Hi guys,
My name is Paul Cheung, I live in Jamaica. I have an off grid PV solar system, it has 12 Panels, The panels eight of them is SUN-ND250HAC from Sun-Elec from Miami. VOC is 38.3 volts, Vmp is 29.8 volts, Imp is 8.4A, Isc is 8.9A. The controller is Midnite Classic 150. The panels are wired in 2 series of 4 panels each series. The battery is 48 volt bank. The other 4 panels is Intenergy INE-240-60; VOC is 37.35 volts, ISC is 8.38A, VMP is 30.89 volts, IMP is 7.77A. these four panels wired in a single series also connected to the Classic 150 controller.
The system installed from last year November 2013 with an Outback FM60 controller. Since this year March 2014 I bought 4 more of the Intenergy panels, I bought a classic 150 controller as the current go over the 60 amps sometime. It works ok so far, but as I learned more about PV system design, my system has a major fault, The VOC on the string is over the controller's limit. We don't have extreme cold weather in Jamaica. But it can be a bit of cold in December in some years as I live in the colder part of the Island.
My question is how does Classic 150 controller deal with high VOC? Does it just cut off the current and switch off until the VOC drop down to safe range? Or it will damage the controller if the VOC go over the 150 Volts in the early morning in the colder months? Should I go through the trouble to rewire the strings with 3 panels? do I have enough volts to deal the voltage loss with 3 panels in a string run about 75 to 100 feet to the controller, and absorb the 48 volts battery bank with 60 volts absorption setting?
Thank you in advance.
Paul, the Classic is made so that it can withstand that temporary high input voltage.
We call that feature, "HyperVOC" and this is exactly what it is for. This works especially well
for 48V batteries like you have.
If you don't want the Classics to ever turn off, you can certainly re-wire them for lower input
voltage which can also help the Classic to run cooler. The decision to run lower input voltage
depends on how far away the PV solar array is from your power center... i.e. how long the
wires are. If the PV array is fairly close, I would wire the array for lower voltage. If the
PV array is say, hundreds of feet away, I would stay at the higher input voltage because
the power loss in the wire/cable will be lower at high input voltage. It depends on which
loss is less offensive. A cooler running charge controller will also be good for its long
life but maybe it is not all that hot running as it is now ? If you can touch the Classic,
it's probably cool enough.
boB
Hi Paul,
Welcome to the Forum.
The two different PV modules are close enough in Vmp to be wired in parallel strings on a single Classic 150.
The Classic Charge Controllers (CC) are unique, in that they have Hyper Voc. This where the CC simply rests when the input voltage from the PVs reaches or exceeds the number value of the specific Classic -- 150 V, in your case. The Classic will make NO power when this 150 V input is reached, but should not be damaged, unless the input voltage exceeds the voltage rating 150, plus the nominal value of the battery voltage -- 48 V, or a total of 198 volts. Above 198 V, the Classic may be damaged, and the warranty would probably be voided.
Your MPPT CCs will operate less efficiently with your four PVs in series, verses running PV strings of three. This lower efficiency results in added heat that the Classic must rid itself of.
So, YES you should rewire your PVs in strings of three, and you will only be able to use 15 PVs, having one in unused PV in reserve.
You may want to use the Classic String Sizing Tool to confirm that your total power is comfortable for the Classic -- about 3960 W STC, which is probably OK.
Classic String Sizer:
http://www.midnitesolar.com/sizingTool/displaySizing.php
More Later, Vic
Thank you guys, so I shouldn't be worry too much about damage to the controller. The wire is about 90 to 100 feet between the panels and the controller, if I rewire to 3 panels, would the better efficiency compensate the lost of 1 panel power?
I am not worry about the lost of power when the voc over 150 volts because that is rarely happen, I just don't want it get damaged if on cloud edge when the rain stop and the panel cool.
Thanks again.
Quote from: boB on September 24, 2014, 06:57:30 PM
If you don't want the Classics to ever turn off, you can certainly re-wire them for lower input
voltage which can also help the Classic to run cooler.
What the heck was I thinking here about not wanting the Classics to "ever turn off" ??
I don't know !
Quote from: Paulcheung on September 25, 2014, 12:40:24 AM
The wire is about 90 to 100 feet between the panels and the controller, if I rewire to 3 panels, would the better efficiency compensate the lost of 1 panel power?
Welcome to this forum, I've been following your discussions about batteries on another forum.
As mentioned, 3 panels in series would be optimal from the controller's perspective. But lower voltage means higher cable losses. In many (not all) systems the over all efficiency of the higher and lower string voltages is the same, but in the higher voltage system more of the inefficiency (and heat production) is in the controller and in the lower voltage system more of the inefficiency (and heat production) is in the cable.
