Axpert 800W - Not charging batteries

[Etienne]

Hi guys,

I had a Axpert 800W (or 1kVA) Inverter / charger installed late last year, to run a small site office, with two computers, a printer and 3G router. I have an issue with it that the batteries continually run flat (2 x 200AH batteries). This is connected on 2 x 250W solar panels in parallel. The installer claims that we're overloading the system, but load reported by the inverter never goes above 40% (40% in extreme...with the fluorescent lights in the container on...normally off). I believe that the inverter is faulty, and not charging batteries when on solar. I have now moved this unit to a place where it can be plugged into 220V (i.e. grid power). After a few days on grid power, it seems that the batteries are charged. As an experiment, I then disconnect the grid power, and the unit works well for about a week, and then the batteries are flat again. To add fuel to the fire on this one, the batteries tend to go flat on a Monday or Tuesday - at a time when they should have had a whole weekend to charge.

I attach a screen snip of Watchpower, while plugged into the inverter. There are no readings on the batteries...this leads me to have more questions than answers.

Are there any clever opinions / comments from the experts?

(Similarly, the PV input voltage tends to fluctuage tremendously...shown here on only 11V...when it should be 24 I think)...

Etienne

[Chris Hobson]

Hi Etienne

Welcome to the forum.

There is sometime fishy for sure. If this screen shot is during the day with sun on your panels I would expect a PV Votage > 24V (I guessing a bit since I do not know whatr your panels are rated at). The PV  current is 0A so your panels are not charging. I see that the rated battery voltage  is 12V.  At 400W fully charged batteries should last 12 hours until the are as dead as a dodo. This is definitely not recommended so discharge of ½ the batteries capacity they should last 6 hours (inefficiencies and losses not taken into account).

Watchpower says it is in battery mode yet  battery discharge current is 0A. Does not make sense. Could you post a screenshot of you settings please.

 

Chris

 

 

[viper_za]

Hi Etienne

Welcome to the forum

Can you maybe supply some more details

Inverter model number
PV panels Ratings

Type of batteries also.

What I'm not 100% sure about is that as far as I remember there is not a 12V inverter from Axpert.
Can you check how the batteries are connected, parallel or serie?

Also suspect that your PV should also be connected in serie but it all depends on the inverter model and the panels ratings.

 

Thys

Edit: Found a 12V model

 

[Mark]

Agree with the above and suggest some of the following:

1.  Is it 12V or 24V?

2.  Can you measure the panel voltage (with a multimeter after unplugging the panels from the Axpert)... be careful doing this.  Just need a bit of sun to have a look if they are not fried for example?

3.  The panels may have there polarity reversed?

4.  The Axpert needs to be set up in SBL or SOL mode?  What is it now?

 

[Chris Hobson]

Is the security guard not watching TV all weekend?

 

[Etienne]

Chris,

I understand what you mean about the batteries getting discharged, BUT, the system runs for a good week before batteries are flat. This tells me that the solar panels are providing power during the day, but in early morning, or late afternoon, when solar is not providing enough juice, it draws supplementary power from the batteries, such that the batteries then slowly discharge, but never get recharged.

The inverter is the Axpert 1kVA, which is a 12V inverter. The batteries, 2x 12V 200AH, are connected in parallel. The solar panels are...umm...I attach a photo of the sticker, is that what we would call a 24V panel? Connected in parallel.

The input voltage from the PV varies dramatically. The screen snip above, in my first post, is 11V. I attach a log from earlier in the month. One can see it goes up to as much as 28 volts...what I'm reading now in the manual, is that potentially, on the 1kVA inverter, we should be using 12V panels?

Ugh. The question I need answered is this: Do you think the inverter is faulty? If so, who do I go to? The supplier just tells me that I'm overloading the system, that's why the batteries go flat. I had that argument with him in November last year. But my mind was made up that something is critically wrong after the December holiday, the batteries didn't charge over the entire time that we were gone...

Etienne

Edit: I tried to upload the Axpert user manual - too big. Here is dropbox link: https://dl.dropboxusercontent.com/u/30819730/AxpertKS-1-5KVA_manual.pdf

History_datas.pdf

Edited March 16, 2016 by Etienne

[Mark]

If the supplier is adamant that the system is fine and you are overloading then ask them to agree to a second opinion.  Get some else to check the install with the supplier present and then see what  happens...

Your Vmp is 30.38 and so you may even get more then 30V on a good day.

The inverter spec says Overcharge Protection = 15.5 VDC so I guess the panels are being blocked as soon as the voltage gets above a certain voltage.  The installer should know (have known this).  Therefore only charging during low voltage periods.

Good luck!

[Chris Hobson]

Hi Etienne

I am not seeing any charging on your historical data Could you please send a screen shot of your settings page.

The panel info is invaluable in terms of problem solving. I could not get to the  manual via dropbox where did you download it?

Chris

 

 

 

 

[superdiy]

Looking at the details, something is clearly wrong, or hopefully reported wrong - it is in battery mode, yet no current is flowing from the battery. No current is flowing from PV either and no current is flowing into the batteries (charging current), but yet you have a load of more than 300W!

