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Axpert 5kva


Alec Swanepoel

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I thought so but was double guessing myself.... also want to add 4x panels to my 2x but was worried about over voltage with 3x big panels in a string.

What max amps do you get...?

Thanks

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1 hour ago, viper_za said:

You keep saying this and this is not true for the Axpert boys, the thing has enough settings to be safe by having a limit on your charging current and still be able to use the rest of your PV to carry the load

Agreed but nor does everyone have an Axpert. Case sample: Camel has a similar setup as me. :P

FWIW - Outback, Victron and Morningstar controllers have programmable settings, DIP switches or computer connected ... I swear!!! :D

 

Just to make sure, for my future comments on this matter. Say I have:
3kw array, 48v 100ah battery bank,
I can set the Axpert to only charge at say 10amps only if there is solar whilst I power say +-2000w at the same time from solar power only?

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31 minutes ago, The Terrible Triplett said:

Just to make sure, for my future comments on this matter. Say I have:
3kw array, 48v 100ah battery bank,
I can set the Axpert to only charge at say 10amps only if there is solar whilst I power say +-2000w at the same time from solar power only?

Yes this is possible, but minimum bank recommended for 5kva units (3000w Solar) is 200ah

So you would limit it to 20A 

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4 hours ago, The Terrible Triplett said:

Therein boys and girls, you always need to match the battery bank with the controller with the array, or you lose something along the line.

7 minutes ago, viper_za said:

... but minimum bank recommended for 5kva units (3000w Solar) is 200ah

I rest my case. :D

 

But my questions still stands.

As per Camel, with our MPPT's, if you limit the charge amps, you limit the max the controller can draw from the array = you lose a bit. 

But then you also said:

25 minutes ago, viper_za said:

Yes this is possible,

So the Axpert MPPT feeds two "circuits":
1) the battery charge circuit - that we have limited to 20amps for 200ah bank.
2) whilst the 5kva inverter can go all tappets wide open drawing every bit of amp the array can provide if the load is high, which say is double the batt charging limit of 20amps?

If this is the case ... I like.

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45 minutes ago, The Terrible Triplett said:

I rest my case. :D

45 minutes ago, The Terrible Triplett said:

Therein boys and girls, you always need to match the battery bank with the controller with the array, or you lose something along the line.

Wrong again, there is a option to limit it at 10A for say 100ah bank but they recommend you use a 200ah bank minimum. If I have gone with what was not recommended and used the 100ah bank and installed 3000w of PV It will still work but I would still not have matched what you stated as things that need to match?

45 minutes ago, The Terrible Triplett said:

If this is the case ... I like

Yes it can

TTT not necessarily wrong but your statement cant be applied to all setups

Edited by viper_za
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On 27/05/2016 at 4:30 PM, The Terrible Triplett said:

Same scenario i.e 25amps at 32v coming in (24v system) via the controller whilst inverter is humming away happily BUT this time the batteries are NOT fully charged. Lets assume they are 50% DOD.

What happens then?
How does the batteries not get damaged with the controller giving all it can from the array to power inverter and charge the batteries?

Same: no current to the battery, no damage to the battery.

Let's say the 32 V is the array voltage, and it translates to 30 A at 26 V at the battery voltage. You can think of electrical current as electrons flowing through a wire, the wires being like pipes that can carry current. It's not totally accurate, and conventional current flows the opposite direction to what negatively charged electrons wouuld flow, but this model is good enough for situation. So the rate of electrons from the charge controller is many squillions (like ten to the 24th power) per second, and we convert from such an unwieldy number to amperes on our meters, and in our heads. So we call it 30 amperes. The load on the inverter, in your exact scenario, is also 30 A. So that means that every electron that comes from the charge controller, goes off to the inverter to power the load. There are just none left to flow down to the battery.

Now let's suppose that the load decreases, such that the inverter is now only drawing 28 A, while 30 A are still coming from the charge controller. That means that there are 2 A that have to flow somewhere. If they didn't, the charge would start accumulating at the junction. The junction is like a very small capacitor; there might be say 20 pF of capacitance from all the cabling to battery negative. That's so small that at 2 A, the voltage across this capacitance would start to climb extremely quickly. Like about 1 volt  every picosecond (or 100 V per nanosecond, or 100,000 V per millisecond, or 100 mega-volts per second); that's very fast. This increase in voltage will cause the battery to look like a good place for those two amperes to flow. So in reality, the voltage at the node that has the charge controller output, the inverter input, and the battery, increases a tiny fraction of a volt, just enough to cause the two amperes to flow to the battery. So now current into the node is zero again (30 A going in from the charge controller, -2 A into the node from (= +2 A going out of the node to) the battery, and -28 A into the node from (again, = +28 A to) the inverter. That's Kirchoff's law: current into a node must always sum to zero. Even if there is a capacitor there, you can make the capacitance explicit, and the law still holds. We say that the excess solar current is being used to charge the battery.

