2 hours ago, pilotfish said:

The MKS Plus version is indeed 145Voc as per the attached brochure, but I would still stay away from 3 panels in series as you have a real possibility of exceeding the max 145Voc under certain conditions.

OK my head hurts. How many versions of the Axpert does Voltronic have?

Yes the specs for the Axpert MKS 3K-24 Plus are confusing. On the Voltronic website here its says MPPT Range @ Operating Voltage is  60~115 VDC but on the spec sheet sent to me by bonanzatech it says 30~ 115 VDC. Both have Maximum PV Array Power of 1500w and Max. PV Array Open Circuit Voltage 145 VDC. Now ive also just noticed while copying and pasting all these specs that the model description on the Voltronic site says : Axpert MKS 3K-24 Plus - 3000VA/3000W and on the specs sent it says Axpert MKS 3K-24 Plus - 3000VA/2400W. Which one is it I wonder? 2400w or 3000w? 

How similar would panels need to be if I try match these to get a fourth? 

Also I finally figured out how to use the Design Tool published somewhere here . Thanks @Chris Hobson and Izak!

2x2 seems the answer. H

Rated PV Array (W)			1200
Rated W at hot temp			1092
Voc			98
Vmp			72
Rated PV Array Current			16.66
Cold Voc			109
Cold Vmp			83

 

@pilotfish you recommend the Axpert MKS 5K. Are you talking about the 24 or 48v one? Cant seem to find the 24v one anywhere and I dont want to go 48v at the moment because I will be losing aH as I would have to put 4 x 105aH  in series to get to 48v but still only have 105aH. My thinking is with 4 x 105aH on a 24v system I can at least get to 210aH for the same initial cost. I know 48v is ideal but all considered I think 24v is a perfectly acceptable solution. 

 

Again thanks to everyone for the input.

2 hours ago, Askari said:

Axpert MKS 5K. Are you talking about the 24 or 48v one?

The MKS 5K is a 48V inverter.

2 hours ago, Askari said:

I dont want to go 48v at the moment because I will be losing aH

You don't care about Ah. What you care about is Wh. 4 x 100Ah batteries have exactly the same capacity as 2 x 200ah, because 4 * 12V * 100Ah == 2 * 12V * 200Ah == 4.8kwh. They will also cost pretty much the same, and you get to use thinner cables with the 48V one. The only downside really is that really good batteries tend to be larger capacities, that is to say, there aren't many good 100Ah batteries but there are a lot of crappy ones.

Things change when you go LiFePO4. Then there are lots of good batteries around the 100Ah mark :-)

2 hours ago, Askari said:

My thinking is with 4 x 105aH on a 24v system I can at least get to 210aH for the same initial cost. I know 48v is ideal but all considered I think 24v is a perfectly acceptable solution. 

No, you would have the same amount of energy stored with 4 batteries;

4 batteries in parallel = 420Ah at 12v = 5.04kWh

2 batt's in series, paralleled with another 2 batt's in series = 210Ah at 24v = 5.04kWh

4 batt's in series = 105Ah at 48v = 5.04kWh

You will run the same load for the same amount of time irrespective of whether  you are using 12v, 24v or 48v arrangement. The difference is at 48v your current (amps) will be half that of a 24v system and 1/4 that of a 12v system. This is a big advantage because at 48v you will have lower current, therefore lower voltage drop, lower power loss, and you can use thinner and cheaper cables. 

Having a 48v system is an advantage over a 24v system

2 hours ago, Askari said:

you recommend the Axpert MKS 5K. Are you talking about the 24 or 48v one?

The MKS 5K is only available at 48v

Oops, @plonkster beat me to it

Just now, pilotfish said:

Oops, @plonkster beat me to it

Great minds think alike, but fools never differ :-P

Just now, plonkster said:

but fools never differ

I beg to differ....

10 minutes ago, plonkster said:

The MKS 5K is a 48V inverter.

You don't care about Ah. What you care about is Wh. 4 x 100Ah batteries have exactly the same capacity as 2 x 200ah, because 4 * 12V * 100Ah == 2 * 12V * 200Ah == 4.8kwh. They will also cost pretty much the same, and you get to use thinner cables with the 48V one. The only downside really is that really good batteries tend to be larger capacities, that is to say, there aren't many good 100Ah batteries but there are a lot of crappy ones.

Things change when you go LiFePO4. Then there are lots of good batteries around the 100Ah mark :-)

EDIT: See some responses were posted while I was typing below. Reading now.

