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alistair

Axpert DOD setting up

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Does anyone know how to go about setting up DOD on an Axpert 3kv/2400w inverter to control level of battery discharge.

I have 2 x 24v battery banks connected.

Thanks

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Hi Alistair.

 

I am not sure what you want to do at a specific DOD. If you want to let the grid charge your batteries then program 12 allows you to specify at what voltage to switch over to grid and charge your batteries and program 13 allows you to set at what voltage to return to using solar and batteries. The problem is that this is determined at a specific voltage rather than DOD. The voltage at a specific DOD varies according to the load being drawn at the time, so knowing the voltage cannot let you know what the DOD is unless the batteries are at rest. Wetkit supplied the following table for SOC for batteries at rest.

 

post-822-0-09024800-1436033609_thumb.jpg

 

The inverter shutdown to save your batteries in program 29 can be set to 24v if program 5 (battery type is set to user defined). This translates to a DOD of between 50 and 60 %.

 

Unfortunately the Axpert is not very versatile in terms of battery management. It has an internal shunt and so is giving a guesstimate in terms of SOC. Not knowing your SOC/DOD is like riding in a car without a fuel gauge.

 

My temporary solution is to use the Dry contact signal to operate a contactor on the output side and remove the load on the inverter at a specific voltage in program 12 and hopefully allow the batteries to charge in the interim. The battery shutdown maximum (24v) is way too low to be of any real benefit.

 

My long term solution is to buy a Victron BMV 702 Battery monitor (spending some of the money saved by buying an Axpert). This will give you real SOC and again one can use the relay to switch off the load on the inverter.

 

 

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Thanks Chris, very useful info and have setup using these settings now and tested and it works perfectly.

However while testing using the monitoring software, i noticed when charging via utility/pv it shows battery capacity as 100% but when i swop to battery only it shows battery capacity as about 60% and declines quite quickly.

Could this be that axpert believes batteries fully charged but in fact not the case? On another topic i had posted about battery issues i had, there was a suggestion to drop the bulk charging setting but not sure on this.

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It may well be you problem. DeepBass9 also recommends a lower charging rate to avoid what you seem to be experiencing. Dropping you bulk charge rate can do no harm to your batteries. It may mean that if you have panels you may waste some energy but if you are using municipal power/Eskom then all that happens is you charge for longer. The one problem is that If you deplete your batteries you may not have you batteries fully charged by the time you next need them. It takes between 107% and 114% to replace energy discharged from a battery. so if you have a 100ah battery that is 50% discharged you charge at 20A you are going to take between 2

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I tried reducing the bulk charge setting but it does not seem to "trick" the inverter which remains indicating 100% charged.

The minute i switch to battery mode only, the battery capacity % starts from 60% odd percent and quickly drops to below 50% (2 bars on battery indicator) at which point i switch back to line mode. Once back on line mode it takes a short while again before battery capacity back to 100% and 4 bars.

Very strange, not sure what is going on. Don't believe batteries would last very long during next load shedding.

Also wondering if having batteries connected in banks (2

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Hey Alistair, If your batteries have a high internal resistance (increases with the age of the battery) or if you are heavily loading them, then it would result in the problem that you described.

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I tried reducing the bulk charge setting but it does not seem to "trick" the inverter which remains indicating 100% charged.

The minute i switch to battery mode only, the battery capacity % starts from 60% odd percent and quickly drops to below 50% (2 bars on battery indicator) at which point i switch back to line mode. Once back on line mode it takes a short while again before battery capacity back to 100% and 4 bars.

Very strange, not sure what is going on. Don't believe batteries would last very long during next load shedding.

Also wondering if having batteries connected in banks (2

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Does anyone know how to go about setting up DOD on an Axpert 3kv/2400w inverter to control level of battery discharge.

I have 2 x 24v battery banks connected.

