oldtrack123 wrote:

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T1 Terry wrote:

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: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

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 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

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

 

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Hope you are feeling better soon Peter. As far as the 2 or more MPPT controllers or even another charging source on a battery while an MPPT controller is also trying to charge the same battery, that is the reason why the story is doing the rounds about either the DC to DC charger or the solar charging at any one time. This is referring to the problems MPPT controllers have with other charging sources on the same battery, it doesn't happen with PWM solar controllers or where a common battery voltage is sensed and all the chargers act as slaves to the master unit. this is how the Victron "Color" controller can operate more than one Victron MPPT solar controller. You really do need to do more research regarding battery charging/discharging because it does not follow the same laws as mains power. There is no fixed voltage involved when it comes to working with batteries, a standing voltage of 10.5v will not remain at 10.5v once the charging commences, especially when lead acid batteries are involved and the higher the charging current the greater the terminal voltage will climb above the 10.5v rested voltage. This is why an MPPT charger must stop the charging process to sample the battery voltage, but if it can't stop all the charging at that time it gets a different voltage to what it thinks will be a standing voltage and this throws the MPPT charger out of wack. If the other charging sources are greater than the battery current acceptance rate the terminal voltage will climb above 13.8v. When the MPPT controller samples what it thinks is a rested voltage and sees 13.8v it immediately stops charging because it senses the battery is fully charged. That MPPT controller will not drop out of float mode until the solar input has been cut, it will then sense the solar voltage when turned back on as a new day and go through the set up process all over again. If you have had much experience with MPPT controllers you will know just how long that can take and during this period the charging is either zero or nothing like the input a PWM controller would supply.

I have experimented with using solid state relays to cut the solar supply to all the MPPT controllers in a group so they would reset every hr, then every 2 hrs etc, it does get around the MPPT shut down issue but it severely limits the total harvest for the day.

 

T1 Terry

 

T1 Terry 

The issues with using 2 MPPTs together becomes cloudy when they are on larger batteries (mine is 1120A/h) and have lots of regular light loads, or a constant light load in addition to heavy loads. Not really an issue on simple, smaller setups.
Such a setup is typically found on big rigs that run AGMs and a larger inverter. Theoretically these batteries never get a full charge, there are always electrons flowing. A whole different fish kettle to ol mate with his 100A/h goldstream looking to add a panel
Its not a simple equation that works =or doesnt work- in every case, real world experience will be the decider in what works for your setup, not theory.
My battery is also quite tired, I suspect this is also critical to the results. There was no real issue with bulk charging during a low SOC, rather when coming off the absorbtion phase to either float or boost. Thats when the 2 chargers become confused sometimes.
By introducing a lag/distance/separation between them there was no further problems.
Now I appreciate how it should be, theoretically, but it simply isn't in real life.

T1 Terry wrote:

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It appears you did not read the Morningstar article you posted a link to Peter

Quote:

 There is a connection from the battery bank to each controllers Voltage Sense Terminal pair. This ensures each controller is measuring the same battery bank voltage. Note: paralleling between controllers Voltage Sense terminals, in order to share a single connection to the battery bank is an acceptable practice.

These Morningstar MPPT controllers have independent battery voltage measuring so they can work together, I think I did mention the requirement ages ago in either his thread or other similar threads.

[a]Most MPPT controllers do not have independent voltage sense but rather use the same cables as the battery charging passes through so the sensed voltage is not the true battery voltage. The all too common practice of connecting multiple charging devices to a common bus bar makes the problem even worse and I have seen factory installs where the battery connections were daisy chained from one charging source to the next and this causes real havoc with any charging device that uses the charging leads to also do the battery voltage sensing.

Sadly, there are very few MPPT controllers with independent voltage sensing and the ones that do are quite expensive, cab you see the OP buying 2 or more of these so he can get them to work together https://www.ebay.com.au/itm/NEW-Morningstar-TriStar-MPPT-Charge-Controller-12-48V-30A/252259301051?epid=1439225211&hash=item3abbd376bb:g:bmIAAOSw6GJZ60L1:rk:4:pf:1&frcectupt=true

 

T1 Terry

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Terry

I am at a total loss as to what you are garbling on about

I read the link in detail

Have you really tried to do that with an open mind????

Of course they each have their own  battery voltage sensing  systems, but that is still parallel operation.

[a]IF the installation is done correctly , both regs should have very little voltage drop between them & the battery

If that requirement is not met no regulator can do the job properly !!!

Do you now accept that the MPPTs have two entirely different functions built in ??

[1]The MMPT section  that operates independent of the battery soc

[2]Then Basically a DC to  DC converter section that controls the battery charging  with that operating as a pwm & subject to the same constraints regarding voltage sensing as any other PWM 

Again that is using a true MPPT , not some cheap so called mppt that does not have the guts to perform those TWO  functions

Perhaps I did not understand when /if you were referring to them

The trouble is you cannot see how  your experiments  with LIs & your panel set would not gain  much  if anything ,but that does not apply when using LAs

As for cost that is for the user to decide which is best ,more panels or more efficient use of existing panels!!

