12v to 24v upgrade

mobywile · April 2016

I am putting together a list of parts and equipment to accomplish an upgrade from a quite old 12v off-grid system to a modern 24v system.
I currently have 18 SunTech 180S-24 panels configured in 6 strings of 3 panels each. These are wired through 3 2-string combiner boxes which feed 2 Midnite Classic Lite 150s. Array output is 24v nominal and charges 16 L-16s in a series-parallel 12v bank. The existing inverters are two Trace 2012SBs stacked and turboed. Yep, the old black SBs are still working as installed in the early 80's.
Now, I would really like to move up to a sine wave inverter at 24v to actually USE all the power I have available. I can't run the well pump when the diswasher is on and the voltage draw-down shuts off some of my new LED lighting. Lots of this type of thing that we have lived with for decades but we'd be very interested in what the 21st century has to offer.
I do have a significant investment in 12v LED lighting that I would like to continue using so I am looking at the Samlex 24v to 12v converter for that. The DC LEDs work great for us and changing the DC main panel over to AC would add to the AC load, and also cause me to look for a lot of LED replacements.
I will run my Sunfrost RF-19 and F-10 on 24v - they are the newer type which will run on 24v or 12v - through a subpanel dedicated to them.
I have found a great wiring diagram for the new battery configuration which eliminates the parallel wiring problems. A bit more and longer cabling, but it looks so much more balanced.
So, the 4024, Samlex Converter, RC-50 remote, and the battery monitor. Other than some new battery wiring, I think I'm set.
I will use my existing Siemens 3-pole disconnect and the existing wiring which has worked flawlessly for a very long time.
Thanks for being out there,
Moby

Vic · April 2016

Hi Moby,

Welcome to the Forum.

We do not know where you are located, but, roughly where are you, and what do you expect for the lowest temperature you expect at the site?

A couple of things come to mind, first, your proposed String Vmp is about 108 V, with the String Voc is about 135 volts at a cell temperature of 25 degrees C. If your site can get fairly cold, your Classics could spend quite a lot of time in HyperVoc, producing nothing.

And, with a 24 volt battery voltage, this conversion ratio is a bit on the high side. Strings of two should work fine with Classics on a 24 V battery, although this increases the number of strings. A 48 V battery bank gets the conversion ratio to a better spot, but still has the same HyperVoc concern, as you would probably want to run strings of three PVs, as, even a 72 volt String Vmp could be a bit low during times of warm/hot weather.

A 48 V battery voltage reduces the number of parallel battery strings to two, fewer parallel strings is a good thing, generally. And you are thinking of replacing the inverter, anyway.

Assume that you now own these ST-180 PVs.

More Later, Vic

mobywile · April 2016

Thanks Vic,
I am in Colorado, just NW of Ft. Collins, at 7400' elevation.
I am feeding my Lites at 36v , not 108v. I know this isn't optimum for the 24v battery bank, but it's what I have to work with, and has kept the Lites right where they want to be charging a 12v bank. Increasing the number of strings would be a challenge, as the array is over 200' from the CCs. Old-timey setup with a million dollars of 2/0 copper in the ground. I'm using it... Zip voltage drop, though.
I am NOT considering the 48v setup as I want to run my Sunfrosts at 24v and I haven't seen a 48v to 24v converter.
I have a battery wiring diagram that will give me 4 series connections that are paralleled using long(er) cables to the inverter connections. It is on a website called Free solar Power. http://www.freesunpower.com/battery_designer
Yes, I do won the ST-180 PVs.
Thanks,
Moby

Vic · April 2016

Hi Moby,

Well, that 108 volt String Vmp voltage in my post, came from something you noted in the first Post, Quote "... I am putting together a list of parts and equipment to accomplish an upgrade from a quite old 12v off-grid system to a modern 24v system.
I currently have 18 SunTech 180S-24 panels configured in 6 strings of 3 panels each ... <"

To me, if one has 18 PV modules, arranged, as you said, configured in 6 Strings of three PVs each, this would mean that each of the three PVs would be in SERIES, as this is the customary method, with each series string having its own circuit breaker of fuse in a Combiner box.

Perhaps, you are somehow paralleling each of the three PVs, and then connecting those to some Combiner ... dunno But, if the Vmp into the Classics is 36 V, then they are obviously not in series.

Will say, that parallel strings of PVs, exceeding two PVs really should have a circuit breaker of fuse to protect each PV module. Do you have this protection for each PV module that is paralleled? Parallel strings of two PVs is OK, but parallel connections of more than two PVs (like three PVs) without over current protection (circuit breaker of fuse) can be dangerous, and have potential to cause a fire.

It is clear that I do not understand how your system is wired, so probably cannot be any help.

Thanks, Vic

vtmaps · April 2016

Vic said:

But, if the Vmp into the Classics is 36 V, then they are obviously not in series.

I don't think the OP ever said his string Vmp was 36 volts. He said "I am feeding my Lites at 36v". I think he means that he is putting three 12-volt panels in series. The Vmp is probably about 54 volts.

mobywile said:
I am NOT considering the 48v setup as I want to run my Sunfrosts at 24v and I haven't seen a 48v to 24v converter.

