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

[ip485]

BTW and more specifically I dont run two MPPT contollers at the same time (having only one) but there is plenty of comment with a little research about doing so;

https://www.morningstarcorp.com/parallel-charging-using-multiple-controllers-separate-pv-arrays/

I have room for another couple of panels which will be of a different type so may well add a second charger controller so this is also useful information.

 

[ip485]

BTW I notice in the earlier referred discussion which I recall reading with greater interest at the time the same gentlemen contributed to that discussion along similiar lines.

Someone else in that thread commented;

I completely agree with geem

"Paul the mistake you are making with this statement "one charger will detect the output from the other charger and think that the batteries are charged "

The one charger is detecting the battery voltage not the charger output. This is because the charger has am output resistance such that the resultant voltage is dependant on the current flow from the charger to the battery. This current flow really as a result of the internal resistance of the charger and battery to gether with the voltage difference between the no load charger voltage and the no charge/discharge voltage of the battery.

The charges will detect this resultant battery voltage and as the battery voltage rises as the battery charger state increases the different chargers will turn off or change charging state at each one reach its turn off voltage. "

This is now much closer to my understanding and experience generally with regard to pretty much any charger. I also have monitored the voltage of the Bank both with and without any charge input throughout the cycle and again this accords with exactly the information the BMV is reporting and it does not appear any of my chargers are shutting down either at the start of the cycle or an any point during the cycle until the voltage and the charge state are very close to a reported 100% charge.

 

[davethedog]

Right after all the discussion I think the simple answer is yes I can connect 2 x mppt controllers to the same battery bank...

 

[PaulRainbow]

Right after all the discussion I think the simple answer is yes I can connect 2 x mppt controllers to the same battery bank...

You can connect 2, as i said earlier. But, one may detect the output from the other and not charge. To say that one smart charger will not "see" the output from the other is utter nonsense.

I can demonstrably stop my Victron MPPT controller in its tracks by turning the mains charger on. At the moment, the Sun is shining brightly here, the output from 260w of solar panels is 0a, the controller is in float. It isn't putting out any charge because the mains charger is on.

I will now turn the mains charger off and see what happens. The solar controller instantly started to output 4.4a and very shortly thereafter went into bulk mode. After turning the mains charger back on the solar output promptly dropped to 0a again. At 10:51 it has gone into absorption. At 10:52 it has gone into float mode.

Although my batteries are fully charged, the above shows just how much one charging source can affect another. I have no need to worry about my batteries not getting a full charge, that's already done, but i'm not going to get any benefit from todays Sun. Different setups and different charging sources can have varying results.

The above also demonstrates that the Victron controller does not subject batteries to long periods of absorption if they are already fully charged.

From post #12

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 a very likely scenario. You need to do as suggested and keep a close watch on things, make sure you fit the Victron controller with Bluetooth to closely monitor the solar yield. You could otherwise be oblivious if one bank of solar panels aren't contributing much at all.

 

[CJ13]

I’ve been following this thread with interest, as i’m planning to add to my existing solar.
The thinking used to be to wire several panels in series to minimise cable size, but I thought the current thinking is that because of shading issues each panel should have its own controller.
This is the opposite of what Paul and others are saying so i’m confused?

 

[lw395]

I’ve been following this thread with interest, as i’m planning to add to my existing solar.
The thinking used to be to wire several panels in series to minimise cable size, but I thought the current thinking is that because of shading issues each panel should have its own controller.
This is the opposite of what Paul and others are saying so i’m confused?

You get less problems with shading by paralleling panels into a single controller.
There are two functions to the controller.
One is extracting the power from the panels, the other is regulating the charging of the batteries.

There are many ways of configuring a system, each with various advantages and pitfalls.

 

[CJ13]

I’ve not heard of parrallelling several panels into a single controller.
In my case i’ll have 3 or 4 panel of differing output. Either 2x 90w + 1 x 150w or 2x90w + 2x 80w.
How would 3 or 4 panels be parrallel wired into a single controller?

 

[VicS]

I’ve not heard of parrallelling several panels into a single controller.
In my case i’ll have 3 or 4 panel of differing output. Either 2x 90w + 1 x 150w or 2x90w + 2x 80w.
How would 3 or 4 panels be parrallel wired into a single controller?

