AVR vs. Hybrid Inverter

[SunshineHarvey7]

Hi again. One of my friends is technically on-grid, but his voltage drops from 220v to 180v with a load of only 5 amps! Am I calculating right that that is an 8-ohm impedance on the line coming from the light-meter (1km away!)? (Not sure if I have my terms right here.)

 

A local electrician says he'll install an Automatic Voltage Regulator (AVR) for 10,000THB. Sounds tantalizing, but I told my friend I don't think this is a good solution. If they try to draw 10 amps, the incoming voltage to the AVR is going to drop to around 140V, and I don't know what the input range is for it (haven't seen any pics or specs on it). Above 10 amps seems even more dubious. Are these doubts well-founded?

 

FWIW, in the short time these friends have occupied their new property, their electric bills show they have averaged under 15 units / KWH per day (not surprising considering that the lights start to flicker if loads exceed ~8 amps). That says to me, their average load over a 24h time is less than 625 watts. I don't think their peak loads have exceeded 2500 watts, although I'd be surprised if they achieved that (but I'm sure they would like to be able to). In other words, whatever kind of power supply they have, it needs to handle peak demands of 2 to 5kw.

 

Without supplemental solar power, I can't recommend that they exceed an average load of 1100-1500 watts (5 to 7 amps @ 220V), but we are aiming for a system that will use solar panels to eventually supply much if not all of their needs.
 

At the present time, I'm thinking they should consider starting with a system that is comprised of:

1. A 5kw hybrid inverter, one that can be set to limit incoming AC charging current to 10 amps or under. The brand-name inverters I've looked at so far (Suoer, Sofar) seem to allow such a limit. (Cost: ~17,000ThB?)
2. LiFePO4 batteries set up in 48V strings with each string having a BMS, sufficient to provide at least 9-10KWH of storage. (If I've calculated correctly, that could be achieved by the equivalent of two 48-volt 100AH LifePO4 batteries. (Cost: ~25,000THB?)

 

As my friends have funds to do so, they could add solar panels to max out the above hybrid inverter's PV input. Before adding the panels, at least the basic setup above should provide them a consistent 220V, rather than experiencing voltage drops to 180V, 150V, etc. And this system should maintain voltage as long as their usage doesn't exceed the inverter's ability to keep the batteries charged.

 

Does this make sense?

 

This is a very expensive way to achieve voltage regulation (~42,000), but is there a better way, especially that offers the option of also utilizing solar?

[Crossy]

How do you anticipate hooking this up as I'm not sure the on-grid hybrids will work like that. Support at Sofar are very good so it may be an idea to email them and run your ideas by them. Do send diagrams as obviously english is not their first language.

 

The off-grid hybrids may be a better choice as they will run the load from solar or battery with the mains as a backup charger when the solar is low (the inverters are cheaper too).

 

The AVR probably isn't going to cut it to be honest.

 

Has anybody looked at putting a bigger cable from the meter (what size is the current cable)? Have any measurements of volt-drop been made at the meter itself? If the voltage is good there a bigger cable could well be the most economical solution. 

 

[Crossy]

It is important to understand that "hybrid" inverters come in a couple of flavours.

 

The cheaper units are basically a mains battery charger, battery and off-grid inverter. The inverter powers the load using a combination of solar and battery power with the mains charging the battery when solar isn't available and the battery is low. There's usually a bypass to allow the load to operate directly off the mains.

 

The more expensive units add a grid-tie facility to the above which can then push excess solar into the grid and offset the bill.

 

In this instance I think the first option is going to be your solution (I suspect this is what you were suggesting in your original post).

 

EDIT Something like this I think is what you are looking at 

 

https://www.lazada.co.th/products/suoer-inverter-off-grid-hybrid-5kva-48v-4000v-mppt-charge-80a-i1643966486-s4549270369.html

 

You should be able to get the manual off the net to check it does everything you want.

 

If you end up needing more solar then nothing to stop you adding more panels and another MPPT controller to charge the batteries in parallel with the inverter charger.

