IS it OK to parallel charge controllers?

[Johann]

Is it ok to wire the solar panel side of an charge controller in parallel with more charge controllers so the total ampacity of all charge controllers would match the total panel ampacity.

In other words.....
If someone has a 40 amp solar panel array. Can they just put two 20 amp charge controllers wired in parallel on the solar panel terminal and parallel wire on the battery terminal?

[electrondady1]

i have no expertise.
 perhaps you could use 3 for an over capacity.

[joestue]

Not likely, because the charge controllers will not share current equally, even if they have exactly the same voltage set points, one will always turn off or on before the other, so for a short period of time any one of them will pass double the amps its rated for.

can you split the panel in half?

if the charge controllers are current limited, true mppt then yes they should parallel just fine, however depending on the algorithm the mppt may fail completely.

[Johann]

Panels could be split, but then the panels would have to be wired for it.

So, should it be like the following ?
# 1 string......Solar panel #1 array to breaker #1 to charge controller #1 to breaker #1A to battery bank.
# 2 string......Solar panel #2 array to breaker #2 to charge controller #2 to breaker #2A to same  battery bank.
# 3 string etc etc  to continue as needed.

[Frank S]

my has 8 130 watt panels each is wired direct to my single 2 AWG feeder lines to a pair of 60 amp PWM charge controllers which are in parallel my bank is 12 golf cart batteries wired in pairs  and 2 4D  all are connected  at a single point to a pair of 500 MCM cables which feed both my inverters. I have 1 disconnect from the array feeder lines. I regularly see 30 amps output from both PWMs and once I saw as high as 72 amps total output. over 3 years like this with no problems

[Johann]

my has 8 130 watt panels each is wired direct to my single 2 AWG feeder lines to a pair of 60 amp PWM charge controllers which are in parallel my bank is 12 golf cart batteries wired in pairs  and 2 4D  all are connected  at a single point to a pair of 500 MCM cables which feed both my inverters. I have 1 disconnect from the array feeder lines. I regularly see 30 amps output from both PWMs and once I saw as high as 72 amps total output. over 3 years like this with no problems

Frank, thank you for this info.

What you have is pretty much what I had in mind.
I have three 100 watt panels up already and wires there for three more panels which I have two more panels here in storage already still in poxes and two or three panels more to come maybe this or next month.

Did you use same brand/model PWM charge controller?
(are in parallel my bank is 12 golf cart batteries wired in pairs  and 2 4D  all are connected  at a single point ).......what is a 2 4D? are those your inverters?

[Frank S]

Frank, thank you for this info.

What you have is pretty much what I had in mind.
I have three 100 watt panels up already and wires there for three more panels which I have two more panels here in storage already still in poxes and two or three panels more to come maybe this or next month.

Did you use same brand/model PWM charge controller?
(are in parallel my bank is 12 golf cart batteries wired in pairs  and 2 4D  all are connected  at a single point ).......what is a 2 4D? are those your inverters?
[/quote]
 Both Charge controllers are exact matches same brand , same model same size
 4d is the size of the  2  12v batteries they are used mostly for starting heavy equipment or as starting batteries for medium sized 200 to 400 KW generators.
 

[Johann]

Frank, thank you for this info.

What you have is pretty much what I had in mind.
I have three 100 watt panels up already and wires there for three more panels which I have two more panels here in storage already still in poxes and two or three panels more to come maybe this or next month.

Did you use same brand/model PWM charge controller?
(are in parallel my bank is 12 golf cart batteries wired in pairs  and 2 4D  all are connected  at a single point ).......what is a 2 4D? are those your inverters?

Both Charge controllers are exact matches same brand , same model same size
 4d is the size of the  2  12v batteries they are used mostly for starting heavy equipment or as starting batteries for medium sized 200 to 400 KW generators.
[/quote]

Thank you for clarifying this.

[OperaHouse]

Sounds risky.  Even with matched controllers the PWM pulses will not be in sync.  That means that one controller will see 100% of total current for short time periods.  It likely only works because these periods are short and the output devices are speced for more than double the current anyway.

[Frank S]

Sounds risky.  Even with matched controllers the PWM pulses will not be in sync.  That means that one controller will see 100% of total current for short time periods.  It likely only works because these periods are short and the output devices are speced for more than double the current anyway.

 OperaHouse ; I started out with only 1 charge controller, but at times I was seeing well over the 60 amp rating so I added a second one. They almost never show the exact same output one or the other will show as high as 40 amps while the other will be around 25 to 30. I've only seen amperage's this high when the bank was low showing the as charging voltage around 12.8 or when the as charging voltage is up to around 14.6 when there is a heavy load on the inverters  1 is a 1800 w PSW  Dimensions (AT&T) the other is a Xantrex 3000 Plus MSW,Most of the time only my 1800 w Dimensions inverter is on. I have seen as high as a 3500 w on that inverter for as long as a couple of minutes. My dimensions interter will not kick off below a 4000 w 30 second load if the bank is nearly full and the charge controllers are showing a combined output of at least 50 amps the Xantrex will drop out at the slightest hint of anything over 3000 w , but I can place a 5000 w combined load on the 2 inverters and see the PWMs showing their highest outputs I've even had my Schumacher 30/60 on at the same time tossing in an additional 45 amps Like I said this has been going on for 3 years now without problems. Right or wrong, it works for me but maybe not for someone else

[Johann]

Do you have fuses or breakers for each controller, or do you just have one fuse or breaker ?

[OperaHouse]

Fuses are a good idea, not only for protection but they act as resistors to create load sharing.

Parallel controllers may work but not for the reasons you think.  The practical current limit for
circuit board traces is about 15A with out going to extraordinary efforts. Look at the leads of
a 60A FET and compare that to the conductor in a 20A fuse.  Device ratings reflect pulse duty
that prevents the leads form vaporizing.  Multiple FET or transistors may be used to limit board
trace currents. Even within the controller it isn't easy to get the devices to share evenly. The
practical limit for device heat dissipation is about 10W due to thermal resistances, even with
an infinite heat sink. All this leads to a lot of redundancy and a good safety margin. That and
a designer doesn't have any control in how the device will be hooked up means there is a lot of
over capacity in good equipment.

Wiring is very critical to load sharing.  Say you have a diode that can carry 20A and you have
a 40A application.  It would seem sensible to place another 20A diode parallel to it. Practically
that will only get you to about 30A at best. Three diodes in parallel would likely work. Even
identical diodes are not identical electrically.  Putting equal resistance in series with each
diode will help to even the load share of each diode. You may have seen lengths of smaller wire
to a common node from diodes.  Fuses are just a resistor in a convenient package.  So, I would
be very careful of wiring to maintain equal resistance and maybe adding some extra resistance
to each controller.

[Johann]

OperaHouse,
Thank you for the information and for trying to explain what is going on.
I know about electrical, but not electronics.
I always wondered how a electronic board can handle so much current with those small conductive tracks that a circuit board has while the wires that are hooked up to such device are relatively large.