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.
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
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?
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
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.
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
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...
Quote from: mammone70 on January 03, 2018, 10:46:39 PM
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
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
Quote from: ClassicCrazy on January 03, 2018, 11:27:17 PMSomewhere 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.
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
Quote from: Matrix on January 05, 2018, 11:00:43 AM
Quote from: ClassicCrazy on January 03, 2018, 11:27:17 PMSomewhere 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
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?
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
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
Vic, that makes sense but I'm not sure what numbers to use for max current. I was using the max output amperage of the controllers: 55A for classics and 60A for the Outback @48V.
I assume you're asking for ISC at STC of each array? 18.82A on each classic and 25.11A on the Outback. Are these the numbers I should be using? I may be misunderstanding how MPPT charge controllers work.
Hi mammone70,
Sorry about the imprecision of my question ...
I should have asked, what is the total power rating of each PV array on each of the CCs (this is the listed power rating, called the STC power rating).
From this, the nominal array output current can be estimated, at a certain battery Absorption voltage.
And, one more question, what is the brand and model number of the battery that the system will use, or, at least, what is the expected Absorption voltage that will be used.
This info can be used to approximate the maximum battery charge current produced by each of the three arrays.
Thanks, Vic
Hey Vic,
2800W on each Classic and 1620W on the Outback.
The batteries are U.S. Battery US 305HC XC2s. 16 total (2 strings of 8). According to the manufacturer, I read it as 58.8 Volts for the absorption voltage.
Thanks,
Matt
Hi Matt,
Thanks for the info.
Using standard rules-of-thumb, seems that the total nominal max current available from the three CCs is about 92 Amps, or so (assuming that about 75% of the rated PV power could be produced by all CCs).
Loads will reduce the amount of current that will go to the battery as charge current.
The Follow Me function of the Classics is very useful, but why not try the two Classics and one MX-60 to start with.
You can try adjusting the exact Absorb voltages to try to make the three CCs behave fairly well on average. In some ways, it is good that the MX, without Follow Me, has a smaller PV array.
More later, Vic