Dual battery disconnect

[atatistcheff]

Looking for some thoughts on a battery disconnect arrangement for an RV mounted solar system. What I'm trying to address is the guidance that you should not connect your solar panels to your charge controller without the battery connected. I've done that accidentally once or twice and haven't broken anything but I'm still trying to follow that best practice.

Using two XT-60/90 connectors for solar and battery I just remember to "connect the battery first and disconnect the solar first" when I'm disconnecting the battery from the RV. However, a more idiot proof design would be a single switch that disconnects both sources at the same time. The issue I'm seeing is that most (all?) battery disconnect switches are SPST. I really need a DPST (or DPDT would work too) with an amperage rated high enough. Now, I'm not running an inverter so the current doesn't need to be enormous but a measly 10A switch probably wouldn't be a good idea.

Any thoughts/recommendations would be appreciated.

 

[HRTKD]

I suppose if you wanted both circuits disconnected at the same time you could use a 4 pole circuit breaker. The amp requirements for the PV side would be different from the battery side, so different sets of circuit breakers.

 

[atatistcheff]

That's a good idea, however again all I can find on Amazon is panel mount circuit breakers. All the surface mount ones are just single circuit. I think perhaps putting two of these side-by-side is about the best option so far. Thanks!

 

[HRTKD]

That's a good idea, however again all I can find on Amazon is panel mount circuit breakers. All the surface mount ones are just single circuit. I think perhaps putting two of these side-by-side is about the best option so far. Thanks!

I like the panel mount method. It takes up less room. I put mine on DIN rail, not in a box.

 

[atatistcheff]

I just looked at those DIN mount circuit breakers. I've never tried them before but that looks like a really good option. Thanks!

 

[HRTKD]

Be sure you're getting breakers that are actually DC breakers. If it mentions Mhz anywhere in the description it isn't a dedicated DC breaker. I made that mistake and bought AC breakers. Fortunately, they weren't that expensive.

 

[atatistcheff]

Yes, I did notice that and ordered the Chtaixi DC Disconnect Switch C50. Thanks again!

 

[HRTKD]

If you're looking for higher quality breakers, check out midnitesolar.com. I've bought a couple from there. Some of them are polarized, so be aware of that when installing.

 

[chrisski]

I use DIN mounted circuit breakers in a project box with a lid installed for access.

 

[SwitchDoctor]

First point - I'm no expert. I've just had to learn a lot to get my system up and running.

Two points i'd like to make:
1) Be VERY careful of DC breakers. Whilst the feed from the panels only goes one way. The battery connections run current in both directions so it's vital to use a non-polarised breaker on your battery connections.
2) I have the same warning on my inverter re connecting batteries first. (Caveat - i know nothing) - I figured that this was due to current inrush (and out) if you connect the batteries to an already live system. I use a TOMZN branded breaker but bypassed with switch and a 500 ohm 25w resistor. That way when i want to connect the batteries i close the bypass switch 1st, the batteries are connected via the resistor and will pre-balance the voltages and so avoid big sparks / current peaks when i close the breaker and the batteries connect.

 

[0truck0]

DC circuit breaker. Dont bother trying to have one that does both at the same time. It is only two, so just flip two breakers!!


Do internet search for "DC circuit breakers" and find all you need. Get the right amperage one, a little higher than what you need is fine.
I have the one on the right and the 2 from the left styles in use, multiple vehicles over the years....
I like the right one best because the bare wire connections will end up protected under the clear caps and no way to short anything out. The others use a rubber cap to protect the connection and can dislodge easy and be left open to a short if something touches it that can short out...

I use one on positive from solar panel, and one on positive from battery.
Disconnect the solar first. Disconnect the battery if needed/desired.
Connect the battery back first, then the solar panel last.

By doing panel this way you are keeping stray and high voltages from hitting the panel and the controller. The battery protects from voltage spikes, is why you disconnect the solar while everything is still on the battery, then reconn the solar last. The battery is the key, it protects.

I also use one between the alternator and the battery bc the solar is usually all I ever need, so almost never connect the alternator

 

[HRTKD]

DC circuit breaker. Dont bother trying to have one that does both at the same time. It is only two, so just flip two breakers!!

View attachment 177009
Do internet search for "DC circuit breakers" and find all you need. Get the right amperage one, a little higher than what you need is fine.
I have the one on the right and the 2 from the left styles in use, multiple vehicles over the years....
I like the right one best because the bare wire connections will end up protected under the clear caps and no way to short anything out. The others use a rubber cap to protect the connection and can dislodge easy and be left open to a short if something touches it that can short out...

I use one on positive from solar panel, and one on positive from battery.
Disconnect the solar first. Disconnect the battery if needed/desired.
Connect the battery back first, then the solar panel last.

By doing panel this way you are keeping stray and high voltages from hitting the panel and the controller. The battery protects from voltage spikes, is why you disconnect the solar while everything is still on the battery, then reconn the solar last. The battery is the key, it protects.

I also use one between the alternator and the battery bc the solar is usually all I ever need, so almost never connect the alternator

In general, we consider the item on the right to be "audio quality" and not good enough for most implementations that include high amperage batteries or loads (inverters). We've seen items like you referred to melting once a nominal load is applied.

Blue Seas (the item second from the right) is good quality and I use those in my system.

 

[Dicko]

In general, we consider the item on the right to be "audio quality" and not good enough for most implementations that include high amperage batteries or loads (inverters). We've seen items like you referred to melting once a nominal load is applied.

Blue Seas (the item second from the right) is good quality and I use those in my system.

I have had many of the audio style breakdown and not function properly. I wouldn,t consider them for any 12 volt vehicle system again. Blue sea are a good product.

 

[0truck0]

I just randomly took a photo off internet search as example.
Anyway, I assume a 50 amp breaker would not melt under 20 amp load. Am I wrong I also have a 100 amp breaker in use that I assume would never melt since it typically only sees 5-10 amps of power.
Are you talking about using under-rated amperage breakers for higher amp use? Or about using the correct amp rating for the application? BC, yes, using a 10 amp breaker and trying to run 50 amps through it would be a problem, I think this is univerally understood. If the breakers are melting when properly used then there is a huge liability issue at play, and America likes to litigate these things...

 

[HRTKD]

I just randomly took a photo off internet search as example.
Anyway, I assume a 50 amp breaker would not melt under 20 amp load. Am I wrong I also have a 100 amp breaker in use that I assume would never melt since it typically only sees 5-10 amps of power.
Are you talking about using under-rated amperage breakers for higher amp use? Or about using the correct amp rating for the application? BC, yes, using a 10 amp breaker and trying to run 50 amps through it would be a problem, I think this is univerally understood. If the breakers are melting when properly used then there is a huge liability issue at play, and America likes to litigate these things...

In the cases we've seen on the forum, the breakers or fuses were properly sized. They just couldn't handle what they were rated for. Sometimes not even close to what they were rated for.

 

[0truck0]

thanks for the heads up. Hopefully this was a defect rather than the norm. No product manufacturing process is without defects, no matter how good the design, build or process, that is just the fact of manufacturing. Hopefully that is what you see on forum post, and who knows what really happened when the fuse burned up, did the person even know what they knew....