2 x MPPT controllers, 4 solar panels and wiring to one battery bank

[davethedog]

Hello all,

Going to start sorting out the solar panel upgrade on the boat in the next few months and looking at the best way to set it all up, as I have currently purchased the following items in readiness:

Rutland 1200 windcharger that comes with a dedicated MPPT controller that can also take 20W of solar, so have also got 2 x 125V rigid solar panels that I will be running through that also.

Have also purchased a further 2 x 125V solar panels, the same make and model, that I plan to run through a separate MPPT controller (Victron?).

Both MPPT controllers will go to the same battery bank (and VSR to charge the start battery and bow thruster battery).

So, will this work?

Cheers

DTD

 

[VicS]

Hello all,

Going to start sorting out the solar panel upgrade on the boat in the next few months and looking at the best way to set it all up, as I have currently purchased the following items in readiness:

Rutland 1200 windcharger that comes with a dedicated MPPT controller that can also take 20W of solar, so have also got 2 x 125V rigid solar panels that I will be running through that also.

Have also purchased a further 2 x 125V solar panels, the same make and model, that I plan to run through a separate MPPT controller (Victron?).

Both MPPT controllers will go to the same battery bank (and VSR to charge the start battery and bow thruster battery).

So, will this work?

Cheers

DTD

I guess you mean 20 amps and 2 x 125 watts ?

 

[davethedog]

Looks I have my amps and watts mixed up doesn't it...lol

 

[PaulRainbow]

Looks I have my amps and watts mixed up doesn't it...lol

So you have a Rutland controller that can take up to 200w of solar and you propose to connect it to 250w of solar ?

 

[VicS]

So you have a Rutland controller that can take up to 200w of solar and you propose to connect it to 250w of solar ?

No he has a Rutland controller that will accept 20 amps of solar and he is proposing to connect 2 x 125watt panels each of which will probably have an output of a little over 7 amps at the MPP ( and a maximum output current somewhat under 8 amps)

 

[davethedog]

yes my mistake, the mpt I have now will accept 20A of solar

 

[PaulRainbow]

yes my mistake, the mpt I have now will accept 20A of solar

OK, in that case the two 125w panels will be OK. As will a pair connected to a Victron MPPT controller. I'd set the controllers to identical charging regimes to minimise the risk of one causing the other to shut down.

You might also consider if it's best to connect in series or parallel. The degree of shading will be the main factor for working that one out.

 

[ip485]

I thought for a long time you couldnt effectively combine charging sources. There is plenty of anecdotal accounts to this effect. I then found some more informed opinion which is that in simple terms most modern chargers dont see the charge being put into the batteries by other charging devices so you can combine a number of chargers. Depending how they are set, they will trip out when the batteries are perecieved to reach a determined charge state. Remember there isnt a charger that "knows" the state of charge of the battery bank, all the best can do is measure the resistance to the charge.

I now run my two chargers at the same time (150 AH and 100 AH) and the MPPT on the solar with 800 watts. When the batteries are around 50% charged for a short while I may see a charge rate as high as 48AH, but this will back off after maybe 30 minutes or so, but settle for some while at a higher charge rate than any one source could achieve in isolation.

As the bank approaches a theoretical 100% state fo charge, the chargers will back off and drop out based on their respective settings, but can be tricked into squeezing in that final few percent by switching on and off.

So, the short answer is yes, this would be an effective set up, and yes making sure the charge rate is correctly set to the type of batteries is CRITICALLY important.

 

[lw395]

I thought for a long time you couldnt effectively combine charging sources. There is plenty of anecdotal accounts to this effect. I then found some more informed opinion which is that in simple terms most modern chargers dont see the charge being put into the batteries by other charging devices so you can combine a number of chargers. Depending how they are set, they will trip out when the batteries are perecieved to reach a determined charge state. Remember there isnt a charger that "knows" the state of charge of the battery bank, all the best can do is measure the resistance to the charge.

I now run my two chargers at the same time (150 AH and 100 AH) and the MPPT on the solar with 800 watts. When the batteries are around 50% charged for a short while I may see a charge rate as high as 48AH, but this will back off after maybe 30 minutes or so, but settle for some while at a higher charge rate than any one source could achieve in isolation.

