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MPPT Charger in parallel with hybrid inverter with mppt charger


Cef
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Hello everyone.
Because I am interested in taking care of my Trojan battery bank according to the manufacturer's specifications and since the configuration of my Inverter is limited, I came up with the possibility of connecting a MPPT Charger in parallel, but apparently the subject is not so simple.
I have also seen that these multiple MPPT connections are made by dividing the energy coming from the solar panels in different proportions, this is because apparently although a bank of batteries can be shared, the mppt must be fed by two different PV arrays.
That does not convince me because my short-term idea is to take the surplus of the Solar Panels (which I do not consume) in the hours of peak sunshine and reinject it on the Grid in order to pay less on my invoice.
I am not seeing another solution but to increase the amount of Solar Panels, leaving a group exclusively for the use of the independent MPPT Charger.
Any new idea ?

Edited: The inverter is an MPP Solar Hybrid V. It is the same as the "InfiniSolar V".

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If you're going to use an Axpert with this I can see no problem. Either you're using it with the BMV+Rpi software solution, in which case the external MPPT will be taken into account (if you put it on the right side of the shunt), or you're using the internal "SoC" of the inverter that is based on voltage, and will work just fine if the raised voltage comes from an external MPPT.

You're absolutely right though, the PV arrays has to be separate, so one array connected to the Axpert, and one connected to the Midnite.

Then the only issue that remains is putting the controllers in sync (absorb or float). It's not a biggie, you may just end up in a strange condition where one controller decides it is time to go to float, while the other wants to remain in absorb. If you can't get the voltage up to absorb using only the panels connected to that particular MPPT, the second array will sit there doing nothing, or very little. Which isn't that big a deal... it will still perform float duty.

The Midnite controllers does support modbus RTU though, so in theory you could use a software solution to sync it to the Axpert. But I would try it first and see how it goes.

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21 hours ago, plonkster said:

You're absolutely right though, the PV arrays has to be separate, so one array connected to the Axpert, and one connected to the Midnite...

Then the only issue that remains is putting the controllers in sync (absorb or float). It's not a biggie, you may just end up in a strange condition where one controller decides it is time to go to float, while the other wants to remain in absorb. If you can't get the voltage up to absorb using only the panels connected to that particular MPPT, the second array will sit there doing nothing, or very little. Which isn't that big a deal... it will still perform float duty.

Thanks for the answers. Everywhere people are recognized who are interested in helping others very quickly.

I think I have the solution (in half) and it is not that their contributions have not been welcomed, but I think that I have not been able to clearly state my objectives and priorities.

My solar installation was made with two fundamental objectives:
1. Pay less electricity or preferably nothing.
2. That my batteries are used for
eventual cuts in the public supply of energy.
3. Hobby :D

My priorities from the start up of the system is:
1. Take care of my batteries to be sure that they will be available in the best possible conditions when you need them and prevent them from premature aging.
2. Do not change any of the equipment I already bought.
3. Monitor my system both locally and remotely.
4. Expand my system and automate it.

Having explained this, I have come to the conclusion that if I buy any other solar charger (I love the MidNite Classic 150
:(), I have to divide my Solar Panel Arrays and I do not justify it just to "charge / care" my batteries if I can fix it Otherwise more efficient and not so expensive. That's why I think the best solution for me would be to buy an AC Charger (220-240 Vac) connected to the same battery bank of the inverter. The problem is that until now I could not find one that ideally has the 4 main modes, can be set and come with automatic volt correction by temperature, preferably.

The problem with putting the chargers in sync I suppose it subsists, but it would not be such a serious problem, apparently...

Any product to recommend?

 

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@Elmichi, I'm unsure what the problem is that you're trying to solve.

The main reason for adding a second charge controller would be either because 1) the one you have isn't good enough, or 2) you have more PV power than your present unit can handle.

If your present CC doesn't do a good enough job -- perhaps it does not sufficiently absorb, do temperature compensation, orsome such calamity --  simply disconnecting it and using another one in its place should be fine. The Axpert uses voltage to decide on switching so it doesn't matter how the charge current gets there. If you use the BMV/ICC solution, it should still work fine, the BMV will see the charge current from your external charge controller.

For the second case, where you have more power than you can handle, you'd split the PV array into two smaller arrays, put one of them on the Axpert's CC, and the second one on another controller, both feeding the same battery. The same argument as above applies: Since voltage and/or BMV SoC is used to do the changeover switching for self-consumption, it will still work perfectly.

