12V DC disconnect recommendation?

_OS_

Up to now I have used the on/off switch on my inverter to switch off the power when leaving my cabin but I plan to run a 12V line from the batteries to my cabin as well and I need something to disconnect the 12V line running to the cabin.

Today I do not have a switch or fuse at all and everything is hard wired which is probably not a good thing.

I have thought about buying one of the famous Midnite Mini-DC disconnects with matching chassis but they do not sell them over here and I guess the shipping charge is high from the US to Norway because of the weight/size.

Another option is to install a marine type battery disconnect like this one (or similar): http://www.boatersworld.com/product/196978266.htm. I can get one for $60.

A third option is to take the 12V from the load terminals on my SunSaver MPPT and use a smaller disconnect since the SS MPPT is limited to 15A only. 15A is sufficient but I do not get the option to disconnect the battery completely with this option.

I guess many of you have been there, done that. Any ideas?

Ole

nigtomdaw

Re: 12V DC disconnect recommendation?

For 12v or 24v these are two automotive cheap alternatives first is a switch second is a fused switch.

http://cgi.ebay.co.uk/BATTERY-ISOLATOR-SECURITY-SWITCH-100A-CUT-OFF-2-KEYS_W0QQitemZ200340965356QQcmdZViewItemQQptZUK_CarsParts_Vehicles_BoatEquipment_Accessories_SM?hash=item2ea54087ec&_trksid=p3286.c0.m14&_trkparms=65%3A12|66%3A2|39%3A1|72%3A1683|240%3A1318|301%3A1|293%3A1|294%3A50

http://cgi.ebay.co.uk/12V-DC-CAR-AUDIO-CIRCUIT-BREAKER-FUSE-140AMP-140-AMP_W0QQitemZ370213541110QQcmdZViewItemQQptZUK_Cars_Parts_Vehicles_Terminals_Cabling_ET?hash=item56327254f6&_trksid=p3286.c0.m14&_trkparms=65%3A12|66%3A2|39%3A1|72%3A1683|240%3A1318|301%3A1|293%3A1|294%3A50

This second one is shown as 140a i think they go as low as 30a definately 60 a

Mods sorry 4 using ebay but quickest way to find product. As OP like me lives in Europe hope this is OK.

You will find these products in automotive stores also

Nigel

BB.

Re: 12V DC disconnect recommendation?

It is OK to point to EBay for information...

But, typically, the links disappear within a month or so and so the thread becomes less useful for the next person who looks up this information.

That is why we try to limit pure EBay links.

-Bill

john p

Re: 12V DC disconnect recommendation?

Go to any good boating shop and you will find very well built dissconnect switches .. and as they are made for marine use they are very resistant to corosion.. much better than you will ever get from an auto parts store.:cool:

_OS_

Re: 12V DC disconnect recommendation?

I have almost made up my mind to order the Midnite Mini-DC disconnect now. My brother is going to buy one as well so maybe we can get a good price for two including shipping. We also want to order five 150VDC DIN breakers each as well.

I have sent e-mails to Wind-sun and Maverick solar and hopefully we will get a good deal. I also wanted to check with the Alternative Energy Store but their web-site has been down a while now.

_OS_

Re: 12V DC disconnect recommendation?

I have today ordered the Midnite 250A Mini-DC disconnect and five DC breakers. My brother ordered the same items so we could save some on the combined shipping. As always I will get back with pictures after I have installed the unit.

Ole

BB.

Re: 12V DC disconnect recommendation?

Also, for you guys in Europe--Feel free to send Nigel / "nigtomdaw" a PM asking about what he stocks in the way of DC switches for the systems/components he sells.

-Bill

_OS_

Re: 12V DC disconnect recommendation?

BB. wrote: »

Also, for you guys in Europe--Feel free to send Nigel / "nigtomdaw" a PM asking about what he stocks in the way of DC switches for the systems/components he sells.

-Bill

Thanks Bill. I have contacted Nigel as well and will add him to the dealers to contact in the future.

Ole

_OS_

Re: 12V DC disconnect recommendation?