2 x 90, + 1 x150 would have to be wired in parallel

2 x 90 + 2 x 80 could be probably be wired in a a series/ parallel arrangement into a suitable MPPT controller with some advantages
The two 90 watts would be in series with each other and similarly the two 80 watts. The two pairs would then be wired in parrallel to the controller provided the specs are suitable

But all 4 could be simply wired in parallel

 

[lw395]

2 x 90, 1 x150 would have to be wired in parallel

2 x 90 + 2 x 80 could be probably be wired in a a series/ parallel arrangement into a suitable MPPT controller with some advantages
The 2 90 watts would be in series with each other and similarly the two 80 watts. The two pairs would then be wired in parrallel to the controller.

But all 4 could be simply wired in parallel

Provided they are all the same nominal voltage and have blocking diodes.

 

[ip485]

You can connect 2, as i said earlier. But, one may detect the output from the other and not charge. To say that one smart charger will not "see" the output from the other is utter nonsense.

I can demonstrably stop my Victron MPPT controller in its tracks by turning the mains charger on. At the moment, the Sun is shining brightly here, the output from 260w of solar panels is 0a, the controller is in float. It isn't putting out any charge because the mains charger is on.

I will now turn the mains charger off and see what happens. The solar controller instantly started to output 4.4a and very shortly thereafter went into bulk mode. After turning the mains charger back on the solar output promptly dropped to 0a again. At 10:51 it has gone into absorption. At 10:52 it has gone into float mode.

I think the issue here is that you have performed the test when the bank is charged, or almost charged. Of course you would expect one of the charging sources to cease charging. If I am running the MPPT controller and both mains charger at the same time, which I frequently do, the settings I use determine which chargers will cease to charge and the order in which they do so.

When the bank is substantially discharged (first thing in the morning) turn on the mains charger and measure the input, then turn on the MPPT controller and again measure the input, then turn off the main charger and measure the input. I would be very surprised if the combination of both chargers doesnt demonstrate that the input is greater working together.

As I indicated with my Outback and nearly 800W of solar this is exactly what I record, and the two working together gives me a far quicker charge rate than either alone.

My routine is to leave the Outback on all the time. In the morning if I am not going to use the engine, I run the Genset, with both mains charger, put the water heater on, the water maker, and maybe do some washing, all of which loads up the Genset as much as possible. At between 50% and 60% charge the bank will absorb as much as both chargers and the MPPT controller can produce, and will very slowly start to back off after about 30 minutes or so. As indicated earlier the hardest part is the last 15% which is where the solar is invalueable, because the mains chargers have done most of the work by well before midday and the solar can then slowly finish off the job when the batteries are resisting the charge the most.

My understanding is that chargers arent really "seeing" the charge introduced into the circuit, but are "seeing" the voltage of the bank. The chargers are really interested in whether there are multiple charge sources, simply that as the voltage of the bank rises, then the charger will reduce the amount of charge. Of course with multiple chargers that point will be reached sooner. In the same way if the bank is very close to 100% a mains charger will be increasing the volts as much as the bank will accept so it is more than likely at that point an MPPT controller will register the bank as full because the mains charger is more than keeping up with any load on the batteries from fridges, freezers, instruments etc.

Does that make sense, or am I talking a load of rubbish?

 

[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.

I just dont believe that is so.

As I have explained above my experience and that of many other contributors elsewhere is the complete opposite.

Perhaps there are some setups that work in a different way, so I dont doubt it is possible, but if batteries are at 50% charge as reflected by the voltage of the bank I find it very surprising that any of the chargers would go to float, unless the bank was very small and the output of one of the chargers was very large. I am not quite sure how that scenario would play out. To be fair my experience is with a reasonably large bank, (800AH, and AGMS) and some reasonably larger chargers. I fully appreciate some cruisers have significantly smaller banks and very different charging set ups.

 

[PaulRainbow]

I think the issue here is that you have performed the test when the bank is charged, or almost charged. Of course you would expect one of the charging sources to cease charging.

The batteries were indeed fully charged, but the point was to demonstrate that on smart charger can cause the other to shut down.