As the bank approaches a theoretical 100% state fo charge, the chargers will back off and drop out based on their respective settings, but can be tricked into squeezing in that final few percent by switching on and off.

So, the short answer is yes, this would be an effective set up, and yes making sure the charge rate is correctly set to the type of batteries is CRITICALLY important.

So much misunderstanding in this post.

 

[PaulRainbow]

So much misunderstanding in this post.

One way of putting it

 

[PaulRainbow]

I thought for a long time you couldnt effectively combine charging sources. There is plenty of anecdotal accounts to this effect. I then found some more informed opinion which is that in simple terms most modern chargers dont see the charge being put into the batteries by other charging devices

This is incorrect. Your "more informed opinion" is total nonsense.

As for the rest of the post, you need to do some more reading and learn the difference between amps, amp hours, watts and volts etc.

 

[lw395]

Hello all,

Going to start sorting out the solar panel upgrade on the boat in the next few months and looking at the best way to set it all up, as I have currently purchased the following items in readiness:

Rutland 1200 windcharger that comes with a dedicated MPPT controller that can also take 20W of solar, so have also got 2 x 125V rigid solar panels that I will be running through that also.

Have also purchased a further 2 x 125V solar panels, the same make and model, that I plan to run through a separate MPPT controller (Victron?).

Both MPPT controllers will go to the same battery bank (and VSR to charge the start battery and bow thruster battery).

So, will this work?

Cheers

DTD

Consider what will happen if your Victron charger wakes up in the morning to find:
Batteries 50% Charged.
Rutland wind charger putting in several amps.

Because the batteries are on charge, albeit at a low rate, the voltage will be high enough that the Victron will 'believe' the batteries are nearly fully charged.
So after one hour it will go from absorption charge to float.

This is the kind of poo-trap you can create by having two chargers.
A 'smart' charger can only do anything smart if the information it's using to make decisions about the state of charge of the battery is not altered by other charging sources or loads.
Different 'smart chargers' make their decisions in different ways, and not knowing exactly what model you've got, I can't be sure what yours will be doing, so this is really just an example of the kind of issue which can happen.
There are ways around this. Like having charger modules that talk to each other on a data link. Or channeling all the power sources through one controller.
OTher options include manual intervention and cunning circuits to force the chargers to make the right decisions.
Or use controllers which have ever more complex ways of estimating the state of charge. I'm told the BMW 3 series has hundreds of lines of code just to fiddle with the alternator!

IMHO, there is no perfect, all purpose smart charger control algorithm, but you need to do a reasonable job to avoid unnecessary problems.
I think it's hard to get away from it being a good idea to keep an eye on what's happening in real life on your boat, the way you use it.
On the one hand, it's amazing what people get away with, OTOH, you hear of too many people having avoidable problems IMHO.

 

[ip485]

Consider what will happen if your Victron charger wakes up in the morning to find:
Batteries 50% Charged.
Rutland wind charger putting in several amps.

Because the batteries are on charge, albeit at a low rate, the voltage will be high enough that the Victron will 'believe' the batteries are nearly fully charged.
So after one hour it will go from absorption charge to float.

This is the kind of poo-trap you can create by having two chargers.

OK, fine, but that is not my experience, or the experience of others.

I have an 800 AH AMG battery bank, and two inteliigent chargers, one a Victron and one a Charles. I was religious about using one or the other, but never both at the same time. I then consulted both the battery manufacturers and the charger manufacturers and was told this was complete rubbish and to run them at the same time. I then mapped the charge rate throughout a complete cycle every 15 minutes, and compared this with the same cycle using one or other charger. I then repeated the same process using the MPPT controller. Sadly (perhaps) I have repeated about 12 times so far from a variety of discharge states. On the basis of the results I am in no doubt that the manufacturers were correct, and that given each of the chargers was configured to the battery bank using the settings provided by the manufacturers the chargers stopped charging also as predicted. None of the chargers showed any signs of confusing each other.

I thought exactly the same as the earlier posters and am sorry to have confused AH with A which I am aware I still do.