I received the Midnite 250A Mini-DC the other day and I must say that the build quality is the best there is. I have not mounted it yet because I plan to do a complete rewire of my system.

Before that I also need to make a wiring diagram of the new system. Does anybody here know of any web-sites with examples of wiring diagrams? I am familiar with the type of diagrams used in the Home Power magazine as well as the diagrams used by Midnite. I will use Visio to make the drawing.

Below is a picture of my system today. As you can see it is a complete mess!

_OS_

Re: 12V DC disconnect recommendation?

Attached is v0.0 of the new wiring diagram. The breakers, shunts and bus bars are located inside the Midnite Mini-DC cabinet.

Does anybody know how to magnify the image in the attachment?

Ole

BB.

Re: 12V DC disconnect recommendation?

If you are using FireFox... There is an "extension or Add-On" that allows you to magnify images:

http://imagezoom.yellowgorilla.net/

Of course there are others too (and the image can break down if there are not enough pixels to zoom in on).

One suggestion... You appear to have to locations where you pull of the Negative Lead... One is behind a shunt (to measure load currents?) and the other comes directly from the charge controller lead... So, anything on that circuit will not directly register/measure current flow (may be OK with your design).

Otherwise--very nice job.

-Bill

_OS_

Re: 12V DC disconnect recommendation?

Hi Bill,

Thanks for the reply.

There are two shunts. The lower one is a 500A/50mV shunt that is supposed to measure all currents in/out of the battery. This is the main shunt. If you look at the picture again there is only one wire connected to the negative terminal on the battery and the other end is connected to this shunt.

In addition I intend to mount a 100A/100mV shunt that measure all 12V loads (except the battery monitor). This is the upper one in the picture.

Agree?

Ole

BB.

Re: 12V DC disconnect recommendation?

Oh--I agree... There was a comment (as I recall) that talked about RF Transmitter -- I guessed that was part of your remote panel display system.

It was just a question if you wanted to specifically remove the direct power readings/logging of the battery monitor/RF transmitter as part of your total system load.

I agree you have the battery shunt in the correct place to measure all battery in/out current.

I could make one other suggestion... You have the DC power tap coming from the battery side of the Inverter DC Breaker. Not a great thing to do...

Ideally, two changes. One is to pull your "other" DC power directly from the battery + common point. There is typically 120 Hz on the Inverter Power harness--and moving your common point back to the battery could give you cleaner power to the rest of your DC equipment.

Second issue is the gauge (wire diameter) of the connection from the battery bus to the distributed breakers. Normally, I would suggest that you put a DC breaker/fuse (rated for wire current capacity) near the battery + Bus connection and then run your distribution wire from there to the rest of the DC distribution breakers. From your drawing, right now you do not have any current limiting device (beaker/fuse) that protects the (smaller diameter) wire that runs to your DC distribution breakers (the drawing may not represent your actual wiring connections and I am all wet :roll: ).

-Bill

_OS_

Re: 12V DC disconnect recommendation?

Hi Bill,

I edited my posting before I saw your reply but I believe we agree.

The reason I have wired it this way is that I want to shut off both the 12V loads and the inverter with the 250A breaker but leave the charge controller and battery monitor connected to the battery regardless of the position of this breaker.

This is to ease the use of the system for other people in the family. When they come to my cabin they turn the big breaker on and when they leave they turn it off. The small breakers should be left untouched.

Ole

westbranch

Re: 12V DC disconnect recommendation?

Ole, I was able to view the image with Mozilla, then have it magnified just by clicking on the image a second time , it will enlarge when you click a third time then the cursor changes to reduce. This tool is /was automatically included in Mozilla. I didn't even know it was there till now.

re Bills question and your answer about having one 'main' power shutoff:
do you have TANDEM or dual (connected ) circuit breakers available over in Norway? like this http://www.acehardwareoutlet.com/(by5ijs55tz0gpu455g5r2j45)/ProductDetails.aspx?SKU=30629
where 2 breakers are 'pinned' together to shut off at the same time?

Usually 2 of the same rating are used here for 240 V where 120 v is used for most appliances except the clothes dryer or a water pump but different ratings can be combined.

just another idea.

