High AC Voltage issue - looking for advice

jetskijumper

Hello,
I am new to the forum and just finished installing my grid tie system (in Mexico, not located in the US).

I am having an issue with high AC voltage from the utility company disconnecting my inverter.

I have a Xantrex GT 2.8 inverter and 12 Canadian Solar 240W panels. They are installed in Mexico, where AC voltage tends to run higher than in the US. In the winter it seems to be around 132-133v. I have already contacted the electric company and requested that they reduce, but they are not willing to right now.

My inverter is about 20 feet from my main service panel, and it is connected using #8 wire.

I have already adjusted the inverter up to it's maximum AC voltage tolerance of 135v. The inverter will stay on for a while, but when something in the house is used that has a big load (a handheld grinder that draws about 9 amps), the voltage sometimes fluxuates up to 134.2v and the inverter kicks offline.

Any ideas or tips you have would be very helpful.

Thank you

BB.

Re: High AC Voltage issue - looking for advice

At least one vendor (appears) to offer the ability to adjust above the typical 132/264 volt upper limit... Have you checked with Schneider/Xantrex/your utility what they can program the upper limit to and/or the utility will accept?

Your only other choice would be to use an autowound transformer/buck-boost/or even a variac/variable transformer.

You could put the transformer only on the GT inverter, or for your whole home.

What is the amperage rating(s) you would need, and is this "120 VAC" only or 120/240 VAC?

For smaller power requirements, a transformer may be the cheapest/quickest way to address the issue.

-Bill

niel

Re: High AC Voltage issue - looking for advice

yikes, with voltages that high you will be having premature failures on many of your appliances and the high voltages do tend to up the current drawn in some things so this artificially bumps up your wattage consumption too. if the transformer idea does not pan out it may be advantageous to go off grid at least partially if not fully.

NorthGuy

Re: High AC Voltage issue - looking for advice

You can use longer wire between the panel and inverter. Every extra 64 ft of #8 copper wire will drop about 1V at your max load (25A) or 0.36V for your grinder. Given enough wire, you can get a bigger drop. However, the longer wire will waste energy. That's why people try to make it short.

The problem with this is that under no load (or very little load) there will be no voltage drop at all. But if the problem only happens when some load is on, this might work.

That's not a great solution. I probably wouldn't do that myself. But it's very simple

waynefromnscanada

Re: High AC Voltage issue - looking for advice

NorthGuy wrote: »

You can use longer wire between the panel and inverter. Every extra 64 ft of #8 copper wire will drop about 1V at your max load (25A) or 0.36V for your grinder. Given enough wire, you can get a bigger drop. However, the longer wire will waste energy. That's why people try to make it short.

The problem with this is that under no load (or very little load) there will be no voltage drop at all. But if the problem only happens when some load is on, this might work.

That's not a great solution. I probably wouldn't do that myself. But it's very simple

Problem as I understand it is not excessive PV voltage, rather grossly excess GRID voltage, and it's that grid overvoltage that's killing his inverter.

NorthGuy

Re: High AC Voltage issue - looking for advice

waynefromnscanada wrote: »

Problem as I understand it is not excessive PV voltage, rather grossly excess GRID voltage, and it's that grid overvoltage that's killing his inverter.

Yes. I thought so too. I was talking about the wire between main service panel (not solar panel) and the inverter

jetskijumper

Re: High AC Voltage issue - looking for advice

Yes, I have already contacted Xantrex/Schneider and done the adjustment to the upper level of 135v on the inverter.

According to the specs of the inverter, the max output is under 12 amps, 240v. I guess I can look into the transformer solution. Is one type better than another? I would probably need to get one for just the inverter. I would assume it would be very expensive for a transformer to run my entire house.

I think I should only need 14 gauge wiring to connect the inverter to the main panel, so I was considering changing that in order to get a little bit of voltage drop.

I have read about possibly using ferrite cores on the ac wiring to help stabilize, what do you guys think about that option?

NorthGuy

Re: High AC Voltage issue - looking for advice

jetskijumper wrote: »

I think I should only need 14 gauge wiring to connect the inverter to the main panel, so I was considering changing that in order to get a little bit of voltage drop.

With 14 gauge wire you will only need 30 ft to drop 1V at 12 Amps. So, at your 20 feet (40 ft of wire), you'll be dropping about 1.3V at full load.

jetskijumper wrote: »

I have read about possibly using ferrite cores on the ac wiring to help stabilize, what do you guys think about that option?

That would filter out high frequency (e.g. radio frequency) if you have a noise. It will provide some reactance to drop voltage, but it's hard to quantify. However, inverter might not like it.

Is your grinder 120V? If so, all 9 Amps fall on one leg (say L1). If neutral is not stable, this may drop voltage between L1 and neutral by pulling neutral towards L1. As a result, the voltage between L2 and neutral may increase. This could create your problem, not the high voltage per se, because your voltage is normally below 135V.

jetskijumper

Re: High AC Voltage issue - looking for advice

Thanks for the help.
Yes, the grinder is 120v.