By all means point out specifically why my post is nonesense and "so much rubbish" - I am very much here to learn BUT my actual experience, those of a number of very technical long term cruisers and the advice I have been given by the manufactuers on how to best charge and look after the battery bank is very different, and also I know different from the view commonly recited, which I am also told is wrong, even though it is so often repeated.

 

[ip485]

This is well worth a read.

http://www.pbase.com/mainecruising/effect_of_charge_rate_on_agm_battery

"Right now, today my Sterling Pro Chrge Ultra, a pretty good charger, tripped into float with my bank at 90% SOC. I turned it off, waited until the remote control was blank, turned it back on, and it’s in Absorption again.
My bank is currently accepting 50 amps from three sources, two chargers and Solar, Solar is about 20 amps which isn’t bad for February. I’m heating water, Wife is washing clothes and in likely an hour I’ll be maybe 93% SOC and I will turn the generator off, and hope that Solar can get that last 7%, it may, it has a chance, it should have at least four hours to do it.

Did you read Maine Sails article? If not, do so it will explain a lot, in particular look at how long that last few percent of charge takes, you’ll spend more than 50% of your time charging chasing that last few percent, but that last few percent determines the life expectancy of an AGM bank, it’s the Achilles heel of an AGM bank. "

This is a quote from the moderator of another forum and long term cruiser which I hope I may reproduce. It is now exactly my experience. When we got down to it, many said the same with far more technical knolwedge than I could muster.

By all means tell me specifically where and how I am wrong, but I find this subject in particular seems so misunderstood. This was also the view of both manufacturers who told me they were horrified the extent to which most cruisers abused their banks by lack of understanding.

Now I have been around long enough to know that we can all be wrong but, if we are going to have the debate lets deal in specifics and tell me why my data and the above posts are so incorrect!

 

[lw395]

Victron make a whole range of products, plus there's a whole load of their legacy products out there.
So, the exact potential problems won't apply equally to everything.
This thread is actually about charging from solar controllers, rather than mains.
But the general principles apply.
If you read the tech spec for the typical marine solar controllers from Victron, it clearly states that time before switching to float voltage is limited according to voltage sensed at wake-up.
That is how they primarily determine initial state of charge.

I'm not familiar with 'Charles' products, but a quick look on the interweb gives their FAQs.
I paraphrase:
Q: Why are my batteries boiling dry?
A: Get used to it. You could tell the charger you've got gel batteries to lower the set point.

http://www.charlesindustries.com/main/marine_sales_support_faq.htm

It looks like the Charles charger isn't making much in the way of 'smart' decisions about state of charge, it's just turning down to float after 4 hours. So no great opportunity for that algorithm to get corrupted by
false data from another charger. KISS has its place.



You raise a good point about technically aware long term cruisers. These people largely have nothing better to do than exercise a great deal of monitoring and manual intervention.
They then report half the information and less technically aware people take it out of context.

 

[ip485]

http://www.ybw.com/forums/showthread.php?321758-Can-I-parallel-battery-chargers

Also so me good comment from CTEK which supports my experience.

As I have said I can only recount my direct experience that my BMV is indicating a very significant increase in the charge running both chargers at the same time, significantly reduced charge times, all within temps, I have probes on the bank, which suits me just fine as I was also told just about the worst thing you can do (short of regular dischargers to less than 50%) is not bring the bank back up to 100% (or as close as - yet another myth that the BMV will indicate its at 100% but over time infact it will degrade and the BMV is not giving an accurate indication) and putting 400AH back into the bank is a time consuming process at the best of times.

I appreciate all this maybe irrelevant to other than longer term cruisers, but I will comfortably use 40% of my bank over night and without shore power I need the most efficient way of getting it back to a full stage of charge. I have a 8KW Genset as well but prefer to keep its run time to a minimium, so combined chargers, solar and a big Balmer work well in combination.

 

[ip485]

LW395 - some good points, but I also have a Outback Flexmax 80 MPPT which I understand is a "highly intelligent" controller and the Balmar with an inteliigent controller and I see the same pattern with all of these as well.

Charles tell me their SP series are also intelligent chargers, but perhaps there are degrees of intelligence.

