Dynamic Current Limiting

[EW Zuber]

The way the industry is dealing with current limiting is basically static and voltage initiated.
I have a 5.5 KW solar array capable of around 100 amps. This allows for improved performance during cloudy periods and heavy loads should the need arise.
Problem is that my battery bank is only 370AH Trojan L16REB @ 48V.
So I can limit the current available from the Classic to 37A for bulk mode charging but if I have a 20A load I will only be putting in 17A and the batteries will not get fully charged and I will have to use my gas generator when I potentially have more than ample reserve current to charge them.
I would like to see the WBJR given the ability to extend the 'absorb end current' function to bulk mode charging.
That way I could have massive loads and not be concerned about the batteries getting charged.
Ultimately I plan on having 20KW of solar so that even on the cloudiest days I will have C/10 charging current available.
But that would not be practical without dynamic current limiting.

[Vic]

Hi EW Z,

There have been a few Threads here on this topic.  Have you seen this one:
http://kb1uas.com/mnsforum/index.php?topic=2696.0

Have not re-read this entire thread,  but in Reply #3,  boB mentions that this will come along at some time,  but no date approximation.

FWIW,   73,  Vic

[dgd]

EWZ,

Vic is correct and its probably not near the top of the urgent list for MN's Classic FW updates.
In meantime...
I would suggest just removing the 37A (c/10) limit from the Classic as those FLA Trojans will easily deal with c/5 charge rate since its only for a relatively short time in Bulkmppt charge mode when there is plenty of PV power available.
Its also unlikely there will often be full name-plate-rating current output from the PV array. The fact that you are considering a 10Kw PV array to achieve 37A in poor weather is sort of indicating that most of the time your weather is custard.

dgd

[EW Zuber]

I suggested this years ago and it seemed that the response was the WBJR function of end amps in absorb mode. Which is great but it is only a matter of time before someone comes up with dynamic current limiting.
I mentioned it to OB but I suspect they will dismiss it.
Sure I can hit the batteries with higher current but I really do not want to. I have an indoor/outdoor thermometer with the outdoor temperature probe on the batteries and higher currents definitely increase battery temperature, which can shorten battery life.
My biggest concern right now is that my stereo system is triamplified with 3 Hafler power amps that all run class A. So at an idle they draw about 600W. Thats cuts into the charge current significantly.

dgd, our late winter / spring time is typically sunny but fall and winter can be very wet and snowy at times.
My goal is to completely eliminate the use of a gas generator. The excess power on sunny days will be used to heat the house electrically and cut down on wood consumption.
Thats one big advantage that solar electric has over solar thermal, when temperatures drop to subzero solar thermal are useless but solar electric provide about 60 ~ 70% of rated power even on the shortest day here (60.5 degrees N. latitude)
Also looking into Thermal Electric Generators for the wood heater. Just 400 watts from a TEG would make a huge difference.

[dgd]

OK, then I suppose the better solution is to size the battery bank closer to the input power available and the load requirements. Maybe a second string of those L16s to double capacity.

Otherwise you could use some external processor (rPi, BBB, Cubie, Arduino etc) that detects when the
maximum allowed current is output from the Classic and diverts (PWMing or selectively rerouting sub array of PVs) to your electric heater (or whatever).
An interesting project but unless you are already familiar with configuring/programming a controller system its probably not practical.

Add more battery capacity 

dgd

[EW Zuber]

Not interested in more battery capacity. I am more interested in keeping the battery bank as small as possible to keep reoccurring costs down.
I would rather put the additional funds to buying more solar power, more generation capacity rather then storage.
Ideally I want to be able to generate 2KW on a cloudy day that yields 10% of array rated power. That would require a 20KW array.
The beauty of the system is that the excess power on a sunny day can be used to heat the house and hot water and the coldest days in winter are the clear ones. Also I suspect panels will likely last 40 to 50 years or longer as I have Arco 16-2000 panels that I bought in the early 1980's that still put out near rated power.
With commercial batteries like L16's 10 years is typically a good lifespan.

