Solar panels - can I use more than one charge controller?

webcraft

webcraft

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I have a single high performance 55W fixed solar panel which performs really well and has its own charge controller.

I want to buy 2 lightweight 100W flexible panels to hang on the guard rails or drape over the spray hood when at anchor.

I know very little about solar, but would like to leave the existing setup as is and connect a separate charge controller for the new panels. Is this sensible/easy/possible?

- W
 
webcraft said:
I have a single high performance 55W fixed solar panel which performs really well and has its own charge controller.

I want to buy 2 lightweight 100W flexible panels to hang on the guard rails or drape over the spray hood when at anchor.

I know very little about solar, but would like to leave the existing setup as is and connect a separate charge controller for the new panels. Is this sensible/easy/possible?

- W
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Did precisely this on the last boat. No problems.
 
Yes, dead easy. You can have as many controllers on to the batteries as each is a completely independent circuit. Your proposed 2x100w sounds like the set up I put on this summer mentioned in a previous thread I started.
 
webcraft said:
I have a single high performance 55W fixed solar panel which performs really well and has its own charge controller.

I want to buy 2 lightweight 100W flexible panels to hang on the guard rails or drape over the spray hood when at anchor.

I know very little about solar, but would like to leave the existing setup as is and connect a separate charge controller for the new panels. Is this sensible/easy/possible?

- W
Click to expand...

Yes. Set them both to the same charge profile.
 
What exactly do you want the controllers to do?
If you just want them all to pump charge into a flat battery, that's pretty easy.
but if you want them to optimally charge a battery, making the correct decision about when to turn to float etc , that might be a little more complex?

Suppose the morning sun hits the first panel, its controller wakes up, decides charging is called for and it raises the volts on the battery to 13.4 .

When the second panel gets some sun, what will its controller do? Will it decide the battery is fully charged and take the day off?

Unless you know exactly how the controllers decide the state of the battery and hence control the charging, it's possible there will be unforeseen consequences.

I can make this happen with cheap no-name Chinese controller if the battery is being slowly charged with a small 'maintenance charger'.
Applying a load (a grumpy diesel heater) drags the volts down and the solar controller starts charging.

I guess that 'proper' systems measure the actual current at the battery terminal with a shunt and network the charging sources together?
Also on a live-aboard boat, the fridge or something will reset the many times a day so it's unlikely to be an issue.
But I have a small boat with no daytime loads if I don't go sailing.

Conversely, I am not sure that multiple chargers might not overcharge the batteries if they each have an algorithm involving a daily boost charge, and the boat is not used?
The documentation I have is sketchy to non-existent of course!

Unless there's a lot of amps, why not route all the panels to one controller so it knows what it's doing?
 
watching the latest video from "cruising the cut" on you tube may give you a much better insight as to just how doable it is.

Average guy average DIY skills = total sucess.

Regards Clive
 
There are issues connecting two or more charge controllers to one battery bank. This worth watching, the guy is not very technical.


The bottom line is two or more charge controllers don't work efficiently or at all unless they are properly interconnected.
 
davierobb said:
The bottom line is two or more charge controllers don't work efficiently or at all unless they are properly interconnected.
Click to expand...

Have you actually tried it yourself?

Connecting two MPPTs in the normal way to the same bank, fed by the same panels does work and I found no difference in charge rate when I replaced the two with one larger one.
 
Multiple controllers are not only OK, they are usually the superior approach, leading to a slightly higher yield due to the better tracking of the maximum power point, especially when solar panels are experiencing different conditions such as shade on one panel.

There can be occasional conflicts, but these are usually minor. A controller with a user adjustable algorithm is a huge help. The popular Victron MPPT controllers are very good in this regard enabling fine user control. Features such as the option to enable "tail current" to be disabled, helps eliminate any conflicts. They can also be easily linked, or synchronized and this is worthwhile, although not essential if you have a contoller without this facility.
 
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Graham376 said:
We had 2 controllers feeding the same banks for a while and they worked OK. My question is - will flexible panels survive? Hanging on guard wires they will be subject to a lot of flexing with wind and boat movement and doubt they will last long. Surely better to have rigid hinged panels.
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Yes. Modern ETFE flex panels will be fine. All of the worry was about older panels.
 
The chargers work purely based on the voltage they see at their charge terminals, the current they are supplying, and the timers in their algorithms setting the duration of their Bulk, Absorption, Float, etc. phases.

Solar is usually fitted in parallel to alternator and shore-power anyway, (which may well have different or no charging profiles) so adding a second solar charge source to an existing one is not going to affect anything - 4 chargers instead of 3.

None of the charge sources can tell if the current they are supplying is actually going into the battery or being used by other loads like the fridge, lights, electronics etc. (unless you have an expensive interconnected system with battery monitoring)

As long as one or more charge sources supply enough current when the voltage starts to drop then the batteries will remain charged - and it's a good idea to match the chargers parameters to the type of batteries being used if possible.

I have shore-power, generator, solar and alternator as charge sources and I can watch the solar kick-in in real-time when I turn on the water pump for example, and if then engine is running before the sun comes up then the solar takes the day off. but kicks in when the engine is stopped.

On shore-power, when the charger is on "storage", the solar kicks in at sunrise and does a short Bulk, Absorb, Float cycle ... and the shore power charger gets confused.

... but it all just works, the fridge runs 24/7, and the batteries don't go flat.
 
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I have 2 alternators, a shore power charger, 1 pwm solar charger, 3 MPPT chargers, a wind-generator and a hydro-generator. The conflict issue is a myth.

All of the charge controllers check the voltage of the batteries (and therefore the whole boat's systems) when determining charge state. The output current of the charge controllers combine to raise the battery to the 'absorption voltage'. In the case where you have an excess of power available from several sources, as one power source reduces its input, the battery voltage will fall and another controller with excess power available will increase its input to maintain the absorption voltage. If the total charging power available is less than the battery can take, then all the controllers will give all the current they've got available to try to raise the voltage.
 
I'm glad to read all that. I had planned slightly different in so much a small panel just to trickle charge the engine battery and a larger panel to charge the two domestic batteries each with their own controller. I just need to find time to fit!
 
roaringgirl said:
I have 2 alternators, a shore power charger, 1 pwm solar charger, 3 MPPT chargers, a wind-generator and a hydro-generator. The conflict issue is a myth.

All of the charge controllers check the voltage of the batteries (and therefore the whole boat's systems) when determining charge state. The output current of the charge controllers combine to raise the battery to the 'absorption voltage'. In the case where you have an excess of power available from several sources, as one power source reduces its input, the battery voltage will fall and another controller with excess power available will increase its input to maintain the absorption voltage. If the total charging power available is less than the battery can take, then all the controllers will give all the current they've got available to try to raise the voltage.
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So how does each controller know when your battery bank has had enough time at absorption voltage?
 
webcraft said:
I have a single high performance 55W fixed solar panel which performs really well and has its own charge controller.

I want to buy 2 lightweight 100W flexible panels to hang on the guard rails or drape over the spray hood when at anchor.

I know very little about solar, but would like to leave the existing setup as is and connect a separate charge controller for the new panels. Is this sensible/easy/possible?

- W
Click to expand...
Just a heads up, Ive just changed my Photronics PWM controller for an MPPT one so have a spare 10amp for sale. £12 to you!
 
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roaringgirl said:
Each controller has the same view of the voltage and the same settings for absorption voltage.
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When the controller is not getting any power from the panel, does it know anything about the battery?

It's possible that some controllers do.
The cheap one I have seems not.
 
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