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64thunderbolt's avatar
64thunderbolt
Explorer II
Dec 02, 2013

My WFCO is taking a dump

I have tested the batt's and they are good & fully charged. My conv is cycling rapidly. What would be a good choice? I'm not interested in the most expensive just a good dependable conv/charger. I've heard the the wfco is not high quality & mine is over 9 yrs old.

49 Replies

  • Salvo's avatar
    Salvo
    Explorer
    Dec 13, 2013
    I bet you never thought those plots would get that much attention and analysis.

    That would be great if you could find time for some scope measurements. A cap bank voltage plot should give a definitive answer to what's bugging the PD. That would be high on my wish list.

    Can't we work with VA? That's what the gen is loaded with.

    I'll be leaving for Baja after Christmas and won't be back till Feb some time.

    Sal

    Wayne Dohnal wrote:
    I was thinking I could re-run this with the new scope that gives an RMS readout, but that would just give VA. I don't think there's an easy route to measure watts. (Don't have time now to do it anyway).

    For these shots I was running the scope uncalibrated to make the picture pretty.
  • Salvo's avatar
    Salvo
    Explorer
    Dec 13, 2013
    It can get complicated very quickly once PD gets mentioned. ;-)

    It's in a class of its own. So also is the Onan Microquiet.

    BTW. 7 years ago, that Onan gen was scheduled to be installed in my newly purchased rig. I wanted to save 100 lbs and didn't get it.

    Sal

    64thunderbolt wrote:
    Boy, I didn't think my simple question would turn into this. I'm out. Thanks everyone.
  • Wayne_Dohnal's avatar
    Wayne_Dohnal
    Explorer
    Dec 13, 2013
    Intuitively Sal's comment about the wider current pulse meaning the capacitors are more discharged makes sense to me. When I look at the details more closely, very little with the Onan trace makes sense. The Onan voltage has a pretty long duration flat top. If the caps were discharged I'd expect the current to peak synchronized with the voltage hitting its peak. But it doesn't, and instead has a nice gradual rise. If the converter was short on incoming power I'd expect the current to stay up there until the flat-topped voltage drops, but it doesn't. The converter's regulation looks "stupid" to me, just like the generator's output. I don't know the details of how the PD regulator works. Is it as simple as mutual confusion between the generator and converter regulators?

    Compare that to the sine wave (Honda) traces where everything appears as it should. In comparing the current pulses the only thing I'm confident in saying is that because of the squaring, the shorter taller Honda pulse likely has a higher RMS value than the longer wider Onan pulse. I was thinking I could re-run this with the new scope that gives an RMS readout, but that would just give VA. I don't think there's an easy route to measure watts. (Don't have time now to do it anyway).

    For these shots I was running the scope uncalibrated to make the picture pretty. The unknown scale was the same for the Onan and Honda shots. I also saw in my notes that with the PD heavily loaded, adding a resistive load with the Honda drives its output down. With the Onan, adding a resistive load results in the PDs output going up, but even with the water heater running, the output with the Honda is higher.
  • Salvo's avatar
    Salvo
    Explorer
    Dec 13, 2013
    DryCamper11 wrote:

    I don't agree that the "current plots tell the story" or that a longer current pulse shows any kind of problem.

    Come on DC, you know better than that!

    AC voltage and current are in phase. If we determine the current pulse has a 3 ms width, then we know the voltage amplitude when current begins to flow. In this calculation I'm assuming the current pulse stops when voltage is at its peak. After the ac voltage hits its peak the diode bridge is back biased by the cap bank and no current flows. Now it's just simple math:

    Vac = V_CapBank_min = 170V*sin(w*t)
    We know
    w = 2*Pi*f
    t = 1/(4*60Hz) - current pulse width

    If the pulse width is 3 ms then t = 4.16ms - 3ms = 1.16ms

    When you do the math you'll find the cap bank starts conducting current at about 72V.

    The Honda may have a current pulse half that of the Onan, or about 1.5 ms. The means the minimum cap bank voltage is 143V.

    The cap bank drops to 72V when the Onan is used and the bank drops to 143V when the Honda is used. These calculations are as accurate as my eye can read the plots.



    The total energy extracted from the generator during each cycle is what we'd really like to know, since that's the energy the charger/converter is sending out its output (minus some efficiency losses). To get that power number, we'd need to consider the shape of the voltage waveform, as well as the current waveform.


    That sounds like what I did in my previous post. You got to realize, there's not much to work with. The voltage and current plots have no scale. Some assumptions need to be made. These are back of the envelope calculations. Nothing is fine tuned.

    Sal
  • DryCamper11's avatar
    DryCamper11
    Explorer
    Dec 13, 2013
    Salvo wrote:
    The current plots tell the story. The current pulse time for the Onan is almost twice as long as the Honda. That means the cap bank voltage drops a lot lower when powered by the Onan. Low cap bank voltage means converter goes out of regulation.

    Onan


    Honda EU2000i

    I don't agree that the "current plots tell the story" or that a longer current pulse shows any kind of problem. For example, a perfect converter/charger would have a power factor (PF) of unity and would draw current as soon as voltage rose above zero. An expensive PF corrected converter charger would have a sine wave shaped current pulse, producing the maximum possible width for each pulse.

    Of course, I'm not saying that the PD has power factor correction, nor that the PD and Onan MicroQuiet combination works as well or better than the EU. It's just that the width of the current pulse alone doesn't seem to tell us much, other than that the charger is taking energy from the gen over a longer period of time - something that is usually good.

    The total energy extracted from the generator during each cycle is what we'd really like to know, since that's the energy the charger/converter is sending out its output (minus some efficiency losses). To get that power number, we'd need to consider the shape of the voltage waveform, as well as the current waveform.
  • 64thunderbolt's avatar
    64thunderbolt
    Explorer II
    Dec 13, 2013
    Boy, I didn't think my simple question would turn into this. I'm out. Thanks everyone.
  • Wayne_Dohnal's avatar
    Wayne_Dohnal
    Explorer
    Dec 12, 2013
    did you use a Tek current probe?
    No, it's a CT that I was very careful calibrating and making sure there isn't distortion from saturation.
  • Salvo's avatar
    Salvo
    Explorer
    Dec 12, 2013
    Thanks for the link Wayne. The current plots tell the story. The current pulse time for the Onan is almost twice as long as the Honda. That means the cap bank voltage drops a lot lower when powered by the Onan. Low cap bank voltage means converter goes out of regulation.

    Still, even with the Honda, I'm not sure if we get 60A out of the PD, and for how long. Converter power must be transferred during the slim current pulse. We got about a 3 ms pulse. If the PD is supplying 60A at 14.0V then output power is 840W and 840W/.8 = 1050W on the input (ac) side. The average ac pulse current needed to supply 1050W is about:

    I = (T/t_pulse) * P_ac / V_ac
    I = 8ms/3ms * 1050W/150V = 19A

    The Honda is rated for 13A max.

    Edit:

    The Honda is rated for 13Arms, or 18.4Apk.

    The calculated 19A average could have a peak current 50% higher, or about 28Apk.

    Do you have any idea what the current scaling is?


    Onan


    Honda EU2000i

    Wayne, did you use a Tek current probe?

    Sal

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