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Hybrid vs. OffGrid
#11
I was searching through my previous posts as this question arrose previously and I did a chart to show what I was trying to explain. The issue mainly has an impact on syncronous or inductive equipment (transformers / motors / compressors) and a lot of other equipment is just exposed to high voltage transients caused by the disconnection (when you disconnect a coil/inductor the coil generates a back EMF spike). With a lot plugged in the voltage spikes are absorbed and may have no issue.

Imagine switching a single phase over to another single phase supply which is 180 degrees out of sync, i.e. switching from +220V to -220V. With the ATS switching from grid to inverter output regardless of timing / syncronisation. Ideal would be to have the ATS switch only when the two grids are in alignment (zero voltage difference between live) as this would at least then just appear as a transient outage the same as occurs on the grid when switching at times.

Agree the UPS option is a brilliant way to fence off and safeguard expensive kit, I went that route and still put things behind a UPS if I'm in doubt but that is typically for short durations while I'm playing trying not to burn the house down, lol.

Just some thoughts.
If you can't quantify how much they cost, it's a deal, I'll buy 5 of them for 3 lumps of rocking horse ......
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#12
(10-17-2019, 06:50 PM)completelycharged Wrote: I was searching through my previous posts as this question arrose previously and I did a chart to show what I was trying to explain. The issue mainly has an impact on syncronous or inductive equipment (transformers / motors / compressors) and a lot of other equipment is just exposed to high voltage transients caused by the disconnection (when you disconnect a coil/inductor the coil generates a back EMF spike). With a lot plugged in the voltage spikes are absorbed and may have no issue.

Imagine switching a single phase over to another single phase supply which is 180 degrees out of sync, i.e. switching from +220V to -220V. With the ATS switching from grid to inverter output regardless of timing / syncronisation. Ideal would be to have the ATS switch only when the two grids are in alignment (zero voltage difference between live) as this would at least then just appear as a transient outage the same as occurs on the grid when switching at times.

Agree the UPS option is a brilliant way to fence off and safeguard expensive kit, I went that route and still put things behind a UPS if I'm in doubt but that is typically for short durations while I'm playing trying not to burn the house down, lol.

Just some thoughts.

I've been reading and I now see what you are talking about.   Even single phase US - the single phase could be out of sync / directly opposite in the wave form. I had read previously that it would not hurt motors, but deeper reading today says that's a myth.. (don't believe what you read on internet). Its also a matter of the motor (power) size and design as to how at risk it is.

 The ATS(s) I'm using have a printed circuit boards with mechanical relays - so maybe they are smart enough to do some syncing and that's why I haven't had problems (i.e. dumb luck in buying a good ATS).   In any case, I've put a direct questions to the manufacturers and will try to get to the bottom of this in my case.     

Thank you!
completelycharged likes this post
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#13
I use Progressive Dynamics and Go-Power ATSs.

Here's a question/answer from Progressive Dynamics:
Question: I'm in a discussion that using automatic transfer switch between grid and inverter can cause my refrigerator motor to burn out during switch over because of out-of-sync 60hz wave from (from grid to inverter power) causing inductive load on the motor. Does your electronics match the wave form to avoid this? or is this true?

Answer:
From: Tech Support [mailto:techsupport@gpelectric.com]
Sent: Thursday, October 17, 2019 1:17 PM
Cc: Tech Support
Subject: RE: Tech Support Notification #GP00049023

Hi,

Thank you for your inquiry.

I have never come across a situation where this would be the case. If it was I am sure I would have heard about it before now

There is usually a delay before the switch, but there is no frequency matching hardware involved.

Regards, Bob
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#14
https://www.thebackshed.com/forum/ViewTo...280#121280
3rd chart, yellow trace.
!!! Important to note that the crossover was at zero volts !!!!!


If your interested in inverter behaviour and building the whole thread is worth reading.
If you can't quantify how much they cost, it's a deal, I'll buy 5 of them for 3 lumps of rocking horse ......
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#15
Take a look at this video for a close up of what happens when your ATS switches mid wave

https://youtu.be/fZhznwksiLA
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#16
The youtube was targeted to MPPSolar which appears to 'sync' the wave form. So it doesn't answer the non-sync case specifically.

After this excellent discussion I get the concern. The Progressive Dynamics ATS technical answer verified that they are *not* doing any wave form matching - but they also report that they have not heard of any issues. The articles I read today on ATS motor generated transient (surge) all say 'large motor' but hey don't specify large. For example, my:
- 50gallon Hybrid Hot Water Heater - is 240v and draws between 380 and 450watts. Small motor?
- Refigerators (2 of them) each draw 2-3a @ 120v = 360w. Small motor?
- Furnace Fan draws 6a @ 120v = 720w. Medium motor?
- Portable AC draws 11a @ 120v = 1320w. Medium motor?
- Next year - adding the AC compressor which draws 22a @ 240v = 5280w. Maybe this will meet the definition of a large motor?

Sometimes there are perfectly valid concerns but the fact details may be too specific to be taken as a general rule. I want to know more about the definition of a 'large motor' and perhaps they types of motors. Perhaps my newer appliances are not as susceptible as older models or something.

However, for me, things are working great and I'm nearing 700 switch overs... so I will continue operations and continue to research/learn about this. The AC compressor is interesting as it may actually be in the range of a 'large motor' and I will watch that very carefully.
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