This morning I was watching my classic 150's output through the local app. The sky was clear (zero cloud)
The array is 4000w 48v battery and strings of 2p 36v panels, 26 deg c day today. I was watching the classic pumping around 3000w into the battery at around 10AM (my max output hr for my panels) Then it would jump up to 3500w for a little while and then it would drop off to almost nothing then jump up again and settle back down to 3000w. Again zero cloud .
Now at this of day I would be expecting more like 3500w or so . So what might be happening it tried for a few seconds to put out 3500w and then did a sweep again. Why is it choosing to settle to a lower output. I am not reaching any MAX setting on the classic .
edit : I was just watching it again sitting at 3350w then it just dropped to 2800w. This it whats happening its sitting at 2800w, 65v pv input, 56.9v bat output then it dose a sweep and then holds 3350w output with a 62v input, 57.8v battery and holds that for like 20 seconds then drops off and sweeps again back to 2800w and holds that steady for a while.
So my question is why cant it hold 3350w? Something doesn't look good as its settled down on 2500w and the sun is dead on my panels now I should be seeing way more. I turned the classic off then back on again and it jumped up to over 3500w then it did a sweep and settled on 2500w . The system was in bulk charge so should be giving it everything it has. I can get it on video if it helps.
Edit: now its settled on only 2200w , 67vpv input bat volt 58v (absorb is set at 60v) So its still in bulk (showing bulk on the classic) and should be giving it more wattage than 2200w.
Link to short video of whats happening http://www.youtube.com/watch?feature=player_detailpage&v=mF_QNeMWh0c (http://www.youtube.com/watch?feature=player_detailpage&v=mF_QNeMWh0c)
Kurt
Ok I think i might have the the answer. It might have something to do with voltage of the PV vs voltage the battery's were at . while still in bulk pumping only 2500w into the battery I turned the electric grill on 3000w load and this dropped the battery voltage down to 55v and the classic is now charging at a steady 3500w.
So this could be A issue with my 35.2v pv in a 2p configuration not having enough voltage headroom?
Kurt
Quote from: offgridQLD on November 02, 2013, 08:35:58 PM
edit : I was just watching it again sitting at 3350w then it just dropped to 2800w. This it whats happening its sitting at 2800w, 65v pv input, 56.9v bat output then it dose a sweep and then holds 3350w output with a 62v input, 57.8v battery and holds that for like 20 seconds then drops off and sweeps again back to 2800w and holds that steady for a while.
4.2volts available for the Classic to MPPT with ::)
Even when it jumps to 65v from PVs when output drops to 2800W there is not exactly a lot of voltage headroom for the Classic to do its thing.
I would agree with your reasoning that there is insufficient voltage headroom in the two series 36v mpv panels.
But didn't we have this discussion a couple of months ago on voltage headroom and whether you should have 2Serial or 3Serial strings but the concensus of opinion (not mine) was 2S was better 'cos the Classic would be less efficient with the higher volttage input from a 3S string?
(about 108v mpv).
Any IMHO (with stress on the H), 3S strings would be better for your application.
dgd
Sorry today I am talking about my old 4000w system 35.2v pv in 2s configuration ( not the new yet to install 36.5v panels) But yes we had a discussion regarding 2s or 3s on the new yet to be installed panels but the decision on that hasn't been made yet on them
(http://farm4.staticflickr.com/3702/9427836206_f8286ff032.jpg)
Today I was just taking note of how the old system is performing before I make decision on how to configure the extra 4000w of pv
Well as you can see in the video link I posted when I turn the classic off the PV input is 73v but I guess then the classic loads the PV to find MAX power point and the voltage drops. My thinking was yes the classic is loading it to 62v and its only 4v to play with but as long as the classic had more voltage that the Battery's at any given time then I was thinking all was fine - less down conversion. This would be all things working not in its favor it as in battery almost in absorb so 57v and pv reasonably hot.
I have never really bothered much looking into how this Mppt realty works loading the pv to get max output . Isnt the classic making the choice what voltage to load the pv to?
