off grid boat system set up

jimbob01

hi guys,trying to finally get everything sorted with my new 24v pv system
i dont want to miss any fuses,breakers etc,im wiring it all myself and building all frame mountings etc.
so far nothing is wired.
this is what i have;
6 x 235w sharp panels 38v ocv
2 x mstar mppt 45s
1 x outback vfx 3024
8 x 200ah powersonic 12v cells
so from the panels im thinking 2 strings of 2 panels in series in to 1 mppt and 1 string of 2 into the other(will prob expand another 2 panels later)
6mm sq cable 4m run to the ccs..
fuses @ 20amp b4 the ccs in each string..
then ccs to batteries;
no 1 cc: 40amp fuse
no 2 cc:20 amp fuse
batteries wired 2 strings of 800ah@12v connected to 24v
battery isolator switch then 2m run of 90mm sq cable via breaker to the inverter
..maybe i need a fuse between the inverter batteries as well?
any thing ive missed or extra bits...could you guys please give your advice?
much appreciated jim

westbranch

Re: off grid boat system set up

your description of batteries is not right , you should have 4 strings @ 24 volts not 8, 2 batteries in series times 4 strings.
Re the fuse at the panels, what does the maker say is needed?

Cariboocoot

Re: off grid boat system set up

You definitely need some form of over-current protection in the wiring between batteries and inverter. Big current potential there.

You are configuring the panels how? If you put three in series on each controller you technically do not need any fuse/breaker on the PV. If you put three in parallel on each controller ... well don't, because you won't have enough Voltage to charge your batteries.

Output from charge controllers should be wired and protected according to their maximum current (45 Amps) if this system is to be inspected. If not you can undersize to the actual expected current. If the panels are divided evenly between the two controllers the output would be identical on each. I think you are putting four panels on one and two on the other?

The inverter, BTW, could draw 125+ Amps if running full out.

The combined current from all panels being just about 45 Amps is going to be a bit slim for 800 Amp hours of battery; barely over 5% charge rate. Do you plan on picking up a couple more panels? If so you'd have four per controller and should wire both for that now, rather than change wiring later.

jimbob01

Re: off grid boat system set up

yes of course...4 strings..
the short circuit current is 8.5 amp on the panels
the over current protection is 15 amp...

jimbob01

Re: off grid boat system set up

i was going to wire 4 panels in to no 1 c.c...2 strings of 2 in series
2 panels in to no 2 c.c in series.
then add some more panels soon as i can get them.. another 2 in series so i end up with 4 panels in each controller..
so a 150 amp fuse in line from the batts to the inverter?

Cariboocoot

Re: off grid boat system set up

jimbob01 wrote: »

i was going to wire 4 panels in to no 1 c.c...2 strings of 2 in series
2 panels in to no 2 c.c in series.
then add some more panels soon as i can get them.. another 2 in series so i end up with 4 panels in each controller..
so a 150 amp fuse in line from the batts to the inverter?

The technical requirement on the inverter is a 200 Amp fuse, as they base it on minimum Voltage of 21 @ maximum output power. Personally I would set the LVD at nominal 24 and use the 150 Amp fuse.

With the panels configured as two parallel strings of two in series you really don't need any fuses on them (only two parallel connections so it is not possible for one set to produce more current than the other set can handle should it short).

jimbob01

Re: off grid boat system set up

ok thanks... jim

jimbob01

Re: off grid boat system set up

if 1 set of panels did short could it not damage the c.c?

Cariboocoot

Re: off grid boat system set up

jimbob01 wrote: »

if 1 set of panels did short could it not damage the c.c?

Nope. A shorted panel set becomes a conductor, rather than a power source. All the controller would see is "no input" while the other set of panels feeds all its current through the short.

jimbob01

Re: off grid boat system set up

ok im learning :-)

westbranch

Re: off grid boat system set up

But you will want some form of disconnect between the PVs and CC.. A circuit breaker does a nice job. ~15A per string or a fuse

jimbob01

Re: off grid boat system set up

ok that would make me feel better also.....:-)

Cariboocoot

Re: off grid boat system set up

Clarification: fuses do not work as disconnects.

BTW, once the system is working you will not find you have a need for a PV disconnect. On the rare occasion when you do want to shut it down, covering the array and disconnecting the wire works fine.

jimbob01

Re: off grid boat system set up

ok thanks......

vtmaps

Re: off grid boat system set up

Cariboocoot wrote: »

BTW, once the system is working you will not find you have a need for a PV disconnect. On the rare occasion when you do want to shut it down, covering the array and disconnecting the wire works fine.

OK, I will concede that he doesn't literally need a PV disconnect. Nor does he need seat belts in a car.

This is not a small system, and I think any system of this size should have a combiner box with breakers. I just don't see trying to cover 1400 watts of panels on a boat, and disconnecting MC4 connectors with a potential 80 volts DC across them. While I'm at it... I think all the wires from the PV to the combiner should be inaccessible, and all wiring from the combiner to the controller should be in conduit.

--vtMaps

Cariboocoot

Re: off grid boat system set up

vtmaps wrote: »

OK, I will concede that he doesn't literally need a PV disconnect. Nor does he need seat belts in a car.

Not comparable at all.

This is not a small system, and I think any system of this size should have a combiner box with breakers. I just don't see trying to cover 1400 watts of panels on a boat, and disconnecting MC4 connectors with a potential 80 volts DC across them. While I'm at it... I think all the wires from the PV to the combiner should be inaccessible, and all wiring from the combiner to the controller should be in conduit.

--vtMaps

If you'd read the whole thread you'd see the panels are divided up between two charge controllers: four panels on one, two (expanding to four) on the other. No need for fuses or circuit breakers from a current protection POV.

Contrary to the nonsense generated by officious bureaucrats who think solar panels are going to destroy the world, they are really incredibly safe things to use and work with. On the extremely rare occasion when he may have to disconnect the array after installing it would not be any great feat to cover them to be sure the current is low enough to simply disconnect the wire. This simply is not something that needs to be done on a regular basis and thus justify installing a disconnect.

We are not looking at a GT install here with potentially hundreds of Volts that can easily arc and should have a 'snap' disconnect. You have to keep things in perspective.

zoneblue

Re: off grid boat system set up

Last weekend i had to gut and rearrange our dc disconnect to fit a deltec and WBJr. It was not ideal not having an outside pv disconnect, but hopefully this the last time ill need to rebuild the disconnect! And... i should have done it properly the first time.

Anyway i waited until it was dark, then got the mrs to hold the flash light while i reconnected the pv hot wire in the dark shed.

Got all the parts from NAWs, including proper carling inverter breaker, phew.

Will probably add a disconnecting combiner at some stage to get around the issue, and make it more code compliant at the same time. External disconnect soon to be required by law here.

Endurance

Re: off grid boat system set up

I found with the solar panels on my boat that you need more panels than you would if you put them on something that doesn't move. If this were on a house or similar fixed location, you would normally aim the panels somewhat south in the northern hemisphere for the best performance. But since a boat might be parked at pretty much angle, the best you can hope for is to put them flat on a roof or similar structure. That cuts into your solar harvest. The controller I have on my boat should max out at about 1,000 watts of panels. I have over 1,700 watts of panels and have never made enough power to exceed the capacity of my controller. It is possible that there could be a cold day in January where I would make too much power, but I don't use my boat in January. That has been my experience for what it's worth.