How about:
http://www.powerstream.com/dc48-24.htm

This site has several DC-DC converters in various power capacities:
http://www.trcelectronics.com/Meanwell/dc-dc-converter-selection.shtml

SolarConverters.com makes a 240 watt 48 to 24 volt converter in a weatherproof NEMA 4 enclosure:
http://www.solarconverters.com/index.php/products/84-dc-dc-step-down-controllers-ppt/163-ppt-48-10-rxx

--vtMaps

Vic · April 2016

vtmaps said:

Vic said:

But, if the Vmp into the Classics is 36 V, then they are obviously not in series.

I don't think the OP ever said his string Vmp was 36 volts. He said "I am feeding my Lites at 36v". I think he means that he is putting three 12-volt panels in series. The Vmp is probably about 54 volts.

mobywile said:
I am NOT considering the 48v setup as I want to run my Sunfrosts at 24v and I haven't seen a 48v to 24v converter.
How about:
http://www.powerstream.com/dc48-24.htm

This site has several DC-DC converters in various power capacities:
http://www.trcelectronics.com/Meanwell/dc-dc-converter-selection.shtml

SolarConverters.com makes a 240 watt 48 to 24 volt converter in a weatherproof NEMA 4 enclosure:
http://www.solarconverters.com/index.php/products/84-dc-dc-step-down-controllers-ppt/163-ppt-48-10-rxx

--vtMaps

Hi vtmaps, Moby,

My comments were based on a Search for the PVs noted in Moby's first Post ... here is a Link to PVs that appear to match that part number:
https://www.altestore.com/static/datafiles/Others/STP180S-specs.pdf

IIRC, the Vmp of one of those PVs is 36.4 volts, and I had felt that Moby was running or proposing running STRINGS of three of these (in series), but this appears to have been erroneous, on my part. Assume now, that three of these PVs are joined, in parallel, but perhaps not really Combined (ie no OCPD at this parallel connection), but these summed PVs are Combined with others which might have breakers of fuses (?))).

And I should apologize to Moby for being too terse in the previous Post, was rushing off to dinner. Sorry Moby.

FWIW, but felt that I had been guessing too much and too poorly to add anything but noise to the discussion.
Vic

mobywile · May 2016

Thanks Guys.
I must also apologize for not being accurate in my post. I speak an archaic form of "solarese" and sometimes stumble. Thanks for putting up with me.

I have connected my panels in parallel and through Midnite combiners that I use as disconnects out at the array(s). I have also installed new disconnects with the proper breakers at the house end of the underground runs to accommodate disconnecting both the input and output of my two Midnite Classic Lites. All that said, I have been using this arrangement to charge my 12v battery bank and it has worked great for the past year. Now, if I read my manual correctly, I can reprogram my Lites to a 24v battery bank and they will work just fine.

I want to stay with the 24v battery bank so I can run my two Sunfrost products on DC. The voltage converter to 12v will be for, almost exclusively, lighting. I have invested lots of $$ in DC LEDs over the past few years and, I hope, they will last many years. This is a full-sized, all weather, year-round residence, and my wife works in her quilt studio every day, all day. Keeping the lighting and refrigeration DC saves inverter space and allows me some freedom in working on the system.

On the hardware upgrade, I will use the 120v output from the Magnum 4024 PAE for now. Later, I may choose to go to 220v. Numerous reasons to just change this much in the first go-round. I probably will not add a second inverter in the future. So, I am looking at the basic remote controller. Also, I have the remote graphics panel for the Midnites already. Any reason I should consider the advanced remote for the Magnum? Also, will the battery monitor be redundant along with the Midnite panel? I am going to install an analogue DC Voltmeter in the panel in the kitchen. I have always had one that I can glance at anytime we are using multiple applances at mealtimes. Makes us both aware of what we're doing.

I looked at the TRC Meanwell 500w voltage converter. Price is excellent. They don't rate its efficiency, though. The Samlex states its efficiency at 92%. Pretty good in my estimation. I have looked at the SolarConverters products in the past and they would have to make me one outside their regular offerings. Probably not worth their time and trouble for a one-off.

Again, I think this change will make all of my larger loads much happier and also help with battery life and maintenance. When this system was originally planned and installed, 12v was to only game in town. It has served us very well all these years. Time to move on.

Respectfully,

Moby

Vic · May 2016

Hi Moby,

Thanks for the concise description of your system. It is good to see that each PV module has its own breaker, this is the safe way to do things.

Your PV modules seem to have a sufficiently-high Vmp (36.4 V, IIRC) for an MPPT CC. Would expect that a bit higher Vmp, with a 24 V Flooded battery would actually be better for MPPT CCs like Classics. But, there seems little risk in trying the existing PV configuration.

Cannot speak to Voltage Converters, or to the Magnum Remotes for the PAE inverters, BUT, just make certain that any remote that you chose will allow a full range of voltage settings (Absorb, Float, EQ), an Absorb time period, assuming that you have a genset, and will want to be able to charge using the inverter/charger. Also Low Voltage Disconnect settability, ahd HighVoltage Disconnect settings are very important. Know very little of the Magnum inverters, and nothing meaningful about their Remotes.

Will note, that folks that I respect have said that Magnum inverters, generally have a bit of a slow voltage regulation response time, which can cause light/LED Flicker with varying loads on the inverter, FWIW.

Good Luck, Thanks, Vic

12v to 24v upgrade

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