Using two controllers

dazz49 · Senior Member

Using two controllers

swamp · Senior Member

HI
From memory in my controller instructions the closer u operate to the max amperage spec there is a few percent of efficiency to be gained .

Hewy54 · Senior Member

Better to use one controller as if you use 2 they tend to fight against each other.
Solar gurus on here may be able to explain it in technical terms.

T1 Terry · Guru

Really depends on the operating platform and the quality of the controllers as to whether that will work together. PWM controllers in general will work together, those with separate battery voltage sensing work even better. Many MPPT controllers have serious issues when working together unless they have a master/slave relationship to each other, then the seem to work ok together.
There is a brand of MPPT controller that isn't over priced for what it offers and has separate battery voltage sensing wires, but these are 60 amp units anyway so not really on topic, but I thought I'd mention it as a case where high cost wasn't the rule for MPPT controllers that will actually play together.

T1 Terry

Bagmaker · Senior Member

I run 2 x 30 amp MPPTs and had some issues initially as they were both feeding a common point in the battery. By moving one of the controller inputs to battery 1 (of 4) and the other to battery 3 they now play happily.

T1 Terry · Guru

Bagmaker wrote:
I run 2 x 30 amp MPPTs and had some issues initially as they were both feeding a common point in the battery. By moving one of the controller inputs to battery 1 (of 4) and the other to battery 3 they now play happily.

A big capacitor (battery 2) between the 2 controller voltage sensors :lol:

T1 Terry

Jaahn · Guru

Hi smile

It is not recommended but hell lots of people do it and it works OK. Certainly I have done it often with PWM regulators with no noticeable problem.

If you had a big system you would set it up properly but for a small one go for it. They will not blow each other up.
jaahn

Peter_n_Margaret · Guru

Generally no problem and it provides redundancy in case of a failure.
Here is a setup on a motorhome with 3 separate 30A MPPT controllers, all feeding the same lithium batteries.

18-11-26 panel output.png

Cheers,

Peter

-- Edited by Peter_n_Margaret on Tuesday 15th of January 2019 08:18:19 AM

T1 Terry · Guru

If that is Julian's set up, maybe you should mention just he he got them to work together and the fact that he does write computer programs .... and maybe mention the problems he had before he made the interface control to make them work together wink

T1 Terry

Peter_n_Margaret · Guru

You are ill-informed Terry. They were operating together happily a long time ago, before he swapped to Li and before he changed to light weight panels.
Cheers,
Peter

T1 Terry · Guru

:lol: You forget that I was at that Taggerty get together when one controller tried to start but shut down again resulting in the battery slowly loosing it's SOC, yet I was reaching 100% SOC by mid afternoon using more power but having less solar capacity using a PWM controller. You can't get much closer side by side testing than that Peter wink I wasn't the one who had to leave early either smile

T1 Terry

Peter_n_Margaret · Guru

As usual, you know everything don't you Terry. Pity you only get the bit of the story that suits your purposes.
Cheers,
Peter

T1 Terry · Guru

Peter_n_Margaret wrote:
As usual, you know everything don't you Terry. Pity you only get the bit of the story that suits your purposes.
Cheers,
Peter

Hmmm..... are you sure you actually know the full story Peter? remember, I was there at the time wink

T1 Terry

Peter_n_Margaret · Guru

Not remotely related to the present Terry, but you know everything don't you. I am sure others here are eagerly waiting for your next response, but I won't be wasting my time or theirs.
Cheers,
Peter

T1 Terry · Guru

Peter_n_Margaret wrote:
Not remotely related to the present Terry, but you know everything don't you. I am sure others here are eagerly waiting for your next response, but I won't be wasting my time or theirs.
Cheers,
Peter

Ummm...... Sorry Peter, you have lost me there. Your claim was that 2 or more MPPT controllers could work in parallel without a sophisticated micro processor interface, I am saying they won't. Even the graph you provided shows they are not working together as such, front left and rear left do not start at the same time yet end at the same time.

The fact you have used the evil "lithium" word shows that are not being used on lead acid batteries and I believe that is what this thread was all about.

Are the 3 MPPT controllers operating independent of any other control system?

T1 Terry

Peter_n_Margaret · Guru

You claim to know all about it, now you ask me? Waste someone else's time Terry.
Cheers,
Peter

Aussie1 · Guru

Wow, 2 massive ego's in action here, very entertaining :):):)

Hewy54 · Senior Member

Keep up the good work guys.
Have you ever thought of using the message system for you personal wars so that the rest us can use this site for useful information.