 

According to the  Voltronic site there is a Axpert MKS 5KP-24 model which is 24v . 

About the battery thing, perhaps Im not understanding correctly but lets say for the sake of argument I have 4 x 105aH batteries. For axample 1) they are connected in series which gives 48v and  105aH capacity. For example 2) they are in a 2x2 array so 24v but 210aH capacity. 

If I connect a light say, in which example will the batteries run out first?

2 minutes ago, Askari said:

If I connect a light say, in which example will the batteries run out first?

They run out at the same time.

But in order to run 5kVA of appliances your cables, fuses etc will be MUCH more expensive on the 24v system because you must cater for a maximum of 200 battery amps whereas the 48v system you must cater for100 battery amps

Well I have been on the wrong track havent I? 

Thanks for clearing that up. Me and electricity have never been best of mates...

13 minutes ago, pilotfish said:

fuses etc will be MUCH more expensive on the 24v system

The fuses are actually cheaper. What makes fuses expensive is the voltage rating. A 80V fuse costs double what a 32V fuse does. But that's still insignificant compared to the cable costs.

24V MPPTs (when you go external) is also slightly less expensive, but that doesn't count here since you're going for an all-in-one device.

And besides, going 24V to save a few bucks on fuses and MPPTs is penny wise and pound foolish... well... let's say if you can afford it. Because those who have been around long know that I have a 24V system myself... why? Because when I bought the system I was strapped for cash and the lower voltage meant expansion was easier (less panels/batteries needed to make up a string). Over the years I bought everything to be 48V compatible and when I got to the point where I could afford a 48V Multi... I decided to buy a LiFePO4 battery instead :-) So I'm on 24V because of a legacy decision... not because it is better.

Well "E Day" arrived and Eskom cut my power even though they assured me this wouldnt happen while the clever area manager/rep/salary drawer was looking into things (which he admitted to not having done when I called him to thank him...)

Any how it is what it is an I have decided to embrace this opportunity to become self sufficient. The wife does not share my enthusiasm  somehow....

Using a small 2kw petrol gennie for a few hours in the morning and a few in the early evening was surprisingly sufficient just slightly annoying having to turn off at night before bed. While this solution was doing the trick I started accumulating panels and goodies from friends who had offered.

I now have the following basic system:

2 x 300w panels in series, a Microcare 60A charge controller, 2 x 105AH New Probe deep cycle batts in series for 24v and a small 1000VA (600W+-) Inverter.

My aim is to use gennie as needed but for the system above to run fridge (150W), laptop (90W) and kids TV (150W) during the day. If nothing else then the fridge. My issue now is that I have tested the system overnight and this is concerning me:

Starting off with both batts fully charged showing 12.6V on the dual batt monitor I turned on the big TV (300W) and watched for 1 Hour then turned off and left on standby. Also turned on one 3.5W light in the passage and left on for 10 hours. Nothing else was on. This morning the batteries are showing RED on the monitors and reading 11.7V!

If I understand correctly my Wh capacity is 2*105Ah*12v=2520Wh . Using half for battery health that is 1260Wh

Usage was as follows: TV 300*1hr=300Wh  Light 3.5*10=35Wh + a little bit? for standby TV = Total of 335Wh so nowhere near the 1260Wh 

I now can think of 3 reasons: 1) My calculations are stupid. 2) The batteries are not fit for purpose. 3) There is something stealing energy. Now having made sure nothing else was on or plugged in I am left wondering if the wiring in the house, specifically the earth leakiage is to blame? I have the system plugged into a wall socket and is being spread around the huse like that. The main circuit breaker to Eskom is off but earth leakage isnt, 

Any ideas or comment from you clever fellows?

Inverter efficiency has to be taken into account too. Many of those 1000VA old-tech jobbies are about 85% efficient at best. So your 335Wh is more like 400Wh. Then you also have to take into account the quiescent draw of the inverter. Of course the quiescent draw itself makes up a large part of the poor efficiency, but that 3.5W light likely had an overhead of at least 20W quiescent power, so that lamp cost you 235Wh, not 35. So I'd estimate your overnight draw-down closer to 600Wh. Conservatively speaking. That's still nowhere near 50%, but perhaps the batteries weren't 100% fully charged or some other calamity. It really is hard to say.

The 20W figure I used is for my Multiplus, which is known to be one of the better inverters in that respect. If you redo the math with say 35W, you're on the other side of 750wh.