[dgd]

EWZ,

Well you are definitely thinking outside the square with a 20Kw array to guarantee 2Kw in poorest weather.
How do you envisage making use of the, perhaps, available power up to 18Kw on excellent weather days?
I mean, how does that power get from the array to where ever its to be used (water heating, house heating etc)?
That sort of capacity is way beyond any solar controller to deal with, possible dynamic current limiting would be a non starter here.

I think thats wishful thinking on PV life expectancy.  Maybe 1980s ARCOs were well built but in those days PV panels were very expensive so manufacturing quality tended to be quite high = longevity in service.

However, these mass produced Chinese PVs at todays well under a $ per watt pricing leave an awful lot to be desired where QC is concerned. I have seen many many of these PVs last only a few years with everything from junction boxes falling off, silicone sealant drying up and powdering away, water getting into the connections, water tracking down the traces under the tedlar backing and rotting the connection away, poor temperature stability with backing material too thin and showing heat stress by changing from nice white colour to muddy brown, and even the solder on the traces over the individual cells showing melting and bubbling that soon breaks the electrical connection or flashes/spike fingers of solder growing away from surface traces.. etc.etc..

dgd

[Halfcrazy]

So I am about to release a firmware update (BETA) that has a feature to current limit on the WBjr amps as well as the classic amps. It also has a 16bit timer changed to a 32bit timer and has stopped ALL of my network crashes on the new code. Give me a few days next week to test it after it is all compiled and I will post it up for everyone

[mike90045]

Why not have the WBJr at the battery only, and tap the inverter feed at the controller.  Wire management (ohmic loss) becomes important, and your inverter may appreciate a super cap at it's input for 60/120hz ripple suppression.

[Vic]

So I am about to release a firmware update (BETA) that has a feature to current limit on the WBjr amps as well as the classic amps. It also has a 16bit timer changed to a 32bit timer and has stopped ALL of my network crashes on the new code. Give me a few days next week to test it after it is all compiled and I will post it up for everyone

Ryan,  this is terrific news!   Will look forward to the release.   Thanks MidNite!   Vic

[EW Zuber]

This is awesome news. Been waiting a long time for this. With panels so inexpensive now the applications for current limiting will become more necessary.
Thanks
 

[EW Zuber]

Why not have the WBJr at the battery only, and tap the inverter feed at the controller.  Wire management (ohmic loss) becomes important, and your inverter may appreciate a super cap at it's input for 60/120hz ripple suppression.

Not following what you mean here. Can you rephrase? Thanks

[BobWhite]

Why not have the WBJr at the battery only, and tap the inverter feed at the controller.  Wire management (ohmic loss) becomes important, and your inverter may appreciate a super cap at it's input for 60/120hz ripple suppression.

Not following what you mean here. Can you rephrase? Thanks

I agree, lm a little lost on that one but it don't take much to get me confussed.
Walt

[EW Zuber]

EWZ,


How do you envisage making use of the, perhaps, available power up to 18Kw on excellent weather days?
I mean, how does that power get from the array to where ever its to be used (water heating, house heating etc)?
That sort of capacity is way beyond any solar controller to deal with, possible dynamic current limiting would be a non starter here.


However, these mass produced Chinese PVs at todays well under a $ per watt pricing leave an awful lot to be desired where QC is concerned. I have seen many many of these PVs last only a few years with everything from junction boxes falling off, silicone sealant drying up and powdering away, water getting into the connections, water tracking down the traces under the tedlar backing and rotting the connection away, poor temperature stability with backing material too thin and showing heat stress by changing from nice white colour to muddy brown, and even the solder on the traces over the individual cells showing melting and bubbling that soon breaks the electrical connection or flashes/spike fingers of solder growing away from surface traces.. etc.etc..

dgd

I plan on using solid state switching with PWM trigger pulses from the classic diversion output to switch loads off and on.

I am not using Chinese modules. I have 1KW of SolarWorld, basically the updated version of the Arco modules, and 3.75KW of REC 250's from the Philippines & ~500W of Arco modules.

[dgd]

I plan on using solid state switching with PWM trigger pulses from the classic diversion output to switch loads off and on.

It will be interesting to read how you have actually implemented this plan.
At least the good news is with the pending Classic FW update to use WBjr based current limiting, that will solve your immediate battery charging issues 

dgd