AC causing PV inverter to cycle into wait mode

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just instantaneous, you might want to check with your HVAC guy to see whether the unit - the AC that is - could benefit from a "start assist". If there currently isn't one on there, or it's just a PTC, or it's bad, it could be taking alot longer to start the compressor than it needs to - long enough that your inverter control sees it as a UT side voltage sag.
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Thank you. Maybe I can address this by addressing the AC unit. I will call the AC contractor who installed it and see if he will come out and assess the situation. Do you have any ballpark ideas what a start assist should cost to install if there is not one? Or what it should cost to replace one if it is bad? This is the first house I have had with central AC and I know very little about it. I do appreciate your help and advice.
It is 100 degrees today and the inverter is going into wait mode every time the AC kicks in. The default timeout for the inverter is 5 minutes and since it happens every 20 minutes, so I am losing 25% of my generation during peak hours (when I need it most).
thanks again,
doug
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When I worked out in The Marshall Islands 20 years ago, one of the computer rooms for a deep space radar had motor/generator sets equipped with large flywheels as a sort of UPS for the electronic equipment. I wonder if a setup like that could work as a surge buffer for starting an AC unit. Could be an interesting project.
[8~{} Uncle Monster
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examples. You should address the sag issue. Forget about the generation part of it when / if you complain to the electric company. They have a load device that replaces the meter temporarily, and the measure the drop when the load is applied. You'll want your inverter locked out while they are playing so as not to "help". Get someone to measure the voltage at the input to your main breaker with a fast recording meter. Look at how low it goes when you put the ~ 100 amp start load from your AC on it. If you go from say 240 to 215 volts for the instant, that would be a 10% drop - way too much for 1/2 load on a 200 amp service. The comment about 268 volts at night is interesting also. I'm thinking transformer issue. The primary side - at most utilities - is regulated within 2.5%. Mention the range you are seeing, and they'll likely put a logger out there, followed by a transformer replacement.
Is your transformer pole mounted or on the ground? If pole mounted, see if you can figure out how many houses are on it. Then look at the number on the side of it. 10, 15, 20, 25, 37.5, 50, etc. That is it's continuous capacity in Kva. 200 amps at 240 volts is 48 Kva. It's assumed that no-one is going to consume 200 amps at 240 continuously. The realistic number is something like 10% of that. The real issue is the total load on that transformer.
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Hi Bill,
It seems like there are $20 ones and ones costing a lot more ($110):
http://americanhvacparts.com/Merchant2/merchant.mvc?Screen=PROD&Product_Code ΚPS805A&Category_CodeΒ
This links shows one that will work with my Lennox h226-060 -- is it any good?

Yes, I'll get them out here to test the line -- I actually just happen to catch it on the inverter meter this morning. I was walking past it when the AC cycled on -- the voltage was low to start (222 VAC) and dropped to 209 momentarily. It then went back up to 221 after the AC cycle up.

Interesting point...about a year ago we lost one leg of our 240 and after several calls, they actually removed the transformer from the pole next to our house and installed a new transformer on a different pole further away from our house, so I probably have a drop line about twice as long as I had before. Because of how they jumpered everyone who was on the old transformer to the new transformer, it is hard to know how many houses it feeds. It is much smaller than the old one, but I assume that is a product of newer technology.
Thanks for all your help.
best,
doug
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Fantastic System!
Keep us informed when the solution is found.
On Sun, 2 Sep 2007 11:58:42 +1200, "Telstra"

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One possible solution (if no other fixes) might be to get a 10,000 BTU window A/C or two, then run these along with your central A/C fan on all the time.
This would keep your central A/C compressor from cycling on as often.
Window A/C units are quite inexpensive these days and very energy efficient.
Also I suppose you could place these units in the rooms you use the most during the day and/or one in your bedroom. Then turn the temp up on your central air, possibly turn central air totally off at night.
"old dirtbeard" wrote in message

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It is possible that the power company transformer size is marginal compared to the load of the neighborhood. You might try giving them a call and mentioning the voltage drop that you are getting. Also, power companies are known to cut back voltage during peak demands such as the summer. That may be a contributing factor. I would also contact the manufacturer of the inverter to see if the minimum voltage setting can be changed.
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Thank you John,
All great suggestions, thanks again. Edison changed out the transformer about a year ago when we lost one leg of the 240 -- I would have hoped that they put in one with "growth capacity," but who knows? I'll check on this one.
We definitely are suffering from low voltage (it dropped from 268 in the a.m. to 208 midday yesterday, so we are wattage challenged. Someone sent me the tech support number for SMA to check if I can alter the minimum voltage (I am told that it is a regulated issue and they probably will not be able to alter it.
Thanks again, John, I appreciate you feedback.
best,
doug
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old dirtbeard wrote:
...

268 is way too high. How and where are you measuring this? 208 is too low. Call your power company and have them put a recording voltmeter on the line for a few days. It sounds like they may have a problem somewhere.
Once the power company solves their issues, your problem may go away.
While I suspect that the cutout voltage on the inverter cannot be changed, I suspect that the 5 minute delay could be reduced without harm.
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The inverter has a digitial readout that monitors quite a few things including the wattage and VDC from the the panels as well at the line votage from the grid. I think it should be quite accurate.

