Which charge controllers can be paralleled to increase current rating?

Lefty Wright · July 2007

I am now running my 12V system on two separate controllers with separate
wire runs from the PV panels to the controllers.

I would prefer to effectively increase my wire size by using only one controller or two in parallel so I could combine my two wire runs into one.

Since my electrical needs change frequently I would prefer to spend the same amount of money on two smaller controllers that can be paralleled rather than on one larger controller.

I can't get the info I need from the retailers and I've already wasted money on one controller because it's manufacurers understated it's ampacity by 5A.

I'm hoping those of you who have done it know which work and which don't.

Windsun · July 2007

Re: Which charge controllers can be paralleled to increase current rating?

Any of the Morningstar controllers can be paralleled. Most Xantrex cannot.

Solar Guppy · July 2007

Re: Which charge controllers can be paralleled to increase current rating?

The Xantrex C-Series Charger controllers can be parralleled

In general, on/off/pwm can be parrallel, mppt ( ie have step down abilities ) can NOT be parralleled.

westbranch · July 2007

Re: Which charge controllers can be paralleled to increase current rating?

Lefty, what are your system specs?

Eric

BB. · July 2007

Re: Which charge controllers can be paralleled to increase current rating?

Just out of curiosity, "paralleling charge controllers" does that mean 1) each controller has its own solar panels but connected to a common battery bus or 2) all panels on common bus and all batteries on a common bus and the controllers just installed in true parallel fashion?

I can see 2) having issues with paralleling... And 1) having issues with how to finish charge (float, equalization)...

-Bill

PS: I can see 2) being a show stopper and 1) not being a serious problem (just coordinating equalization with manual starts)...

crewzer · July 2007

Re: Which charge controllers can be paralleled to increase current rating?

Lefty,

In general, there's no problem with parallel connecting the battery outputs of similar charge controllers to a common battery bank. However, each controller's input is usually connected to an independent PV array. For example, the OutBack MX60 charge controller is frequently used this way ( see this link with two MX60's on the right hand side), and Morningstar says it's OK to parallel the outputs of their controllers as well.

HTH,
Jim / crewzer

Windsun · July 2007

Re: Which charge controllers can be paralleled to increase current rating?

Solar Guppy wrote: »

The Xantrex C-Series Charger controllers can be parralleled

In general, on/off/pwm can be parrallel, mppt ( ie have step down abilities ) can NOT be parralleled.

You're right, dunno what I was thinking.

The old C-30 Xantrex could not be, but all the electronic ones can be.

However, all current MPPT controllers also can be, like the MX60, the Apollo, and the new Morningstar MPPT that is due out soon.

There are some issues though with paralleling any controllers - if one goes out or fails to turn on, it can force the other one to take all the current. We have seen this a couple of times with C40's used as diversion controllers. Which is one reason I am not a fan of diversion control.

Lefty Wright · July 2007

Re: Which charge controllers can be paralleled to increase current rating?

BB: by parallel operation I mean wiring multiple PV panels into a common run to two controllers.

West Branch; right now I have PV panels in two different locations with two separate wire runs going to two separate controllers charging a common battery bank. But they can't be paralleled. One controller is a pwm and the other is mppt.

I'd like to put all my panels on one tower. My tower is 455 feet from the house and has two 1" conduits and an 8-4 buried cable running to the house.

I know the sensible thing to do is purchase a charge controller that can handle all the current I ever expect to generate.

But I don't know how much current that may be. This setup will change when my new house is finished and this one becomes my workshop.

As my load has increased I have been making incremental changes to my system. Not the best way to do it as I tend to out grow my charge controllers.

I'd like my next one to be able to be paralled instead of discarded.

niel · July 2007

Re: Which charge controllers can be paralleled to increase current rating?

firstly, you may not gain anything by just combining the wires, controllers, and pvs, plus it's not recommended to parallel pvs to paralleled controllers. each controller should have its own pvs. if it is to go into an inverter then with a run like you have, maybe you should consider having the inverter and controllers in a ventillated, but waterproof enclosure near the pvs and then send the 120vac on that long run. if it must stay at dc potentials for the run and using an inverter then i recommend upping the dc voltage to 24v, or better yet, 48v to overcome resistive losses. does the controller you have allow higher voltages? you would need to have an inverter that can take the higher voltages as inputting 24v or 48v into a 12v inverter could damage the inverter as it's not made for that inputted voltage.
what i'm trying to say is you have a bigger problem with resistive losses for that long of a wire run as you would see if you tried using the excel voltage calculator in the sticky. using dedicated pv strings to their individual controllers isn't the problem you visualize it to be. the outcome is the same for x number of amps going on say a #1 gauge wire as it would be if it were 2 seperate runs of #4 of equal length to the #1 run with half the current flowing. for the record, 2 number 4 wires paralleled is about equal in resistance to a number 1 wire.
now if you don't have excel you can use an excel clone. if you can't do that then you could give me the information and i'll calculate it for you. it would be important to know the wire run length (from pvs to controllers) more accurately at what gauge number or numbers if paralleled wires and the current you intend to have flow on it. this could be just from the pvs on one of the wire runs to one of the controllers if the other is an exact duplicate of this.

boB · July 2007

Re: Which charge controllers can be paralleled to increase current rating?

One scenario I know of that would make it nice to be able to parallel MPPT controllers, is an existing system with one pair of already big wire (like 2 or 4 ought) run for hundreds of feet and they don't want to have to re-dig and run more expensive copper. In this case, the wire size is way big enough and they could just add another array at the remote site and parallel controllers at the battery end.
This will be a good reason to be able to parallel MPPT controllers.

boB (I don't work for NAWS either... The commute would be too long)
K7IQ

Lefty Wright · July 2007

Re: Which charge controllers can be paralleled to increase current rating?

Yes Bob, that is exactly what I want to do.

With #2's pulled into my 1" conduits the circular mill area of my combined #8's and #2's falls halfway between 1/0 and 2/0.

Neil has a point about dividing my loads across two conductor runs, thereby halving my effective voltage drop. In that case even dissimilar charge controllers would work.

I'm a little irked about spending my money on a controller and finding that it's advertised rating was just advertising hype. I bought it from a reputable dealer. But by the time I discovered the problem lots of time had passed so I ate it.

That is why I asked if anyone had hands on experience with paralleling these things. From reading the limited info manufacturers supply I can't even tell which input voltages some of these controllers can accept.

niel · July 2007

Re: Which charge controllers can be paralleled to increase current rating?

boB is quite right that this is a good situation for a downconverting mppt controller as you get the advatage of sending the dc at a higher voltage and not have to have greater than a 12v battery/inverter that you may already have.
what will you do with the other controller? you can sell it here as long as it is not part of a business venture. personnal solar items are ok to sell here, but alas, not many used items windup being sold as much as we would like.

Which charge controllers can be paralleled to increase current rating?

Comments

Categories