Here's a recent analysis of higher vs lower string voltage for another system:
http://midniteforum.com/index.php?topic=2008.msg18796#msg18796
Does this analysis and conclusion apply to your system? Depends... what size cable do you have installed? If you have a small cable and want to add panels to it, you may need high voltages. If lower voltage is practical (cable size, distance) it is a better design.
--vtMaps
Quote from: Paulcheung on September 25, 2014, 12:40:24 AM
Thank you guys, so I shouldn't be worry too much about damage to the controller. The wire is about 90 to 100 feet between the panels and the controller, if I rewire to 3 panels, would the better efficiency compensate the lost of 1 panel power?
I am not worry about the lost of power when the voc over 150 volts because that is rarely happen, I just don't want it get damaged if on cloud edge when the rain stop and the panel cool.
Thanks again.
I would doubt the minor increase in overall efficiency of a 3 serial PV string and 15 PVs in total in five parallel strings, would make up for the loss of one PV panel.
Sixteen panels in four strings or 4 in series would be the way I would go.
These 30v mpv panels would make about 120v, this is easy for the Classic without significant overheating.
dgd
Quote from: dgd on September 25, 2014, 11:06:54 PM
I would doubt the minor increase in overall efficiency of a 3 serial PV string and 15 PVs in total in five parallel strings, would make up for the loss of one PV panel.
I suspect that you are correct, but sometimes its not just about getting the most power. The OP is expanding to a 4000 watt array. The Classic 150's maximum power handling is 4438 watts with an input voltage of 120 volts, and 4847 watts with an input voltage of 90 volts. The reason the Classic is derated by 409 watts at the higher input voltage is because it produces so much extra heat that it must derate itself to avoid damage.
I believe that a good conservative design does not push the equipment near to its limits all day. The OP is in a warm-hot climate with long sunny days. The equipment will be happier (cooler) and last longer with the lower input voltage.
We still haven't heard back from the OP about what size cable is in place and whether he will upgrade it... he may have to stay at the higher input voltage.
--vtMaps
Quote from: vtmaps on September 26, 2014, 05:25:45 AM
The Classic 150's maximum power handling is 4438 watts with an input voltage of 120 volts, and 4847 watts with an input voltage of 90 volts. The reason the Classic is derated by 409 watts at the higher input voltage is because it produces so much extra heat that it must derate itself to avoid damage.
I see from the panel specs provided that the max power would be 4Kw with sixteen panels,
BUT with warm-hot climate the OP would probably see somewhere about 75-80% of this once the PVs get hot
Ok, he may get full rating with MPV early morning or on a cool day with clear (or slight clouds) but the 150's rated 4438 watts is probably enough margin.
Quote
I believe that a good conservative design does not push the equipment near to its limits all day. The OP is in a warm-hot climate with long sunny days. The equipment will be happier (cooler) and last longer with the lower input voltage.
Yes I would completely agree with this, it would be interesting to know what sort of daytime power is generated from the existing twelve 250w pvs when they get hot, also, as you have asked, what is the guage that 100feet of wiring.
dgd
Sorry I didnot know someone did more reply after I did my last post.
The wires are the same size wire that come with most grid tie panels. (4mm2?) it has 3 wires from the combiner box going to the charge controller down stairs. 2 positive with 2 strings of 4 panels each wire and all the negative wire are connected to 1 wire, the output current to the battery bank is around 40 to 55 amps at about 100 to 110 volt input, the classic controller does not report incoming currents.
I live in a place that has alot of clouds passing by even the weather is not overcast. the panels are aim to sun for winter season because we got exceesive sun hours during summer months. I got the highest haveast in one day is about 18KWH with 16 panels and around 14KWH with the 12 panels. with long sunny day like that the controller do goto absorb mode and cut off some of the current.
I only see the panels name rated power right after the cloud edge. the time is hot even in winters so I take the chance leave the panels in 4 in a series.
I lean the other way guys. Having studied as many controller outut curves as i can find, and watched those who have struggled with hot classics at high voltages, i suggest 3S strings would be better for you. When i did the math on our system i was going to lose more watts in the classic than in the cable when comparing strings of 2 to strings of three. Even if its in the same or near ballpark, that amount of heat is a LOT easier to disipate in teh cable than in the controller.
However... for the home run 4mm2 for 90 feet is not really suitable. Copper is expensive but its not that expensive. Off grid home run cables are typically in the order of 16-20mm2 (6awg to 4awg). You can model and compare these losses very roughly by assuming that the controller will be 2% less efficient for each addition to the string length. Thats an unofficial measure that i beleive originates from the FM controller curves. It would be helpful if midnite published there curves, (they have done all the testing anyway.) And make string design a much simpler process.