I also appreciate your comments about long term cruisers having nothing better to do, but so far as my set up goes there is no manual intervention, I simply run the chargers together for as long as I can put up with the noise, and then leave just the solar running.

As to my Victron its two years old as is the Flexmax so hopefully reasonably up to date.

The AGMs are Lifeline.

 

[lw395]

This is well worth a read.

http://www.pbase.com/mainecruising/effect_of_charge_rate_on_agm_battery

"Right now, today my Sterling Pro Chrge Ultra, a pretty good charger, tripped into float with my bank at 90% SOC. I turned it off, waited until the remote control was blank, turned it back on, and it’s in Absorption again.
My bank is currently accepting 50 amps from three sources, two chargers and Solar, Solar is about 20 amps which isn’t bad for February. I’m heating water, Wife is washing clothes and in likely an hour I’ll be maybe 93% SOC and I will turn the generator off, and hope that Solar can get that last 7%, it may, it has a chance, it should have at least four hours to do it.

Did you read Maine Sails article? If not, do so it will explain a lot, in particular look at how long that last few percent of charge takes, you’ll spend more than 50% of your time charging chasing that last few percent, but that last few percent determines the life expectancy of an AGM bank, it’s the Achilles heel of an AGM bank. "

This is a quote from the moderator of another forum and long term cruiser which I hope I may reproduce. It is now exactly my experience. When we got down to it, many said the same with far more technical knolwedge than I could muster.

By all means tell me specifically where and how I am wrong, but I find this subject in particular seems so misunderstood. This was also the view of both manufacturers who told me they were horrified the extent to which most cruisers abused their banks by lack of understanding.

Now I have been around long enough to know that we can all be wrong but, if we are going to have the debate lets deal in specifics and tell me why my data and the above posts are so incorrect!

This is really terminal (sic) thread drift.
I can't see what point you are trying to make which has any relevance to the OP.

There are some interesting issues related to charging at high fractions of 'C'.
But from a professional perspective anyone who works with 12V batteries and criticises others for incorrect subtle definitions of 'bulk' and 'absorption' while measuring his voltages to one decimal place (+/-1 count +/- ?%) is probably a knob end amateur.

 

[lw395]

http://www.ybw.com/forums/showthread.php?321758-Can-I-parallel-battery-chargers

Also so me good comment from CTEK which supports my experience.

As I have said I can only recount my direct experience that my BMV is indicating a very significant increase in the charge running both chargers at the same time, significantly reduced charge times, all within temps, I have probes on the bank, which suits me just fine as I was also told just about the worst thing you can do (short of regular dischargers to less than 50%) is not bring the bank back up to 100% (or as close as - yet another myth that the BMV will indicate its at 100% but over time infact it will degrade and the BMV is not giving an accurate indication) and putting 400AH back into the bank is a time consuming process at the best of times.

I appreciate all this maybe irrelevant to other than longer term cruisers, but I will comfortably use 40% of my bank over night and without shore power I need the most efficient way of getting it back to a full stage of charge. I have a 8KW Genset as well but prefer to keep its run time to a minimium, so combined chargers, solar and a big Balmer work well in combination.

Still negligible relevance to the OP and his solar/wind mix.

 

[ip485]

I thought the OP was asking about operating two MPPT controllers at the same time?

The usual comment I have seen - is that it will not work, and it is pointless runing them at the same time - which, with respect, was repeated here.

I was seeking to explain that in my experience it may well work, and there may be advantages for the OP in doing so, not least that the quickest way of destroying batteries is to repeatedly fail to achieve as near as possible to 100% charge.

My experience amoung people who go cruising, rather than spending most of their time between shore power points, is that maintaining a high level of charge is a challenge, because charging sources are inadequate in the first place, and, in the second place, are not used at the same time, thus contributing to the problem.

What the OPs intentions are of course I can only speculate but this might be interesting information for anyone following this thread for the reasons I have said.

I also accept your comments regarding some of the technical stuff which may seem remote from the real world, which is why I recounted my personal experience which is, for me, it works really very very well. Maybe I am just lucky with the way I have set it up, but that may be true for others who have long held the commonly expressed view that on no account should you run different charging sources at the same time.