Author Topic: U-Set Charging option ?  (Read 382 times)

ClassicCrazy

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U-Set Charging option ?
« on: March 22, 2017, 11:50:27 AM »
From the Kid manual
"U-SET VOC%
This is a fully manual mode based on a percentage of VOC. The Kid will sweep based on the user set
time in minutes and then park at a user set % of the VOC the Kid found on that sweep. This mode is
useful for testing or constant voltage sources. Press Save then press menu back when done. Modes
will revert to OFF if the up or down arrows are pressed before exiting."

I don't really get this .
Could someone give me some examples of how this would be used with constant voltage source ?


Thanks,
Larry
system one
Classic 150 , 20 Kyocera 135watt , 12s Soneil 2v 540amp lead crystal for 24v pack , Outback 3524 inverter
system two
Classic 150 ,5s 135 watt Kyocero , 16s Calb 100AH LiFePO4 , Outback VFX 3648 inverter
system three
Midnite KID MPPT 24 DC in to  12 volt AGM batterie

suits

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Re: U-Set Charging option ?
« Reply #1 on: March 22, 2017, 12:15:47 PM »
The best I've been able to come up with is that U SET % essentially allows you manual control over the MPPT settings that are normally recalculated automatically during each sweep.

How this would be an advantage for a constant power source is you should be able to essentially disable the voltage tuning that is being used to maximize output power from the panels since, with a constant voltage source this would serve no purpose as you have no panels to maximize output of. What settings are required to basically disable the MPPT functionality I don't have the slightest idea on.

Hopefully others have some further knowledge on this as I'm curious myself as to its exact function.
Main System
4 x 260W C-Sun Panels - Kid Charge Controller - 24V - 240Ahr Bank - 1500W PSW Inverter
Backups
Custom Built 40Amp(@24V) DC Generator - Devil Watt 200Watt Thermoelectric Generator System

ClassicCrazy

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Re: U-Set Charging option ?
« Reply #2 on: March 22, 2017, 01:48:51 PM »
I don't understand the %VOC setting .
And now I won't be able to experiment easily because I just cut the 24v input wires from the bigger battery bank that was charging my 12v battery . I hooked the Kid up to my original 2 Arco 50 watt panels that I bought in either late 80's or early 90's . I think they were about $6 a watt then.
Larry
system one
Classic 150 , 20 Kyocera 135watt , 12s Soneil 2v 540amp lead crystal for 24v pack , Outback 3524 inverter
system two
Classic 150 ,5s 135 watt Kyocero , 16s Calb 100AH LiFePO4 , Outback VFX 3648 inverter
system three
Midnite KID MPPT 24 DC in to  12 volt AGM batterie

suits

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Re: U-Set Charging option ?
« Reply #3 on: March 23, 2017, 12:36:38 PM »
Some light reading on the subject

Quote from: Wikipedia
The term "constant voltage" in MPP tracking is used to describe different techniques by different authors, one in which the output voltage is regulated to a constant value under all conditions and one in which the output voltage is regulated based on a constant ratio to the measured open circuit voltage (VOC). The latter technique is referred to in contrast as the "open voltage" method by some authors.[22] If the output voltage is held constant, there is no attempt to track the maximum power point, so it is not a maximum power point tracking technique in a strict sense, though it does have some advantages in cases when the MPP tracking tends to fail, and thus it is sometimes used to supplement an MPPT method in those cases.

In the "constant voltage" MPPT method (also known as the "open voltage method"), the power delivered to the load is momentarily interrupted and the open-circuit voltage with zero current is measured. The controller then resumes operation with the voltage controlled at a fixed ratio, such as 0.76, of the open-circuit voltage VOC.[/u][23] This is usually a value which has been determined to be the maximum power point, either empirically or based on modelling, for expected operating conditions.[18][19] The operating point of the PV array is thus kept near the MPP by regulating the array voltage and matching it to the fixed reference voltage Vref=kVOC. The value of Vref may be also chosen to give optimal performance relative to other factors as well as the MPP, but the central idea in this technique is that Vref is determined as a ratio to VOC.

One of the inherent approximations to the "constant voltage" ratio method is that the ratio of the MPP voltage to VOC is only approximately constant, so it leaves room for further possible optimization.
Main System
4 x 260W C-Sun Panels - Kid Charge Controller - 24V - 240Ahr Bank - 1500W PSW Inverter
Backups
Custom Built 40Amp(@24V) DC Generator - Devil Watt 200Watt Thermoelectric Generator System