With mppt there is a tiny bit of a contradiction, unfortunately, that while mppt allows longer string lengths the efficiency is decreased undoing some of the gain of mppt in the first place. On balance the sweet spot is an array vmp of somethng like twice the system voltage.
The weak point in all electronics is electrolytic capacitors, and they have notably short lifes, and accelleratingly so with each degree in extra temperature.
Quote from: zoneblue on June 17, 2015, 04:06:07 PM
When i did the math on our system i was going to lose more watts in the classic than in the cable when comparing strings of 2 to strings of three. Even if its in the same or near ballpark, that amount of heat is a LOT easier to dissipate in the cable than in the controller.
Total agreement. I've also done the math.
Another point in favor of the lower voltage string is that the power loss in the cable goes as the square of the current in the cable... therefore at typical (less than max) power levels the cable loss is much much lower than what you calculate at max power.
On the other hand, the controller inefficiency persists at all power levels.
--vtMaps
What is the most efficient input voltage for the Classic 150 with 48 volt battery system that the battery bank voltage is mostly at 52 to 60 volts?
Hi again Paul,
IMO, there is a sweet spot at around 90-ish Volts for Vin for the Classic 150 on a 48 volt battery.
Three PVs in series per string, is what I run on some systems here, and would run, if I were you. But this would leave one PV unused.
There is one additional issue with running strings of four 60 cell (30-ish volt Vmp) PVs. This is, that when later stages of Absorb, and in Float, the PVs are often lightly loaded (unless there are largish loads on the inverter/s), this makes the PV voltage into the CC rise, closer to Voc for the temperature of the PVs. This makes the Vin even higher than it was when the PVs were at temperature-corrected Vmp for the solar input. You could be seeing about 130 or 135 volts into the Classic when in Float. This results in a lot of extra power lost in the CC, even when considering the relatively low output current from the CC under these conditions.
You might well have some Opportunity loads, like A/C that could help load the PVs, and reduce a relatively high Vin when in Float, but from direct personal experience, MPPT CCs do not run efficiently with Vins fairly close to the maximum specified for that CC.
FWIW, opinions, Vic
Quote from: Vic on June 17, 2015, 10:04:08 PM
IMO, there is a sweet spot at around 90-ish Volts for Vin for the Classic 150 on a 48 volt battery.
That is certainly correct for typical 'grid-tie' panels with a Vmp of 30 volts.
I think that if you were constructing your array from true 12 or 24 volt panels, you could aim for a Vmp that is about 76 volts as a ever-so-slightly sweeter spot. ;D
Of course, every system is different... if you live in a very hot climate and refrigerate your batteries, a Vmp of 76 volts might not be high enough to give the controller the headroom it needs.
--vtMaps
Thank you guys,
However my system has never gone to float yet, according to Rolls battery Manual, the absorb charge time would be 4.5 hours. My battery bank is fairly small compare to my load. I consume 20 to 24KWH daily and my battery bank is 750AH @48 volt. My battery supply around 10 to 12KWH daily and where I live is kind hot and always has clouds passing by.
Thanks again.
Quote from: vtmaps on June 18, 2015, 05:31:32 AM
Quote from: Vic on June 17, 2015, 10:04:08 PM
IMO, there is a sweet spot at around 90-ish Volts for Vin for the Classic 150 on a 48 volt battery.
That is certainly correct for typical 'grid-tie' panels with a Vmp of 30 volts.
I think that if you were constructing your array from true 12 or 24 volt panels, you could aim for a Vmp that is about 76 volts as a ever-so-slightly sweeter spot. ;D
Of course, every system is different... if you live in a very hot climate and refrigerate your batteries, a Vmp of 76 volts might not be high enough to give the controller the headroom it needs.
--vtMaps
Well, first, the OP indicated that 60 cell PVs were being used with a Classic 150. I did not qualify my statement about My Opinion regarding the sweet spot.
In my limited experience, believe that (generally) the Classic seems to like a bit higher string Vmp than some other MPPT CCs, like the OB MX-60.
AND, since we are discussing Classic CCs, which implies medium/large systems (again IMO), is seems less likely that true 12/24 V PVs would be used, at least for new installations.
Furthermore, True 12 V PVs run about 17.8 - 18.25-ish STC Vmps -- 35.4 to 36.5 V for true 24 V PVs. This is a bit short of "76 V" when making strings of 144 cells (four 12 V or two 24 PVs).
One system here, with Classic 150s does run True 24 V PVs (35.4 V STC Vmp), in strings of three for a nominal 106 V string Vmp ... yes, this is a bit high, but this system has been in service for 10 years, and the Classics replaced a venerable MX-60.
