Separate Charge Controllers

Re: Separate Charge Controllers

adam1984 wrote: »

Example 1: different charge controllers/ same panels
6 of the exact same panels. Set up in separate strings of 3 (2 strings not connected). Can I use two different models of charge controllers and then tie them both in to the battery bank?

Yes, in general, you can connect multiple charge controllers to one battery bank (within proper voltage/current limits).

Some high end controller can be networked together so that they change charging states (bulk, absorb, float) at the same time. If the controllers are not sync'ed--they will change states and make their own decisions on exact current/voltage levels. Will not hurt anything.

Not sure about 3 strings/two of them isolated. In general do not share a common solar array across multiple controllers across multiple battery banks.

• Multiple MPPT controllers should never share one solar arrays.
• You can, in some cases, share one solar array among multiple PWM controllers on multiple battery banks--as long as the PWM controllers have the same internal/common ground (negative) and the battery banks have the same negative ground too.
• You cannot share one very large current array with multiple PWM controllers feeding one or several battery banks. PWM controllers do not limit or share current (as I understand them). The PWM (shared array or not) must be rated to manage 100% of the voltage/current of the array.

Example 2: different panels/ same charge controllers
3 panels 30W 24V and 3 panels 50W 12V, set up in separate strings of 3 (2 strings not connected). Each is wired into its own charge controller (same model) (Assume it has DC/DC conversion so not worried about efficiency). Can i do this?

Matched solar panels on a single MPPT or PWM controller (assuming meet V/I/P requirements) are fine.

Matched or unmatched strings on their own MPPT or PWM controllers connected to a single battery bank--is fine (see question #1). Mixed type/model/brand is OK.

Example 3: Different panels/ different charge controllers
one string of 3 panels, and a separate string of 2 different panels. The 3 go into one type of charge controller and the string of 2 go into the other model of charge controller. Can I do this?

Multiple "Isolated" panels+controllers sharing a battery bank is fine.

In many cases, you can share the Negative Grounds of the Solar Panels + Battery Banks instead of going through the Negative Terminal of a solar charge controller...

However, there are exceptions--The Xantrex MPPT 60 amp solar charge controller has current sense in the solar panel negative lead circuit--bypassing array current around the controller will confuse it. I do not know about the new Morning Star MPPT series controllers.

Example 4: Can i have an unbalanced load, meaning could I tie the two strings of different voltage modules in parallel? My engineering background says no.

In general when working with MPPT based charge controllers/ GT inverters, for series solar panels, match the Imp ratings of the panels within 10%.

For parallel connections, match the Vmp ratings within 10%.

For Solar Panels the peak of the Pmp curve is fairly flat--If you miss-match by 10% or less, you will probably not lose a measurable amount of power.

Greater than 10% miss-match with MPPT controllers can give multiple Pmp peaks--and there is no guarantee which local peak the MPPT controller would lock on (may miss the "real" peak).

You can mix and match smaller panels in series/parallel and then add them to a larger array. However, Isc of the panels (short circuit current) gets complex to provide proper fire protection. And many smaller panels tend not to be rated for higher voltage operation such as the 600 VAC rating of panels designed for GT inverters in high voltage strings. Older/smaller panels may be rated at 70V or less.

For PWM controllers--As long as Vmp>Batt-Chrg+2volts or so--you can add Vmp=17volts in parallel with panels rated at Vmp=28volts --- There is no "extra power loss" -- it is the sum of the Imp's that are giving you Ibatt current for charging. (the 17 vs 28 volts extra P=I*V power is lost anyway with PWM controllers).

I am taking a guess that I answered the questions you intended to ask... I got a bit lost in the details of your generic questions.

Is there a specific problem you are trying to understand/resolve?

-Bill

Re: Separate Charge Controllers

If those are true Vmp numbers... The 12 volt is too low to charge a 12 volt battery--so putting them in series is a must. Vmp!~17 volts is a good number for charging a 12 volt battery.,. The "loss" using PWM:

• 24v * 4 amps = 96 watts
• (24v-17v) * 4 amps = 28 watts loss

The 15 volt panels are right on the edge--You could use them in cool weather to charge a 12 battery bank (~14 volts) with a PWM controller as is--or put the three in series behind a MPPT controller:

• 3 * 15 volts * 5 amps = 225 watts

However, MPPT controllers are pretty expensive.

Your other choice would be to simply parallel the 15 panels with the 2x12v=24 volt panels (series connected) and put them behind a PWM panel rated to carry the total current (15 amps + 4 amps = 19 amps) and maximum voltage (Voc close to 30 volts). Of course, you could use two smaller PWM controllers to carry 10 and 9 amps each--or whatever you have handy to split the "4 strings" into.

And then measure the Vpanel and Ipanel of the two strings and see if the 15 volt panels are "sharing the load current" while charging the battery bank.

If the 15 amps panels carry most of their loads through the PWM controller--then I would not waste the money on a MPPT controller.

-Bill