RetiredTech

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Re: U-Set Charging option ?
« Reply #4 on: March 29, 2017, 05:47:36 PM »
Hi Larry
My understanding of the two settings in the U-SET VOC% section is the following:
When you enter a % value The controller will look at the unloaded open circuit voltage then apply an increasing load on the input . It will increase the load drawing the input voltage down over the time you have specified, until it has dropped the input voltage to the %  of the open circuit voltage that you have programmed. At that point it stops. To me it is only a way to slowly cycle through the MPP process to let you gather data so you know what the voltage and current is at the MPP .
If you wanted to test a constant voltage power source here are some considerations:
Every power supply that is said to be constant voltage will be so when providing a current to a given load that draws  between 0A and the rated output current of the power supply. As the load resistance decreases to the point that the “constant voltage” power supply has reached it’s rated output current limit then the output voltage will no longer remain constant but decrease below the “constant voltage” that the regulator is set for. If a power supply was the input source that was going to be used for the MPPT controller I would start testing with settings of 100% and maybe move down to 95% or 90% . Doing this with a fixed load on the output terminals of the controller that would simulate the max output current of the controller, at the max charge voltage that it would be putting out. Let’s say use the absorb setting you have programmed in. That’s not to say that on BULK MPPT the controller seems to put out a higher voltage than the absorb setting if the output current hasn’t exceeded the max current setting of 30A or lower if you have set it lower. Say you set absorb at 14.2V and left max current at 30A. That would be a load of R=E/I  or   14.2/30= .4733 Ohms. That’s a hefty stack of resistors to handle the  426W of power being consumed in the load. OUCH  HOT! Setting the sweep interval for about a minute you could watch the displayed voltage, current, and wattage to try to correlate a MPP. Repeating the exercise for settings of VOC % from  100% down to 90% to show what produced the max wattage. This would determine the best VOC% setting to use for that setup. Two  caveats .One; The voltage of the power supply must be the recommended 30 % higher than the output voltage of the controller to allow for worst case equalizing voltage conditions. Two;  The current rating of the power supply must be high enough to satisfy the input current requirements of the controller or the power supply drops out of regulation.
A 24V battery as a source for a controller producing 12V is a bit of a different animal.  Not getting too deep into battery specs lets look at an example of a battery plant rated at 150AH at C10 meaning that at a load drawing 1/10th of the  AH capacity for 10 hours would drop the terminal voltage from it’s full charged voltage to it’s discharged voltage in 10 hours. That should be a large enough 24V battery plant to run only the downstream controller.  In the meantime that 24V battery could be in some state of being recharged say by another MPPT controller and PV system.  So the controller you are testing could have applied to it’s input anywhere between the highest EQ   charge voltage (28 to 30V) and the lowest battery discharged state voltage. In that case I think  setting the U-SET VOC%  setting   should not be used. Setting for normal solar would allow the controller to hunt through the changing input voltages and constantly be finding the MPP .

Comments?

Brad
Midnight Kid
12V 300AH 6Hawker SBS60 AGMs
Up to 4 Can. Solar 260W panels
1000W pure sine inverter  for Cputer and internet
Volt/Bidirectional Ammeter 100A net in/out of battery
Amateur Radio gear and 12V neg grounded

ClassicCrazy

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Re: U-Set Charging option ?
« Reply #5 on: March 29, 2017, 08:44:17 PM »
Thanks Brad - I will have to read through that a few more times to get it to sink in better. But I get the gist of it .  I like the very last part about if you have input of another  battery that using Solar would probably be best because that is exactly how I have had it for a very long time !  Never seemed to be any issues .

The only issue with the Kid and a fixed power source is that the data  logger does not work since it seems to need a night time resting to start the logging over .

Larry

system one
Classic 150 , 20 Kyocera 135watt , 12s Soneil 2v 540amp lead crystal for 24v pack , Outback 3524 inverter
system two
Classic 150 ,5s 135 watt Kyocero , 16s Calb 100AH LiFePO4 , Outback VFX 3648 inverter
system three
Midnite KID MPPT 24 DC in to  12 volt AGM batterie

boB

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Re: U-Set Charging option ?
« Reply #6 on: March 31, 2017, 05:40:42 PM »

If you look at an un-shaded PV array and note its Voc voltage and its MPP voltage that the normal MPPT tracking
algorithm finds, it will be somewhere around 75% to around 83%  of that Voc.  The Classic, in this mode, opens up
the array voltage to find the Voc voltage once every sweep interval (3 minutes default).  Then, the Classic drops
its input voltage (and thereby the PV voltage) down to that percentage of the Voc it saw when it opened up.

It's just another way is all..  I first did this with the Outback MX60 but it was called "U-Pick"  I had to call
it something different here.  The  REASON that I put that mode in there was two-fold.  One, because
I could, and it can have some usefulness.  Two, to prove a point.  Rick  at then RV-Power Products
had a patent on his wonderful MPPT controller at the end of the 1990s.  One thing it mentioned was to open up
its input, measure the Voc and then operate the PV array at a constant "OFFSET" voltage below Voc.

This is not really what he does I don't think, but that's what his patent mentioned.  We learned about him
from his attorney who sent us a letter to warn us that we might be infringing on his patent and should
license his patent.  We told him this i NOT what we were doing but FINALLY found out that it wasn't the
tracking technique they were warning us about but instead, the fact that it was an MPPT controller
with constant voltage charge cycle (Absorb).  Well, we know of prior art from the 1990s from a small
company in Australia that had been doing this so I got a letter from Dennis, the owner of that company
and he had a great response.  This pretty much made RVPP go away, BUT they still told us that it would
be good to license their technology!  Yeah, right !  All this was before the MX60 was even on the market !