To me, about the best string V for a Classic 150 might be two 80 cell Pvs (like the Kyo 315 - 325s), but these are rare, in the scheme of things.
Again, just My Opinions, YMMV, etc. Thanks, Vic
Quote
I think that if you were constructing your array from true 12 or 24 volt panels, you could aim for a Vmp that is about 76 volts as a ever-so-slightly sweeter spot.
Nice vt!. Theres lots to like about 72 cells if you can cope with their phyical size. Shippings a bit of a b*tch.
Quote
seems less likely that true 12/24 V PVs would be used, at least for new installations.
When i was shopping here 72 cell panels were cheaper than 60 cell, in tier one panels at least.
Quote
Vmps -- 35.4 to 36.5 V for true 24 V PVs. This is a bit short of "76 V"
I woud have thought (hunch) that 40V ought to be enough headroom? Any DC converter ive ever come across was happiest when the output wasnt too far from the input. My laptops run of a 24-19V converter, and that thing is barely tepid with 3 laptops.
Here the headroom is about 30V. But i have no way to monitor this more accurately, because the classic PV amps is too squishy. It would need 2 shunts and a four channel 1% ADC logger to get a decent throughput effiency measure. I suppose we could design something and mail it to each other to test each configuration.
I have two classic 150's both with 4000w arrays on them. One has 2s (80v) the other 3s (120v). The 80v classic runs so much cooler for all the reasons already mentioned. I run Lifep04 lithium batterys so Im dealing with a charge voltage scope of 53V-56V. So less than the typical FLA that needs 60v+ for EQ . I will be reconfiguring the 3s arrays down to 2s this winter in preparation for a cooler running controller over summer.
My vote is keep the voltage as close to the battery voltage as you can get away with. keep the heat out of the controller.
Kurt
I was limited by the wire gauge I could add to my existing conduit, and went with a 170VMP array for nominal 65V charging (NiFe 48V bank) and just with a 2Kw array, controller is toasty hot. The fans are managing it, and I'm glad I don't have to listen to them.
Quote from: mike90045 on June 25, 2015, 02:06:30 AM
I was limited by the wire gauge I could add to my existing conduit, and went with a 170VMP array for nominal 65V charging (NiFe 48V bank) and just with a 2Kw array, controller is toasty hot. The fans are managing it, and I'm glad I don't have to listen to them.
Mike, how hot is "toasty" hot ?
boB
Quote from: boB on June 27, 2015, 03:18:10 AM
Mike, how hot is "toasty" hot ?
boB
FET's run about 48°C, almost painful to touch the case/heatsink.
Quote from: mike90045 on June 27, 2015, 02:52:56 PM
Quote from: boB on June 27, 2015, 03:18:10 AM
Mike, how hot is "toasty" hot ?
boB
FET's run about 48°C, almost painful to touch the case/heatsink.
48C for the FETs ? That's very cool actually. UNLESS the temperature is
not reading correctly. What is the PCB temp reading ?
Some people have more of a problem with heat than others do of course.
boB
You seem to be pretty much ideally set up to test this. Comparing current and voltage readings in and out of both controllers should give us a quick and rough guide to the actual difference in efficiency. Even just a clampmeter job. The tricky thing when i tried it was that you really need 2 clampmeters plus two voltmeters. To get readings at the same time. However if you did this around noon, on a clear day, and at a time when both controllers were mid bulk, thats about as stable a condition for the controllers as youll get. Then as quick as you can, measure all 4 currents with the clampmeter, then all 4 voltages with the same meter one at a time. Mutliply them out, should be interesting.
Quote from: offgridQLD on June 23, 2015, 08:10:56 PM
I have two classic 150's both with 4000w arrays on them. One has 2s (80v) the other 3s (120v). The 80v classic runs so much cooler for all the reasons already mentioned.
Clamp meters aren't very good for efficiency testing but would give you a ball-park figure.
They must be very close in readings to each other and of course input current is going to
be less than output current.
I like to use a camera to take pictures of the readings so then the calculations can be done
easier.
But I would use some kind of temperature measurement first because 48C just isn't
very hot for a charge controller.
boB
Quote from: mike90045 on June 27, 2015, 02:52:56 PM
Quote from: boB on June 27, 2015, 03:18:10 AM
Mike, how hot is "toasty" hot ?
boB
FET's run about 48°C, almost painful to touch the case/heatsink.
I know that feeling of hot & 48C on the FETs .. Im thinking my next build is to have a heat sink that's cooled into the ground rather than a wall of wood . Big steel sunk into the soil & then cemented & drill tap the controllers to that plate & extract the heat into that steel mass. If need be have a steel heat fins above for the heat exchanger ..
VT