Thanks

 

Hi alistair

 

I've ordered one of these for my dad, but still waiting for it to be delivered. In the mean time I'm trying to get batteries for it, but that is a whole different story. According to the manual, I've downloaded a few months ago, the minimum charging current on the 3KW 24V MKS Axpert is 20A.  Can you confirm this or have they perhaps added a lower value in the mean time. I assume a simple firmware change should be able to give you more options, but I cannot seem to find any firmware related posts for the infini or Axpert inverters anywhere on the web.   :(  With 20A you'll have to have at least a 200AH deep-cycle battery bank or a 400AH gel battery bank, in order not to harm the batteries.  :(

 

Thanks

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Hi SuperDIY

 

I also ran into this "problem". It appears to be a typo (manual deficiency) the 5kVA goes down to 10A PV and 2A and then 10A on AC. Comfirmed last night that the AC charge values are expressed as DC (If that makes sense?). 19 Amps was just over 5 A 240 VAC.

 

Chris

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Hi SuperDIY

 

I also ran into this "problem". It appears to be a typo (manual deficiency) the 5kVA goes down to 10A PV and 2A and then 10A on AC. Comfirmed last night that the AC charge values are expressed as DC (If that makes sense?). 19 Amps was just over 5 A 240 VAC.

 

Chris

 

Hi Chris

 

I don't think the 2A and 10A etc. charging from AC is a typo - what they mean by that is that the AC charger can charge the batteries at 2A / 10A etc. which is the actual DC current flowing to the batteries. It would not make sense to say how much AC amps it charges at, since then you have to keep charger losses and specific voltages on AC and DC into account to calculate the actual DC charging current and it would just not make sense to do it that way.

 

The reason why I asked the question is because the inverter I bought is a 3KVA model and the manual I've downloaded a while ago covers the 1KVA through to 5KVA models and according to the my manual the 4KVA and 5KVA inverters have the 2A and 10A options as well as some more options above 30A, but the 3KVA 24V (not Plus) inverter only has 20A and 30A (default) options according to my manual.

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The 5kVA program 2 options are 10 - 120A. I think the manual is poorly laid out.  I cannot imagine that they would allow a 5kVA model to charge at 10 A and not a 3kVA model. If you look at the manual it appears that the 5kVA minimum is 70A (and that is not the case). 

 

Easiest if Alistair just looks for you.  - Aaaalistair!

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The 5kVA program 2 options are 10 - 120A. I think the manual is poorly laid out.  I cannot imagine that they would allow a 5kVA model to charge at 10 A and not a 3kVA model. If you look at the manual it appears that the 5kVA minimum is 70A (and that is not the case). 

 

Easiest if Alistair just looks for you.  - Aaaalistair!

 

What I understand from the 70A in the manual (in your case / 4KVA & 5KVA) is that the 70A is the combined charging current - 60A from PV and 10A from Utility, but then again, Utility charging current can be set to 2A (4KVA & 5KVA) as well - then there should have been a 62A option for combined charging as well.   :huh:

 

I any case, it is not a big issue, I'll just wait for the inverter to arrive and check it out myself and then decide on the battery types and Ah's.  :)

 

Thanks Chris

 

Edit.

 

Re-reading your post now..  You say you have options 10A - 120A for option 2?  As I understand the manual the options for the 4KVA & 5KVA's are 70A, 80A, 90A, 100A, 110A and 120A only - is that not the case on the inverter itself?  Then the manual is definitely unclear. Guess it would be best to wait until I get the inverter and can confirm it.

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The manual leads one to believe one cannot restrict the charging rate in solar for the 5kVA model. (70A would be 60A solar and 10A grid). I was panicking as I only had 260 Ah batteries and I would definitely overcharge if I could not restrict the solar charging. Now that I have my Mecer/Axpert I have set program 2  to 20A and program 11 set to 20A.

 

 I could set program 2 to 10A and program 11 to 2A as an absolute minimum.

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The manual leads one to believe one cannot restrict the charging rate in solar for the 5kVA model. (70A would be 60A solar and 10A grid). I was panicking as I only had 260 Ah batteries and I would definitely overcharge if I could not restrict the solar charging. Now that I have my Mecer/Axpert I have set program 2  to 20A and program 11 set to 20A.

 

 I could set program 2 to 10A and program 11 to 2A as an absolute minimum.

 

Hi Chris

 

That is great news, thanks. I hope the 3KVA can also go that low. I'll report back after I've received and checked mine.

