60V system to meet low voltage requirements for NEC/RVIA

cptdondo

I was going to add a couple of 300W panels in series with a 30A controller.  Then someone reminded me that to meet RVIA and NEC low voltage code, the max voltage in the system cannot exceed 60V at any time.

Which pretty much knocks the two panels in series out.

So... 

Any suggestions on building a large-ish (600-1000W) mobile array, that doesn’t exceed 60V?

The batteries are 48V nominal, and yes, the system has to meet RVIA/NEC code for low voltage systems.

Photowhit

You will need to start from scratch. Can you reconfigure your battery bank to 24 volts?

Assuming a lead acid battery bank, charging requires voltages of 60 volts or more for any practical system. Most Charge controller are designed to 'reduce' voltage from a higher voltage to a lower voltage. Their have been a very few designed to increase voltage, but I'm not aware of any from a major manufacturer. The terminology for increasing voltage is 'boost' and searching will be confusing since BlueSky and others like to use 'Boost' to describe their charge controllers, because in theory it 'boosts' output.

Photowhit

BTW - Assuming lead acid batteries some manufactures for flooded lead acid suggest a daily absorb voltage of 60 volts.

cptdondo

Unfortunately, the battery bank I am working with has a charge voltage of 58 volts (automotive lithium batteries).  The manufacturer says that the system can use solar to maintain charge, so I’m trying to figure out how to do that.  Off hand I don’t see how I can charge at 58 volts without at least 70+V at the solar array, but then I run into the RVIA / NEC 60V limitation.  

I don’t have the full picture yet - the NDA hasn’t been signed - but I’m trying to get myself up to speed on what’s available before my interview with the company next week.

The one possibility is to use a 24V MPPT controller, and then go to a 24 to 48 DC-DC charger, something like a Victron VTC1015-24-48. Still, not sure how to do that without some sort of battery on the 24V side, and it would have to have enough intelligence to modify charge current based on what’s coming in from solar.

BB.

Are you sure that you are "reading" the NEC and such correctly?

In general, the way I have understood the code is that anything >60 Volts or (asked UL years ago) if that was AC or DC voltage, and was that nominal operating voltage or never to exceed (I designed telephone voice mail systems that ran off a 48 to 72 volt battery banks (which had to comply with Telcoria specs--But we also sold into large businesses too).

In any case, as I understand that the 12 to 60 volt limit there are several energy limits starting at 12 VDC and 8 amps that allowed untrained people to access (and less than 12 volts, touch--As I recall, that was decades ago... But anything >60 volts had to be behind locked or tool required access (locked doors, panels with screws, limits to ventilation openings/slots, etc.). 

In an RV--You have 120 VAC (or even 240 VAC) power from your AC inverter/genset--So that 60 volt limit is not a "hard" limit.

If you run a 48 volt battery bank--In theory, you do not have to be a trained service person to access the battery terminals/DC wiring. However, a 48 volt bus with XXX AH or larger storage capacity, certainly exceeds the "touch safe" limits for untrained personnel.

On the solar panel side, the panels are rated from 600 Volts (USA) to 1,000 Volt (Europe) operation... So you can put X or even XX panels in series, with the proper wiring (in conduit if you want the wiring to be in areas where people can get at it (or in a wall as ROMEX, etc.). 
And any Jboxes need screws. And the terminal block at the charge controller needs to be "touch safe" too (there is a "child's finger model" to see that the terminal screw is recessed in a small hole, etc.

There are other requirements that could be required such as remote array power shutdown, arc fault protection, water proof jboxes, even roof access for firefighters (at least for home/business roofs), etc...

But since GT inverters run solar panel strings at 600-1,000 VDC maximum (in reality, typically around Vmp-array of 400 VDC or so max for many). And that is already in the NEC (normal house wiring insulation/standard wall outlets/extension cords/120-240 VAC devices are rated to 600 VAC and factory hipot tested to 1,800+ volts)--I am not sure what would stop you from running a higher voltage array on an RV (other than overeager inspectors and such).

