A couple questions on SSC choice

[Fenachrone]

Question 1: I have an Outback MX60, but with the addition this spring of several new and more powerful panels to my system, have decided (based on advice here) I'll need to add a new charge controller.

I have a LiFePO4 battery bank, for which the MX60 isn't superbly well matched, but it's been working OK. I'd like to add a Midnite Solar Classic (200 SL or 250 SL). Can these two play together in managing battery charging?

Question 2: I'm having a bit of trouble determining what the difference is when making a choice between the 200 SL and 250 SL. The 200 is rated for more amps (65-74 for the 200, vs 55-60 for the 250), but the 250 is rated for for more voltage (250 vs. 200, of course). Under what circumstances do these differences become important? Or is it all about the MAX VOC?

 

[Prince Of Darkness]

If you have not yet seen, this Comparison Chart, it might help:

https://midnitesolar.com/pdfs/Classic-Lite-SL-Chart.pdf

I have been running Classics since late 2010, and they are very solid.

boB, at MN, is presently working on some improvemets to the Classic FW, which should make maanaging Li batteries even better.

Good Luck, 'Luke'

 

[Prince Of Darkness]

In addition to the above;

The Classic SLs lack the Ethernet port, so, using the Application that runs on a Windoze computer, and the ability of Classics to report Status into the MidNite web site -- MyMidnite II will not be available via a Classic SL.

The Classic SL is ideally teamed with at least one standard Classic CC, where this standard Classic will be able to report status.

As you know, each MPPT CC will need separate PV arrays ...

More later, Luke

 

[Cmiller]

Max VOC and total PV wattage you want to run on the controller are your deciding factors. I feel like usually the CL200 seems to end up being the nicest balance between the 2... Once in a while if you have an extra long distance to run from PV to controller, it make sense to run a little higher voltage because of potential voltage drop. But honestly that one panel difference in string length usually doesn't make sense with the drop in total PV capability. What I mean is that your wire size is still going to have to be nearly as big, as any voltage drop is lost power...

Remember, volts x amps = watts.

I don't know what battery voltage you are running, but here is a screenshot of Midnite Solar's sheet showing wattage and voltage on each unit:



Note there is some variation on max amps/watts depending on the pv voltage you are running at.

On a CL200 you can comfortably run a 4s string of 60 cell panels (~30-32v mpp, 46-48VOC), or a 3s string of 72 cell or split 144 cell, a.k.a. half cell (~44v mpp, ~50VOC)

A CL 250 would basically let you go to 5s of 60 cell and 4s of the 72/split 144 cell.

Remember to give an additional 25% headroom on your calculated VOC of a string for cold weather overvoltage. That can happen even at 40F with full direct sun! (So, take panel VOC x number in series in string. Take that total x 1.25 for your cold weather overhead.)

 

[Fenachrone]

In addition to the above;

The Classic SLs lack the Ethernet port, so, using the Application that runs on a Windoze computer, and the ability of Classics to report Status into the MidNite web site -- MyMidnite II will not be available via a Classic SL.

The Classic SL is ideally teamed with at least one standard Classic CC, where this standard Classic will be able to report status.

As you know, each MPPT CC will need separate PV arrays ...

More later, Luke

Yes, thanks for that. For my uses, I don't think the status reporting will be critical. I hear you on teaming the SL with another Midnite. I think I should plan on going that route to be able to match up the charging parameters.

 

[Fenachrone]

Max VOC and total PV wattage you want to run on the controller are your deciding factors. I feel like usually the CL200 seems to end up being the nicest balance between the 2... Once in a while if you have an extra long distance to run from PV to controller, it make sense to run a little higher voltage because of potential voltage drop. But honestly that one panel difference in string length usually doesn't make sense with the drop in total PV capability. What I mean is that your wire size is still going to have to be nearly as big, as any voltage drop is lost power...

Remember, volts x amps = watts.

I don't know what battery voltage you are running, but here is a screenshot of Midnite Solar's sheet showing wattage and voltage on each unit:

View attachment 215120

Note there is some variation on max amps/watts depending on the pv voltage you are running at.

On a CL200 you can comfortably run a 4s string of 60 cell panels (~30-32v mpp, 46-48VOC), or a 3s string of 72 cell or split 144 cell, a.k.a. half cell (~44v mpp, ~50VOC)

A CL 250 would basically let you go to 5s of 60 cell and 4s of the 72/split 144 cell.

Remember to give an additional 25% headroom on your calculated VOC of a string for cold weather overvoltage. That can happen even at 40F with full direct sun! (So, take panel VOC x number in series in string. Take that total x 1.25 for your cold weather overhead.)

Thanks for that very detailed response.

My system is 24 V. You mentioned overvoltage vis a vis cold temperatures. I had that condition late last fall and the MX60 shut down -- not surprisingly, considering its voltage limitations. But it seems having extra capacity (with the SL250) for a hundred bucks more might be worth the insurance.

 

[Cmiller]

Thanks for that very detailed response.

My system is 24 V. You mentioned overvoltage vis a vis cold temperatures. I had that condition late last fall and the MX60 shut down -- not surprisingly, considering its voltage limitations. But it seems having extra capacity (with the SL250) for a hundred bucks more might be worth the insurance.

One note regarding that overvoltage potential. The Classics do have Hypervoc, which allows a top voltage of max rated volts + battery volts. So for instance, if you had a CL200 on your 24V battery bank, you could have a max PV voltage of 200+24V=224V without the CL letting out the magic smoke.

Hypervoc is what the charge controller can take without getting fried, however, when in that "special" hypervoc range the unit will not be producing power. It will shut down and say "Hypervoc", but it won't fry.