 

Thanks

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Hi alistair, I had the same issue with my Axpert 3KVA. The battery capacity % is directly linked to your battery cut-off voltage setting (21V by default, calculated 10.5V x 2). The software assumes that at 21V your batteries are at 100% DOD so when you change the cut-off voltage to say 23V the software thinks your batteries are empty at 23V which they are not. The Axpert doesn't calculate SOC accurately the % will change quickly depending on load. Unless you have a battery monitor like the Victron BMV 700/702 you're driving a car without a fuel gauge but that's okay if you're willing to do a few calculations.

 

There is nothing is wrong with your batteries or charger don't try to trick it by reducing the bulk charge voltage you will under charge your batteries, the charger doesn't look at your % reading but at voltages so if you're on AC and the battery is at 100% your batteries are actually full. The battery cut-off voltage setting when changed from default (21V) is calculated incorrectly when you switch to battery mode thus giving you the 60% SOC.

 

I have 2x 12V 150Ah C/10 batteries connected in series:

 

How I calculate DOD in it's simplest form.

----------------------------------------------

Formula: Volts x Amps/H = Watts/H

----------------------------------------------

In my case this is 24V x 150Ah = 3600 Watts/Hour

so if I pull a average 600W load that will give me 3600W / 600W = 6 Hours

but I only want to use 50% DOD so 6 H / 2 = 3 Hours

with this calculation I then run a test to see what my voltage is after 3 Hours under an average 600W load.

These calculations assume the inverter runs at 100% efficiency which it doesn't so I always take off 10Ah from my calculation to compensate for energy loss to be safe.

 

Another way would be to look at the average amps/hour, the Axpert 3KVA will give you a reading eg. 25Ah @ 600W you divide this by your capacity.

So if I want to use 50% DOD that will be 150Ah / 2 = 75Ah.

75Ah / 25Ah = 3 Hours @ 600W. 

 

You can also use this online calculator which takes Puekert

post-1034-0-06505400-1441854241_thumb.jp

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Guest

DJacobs, may I ask, why on earth did you take 12 x 105ah leisure batteries?

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Guys / gals, shoot me if you feel the need but I think this needs to be said.

Battery use for discussions have to start with: What is your load, for how long must it run?

The answer to those two questions are then used to deduce the exact run-times of said loads, the best system volts, right sized batteries to not exceed 50% DOD of the bank, best charging amps and panels required etc, THEN you decide the make and model inverter.

I would be careful to buy any inverter, slap some batteries on it, throw a few panels on the roof and then rely on a few calcs (especially no Pheukerts) that do not take losses into account. You stand to misuse the batteries, for just about none of the inverters here uses proper SOC calculates, not even my own. 

Now I do have a few other worries for the battery banks out there ito how the batts are charged, the amount of panels, and the max volts the chargers can give for if one gets this wrong, someone is going to damage their batteries in due course, and then no-one can blame Voltronics or worse, the battery manufacturer. And if you are using the 105ah batteries, chances are 10 to 1 that they are leisure batteries, not deep cycle, so your chances of damaging them are even easier in a few months to a year or two. And if the 105ah batteries have caps that you can check their water levels, those are very good training batteries.

Batteries are simple devices, but you need to make sure what your load is to estimate the DOD, and then how you are going to recharge the batteries.

Shoot me (or like the kids want to #owned me) if you want, but I have posted the maths here once or twice, ... honestly though, I did not like the answers they pointed out to me either when I started. :D

So I think we need to focus more on loads and run-times than trying to make what is fit, so that we can make more informed decisions when we next have to buy equipment and more importantly, for the guys who want to start out.

 

Below are the calcs again, which I took off another site I follow every day, advice from guys that are running 15+ years on batteries completely off-grid. Now I know, we are not off-grid in the true sense, but the maths for the batts and panels stay the same if you run off solar daytime.

Also to note: If you use Eskom to charge the batteries whilst powering the load using the inverter, you are not going to be saving any monies at all because of losses. See, running a inverter and charging batteries are quite inefficient compared to using Eskom direct to power the same loads.

