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System "overloading" - advice required


Chrono
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My solar system was installed in March 2016. It consists of 10 x 300W panels, 12 x 12V 102 Amp batteries and an Axpert 5 KVA hybrid inverter. The installer is a building contractor who is a sort of Jack of all trades. He conducted an investigation beforehand to measure peak usage at my home. Together with our converted-to-solar geyser there is a reduced electricity usage of 60% plus. The installer has been back to my home on many an occasion to tweak the system but we are experiencing problems that he seems unable to fix. Our problem is that the mains switch falls when too many appliances that consume a lot of electricity are switched on simultaneously. The geyser is on from 5 - 8 am and if the tumble dryer or even my wife's hair dryer is switched on as well, chances are that the system will trip. I am a total novice when it comes to electricity but I read the Axpert manual and tried to make adjustments to the settings, but, to now avail. My questions: 1. Do we need to split the DB so that for instance the tumble drier, dish washer, washing machine and stove are run only off Eskom power? 2. Can I address my problem via settings to the inverter? Further, I realise from postings on this forum that I am probably neglecting my batteries. I think I need equipment that will inform me about their state, performance etc. Please help me with advice in this regard. Please keep it simple otherwise I will have to pester you with more questions.   

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Hi. The Axpert 5kva is a 4kw inverter. So that means you can draw max 4000 watts. It sound like you have way to much load than what the inverter can handle at one time. You have a couple of options. 1) Add a second Axpert to handle the spike up to 8Kw. 2) Split your db and run all the heavy loads on Eskom. 3) Replace the Axpert with a Grid tied inverter and put your load en the grid feed side (if you are allowed to feed back) 

 

I would start to see what the spikes are and get a usage profile to see what that is. Sound like your system is not sized correctly.

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You read "12 x 102Ah" and you die a little inside...

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Thank you for your reply. Ok, it's obvious that you disapprove, but can you provide specs for something better please? We are 3 adults in our home. We have a swimming pool. The current effort is supposed to be a first phase. That being the case I am ok with running certain appliances off Eskom, but I want to have a backup in the form of batteries if Eskom is inavailable. Of course I do not expect to run high consumption appliances with battery power.

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Hi. The Axpert 5kva is a 4kw inverter. So that means you can draw max 4000 watts. It sound like you have way to much load than what the inverter can handle at one time. You have a couple of options. 1) Add a second Axpert to handle the spike up to 8Kw. 2) Split your db and run all the heavy loads on Eskom. 3) Replace the Axpert with a Grid tied inverter and put your load en the grid feed side (if you are allowed to feed back) 
 
I would start to see what the spikes are and get a usage profile to see what that is. Sound like your system is not sized correctly.


Thank you. I appreciate your observations and advice.

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44 minutes ago, Chrono said:

it's obvious that you disapprove, but can you provide specs for something better please?

It's a bit of a long-running theme on this forum, no offense was intended. You didn't say what brand it was, but just hearing 102Ah means it is likely a Lead Calcium high-cycle battery. Ask @KLEVA, he almost had his house burn down with these faux deep-cycles. You see them at Builders- and Outdoor Warehouse, for the 4x4 and weekend markets. The problem is two fold: Those aren't real deep cycle batteries, and you have three strings of them.

You'd have been much better off with two strings of 150Ah gel batteries (Sonic for example) or perhaps even just one string of 225Ah (Trojan T105) or 250Ah (Sonic gel), which even if the capacity is smaller, it's just overall a better battery and a better arrangement.

Less batteries of a larger capacity is better.

No worries, I walk into a little weekend place yesterday on a Karoo farm. It has a 12V fridge, 4 x 100Ah batteries in parallel in the back, and what looks like around 600Wp on the roof. No inverter, just DC for lights, cell-pone charging and the custom-built fridge. My immediate thought is I would throw out the 12V fridge and put in a Bosch A++ unit, with a 350VA sine wave inverter, and use a 24V battery bank, with a buck converter for the 12V LED lighting. Then chuck the 4x100Ah batteries (4 strings of 1 battery) and put in one string of 2 x 200Ah batteries. And NOT use the EnerCell (or whatever brand it was) they had there. Ugh. Same capacity, possibly same price too, and a lot less trouble.