 

Maybe you should re-calculate your system requirements again, because I think it is totally incorrect as is.

Currently you have 2 panels with combined power of maximum 500W when the sun hits them at 90° on a clear summer day under ideal conditions.

You have a load of at least 300W - 24 hours a per day - keep in mind that you have to look at the apparent power when the source is DC (PV or Batt), because that would be what would be drawn from DC (losses ignored).

Lets ignore losses and assume everything is running 100% effective, you then have 500W - 300W => 200W left to charge a 400Ah battery bank. To charge a 400Ah battery bank you would need about 40A for more than 10 hours to charge the bank up to 100% - actually you need more time, but lets ignore that for the moment. With 200W @ 12V you can achieve a maximum charge current of 200W / 12V => 16 Amps - if your inverter charges the batteries at 16 Amps you'll need at least 400Ah / 16A => 25 hours at full sun to charge the batteries.

Normally you work on 5 hours sunshine per day, so you would actually need 25/5 => 5 days or 5 x the amount of panels you currently have - so 8 more panels - and that is if you run the batteries down to 100% DoD overnight on a daily basis, which you also do not want to do. You actually want to run the batteries down to between 30% and maximum 50% DoD, so that means that you have to at least double the 10 panels to 20.

[Mark]

You could buy a cheap solar charge controller and wire the panels through this instead of the Axpert as a fall back.  As long as the controller can handle the panels.

You then just use the Axperts Inverter Charger functionality.

eg:  http://www.mantech.co.za/ProductInfo.aspx?Item=372M0901

[Chris Hobson]

Hi Etienne 

SuperDIY raises a valid

point. I assumed you had zero draw after hours. Looking at average efficiencies on the website PVOutput I would say 3kWh per kW panels installed would be average solar production. I battle to produce 5kWh per kW even with my system ideally orientated and living in the Karoo.

So I would say 1500Wh of power per day and your consumption if it is on for 8 hours is 2400W. It still concerns me however that mid afternoon I am seeing no solar production.

18 minutes ago, Mark said:

The inverter spec says Overcharge Protection = 15.5 VDC

That is for the battery. With a 50VDC max for PV voltage the installer has done the right thing and installed the panels in parallel.

[viper_za]

Just now, Chris Hobson said:

That is for the battery. With a 50VDC max for PV voltage the installer has done the right thing and installed the panels in parallel.

Yes he just does not have enough panels for the size bank and constant load during the day

[Guest]

Ettienne, what the guys said.

I want to add, having been where you are, reduce the load first, yes you can add more panels, but by reducing the load, you may need less panels and batteries.

It is allway a case of Needs vs Wants. Needs are cheaper than Wants.

Load:
Fluorescent tubes, get LED tubes instead. Be sure to remove the ballast AND transformer, if there is one. I did not, what a waste.
Printer, try not to have it on unless it is used. At night, unplug it. Laser printers can draw a few watts just sitting there.
Computers, if they are Pc's replace them with smaller PSU units  like NUKS or some such or use laptops.

Either spend the monies on panels and batteries, or spend it to reduce the loads. Either way, 'die wet van Transvaal is op jou'. 

[Chris Hobson]

I think another 2 panels would do the trick.

Total consumption is 2400W for 8 hours. 1 kW panels would provide 3-4Kwh per day.

If all your kit is on all day (24hrs) consumption is roughly 7200W you would need 8-9 panels. You now going to need monster cables to carry that current at ~30VDC to use the Axpert's built in SCC.  So if this is the case Mark's suggestion of a separate SCC is a good one.

[Guest]

Chris, not sure if I agree with monster cables. 300w AC on 12v DC is not a lot.

[Edit] Nor is 800w AC on a 12v DC system. 

From panels to separate charge controller, and I would not go cheap here, been there done that, to batteries, are also not that problematic IF you use a MPPT from high volts to 12v battery system.

What am I missing?

Eugene, ONE things I have learned with separate charge controllers, you need space to move when things change i.e. need more panels, system volts change and all that.

I would look at ranges from Morningstar Tristar MPPT and Victron MPPT. I know them both and broer, they work, have support and are not full of drama AND they can be adjusted to fit the batteries needs. Not like some of those Voltronic goeters people are using.  

[viper_za]

28 minutes ago, The Terrible Triplett said:

Chris, not sure if I agree with monster cables. 300w AC on 12v DC is not a lot.

[Edit] Nor is 800w AC on a 12v DC system. 

From panels to separate charge controller, and I would not go cheap here, been there done that, to batteries, are also not that problematic IF you use a MPPT from high volts to 12v battery system.

What am I missing?

Eugene, ONE things I have learned with separate charge controllers, you need space to move when things change i.e. need more panels, system volts change and all that.

I would look at ranges from Morningstar Tristar MPPT and Victron MPPT. I know them both and broer, they work, have support and are not full of drama AND they can be adjusted to fit the batteries needs. Not like some of those Voltronic goeters people are using.  

