When is a battery shutoff switch actually needed?

[livingthefreeway]

I am in the process of creating plans for a large scale RV solar installation. It will be a 48V system, and with that comes some caveats of having the added difficulty of finding 48V nominal rated components. For example, at first I had planned on using simple Blue Sea Systems 6006 battery switches to act as a battery disconnect, only to find out from this forum that they are rated at a max voltage of 48V, meaning the would not be suitable for a 48V system that typically sees charging voltages of ~55V.

I was able to find one battery switch that is rated for up to 64V, however it is also quite expensive ($200 USD).

This leads me to my question, if my system is already accounting for emergency disconnect via fusing, (a Class T fuse as a SHTF fuse, and a ANN fuse inside the lynx shunt as a working fuse.), is the manual activated battery disconnect switch simply just a convenience for mateniance, and not a necessity? Or is there some other situation I'm not accounting for?

See my two attached solar wiring diagrams. One with a $200 battery disconnect switch, and one without.

Thanks for your replies

 

[DIYrich]

I have batteries without a switch. I tried a switch, it overheated, so I returned it. If I have to do something with a battery, I have to shut the batteris down, and turn off the breaker at the inverter. If I don't, I get sparks when attaching, detaching, and risk shorting something.

Not a big deal shutting down all the batteries. Hassle when first putting it all together, and making minor tweaks.

Note: the bms will turn off the battery, but the Energy from the inverter is still there. Hence needing a full shutdown.

If your victrons don't have a battery breaker, then you will want a switch to avoid having to shutdown the entire system.

 

[Checkthisout]

Switch is a convenient place to disconnect power. You can use two more affordable ones in parallel if you like.

 

[timselectric]

Disconnect switches are for maintenance and emergencies. Handy for the first, hopefully never needed for the second.

 

[livingthefreeway]

I have batteries without a switch. I tried a switch, it overheated, so I returned it. If I have to do something with a battery, I have to shut the batteris down, and turn off the breaker at the inverter. If I don't, I get sparks when attaching, detaching, and risk shorting something.

Not a big deal shutting down all the batteries. Hassle when first putting it all together, and making minor tweaks.

Note: the bms will turn off the battery, but the Energy from the inverter is still there. Hence needing a full shutdown.

If your victrons don't have a battery breaker, then you will want a switch to avoid having to shutdown the entire system.

If I understand correctly, are you saying your inverter still draws enough current to create sparks on detaching even with your inverter turned off?

I do not have a switch or breaker on the DC side of my inverters. (Although I do have a fuse) The inverters do have an on/off switch on the case to power on or off the inverter function. Would it be likely that I’d still see sparks on detaching even with the inverter fully powered off?

 

[DIYrich]

If I understand correctly, are you saying your inverter still draws enough current to create sparks on detaching even with your inverter turned off?

Inverter has a capacitor on the battery side.

I do not have a switch or breaker on the DC side of my inverters. (Although I do have a fuse) The inverters do have an on/off switch on the case to power on or off the inverter function. Would it be likely that I’d still see sparks on detaching even with the inverter fully powered off?

Maybe. Depends on whether the inverter discharges the capacitor when it turns off. May not be able to if it is directly connected to the battery.

 

[chrisski]

If I understand correctly, are you saying your inverter still draws enough current to create sparks on detaching even with your inverter turned off?

In my 24 RV build, My 3000 watt inverter, 70 amp 24 volt DC—> 12 volt DC Converter, and 37.5 amp AC to DC Converter in my 24 volt system created a Spark I could see through the plastic case of a Blue Sea Switch. Mostly was the inverter that sparked, but those other two components sparked also.

I recommend having a way to precharge that system witgh a resistor so it does not spark. I used this to build mine:

Inverter Disconnect Switch with Precharge

To get the paper, click on the orange button at the top of this page. This circuit is designed as a disconnect switch that allows the user to pre-charge the inverter capacitors before turning the switch completely on. 26 June 2020 update: At...

diysolarforum.com

 

[OffGridForGood]

Or just wire in a parallel 2P momentary switch on a resistor to the 2P disconnect, and label it "Pre-charge circuit, hold for 10-seconds"
okay low tech, but it works for me!

 

[JoeHam]

You don’t NEED a switch just like you don’t need air conditioning in the summer.

But it’s sure nice to have sometimes.

And a switch is such a small cost of your system it seems prudent to have one.