MPP Solar PIP 8KW + Victron MPPT + Solar Assistant - 120A charging limit!

[timselectric]

Well, my conclusion was: IMPASSE.

I have already attached quick and dirty schematics how is everything connected, so here it is again:

View attachment 268081

So basically this is it, a very simple, I have not added any protections in place, which I of course got so I can switch off all arrays and battery if needed but the drawing is otherwise accurate and shows you every connection.

Yes, I seen that drawing.
But sometimes actually seeing it, will produce an "ah ha" moment.

 

[Red Dingo Homestead]

What is in the distribution box, just busbars?

 

[Red Dingo Homestead]

 

[Red Dingo Homestead]

Please, ignore the mess, it was very tidy before, but when I have added the Victron, I was dealing with a little space left so it's looks messy and I'm not proud of it.

As soon as it is warmer outside, I am planning to dig a small tech room under the house and move the equipment there... So don't judge me fast ...

 

[timselectric]

Please, ignore the mess, it was very tidy before, but when I have added the Victron, I was dealing with a little space left so it's looks messy and I'm not proud of it.

As soon as it is warmer outside, I am planning to dig a small tech room under the house and move the equipment there... So don't judge me fast ...

No worries, I'm just looking for something to jump out at me and say "here I am".
But sadly it hasn't happened, yet.

 

[Red Dingo Homestead]

Much appreciated matey ... I really mean it. That's why I have created this thread to get another pair of eyes to find what I am missing here ...

 

[Zwy]

This is a possible solution, but I don't need/want another MPP solar box, even though it's cheap, even cheaper than 2x Victron MPPT's. That's why I added addition to my setup one new Victron 250/70, thinking that I will get 120A from the MPP and 70A from the Victron (theoretical max), giving me a beautiful 190A going to the battery at max. I was not aware that the MPP will limit it's own MPPT's if/when it sees additional amps flowing to the battery ...

First off, the max charge current stated in the specs is 120A max.

Second, the MPPT's will see higher battery voltage when another MPPT is added into the mix. It is not additional amps/current.

If the MMP Solar MPPT charging voltage is raised higher, what occurs? The float voltage shown is too low when it comes to MPP, you need to get it higher. This also affects the MPPT as it will throttle charge current as float is reached. I've noticed this behavior, the bank doesn't reach bulk charging voltage but starts to throttle the current as float charge voltage is reached. Increase the float voltage to about 0.5V below bulk and see what happens.

 

[ricardocello]

Ok, assuming we are dealing with only voltages, with no communication between battery, MPP, and Victron.

With a voltmeter, can you measure the voltage drop between the battery + and the charger output terminal of the MPP?
Likewise for the Victron. Preferably when lots of current is flowing.

The objective here is to calculate the resistance in milliohms of the cables, lynx in, etc. for both voltage paths from charger sources to battery.
Even if both devices output the exact same voltage, by the time it gets to the battery there may be an imbalance.
You may find that the voltage drop on the MPP path is much worse, so the Victron does all the heavy lifting.

The MPP could be given a small nudge upward to compensate, see Emperor @Zwy comment above.

 

[Zwy]

For the newbies here - if you think you can get 8000W out of your 8KW system with MPP solar and it's 2x MPPT's, well, that's not true, it will only deliver 120A, so theoretical max about 6500W.

This is very good info - thank you!

That is all it can have. 120A x 54V = 6480

I don't know where he had the idea it could take 8Kw thru the MPPT's to the batteries. It could never do it with 120A max charge current. It doesn't matter what brand of MPPT, you always take the max charge current x voltage and that is the max it can put out in watts.

 

[Zwy]

With voltage based charging, the only factor is voltage.

Yes, that is the key.

I finally saw the wiring diagram and with the MPPT's both connected to a common busbar, the output voltage of the Victron is higher probably due to cable length.

This will cause the MPP to throttle output once it nears float voltage.

 

[Red Dingo Homestead]

That is all it can have. 120A x 54V = 6480

I don't know where he had the idea it could take 8Kw thru the MPPT's to the batteries. It could never do it with 120A max charge current. It doesn't matter what brand of MPPT, you always take the max charge current x voltage and that is the max it can put out in watts.

Zwy, please, don't get confused here. Re-read the thread, maybe you have not read everything what has been said there.

