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Need help to parallel Mecer Axpert MKS1 5KW


RobG
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I have an existing Mecer Axpert MKS1 5KW. It is about a year old and has a parallel card in it. I have 4x Pylontech 3000, 4725w of PV with 725W on a solar tracker I made.

The idea is to parallel the 2 inverters and have the tracker array on it's own MPPT on the new inverter.

Will having the 2 inverters MPPT's with different wattage coming in from the PV's create any kind of problem?

Is there a cable that connects the 2 Axperts together. How long is the cable?

What DC battery isolation switch is recommended?

Any help greatly appreciated.

Thanks

Rob

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11 hours ago, RobG said:

The idea is to parallel the 2 inverters

You only have 1 now, by the sounds of it. You will need to get another one of the exact same model (not necessarily branded the same), and will likely have to update the firmware in one or both to make sure that they are the same revision.

11 hours ago, RobG said:

Will having the 2 inverters MPPT's with different wattage coming in from the PV's create any kind of problem?

That's no problem at all.

11 hours ago, RobG said:

Is there a cable that connects the 2 Axperts together. How long is the cable?

Yes, it's about 1 meter long. Basically, the two inverters need to be side by side, or very nearly so. Didn't a pair of paralleling cables come with the original inverter? Each paralleling card comes with one of each cable (one twisted pair, one white one with what looks like VGA connectors at each end). You need one pair of cables per paralleling card, so two pairs total for two inverters. The new card will likely only come with one pair.

You may be confusing the paralleling board with the communications board; they live very close together. Note the four connectors (from https://www.communica.co.za/products/vp-mks-5kva-parallel-kit:

I1146792589_2000x.jpg?v=1562607081

11 hours ago, RobG said:

What DC battery isolation switch is recommended?

I'll let locals comment on what's available in South Africa. I use my removable 100 A fuses as isolators. You will need separate isolators for the two AC-outs as well. You probably have some way of isolating AC-in already; I don't use separate isolators for AC-in, although occasionally I wish I did.

Edited by Coulomb
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  • 3 weeks later...
1 hour ago, RobG said:

Why do you feel 2 AC switchers would be an advantage?

Mainly so I could put one completely to sleep when I don't need much power, and there is little solar, so I don't want to waste solar on an inverter that I don't need (for now). With AC-in connected to the grid, turning off the switch will never cause it to turn off.

It's also handy for some troubleshooting.

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17 hours ago, 87 Dream said:

Purely for isolation purposes. If a unit is faulty in order to isolate each inverter. You can also trouble shoot in this way. Classic example is if one of the inverters goes into a fault mode & you need to reset it by doing a power down. Imagine you can carry out the reset on the faulty one without interrupting the good one. 

If I may add a comment as an add on to what @Coulomb has mentioned. When you parallel these units make doubly sure that the are Sharing the same AC output current wires & wire lengths. In other words do not have one inverter feeding 7plugs & the other feeding 6lights. 

The inverters work together as a unit & power the AC output loads & share the current usually equally. Whatever you do, also make sure that you set them up as parallel in the settings before you add the cables otherwise you can blow the AC fuse. I have been there & done that.

87

 

Thanks for the advice 87

I have a change-over switch - grid/generator - feeding AC into the inverter. So I should put an ON/OFF switch before each inverter?

Presently the existing inverter is wired directly into the DB. If I understand: I need to use the same length wire to 2 AC switches then 2 same length wires to the DB? They don't run independent plugs etc. so loads will be balanced.

I'm using ICC so would both inverters need to be plugged into the Pi USB?

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6 hours ago, RobG said:

I have a change-over switch - grid/generator - feeding AC into the inverter. So I should put an ON/OFF switch before each inverter?

The inverters should have a circuit breaker on their inputs. We're saying it can be handy to have two separate breakers, one for each inverter's AC-in port.

If you have a changeover switch for grid versus generator, that would go before the two (or one) breaker(s). Breakers are useful for isolating as well as current limiting, and they're generally more convenient to use than on/off switches. The breakers would generally be close to the inverters.

6 hours ago, RobG said:

If I understand: I need to use the same length wire to 2 AC switches then 2 same length wires to the DB?

You don't need separate cables all the way to the DB, though it sometimes works out better that way with cable sizes, especially if you sized the cable for a single inverter. I had to do that with mine; I ended up with two 4 mm² cables all the way to the DB. But you could have two cables to two breakers near the inverters, arranged in such a way that the total length of wire for each inverter to the paralleling point is the same. Then use one cable from there to the DB. It should be at least 6 mm² for 2 x 5 kVA inverters, assuming that you'll never have more than about 40 A (8.8 kVA @ 220 V) in loads continuously.

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  • 2 months later...
On 2021/07/08 at 9:44 AM, RobG said:

Thanks for the advice 87

I have a change-over switch - grid/generator - feeding AC into the inverter. So I should put an ON/OFF switch before each inverter?

Presently the existing inverter is wired directly into the DB. If I understand: I need to use the same length wire to 2 AC switches then 2 same length wires to the DB? They don't run independent plugs etc. so loads will be balanced.

I'm using ICC so would both inverters need to be plugged into the Pi USB?

I got just about the same setup: 2 MKS5 5kW units in parallel. Works nicely. I installed on each inverter a 3-pole 60A isolator switch in a wall box as normally used for the mandatory cooking stove isolator. This allows me to totally isolate each inverter individually from AC. From there I have about 22m of 3x6mm² wire to the DB main input 60A and fault protection breaker. 1 phase wire to the inverter/charger, 1 phase wire from the inverter to DB and 1 wire for the common neutral. In the DB is a 32A output breaker for the two inverters. At the battery I have a high power 125A fuse for each inverter +. The negative is not fused, only an isolation possibility. Each of the four battery packs has also its own 125A breaker.

PICT1348.thumb.JPG.e74121c77941ea12fc86417e29791b05.JPG

As you can see the two each communication/synchronization and load sharing cables are outside the trunking for the power wires. To the right the fuse box for the two PV banks, one fuse for each MPPT. The negatives are not fused.

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On 2021/07/08 at 9:44 AM, RobG said:

I'm using ICC so would both inverters need to be plugged into the Pi USB?

I have two ways to monitor the inverters:

First I installed an Axpert/Voltronic remote panel in my office/shack. It works well but can only monitor the inverter it is connected to. Its supposed RS232 output badly does not work as I reported in another thread.

Second I installed a small trow over switch in the RS232 line from the inverter that gives me the possibility to alternatively connect it to a laptop with a RS232 to USB adapter. I use the WatchPower software to monitor. It can to my choice display the data from ether inverter and in addition display total AC output power and total battery charging current of the two inverters. It also features the more convenient possibility to change parameter settings of the inverters.

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