14 hours ago, RobG said:

I have to get the new mks ll 5kw which can handle 4.5KW of pv

Be careful, my understanding is that the Axpert MKS II is the one with the 450 V solar charge controller. What they call the Axpert MKS (without the II) is the PF1 5 kW model, and they upgraded to 80A solar charging in late 2015.

So if you don't want to rewire your panels, don't get the II model. I'm pretty sure that you can still get the non II model.

Thanks Coulomb

Yeah I'm going to have to get the mks l 80A. 

But  I'm still told that I have to get the exact same 250w panels to expand the array to 4000w. I can get 250w panels as explained. 

We reconfigured the strings to 3 panels per string 750W per string x 4. This is 3kW. If you add 4x275 =1100W then I would have 4.1kW. One panel per string. 16 panels in total. It should work on the 80A Axpert. 

17 minutes ago, RobG said:

Thanks Coulomb

Yeah I'm going to have to get the mks l 80A. 

But  I'm still told that I have to get the exact same 250w panels to expand the array to 4000w. I can get 250w panels as explained. 

We reconfigured the strings to 3 panels per string 750W per string x 4. This is 3kW. If you add 4x275 =1100W then I would have 4.1kW. One panel per string. 16 panels in total. It should work on the 80A Axpert. 

Can can use higher wattages panels as long as the Voc and Isc is close to what you have right now.

Now again I'm very confused. 

An installer tells me that I can add another 1000w to my pv array, despite the spec sheet shows maximum pv array of 3000W, which is installed. The label on the Inverter shows maximum 60A MPPT. 

I'm already getting 56amps in when there's cloud flare. 

Is this a clueless technician or is there any validity in what he says? 

 

Personally I wouldn't exceed the max spec, but that is just me. There should be a factor of safety built in to that limit, but why push your luck?

Wouldn't exceed the manufacturer's specification as a general rule. That being said, depending on the angle of the actual installation, east, west, etc  your actual peak power generation could be lower than the nominal installed wattage. Maybe your installer has done a calculation. Or not.

2 hours ago, RobG said:

Now again I'm very confused. 

An installer tells me that I can add another 1000w to my pv array, despite the spec sheet shows maximum pv array of 3000W, which is installed. The label on the Inverter shows maximum 60A MPPT. 

I'm already getting 56amps in when there's cloud flare. 

Is this a clueless technician or is there any validity in what he says? 

 

Hi Rob

Many MPPT Chargers will limit the output current into the battery to a safe value, irrespective of the available PV Power.  If this is the case for your MPPT, the technician may be correct in that you may benefit from the extra power during Winter/low-light conditions. A possible down-side of this approach is that the MPPT will be running at maximum power for extended periods during Summer/bright-light conditions. Even if you have adequate cooling, this may impact on the overall reliability of the MPPT.

15 hours ago, RobG said:

The label on the Inverter shows maximum 60A MPPT. 

Axperts, confusingly, only ever quote battery-side charge current. It's called a 3000 W MPPT because the rounded battery voltage is 50 V, and 50 V x 60 A = 3000 W (on the battery side). To get 3000 W on the battery side, you need at least 3061 W of panels, more if the battery voltage is higher (and it nearly always is).

It should certainly be safe to add an extra 12.5% over the nominal power, but that's only 3000 x 0.125 = 375 W, so 3375 W. That's based on later models, where they do specify a realistic maximum PV power. Others say an extra 20% is OK, so that would be 3600 W. I'm sure that 4000 W will work, but there could be overshoots and undershoots that may slightly affect battery life.

The MPPT will certainly limit the charge current to a safe value. MPPT failures seem to be rare, and I don't know of any that were due to over-sizing, unless they were ridiculously over-sized, like twice nominal power.

On 2018/12/26 at 1:37 PM, Jaco de Jongh said:

Or install a  Victron MPPT, with some more PV, configured to take care of the Charging, leaving the existing PV to take care of the loads

Jaco, this is a very interesting suggestion which makes a lot of sense to me.

How many solar panels would a mppt require to put out 40a to charge a set of Pylontech batteries? Has anybody setup a system like this to trial it in the real world? Is it possible to charge batteries from a separate charger whilst simultaneously drawing power from it via an inverter?

I tried to google the topic but nothing came up.

All info would be much appreciated.

I really hope you are better after the mishap.

Edited April 30, 20197 yr by Johandup

Yes, because everything goes through a common point to the batteries. I have 2 mppts, a wind generator and generator charger all connected to the battery bus bars, and the inverter takes power as required.

Edited April 30, 20197 yr by DeepBass9

16 minutes ago, Johandup said:

Jaco, this is a very interesting suggestion which makes a lot of sense to me.

How many solar panels would a mppt require to put out 40a to charge a set of Pylontech batteries? Has anybody setup a system like this to trial it in the real world? Is it possible to charge batteries from a separate charger whilst simultaneously drawing power from it via an inverter?

I tried to google the topic but nothing came up.

All info would be much appreciated.

I really hope you are better after the mishap.

hmmm... 1 or 2 or 3 MPPT's won't make much of a difference, you can't dedicate the MPPT to a job as the panels connect to MPPT, the MPPT/s (notice the "s") then all connect to a buss bar, this bus bar is then connected to your batteries, also connected to this bus bar is the input vIN on your inverter.

G

8 hours ago, Johandup said:

How many solar panels would a mppt require to put out 40a to charge a set of Pylontech batteries?

Not taking losses into consideration, to charge Pylons at 53Volt and 40 Amps you would need 2120wh PV. With normal losses 2800wh should be sufficient.

8 hours ago, Johandup said:

Has anybody setup a system like this to trial it in the real world?

I have as a test and it worked..

8 hours ago, Johandup said:

 Is it possible to charge batteries from a separate charger whilst simultaneously drawing power from it via an inverter?

Yes it definitely is. A Victron system is build around this concept, you are just going to be applying it to another system. Remember to adjust the settings so that you dont have 2 mppts both trying to charge at full amps.

8 hours ago, Johandup said:

I really hope you are better after the mishap

Recovery is slow, but yes, I am doing better...