During this time, I had found a paper from the late 1970s that spilled the beans (it was published) that
talked about running a charge controller at a percentage of the open circuit Voc of the array and I placed
a reference to that paper in the MX60 manual.  The two techniques, percentage or offset are about
the same thing except that %-Voc should work even better than offset.  Inside the RVPP controller was
a trim-pot you had to adjust instead of changing it in an LCD menu.  That method does NOT work
for PV arrays with partial shading issues.  You NEED to track the PV array in that case.  I think that the
RVPP unit did percentage of Voc as well but I didn't look at it that closely.

There are SO many bogus patents out there and especially in our field.  I have very little faith in the
US patent system but once in a while there are good patents drawn up.

boB




K7IQ

ClassicCrazy

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Re: U-Set Charging option ?
« Reply #7 on: March 31, 2017, 08:50:48 PM »
I remember way back at the Midwest Renewable Energy fair hearing something about how Bluesky  had some patent on MPPT controllers and remember that theirs were really expensive. Thanks for this history Bob - and glad that you and everyone  were able to work around that legal stuff - it would have certainly stifled a lot of innovation that has happened since.

Larry
system one
Classic 150 , 20 Kyocera 135watt , 12s Soneil 2v 540amp lead crystal for 24v pack , Outback 3524 inverter
system two
Classic 150 ,5s 135 watt Kyocero , 16s Calb 100AH LiFePO4 , Outback VFX 3648 inverter
system three
Midnite KID MPPT 24 DC in to  12 volt AGM batterie

CDN-VT

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Re: U-Set Charging option ?
« Reply #8 on: March 31, 2017, 11:00:31 PM »

If you look at an un-shaded PV array and note its Voc voltage and its MPP voltage that the normal MPPT tracking
algorithm finds, it will be somewhere around 75% to around 83%  of that Voc.  The Classic, in this mode, opens up
the array voltage to find the Voc voltage once every sweep interval (3 minutes default).  Then, the Classic drops
its input voltage (and thereby the PV voltage) down to that percentage of the Voc it saw when it opened up.

It's just another way is all..  I first did this with the Outback MX60 but it was called "U-Pick"  I had to call
it something different here.  The  REASON that I put that mode in there was two-fold.  One, because
I could, and it can have some usefulness.  Two, to prove a point.  Rick  at then RV-Power Products
had a patent on his wonderful MPPT controller at the end of the 1990s.  One thing it mentioned was to open up
its input, measure the Voc and then operate the PV array at a constant "OFFSET" voltage below Voc.

This is not really what he does I don't think, but that's what his patent mentioned.  We learned about him
from his attorney who sent us a letter to warn us that we might be infringing on his patent and should
license his patent.  We told him this i NOT what we were doing but FINALLY found out that it wasn't the
tracking technique they were warning us about but instead, the fact that it was an MPPT controller
with constant voltage charge cycle (Absorb).  Well, we know of prior art from the 1990s from a small
company in Australia that had been doing this so I got a letter from Dennis, the owner of that company
and he had a great response.  This pretty much made RVPP go away, BUT they still told us that it would
be good to license their technology!  Yeah, right !  All this was before the MX60 was even on the market !

During this time, I had found a paper from the late 1970s that spilled the beans (it was published) that
talked about running a charge controller at a percentage of the open circuit Voc of the array and I placed
a reference to that paper in the MX60 manual.  The two techniques, percentage or offset are about
the same thing except that %-Voc should work even better than offset.  Inside the RVPP controller was
a trim-pot you had to adjust instead of changing it in an LCD menu.  That method does NOT work
for PV arrays with partial shading issues.  You NEED to track the PV array in that case.  I think that the
RVPP unit did percentage of Voc as well but I didn't look at it that closely.

There are SO many bogus patents out there and especially in our field.  I have very little faith in the
US patent system but once in a while there are good patents drawn up.

boB

LIKE !! :-)
Canadian Solar 350W 37.6 VOC  30.6 VMP 8.22 ISC 7.87 IMP ,-15 c +30c max  4 strings in 2 in Series for 24v Classic 150 -1020 Ah  Freezers & fridges ~~~ Second Array same panels of 3sx3 parallel for 24 V Classic 150 -440 Ah Outback Barns & out blds.
48Vdc almost done.

TomW

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WRT patents..
« Reply #9 on: April 01, 2017, 10:46:24 AM »
My biggest  problem with patents is they assume 2 completely isolated entities could not possibly come up with the same solution.

Not to mention that, personally, I think knowledge should be free.

Tom
Do NOT mistake me for any kind of "expert".

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Highflyer

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Re: U-Set Charging option ?
« Reply #10 on: April 18, 2017, 05:13:43 PM »
Bob,
Would this option be a useful way to set up a hydro charging system?


Thanks for the history.
Brian

The one thing is the one thing