 

[SunshineHarvey7]

52 minutes ago, Crossy said:

It is important to understand that "hybrid" inverters come in a couple of flavours.

 

The cheaper units are basically a mains battery charger, battery and off-grid inverter. The inverter powers the load using a combination of solar and battery power with the mains charging the battery when solar isn't available and the battery is low. There's usually a bypass to allow the load to operate directly off the mains.

 

The more expensive units add a grid-tie facility to the above which can then push excess solar into the grid and offset the bill.

 

In this instance I think the first option is going to be your solution (I suspect this is what you were suggesting in your original post).

 

EDIT Something like this I think is what you are looking at 

 

https://www.lazada.co.th/products/suoer-inverter-off-grid-hybrid-5kva-48v-4000v-mppt-charge-80a-i1643966486-s4549270369.html

Yes, Crossy, you guessed correctly. I am not aiming to feed anything back into the grid... Just want to charge the batteries when the panels can't keep up with the needs. Due to the severe voltage drop, I don't anticipate ever passing the grid power straight through.

 

There is no significant voltage drop at the meter, and I appreciate your recommendation to look into bigger wire from the meter. I must do that. I'll be looking for an online calculator to help recommend a gauge. I'm not sure if I'll be able to figure out the existing wire gauge (as I'm sure the existing writing has long since faded).

 

Regarding manuals for Suoer & Sofar inverters, it didn't seem like either manufacturer had their manual online. I can do some more hunting...

[Crossy]

Doncaster cables have a good online calculator https://www.doncastercables.com/technical-help/ it's optimised for copper so just go one size bigger for aluminium. I recommend Al cable as it a lot cheaper and less likely to wander off in the night.

 

For an example 1km at 15A and 5% volt drop is looking at 95mm² THW-A cable. To compare with what's there already this cable will be about 17mm in overall diameter.

 

You will need a specialist supplier for long lengths of larger cables.

 

I have found both Sofar and Suoer manuals on the manufacturer's websites.

[SunshineHarvey7]

1 hour ago, Crossy said:

Has anybody looked at putting a bigger cable from the meter (what size is the current cable)? Have any measurements of volt-drop been made at the meter itself? If the voltage is good there a bigger cable could well be the most economical solution. 

I found a very handy wire gauge calculator here to recommend a size given all the factors. And there's another one here that tells me what voltage drop I could expect if I tell it what size wire I'm using. Based on those calculators, I am realizing the gauge of the feed must be a much smaller gauge than I thought (maybe not bigger than 6mm²). I just arrived at the property so I'll check. Will try to keep you updated. Yes, upgrading the wire may be the most economical solution.

[SunshineHarvey7]

22 hours ago, Crossy said:

Has anybody looked at putting a bigger cable from the meter (what size is the current cable)? Have any measurements of volt-drop been made at the meter itself? If the voltage is good there a bigger cable could well be the most economical solution.

 

The cable that terminates the 1000-meter run at the knife breaker at the corner of the property is sized at 25mm². I called PEA, and that is the size they recommend, based on using a 15(45) light meter. The cable has marking on it like this:

 

 

However, at the light meter, it is not the same cable (as there were many splices along the 1000-meter run, and the marking on the cable is unintelligible, but another cable that appears to be the same size looks like this: 

 

 

Question: Could one brand of aluminum cable that is marked 25 SQ MM (in English) be the same size as another cable that is marked 2 x 6 (followed by Thai annotation)? It's still 1 conductor (not 2), so does that mean a bundle of 6 wires, each of which is 2mm²?

 

Passing back and forth along the 1km stretch between the light meter and the property, I've observed that the wire does change sizes, and it appears that the majority of the run is with a smaller gauge. Since I don't have a tall ladder, I can't get up and check the wire size, but I agree, @Crossy, probably the best solution is to replace with a consistent 25 sq mm the whole way, with as little splices as possible.

 

FWIW, the voltage at the pole/meter stays between 225-230V. The supply voltage at our main breaker (if it's open) also reads about the same, but if we close the breaker and have any sort of load on it, the voltage varies from 215V (minimal load) down to 150V or below.