 

Take as an example, the following load:
Full size Energy Star Rated refrigerator: 400kWH per year / 365 days per year = 1.1kWH = 1100WH per day
Add more loads running 8 hours per day: 337.5Watts x 8 hours = 2700WH per day
2700 + 1100 WH per day = 3800 WH per day - which is not a lot.

The batteries - you need the load and time it must be powered, to what DOD:
Say you want 2 days of energy storage and 50% maximum battery discharge:
3800WH per day x 1/0.85 AC inverter eff x 1/24 volt battery bank x 2 days storage x 1/0.50 max discharge = 745 AH @ 24 volt battery bank
If you use golf cart batteries (6 volts @ 200 AH per battery) you need 4 x parallel strings of 4 batteries per string = 800 AH @ 24 volt battery bank.

Now that is a big battery bank if these are your needs.

Panels required:
Now, after the above shockers, this is where it gets really interesting, if you want panels to re-charge the batteries daytime, no Eskom:
24v 800AH x 29 volt charging x 1/0.77 panel and controller de-rating x 0.05 rate of charge = 1506 Watt min array
24v 800AH x 29 volt charging x 1/0.77 panel and controller de-rating x 0.10 rate of charge = 3013 Watt nominal array
24v 800AH x 29 volt charging x 1/0.77 panel and controller de-rating x 0.13 rate of charge = 3917 Watt cost effective maximum array

Adjust all the above as per your load and needs.

Voltronics came about crafting very clever UPS'es. They can make it an even more awesome product when their charge controllers have adjustable charge, absorption and float adjustable values, their chargers can be adjusted better for specific batteries and most importantly, they use Pheukerts formula to determine the battery SOC.

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9 hours ago, The Terrible Triplett said:

Voltronics came about crafting very clever UPS'es. They can make it an even more awesome product when their charge controllers have adjustable charge, absorption and float adjustable values, their chargers can be adjusted better for specific batteries and most importantly, they use Pheukerts formula to determine the battery SOC.

Hi TTT

The Voltronic inverters do have adjustable charging values (just not the best range maybe)

Very important to get batteries that fall in these values.

Bulk\Charge (Constant current phase) Increments of 0.1V

48v = 48.0V to 58.4V

24v = 24.0V to 29.2V

Absorb (Constant voltage phase)

Does not need adjustment in voltages as far as I understand it uses the same volts as the Bulk phase and only lowers current until the battery is almost full.

Float Increments of 0.1V

48v = 48.0V to 58.4V

24v = 24.0V to 27V

The thing they are missing is equalization.

I agree 100% with the SOC statement 

 

Thys

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I must now be very careful. :D

Yes, I am aware of that. Since I joined this forum I was wondering if we, me myself and I (aka TTT), was the one who missed the plot. As I read the questions here I will give Voltronics credit for crafting a very nice UPS with adding a solar MPPT controller as a very clever marketing ploy. 

As you may be aware I build me a solar powered UPS back in 2011-2012 with very limited knowledge, barely grasping the problems that one needs to deal with when you have an inverter / batteries on the same circuit as say Eskom. Then only to discover how little I knew about batteries and the loads, not to mention charge controllers and batteries, using a limited budget.

Understand this, correct me if I am wrong, but if you use a Voltronic device as a UPS it will, with enough Eskom failures, destroy any battery bank.
(Actually that goes for  every single UPS and solar system out there today.)

You can only stop that 2 ways:
1) Get the battery bank and load specced to the T - very expensive..
2) Or you you stop the inverter, under load, at say 50% battery SOC. You cannot use volts for that, you have to use the battery SOC for that.

And if you have say Trojans as your preferred batteries, a very good choice(!) by the way, and the Voltronic charger (solar or Eskom) cannot be set for them specifically, it actually slightly angers me for Voltronics entered a mature market where batteries, MPPT charge controllers and calculating SOC has been fine tuned years before their first Voltronic device was ever designed.

Voltronics today craft very good UPS'es but they are not yet real true blue blood solar UPS equipment. Maybe they are going to upgrade their firmware one day to become the leader, for what they have built has a very real market, especially at that price, and when they can do what I can today, I will sell my Victron and the rest of the equipment and get a Voltronic device.

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