diy solar

diy solar

What disconnect did you guys use?

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Stewfish

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Oct 20, 2020
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I'm leaning towards a few of these so my wife or any visitors can easily see how to turn off the power. https://www.amazon.com/dp/B000MMC824/ref=cm_sw_r_cp_apa_fabc_6ZSH6ENZFQH6XBDAWNYV?psc=1

I like this style though, but it's $846

I have a combiner box, but if I'm running up to 100a controller to my batteries I want a legit easy to find emergency shut off switch at the batteries and maybe also at the combiner box 100ft away for our RV/camp setup where the panels are.

Midnight solar combiner with red switch:
For our future build this summer on our other cabin property with 50 panels I was thinking the midnight solar combiner box with built in switch on the front.

Current setup:
For the current RV combiner box it has a main breaker that feeds the batteries. I thought a big red switch or something below the combiner box and in the RV above the batteries in the battery compartment would be good/ safe/ and smart for my wife or someone who doesn't know my layout. Stickers warnings would be good too.

Disconnects I have seen:
An electrician installed a huge switch on my Dad's generator to turn off grid power, it was a lot bigger than the home depot 60amp 240v, but that was AC.
I've seen pull tabs, but that requires lifting the lid and then pulling it out and I'm not sure my wife or a friend would do that easily with adrenaline coursing through their veins. I need a big switch.
I have seen people use the blue seas battery switch like above, but I was thinking a large lever type. That's a lot of amps tlwith big arcs possible.

I didnt think I could use a home depot/Lowes AC switch with low volts high amps DC.

Thanks guys!


Another marine switch, 360a and for DC, but not quit just an on/off for emergencies.
 
Last edited:
First: Don't use a switch on DC that is not specifically rated for DC. DC arcing is a lot worse than AC arcing.

What are you talking about disconnecting? Battery? Solar Panels? Inverter?
 
FilterGuy said:
First: Don't use a switch on DC that is not specifically rated for DC. DC arcing is a lot worse than AC arcing.

What are you talking about disconnecting? Battery? Solar Panels? Inverter?
Click to expand...
Yeah, that's what I thought, stay away from AC. I'd like to switch all if them for safety, well I don't have an inverter though, just RV batteries that run my furnace fan and other 12v stuff. May want to put in an inverter someday so I'm researching.

I read fuses can still arc when blown so I need to research that more about between the batteries and inverter. For now between the panels and batteries is my goal.

I'd also like to look at designs of systems to make sure I don't forget something, but also to see pros and cons of systems. I do know I want to go with combiner boxes with breakers versus inline branch connectors and MC4 fuses.

Saw this for example:
Screenshot_20210130-223712.png
 
Last edited:
On an RV?
List what voltages and currents you intend to switch.
That would be Voc and Isc for PV array, maximum DC loads running off 12V, etc.
If you add an inverter (that doesn't have a built-in switch), it's maximum input current.

Fuse at your battery should be capable of interrupting whatever it can deliver into a dead short. If the batteries have a CCA rating (e.g. 700A for some car batteries), short circuit current will be 3 times that (e.g. 2100A). If you have a lithium battery it could be 20,000A. There are fuses and breakers intended for those applications.

"Birdhouse" is a special disconnect to meet code requirements for houses, not applicable to your RV.
Those rotary switches and solar safety disconnects have their applications. The big knife switch is like some I use for 600VDC PV arrays, but you wouldn't have that. The rotary switch would be a good battery disconnect, but I don't need it because my inverters have breakers inside.
 
Hedges said:
On an RV?
List what voltages and currents you intend to switch.
That would be Voc and Isc for PV array, maximum DC loads running off 12V, etc.
If you add an inverter (that doesn't have a built-in switch), it's maximum input current.