From what I understand, the inverter checks the voltage between L1 and neutral, and also between L2 and neutral.

You have a point about the neutral, how would I go about verifying if I have an unstable neutral and what could I do to solve or help the situation?

Thanks again.

BB.

Re: High AC Voltage issue - looking for advice

Note that "voltage drop" from the GT inverter is actually "voltage rise"... If you use too small of gauge of wire, that 1-2 volts will "add" to the high line and make it worse, not better.

I though that this was a 240 VAC inverter. Technically, they don't even need a neutral voltage reference, and it was only added a few years ago by UL as a requirement.

If your neutral is not balanced (once side reads 135 volts, and the other reads 110 volts), then you have some other problems. You could put a resistor divider from L1 to Neutral to L2 and generate a false neutral--But that may not be safe, and I don't know the current requirements of the voltage sense (it is probably not much, and you could use higher value resistors--That could be a work around).

The transformer becomes more of an issue--You need to adjust both L1 and L2 and relative to Neutral. So, a single autowound transformer may not work (perhaps a local electrician can help find you some cost effective transformer solution). But, again depending on your needs (just the GT inverter or the whole home), a pair of autowound transformers would not be the end of the world--But remember transformers have their own losses too.

-Bill

NorthGuy

Re: High AC Voltage issue - looking for advice

I would measure all voltages - between L1 and neutral and between L2 and neutral - both at the inverter and at the main service panel. I would do it with grinder on and with grinder off. This way you would see what is going on and what trips the inverter.

BB is right - adding wire between GT inverter and the service panel will not drop the voltage. My mistake. I didn't read your first post well and didn't see it was GT. Just was browsing "Off grid" forum and your post somehow came up. Sorry for the confusion.

waynefromnscanada

Re: High AC Voltage issue - looking for advice

BB. wrote: »

Note that "voltage drop" from the GT inverter is actually "voltage rise"... If you use too small of gauge of wire, that 1-2 volts will "add" to the high line and make it worse, not better.

-Bill

Exactly! If current was flowing from Grid to inverter, yes the voltage could be lowered at the inverter while current was flowing, but it's not flowing in that direction. It's flowing from inverter to grid, so the voltage at the inverter would end up being even higher as it tried to push current through the longer and/or smaller wire and out onto the grid.

NorthGuy

Re: High AC Voltage issue - looking for advice

waynefromnscanada wrote: »

Exactly! If current was flowing from Grid to inverter, yes the voltage could be lowered at the inverter while current was flowing, but it's not flowing in that direction. It's flowing from inverter to grid, so the voltage at the inverter would end up being even higher as it tried to push current through the longer and/or smaller wire and out onto the grid.

Yes. And the amount of rise wouldn't depend on loads, but rather would be proportional to solar production.

For some reason I thought he had an off-grid inverter with current going from the main panel to inverter and then from inverter to a sub panel where loads are connected. I guess I imagined this all out because the OP told that his grinder affected inverter, so I though the grinder was connected to the inverter.

BB.

Re: High AC Voltage issue - looking for advice

If you had a poor neutral connection (dirty/bad electrical connections, too small of neutral wire vs load, etc.)--A heavy 120VAC load (like a motor starting) can shift the neutral (drop a few volts on L1 with the load, and rise a few volts on the unloaded L2). If L1 to N and L2 to N are almost always identical (under heavy 120 VAC loads), then that is not your problem.

-Bill

NorthGuy

Re: High AC Voltage issue - looking for advice

BB. wrote: »

If you had a poor neutral connection (dirty/bad electrical connections, too small of neutral wire vs load, etc.)--A heavy 120VAC load (like a motor starting) can shift the neutral (drop a few volts on L1 with the load, and rise a few volts on the unloaded L2). If L1 to N and L2 to N are almost always identical (under heavy 120 VAC loads), then that is not your problem.

Could be quite significant. I have a barn, which is about 400 ft away and it is fed with USEB-2 cable with reduced neutral. When I turn on a 15A saw on L1, the lights, which are on L2 get significantly brighter. Could easily be 10V increase.

inetdog

Re: High AC Voltage issue - looking for advice

NorthGuy wrote: »

... and it is fed with USEB-2 cable with reduced neutral.

A reduced neutral is never a good idea when you have single-phase loads in a wye configuration or a simple single-phase 240/120 with 120 volt loads.

NorthGuy

Re: High AC Voltage issue - looking for advice

inetdog wrote: »

A reduced neutral is never a good idea when you have single-phase loads in a wye configuration or a simple single-phase 240/120 with 120 volt loads.

True. The only big load was a 240V heater, so I didn't need much of a neutral. It's gone now and almost no loads except lights. However, where you occasionally bring some power tools, it shows.

The OP's grinder is 9A load. May cause similar effects.