When the bank is substantially discharged (first thing in the morning) turn on the mains charger and measure the input, then turn on the MPPT controller and again measure the input, then turn off the main charger and measure the input. I would be very surprised if the combination of both chargers doesnt demonstrate that the input is greater working together.

I can easily see what is happening, i have the solar controller and a battery monitor connected to a laptop by USB adapters and a remote battery monitor for the mains charger. The results with partly charged batteries might vary slightly, but the solar controller will still "see" the output from the mains charger and be influenced by it, that's how smart chargers work.[/quote]

As I indicated with my Outback and nearly 800W of solar this is exactly what I record, and the two working together gives me a far quicker charge rate than either alone.

I'm not going to try and pick your findings apart, suffice it to say (as i've said before) different setups and different chargers can and will yield different results.

My understanding is that chargers arent really "seeing" the charge introduced into the circuit, but are "seeing" the voltage of the bank. [/quote]

This is not correct. You cannot measure battery voltage at the terminals independently of the charge voltage being applied to the bank, anymore than you can accurately measure it if the bank is under load. If the mains charger is charging at x volts, that is what the solar controller will sense, it may well be that if the battery was disconnected and lef to rest the actual voltage will be much lower.

Does that make sense, or am I talking a load of rubbish?

Let's just say that you have a few misunderstandings

 

[PaulRainbow]

I just dont believe that is so.

As I have explained above my experience and that of many other contributors elsewhere is the complete opposite.

That is exactly what would happen and that is highlighted to some extent by the brief tests i did earlier. The Victron MPPT controller will sense the battery voltage when the Sun starts to shine and it begins to work. It will base the max duration of its absorption mode in part on the battery voltage at startup. So, if the windgen is charging the MPPT controller will sense the output voltage of the windgen controller and this will cause the solar controller to go into float early.

Perhaps there are some setups that work in a different way, so I dont doubt it is possible, but if batteries are at 50% charge as reflected by the voltage of the bank I

This seems to be a key misconception, not only by yourself. What is measured at the battery terminals does not have to be the true battery voltage, it's likely just a surface voltage. Take a partly discharged battery and put it on charge, if you measure the voltage at the terminals you will get the charger output voltage. Turn the charge off and watch it drop. Or, take a fully charged battery and subject it to a large load, the voltage reading will drop. Remove the load and the voltage will rise again.

Smart chargers will also measure the current going into a battery, but that can also be influenced by loads. With different setups, different results can be found.

 

[ip485]

Rainbow Marine - I think we are closer to agreeing now.

However, my point is that using two charge sources, or more, will significantly reduce the length of charge time, given that most people's chargers fall way short of being of the ideal size in relation to the size of the battery bank.

If one chargers goes to float earlier than it might if that charger were operating in isolation - does it matter? For the time the two chargers were operating together the batteries will charge significantly more quickly.

I did a small test today and drained the bank to 60% overnight. The voltage was 12.4V albeit under load, I then swittched on the first charger and the voltage was 12.7V (again under load) and then 5 minutes later the second charger and the voltage was 12.85V, under the same load. The BMV recorded a 75% increase in the rate of charge when the second charger was switched on. On another occasion I will monitor when the second charger goes to float, but obviously this is more difficult because every time the charger is switched off it well reset.

 

[lw395]

....
If one chargers goes to float earlier than it might if that charger were operating in isolation - does it matter? ......

It certainly will if the other charge source doesn't make up the shortfall.
As can very conceivably happen with the wind/solar mix discussed here.

 

[ip485]

It certainly will if the other charge source doesn't make up the shortfall.
As can very conceivably happen with the wind/solar mix discussed here.

I dont think so.

I think we are giving the intelligence of chargers far greater credit than we should, and I had previously believed was the case.

I have also been having quite a technical discussion here, which if anyone is interested I think provides some of the best answers I have found (http://www.cruisersforum.com/forums/f14/understanding-intelligent-chargers-209917-4.html)

Please let me know your thoughts if you can be troubled to wade through the discussion.

I admit there are still elements I dont fully understand. You may say why so much interest, but I enjoy trying to understand why the chargers are behaving in the way I observe, rather than the way most people seem to think they should.

