will i need a combiner box or can panels safely be paralleled without one?

[humbll]

I am setting up a 4 panel (100w ea) 12v off grid system. I found a y connector which allows me to connect all 4 panels together (m/ffff and f/mmmm MC4 "y" cable). Is it safe to connect these 4 panels in parallel without going through a combiner box? I intend to put a fuse between the panels and the charge controller, also a fuse between the controller and battery bank, and another between battery bank and inverter. Thanks for the help.

[inetdog]

I am setting up a 4 panel (100w ea) 12v off grid system. I found a y connector which allows me to connect all 4 panels together (m/ffff and f/mmmm MC4 "y" cable). Is it safe to connect these 4 panels in parallel without going through a combiner box? I intend to put a fuse between the panels and the charge controller, also a fuse between the controller and battery bank, and another between battery bank and inverter. Thanks for the help.

Safety, and the National Electrical Code, require that when three or more panels or strings of panels are paralleled there must be an individual fuse for each panel or string of panels.
This is to protect a damaged panel and its wiring from being subjected to high reverse current supplied by the other two or more panels working together.

You do not need a combiner box, but it is the simplest way to mount the needed string fuses. You could use inline fuse holders instead if you can find any with MC4 connectors and a suitable DC current interrupting rating.

[humbll]

ok thank you very much

[humbll]

do you happen to know what amp rating the fuses for each panel should have?

[littleharbor]

Something like this should work.
Fuse rating should be on the data label on your panels.MC-4 fuse holder.jpg

[ButchDeal]

Or you could switch to an MPPT CC and put the modules all in series. You would get better performance and eliminate 4 fuses and the 4 way cable harness.

[SunEagle]

Or you could switch to an MPPT CC and put the modules all in series. You would get better performance and eliminate 4 fuses and the 4 way cable harness.

Which would be a better plan since the OP has 400 watts of panels and a PWM CC would be wasting wattage.

[inetdog]

do you happen to know what amp rating the fuses for each panel should have?

The label on each panel should list the maximum series fuse size. You can use any value between about 1.25 x Isc and the listed maximum.

[Sunking]

Why are you using Battery Panels and a PWM charger? You are pissing away money and materials. You could have done this for 1/2 the cost you paid.

[humbll]

Why are you using Battery Panels and a PWM charger? You are pissing away money and materials. You could have done this for 1/2 the cost you paid.

my goal with this system is to make the batteries last as long as possible, i read that PWM controllers do a better job of keeping batteries alive longer.

[humbll]

i decided on 12v volt system so that if a panel or battery failed i could simply remove it from the system and still have some power. This is an emergency laptop charger/rechargable battery charging battery station/run small 12v trucker fan for in case SHTF. If I go with MPPT and hook everything in series then a battery fails i would have to have a different inverter, and i had read that the PWM CC are better at keeping batteries alive longer.

[SunEagle]

i decided on 12v volt system so that if a panel or battery failed i could simply remove it from the system and still have some power. This is an emergency laptop charger/rechargable battery charging battery station/run small 12v trucker fan for in case SHTF. If I go with MPPT and hook everything in series then a battery fails i would have to have a different inverter, and i had read that the PWM CC are better at keeping batteries alive longer.

You were told wrong. It is not the charger that normally determines the battery life. It is how big of an inverter is used and how much you drain your batteries daily. The MPPT charge controller allows you to utilize your panel wattage more efficiently by converting all input wattage to output charging wattage. A PWM CC converts input amps to output amps for charging and usually throws away about 33% once you get above 250 watts.

[humbll]

You were told wrong. It is not the charger that normally determines the battery life. It is how big of an inverter is used and how much you drain your batteries daily. The MPPT charge controller allows you to utilize your panel wattage more efficiently by converting all input wattage to output charging wattage. A PWM CC converts input amps to output amps for charging and usually throws away about 33% once you get above 250 watts.

well it isnt too late to switch to MPPT, i can send the PWM CC back, it has not even arrived yet. That was my main concern, battery life. If Shtf i will not be able to buy a new battery or inverter... so i figured to buy a couple inverters and keep the batteries wired for 12v, and if one or more failed then i would still be able to run the inverter to power my laptop.

[SunEagle]

well it isnt too late to switch to MPPT, i can send the PWM CC back, it has not even arrived yet. That was my main concern, battery life. If Shtf i will not be able to buy a new battery or inverter... so i figured to buy a couple inverters and keep the batteries wired for 12v, and if one or more failed then i would still be able to run the inverter to power my laptop.

Well having batteries wired in parallel is also a double edge sword. It gets you more Ah but it can lead to unequal charging and discharging which will kill off one or more of the batteries. IMO that is a SHTF event when a battery banks dies an early death.

[humbll]

Well having batteries wired in parallel is also a double edge sword. It gets you more Ah but it can lead to unequal charging and discharging which will kill off one or more of the batteries. IMO that is a SHTF event when a battery banks dies an early death.

the only other option i can think of is to buy several inverters capable of running at different voltages, one for the 3 batteries in series at 36v, one for 24v for in case 1 battery fails, and 1 for 12v for if 2 batteries fail. If i am using 1/0 cable between the batteries that seems like it would allow the system to function properly, but then again i am new to the world of solar.