Ron-D · Guru

We cant have one so called guru dictating things here can we?we need differences of opinion,as long as there sensible and not boring .and theres quite a few here that are very knowledgeable ,the way it used to work here some one would express there views ,and others would also express there views and thats where it ended mutual respect ...

oldtrack123 · Guru

Aussie1 wrote:
Wow, 2 massive ego's in action here, very entertaining :):):)

No ,just one big BIG ego who has to have the last long post on virtually every subject, no matter who posts

Have you stopped to think about the incorrect info that you may get If only that poster was on this forum ,answering such tech questions???

Quote "You can lead a head to knowledge but you can't make it think. One day I'll know it all, but till then, I'll keep learning."end quote

But some do not want to learn smile

-- Edited by oldtrack123 on Friday 18th of January 2019 05:08:33 PM

Aussie1 · Guru

Doesn't bother me, when I need "technical" advice information my preferred action is to seek local professional advice. works for me because I have no knowledge or confirmation that so called "experts" on forum sites have any idea of what they are talking about. to me this forum offers me really good information about general stuff such as up to date information on general (non technical) stuff that adds to the pleasure of camping etc. Information I really appreciate. And to those members I say thank you.

Have a great time out there on your travels. I know we are :)

Ron-D · Guru

oldtrack123 wrote:
Aussie1 wrote:
Wow, 2 massive ego's in action here, very entertaining :):):)

No ,just one big BIG ego who has to have the last long post on virtually every subject, no matter who posts
Have you stopped to think about the incorrect info that you may get If only that poster was on this forum ,answering such tech questions???
Quote "You can lead a head to knowledge but you can't make it think. One day I'll know it all, but till then, I'll keep learning."end quote
But some do not want to learn

-- Edited by oldtrack123 on Friday 18th of January 2019 05:08:33 PM

Common sense oldtrack some dont have it biggrin

T1 Terry · Guru

Beats me, Peter puts up a graph, I question if it is 3 MPPT controllers working together without a special interface not available to the average user to clarify the claim and I'm under attack. Peter for what ever reason doesn't want to actually answer the query but rather divert attention by attacking me, yet no one seems to think that is a bit odd confuse

It's no skin off my nose if people want to be mislead and end up with a system that doesn't actually work as seems to be suggested here, it's not like I'm selling them anything, I'm just putting forward information I've uncovered at my own expense to save others having to go through the same wallet pain.

So all you keyboard warriors, put your hands in your pockets and prove me wrong with genuine level playing field testing with the parameters clearly set out so others can duplicate your tests to see if they come up with the same results.

T1 Terry

dorian · Guru

ISTM that the situation with two or more solar controllers directly connected to the same battery is a little (or a lot) different than connecting two or more PSUs to the same load. In the latter case the PSUs are trying to regulate the voltage at the load, which means that they would be interfering with each other's voltage sensing. However, in the case of two or more solar panels, each with its own MPPT controller, the controllers are regulating the panel's power output, at least in bulk charging mode. No controller can see any panel other than its own. Moreover, the controller doesn't really care about battery voltage until it reaches 14.2V or thereabouts. Until then it just dumps as much current as the panel provides. However, ISTM that when a controller switches to absorption mode and finally float mode, these final stages could result in "contention" problems.

oldtrack123 · Guru

dorian wrote:
ISTM tht the situation with two or more solar controllers directly connected to the same battery is a little (or a lot) different than connecting two or more PSUs to the same load. In the latter case the PSUs are trying to regulate the voltage at the load, which means that they would be interfering with each other's voltage sensing. However, in the case of two or more solar panels, each with its own MPPT controller, the controllers are regulating the panel's power output, at least in bulk charging mode. No controller can see any panel other than its own. Moreover, the controller doesn't really care about battery voltage until it reaches 14.2V or thereabouts. Until then it just dumps as much current as the panel provides. However, ISTM that when a controller switches to absorption mode and finally float mode, these final stages could result in "contention" problems.

Exactly biggrin

And it is when the LA battery is in a low SOC that shows up the most [batteries with a voltage range from 14.5 down to flat .

however batteries with a fairly constant output voltage around 14V [Li] will not get the same result ,especially if the panels also have low PPP voltage

-- Edited by oldtrack123 on Saturday 19th of January 2019 05:19:50 PM

T1 Terry · Guru

:lol: Peter, try reading what Dorian posted and see how it conflicts with what you seem to think agrees with your theory. If the battery is ata low state of charge the voltage will be low and the MPPT can make better gains because the input voltage is different to the battery voltage. But what happens when another source of charging is active on the battery while the MPPT controller is taking its voltage measurement? Won't the MPPT controller see a higher voltage than if there was no other charging occurring at the battery terminals?
Can't you see this is what happens when 2 or more independent MPPT controllers are charging the same battery? MPPT controllers are not like PWM controllers in the sense that they ignore any battery voltage that is lower than the target voltage, MPPT controllers are looking to gain the max they can and they need to sense a low battery voltage to make that happen.