Chris is referring to the cables from the PV to the inverter I think (Doing the Max 50A the Inverter can provide over PV, 40A for batts + x for load)

 

I honestly believe the installer did not provide you with the correct setup for your needs

[superdiy]

1 minute ago, viper_za said:

I honestly believe the installer did not provide you with the correct setup for your needs

ditto

[Chris Hobson]

10 minutes ago, viper_za said:

I honestly believe the installer did not provide you with the correct setup for your needs

 

8 minutes ago, superdiy said:

ditto

I think everyone is in agreement on that. The solar production or lack thereof from data and screen shots submitted is still troubling.

[Guest]

Yes we are.

BUT ...

1 hour ago, viper_za said:

.. cables from the PV to the inverter I think (Doing the Max 50A the Inverter can provide over PV, 40A for batts + x for load)

Makes no sense. 

Wire thickness between panels and controller is one issue, heavily dependent on how the array has been optimally configured for the MPPT controller.

To keep the wire requirements low, you go for the highest volts you can from the array to the controller.

MPPT controller will sort that down to 48/24 or 12volts of the battery bank, at the amps the batts need to be charged at.

The wire thickness between controller and batts, totally separate matter.

[viper_za]

Just now, The Terrible Triplett said:

Yes we are.

BUT ...

Makes no sense. 

Wire thickness between panels and controller is one issue, heavily dependent on how the array has been optimally configured for the MPPT controller.

To keep the wire requirements low, you go for the highest volts you can from the array to the controller.

Controller will sort that down to 48/24 or 12volts of the battery bank, at the amps the batts need to be charged at.

The wire thickness between controller and batts, totally separate matter.

The specific inverter makes use of PWM not MPPT so that's +-8A for each panel since it will only be possible to parallel as series would be more than the Max Open Voltage Circuit.

So now with 2 panels we already at 16A and as we all determined it's not enough for his system adding another two puts us at 32A so now thickness will start to matter depending on the distance

[Guest]

The whole idea with arrays with higher volts, are to reduce cable requirements.

Lets say you have 4 x panels (each +-30v +-8a) in series, you have 120v at 8 amps coming in, sorted magically by the MPPT controller for your 12v bank. Perfect!

Or, you be brave and go parallel, 30v at 32a - but why do that if you have a MPPT? This is just complicating things ito cable thickness over length from panels to controller.

 

[Guest]

5 minutes ago, viper_za said:

The specific inverter makes use of PWM not MPPT so that's +-8A for each panel since it will only be possible to parallel as series would be more than the Max Open Voltage Circuit.

Therein the suggestion before to get a separate controller, I suggest a MPPT, and not use the limited Voltronics built in one. 

[viper_za]

9 minutes ago, The Terrible Triplett said:

The whole idea with arrays with higher volts, are to reduce cable requirements.

Lets say you have 4 x panels (each +-30v +-8a) in series, you have 120v at 8 amps coming in, sorted magically by the MPPT controller for your 12v bank. Perfect!

Or, you be brave and go parallel, 30v at 32a - but why do that if you have a MPPT? This is just complicating things ito cable thickness over length from panels to controller.

 

The point is the cheapest way for him to make this work is add more panels that he would need no matter what controller he has.
So the PWM will work just with more panels

 

4 minutes ago, The Terrible Triplett said:

Therein the suggestion before to get a separate controller, I suggest a MPPT, and not use the limited Voltronics built in one. 

If he wants to go this route it would be cheaper to do a different Voltronics model with MPPT

[Guest]

30 minutes ago, viper_za said:

If he wants to go this route it would be cheaper to do a different Voltronics model with MPPT

Would it?

As rightfully stated the problem is the 2 x 200ah giving 400ah at 12v with the load not getting sufficient current left over to charge them.

Plus, if you only want +-300w, the 800w 12v model is perfect so fix the problem by getting a separate MPPT charge controller.

And, do not forget, small loads like this, 12v is MUCH cheaper ito batteries by a HUGE margin than 24 or 48v units. 

And to sell the 800w (ideal for the needs specifed), what are you going to get for it?

Because to get the 40amps, 10% charging rate for 400ah (BUT better to go above that being off-grid), take 50a charging so looking quickly at a BlueSolar MPPT 100/50 (12/24V-50A) is wot, about +-R5k that can charge the required 50amps if you have the panels installed in series to reduce the wire requirements. 

Problem solved for the 400ah bank, after the load reduction has taken place to boot.

Win win in my opinion.

[Guest]

See, pushing the Voltronics PWM to max power, with the PWM being inefficient to boot and it being uncomfortably high DC amps, it is being pushing very hard.

And with it being in a container office their are the temps to consider on top of the PWM operating flat out (read heating up).

For I vaguely recall reading that you guys have mentioned the Voltronics are not the best at cooling, and this one is 800w, therefor probably even less so?

So I would split the inverter from the charge controller, as the 800w is more than enough for the load, just not for the batts, and at 12v ... cheaper solution.

Use it, or not, Etienne's choice at the end of the day.