Cutoff switch from solar controller

[GlennWest]

I have 175amp fuses at batteries. When I do solar should I have a disconnect after it. 

[Randyretired]

I install fuses or breakers going from the batteries to the solar controller sized for the wire.  If you tap on to the wire after the existing fuse it still requires a breaker or fuse since the wire going to the solar will likely be smaller.  Either direct wired or through an existing fuse is acceptable as long as the solar wire and controller have adequate protection.

[GlennWest]

On mine my 175amp fuses are on batteries post. Goes from there to a bussbar. Solar, inverters, dc/dc converter all hook up on bussbar. So need fuse there leaving busbar? 85 amp inverter. 

[Sehc]

Fuses are sized to protect the wire or cable. You need a fuse to protect the wire from battery to bus bar. A fuse at bus bar to protect any change wire size. Example; 2/0awg battery to bus bar, 250-300 amp fuse at battery. 2awg bus to fuse panel, 150 amp fuse at bus bar. 

[GlennWest]

OK, I have #4 from batteries to bussbar. 175amp fuse at each battery. 3 batteries. From bussbar to solar controler also #4. So another fuse?

[oldjohnt]

Glenn, FWIW I agree with Randy and sehc's great advice above, here's my take and explanation, BUT I'm rusty as an old nail being retired for yearssssssssssssss as a power distribution engineer and codes change SO NO WARRANTY LOL .

1) To provide proper OVERCURRENT protection for CONDUCTORS wired to the battery, you match the fuse to the conductors rated ampacity. For example, if you used say 200 Amp wire FROM battery TO Buss Bar, you need a 200 amp fuse at the battery

2) However, if you attached say 100 amp wire FROM buss Bar TO another device YOU CANT PROPERLY PROTECT 100 AMP RATED WIRE WITH THAT PRIOR 200 AMP FUSE !!!!!!!! If 200 amps flowed it could overheat the 100 Amp wire !!!!!!!!!!!!!!!

3) THEREFORE to provide proper overcurrent protection for that smaller 100 Amp wire YOU NEED A 100 AMP FUSE TO PROTECT IT

 Take care Glenn

John T

[GlennWest]

But it is the same size wire. They will not be but 85 amps coming down it. Now If I need to protect the Victron 150/85. I have too much fuse then. The 175amp fuses are actually for the magnum inverters but they are on the batteries.

 

 

Edited May 21, 2020 by GlennWest

[Randyretired]

I am not sure I understand your system but it sounded as if 3 batteries each with a 175 amp fuse to the buss bar?  That can provide 175 amps x 3?  In any case I would want a disconnect for the solar controller.  If the solar controller  has a maximum of 85 amps I would probably install a fuse close to that such as 100 amps.  Fuses that size are pretty inexpensive and also function as a disconnect.  There are also DC breakers available that would work really well for this application.  I also fuse or add a breaker from the solar panels to the controller.  While the panels output is limited it provides a disconnect for safe maintenance. 

[GlennWest]

On the panels, you stated a breaker or fuse. Seeing only 40ish amps, is it necessary? Also panels are 4ish amps each. I was considering a cutoff switch there.

[justRich]

I put a marine on/off switch (a disconnect switch) between the solar panels and the charge controller.  
My feeling is that is an absolute must.

Is that what you mean by a "disconnect"?

 

[GlennWest]

yes. 

[oldjohnt]

Glenn, I'm not sure just what you're doing, so I will just offer a few thoughts.

An overcurrent protection device is 1) To protect the CONDUCTORS and 2) Placed at or near the source of energy that supplies the current such as a battery. If a battery feeds say an Inverter, the conductors are fused at the battery because if you waited until downstream at the inverter input to place a fuse, the conductors between battery and inverter are NOT protected. Yet if you like there's no harm in adding an On Off switch at an Inverter input, but the overcurrent protection is already taken care of. NOTE overcurrent protection could be EITHER a fuse orrrrrrrrrrrrrrrr a switch rated circuit breaker that provides BOTH a switch and protection

Typically the OUTPUT output of a device such as an Inverter or Generator or Solar Charge Controller have their own built in output overload protection TO PROTECT THE UNIT, not so much the outgoing conductors, although if the conductors were 40 amp and the units built in overload protection prevents more then 40 amps, BOTH are protected.

For safety and convenience I like a manual Cut Off switch on the PV input of my Solar Charge Controller. The conductors to a device if already don't need more overcurrent protection ONLY a switch if needed for safety and/or convenience.  As far as say where the huge cables connect to an Inverters input, the conductors are already protected at the battery, yet if you wanted for convenience you could use an extra On Off switch  there or you could have a switch (in addition to overcurrent protection) back near the batteries.

Overcurrent protection is required to protect the conductors, while an On Off switch may be used for convenience and/or added safety...........A switch rated circuit breaker can provide BOTH On Off switching PLUS overcurrent protection if needed and not located elsewhere. 

In places where you don't need any On Off switching, just overcurrent protection, I like to use fuses. However a proper rated switch rated Circuit Breaker TAKES CARE OF BOTH. 

FWIW I would advise a master On Off switch at say the battery output,,,,,,,,,,,,Catastrophic Fuse Protection at the battery output,,,,,,,,,fuse protection for any smaller wires leaving a master buss,,,,,,,,,,,,,,,,,,,,On Off switch at the PV Input on a solar charge controller

I like fuses in situations where its more for catastrophic protection and you're NOT going to need On Off switching. If you need BOTH switching and protection, I like switchable breakers. 

Glenn, your system is very complex and Im not there and have no diagrams so its hard sitting here to answer all your questions, I apologize, this is the best I have to offer from here I hope you can take my theory and reasoning and figure it out?????

