Building Reserve and Using KWH

[DanS26]

Bruce you said you keep a couple of Fronius 7.5 inverters as backups. I found a Sunpower badged Fronius 7.5 inverter on E-bay recently and went for it cheap. It came new in box both top and bottom unit absolutely spotless. Since Sunpower panels are/used to be positive ground I was a little concerned about the internal wiring in the Fronius inverter. But lo and behold it was still wired for negative ground. So into my parts supply area it went. Sometimes you just get lucky. I'll rip that Sunpower badge off if and when I have to hang it on the wall.

But I do have a concern about the shelf life of the capacitors in this unit. My understanding that these electrolyte capacitors have an 8 to 10 year shelf life is left unused. Does this concern you?

[bcroe]

Bruce you said you keep a couple of Fronius 7.5 inverters as backups. I found a Sunpower badged Fronius 7.5 inverter on E-bay recently and went for it cheap. It came new in box both top and bottom unit absolutely spotless. Since Sunpower panels are/used to be positive ground I was a little concerned about the internal wiring in the Fronius inverter. But lo and behold it was still wired for negative ground.

But I do have a concern about the shelf life of the capacitors in this unit. My understanding that these electrolyte capacitors have an 8 to 10 year shelf life is left unused. Does this concern you?

I had not considered the issue of positive ground operation. That might affect the wiring of the
1 GFI fuse on the Fronius, I have no idea how the inverter makes that change. Guess my array
would not care if it was turned upside down.

The backups are labeled SUN POWER, and I can see some differences. They have a
disconnect switch coming out the bottom, not on my originals at that position. Perhaps I
should investigate more, even try running them one day. At least, I should not need to do
any high line voltage setup, the PoCo has tamed it and local increase is quite small.

I believe the inverters I bought were newer than mine, still sealed in the box. In operation a
switcher is really tough on the caps in the power conversion switching section, big currents
flowing in and out at the conversion frequency. Have seen that in many constructs here. That
is why some caps are rated for very low ESR. My Fronius are into their 8th year, running flat
out clipping all day long whenever the sun shines, they each draw the line at 100W more than
their rating. And at least keeping busy under clouds. So they have survived very well, but I
presume they may have aged a lot more than the ones sitting quietly on the shelf.

When they do fail, I will no longer hesitate to pull them apart and see if DIY repairs are possible.
My hope is to replace all hard stressed caps, being prepared to do the same later for the ones
on line. Could be the failure will damage beyond repair. Meanwhile, I have one backup inverter
mounted close by, all I need to do is move over the power wiring (conduit already connected) to
put it in service.

Meanwhile we are FINALLY seeing a run of pretty much sunny days, a dozen more this month
might set a record KWH reserve heading into winter. A bit over 100 KWH today under just a
bit of clouding. Reserve is helped a bit by my more efficient AC power wiring, only 1% loss
around a 600 foot loop. My DC losses are more than that at peak, but it does not matter since
the inverters are clipping anyway. At reduced (cloudy) levels, the percentage wiring loss declines
for both. Bruce Roe

[Mike90250]

Capacitor shelf life
As long as they are well manufactured and stay hermetically sealed, they should have a 30+ year shelf life. But if supplied by the lowest bidder.......
Operating life is dependent on Voltage % of max voltage and temperature, well designed gear should run at least 10 years, maybe more. My XW just hit 10 years, and I have a spare in box ready to go.

Capacitor forming. used to be needed with old aluminum paste caps, started off at a low voltage, and slowly ramped up over a period of hours to re-form the oxide layer that insulates the foils. Modern ones don't need it for a couple years. Might not be a bad idea to fire up the inverter, applying the DC voltage over a period of a couple minutes, and let it idle for half an hour before you pack it away for several more years.

[DanS26]

I called Fronius awhile back about their SunPower badged inverters. Talked to a knowledgeable tech.....he said that the upper units are exactly the same as all similar rated inverters. The bottoms are usually wired for negative ground and are normally converted to positive ground at the field location for SunPower panel installations. The only real difference is the operator/installation manual put in the box to guide installers on how to wire for positive ground. Some factory orders will specify positive ground be made before leaving the factory but that specification only affects the bottom unit.

I found negative ground in the box so I have confidence that the unit will work when needed and without modification but I will probably only need the top unit anyhow..........if the capacitors are still good......

[DanS26]

...............When they do fail, I will no longer hesitate to pull them apart and see if DIY repairs are possible.
My hope is to replace all hard stressed caps, being prepared to do the same later for the ones
on line. Could be the failure will damage beyond repair. Meanwhile, I have one backup inverter
mounted close by, all I need to do is move over the power wiring (conduit already connected) to
put it in service...........

I couldn't help myself and opened up that big upper transformer box a few months ago just to see what was inside. Lots of big caps that I don't think one would want to short with screwdriver before removing. Bleeding those big boys off with a resister would make a lot of sense.

IMO very beautiful engineering inside.....I especially liked the active cooling design.

[bcroe]

I couldn't help myself and opened up that big upper transformer box a few months ago just to see what was inside. Lots of big caps that I don't think one would want to short with screwdriver before removing. Bleeding those big boys off with a resister would make a lot of sense.

IMO very beautiful engineering inside.....I especially liked the active cooling design.

So, show us the pictures. Does it hinge open just like the bottom section? Bruce Roe

[Mike90250]

Generally, those big caps, are on the battery wiring, and the controller internals bleed residual voltage down in half an hour, which is why inverter cables spark at initial hook-up.