HTH

Eric

_OS_

Re: 12V DC disconnect recommendation?

Hi Eric,

I have ordered all my DC breakers from a dealer in the USA because I have not found them over here. The only breakers I can find in Norway are the regular 220V/10A, 220V/15A and so on.

That said I am not sure if dual connected breakers would fit in the Midnite Mini-DC cabinet since it it is the big 250A breaker we talk about. Check the picture in the link below. There is a cut out for one 250A breaker in the upper part of the cabinet and cut outs for five regular breakers in the lower part:
http://www.mavericksolar.net/midnite/mini-dc/MINI-DC_PW_12_600.jpg

Ole

westbranch

Re: 12V DC disconnect recommendation?

Morning Ole, I called Midnight and spoke to a tech. Short answer is NO, tandem /gang breakers are not feasible on the Mini box. He suggested an additional buss bar for 12 v loads tapping right off the battery. this avoids a lot of wiring on the bottom stud of the main breaker.

Question, what are your 12 v loads?
Is it critical they be shut off or can the Panels/batteries keep up to the loads if 'inadvertently left on'?

I installed a master disconnect for all my 12 V loads and the inverter has a separate switch. I too would like to have just 1 switch to throw... but the physical layout of all components does not currently allow it. Battery and distribution in one room outside the cabin , and CC, XBM, inverter and main shutoff inside.

cheers,
Eric

_OS_

Re: 12V DC disconnect recommendation?

Hi Eric,

Thanks for checking this. My 12V loads are bedside lights, and gas alarm and maybe other loads later. By going to 12V on these loads I can switch off the inverter during night.

This said I can't see any problem switching off everything with the 250A breaker and use a separate breaker for the 12V as indicated on my drawing above. I do not think noise from the inverter would be any problem.

I started wiring the Mini-DC this weekend and noticed that the small breakers had a writing on them to wire them the correct way. They all had a + sign on the bottom so this would be connected to the battery + for any loads. What puzzles me is the drawing in the Mini-DC manual where it looks like they have wired the breaker from the battery + output on the charge controller to the top of the breaker. I am talking about the small 60A breaker to the left in the drawing on page 3 in this document:
http://www.midnitesolar.com/pdfs/MNDC_Instructions.pdf

Shouldn't it be connected the other way since the B+ terminal on the charge controller is more positive than the battery + terminal?

Ole

Robin Gudgel

Re: 12V DC disconnect recommendation?

I remember talking to someone last week about making a tandom breaker inside the MNDC. It is not practical to try to tie the 250 amp breaker to a 60 amp breaker. They are located in separate positions and are different sizes. You can of course handle tie any of the five din rail mount breakers together. We are now also including an additional cover plate that accepts up to three panel mount breakers. It is an either/or situation for the additional breakers. Din rail or panel mount.
The diagram showing the output of the charge controller going to the top side of the breaker is actually correct. This situation is always confusing. The output of the charge controller when operating is the same potential as the battery plus terminal. No real difference and thus no sparking or welding breaker contacts together. Now let's look at what happens when the charge controller fails. When charge controllers fail they short the plus output terminal to the minus terminal. Ut oh.... this is a direct short across the battery! Bad things happen real fast and at current levels capable of causing a fire all along the cabling. During this condition, the battery plus terminal of the battery bank wins. It is the most positive. This is why you want to have the battery plus connection going into the bottom of the breaker. If it was an 80 amp panel mount breaker, you want the "Line" terminal of the breaker connected to the battery plus terminal of the battery bank. In a 12 volt system it really won't make a lot of difference since the arcing is small. When we tested the din rail mount breakers at ETL, we found out that at 165 volts it does make a difference though.
Check out the ETL testing document on our website under documents then educational. We just finished testing the 250VDC breakers at 300VDC. We decided rather than do this at our factory, we would let ETL find a better equipped place. There is something about shorting out 26 12V batteries all in series that bothered us a bit. At this time we don't have any expendable technicians!
Robin

_OS_

Re: 12V DC disconnect recommendation?