Hi Kurt,
Similar situations have been discussed here before.
Have you tried setting "Legacy P&O" in the Mode menu? This has been recommended in situations where string Vmp is too close to the battery voltage.
FWIW, Vic
I just did I full reset on the classic . Holding down both arrow keys on boot up. As I don't think I did that after the last update.
Will see how that works out for me next weekend.
If I notice the same issues then I will have a play with the legacy setting. The system has been up and running for over a year and has no trouble achieving 20kwh+ a day so its doing ok. It was just today when I was taking note of the output from starting from around 7 am this morning and taking particular note around 10AM (my max performance hr) so I noticed the odd behavior as I was expecting the typical 3500w+ at around 10AM, it wasn't typical behavior.
SO I just thought it was odd and low. I know the system has voltage in reserve to charge at way over 3000w even right at the end of the bulk stage when the battery voltage is just under 60v and about to go to absorb.
Have a look at the screen grabs from a while back similar time of day) and you can see why I was concerned about the it settling on just 2500w output today during my peek charge hr in full sun. Looking back on the past performance I don't think the 2 series is a issue regarding low voltage now.
At just 67v input and bat V of 56.2 in this capture I am getting the full rated output of the 4kw system
(http://i1105.photobucket.com/albums/h352/kurtthrun/power.jpg)
again holding 3200w although in absorb and most likely backing down a little
(http://i1105.photobucket.com/albums/h352/kurtthrun/Capture3-1.jpg)
Kurt
I "Think" the issue was caused by the lack of the factory restore. I noticed the "OCP is Off" statement indicating it has had a recent firmware update. We have seen this type of behavior on some updates like that and a factory restore fixes it.
That said the PV voltage is pretty low and may cause some anomalies going to 3s would be a solution for that, going to Legacy P&O would be another
Ryan
I will take note of the peek output next weekend if I see the typical 3500 - 3900w and it holds there for a while (clear sky and all) then I am happy with that and wont fiddle.
Though I will defiantly give stronger consideration to putting my additional (yet to be installed) 21 panels and new classic in 3 series config.
One thing I love about the classic charge controllers is you have all this monitoring and you can catch odd behavior and fix things before there is a issue.
Two weeks ago I noticed my classic was pumping over 22kwh into my battery on a week day when I wasn't there (typical is 5kwh). I made a emergency trip to the home on the Tuesday. Turned out to be a garden tap running onto the ground 24/7 draining my 50,000lt water supply. If I didn't have online monitoring I would have turned up to our off grid house on the weekend with no water (Its the beginning of summer here so not a good thing) and a very very soggy green lawn. It was a real life saver.
Well i always recall the midnite guys recomending something like half vbat headroom.
>At just 67v input and bat V of 56.2 in this capture I am getting the full rated output of the 4kw system
Maybe youve just shown that 7v may be enough! But really i can imagine how 4v is really pushing your luck.
+1 on the monitoring.
I guess my main concern with 3 series is potential inefficacy and what that means in regards to heat and component life. Its a warm climate where I am.
My thinking was the bulk of your heavy charging is done around 53 -56V and then once the battery's are full (9 - 10am for me) then your covering loads at B float voltage 54v so my charge controllers are usually working hard at maintaining this voltage under heavy loads , charging ev, running washing machine, workshop. The time the pack spends from 57-60v is relatively short on a hot day perhaps only 30 min.
What was the rule of thumb 2% loss for every additional nominal B voltage over your base B voltage. So at 110v on my 48v B I would have 2% loss on a 4kw array so 80w. The trouble is this loss isn't in a long copper wire the 80w is being shed inside the classic. It doesn't sound like much but I think it is worth considering.