Also, and from a far more practical view point, it has made life a lot easier for me maintaining my battery bank. I can recharge the bank in a lot less time, and, I think until you spend sometime off the grid, most people just dont realise on any yacht that uses a reasonably large amount of power, just how important it is to be able to manage putting the power used back into the bank - which is far from easy.

Hence back to the OP, I am still convinced that in the vast majority of cases you are far better off running multiple charge sources if you are able, and that there is generally no circumstance in which this would not have advantages.

 

[GHA]

However, my point is that using two charge sources, or more, will significantly reduce the length of charge time, given that most people's chargers fall way short of being of the ideal size in relation to the size of the battery bank.

Maybe not as much help as you might think to get to full charge - a lot of the time is spent at constant voltage - this for AGMs
https://marinehowto.com/how-fast-can-an-agm-battery-be-charged/

100Ah to full took 12 minutes longer to full from 50% with a 20A (0.2C) charger compared to a 40A (0.4C) charger.

Here we are at 100% SOC at the .2C charge rate and it took 5:42 minutes.

Yes, it took longer to attain 100% SOC (per Lifeline battery tech manual) but that time was only about 12 minutes different with double the charge rate.

 

[PaulRainbow]

Hence back to the OP, I am still convinced that in the vast majority of cases you are far better off running multiple charge sources if you are able, and that there is generally no circumstance in which this would not have advantages.

Only if you completely ignore all that has been said about how the windgen output will seriously affect the output from the Victron solar controller.

Your findings are your findings, they do not apply to all installations.

 

[lw395]

I dont think so.

I think we are giving the intelligence of chargers far greater credit than we should, and I had previously believed was the case.

I have also been having quite a technical discussion here, which if anyone is interested I think provides some of the best answers I have found (http://www.cruisersforum.com/forums/f14/understanding-intelligent-chargers-209917-4.html)

Please let me know your thoughts if you can be troubled to wade through the discussion.

I admit there are still elements I dont fully understand. You may say why so much interest, but I enjoy trying to understand why the chargers are behaving in the way I observe, rather than the way most people seem to think they should.

Also, and from a far more practical view point, it has made life a lot easier for me maintaining my battery bank. I can recharge the bank in a lot less time, and, I think until you spend sometime off the grid, most people just dont realise on any yacht that uses a reasonably large amount of power, just how important it is to be able to manage putting the power used back into the bank - which is far from easy.

Hence back to the OP, I am still convinced that in the vast majority of cases you are far better off running multiple charge sources if you are able, and that there is generally no circumstance in which this would not have advantages.

A lot of people making observations which apply to different installations.
Different chargers/controllers use different means to decide when to reduce absorption voltage to float voltage.
Many Victron products use the voltage at wake-up to indicate state of charge. This is then used to set a time limit for absorption charging.
If your second source affects that wake-up voltage, then the Victron will switch to float early. You're then reliant on the second source being able to hold absorption voltage for long enough. That may not happen if it doesn't have enough wind or solar input.
Or your second source may already have switched off depending on how it decides when to end absorption.

There is perhaps one thing more important than fully charging your batteries, and that's not overcharging them day after day after day.... I think this is why Victron use this model.

 

[ip485]

Many Victron products use the voltage at wake-up to indicate state of charge. This is then used to set a time limit for absorption charging.

Yes, maybe, but he view seems to be if you switch on the Victron first and will not effect the second because it will have already determined the alogrithm to follow.

Or your second source may already have switched off depending on how it decides when to end absorption.

Yes, but it would seem almost all controllers are no where near as intelligent as we think and nearly all a lot less intelligent than Victrons.

There is perhaps one thing more important than fully charging your batteries, and that's not overcharging them day after day after day.... I think this is why Victron use this model.

but the view would seem to be it is almost impossible to do so for any of the alogrithms and if the second charger backs of first because it has been slightly fooled by the SOC, the first charger will do no more than complete the charging process.

Only if you completely ignore all that has been said about how the windgen output will seriously affect the output from the Victron solar controller.

but others seem to indicate very strongly it will not, especially if the Victron is switched on first. Once it has seen the SOC it will simply perform ina ccordance with its alogrithm until the initial stage is complete.