The above arguments does not apply to a hybrid like the Infini. Just to cover myself :-)

Placing two charge controllers onto the same PV array is always looking for trouble. If I had to do it -- for example to do an equalisation charge that is not supported by the Axpert -- I would always use a changeover switch so that I could use either the one or the other one.

I hope I'm clear enough? :-)

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To dumb it down as much as I can: Though the Axpert has an inverter, transfer switch, and charge controller built into one unit... they are still separate devices, and you don't have to use all of them. Just disconnect the one you don't need.

For example, in an off-grid situation you would never use the transfer switch component. Similarly, you can also disconnect the PV from the inverter and connect it to an external (Midnite classic for example) controller instead.

But as I said, not quite clear what the problem is that needs solving.

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First of all thank you very much for the answer!

6 hours ago, plonkster said:

The main reason for adding a second charge controller would be either because 1) the one you have isn't good enough

Yes, that is the problem !!!

6 hours ago, plonkster said:

...orsome such calamity --  simply disconnecting it and using another one in its place should be fine.

If I could configure the inverter to disconnect the internal mppt loader it would be the "perfect solution", but I'm not sure if it can do it or at least I like doing it from the Control Panel. I do not recognize any configuration program that allows you to tell the inverter: "Never charge the batteries with the internal mppt" or something like this, it is only possible to configure the load priorities (Solar and Utility).
As very possibly there is something that escapes me, I passed the Inverter Manual Link: http://www.mppsolar.com/manual/HYBRID V/Hybrid V series manual 20160517B.pdf

My system is very new, as I have not yet installed the configuration software "Solar Power" for RS232 maybe what you tell me can do from there. Thank you very much for the information, if it gives result would solve the problem in the simplest way 
:)

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But as I said, not quite clear what the problem is that needs solving

Hi Plonky I think Elmichi's problem is the high recommended charging voltage and equalisation voltage of the Trojans in conjunction with having an Axpert. He wants to be able to cater for their requirements and this excludes using the Axpert's MPPT.

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Just disconnect the PV cables from the Axpert? Then connect your panels to the external MPPT and connect that to the battery? So then the Axpert doesn't know that charge is coming from somewhere, but as I understand it, it doesn't need to.

There seems to be two ways in which people use their Axpert to do self-consumption. Either they use the voltage-based method of the inverter itself, or they switch it with ICC based on an SoC number you get with a BMV. Both methods will work just fine if the power is injected using an external MPPT.

Won't it? The Axpert guys just need to confirm this.

And again, just as a disclaimer, I'm pretty sure it is not going to work the same way with the smarter inverters (such as the infini). Those inverters need to know how much PV is coming in to balance grid feedback with generation and keep the batteries full.

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Let me dumb it down again. Pretend it is permanently night, but you have a wind generator pushing power into the batteries. The Axpert should work just fine as the wind turbine will keep the voltage and/or SoC up.

Now just replace the Wind Turbine mentally with a solar array and an external MPPT :-)

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Please just remember that the Apert has a low (high voltage) limited - 60V I think so it will shut down if the voltage gets to high.  This actually is the issue in that you still can't equalise the Trojan's.  You have to disconnect the Axpert and manually equalise with the 2nd MPPT.  I have a Microcare 40A and if I had Trojan's that's what needed.

I think the issue is bigger than just the 2nd MPPT. in this case.

Regards

Mark

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3 hours ago, Mark said:

Please just remember that the Apert has a low (high voltage) limited - 60V I think so it will shut down if the voltage gets to high.

True, but the external controller will give two everyday advantages. You can go a little higher on the absorb voltage (higher than the Axpert supports), and you will probably avoid the high-voltage overshoots too.

In addition, when you want to equalise (a rare occurrence really), you can switch off the inverter and do it with your excellent external energy effecting device (aka mppt). So that's three advantages.

Edit: A quick bit of research. Axpert allows a max of 58.4V for absorption. The Trojans want 59.2V. The inverter itself will shut down at 60V. It should be possible to push the voltage to 59 (ish) without triggering a shutdown, under normal operation. Don't quote me on it though, I don't know these things and the mere knowledge that we're skirting the 63V rating of the DC-bus caps so closely makes me feel all daredevilly...

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