Fuse at your battery should be capable of interrupting whatever it can deliver into a dead short. If the batteries have a CCA rating (e.g. 700A for some car batteries), short circuit current will be 3 times that (e.g. 2100A). If you have a lithium battery it could be 20,000A. There are fuses and breakers intended for those applications.

"Birdhouse" is a special disconnect to meet code requirements for houses, not applicable to your RV.
Those rotary switches and solar safety disconnects have their applications. The big knife switch is like some I use for 600VDC PV arrays, but you wouldn't have that. The rotary switch would be a good battery disconnect, but I don't need it because my inverters have breakers inside.
Click to expand...
-PV is 30voc each at 3s = 90voc 8amps each panel
-Charge controller is 100a going to 12v battery
-The RV max main load circuit breaker is 30a between the battery and the + bus bar.
I don't plan to have an inverter until I put together my 48v system this summer. So it would all be to just run my 12v system in the RV.
My RV batteries are 4 golf cart 6v lead acid batteries in 2s2p.


Here is a video about how normal glass fuses don't work. Just like Hedges references about high amps like 20,000a. It Looks like the JJM350 class T is a solid fuse I could mount off the battery lug. Or the Seimens NH00 knife type fuses for individual PV strings. But still, what about the best bang for buck on/off switch. Whats the knife switch you mentioned? I'm thinking those blue seas are best for my wife, no exposed metal, easy on off labels.

Knife switch like this?
 
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That knife switch isn't snap-action.
I meant like the Siemens solar safety disconnect you listed. I have the Square-D Heavy Duty 600V 30A 3-pole switch between PV string and an inverter.
Graingers has good selection, but look around and prices can be 1/2 or 1/3 of their msrp prices.

For PV string ...

90Voc DC at 8A, circuit breakers from Midnight are one way to go. Most are polarized, interrupt current in one direction so I have a concern about using them for 3 or more parallel PV strings where backfeed over-current protection is required.

Square D Q0 2-pole circuit breakers would also work. Although UL listed up to 48V (that's for a single pole), Square D says with two poles interrupting both positive and negative they're good up to 125V. AIC rating up to a few kA so OK for small battery banks.

For charge controller ...

This is a bi-directional application (intended charge current and battery discharge into a fault) so I don't like polarized breakers. Midnight and Schneider have some non-polarized breakers. Midnight has 175A and 250A non-polarized breakers with high AIC ratings for fault currents.

Whatever battery can deliver is available as fault current, so either this breaker or a main few behind it needs to be able to interrupt that (could be 3kA to 20kA)
Without looking them up I'll assume your golf cart batteries can deliver 3000A into a short circuit, so 2s2p could deliver 6000A. After evaluating cable resistance to the first possible short circuit, you could reduce that amount.

The red switch you showed would work for disconnecting charge controller and inverter, up to its voltage rating (some of those switches are ok to 32V but not 48 ... 60V.)
I'm assuming switch might be opened under load, but not while a short carries fault current - fuse should blow in that case; switch just has to carry current long enough.

Some switches especially for European market have full ratings for AC but greatly reduced voltage/current when interrupting DC. But they also note they can carry full current at DC so long as not switched while carrying current. Would serve as a disconnect to prevent battery drain but not to shut off during operation.

Good to have a fuse able to interrupt battery short-circuit current. Could be MRBF at each battery positive terminal, class T for the bank ...
With relatively low voltage and short-circuit current capability of your present golf-cart batteries, the cheaper options could be sufficient. I think some brands of ANL have ratings high enough.
 
Hedges said:
On an RV?
List what voltages and currents you intend to switch.
That would be Voc and Isc for PV array, maximum DC loads running off 12V, etc.
If you add an inverter (that doesn't have a built-in switch), it's maximum input current.

Fuse at your battery should be capable of interrupting whatever it can deliver into a dead short. If the batteries have a CCA rating (e.g. 700A for some car batteries), short circuit current will be 3 times that (e.g. 2100A). If you have a lithium battery it could be 20,000A. There are fuses and breakers intended for those applications.