Being cautious is good, a 60W incandescent light bulb should bleed them in a timely manner

[bcroe]

Being cautious is good, a 60W incandescent light bulb should bleed them in a timely manner

Incandescents are more efficient bleeders, because the resistance drops as they cool
for near constant current. For our 400VDC stuff you might need this. Bruce Roe


PVtestLt.JPG

[DanS26]

So, show us the pictures. Does it hinge open just like the bottom section? Bruce Roe

Here's a peek inside......dual MPPT.....hinge on side.


IMG_0684.JPG

[bcroe]

. Here's a peek inside......dual MPPT.....hinge on side.

That looks great, I went and opened the cover of my unpowered standby Fronius for the
first time, and it looks just like that. Apparently 2 inverters the same size, I knew they
shut one down to increase efficiency for light loading. The whole thing made possible by
the development of the microprocessor (control) and power MOSFET transistors (muscle),
not to mention economical solar panels. I had used them and IGFETs, but now I guess
silicon carbide transistors or the like have taken over.

Just amazing how something that light and cool running can handle that much power.

I looked at the bottom section, looks like the fuses are connected to the plus red leads, so
I guess that means it is set for negative ground. I think this one came with fuses, my
originals had shorting slugs. Bruce Roe

[bcroe]

. A non vented electric clothes drier would be the
other item, except they are pretty small. Bruce Roe

Today I see a 7.4 cu ft heat pump hybrid unvented electric clothes dryer, seriously considering
getting one. There have been small unvented ones, but this one is full sized. I always hated
blowing all that heat outside, and the vent leaks plenty of air the rest of the time. Whirlpool.
Bruce Roe

[bcroe]

I was wondering if anyone knew, how many revolutions of a spinning disc meter, equal one KWH?
My estimate is somewhere around 150 revolutions. I see a lot of calibration marks on the disc,
wonder if they serve for factory calibration? Bruce Roe

[J.P.M.]

I was wondering if anyone knew, how many revolutions of a spinning disc meter, equal one KWH?
My estimate is somewhere around 150 revolutions. I see a lot of calibration marks on the disc,
wonder if they serve for factory calibration? Bruce Roe

You're going to make me dig into my archives/notes. As I recall, there was a meter constant in the lower right side of the old dial meters that was used to find what you're looking for. Using that and a stop watch was a good way for me to get definitional info on steady state draw for appliances/HVAC equipment and even kill-a-watt meter comparisons. The numbers seemed to work out and make sense.
I'll root around and see what I can find. Give me a day or so.

As I seem to recall, my old rotary meter constant was 7.2 which meant that 7.2 Watt-hours of energy have been expended for each complete dial revolution - at least when it got manufactured. Your meter may have a similar constant. I believe the meter constants are often printed in the lower left (~ 4 o'clock) position of most of the old rotary meters. 7.2 is a common one for old G./E. meters but they vary a lot. I usually used 100 revs to measure appliance usage and did the measurement several times. The method seems good for steady state operation but is mostly useless for guessing at startup transients or power factor penalties.

For my steady state energy appliance use estimation, I checked the difference in dial rotation speeds/times with most everything in the house off at the circuit breakers, particularly cyclic appliances like fridges and measured the difference in rotation times 100 disk revs with a stopwatch when various "semi" known things got turned on like a 100 W incandescent bulb, a spot heater w/ 3 range settings, etc. and got numbers that seemed to make sense.

For things like the A/C w/ 2 electricity draws, I figured out the compressor and air handler drew a total of something like ~ 6,000 W at steady state conditions but, as I implied above, I don't have my notes handy. Anyway, I checked the air handler w/a kill-a-watt meter at 842 running watts. I have that because I had to replace the air handler motor a couple of years ago and I have a dedicated kill-a-watt meter on the blower it to record approx. A/C system run time.

[bcroe]

. As I seem to recall, my old rotary meter constant was 7.2 which meant that 7.2 Watt-hours of energy have been expended for each complete dial revolution - at least when it got manufactured. Your meter may have a similar constant. I believe the meter constants are often printed in the lower left (~ 4 o'clock) position of most of the old rotary meters. 7.2 is a common one for old G./E. meters but they vary a lot.

For my steady state energy appliance use estimation, I checked the difference in dial rotation speeds/times with most everything in the house off at the circuit breakers, particularly cyclic appliances like fridges and measured the difference in rotation times 100 disk revs with a stopwatch when various "semi" known things got turned on like a 100 W incandescent bulb, a spot heater w/ 3 range settings, etc. and got numbers that seemed to make sense.

That is what I needed, thanks. I see my Sangamo meter (originally used on this 70s house)
has a 7.2 at 4 o'clock position, which would equal 138.88.. revolutions per KWH. My best
estimate had been 144, but not done with great precision. 138.88 would correspond to 35 rpm
(really honking!) when the array peaks and nothing else runs, just about what was observed.

I have also done the stop watch thing, but also used the Kill-A-Watt meter for totals on cycling
stuff (fridge). Have also wired a disc meter in series with a double breaker output for 240VAC
stuff. With several disc meters here from varied sources, guess I now have the means to check
them out. Bruce Roe
ENEmeter.png

[J.P.M.]

That is what I needed, thanks. I see my Sangamo meter (originally used on this 70s house)
has a 7.2 at 4 o'clock position, which would equal 138.88.. revolutions per KWH. My best
estimate had been 144, but not done with great precision. 138.88 would correspond to 35 rpm
(really honking!) when the array peaks and nothing else runs, just about what was observed.

I have also done the stop watch thing, but also used the Kill-A-Watt meter for totals on cycling
stuff (fridge). Have also wired a disc meter in series with a double breaker output for 240VAC
stuff. With several disc meters here from varied sources, guess I now have the means to check
them out. Bruce Roe
ENEmeter.png

You're at least most welcome.

Unless you advise you need more info, I'll cancel my walk down memory lane with my notes.

Respectfully,