 

I think we're on to pricing wire and finding an electrician for a quote on replacing it.

[Crossy]

38 minutes ago, SunshineHarvey7 said:

consistent 25 sq mm

 

25mm² Al is about 1.2 ohm per km, so 2.4 ohms round-trip. That would drop 24V at 10A, if that's acceptable then go for it, however I'd be going for at least 35 or 50mm² Al as a minimum. You really don't want to get the cable up and find that things are still unacceptable.

 

Make sure your contractor uses the correct aluminium joiners with the right type of sleeve. It will need a smaller copper pigtail on each end so it will fit in the meter and distribution board.

 

It's certainly worth speaking to PEA, they obviously have the correct kit (a km of poles using a cherry-picker or two is far less hassle than using bamboo ladders) and can supply the cable and many crews are available for a spot of moonlighting.

 

2x6 is two separate 6mm² conductors (the Thai says "sq-mm").

 

It really does look like the original cable is something of a bitsa, every splice is a bit more volt drop.

 

[SunshineHarvey7]

36 minutes ago, Crossy said:

25mm² Al is about 1.2 ohm per km, so 2.4 ohms round-trip.

 

25mm² is about the same as 3AWG wire, then, right? You recommended 35mm or 50mm. Is 50mm about the same as 1/0 AWG? (I'm finding a lot of wire gauge calculators refer to AWG sizes rather than mm² sizes.)

 

Also, what voltage drop calculator are you using? I found this one that allows me to enter an arbitrary sq mm size of wire, but it comes up with a voltage drop of 20 volts, not 24 volts. No big deal, but I'm just curious if you found a better a calculator than I've found so far.

[Crossy]

In this case I went back to basics and used Ohm's Law, but I generally use the calculator from Doncaster Cables, it's optimised for copper but generally going one size bigger works fine for Al.

 

I found various resistances for 25mm² Al ranging from 1 to 1.4 ohms per km (cable varies more than somewhat). Is your "1km" actually 1000m?

 

The whole world of electrics is all about approximation there are few absolutes. For example a 20A breaker will quite happily carry a 10% overload (22A) pretty much forever, the "20A" (installation location and method can change the rating significantly) cable connected to it will likewise be perfectly happy. Don't even ask me what you can do to an electricity meter

 

I know not this "AWG" thing of which you speak, Thailand is a metric country and uses square mm. Of course I know what AWG is but there are few direct equivalents and tolerances/estimates can add up in a bad way, suddenly your wires are too small.

 

For the record, 25mm² is too small. If you have the smallest meter available (5/15) then the "correct" (5% volt drop) cable is 70mm², if you have a 15/45 meter then look at 300mm²!  Since someone has to pay for the cable and we know their load is small (but could increase of course) we can take a pragmatic approach, hence my 35/50mm² suggestion.

 

That said, 25mm², particularly if you can get it in one piece, will be infinitely better than the wet string they have now.

[farmerjo]

Speaking from having done a long run(800 metres) with 25sq and 15/45 meter.

If you're not going to install an AVR i would go with a minimum of 50sq.

That's if they want to use a bore pump or have a hot electric shower in the future. 

[Crossy]

@farmerjo was that in copper or aluminium?

 

[farmerjo]

4 minutes ago, Crossy said:

@farmerjo was that in copper or aluminium?

 

Hi Crossy

I still have the 25sq aluminium with the AVR.(600 metre run now)

Next step is to replace the cable with the 50sq aluminium to stop the 3 second over current blackout when friends turn the hot water system off to quick because of the cable size. 

It doesn't happen often but enough to warrant upgrading the cable.

[SunshineHarvey7]

58 minutes ago, Crossy said:

I found various resistances for 25mm² Al ranging from 1 to 1.4 ohms per km (cable varies more than somewhat). Is your "1km" actually 1000m?

Yes, perhaps a little more than 1000m, but not much. Satellite measurements come in right around 1000m, and so does my truck odometer. (I'd plan to purchase at least 1100m to be safe if was purchasing the wire.)

