Jump to content

Axpert MKS 5KVA Inverter - 48V


Johan Brits

Recommended Posts

Just now, plonkster said:

No. We spent it. On the extra cables and charge controllers :-P

I still prefer my charge controller to go directly to the battery with a separate (thicker) cable from the battery to the inverter, and a large fuse between the inverter and the battery. In my mind's eye I imagine what happens when you have the inverter and the MPPT hard-wired to each other on a bus, with a fuse between that bus and the battery, and then the fuse goes while under full load. So now the inverter and the MPPT are duking it out and it's clear things won't go well and in the best scenario a shutdown will follow. The MPPT is going to back off as the load changes... but will it do so quickly enough not to cause a severe overvoltage situation and blow stuff up? I would like to think that the designers thought of that... really, I would :-)

Yup. From experience, when the battery fuse blows, on an Axpert inveter, you sit in the dark. My Axpert at home blew a 250A fuse last year! Still don't know what caused it to blow since the calcs showed that the inverter should have tripped instead. 

Quick tip, to the Axpert users: When the battery fuse blows, DISCONNECT the PV string before you try and replace the fuse, even if the inverter is OFF, purely since the battery and PV connect to the same DC bus. It is still LIVE. This is where I agree with plonkster, it is better to have a separate MPPT from the inverter. It's more expensive but allows for more redundancy. 

Link to comment
Share on other sites

Fritz: re 7 strings. No, remember that the 60 A limit is at the output of the MPPT. With say 90 V at the panels and say 53 V at the battery, you have 90/53=1.7x less current at the input of the MPPT. So that's a limit of some 60/1.7=35.3 A, say 36 A with losses. So to max out the MPPT when the battery is at 53 V you need 90 x 36 = 3240 W of panels. Working with panel current, that's 36/8.5=4.2 strings. That's about1.7x less than the 7.1 you came up with.

But that's at maximum panel output, which you rarely see. It's better to have more panel power available, so you get more use of the MPPT in cloudy conditions, at the expense of some clipping on sunny days around noon. So 7 strings is probably a reasonable number, just for the wrong reasons ☺

Edit: actually, 1.7x (as pointed out in an earlier post, it varies with battery voltage) is a bit high for an "overclocking factor". 1.3x is more reasonable, so 5 or 6 strings (4.2x1.3=5.5).

Edit 2: ising Solamahn's factor of 1.4x, that would tip it towards 6 strings.

Edited by Coulomb
Link to comment
Share on other sites

What i dont like/understand about you calculation is the following:

PV input 90V batt @ 48V

Thus 90/48 = 1.875   60/1.875 = 32A   90V x 32A =  2880W

PV input 90V batt @ 58V

Thus 90/58 = 1.55  60/1.55 = 38.6A   90V x 38.6 = 3474W

So you need more input power when batt voltage is higher (more charged)?

 

Link to comment
Share on other sites

19 hours ago, SilverNodashi said:

Yup. From experience, when the battery fuse blows, on an Axpert inveter, you sit in the dar

Perhaps its my allergy to having to wait for the courier to bring in supplies to our "dorp" but I keep a store of solar and battery fuses probably R400 worth. Nothing worse than having your entire system not working for want of a R50 fuse, which even in a metropolitan area you going to struggle to source on a Saturday afternoon and the rugby is on. Mind you with the way rugby is going you may well find someone who is prepared to open up his shop rather than endure 80 minutes of misery.

Link to comment
Share on other sites

2 hours ago, Chris Hobson said:

Perhaps its my allergy to having to wait for the courier to bring in supplies to our "dorp" but I keep a store of solar and battery fuses probably R400 worth. Nothing worse than having your entire system not working for want of a R50 fuse, which even in a metropolitan area you going to struggle to source on a Saturday afternoon and the rugby is on. Mind you with the way rugby is going you may well find someone who is prepared to open up his shop rather than endure 80 minutes of misery.

I also keep a couple spare fuses, both for the batteries and solar panels, and always supply clients with 3x spare fuses for everything. 

Link to comment
Share on other sites

6 hours ago, Fritz said:

So you need more input power when batt voltage is higher (more charged)?

Yes, exactly. Think of it as pushing against a higher pressure (higher voltage). That higher pressure (voltage) can do more work per time )power) with the same flow (with the same current). So you need more power now (charging a battery with rising voltage) so that the battery can provide more power later (58 V at 100 A is more power than 48 V at 100 A).

Conservation of energy.

Link to comment
Share on other sites

  • 1 month later...

Hi all,

I am new here and am looking at getting my own setup going soon. It's nice to be able to see everyone's projects and learn from the pro's. :)

I'm interested in the Axpert Inverter but have read on another forum that the unit can't combine power sources to supply the requested load. This comparison for example between the Axpert and Infini:

Quote

Axpert:
If you have a 1kW load running, but you are only able to get 800W from PV (i.e. you're 200W short), the entire 1kW load is switched into bypass mode (i.e. pulled from Eskom), or it adds the missing power from battery - potentially draining your batteries just before load shedding is scheduled to start. i.e., it pulls from only one supply in order to facilitate the load.