"Birdhouse" is a special disconnect to meet code requirements for houses, not applicable to your RV.
Those rotary switches and solar safety disconnects have their applications. The big knife switch is like some I use for 600VDC PV arrays, but you wouldn't have that. The rotary switch would be a good battery disconnect, but I don't need it because my inverters have breakers inside.
Click to expand...
Does anyone know about these 200a + blue seas breakers? I know it's not rated to 20000a fornlithium for arcs, but its 5000 @12v. Might work good for my four RV lead acid batteries (not sure how that's calculated). I have a class T fuse coming, but it will be 2 weeks and this would be here tomorrow :(

Blue seas is the highest quality boat stuff you can buy.
 
Stewfish said:
Does anyone know about these 200a + blue seas breakers? I know it's not rated to 20000a fornlithium for arcs, but its 5000 @12v. Might work good for my four RV lead acid batteries (not sure how that's calculated). I have a class T fuse coming, but it will be 2 weeks and this would be here tomorrow :(

Blue seas is the highest quality boat stuff you can buy.
Click to expand...

187-Series Circuit Breaker - Surface Mount 200A - Blue Sea Systems

Thermal circuit breakers provide heavy duty circuit protection for 25 to 200 Amp loads when switching and circuit protection are both required.
www.bluesea.com www.bluesea.com

"
Interrupt Capacity
information.png
5000A @ 12V
3000A @ 24V
1500A @ 42V
"

So long as an authentic Blue Sea breaker and not a knock-off or counterfeit, that is reasonable for 12V LA battery.

I've seen mention of 4000A short circuit current for a 100Ah 12V AGM.
Do you have a "Cranking Amps" spec for your batteries? That's current into 7.5V, and based on internal resistance. Multiply by 3 to get an estimate of short-circuit current per battery.

Compute internal resistance from that spec and add calculated cable resistance to first location where a short could happen, and you should have a reduced available short-circuit current.
 
Hedges said:

187-Series Circuit Breaker - Surface Mount 200A - Blue Sea Systems

Thermal circuit breakers provide heavy duty circuit protection for 25 to 200 Amp loads when switching and circuit protection are both required.
www.bluesea.com www.bluesea.com

"
Interrupt Capacity
information.png
5000A @ 12V
3000A @ 24V
1500A @ 42V
"

So long as an authentic Blue Sea breaker and not a knock-off or counterfeit, that is reasonable for 12V LA battery.

I've seen mention of 4000A short circuit current for a 100Ah 12V AGM.
Do you have a "Cranking Amps" spec for your batteries? That's current into 7.5V, and based on internal resistance. Multiply by 3 to get an estimate of short-circuit current per battery.

Compute internal resistance from that spec and add calculated cable resistance to first location where a short could happen, and you should have a reduced available short-circuit current.
Click to expand...
I think bc they are golfcart batteries it it doesn't mention the cold cranking apps so here's a picture of the label. They are four Costco interstate golf cart batteries in 2s2p. I'm thinking it's high amo output in order to move a golfcart.


IMG_20210208_110529365.jpg
 
I don't find the exact model at Interstate. One has same 210 AH, but RC 383 instead of 105?

Probably reasonable to use the breaker. Just avoid causing shorts.

Under load, see how hot everything is reading. Including that oversize ring terminal with hammer crimp.
Breakers, fuses, connections ... lots of things show the effect of I^2R when I is 100A or more.
 
I ordered the next day delivery breaker until the Class T fuse arrives. I do have a point and shoot thermometer from before they got popular that I use to check my bearing hub temps, etc so I will keep n eye out for sure.
 
Stewfish said:
Found these indoor midnight solar disconnect switches

Panel mount breakers in a mini DC disco box
Click to expand...
There's a YouTube video that shows the electrical code needs to break both the positive and negative connections. This was just changed recently (2020?).