 

1 hour ago, Crossy said:

I know not this "AWG" thing of which you speak, Thailand is a metric country and uses square mm.

I understand. It's just that some wire calculators give AWG recommendations. Fortunately there's a chart here

that helps convert up to the next available size in sq mm.

 

1 hour ago, Crossy said:

For the record, 25mm² is too small. If you have the smallest meter available (5/15) then the "correct" (5% volt drop) cable is 70mm², if you have a 15/45 meter then look at 300mm²!  Since someone has to pay for the cable and we know their load is small (but could increase of course) we can take a pragmatic approach, hence my 35/50mm² suggestion.

 

That said, 25mm², particularly if you can get it in one piece, will be infinitely better than the wet string they have now.

Really appreciate your approach. Since my friends to plan to expand (add buildings and people), I'm laying out the options for them to string wire that would match closer to the capacity of their meter as well. It would truly be a shame if they put up new wire and then exceeded its capacity.

 

Thanks again for all your time and answers. What I'm learning will be helpful for this situation as well as some other friends that just purchased property off grid here in Thailand.

[Crossy]

16 minutes ago, SunshineHarvey7 said:

I'm laying out the options for them to string wire that would match closer to the capacity of their meter as well.

 

Exactly!! 

 

One has to play what's "correct" against what's practical and affordable.

 

Note that there's nothing to stop you running 25mm² now and adding another 25mm² in parallel when the volt drop becomes intolerable. Personally, I'd only do that if the budget was being tightly squeezed!

 

Just as a comparison, our source impedance measures at about 0.5 ohms which is barely tolerable for the technology. So we have an AVR which makes stuff happier as well as 6kW of on-grid solar and a 6.5kVA genset for when the juice goes off in the dark and wet (it's always dark and wet).

[SunshineHarvey7]

On 2/7/2021 at 2:25 PM, Crossy said:

I have found both Sofar and Suoer manuals on the manufacturer's websites.

Hi again, @Crossy, just wondering, where did you find those manuals? Or are you referring to their specification charts? I bought a Suoer ST-H1220 (for another application). Bought it from someone who pieced it together with an inverter all assembled on a board. Nice, but no manuals. ???? I can't find a manual anywhere online. I guess we can just plug-n-play, but it bugs me when I don't know 100% what I'm doing when I step through the settings. ????

[Crossy]

12 minutes ago, SunshineHarvey7 said:

Hi again, @Crossy, just wondering, where did you find those manuals? Or are you referring to their specification charts? I bought a Suoer ST-H1220 (for another application). Bought it from someone who pieced it together with an inverter all assembled on a board. Nice, but no manuals. ???? I can't find a manual anywhere online. I guess we can just plug-n-play, but it bugs me when I don't know 100% what I'm doing when I step through the settings. ????

 

Best I can find right now is this http://www.chinasuoer.com/mppt-solar-controller/251.html but I'm sure I got Suoer manuals off the web previously just can't find them now.

 

[SunshineHarvey7]

Okay, an update to the overall "AVR" plan: I purchased

• a Suoer MPS 5KVA-48V Hybrid Inverter
• 16x100AH Sinoplus LiFePO4 batteries, and
• a Daly 16S 48V 150A "Smart" BMS (R32U GC04, with Bluetooth)

Now I'm full of questions: First, anyone know where to find a user manual for the Daly Smart BMS? (I'm so not used to buying equipment that doesn't ship with a manual and doesn't have a decent one online!!!)

 

Since I understand the BMS won't "turn on" unless it sees a charger voltage applied that is ~0.5v higher than the batteries, I connected all the BMS wires to the batteries, and then I connected the BMS and battery pack to the inverter. Turned the inverter on, and it would not "turn on" because it didn't "see" the battery pack. I shorted B- to P- for several seconds, and then the inverter turned on. I was pleased UNTIL it appeared to me that it was not charging the batteries. I suspected that the BMS was still not firing up, so I shut down the inverter. After a bite to eat, I went back and tried to fire it up again. Had to short out the BMS B- & P- again to get the inverter to come on.