Another consideration. The system I have now they went reasonable light on the cable from the pv to the power room 20m distance and I think there some unnecessary V loss there. My thinking with the new array I would use a more adequate cable size and also noting the old panels are 35.2v and my new panels are 36.5v so a couple of volts gained. So perhaps a 2 series config might be ok and keep the classic running cooler. Another consideration why I don't want potential extra heat to deal with on a 3 series config is its a fairly big array at 4kw on the just one classic so its working the classic reasonably hard to start with soing its thing with that size pv feeding into it + a potential 80w of heat to shed on top of that . If it only had a 1kw or 2kw array feeding into it you might have the headroom but 4kw on a 38 deg C day? (Could be a walk in the park I don't know)
I'm not saying I have the answers or know what I am talking about ;D just things I am considering in making my choices. Yes I do agree perhaps 4v was on the cuff of whats workable in (solar mode)
Kurt
I understand a buck DC-DC converter (Classic charge reg topology) needs at least 20% headroom eg 60volt*1.2 = 72 volts min would be ideal. ??
Well I got the latest firmware into the classic today ready for my new WBJR unit that just came in the mail. I did the VMM after the firmware install and gave Legacy P&O a go :o :o :o It turned my classic into a watt producing animal! I was seeing numbers way over what my system is rated at 4000w but I was consistently holding 4500 - 4700w (don't you just love it when you get more than you payed for). The little current limiting orange led was showing on the front of classic a few times. Ok admittedly it was a nice sunny day with some cloud about and the cloud edge effect had something to do with the big numbers but not all. It wasn't shying away from holding 4000w for log periods of time.
(http://farm4.staticflickr.com/3736/10688825773_e87ee56f10.jpg)
What exactly dose Legacy P&O mode do (it's working) but It would be nice to understand why its working so well and are there any negatives to using it over Solar mode. I noticed there is a adjustment for sweep depth I think its set at 10w by default.
Thanks for the tips on improving the output . now i just need to get the classic to dial into mymidnite again after the firmware update its suddenly vanished.
Kurt
Nice! 88amps out. Go sunny queensland. Well, looks like your theory is panning out. Now all you need is couple of shunts and a datalogger and youll be able to monitor the efficency running at low array voltages...
Kurt,
I'm a bit confused about the first local app screens you included, the input voltage meter goes to 200v and the output current max is 68A I thought these were the settings for a Classic 200 yet the info box says its a 150.
In your local app screen in your last posting it still says its a 150 but now the input voltage meter only goes up to 150v and the current is near 90A.
Have I missed something with the local app and you can now select the input voltage and output current ranges?
Of did you have a Classic 200 and swapped it out for a Classic 150?
If so then this would explain the higher output as the 200 was at it current limit and the 150 is not.
Or is there something else happening :-X was your 150 running 200 firmware :o
Anyway its good to see you getting this sort of power
dgd
DGD,
I see what your saying. I haven't changed classic I only own two and they are both classic 150's. Its the same classic 150 that the first screen grabs of the local app were taken from. I cant be sure they were the same local app version though.
I have a feeling the meters were perhaps Auto ranging and I just hadn't hit more than that amperage for the day yet.
I haven't installed 200 firmware on it that's for sure and it wasn't at current limit at 68A as it went over that in the past. I think it was just Auto ranging meters on that local app.
Also my issue with it not dialing into mymidnite has fixed its self during the 12:00 auto restart and its logging better than ever (no big gaps in the log now) ;D
Just need to split up my main battery cable, or add a little extension to it this weekend and get my new WBJR installed inline :)
Just a entertaining story about thick main battery cable... When I first took possession of the offgrid house I went snooping around in the power room. The inverter and charge controllers are installed in a large industrial metal cabinet without no front door to give air flow. It was almost dark but I could see what looked to be a big coil of 0 gauge or even 00 gauge cable jammed between the inverter box and the cabinet.
Concerned it was blocking airflow I reached in to remove it. It wasn't until I pulled it out and had it in my hand that I noticed it was a live snake that had been warming its self on the inverter :o. . Stumbling and tripping back onto the ground with the snake slithering back over top of me to hide. Lets just say anything that looked like a hose, cable, pipe or stick for months made me jump!
Kurt