Ungrounded system

[carilchasens]

With Classic 150:
My DC system is ungrounded 12 volt, PV is 62.6 Vpm,ungrounded.  With a completely ungrounded system, do I simply disconnect the GFP jumper, disable GFP in the TWEAKS menu, and insert the respective battery negative, battery positive, PV negative, PV positive in the labled places in the terminal connector?
Are the negative terminals common? If yes, how would it work with the 12 volt battery negative connection and something-over-sixty volt PV negative wire on a common connection?
What would be the effect if the chassis of the Classic 150 is ungrounded? (Placement of the unit would make a short from chassis to ground EXTREMELY improbable)

[Westbranch]

one of the rules of thumb used is to design the system with an array voltage that is ~ 2 times the battery voltage, so 12 V would use 2 '12 volt' nominal PVs in series (Vmp ~ = 17v) ,  for 48 V bank double that...
so unless you have long distances from the array to the Charge Controller and battery bank you will be wasting energy  inside the CC, in the form of heat produced. Better to have the energy in the battery...

An ungrounded system runs the risk of being a crispy critter....

[Resthome]

An ungrounded system runs the risk of being a crispy critter....

Boats are essentially ungrounded systems unless you want to consider a metal hull boat sitting in water being grounding. Then there are fiberglass hull.  I just disable the Ground Fault functions and Arc Fault of the Classic. Just make sure to use all the proper wiring size and breakers for your system and make sure to torque your connections to spec.

[zoneblue]

As always we need to distinguish grounding from bonding. A boat or RV can have a negative to chassis bonding scheme without being grounded to the planet.

If you use a true "floating" DC system, you should use ganged breakers on the negative and positive lines (fire safety). Floating systems do have a couple of minor advantages, but as a rule we tend not to do it when the array voltages get much over 18V. And many jurisdictions will require grounding when the array voltage exceeds some threshold, 50V in some places, 120V in others. Which is a shock hazard safety consideration.

As WB said if your PV modules are 60 cells, 1S configuration is generally best for 12V.
As RH said, ground fault off.

The classics two negatives are commoned, so you can terminate PV and battery negative there, or at your negative bus bar.

[CDN-VT]

carilchasens

I run two un-grounded systems , boat & golf cart  :http://kb1uas.com/mnsforum/index.php?topic=3142.0

Tell us more about the build of your system & the batterys to panels & all the info , Then you can pick the replys.
Golfcart runs a KID & gfci receptacle for the 15 Amp , for the 30 amp 120V nope , & im welding .

VT

[carilchasens]

So , there is no problem - say, with battery chemistry or the controller - with having the negative From the 12V and 60V on an ungrounded common?... 

[zoneblue]

You HAVE to tie the negatives. Thats how it works.

[carilchasens]

Thank you very much for your help, folks.

[carilchasens]

one of the rules of thumb used is to design the system with an array voltage that is ~ 2 times the battery voltage, so 12 V would use 2 '12 volt' nominal PVs in series (Vmp ~ = 17v) ,  for 48 V bank double that...
so unless you have long distances from the array to the Charge Controller and battery bank you will be wasting energy  inside the CC, in the form of heat produced. Better to have the energy in the battery...

I consulted tech assistance on this, and got the reply "You have the concept correct, the greater the difference between the PV input and battery voltages, the less the efficiency. However, 62.6 should not be an issue at all and I would not change that. Efficiency loss will be very small."

[Westbranch]

IIRC 62.5 is the Pv VoC and the only way to change that is  a different PV. 
Otherwise you need to increase the battery bank  to 24V from  your present 12V battery bank...

[carilchasens]

Westbranch , can you suggest a reference or two  or a keyword for

one of the rules of thumb used is to design the system with an array voltage that is ~ 2 times the battery voltage

?
I have been googling around without much luck.

[Westbranch]

Sorry, I can not find any posts on that either...  it is just one of the things you pick up over time...

BTW the efficiency is a complex set of +'s and -'s that one needs to be aware of and each one is different as few systems have exactly all the same settings, setup etc....

ie, the 2x comes about from a combo of the losses in down shifting the incoming voltage against line losses incurred by using the lowest voltage and size of wire needed  over Y distance, Charge controller heat losses, etc...

hth

[CDN-VT]

Ok ,,So my cart has all neg tied & a dropping /drag ground tether .
Boat now needs to deal with the hull potential of base floating ground for all around OR supplier .
Thats the trick on water !
VT

[Resthome]

Ok ,,So my cart has all neg tied & a dropping /drag ground tether .
Boat now needs to deal with the hull potential of base floating ground for all around OR supplier .
Thats the trick on water !
VT

And for a boat it really gets crazy when you tie into shore power at a marina with 100s of other boat and all their crazy wiring.

[CDN-VT]

I use a shunt from boat ground / bond & shore base ground , If I see Im the ground or Supply of others around , I change the value with a huge carbon pot.

Zinks or bottom scum , we balance . Every marina is different PLUS , So You know ! Kewl