Until you can accept those facts  every one is wasting their time

 Please don't bother trying to post more red herrings ,you are close to making a fool of yourself 

You seem to continually change tack  to try & prove your self correct

I said earlier no more replies but this is it

Nothing will convince Terry  or get Terry to change his views or forget his preconceived prejudices

-- Edited by oldtrack123 on Monday 21st of January 2019 06:48:36 PM

T1 Terry wrote:

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Peter, try reading all the posts on the thread thegreynomads.activeboard.com/t65225544/using-two-controllers/
You jump from one theory to the next so quickly I doubt anyone can follow what your ideas are now Peter.

[a]

For a quite a while you suggested the MPPT controller sensed the incoming solar voltage and current and the battery terminal voltage and came up

with the best combination to get the max current at the lower battery voltage.

[c]

Now you appear to be claiming the MPPT section sets a generic charging voltage suited to the type of battery chemistry selected and fine tunes the solar input to get the most output at that particular charging voltage and use a separate PWM control to keep the battery from over charging.

[c]

That theory conflicts with your other theory that the lower battery voltage of a seriously discharged battery gives the MPPT controller the greatest advantage.

Are you sure you actually understand any of what you are saying Peter?

T1 Terry

 

You are talking BS

I started with a simple ,not complex, post , not like  your usual loooong  posts tying to show how much you know..

But I had to enlarge in an endeavour to help you understand & overcome your bias against True MPPTs

I have tried to put my posts in different ways . Hoping that some how I would get it through to you ,that a MPPT has two functions 

[a]to seek & utilize the MAX power point @that time to charge the batterry

'I had hoped that the significance of the 2nd /output stage being similar to a Dc/Dc charger ,[we are talking about power to charge the battery] would sink in.Sadly it seems it has not.

[c]Show me where I have ever made that statement!!

What I have said is that the 2nd stage acts similar to  DC/Dc charger, utilizing all the power available to it ,to charge the battery. & as  pwm controller, as do all dc dc chargers.

If you cannot see the the significance of the highly variable SOC voltage of LAs compared to the relatively constant voltage of Lis & why with your set ups a MPPT would have near zero gain, you will never understand!!

DO not waste your, mine or members time coming back again.

I know nothing will change your views or prejudices

It's been months ago since I've been here

Nothing has changed them old farts are still going at it

Some of them they don't care what other people think and keep hammering for what they think is right what an Bull s...

No wonder a lot of people left this site

 

It will be months again I think before my return

Get at it fellows you've got my blessing

Cheers

You win Peter, I can't follow just what you are saying when it comes to how an MPPT controller works better on LA batteries because there is such a wide variation in terminal voltage. You quite often mentioned a deeply discharge LA voltage of 10.5v and use the difference between that voltage and the Vmp marked on the back of the solar panel as the basis of why an MPPT controller is superior ....... now you tell us the MPPT controller doesn't even look at the battery voltage and only uses a PWM control to limit the output voltage when the battery reaches the set point for bulk charge, absorption and float.

Am I the only one who is totally confused now about just what advantages an MPPT controller has if it does not use the battery terminal voltage as part of the MPPT algorithm? Am I understanding correctly that is what Peter is now claiming about how an MPPT controller works?

T1 Terry

I don't think I'm the only one who thinks the basic battery charging type solar controller gains nothing by using an MPPT type device. Morningstar actually recommend the PWM unit for those in a hotter climate because their MPPT unit derates above 40*C internal temperature. Plasmatronics, the number 1 Australian solar controller builder who has been in the business for a very long time, does not make MPPT controllers and they explain quite clearly why they don't on their website.
The well known solar controller and battery management builder in Canada, ElectroDacus only uses MPPT for his waste solar diverter unit that stores the excess solar as heat in blocks of concrete. All his battery charging designs remain PWM and he lives in a rather cold climate, you would think the lower panel temperature would suit the MPPT design, but apparently that is not the case.
These people are actual engineers who specialise in solar and battery charging with many yrs of practical knowledge Peter, not someone who has only dabbled in the theory side and never put their ideas to the test. Perhaps it is you that doesn't fully understand all the principals involved and just how dynamic the whole process is, not a fixed voltage or current either from the solar input side or the battery charging side. If you actually had put your theories to the test you would have seen with your own eyes that the reality is not the same as the theory you are using, only someone who is deluding themselves would not be willing to actually put their theories into practice using the basic scientific approach.

T1 Terry

OK SILLY ME I HAVE A QUESTION,,,,,, i'm a machosist so here goes. Please answer in plain English, and concise. Reading this post,,,,WHY do you need a battery voltage sensing connection to MPPT controller (like mine) when i have virtually zero voltage drop between battery bank and Mppt controller (that's good isn't it?),,,,, surely with no voltage drop, the B+ voltage at the Mppt controller AND the battery sensing voltage would be the same.

Ok thanks Jaahn MUCH appreciated