I'd start by measuring the quiescent draw of the inverter. Without that we're just spitballing.

Oh... and...

17 minutes ago, Askari said:

I have the system plugged into a wall socket

Suicide plug. Please don't do that... :-)

4 minutes ago, plonkster said:

Oh... and...

Suicide plug. Please don't do that... :-)

Yea I know I know. Choices I dont have at the moment. This is a work in progress.

How would I measure the quiescent draw of the inverter? Just leave it running with no other draw and see what it does to the batteries? 

24 minutes ago, Askari said:

Yea I know I know. Choices I dont have at the moment. This is a work in progress.

I know.... the kind of thing you do but tell nobody about. We've all been there :-)

24 minutes ago, Askari said:

How would I measure the quiescent draw of the inverter? Just leave it running with no other draw and see what it does to the batteries? 

You have a DMM (digital multimeter)? Put it on the current range, and in the positive line of the inverter, with no load on it. Measure the current and multiply by battery voltage.

And the other lead?

2 minutes ago, Askari said:

And the other lead?

Current meter goes in series with the inverter... red probe to the battery, black probe to the red cable that goes to the inverter, so the power flows THROUGH the meter (and then through the inverter and back via the negative cable).

Do I disconnect the main lead from batt +ve to Inv +ve  and essentially replace with DMM so red lead on batt+ and black lead on inverter +?

 

1 hour ago, Askari said:

Do I disconnect the main lead from batt +ve to Inv +ve  and essentially replace with DMM so red lead on batt+ and black lead on inverter +?

 

Yes.

Though the fact that I have to explain this in so much detail makes me a little worried, no insult intended. You sorta have to know what you're doing. Multimeter has to be capable of the current (I'd say at least a 10A range to be safe), you have to have the leads in the right sockets on the multimeter (on many of them there is a separate socket for the 10A range)... we already have one smoke releaser on this forum :-)

8 hours ago, plonkster said:

we already have one smoke releaser on this forum :-)

Haha, I didn't want to say anything when I read your post earlier - but I foresee some smoke!

You would kinda need to know the difference between A/mA, AC/DC, and voltage tests in parallel while current tests in series - if this is Greek then get someone else to do the tests for you, it will be cheaper than most multi-meters.

12 hours ago, pilotfish said:

cheaper than most multi-meters

The very cheapest ones are around R100. You generally don't want to use them on anything above single-phase low-voltage sort of stuff, I would not even try them on a 3-phase 380V setup. Even if they do have a 1000V range... that's just false advertising.

Hehe. Stop worrying so much. When you said "in series" I had a brain fart. I was just checking you meant "in line" like my brain was speaking.

OK so the inverter (which is a UPS type pure sine wave) is drawing 1,6A with nothing else running off of it so by my calcs thats just shy of 40w

Last night ran the 3,5w light only and still batteries bordering on 11,8v

3 hours ago, Askari said:

OK so the inverter (which is a UPS type pure sine wave) is drawing 1,6A with nothing else running off of it so by my calcs thats just shy of 40w

Well, I suppose it is possible to make the numbers fit. To start, an empty battery has an open circuit voltage of 10.5V. You're seeing 11.7V with at least a 40W load on. It may well be that at 11.7V they are only 50% discharged. We simply don't know, not without adding more accurate measurement equipment such as a Victron BMV.

We also don't know the actual capacity of the batteries. They are advertised as 105Ah, but one has to wonder how it is that they got the extra 5Ah... sounds to me like marketing got involved, they likely used the C100 rate to get an extra couple Ah out of it.

Next, Peukert's law. At a 350W draw while watching TV, you're drawing a good 30A from the batteries. That's almost C5 for your combined +-200Ah (discharge over 5 hours) which is a very heavy load. When you discharge faster, your usable capacity is reduced. Most of this is voltage efficiency: Under such high loads, the voltage drops and the inverter compensates by drawing more amps, so a 350W load might well be doing the work at 11V, close to 32A. Combined with other losses, That's might well account for 20% of it.

That is to say, it doesn't sound like a good situation to be in, but it also doesn't sound completely wrong. That might very well be what live is like with two faux "deep-cycles" at C5.

So.... given your original question... I'll go for "you need better batteries". :-)

Your time and input is much appreciated. 

One would hope that 2 batteries would be able to run a small light for a night and a TV for an hour or two....

Im going to send those batteries back. The magic eye thingy is also not looking right.