PV Inverters

[George Stolz]

Re: PV Inverters

Originally posted by physis:

Some neutral current would be tickling the unused inverter

The Samtronix inverters that I use aren't ticklish.

If you have a motor and an open switch connected in series across outputs A and B what's happening that would involve the neutral?

I mean, a 120V load on inverter "A". When the neutral completes the circuit, wouldn't it tickle "B"'s neutral, kicking it on?

Both inverters would be on virtually all the time, it seems to me.

Edit: If the B output is used to make the 240 for the pump, and the pump switch is open, there is no circuit through the B inverter. No neutral concerns. Only the A output inverter is working.

Wouldn't that be the case if I breakered the panel only on the "A" phase?

In general, to keep one of his inverters "off" as he desires, I'd have to have a 120V-only panel, and then a small panel for his 240V concerns. Wouldn't I?

 

[physis]

Re: PV Inverters

Yes, the inverter might be working although there's no load on it. But just consider the output section. Think of it like a transformer where the DC input side is the primary and the output is the secondary. I'm not really trying to draw an analogy but it's close enough for understanding this.

If you can correctly answer the question:

Is there current flowing through the output section of inverter B when the pump isn't runnung?

Then I think you'll see what's happening.

 

[hurk27]

Re: PV Inverters

Sam
I'll be Darn

 

[physis]

Re: PV Inverters

For a PV system a real sine wave would be the only way I'd want to go. I think. I haven't really looked at how the systems are configured.

I opened the link but it was 120 somthing pages of PDF and my machine gets clogged up with the overhead from all that so I didn't look through it. But my calculator's telling me you'll need 16.36 volts at 100% efficiency to get 3600 watts from 220 amps. Maybe they're rated for an input voltage that you probably wont be using and that's what they base their figures on.

This is a fun topic (to me at least) but this is really just an application for a transformer. No need for any fancy or unusual stuff. I'm sure it would be much cheaper, more reliable and far simpler. All the basic engineering concerns.

 

[George Stolz]

Re: PV Inverters

Originally posted by physis:
If you can correctly answer the question:

Is there current flowing through the output section of inverter B when the pump isn't runnung?

Then I think you'll see what's happening.

Granted, the inverter is not producing current.

My understanding (which is small) is that the inverters activate when they sense a load to be served. Whenever an inverter is active, it will draw power to be ready to supply power.

This (magic) means to detect a load to be served seems as though it would be tricked by sensing "action" on the neutral.

My question is: If the goal is to have one of two inverters inactive until a 240V load needs power, this configuration will not do it. Right?

In addition, To attempt to achieve this, my "B" phase should be totally avoided to attempt to keep that inverter inactive, right?

For perspective, I am being made to install switches ahead of every GFI and proposed computer locations in the attempt to get the inverters shut down when not in use. This guy is obsessed with phantom currents.

 

[hurk27]

Re: PV Inverters

I believe George the best system would use a seperate 240 volt inverter sized just for the pump and keep all the 120 volt loads to the 120 volt inverter.

Here is one site I did some reading on and look at these inverters as they even sell the DR series as a entry level inverter. H'mmm?

Here's the link:
Southwest Photovoltaic

 

[physis]

Re: PV Inverters

This (magic) means to detect a load to be served seems as though it would be tricked by sensing "action" on the neutral

It would probably be done by looking for a minimum value of resistance across the output terminals. Any decent design would attempt to ignore everything that isn't exclusively associated with only the output terminals.

Edit: And there still isn't any current on the B inverter output for a sensor to see when there isn't a load connected. The fact that an output terminal of the inverter is connected to a cunductor that's carrying current doesn't mean that any of that current can flow through the inverter.

Think of one side of a light bulb filiment on the hot condutor feeding some load. The other end of the filiment goes nowhere. (Like the other output terminal of the inverter). The load's energized. Does the bulb light up? There's current going through the hot conductor. You're saying, "yeah, but Sam, the load sensing thing would be waaaaay more sensitive than trying to light this big ole filiment". Ok, so it's a matter of magnitude then. We just have to agrivate the filiment waaaaay more than the load sensor to make it light up. I'll let you put as much current through the hot conductor as you can find. You know you wont get the light bulb to glow. And it's not because there's not enough current going through the bulb. It's because there's no current going through the it.

My question is: If the goal is to have one of two inverters inactive until a 240V load needs power, this configuration will not do it. Right?

If the inverter's using load sensing it shouldn't be detecting a load unless there is one. If you assume that the Samtronix inverters have load sensing (that works) then this configuration will satisfy your inactive inverter requirement. If I change the schematic so the inverters say "load sensing stand by technology" everything should be fine.

In addition, To attempt to achieve this, my "B" phase should be totally avoided to attempt to keep that inverter inactive, right?

Well, if you don't want it to run you probably shouldn't make it turn on.

[ July 05, 2005, 05:56 AM: Message edited by: physis ]

 

[George Stolz]

Re: PV Inverters

Originally posted by physis:
Well, if you don't want it to run you probably shouldn't make it turn on.

So I guess I could still be dealing with a 120V system, despite the one 240V load. I'll try to keep my options open. Hope to see the PV guy today, maybe.

Thanks for the help guys. I'll try to bring my camera today, to get some pictures of the SIP panels.