-Bill

cptdondo

Food for thought.  My understanding is that you need an electrician license if the voltage exceeds 60V DC or 50V AC.  I’ll have to check the NEC again and see what RVIA code says.  It would be easier to put two 300W panels in series and run them into the MPPT controller at 72V.

Photowhit

cptdondo said:

It would be easier to put two 300W panels in series and run them into the MPPT controller at 72V.

That's really not high enough VMP, or maybe just for lithium, Midnite suggests; "To ensure proper start up and MPPT operation, the minimum initial PV input voltage should be at least 30% higher than the highest expected battery voltage." Remember that the NOCT Voltage will be lower than the STP VMP. Examples below;

mike95490

Your post just made every 48V system illegal.  They all require 60+ v for EQ and the PV arrays are +90V

Or you are mis-reading something.

cptdondo

mike95490 said:

Your post just made every 48V system illegal.  They all require 60+ v for EQ and the PV arrays are +90V

Or you are mis-reading something.

Not illegal, just requiring a licensed electrician instead of an RV tech and high voltage type of wiring standards.

Photowhit

cptdondo said:

mike95490 said:

Your post just made every 48V system illegal.  They all require 60+ v for EQ and the PV arrays are +90V

Or you are mis-reading something.

Not illegal, just requiring a licensed electrician instead of an RV tech and high voltage type of wiring standards.

I'd really like to see anything in NEC that requires a licensed Electrician. As far as I'm aware, it's just a set of instructions/requirements for installations. States likely make requirements as to who can or should install.  Home owners are usually allowed to make their own mistakes...lol. 

I've heard tales of other states that don't require outside/away from the home to meet home standards. There are different safety standards for Home UL1741 and Auto UL458 (as well as telecommunications and boating I believe). My free standing array is not required to meet ANY standards for my power company, the only thing they are interested in is that the grid tied inverter meet and installed to Safety standards, at least back 10 years or so last I checked before deciding to remain off grid.

Dave Angelini

Overthinking on this thread and the group here is trying to tell him that. Gobble Gobble!

BB.

I will give you some warnings... Just because an electrician is licensed or part of large company, it does not mean that they know everything about electrical power systems or can even install the parts correctly (or even find/understand the correct parts and installation tools such as crimpers and installation wrenches).

For example, have seen way too many goofed up and dangerous installs with larger power systems like air compressors. They are installing a new 5 slot EV charging station a few blocks from my home. There is now a EV power electrician in the parking lot that is debugging/redoing the original install before the system goes live because the first electricians miswired the 480 VAC 3 phase power distribution to the EV charging Islands.

There have been home connects where the electrician attached the ground rod to L1 or L2 of a 120/240 VAC split phase North America home--Instead of the Neutral from the pole transformer. One such misinstall was found much later when the owner was wondering why the snow was melting around the ground rod.

And for solar power systems, it appears that Power=Voltage*Current is not on the licence exam... You want a 1,500 Watt capable wire... They have been wiring 14 AWG (rated for 15 amp nominal max) "forever"... So slap that on a 12 volt battery bus to AC inverter and be done with that (>150 Amps @ 12 VDC).

And in our area--Don't think because the local building department inspected after the contractor was done that means much... Inspectors are not liable for "missing" or letting unsafe designs and construction through and giving final sign off.. Liability (at least in our neck of the woods) falls to the contractor.

https://forum.solar-electric.com/discussion/3375/panel-fire-question/p1
https://duckduckgo.com/?q=panel+fire+question+solar&atb=v122-1__&ia=web
https://www.businessinsider.com/tesla-project-titan-replace-bad-solar-panel-parts-2019-8

The issues with solar power systems is that they use high(er) voltage DC (more or less any DC voltage over ~12 VDC can become the equivalent of a very nice DC arc welder) which has the potential for Arc Faults (AC voltages/installations typically do not Arc Fault--It is the "nature" of the DC beast):

https://www.acsolarwarehouse.com/news/solar-fires-dc-arc-faults-on-solar-systems/

-Bill