 20-30 minutes run-time. When the power fails, the
    UPS connected to my PC will keep it running until I use the 2nd UPS
    with the large external batteries to power the UPS protecting my PC.
    This way I could keep my PC running for up to 12 hours without
    interruption.

    Is there any other way to solve my problem, besides using very large
    caps?

    Cheers,
    Ben

     
  6. MassiveProng

    MassiveProng Guest

    Yes. Get and USE a power supply that can handle the demand. You
    don't need all those cap banks if your supply rail doesn't have all
    that ripple in it to start with.

    Refrain from top posting in Usenet.
     
  7. Mark

    Mark Guest

    He means leave the internal batteries in place and connect the
    external batteies in parrallel across the internal batteries...

    The internal batteries supply the ripple current and the external
    batteries suply the average current.

    I have done this and it works OK as long as you keep the batteries
    charged/discharged together.

    Mark
     
  8. Guest

    Please don't be rude. As I said, the power supply is 1500VA which is
    more than powerful enough to start a monitor without straining. I have
    a 425 unit which can do the same. My PC uses around 20% of the power
    the 1500VA unit can deliver.
    This post is about solving a problem, not buying another unit.
     
  9. Guest

    Hi Mark,
    Thanks for the response. I have thought of that, but dismissed it
    since an inverter that is actually designed to run off external
    batteries would not need this. Also, this unit "cooked" the last set
    of internal batteries, which was unrelated to the fault that I
    repaired. I just want to be rid of them, if possible.
    Could an LC filter be made powerful enough? I am hoping this could
    still be fixed with a filter.
     
  10. jasen

    jasen Guest

    cables seem kind of long.
    you probably don't need the inductor just some big capacitors
     
  11. legg

    legg Guest

    Try reducing the loop area of your cables. If they are twisted/wrapped
    around each other, their inductance will be reduced. Multiple smaller
    cable pairs, similarly twisted, might work better as a more easily
    manipulated substitute.

    Local capacitive decoupling at the load is the simplest first step.
    Fill up the area where the batteries used to be with low esr parts.
    Low impedance, not high capacitance is the goal.

    RL
     
  12. MassiveProng

    MassiveProng Guest

    **** OFF, ASSWIPE!

    YOU learn about Usenet, and fucking STOP TOP POSTING, you retarded
    twit!
    Unless the fucking thing has piss poor specs, dipshit. It isn't
    about straining, it is about living up to declared specifications.

    I shouldn't even answer your retarded ass, since you cannot even
    follow Usenet posting protocols. There was a time when twits like you
    merely got ignored, or even filtered.
    Idiot. A power supply rating is not what it uses. It is what it
    WOULD use under full loading. Your PC does NOT fully load its power
    supply. If it did, with these chinese POSes we have, you'd be seeing
    smoke right quick.

    The rating of a supply is what it CAN do, not what it does do.

    So, if your pathetic 1500VA POS feeds noise into your gear at less
    than full loading, it obviously
    does NOT fucking live up to its declared spec.

    Pretty simple shit. So is learning how to post properly in Usenet.
    This ain't your fucking email, you goddamned GoogleTard.
    If the Unit SUCKS, you can't use it. The options after that are
    yours, you dumbfucktard.

    Look up TOFU (NOT the food, dumbass) on your precious GoogleTard
    pages. You are a TOFU retard.

    So AGAIN, REFRAIN from top posting in Usenet. You thick skulled
    utter idiot.
     
  13. ehsjr

    ehsjr Guest


    It may be that your big batteries are not fully charged.
    The charger in the UPS was capable of charging 7 AH
    batteries, but may not be able to give the 65 AH batteries
    a full charge.

    Ed
     
  14. Guest

    Thank you for your response. I'll try shortening my leads further. In
    addition to low esr caps, will also try adding mylar caps for the high
    frequency harmonics. I can check with my CRO if the mylars make any
    difference and post an update in a few days.
     
  15. Guest

    Good thinking, you are right; I should have mentioned that I do not
    supply the unit with mains power anymore and disconnect the deep cycle
    batteries to charge them with a car battery charger.
     
  16. MassiveProng

    MassiveProng Guest

    And may also be delivering a LOT of ripple while they attempt to
    charge them.
     
  17. Tim Williams

    Tim Williams Guest

    Sorry, forgot to warn ya- 'Prong here is the local fucktard. Just put him
    in your killfile and relax.

    Tim
     
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