Thanks -- I'll give them a call and see when they can come out.
best,
doug

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old dirtbeard wrote:

Hmmm. Your inverter may (or may not) be accurate for measuring the AC voltage at the inverter. Of course, where the power company is interested is at your service entrance. When your PV system is running, the voltage at the inverter will be a little higher than at the service entrance, and the voltage at the service entrance will be a little higher than if the PV system was not running. If there is a large difference between the voltage at the inverter and at the SE, then you have a problem on your side.
What you should do (probably before the power company comes out), is measure the voltage at the service entrance several times during the day, with a good meter, and with the PV system shut down, and record it. I suspect that the power company will insist that the PV system be shutdown while they are doing their measuring, so you might as well get your own estimate of what they will find.
You may find it useful to get an estimate of the difference that the PV system makes to the voltage. That can give you an estimate of the effective impedance of the transformer, service entrance cable, feeder cables, etc. all together.
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Ahh, that is the interesting thing about these grid-tie inverters. The inverter has to sync itself to the current line voltage and frequency supplied by the grid. By code, it has to match the line voltage.
On the DC side it will accept anything from 250-600 VDC, and when jumpered for 240 VAC, it will sync with any line voltage between 211 to 264 VAC. By code it cannot increase the line voltage. You are right, though, if the inverter is pumping out 25 amps, it probably will stop the air conditioner from further depressing the grid voltage by making up some of the shortfall.

Yes, I am sure they will want it disconnected. I have a good old Simpson 260 meter to do some tests with the array turned off. We have a DC-side disconnect and an AC-side disconnect for the inverter. When the utility folks have been out during the installation, they do not want to have anything to do with it. I think some of the folks at the utility see me as an unwelcome presence on their grid. :)
best,
doug
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old dirtbeard wrote:

Sort of; in theory. In reality, all electrical components: wires, transformers, etc. all have some non-zero resistance. If the voltage drop across the wire was exactly zero, the current in the wire would also be zero (Ohm's law), and your PV system would be doing exactly nothing. So the voltage at your inverter will never be exactly the same as at the service entrance if your PV system is operating.
How long is the wire from your inverter to the service entrance and what gauge wire is it?

I would suggest buying or borrowing a modern digital meter. The technology really has improved greatly, as has the price/performance.

I can understand their point of view. With any customer owned generation system you have potentially lethal voltages coming from an unexpected direction.

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It is only about two feet and is done in 10 gauge -- the inverter was mounted as closely as was possible in March by a professional PV firm.

Say it ain't so -- I love my old Simpson meter. I think it actually beats digital meters for monitoring flucuation rates and trends:
http://www.simpsonelectric.com/uploads/File/datasheets/2608.pdf
It is accurate within 2% for the entire scale -- it probably is better than I am. :)

That is one of the reasons why they have required "anti-islanding." If the inverter cannot sync on the grid frequency and voltage, it automatically disconnects from the grid. Which is what it is doing at this moment as we only have 202 grid VAC right now here on the Edison grid in Los Angeles. My panels are baking in the sun, but I cannot reconnect to the grid until the inverter sees at least 211 VAC. It is a pity -- I could be sending 25 amps out but it is 100 degrees right now and poor old Edison cannot meet the air conditioner demand. This is why many PV systems go with batteries, but that adds a great deal of additional cost, maintenance and complexity.We are in an extraordinary heat wave right now that is magnifying my other AC and grid problems I am having. I am fortunate to even have power right now given the current load on the grid.
The PV systems are just different than what the utility workmen typically see and they, of course, have no way of knowing if it was installed right, is anti-islanding, etc. I don't blame them.I had the old analog meter on the house for a month before they came out and installed the digital meter (it was not necessary as the old analog ones run forward and backwards, but I think they can read the digital meters remotely). They came out and said they had to change the meter as it would not run backwards (which it was and was recording the spin-down). It is just new for most of them.
Thank you,
doug

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old dirtbeard wrote:

Actually, according to your link, 3% of full scale (when the meter was new, if you read it very carefully). That means that if you are measring 240V, +/- 7.5V; if you are measuring 268, +/- 15V.

That seems too low. California ISO is not indicating a shortage now. ( http://www.caiso.com/outlook/outlook.html ) Maybe they have some local problems. 202 is low enough to cause problems for some motors and other equipment.

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You are right -- DMM's are accurate to .25% or better and that the 260 is only accurate to 2 or 3%). This is a question not a claim -- but isn't 3 percent of 240 is 7.2 V?
I also think Simpson is very conservative in their ratings because of who they supply. Right now I have the Simpson plugged in next to the inverter, and the readings from the 6 mos. old digital meter on the inverter and the 20 year-old Simpson are identical. I guess they both could be wrong exactly the same, but I do have a great deal of faith in that meter. I sent it in for calibration some years ago and it still was in spec.
I am not trying to get you to buy one, but when I worked for the railroad as a signalman -- installed and maintained the train signals and the crossing protection (gates at the crossings), we were issued 260's to test and calibrate the signals and gates. Human life depended on accurate readings. Technology has progressed, and I will not argue the point that DMM's are not more accurate, but I would like to believe that the 260 is accurate enough for me to read line voltage.

best,
doug
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I would ask the inverter manufacterer if they can modify the protection circuits to add a time delay so that it does not kick off line for a momentary problem...
Voltage dip during compressor startup is just a fact of life and the inverter should be designed to deal with it.
Mark
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old dirtbeard wrote:

percentage of full scale, not a percentage of the reading. So for 240 V you would use the 250 V scale. For 268 V you would use the 500 V scale with an accuracy of 15 V.

It all depends upon what you are trying to do. It probably is (or with careful use, can be) accurate enough for most uses.
I just noticed what appears to be a revision date "11/2/04" at the bottom of the spec sheet. Do they still make it?

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Yes, industrial supply houses like Grainger and MSC sell them. I think McMaster-Carr also:
http://www.grainger.com/Grainger/wwg/productIndex.shtml?originalValue=simpson&L2=Multimeters&operator=mfgRefinementSearch&L1=Simpson+Electric

Hand-made in the US, phenolic cases, they really are a joy to use.
best,
doug
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