T1 Terry

oldtrack123 · Guru

T1 Terry wrote:
:lol: Peter, try reading what Dorian posted and see how it conflicts with what you seem to think agrees with your theory. If the battery is ata low state of charge the voltage will be low and the MPPT can make better gains because the input voltage is different to the battery voltage. But what happens when another source of charging is active on the battery while the MPPT controller is taking its voltage measurement? Won't the MPPT controller see a higher voltage than if there was no other charging occurring at the battery terminals?
Can't you see this is what happens when 2 or more independent MPPT controllers are charging the same battery? MPPT controllers are not like PWM controllers in the sense that they ignore any battery voltage that is lower than the target voltage, MPPT controllers are looking to gain the max they can and they need to sense a low battery voltage to make that happen.

T1 Terry

What can I say, Except you love to throw red herrings into every post

Suggest You try to understand a little more about electrical facts.

Even with two charging sources the Battery voltage is the battery voltage. but will be slightly higher with two sources than one

So it seems you are now going along the path that you cannot have two charging sources to the battery at the same time confuse

Suggest you do a bit of research on that subject or should we all believe only in T1's electrical laws ??

I 've had enough for today, after two weeks in hospital [out yesterday] still not feeling the best

Ron-D · Guru

Its not possible to have the last word with that guy oldtrack.

dorian · Guru

AIUI, here is how MPPT controllers operate. The two diagrams show the current flows when the MOSFET chopper is switched on and off via the PWM output of the MPPT controller. The controller regulates the panel's power output by varying the duty cycle on the MOSFET's gate.

                   Id = Ip + Ic
                    -->
         Ip                           Ib = Ip + Ic
         -->     .--|<--.      L      -->
  .---.  ___     |      |     ___     ___  .---.
  | + |-|___|--+-+--+|+-+-+---UUU----|___|-| + |
  |   | Rp     |    |V| Q |           Rb   |   |
  | P |     ^  | C  ===   | ^              | B |
  | a |  Ic | ---     |   - | Is = 0       | a |
  | n |     | ---     | S ^ |              | t |
  |   |        |      |   |                |   |
  | - |--------+------)---+----------------| - |
  '---'             .---.                  '---'
                    |PWM|
                    |on |
                    '---'

                   Id = 0
                    -->
         Ip                           Ib = Ip + Ic
         -->     .--|<--.      L      -->
  .---.  ___     |      |     ___     ___  .---.
  | + |-|___|--+-+--+|+-+-+---UUU----|___|-| + |
  |   | Rp     |    |V| Q |           Rb   |   |
  | P |     |  | C  ===   | ^              | B |
  | a |     | ---     |   - | Is = Ip + Ic | a |
  | n |     v ---     | S ^ |              | t |
  |   | Ic = Ip|      |   |                |   |
  | - |--------+------)---+----------------| - |
  '---'             .---.                  '---'
                    |PWM|
                    |off|
                    '---'

Ip = panel current

Ic = panel filter capacitor current

Ib = battery current

Id = MOSFET drain current

Is = Schottky flywheel diode current

PWM = Pulse Width Modulation control output from MPPT controller

Rp = panel current sense resistor

Rb = battery current sense resistor

C = panel filter capacitor

S = Schottky flywheel diode

Q = MOSFET chopper (with body diode)

L = inductor in buck converter

When the MOSFET is switched off, the panel's output charges capacitor C. Battery charging current continues to flow (ie decay) in a loop consisting of the Schottky flywheel diode and inductor. When the MOSFET is switched on, both panel current and capacitor current flow through the MOSFET and into the battery. That is why the battery current is greater than the panel current. The battery current remains fairly constant due to the flywheel action of diode S.

-- Edited by dorian on Sunday 20th of January 2019 12:16:51 PM

Jaahn · Guru

Hi Dorian smile

That IAUI also, BUT as I pointed out earlier somewhere, that is only half the story.

The other half is the 'smart' controller and the 'firmware' program that it uses to search for the MPP and tracks it to get the maximum power out of the panel in the prevailing conditions. And as they vary in a timely manner. hmm

This is the area that I believe the fakes fail at. It is actually the heart of it, the rest is just hardware that anyone could build with a few components and the internet. As they do disbelief

Jaahn