And let's focus a swell. I know I can't get more than 120A from the MPP Solar box, this has been established here.

I have added a Victron MPPT to the mix, and another 4kw array. What is happening here, that under the ideal condition you won't see the following:

120amps going from MPP Solar to battery
70amps going from Victron to battery

The "system" will cap this to the MPP Solar settings - 120A.

And this is what we are discussing here and what we are trying to find an answer for.

Thanks.

 

[Zwy]

And there it is, short cable to central busbar.

You need to have circuit resistance almost the same for all MPPT's. Otherwise the circuit with less resistance will raise busbar voltage.

 

[Red Dingo Homestead]

Zwy, the useful information you have provided is the following:

"This will cause the MPP to throttle output once it nears float voltage."

So let me ask you and please explain it to everyone - why would this happen?

You have 2 sources which can charge the battery, one can push 120A, another 70A, so why the whole system then caps this to 120A only?

That's the whole purpose of this thread. Once we find the answer, we can look for the fix.

 

[Zwy]

Zwy, please, don't get confused here. Re-read the thread, maybe you have not read everything what has been said there.

Nothing to be confused about, the max charge current for the MPPT's is 120A. You made the comment the max it could put out is 6500W and not 8Kw.

And let's focus a swell. I know I can't get more than 120A from the MPP Solar box, this has been established here.

It is a system flaw due to resistance plus settings. That is all.

I have added a Victron MPPT to the mix, and another 4kw array. What is happening here, that under the ideal condition you won't see the following:

120amps going from MPP Solar to battery
70amps going from Victron to battery

The "system" will cap this to the MPP Solar settings - 120A.

And this is what we are discussing here and what we are trying to find an answer for.

Thanks.

Turn off the Victron with the short cables to the busbar and the MPP will output the max.

 

[Zwy]

Zwy, the useful information you have provided is the following:

"This will cause the MPP to throttle output once it nears float voltage."

So let me ask you and please explain it to everyone - why would this happen?

You have 2 sources which can charge the battery, one can push 120A, another 70A, so why the whole system then caps this to 120A only?

Because you have a short cable to the busbar from the Victron MPPT.

That's the whole purpose of this thread. Once we find the answer, we can look for the fix.

 

[ricardocello]

The 250/70 has a shorter path and therefore lower resistance to get to the busbar.
It wins the voltage war.

Use the same length identical cables from the MPP and the Victron, and everything will balance out.
Then you will get your power.

Or raise the voltage of the MPP so it balances out.

 

[Red Dingo Homestead]

View attachment 268115

And there it is, short cable to central busbar.

You need to have circuit resistance almost the same for all MPPT's. Otherwise the circuit with less resistance will raise busbar voltage.

Le me explain the image, I'm happy to learn from you:

1. we can see the top left 2 cables are coming from the Victron MPPT
2. the top right is the connection from the MPP AIO Box
3. the right connections go to the battery

So yes, there is much shorter connection between the Victron and Lynx compared to MPP AIO and Lynx, then they share the same path going to the battery.

So my question to you is:

How the hell the system knows to throttle the charging current exactly to 120A? Even if we account the difference in resistance ...

That's all I want to know. Once I know it, I'll fix it.

 

[ricardocello]

How the hell the system knows to throttle the charging current exactly to 120A? Even if we account the difference in resistance ...

That's all I want to know. Once I know it, I'll fix it.

The system doesn’t know anything.
You are being victimized by Ohm’s Law
It just worked out that way.

 

[Zwy]

I have already explained it, the busbar voltage is high due the short cables from the Victron MPPT. Cable has resistance, the shorter the cable, the less resistance. Turn off the Victron and watch what the MPP MPPT's put out.

Any Voltronic MPPT will need float voltage close to bulk. It has always been like that.

Edit: had shorted- should be shorter

 

[Red Dingo Homestead]

ZWY:

"Turn off the Victron with the short cables to the busbar and the MPP will output the max."

I have already mentioned in my post, that this is indeed the case and you are 100% correct. My tests confirmed this already.

And now you have provided a useful tip:

"Any Voltronic MPPT will need float voltage close to bulk. It has always been like that."

This is what I was looking partially for. So let me test this next sunny day to see if there is a difference.