Anyway, I agree with the others. Either you're hitting the limit on the inverter itself, or the voltage on the DC side drops so far under load that the inverter shuts down because of a low voltage condition. I have a sneaky suspicion it's the second one.

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Hi Chrono,

Unfortunately there is no setting on your inverter to fix your problem. Your base load far exceeds your inverter capacity. You definitely require an additional inverter to run in parallel with your existing inverter. Even that will at times not be sufficient,looking at your base load. Secondly, you are on the right path splitting your DB. Just taking your oven and oven off the load and running them from Eskom, will make a huge difference. Looking at your base load I would guess take a rough guess that you have battery capacity for about 1 and a half hours, running them down to about 75%. Your batteries should only be used for Eskom outages, i.e. load shedding. If you run the every night for 4-5 hours until they shut down due to low voltage, they will not last 18 months.  

You need some energy monitoring software to manage your load and give you a better grip of what is happening. For a start, try and run WatchPower software that came with the inverter or download it from the internet.

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The cheapest option would be to get rid of the wife! You cut out the following from your load. No stove, no oven, no frying pan, no toaster, no microwave, no slow cooker, no dishwasher, no washing machine, no tumble dryer, no iron, no hair drier, no refilling 300lt geyser after a shower, lololol. 

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On 12/27/2016 at 1:50 PM, plonkster said:

It's a bit of a long-running theme on this forum, no offense was intended. You didn't say what brand it was, but just hearing 102Ah means it is likely a Lead Calcium high-cycle battery. Ask @KLEVA, he almost had his house burn down with these faux deep-cycles. You see them at Builders- and Outdoor Warehouse, for the 4x4 and weekend markets. The problem is two fold: Those aren't real deep cycle batteries, and you have three strings of them.

You'd have been much better off with two strings of 150Ah gel batteries (Sonic for example) or perhaps even just one string of 225Ah (Trojan T105) or 250Ah (Sonic gel), which even if the capacity is smaller, it's just overall a better battery and a better arrangement.

Less batteries of a larger capacity is better.

No worries, I walk into a little weekend place yesterday on a Karoo farm. It has a 12V fridge, 4 x 100Ah batteries in parallel in the back, and what looks like around 600Wp on the roof. No inverter, just DC for lights, cell-pone charging and the custom-built fridge. My immediate thought is I would throw out the 12V fridge and put in a Bosch A++ unit, with a 350VA sine wave inverter, and use a 24V battery bank, with a buck converter for the 12V LED lighting. Then chuck the 4x100Ah batteries (4 strings of 1 battery) and put in one string of 2 x 200Ah batteries. And NOT use the EnerCell (or whatever brand it was) they had there. Ugh. Same capacity, possibly same price too, and a lot less trouble.

Anyway, I agree with the others. Either you're hitting the limit on the inverter itself, or the voltage on the DC side drops so far under load that the inverter shuts down because of a low voltage condition. I have a sneaky suspicion it's the second one.

I would stick to 12V, in this particular application though. OR, if you really wanted to, run 24V batteries and use a 24V->12V buck converter. The losses would be a little less and the setup still very simple. And then put in 2x 200A batteries as you say. 

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Had a discussion with someone this morning and I would like to retract the "Sonic Gel" advice above, in case someone follows it. Apparently they aren't all they are cracked up to be. Well, maybe for a weekend application... :-)

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On 12/26/2016 at 5:10 PM, Chrono said:

My solar system was installed in March 2016. It consists of 10 x 300W panels, 12 x 12V 102 Amp batteries and an Axpert 5 KVA hybrid inverter. The installer is a building contractor who is a sort of Jack of all trades. He conducted an investigation beforehand to measure peak usage at my home. Together with our converted-to-solar geyser there is a reduced electricity usage of 60% plus. The installer has been back to my home on many an occasion to tweak the system but we are experiencing problems that he seems unable to fix. Our problem is that the mains switch falls when too many appliances that consume a lot of electricity are switched on simultaneously. The geyser is on from 5 - 8 am and if the tumble dryer or even my wife's hair dryer is switched on as well, chances are that the system will trip. I am a total novice when it comes to electricity but I read the Axpert manual and tried to make adjustments to the settings, but, to now avail. My questions: 1. Do we need to split the DB so that for instance the tumble drier, dish washer, washing machine and stove are run only off Eskom power? 2. Can I address my problem via settings to the inverter? Further, I realise from postings on this forum that I am probably neglecting my batteries. I think I need equipment that will inform me about their state, performance etc. Please help me with advice in this regard. Please keep it simple otherwise I will have to pester you with more questions.   