 

Take care Glenn

 

John T

[Randyretired]

How the solar panels are wired will determine the voltage and amps.  Panels wired in series increase volts and parallel increase amps.  Solar panels are rated in watts but different types of panels produce the watts with different amps and voltage.  Some panels can be optioned to provide 2 or more voltages but the watts stay the same.  High voltage DC can be very deadly.

On ebay and other places a number of DC breakers for various amps and voltages are available and relatively inexpensive.  These provide easy disconnect and overload protection.   I have used these for our solar and these have worked for us. My recommendation would be to use these (sized correctly)  on the wire leading to the solar controller and from the panels to the controller.  That would be the safest way but I don't think anyone will be checking so it is your choice.

[GlennWest]

Randy you mentioned Ebay for DC breaker. Are you stating cheap chinese breaker are ok? I was planning if going that route, Morningstar breakers

[Randyretired]

I have used some cheap breakers without a problem but we probably get what we pay for.  I would certainly have more confidence in Morningstar.  Many name brands are also made in China but usually to a better standard.

[DesertMiner]

Glenn... what are you looking at for voltage coming from your solar?  Make sure the c/b’s are d/c rated for your needs.

 

[oldjohnt]

Glenn, in our shop we leaned towards Square D and GE etc when specifying circuit breakers for our contractors or in house electricians,  but that's NOT to say a cheaper brand may not suffice. That has to be your choice and based on your research and budget.   You already know you need them rated for DC and to have an adequate voltage rating based on your configuration (see below) and likewise current based on the same. Since an individual solar panel (relative low energy, maybe a few hundred watts, NOT a battery with thousands of amps capability) has its own inherent max current and max short circuit current capacity, breakers there aren't as much of a life safety concern (to me, my opinion) as those in my house panel, yet sure if you have 1000 or more watts up on the roof (or sure even lower for that matter) such still can use protection. NOTE due to the solar panels relative low energy, low max current or relatively low max short circuit current capacity "some" people don't use circuit breakers up top. The ONLY reason I mention that is I "thought" you asked about  a "switch" up there ??? If I was going to add something UP THERE it would be a circuit breaker NOT a simple switch. Again this is YOUR choice  not my personal engineers opinion. As you have already decided (I think?) a cut off switch is good to have at the controllers input.

 I thought you already designed your solar panel layout ?? I like using what are called 24 Volt Panels (Vmp higher) versus so called 12 Volt,,,,,,,,,,,,,,I like series and/or series/parallel yet don't like to go over a net voltage of so called 48 Volts sent down from panel combiner boxes to the Solar Charge Controller which is what I'm running and my Vmp is often over 70 volts. While an MPPT controller may accept over 100 Volts PV input, I feel better keeping under 100 which my 70+ falls within.........If you configured at a so called 96 volts up top (say two 48 volters in series) you could be looking at well over a hundred volts down.  Of course higher voltage (series connections) up top = less current you have to bring down. 

There's also the concern with possible shading and roof real estate when deciding on series or parallel or series/parallel all based on your RV but that's too much to get into not being there....   

 You ask good questions, you got this

John T 

[Sehc]

Three batteries. Three 4awg cables to one bus bar. Three separate 175 amp fuses. One 4awg from the bus bar to load. Dead short in last 4awg could pull 525 amps from the bank. 4awg can not handle that.  I use marine grade wire so my ampere ratings could be different than yours. Marine wire is rated at 205 degree Celsius. I would have 150 amp fuses at each battery and another 150 amp fuse at the other side of the bus bar.  

As breakers. The DC "interrupt capacity" is the rating you want to know. Remember a shorted battery can have tens of thousands amperes for a short time and weld the contacts in a breaker.  Blue Sea, known for their quality, only have DC Breakers up to 200 amps.

The panel to controller usually doesn't need fusing. There are exceptions with more than 3 panels in parallel. But a switch is good to have if needing to disconnect batteries or controller for any reason. . 

[GlennWest]

The #4 is to/from solar controller. I will have #2/0 to inverters. Also I have decided on my system. I was asking about disconnects for anything that might go wrong. Also you got me questions my fuses now. I put protection as close to battery as possible but have opened up 525amps to supply a inverter. Going to remove those fuses and use on bussbars to inverters. 

Edited May 22, 2020 by GlennWest

[hemsteadc]

Imho  there's nothing in solar that needs to be fused. A cutoff between panels and controller is nice.

Edited May 22, 2020 by hemsteadc

[Randyretired]

When I installed my solar the Outback installation manual specifically called for DC breakers between the controller and the batteries and between the controller and the panels.  What does your solar controller installation manual state?  That is what I would follow.

[GlennWest]

I am planning on the Victron 150/85. It does not have a fan. Fully programable for my lithium paks. Not overly costly. It will handle 4850 watts solar at 48v. My planned set up will be near 4300 watts solar. Victron call for a 120amp fuse after the controller. Mentions nothing on incoming.

Edited May 22, 2020 by GlennWest

[DesertMiner]

Glenn....Have you given any thought to using multiple MPPT's for you setup?  With larger arrays it can be beneficial to have multiple "smaller" systems working together. 

On edit: Looks like your 150/85 is on sale if you are looking to buy soon.

Edited May 22, 2020 by DesertMiner

[GlennWest]

Panels I am looking at, can fit 7 on each side. Total of 4830watts. wired 2of 7 gives me VMP 114.6, VOC 136,04, IMP 42.14,  83.9 charging amps. That is border line for  the 150/85 but according to Victron selection chart this is one recommended. It should never see this high though so. Emarine has it for $638.

Edited May 22, 2020 by GlennWest

[Zulu]

Do you have a wiring diagram? Even a rough one?