Midnight Solar looks like they only break the positive connection. I instead went with a Siemens GNF221RA disconnect. Just ordered it. Hopefully it works.

SIEMENS 2P 30A 240V General Duty Safety Switch Outdoor, Non-Fusible, ANSI 61 Grey - - Amazon.com

SIEMENS 2P 30A 240V General Duty Safety Switch Outdoor, Non-Fusible, ANSI 61 Grey - - Amazon.com
www.amazon.com
 
I feel better with both PV poles disconnected.
Some Midnight breakers use two poles to get 300VDC out of a 150VDC breaker. You can wire that to break positive and negative.

That Siemens switch appears to be for AC only, not DC.

There are a variety of options, depending on voltage and current rating you need.
Some Square D QO breakers can be used for 48VDC (single pole) or 125VDC (two poles.)

Here's one DC switch I use. Paid less that this somewhere.
600V AC/DC, 30A, 3PST non-fusible.
That was originally to open just the positive of high voltage PV strings.

https://www.graybar.com/heavy-duty-disconnect-non-fusible-single-throw-30a-600vac-dc-3p3w/p/88240967

My new inverters have rotary DC disconnect included. I plan to use these switches to interrupt the PV string in another location, then have MC connectors inside I can plug/unplug to rearrange which inverter some panels go to.
 
Hedges said:
I feel better with both PV poles disconnected.
Some Midnight breakers use two poles to get 300VDC out of a 150VDC breaker. You can wire that to break positive and negative.

That Siemens switch appears to be for AC only, not DC.

There are a variety of options, depending on voltage and current rating you need.
Some Square D QO breakers can be used for 48VDC (single pole) or 125VDC (two poles.)

Here's one DC switch I use. Paid less that this somewhere.
600V AC/DC, 30A, 3PST non-fusible.
That was originally to open just the positive of high voltage PV strings.

https://www.graybar.com/heavy-duty-disconnect-non-fusible-single-throw-30a-600vac-dc-3p3w/p/88240967

My new inverters have rotary DC disconnect included. I plan to use these switches to interrupt the PV string in another location, then have MC connectors inside I can plug/unplug to rearrange which inverter some panels go to.
Click to expand...

The first picture on Amazon shows it's rated AC and DC. This is just a knife switch and would work for either. I'm using inline MC4 fuses on my 4P2S 800 watts solar total, circuit breakers not necessary. At $54, outdoor rated, and 2 day delivery, this seems okay for my usage. I'll try to reply back with any pros/cons.
 
You're right - the label in the picture does say 250 VDC.
The text didn't and most listings only said AC, but I found one that shows DC (funny how wide a range of prices at different stores):


Others show same label, but didn't mention DC in text:



Here's a listing that shows inside (but picture is of a 3-pole, not 2-pole)

breakeroutlet.com

GNF221RA Outdoor Non-Fusible A/C Safety Single Phase Switch 30A Siemens

Siemens, Top of the Line General Duty GNF221RA Indoor single phase
breakeroutlet.com breakeroutlet.com

Let us know if it has a spring-loaded snap-action mechanism.
 
Hedges said:
You're right - the label in the picture does say 250 VDC.
The text didn't and most listings only said AC, but I found one that shows DC (funny how wide a range of prices at different stores):


Others show same label, but didn't mention DC in text:



Here's a listing that shows inside (but picture is of a 3-pole, not 2-pole)

breakeroutlet.com

GNF221RA Outdoor Non-Fusible A/C Safety Single Phase Switch 30A Siemens

Siemens, Top of the Line General Duty GNF221RA Indoor single phase
breakeroutlet.com breakeroutlet.com

Let us know if it has a spring-loaded snap-action mechanism.
Click to expand...

Just received it yesterday. It's a simple knife switch on a rotating shaft. It's not spring-loaded, just manual rotation. Yes, it's rated 250VDC, UL listed.

I

1622724999914.png
 
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