 

[apauling]

Re: PV Inverters

Last night I read the stacking info on one of the sites and it said only for 120 volt operation on the bottom of the info. That indicates to me that it is only stacking and syncing the one sine wave,. and not producing 220v.

paul

 

[hurk27]

Re: PV Inverters

Paul go up to Ron's post and click on his link. The inverter in it has isolated sync cable that sync's the two together and they wire just like a transformer. The neutral from one goes to neutral of other and this becomes the new neutral.

P.S. the PDF file is 180 pages so I hope you have broad band.

[ July 06, 2005, 01:02 AM: Message edited by: hurk27 ]

 

[hurk27]

Re: PV Inverters

This is from the spec's of the DR inverter from my link:

Expandability offers more power. Load capacity can be doubled by "stacking" a second inverter, using a simple stacking cable kit (DRI). Connected in series, a pair of DR inverters produces both 120 and 240 VAC power - enough for tough household loads like deep well pumps or heavy power tools.

And can be read HERE

 

[physis]

Re: PV Inverters

By Wayne:

P.S. the PDF file is 180 pages so I hope you have broad band

I got 122 I think.

Even if you have DSL, I hope you run at a GHz or better and have a Gigabyte of memory to look at it with acrobat.

I might be wierd but I avoid PDF's because of the resources demand. A friend of mine really loves Adobe though. Go figure.

 

[hurk27]

Re: PV Inverters

DSL

I have cable through Comcast and they have brought us back up to 6mbs. I do have 1 GB mem but it is just 100mhz SDRAM and a slot1 Pentium @ 650mhz

But the trick is not the processor or mem, it's the video card.
128 MB DDR on-board ram 8x AGP

 

[physis]

Re: PV Inverters

Yeah, you're a little ahead of me in most departments but my video's only like 4 meg's, and the whole machine, not that it's very current, has to wait for the video card.

I got XP pro and some folks are surprised my machine can run it. ?

 

[hurk27]

Re: PV Inverters

Yep it's the video card
see when the video card runs out of mem the processor sends it to your ram when that runs out windows sends it to your hard drive that is filling in for lack of ram it called virtual memory. So your video starts running like your hard drive Sloooooow. So its kind of like a cascading effect. and the problem with older MB's is they don't support the newer video cards.

I don't think I'll build any more puters though as I can buy a Dell much cheaper and with there warranty you cant beat it.

 

[physis]

Re: PV Inverters

Yeah, I'm hep to how they work. And window's insistance on using a hard drive for memory. Cause it's such a pig. I know you can "sort of" control it's use of the hard drive, but unless you completely forbid it to use it it'll still pretty much do what it wants to. Fortunately though I do have a pretty fast hard drive.

And I have a good handle on what does and doesn't belong running in the background so I can fairly easily keep it running pretty lean. That's a huge factor in my opinion. Windows really is an untamed wild animal that needs to be kept in it's box by force. Not to mention the garbage that installs itself from the internet, friend and foe.

 

[George Stolz]

Re: PV Inverters

I'm confused (and the cryptic messages I get from the PV guy and homeowner don't help).

690.14(C)(1) seems to want the disconnect for inverted 120V power to be outside, like a service disconnect. But what do you do if the batteries, controller, inverter are in the house already? Run them outside to a disco and back in again?

As it is, the PV guy (or at least, his letters ) has stated that the only disconnect that he needs is for the conductors that enter the house from the panels (apparently for compliance with 690.13?)

That seems truly stupid to me, as when the fireman shows up for the fire (God forbid), and throws the disconnect on the wall to kill the house, both sides of the diconnect are hot, the lights are still on in the house, etc etc.

Oy vey.

 

[iwire]

Re: PV Inverters

Originally posted by georgestolz:
That seems truly stupid to me, as when the fireman shows up for the fire (God forbid), and throws the disconnect on the wall to kill the house, both sides of the diconnect are hot, the lights are still on in the house, etc etc.

Oy vey.

George this is something I often think about in the buildings we work.

In a large multi tenant building it is not surprising to find 1/2 dozen generators each owned by various tenants and a generator owned by the building.

Sure go ahead kill the service disconnect, instantly you have a bunch of UPS systems kicking in, seconds after that all the gensets come on line.

Good luck really killing the power. :roll:

 

[hurk27]

Re: PV Inverters

But what do you do if the batteries, controller, inverter are in the house already? Run them outside to a disco and back in again?

I hope these battery's are well ventilated. I would not want wet cells in my house anywhere! We had a boat explode once because of the hull vent blower quit working and there was no alarm on it. Luckily nobody was aboard.

 

[George Stolz]

Re: PV Inverters

Wayne, did I recall you having some sort of nice fan in your van? I think a 12V fan or two would be safer than relying on his inverter.

Oh, I had an epiphany about the evil phantom currents yesterday: AFCI breakers probably draw a phantom current!

I put them on a dedicated home run; when we leave the house, they will be energized. I'm thinking about having him sign something, or something. I've done the right thing, haven't I?

Batteries:

Actually, the h/o had a similar experience on a smaller scale: He had a solar setup in his barn that he had thrown together. Since the place was in BFE, he hadn't been out there in months, and finally came back up for the day.

He figured that since he hadn't maintained the system in several months, the batteries were probably dead.

So he opened the lid on his well-sealed battery box, and bent over to test the voltage with a multimeter. As the touched the posts on the battery, he heard a small arc, and thought to himself "Oh, good, the batteries are still charged."

By the time that thought crossed his mind, the battery exploded, breaking his glasses and covering his face in battery acid.

It knocked the hat off his wife, sitting behind him about 10' away. He said it sounded like "two shotguns going off at the same time."