Follow-Me Current Limiting

[malkierian]

So I searched and found https://midniteftp.com/forum/index.php?topic=3796.30 at first, but considering how old it was, I was hoping for more up-to-date information. I currently have a 1900ah 24v battery bank that is being fed by 5 Classic 150s. I am in the process of oversizing my solar (from theoretical ~12kWh to theoretical ~24kWh) for the purpose of being able to charge on more cloudy days and not need to use my generator nearly as much, but I am concerned about charge current being too high on sunny days. So, I need to know if I need to get more Whizbang Jrs like the linked thread indicated (I assume having half of the CCs with WBJs would be enough?), or if Follow-Me has been upgraded to be able to limit slaves' output accordingly (or perhaps none of this is necessary anymore?).

[ClassicCrazy]

The Whizbangs do not limit current. Each Classic has a current limit setting that would work with or without a Whizbang on it.
One Whizbang on the battery would tell the total of the combined Classics if you have them wired up correctly ( with negatives on non battery side of shunt)
Not sure if you mean the charge would be over the limit of each individual Classic or if the charge would be over the limit you want the battery to charge at ?
There is a way to just limit the output of Classic to battery while still letting it supply the loads with all available power.
If you are concerned about too much power into the Classics over their rated limit, there was a recent discussion about that and what is considered acceptable . https://midniteftp.com/forum/index.php?topic=6303.0
Larry

[malkierian]

Yes, I know the WBJrs don't limit current, but they do provide the classics with the info necessary to properly limit. I want to limit the total output from all the CCs to the battery bank so it doesn't overcurrent that, as they absolutely will be able to once the full 24kW system is hooked up. However, the implication from that other thread was that each CC I wanted to limit itself based on the total instead of just its own output would need a separate WBJr, and I wanted to make sure that was still the case before I invested in more.

[boB]

Yeah, this would be a great addition.  It CAN be done with multiple Classics and ONE Whizbang Junior but hasn't been done yet.  I looked into it but it was going to take quite a bit of time.

But I seem to remember that it basically works with 2 Classics but only because one Classic without the limit and information coming from the WB Jr  could be set to limit right about at the battery current limit and then the Classic with the WB Jr. can take care of the rest of the current limiting from the extra available current from having two arrays.

Our new stuff of course is fully networked so it should work well with as many controllers and inverters (Rosie) as you can give it.  And with only one WB Jr.

boB

[malkierian]

Well, I already have the classics, so do I need half of them to have WBJrs?

[Vic]

 ...  snipped from Halfcrazy's Post in the OP's Link in the first post.

Halfcrazy said,
"It still exists. You basically need one WBjr per Classic that you want to back off. So lets say you have 4 Classics and each can do 50 amps (200 total) but you want to limit to 50 amps.

Put a WBjr on Classic 1, 2 and 3 and set all 3 to 50 amps as shown in the attached document. Essentially it is not truly global as it only manipulates the one classic that is why the need for multiple WBjr's"

The above,  is the way that I understand how this current limiting does work.   I have not tested it,  or played with this function,  for too many years.

Halfcrazy (now using the Moniker, "FNG"),  and boB know much more about this function,  than I.

Glad that you were able to find this old Thread!  Vic

[malkierian]

I need to ask a follow-up question to this. What setting, exactly, am I changing to limit an individual WBJr-enabled Classic's output based on shunt power? Does the Output field in Limits work based on the WBJr's reading automatically, assuming I have the WBJr setup correctly on that Classic?

[Vic]

I need to ask a follow-up question to this. What setting, exactly, am I changing to limit an individual WBJr-enabled Classic's output based on shunt power? Does the Output field in Limits work based on the WBJr's reading automatically, assuming I have the WBJr setup correctly on that Classic?

Hi malkierian,

As noted perviously,  in this Thread, I have NOT played with this function,  for seven-ish years,  and, then,  not much playing at all.

As I read that doc,  as attached in the first Post in your Linked thread,  you should set the maximum TOTAL battery charge current you wish all of the Classics to provide to your battery bank.

Your system needs a WbJr for each of the Classics that will need to have its share of current reduced to accommodate this total maximum batttery current.

The Classics which have a combined total charge current capability that is within the maximum that the battery can accept,  and be at or below the max current spec that your battery can accept,  do NOT need WbJrs  --  as I read that document.

There may be a person in MN Tech Support who might be able to confirm this.

More later, sure do wish that I really knew the details of this,   based on personal experience.  Good Luc, Vic

[malkierian]

That is unfortunate, because the maximum battery current is almost 300 amps, and I don't think the Classics can go above 100, but I'll double check.

[Vic]

In the following .pdf,  beginning on pp15, there are Power Graphs for the different Classid models:
https://www.midnitesolar.com/pdfs/theClassics.pdf

These currents vs batt V, and PV input voltages may not be absolute.

FWIW,  Vic

[ClassicCrazy]

I need to ask a follow-up question to this. What setting, exactly, am I changing to limit an individual WBJr-enabled Classic's output based on shunt power? Does the Output field in Limits work based on the WBJr's reading automatically, assuming I have the WBJr setup correctly on that Classic?

Take a look at these instructions on how to limit current to battery but it will still let Classic provide all available power to loads.
https://www.midniteftp.com/support/kb/faq.php?id=37
Larry