Ripple Voltage

rama
rama Solar Expert Posts: 36 ✭
in Solar Beginners Corner #1
Hello - what is the significance of the Output Ripple Voltage of a charge controller? I was talking to a friend about a MPPT controller that has a ripple voltage of "< +/- 1V". Is this any good? I tried googling a bit but could only make out that it was something to do with undesirable vibration of DC as a result of incompletely suppressed conversion of AC waveforms.

But in the off-grid context, it doesn't seem to make sense because everything up until inverter it's still all DC-DC. :confused: Is this important at all?

thanks...
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  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    #2
    Re: Ripple Voltage

    I think it's a non-issue. What is more likely an issue, is your inverter drawing so much power, it creates a ripple voltage on a too small of a battery bank, and that ripple confuses the charge controller.
    Ripple from any source can also be heard as "hash" or "noise" on local radios.
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,623 admin
    #3
    Re: Ripple Voltage

    Also, what kind of load do you have where ripple voltage will be an issue?

    Simple PWM controllers simply "turn on" and "turn off" (100% current to 0% current) from a few times a second to 10,000+ Hz... The ripple voltage is usually a function of battery capacity -- and possibly improper wiring.

    At least one manufacturer (MorningStar) has a "Telecom" setting that drop the switching frequency to below audio frequencies to try and limit switching noise from entering phone equipment.

    The newer MPPT controllers probabably have much less variation in current--and the "good ones" will also have FCC Class A or (better) Class B rated equipment (reducing radio emissions--a good thing for HAMs and others). Also, typically, units which pass Class A or Class B FCC (and CE equivalents) tend to perform better in electrically "noisy" environments. (better shielding for emissions usually means better protection against static discharge, RF transmitters, etc.).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • Solar Guppy
    Solar Guppy Solar Expert Posts: 1,989 ✭✭✭
    #4
    Re: Ripple Voltage

    Look up AC current ripple ....

    The voltage variation is caused by the 120hz sine wave load pulling peak current from the batteries ( inverters ). If excessive, charge controllers that use that battery values for the Mppt algorithms will fail to track properly.

    As BB mentioned, the smaller the battery bank, the worse the ripple will be for the same AC current draw. The Only fix the user has is either increasing the battery bank size.
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  • RCinFLA
    RCinFLA Solar Expert Posts: 1,485 ✭✭✭✭
    #5
    Re: Ripple Voltage

    AC ripple due to the 120 Hz full wave rectified sinewave shaped current pulses from a sinewave inverter is a possibility.

    Other possibility is MPPT hunting and PV output fluxuations for clouds going by. This would be slow enough to be observed by a connected voltmeter.

    When a lead acid battery is fully charged, running at float levels, its internal resistance to boosts in charge current is fairly high resulting in significant observed voltage ripple.

    If the battery holds up to heavy loads don't worry about it.
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  • rama
    rama Solar Expert Posts: 36 ✭
    #6
    Re: Ripple Voltage

    thanks for all your inputs! I'm going to need some time to digest that.
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