So yes, the cables are different lengths, so the resistance will be different. What I can't comprehend that under this conditions the system will basically use the limit set on MPP Solar AIO - 120A. So no, it won't be like 120A from MPP and 20 or 30 from Victron, it will just be 120A. This is when my math skills are just maybe not matching yours. We can see that all 3 MPPT's will add to the 6,5KW so it's like having a second wife - she'll compliment the first one, and the first one would have to do much more when she is not available...

I have to purchase more cables in order to make the connection between Victron and Lynx the same length ...

But what you are saying then is that if I do that I might finally see 4kw from Victron and 6,5kw from MPP? I do would like to test the system by raising float value on MPP, again, this is something which I have not tried, as I mentioned before the values are identical on both systems.

Thanks.

 

[ricardocello]

I have to purchase more cables in order to make the connection between Victron and Lynx the same length ...

But what you are saying then is that if I do that I might finally see 4kw from Victron and 6,5kw from MPP? I do would like to test the system by raising float value on MPP, again, this is something which I have not tried, as I mentioned before the values are identical on both systems.

Recabling is unnecessary, though it would prove the point.
I would bump up the charge voltage on the MPP, and see what your total wattage does.
Might have to do it a few times until you hit optimum power.

Or measure your cable resistances and compute what the voltages need to be with Ohm’s law.

 

[timselectric]

Or lower the victron charge voltage.
Just small increments to fine tune the balance between them.
I think we found the problem. It should have smacked me in the face. lol
More eyes always helps.

 

[Red Dingo Homestead]

Recabling is unnecessary, though it would prove the point.
I would bump up the charge voltage on the MPP, and see what your total wattage does.
Might have to do it a few times until you hit optimum power.

Or measure your cable resistances and compute what the voltages need to be with Ohm’s law.

Yes, that's what I have just done I will do a better cabling when I move the whole system, but until then I hope changing the float setting on the MPP Solar box and as you said - finding the optimum power could be the temporary fix.

As mentioned before, I had the exact same settings on both units:



I will keep the Victron settings the same as above (absorb/float) and will raise the MPP float to closer match the abs charge V... I will update this thread with more finding ...

And yes, the other option is to go and lower the Victron values as well.

Thanks guys, let's hope the sun will shine soon so I can fix this and hopefully those finings will help more people in the future.

 

[Zwy]

Recabling is unnecessary, though it would prove the point.
I would bump up the charge voltage on the MPP, and see what your total wattage does.
Might have to do it a few times until you hit optimum power.

Or measure your cable resistances and compute what the voltages need to be with Ohm’s law.

That cable is very short. The cabling from the MPP could be small AWG. I always bump up cable sizes. If the amperage indicates 2 AWG, I'll bump it up to 1 AWG if any distance.

Yes, I'd try adjusting voltage on the MPPT's but some things are hard to overcome.

On the pair of EG4 MPPT's I'm using, you can see the difference in output voltage between the 2 charge controllers. The one with the shorter cable to busbar will be 0.1V higher than the other. As full charge is reached, the upper charge controller with longer cables will throttle output just ever so slightly. Which can be an advantage to slow down charge current as balancing takes place.

 

[Red Dingo Homestead]

Let me update this thread. Today it was a snowy day, actually, it was snowing since early morning, but surprise surprise, a sun peaked through the clouds and my batteries got fully charged pretty fast. I have tried to change the MPP Solar's battery float/bulk charge to be much higher than Victron's, but during my testing it made absolutely no difference. So the suggestion to try this showed no benefit at all.

However, I was able to observe what was happening and without a further a due let me present some screenshots:





So for those following this thread, you already know it's a middle of January, I got 12kw in solar panels connected to 3 mppt's and struggled to see more than 120Amps before.

So maybe it was just reaching the highest potential before, but today even with the original setup the system was able to push more than 120amps to the battery.

So yes, there is more then likely some resistance due to the different lengths of cable, but if the conditions are right I can get more than 120amps... question is how much more....

In the end of the day, I got 45kw stored in the batteries, now I know I can get at least 7.2kw from the panels, possibly even more. During the summer months this is irrelevant because the batteries are full at 9/10 in the morning ... And during the winter months you won't get 5kw, that's why I got 12kw in order to get as much as possible from the solar panels.

When I move my system to a new place, I'll change the length of the cables, but now I feel a little happier knowing I can get more from the system than just the 120A.

Would you agree with these findings?