Some suggestions:

1) Use the batteries you have till they die and buy better batteries. Either GEL, AGM or Lithium, depending on your budget

2) split the DB board and run the geyser off eskom. OR, put in something like this, which will cut-off the geyser when other larger appliances use electricity: https://www.cbionline.co.za/products/energy-control-unit-electronic

3) Adapt your lifestyle so that utilize the solar energy as much as possible. i.e. don't use the washing machine, dish washer, etc at night - use it when the sun shines. 

4) IF you haven't done so already, replace all your lights with LED and see what other, old appliances you can replace with more efficient appliances. 

 

The trick is to use the batteries as little as possible. IF you can, go prepaid and ask see if your municipality offer "Free Basic Electricity" if your average usage is under a preset amount every month. IF you want to live off-grid, you'd have to ensure as little as possible is drawing electricity at night. 

 

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Just now, plonkster said:

Had a discussion with someone this morning and I would like to retract the "Sonic Gel" advice above, in case someone follows it. Apparently they aren't all they are cracked up to be. Well, maybe for a weekend application... :-)

They don't like the heat we get in many parts of South Africa. If you can keep then cool, they're not too bad. 

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1 hour ago, SilverNodashi said:

If you can keep then cool,

That's nogal a problem. It doesn't quite reach the 30s, but it gets close. Today is not doing too bad:

[email protected]:~# dbus -y com.victronenergy.solarcharger.socketcan_can0_di0_uc30688 /Dc/0/Temperature GetValue
value = 25.850006103515625

I just love how I can query this thing remotely...

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On ‎2017‎/‎01‎/‎01 at 0:35 PM, SilverNodashi said:

Some suggestions:

1) Use the batteries you have till they die and buy better batteries. Either GEL, AGM or Lithium, depending on your budget

2) split the DB board and run the geyser off eskom. OR, put in something like this, which will cut-off the geyser when other larger appliances use electricity: https://www.cbionline.co.za/products/energy-control-unit-electronic

3) Adapt your lifestyle so that utilize the solar energy as much as possible. i.e. don't use the washing machine, dish washer, etc at night - use it when the sun shines. 

4) IF you haven't done so already, replace all your lights with LED and see what other, old appliances you can replace with more efficient appliances. 

 

The trick is to use the batteries as little as possible. IF you can, go prepaid and ask see if your municipality offer "Free Basic Electricity" if your average usage is under a preset amount every month. IF you want to live off-grid, you'd have to ensure as little as possible is drawing electricity at night. 

 

1) I have decided to do this.

2) The geyser has been "solarised". It works fine.

3) We are doing this already.

4) Have done so.

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On ‎2016‎/‎12‎/‎27 at 8:10 PM, Don said:

The cheapest option would be to get rid of the wife! You cut out the following from your load. No stove, no oven, no frying pan, no toaster, no microwave, no slow cooker, no dishwasher, no washing machine, no tumble dryer, no iron, no hair drier, no refilling 300lt geyser after a shower, lololol. 

I still like her a lot, so, must pass on that advice.

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On ‎2016‎/‎12‎/‎27 at 7:43 PM, Don said:

Hi Chrono,

Unfortunately there is no setting on your inverter to fix your problem. Your base load far exceeds your inverter capacity. You definitely require an additional inverter to run in parallel with your existing inverter. Even that will at times not be sufficient,looking at your base load. Secondly, you are on the right path splitting your DB. Just taking your oven and oven off the load and running them from Eskom, will make a huge difference. Looking at your base load I would guess take a rough guess that you have battery capacity for about 1 and a half hours, running them down to about 75%. Your batteries should only be used for Eskom outages, i.e. load shedding. If you run the every night for 4-5 hours until they shut down due to low voltage, they will not last 18 months.  

