Midnite Classic 250s in Parallel with Outback Charge Controller

[mammone70]

Hello,

I'm expanding my off grid solar system. The existing system uses an Outback MX60 MPPT charge controller to charge the 48v battery bank. I've purchased 2 Midnite 250s to handle my new panels. I would like to utilize the energy from both sets of panels. Can I charge the same battery bank with the 2 Midnites and the Outback controller in parallel or do I need to purchase another Midnite and run all 3 with the "Follow Me" function?

Thanks.

[ClassicCrazy]

I updated my friends system with a new Midnite and used their existing Outback. I just set the Outback to a volt or so lower so it would cut out and then let the Midnite finish up the battery charging . But I think someone also commented that it doesn't matter if you leave the Outback with the same setpoint because they will both do their thing independently and won't over charge the battery either way .

So I guess you have a couple choices and can experiment to see what works best for you . But yeah you can can continue to use the Outback.

The other thing to consider is just how much power can the battery pack take in so they will all be cutting down their power soon as it goes to Absorb.  But if you have a big enough battery pack that can take a huge amount of current is one thing - it will still make all the power from the PV available during the day when you put on big loads .

Larry

[Matrix]

Larry,  what about amps from the 2 different sources?  I was running my MN Classic 150 in tandem with my Conext SW inverter/Charger and it seemed the charge amps were double what either was set.  The charge seemed to be the sum total of both chargers.  So does that mean one needs to lower the charge amps?  Or was I doing something else wrong?

[ClassicCrazy]

Either charge controller is going to do the same thing - when it gets up to Absorb setpoint then it will keep the voltage but reduce the current  until whatever ending point is reached - ending amps or Absorb time. 

If both charge controllers are putting out 5 amps each into the battery then the total the battery sees will be 10 amps.  If the shunt is placed like it should be and there is only one connection between one side of the shunt and the negative battery terminal then the Midnite monitoring  will still be able to count both the Outback and Classic  amps for the SOC percentage and you would be able to see them in the system amps on Midnite monitoring programs.

Larry

[mammone70]

Thanks Larry.  Good info. My biggest concern was the charging amperage on the bank.  It's pretty big but I wanted to be sure that if all 3 controllers put out their max amperage at the same time, it wouldn't be too much for the bank.

[ClassicCrazy]

Depending on your battery and how much PV you have - when they are in Bulk they could put out more than your batteries call for . But the Classics have a feature where you can limit the charging amps but still let them provide full current for loads. Note that this is a different setup than the current limits that you will see in setup menu  - that one limits all current . So for example if you used that limit to 20 amps it would limit the charge current to 20 amps but also the current for loads to 20 amps. The first one I mentioned you could set up to limit charge current for battery  to 20 amps but let the full 80 amp current be available for loads. Somewhere on the forum here it explains how to set that up if you need to .

So you will just have to do a bit of planning on what your batteries specs are for maximum charge current.

Larry

[Westbranch]

I would only add that you might want to make your decision on which CC leads and shuts off first based on the size of the array feeding the CC or CCs....

IIRC the MX60 I have has less ability to be fine tuned via the 'offsets' than the Classics.  It's been a while since I looked at  the setup of my old MX60... so I might be wrong on that...

[CDN-VT]

Thanks Larry.  Good info. My biggest concern was the charging amperage on the bank.  It's pretty big but I wanted to be sure that if all 3 controllers put out their max amperage at the same time, it wouldn't be too much for the bank.

Here I would make sure that the WIRE SIZE is great & You should use a shunt & a WBjr for the classics , let the MX just do it's thing & the classics will throttle back .

If the  Outback MX60 MPPT charge controller uses a shunt , just double up on the Shunt & make sure that the WBjr & all other sensors are well secured & no galvanic or electrolysis .
Use SDG & all tinned bits & stainless .

VT

[boB]

Here's an idea...
If a Classic has a Whizbang Junior connected to a shunt to the battery, that Classic can be set to reduce its charge current if  its contribution of current puts the total current over your desired current.  If your other loads on the battery at the time are high, then that Classic will put out more.

Let's say that the MX60 and one Classic can't over-current your battery but just a little bit more will...  That second Classic with its WB Jr. and the limit being set will be enough.  If only two charge controllers can over-current the battery, then you will need two WB Jrs, one for each Classic but they can bot be connected to the same shunt. It's a pretty cheap addition since WB Jr's list price is only $59 each.  I don't know how much they are online but probably less than that.

boB

[Matrix]

Somewhere on the forum here it explains how to set that up if you need to .

Did a link to this discussion ever get located?  I am not having any luck.

[Vic]

Matrix,

Sorry,   been busy,   and did not have the time to reply earlier:

At the foot of the first Post in the following Thread is a terse White Pater:
http://midniteftp.com/forum/index.php?topic=3796.0

Later,Vic

[ClassicCrazy]

Somewhere on the forum here it explains how to set that up if you need to .

Did a link to this discussion ever get located?  I am not having any luck.

It is called Global Current Limiting and is explained in file I attached here
Larry

[mammone70]

According to the battery manufacturer, the bank can only handle 100A of battery temperature compensated charge current.  So it sounds like I will need whizbang jrs on both Classics.  I don't believe my current power panel/center has room for two more shunts and 2 whizbang jrs.  Any recommendations on a box for all these components?

[Westbranch]

you can piggy back 2 WBjr's on one shunt.... read the install instructions

http://www.midnitesolar.com/productPhoto.php?product_ID=519&productCatName=Charge%20Controllers%20-%20Classics&productCat_ID=21&sortOrder=9&act=pc

[Vic]

Hi mammone70,

What is the STC rating of each array on each of the Charge Controllers (CCs)?

From that White Paper,   and the discussion in the  Linked-Thread,  each Classic that must have its current Limited will need its own separate Shunt and WbJr.    But,   it is possible that the combination of the MX-60's plus one Classic 250's uncontrolled/unLimited  battery charge current  will not exceed the maximum permissible battery charge current.   Meaning that perhaps only one Classic 250 might need its own Shunt/WbJr for battery current control ...
Believe that this is what was alluding to.

Thanks,  Vic