Infini:
If you have a 1kW load running, but you are only able to get 800W from PV (i.e. you're 200W short), the remaining 200W is pulled from Eskom. i.e., it pulls from all supplies simultaneously in order to facilitate the load.

Is this correct?

Regards,

Francois

Link to comment
Share on other sites

francois, that is correct. The Axpert cannot mix AC and DC sources, the Infini range can do that and is a lot more flexible. Disadvantage is that the 5kW Infini is quite pricey and is the only model that you can cluster as far as I know. I use the 3kW Infini and has often "overloaded" it up to 5-6kW for shortish periods of time (1-5 minutes). I know other members on the forum also doing the same. You can only do that if you have PV and grid available as far as I know. If and by how much it shortens the expected life of the inverter? No idea.

Link to comment
Share on other sites

1 hour ago, francois said:

Axpert:
If you have a 1kW load running, but you are only able to get 800W from PV (i.e. you're 200W short), the entire 1kW load is switched into bypass mode (i.e. pulled from Eskom), or it adds the missing power from battery - potentially draining your batteries just before load shedding is scheduled to start. i.e., it pulls from only one supply in order to facilitate the load.

Infini:
If you have a 1kW load running, but you are only able to get 800W from PV (i.e. you're 200W short), the remaining 200W is pulled from Eskom. i.e., it pulls from all supplies simultaneously in order to facilitate the load.

I'm pretty sure those are my words....:D

Link to comment
Share on other sites

  • 2 weeks later...

I have 2x 5kva mks in parallel at home and 1x 3kva mks at my office. They are awesome off-grid inverters. The only issue I have is when they switch back and forth from grid to battery and from battery to grid. The switch over is quite crude and my Sony tv at home does not like the dip in power. I have to unplug it for 5mins almost every time it switches over so that it can reset. Running it through a standard inline ups doesn't help either and I am not prepared to spend R3k on an online ups. Any advice?

Link to comment
Share on other sites

3 minutes ago, Johann1982 said:

The switch over is quite crude and my Sony tv at home does not like the dip in power.

@The Terrible Triplett is the man who knows about UPSes and the transfer time. We've had some discussions about the transfer times of inverters, and how even our favourite expensive blue units still have a fairly slow transfer of a whole 16ms! At 16ms my television seems happy enough. The Yamaha AV receiver will sometimes click in and out (it has the old-fashioned speaker-pop protection relay), but that's it.

I'm half-inclined to suggest replacing the television :-)

 

Link to comment
Share on other sites

8 minutes ago, superdiy said:

Well, seeing that it is a Sony it is maybe not a bad idea.  Ek sê altyd: "Ek sounie dit gekoop het nie"

Not that the Bravia (for example) is a bad TV. Nor that any of the others are necessarily much better. They all come from China now, some are locally assembled (eg Samsung, Hisense, Sinoteq aka Prima). Still, strikes me as odd that the TV can't handle the kind of dip most things with a decent power supply can.

Link to comment
Share on other sites

What's the transfer time on the Axpert, for interest sake?

I've been up and down on the documentation of my own inverter, because I'm unsure whether the benchmark quoted and remembered 16ms is even correct, but I can't find anything for my own inverter. Just something in the documentation indicating that it wants to sync the waveform before it switches, so from the time it makes the decision to switch until it does is 0.5 seconds (time it takes to sync the voltage and frequency), and then I'd expect the actual changeover to be quite smooth. I wonder how the Axpert does it (or if it even does something as sophisticated as this). Might have nothing to do at all with the switching time :-)

Link to comment
Share on other sites

6 minutes ago, Johann1982 said:

 Maybe some sort of capacitor to smooth out the transfer?

Cap won't help on the AC side, maybe if you open up the TV and add one or more to the DC rails of the SMPS.

Edit: Or even a bigger cap on the input stage (after rectification) of the SMPS.

Edit 2: But if you increase the capacitance on the SMPS input stage, you might have to change the value of the fuse as well, because the inrush current will increase if the capacitance is increased. 

Link to comment
Share on other sites

As far as I can remember the axpert manual quoted 8 or 10ms in UPS mode. Sometimes when the load is below 500w it would not dip. The bigger the load the bigger the delay. I can't immagine that this is good for electronic equipment. My DSTV decoder also sometimes gives the red "!" when the power dipped, but I am getting rid of that rubbish end of the year when my contract runs out.

Link to comment
Share on other sites

29 minutes ago, superdiy said:

According to the manual, on APL (appliance mode) the transfer time is 20ms typical and on UPS mode the transfer time is 10ms typical.

4 minutes ago, Johann1982 said:

As far as I can remember the axpert manual quoted 8 or 10ms in UPS mode. 

on APL (appliance mode) the transfer time is 20ms typical

on UPS mode the transfer time is 10ms typical

Link to comment
Share on other sites

7 minutes ago, plonkster said:

I wonder how the Axpert does it (or if it even does something as sophisticated as this). Might have nothing to do at all with the switching time :-)

@Coulomb Mentioned somewhere that even though it is not a grid tied inverter it always seems to have the frequency synced to the mains (I see this on my own) to be able to do the fast switching.
No routers, tv's or even the microwave complains when I switch mine

Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

×
×
  • Create New...