One more scenario to complete the example. Suppose the load now increases such that the inverter is drawing 33 A, but again the charge controller is still outputting 30 A. Now there is a shortage of electrons; the inverter is sucking them in at a rate of 33 amperes, but only 30 A worth are arriving from the charge controller. You can guess where the other three amps has to come from - it will come from the battery. Again, the unbalance of currents this time causes our 20 pF capacitor to discharge slightly, making the node voltage decrease (this time), so there is incentive for electrons stored in the battery to "roll down the hill" from the battery to the node. We say that the battery is providing the deficit between the solar input and the inverter output.

The other key concept that beginners need is that even though there might be say 25 A at 32 V available from the array due to the amount of solar energy falling on it, the controller doesn't have to draw that current at any particular time. Suppose the load is very low, and the inverter is only drawing 5 A. Sure, if the controller let it, the 25 A at the array (30 A at the battery voltage) would mean that 25 A would flow into the battery, charging it. If it's full, or is of a size such that 25 A would damage it, then that's not good. But that's why we put smarts into the charge controller. It should sense what the battery needs, and adjust its output so that the battery isn't overcharged or otherwise damaged.

That's one reason that an integrated solution like the Axpert has an advantage; it can be aware of the battery current separately to the charge controller's output current. For a stand alone charge controller, this may not be possible, so it might not provide all the available solar power if the inverter is using some or all or more than all of it; the charge controller thinks it's all going into the battery. Another example. Suppose I have a small battery pack that can safely be charged at 20 A maximum. Suppose the inverter load is high, 50 A. I have a stand alone charge controller that isn't aware of the inverter's load. I have a huge array, capable of 60 A at battery voltage. Battery is at 50% SOC, so I'd like to charge it. Since the inverter is using 50 A, I'd like to output all 60 A from the charge controller, so I'd have the left-over 10 A for charging the battery. But I had to limit the charge controller to 20 A, because if the load is zero from the inverter, that's what the charge controller has to limit itself to. So I have 60 A available, but I'll only be supplying 20 A, so instead of charging the battery at 10 A like I'd want, it's discharging the battery by 30 A instead! With a correctly set-up Axpert-like system, I would instead be using all available 60 A (at battery voltage) of solar current. This is a bit of an extreme example; I should not be using such a small battery. Hopefully, I'd be using a battery that is large enough that I don't have to limit the output current of the charge controller at all, so then this advantage (of an integrated system) goes away.

I hope I haven't confused everyone with the extra scenarios.

[ Edit: I don't read all these posts; I usually limit myself to the inverters forum. So my apologies if this has been discussed already. ]

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On 27/05/2016 at 5:05 PM, Chris Hobson said:

Hi Coulomb 

Do you know of anyone in Oz who has oversized their PV array with the PIP/Axpert?

I'm pretty sure it's quite common. For example Solamahn (who isn't in Australia, but frequents the AEVA forums):

http://forums.aeva.asn.au/forum_posts.asp?TID=4332&PID=57466&title=pip4048ms-inverter#57466

"I have had no problems with the 4048ms scc even with 15 x 280w connected 5 x 3 and all facing the same direction. "

So that's 4200 W nominal of solar panels. Back then, all SCCs (solar charge controllers) in the PIPs (like your Axperts) were 3000 W capable. So that's a 40% "overclocking".

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4 hours ago, Coulomb said:

Same: no current to the battery, no damage to the battery.

I hope I haven't confused everyone with the extra scenarios.

[ Edit: I don't read all these posts; I usually limit myself to the inverters forum. So my apologies if this has been discussed already. ]

Thanks alot Mike ... lovely detailed post.

The benefits of a combination Inverter/MPPT like the Axpert (even better the Inifini - which can also add Grid seamlessly instead of Battery)

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I know that when you have the ve-bus to ve-can cable on a Victron system, the hub-1 assistant in the inverter can adjust the charge controller, and that gives you similar functionality to the axpert: In your hypothetical situation where you have a potential of 60A coming in and want to limit the battery to no more than 20A, the inverter can adjust the MPPT so that it pumps enough to satisfy the constraints. I'm not sure exactly how it does that. I also know the cable is rather expensive, and that hub-1 can work without it (basically by looking at the configured float/absorb voltages, more detail there that's not really applicable here).

I have the documentation somewhere of how to read/write the vecan registers in the can-bus controllers, and I also have the hex protocol documentation for writing settings to the ve-direct controllers. So in theory... it can be done with the blue controllers and a suitable embedded solution. The danger here would be if your embedded little controller crashes while it has the taps open at full blast... and then your load drops :-)

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@Coulomb Thank you, it makes a lot of sense for the 1st time.

I think the next generation stand alone charge controllers should have 2 circuits. One for inverter and one for batteries.

@viper_za - NO, I am still not getting a Voltronic device. I like Victron more.
Will just do the effort to match the batteries to the load, the controller and array matched for the batteries with Eskom as backup ... setup and forget. :P

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3 hours ago, The Terrible Triplett said:

I think the next generation stand alone charge controllers should have 2 circuits. One for inverter and one for batteries.

For a second I thought you hit the jackpot! So simple really, just add two hall sensors in the charge controller with two outputs, feed both current signals into the microcontroller, twiddle some lines of code, and voila, you're done.

