[RE-wrenches] Magnum inverters (not really a power factor issue)

[boB Gudgel]

Matt Tritt wrote:
> The next time I'm up there I'll take another tech with me, plenty of 
> meters and go through every DC and AC connection (they all looked good 
> first time around) to try and get to the bottom of the problem prior 
> to taking a harder look at Magnum. I have to say, though, that I have 
> heard a couple of comments that tend to suggest that the inverter 
> might turn out to be one logical place to look. I like these inverters 
> a lot, and I really hope that we find some other issue.
The inverter is always something to look at.  An installer should always 
carry a decent meter, (Fluke or otherwise), and maybe a clamp-Ammeter
with them when trying to troubleshoot. Some Flukes can be set to read 
the minimum and maximum voltage, so that might also help to check surges 
with.

The Magnum inverter might sag for a moment under a load surge, but its 
voltage will regulate back to normal voltage in a second, or 2 or 3...  
So, if it was
a voltage sag, it would be within range again, momentarily and I would 
expect the pump to start again.   What kind of pump is this again ?  Could
it have some kind of lock-out circuit to keep it from burning up or 
something ?


>
> To replay the symptoms, there is no audible or visual (as in motor 
> starter noises or dimming light) indication that the pump is 
> attempting to do anything other than sit there when inverter voltage 
> is connected to it.
I agree that it isn't trying to start. Light dimming you would probably 
see.  But I wouldn't expect you to actually hear
a submersible pump buried deep in the ground ? 

I still haven't heard, Matt, if the generator is connected in the normal 
way and passes ~through~ the Magnum internal relay and output L1 and L2 
or not.
Is there a separate circuit ?  If the generator (which makes the pump 
work) does not pass through the Magnum inverter, then I would suspect a
bad connection after the inverter output, going to the pump wires.

If the generator is running through the inverter when the generator runs 
the pump, then all of that AC wiring would be verified as working fine.

> When the genny power is applied, there is a discernable working under 
> a load sound from the engine, and the pump works.
These high frequency inverters ~can~ be dead silent, and often are.  A 
generator engine would be a different thing.  If the generator engine
changes when the pump starts, then its output voltage and/or frequency 
is probably changing too ?


> I only had the homeowner's lousy dime store anaglog meter to work 
> with, but the voltage from the inverter was right on 120 volts per 
> leg. When I checked phase to phase I also only got 120 - that's kind 
> of weird, but it might simply be the meter.
Well, 120VAC, L1 to neutral and  120VAC L2 to neutral would be 
correct.   240Vac L1 to L2.


> All the household loads run flawlessly (but this is a pretty 
> fundamental cabin, so the TV and DVD player are the most exotic things 
> plugged in. The run to the pump is adequately sized - - - - - in other 
> words, it all seems run of the mill, except that the pump only ran 
> successfully one time and not on any further attempts. Golly..
>
 The Magnum inverter, although it might not be the fastest surge, has a 
very good waveform. A 3/4 HP pump should be
a piece of cake for it.

Golly is right !


AND Darryl Thayer said:

>>BoB are you saying that wires that are so fat and really not very long less than 10 feet can have significant inductance?  >>I thought that inductance was from small wires wrapped into coils?  

All cables have inductance.  Even big fat 10 foot battery cables.
We see L-C resonance (from battery cables) all the time when designing inverters,
choosing capacitor sizes, etc... This is why you want to keep the positive and negative
battery cables as close to each other as possible.  Inductance can also cause the sine-wave
waveform to distort under high current loads.


>>Anyhow I thought the problem was battery internal resistance, and the building of the sine wave from pulses caused the >>problem..  I have seen battery breakers (thermal type) trip at lower current when feeding a pulse load.  To supply a 1000 >>watts it takes and average current of 80 amps at 12 volts, If that is supplied by a repeating half sine wave, it requires >>a peak current of 112 amps.  If the sine wave building pulses have a 50% duty cycle, the current could be as high as 224 >>amps peak.  

There are all sort of weird things that can happen for sure !


>In Larry's case the simple inverter that takes only big pulses, the peak current for the  1000 watt load is only 80 amps.  >(much easier on the battery.)
>Darryl      


A battery can make a great filter,  and it's best when it's REAL close 
(electrically) to the batteries, but battery impedance is
higher at higher ripple frequencies, and the the AC load can reflect 
itself back to the battery so a capacitor is sometimes a good
addition.   There ~should~ be enough capacitance built into the inverter 
itself, BUT, the inverter manufacturer has to assume
that the battery cables are only so long.  SOME inverters, like the old 
Statpower Pro-Sine do not have this problem so much.

boB