 

Now, after coming on for a few seconds, the inverter goes into a fault mode, reading error 09, which the manual says means "bus soft start failed." In another place, the manual states that the possible cause of this error is "Internal components failed," and I will need to "return to repair center."  ????I've emailed the mfr to see if there might be another alternative, but I don't have my hopes up. Anyone have a suggestion?

 

I must admit, my initial experiences with the Suoer brand of inverters / charge controllers has been a bit sour! ????

[Crossy]

Have you got mains to the inverter?

Solar panels?

 

Many of the Chinese manufacturers are actually very responsive in English.

 

What's the state of charge of your batteries? I've had problems with a BMS that wouldn't start, had to charge the batteries with a charger to get things to a level everything was happy, it's not stopped since.

 

EDIT If you are getting errors, try the turn it all off (disconnect all power), have a coffee and turn it back on again technique. It's amazing how often it works.

 

EDIT 2 Have you managed to BT to the BMS? anything useful on the user interface?

[SunshineHarvey7]

23 hours ago, Crossy said:

Have you got mains to the inverter?

Solar panels?

 

Many of the Chinese manufacturers are actually very responsive in English.

I do have the mains connected. No solar (yet). 
 

I sent an email to Souer on Friday. Hope to hear back soon. 
 

I did try the inverter again after it rested for about 36 hours. I must say I was surprised when it fired up without the 09 fault code. It ran for over an hour with no trouble. Then for no obvious reason it shut down again with the same fault. 
 

All of my Lifepo4 batteries read ~3.33 volts. Total ~53.3.
 

While I had the BMS B- & P- shorted, I discovered that I could Bluetooth to the BMS. There I discovered that it thought that cell #2’s voltage was 2.65 volts—which I guess is below the low voltage shutoff. I suspected I must have done a bad cramping job on the connector for that cell. After replacing it, Yippee! the BMS worked! ????

 

I still can’t understand what’s causing the inverter’s fault code. In the mean time, I’ll be on a week long trip to visit friends. 

[maxpower]

1 hour ago, SunshineHarvey7 said:

I still can’t understand what’s causing the inverter’s fault code.

 

The Voltronic boards used in many inverter brands issue fault code 07 - 09 when abnormal voltage is detected in the power switching circuit. This is usually down to component failure.

 

Fortunately the power stages of these very common are easy to test and repair.

 

Try one of the Tube fixers, there are many in LOS.

 

https://www.youtube.com/c/FmlamphunChannel/videos

[SunshineHarvey7]

18 hours ago, maxpower said:

 

The Voltronic boards used in many inverter brands issue fault code 07 - 09 when abnormal voltage is detected in the power switching circuit. This is usually down to component failure.

 

Fortunately the power stages of these very common are easy to test and repair.

 

Try one of the Tube fixers, there are many in LOS.

 

https://www.youtube.com/c/FmlamphunChannel/videos

 

Are any of these videos in English? (I don't understand much more than very basic Thai.)

 

And pardon my ignorance--what does LOS mean? ????

[Crossy]

23 minutes ago, SunshineHarvey7 said:

And pardon my ignorance--what does LOS mean? ????

 

Land Of Smiles i.e. Thailand ???? 

[maxpower]

53 minutes ago, SunshineHarvey7 said:

 

Are any of these videos in English? (I don't understand much more than very basic Thai.)

 

And pardon my ignorance--what does LOS mean? ????

 

I posted the YouTube link as a method to find a repair service, I doubt watching the videos will help much.

 

Most provide a Facebook or Line contact for those looking for inverter repair/test service.

[SunshineHarvey7]

On 4/6/2021 at 10:59 AM, maxpower said:

 

I posted the YouTube link as a method to find a repair service, I doubt watching the videos will help much.

 

Most provide a Facebook or Line contact for those looking for inverter repair/test service.

Thanks again for sharing the info. I may need that repair guy, if the warranty repair doesn't fix the problem.