Then I started wondering what I am missing... and soon (I hate it when this happens) I had like a hand full of issues. I even thought of Hannes who burned a CC when the (Lithium Ion) battery bank tripped and the inverter/charger and the CC ended up duking it out, with the CC hitting the planks.

So the question here would be, where do I put the battery disconnect/fuse arrangement. When you hit the disconnect, or when the fuse blows, you want the charge controller and battery on one side of the fence, and the loads on the other side.

So this is definitely going to complicate the charge controller a bit, if you want it to be safe and all.

My alternative would be that you use something like the shunt that comes with the BMV in the inverter line, and feed the voltage signal into the MPPT. That way you can still use external safety equipment. MPPT then simply reads the analog input, and adds that on to the maximum battery current. This has the additional upside that on a system where you don't want this... you don't pay for something you don't want.

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If Axpert did it safely, why don't we work out the details and do same here on the Forum with external charge controllers?

EDIT: Then we send the details to Outback, Morningstar and Victron?

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17 minutes ago, The Terrible Triplett said:

If Axpert did it safely, why don't we work out the details and do same here on the Forum with external charge controllers?

....TTT kry klaar ...... just buy an Axpert :D. Victron certainly not going to want to copy a cheap Chinese designed scc/inverter.

 

I have often said an Axpert is like a long term girlfriend. Yes it is not perfect but you too scared to trade her in for a Claudia Schiffer or another super-model because you heard she can't cook. 

P.S. I have nothing against Claudia Schiffer I understand she is a very nice person and actually down to earth considering her success -reference to her for illustrative purposes only. :P

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30 minutes ago, The Terrible Triplett said:

If Axpert did it safely

I'm sure they put in proper protection for that. What I am talking about it this hypothetical situation: Your inverter/charger is charging the batteries at full blast when someone breaks into your shed, uses an axe to chop off the cables going to the battery, and drives off with your batteries. In that instant, the entire shock wave of charge current has nowhere to go but backwards through the charge controller. Before the charger can pull back, the voltage rises above 70V and the SMPS in the charge controller burns out...

The fix might be as simple as a fuse and a surge arrestor (Zener diode?) to protect that part of the circuit, but in the two charge controllers I saw, they don't have that.

So I'm just saying, you need to design the CC to be able to deal with a sudden loss of battery if you're going to connect it that way, or you'll need to incorporate the disconnection devices into the charge controller. That creates an entirely new model of charge controller with a limited market (those who want it can just go buy an Axpert). So not shooting down the idea, I still like the idea, just thinking that I personally would like this functionality as an optional add-on. It would literally be a box with two terminals on it, a hall-effect current-sensor (or a shunt) inside, and two signal wires going to the charge controller. So literally all that needs changing in the charge controller is 1) it needs an extra analog input, and 2) the software needs to scale that analog input into a current and add that on top of the maximum configured.

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Suggest it to Victron ... ?

By the way, if you chop your batt cables today, with your controller running at full operating parameters, what protection is there today?

I think that sometimes one has to take certain situations as not likely, and take the resultant minuscule risk of wot, 1 in a 1 000 000.

If someone chopped my batt cables to steal them, well, they need to get past me and if I am not here, both instances will be a insurance claim for a new controller. ;)

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41 minutes ago, The Terrible Triplett said:

what protecting is there today of it?

I have two separate cables going from the batteries to the CC and the inverter. You'd have to chop them separately and that inherently guarantees that such a situation will not occur.

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When you connect the inverter to a second terminal on the charge controller, you modify this safe topology. My cable-chopping example is also just that: a silly example. Hannes' li-ion BMS tripping is a real life example of a battery jumping off the seesaw at an inopportune moment :-)

Sent from my GT-I9195 using Tapatalk

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37 minutes ago, plonkster said:

Hannes' li-ion BMS tripping is a real life example of a battery jumping off the seesaw at an inopportune moment :-)

Kyk, that was a really bad one!

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  • 11 months later...
On 5/27/2016 at 5:05 PM, Chris Hobson said:

Hi Coulomb 

Do you know of anyone in Oz who has oversized their PV array with the PIP/Axpert? I am getting mixed response from the supplier in SA. This may be due to them wanting to sell me a second unit.

Chris,

only a year late (only just noticed this post due to Barezzi liking one of mine from a year ago)... Solahahn in this post said:

Quote

 I have connected 24 x 300w panels to this model and no problems.

"This model" refers to the PIP-4048MSD, a dual MPPT version of the Axpert 5 kVA. So that's 7.2 kW nominal, an overclocking factor of 1.2:1.

Ok, Solamahn is from Papua New Guinea (you asked for anyone in Oz), but he posts on the Australian forum. He has experience with dozens of installations, some of them quite large.

OffgridQld has 8.2 kW of panels; it's not clear if all of that is connected to his single MPPT PIP-4048 inverter, but probably at least half of it is.

I myself have 4.4 kW on a single MPPT model, though only 3.2 kW nominal of that is connected to the PV input of the inverter (the other 1200W goes via a Blue Sky Energy charge controller). 

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