You need some energy monitoring software to manage your load and give you a better grip of what is happening. For a start, try and run WatchPower software that came with the inverter or download it from the internet.

Don, do I understand correctly that I cannot set the Axpert inverter to only use battery power when Eskom is unavailable? I checked and that is my conclusion. The very first setting has an option that will exclude both solar and battery power when Eskom is available and hence solar will not be utilised then. That us UtI. Will I then be able to achieve what you suggest with software?   

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2 hours ago, superdiy said:
On 1/1/2017 at 2:22 PM, plonkster said:

value = 25.850006103515625

Are you sure that is accurate? 

That's floating point inaccuracy.... :-)

You probably know this already (hence the smiley), but just in case there are people who don't: Contrary to popular belief, there are floating point numbers (infinitely many of them!) computers have trouble representing, so what you get is the closest one. What you see there is the closest FP number to 25.85 :-)

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12 hours ago, Chrono said:

Don, do I understand correctly that I cannot set the Axpert inverter to only use battery power when Eskom is unavailable? I checked and that is my conclusion. The very first setting has an option that will exclude both solar and battery power when Eskom is available and hence solar will not be utilised then. That us UtI. Will I then be able to achieve what you suggest with software?   

Chrono, if you select Utl, the inverter will use solar and battery when Eskom is unavailable. Solar will be the priority. You cannot select battery only. The only way you can use battery only, is if you disconnect the solar via the disconnect switch, i.e.the inverter does not see solar connected and will thus only use battery as backup when Eskom is unavailable.

I suggested you make use of any software to give you a better understanding of what your load is during the day. You will quickly realise that 1 x Axpert 5kVa inverter in your case, is not sufficient to cater for your loads, as you exceed the maximum capacity of the inverter at regular intervals. I would suggest you will need to install a second unit. The two inverters will then run in parallel, doubling your inverter capacity. Even adding an additional inverter will at times not be sufficient when you switch on the oven, stove frying pan and microwave at the same time, with the tumble dryer running in the background. Therefore it would be a good idea to split your db board and remove the stove and oven from your load and run it directly from Eskom. If Eskom is unavailable, you don't have a stove or oven, but at least you will not overload your inverters.

 

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23 hours ago, plonkster said:

That's floating point inaccuracy.... :-)

You probably know this already (hence the smiley), but just in case there are people who don't: Contrary to popular belief, there are floating point numbers (infinitely many of them!) computers have trouble representing, so what you get is the closest one. What you see there is the closest FP number to 25.85 :-)

It isn't specifically a computer problem. More like a base 2 problem. We as humans represent numbers in base 10. Which is made up of the prime numbers 2 and 5. So 2 * 5. Therefore base 10 can represent floating point numbers of base 2 & 5 and multiples thereof correctly.

However, what if I create a computer that works in base 70. Then I can correctly represent 1/7 (which is 0.1428571429.... in base 10). Then does that suddenly mean that humans struggle with FP numbers? Not really, since it is a limitation of representing a decimal as a floating point number in base 10.

Point being, computers aren't bad at floating point. Humans are just bad at math. (or maybe the understanding of number systems which is a very complicated field, granted)

The fact is, that number was probably generated from a 10 bit Analogue to Digital converter which has 1024 distinct values (Maybe 12bit if they really splurged). So the bottleneck of accuracy was hit long before the inaccuracy of a base 2 floating point became a problem.

#JustSaying

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I completely forgot how the mantissa/exponent stuff works, but there is a whole world of fun that way of which floating point underflow is the must fun. I should probably read up on that again some time.

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On a lighter note; these floating point issues contribute to "why some clocks drift". i.e. if you have a digital pool timer, stand alone sprinkler timer or use a geyser wise timer, you might notice that over time (months to years) the time is off by a few minutes. Basically, anything not connected to the internet, and not using "traditional watch mechanism" can drift over time. 

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