Hi Robin,

Thanks for the reply! I understand now. I will post a picture of my wiring here when done.

Regards,
Ole

westbranch

Re: 12V DC disconnect recommendation?

Hi Ole, my limited view on the wiring diagram is that:
the Battery is far more powerful than the PV, when short circuited, eg I have a set of 100 Ah batteries that will short circuit over 1000A's.

That small 60 A breaker is there to protect the CC (and other items that might be wired to it) from a short from the battery to the CC,
thus the + mark is towards the battery for it to work properly.

whereas the 250 A breaker protects the Inverter, and a bigger breaker is needed as the required draw is larger ... say 2000 W @ 12V but anything more is too much and the CB will kick in

A local electrician once explained CBs as there to protect the wiring, which in houses is usually at the minimum. In that way fires starting from overheated wiring are almost eliminated.

While in our PV cases we seem to overwire to minimize losses, so the CBs first protect our equipment CC's etc, and second also protect the wiring which still could start a fire from unlimited battery power .

HTH

If I am off base I am sure the others will step in.;)

Eric

_OS_

Re: 12V DC disconnect recommendation?

Hi Eric,

Yes I understand what the purpose of the breakers are. It was the text on the breakers about wiring them the correct way that made me wonder. I thought that it meant that they only could break current in one direction. In a house where you have AC the two terminals on a breaker are equal.

Ole

_OS_

Re: 12V DC disconnect recommendation?

Attached is an updated version of my drawing where I have increased the size of the text such that it is easier to read. I have also removed the bus bars since I thought the mini-DC included them but it didn't. I will now wire the common minus cables to the shunts and the plus on the bottom of the breakers. I have also added one more 2A breaker for my DIY control/meter. More on the DIY meter later.

Ole

niel

Re: 12V DC disconnect recommendation?

ole,
i believe i understand the need to make connections due to no busses, but in so doing i must let you be aware that the doubled up connections to the output of the 250a breaker will cause any loads up to the max of the 2nd inline breaker to be subtracted from the total available power to the inverter. if your smaller dc loads are present at for example 35a then 250-35=215a available to the inverter. nothing limits the inverter other than its own capabilities and the loads presented so if for example a prolonged load surge should occur on the inverter at 215a or higher it could trip the 250a breaker. most times i'd say you would be fine with it and i'll bet you are glad you don't live in the states as doubling up connections to breakers would most likely be frowned upon. ideally the inverter and its cb should be independant of any other circuits.

_OS_

Re: 12V DC disconnect recommendation?

Hi Niel,

Thanks for the reply. Currently I have a 1200W inverter that can surge up to 2000W before it shuts off. This means I have plenty of room before the 250A breaker trips. But I will reconsider my wiring and maybe wire the 12V breaker directly to the battery. I guess nobody in my family dear to use the cabin without me present anyway...

Do you see any other suspicious connections in my wiring diagram?

Ole

Solar Guppy

Re: 12V DC disconnect recommendation?

One nice thing of having separate breakers, you can shut off the inverter and have the other loads powered

niel

Re: 12V DC disconnect recommendation?

ok ole i see you may have over rated the cb here to compensate which i would not have done, or is it a case that the inverter called for that value? it will technically still work, though.
2000w/12v=166.67a and round up to the nearest commercially available cb value.
sg is right about separate shutoffs too.

_OS_

Re: 12V DC disconnect recommendation?

Niel,

Yes I was considering the 175A breaker but ordered the 250A in case I upgrade to a larger inverter. The inverter also have its own internal fuse.

SG,

Yes I agree and I have now made up my mind and wire the two breakers directly to the battery as suggested above (new diagram below). I will also add status LEDs that all should be off when people leave the cabin; one for the 12V breaker, one for the 250A breaker and a combined LED for three of the other breakers that turns on if the breakers are switched off (charging, battery monitor and PV array). This way it will be easier for other members of the family to use the system.

Ole

mike95490

Re: 12V DC disconnect recommendation?

Just a side question here, anyone know which has less insertion resistance,
a fuse or breaker ? (100A for example)

_OS_

Re: 12V DC disconnect recommendation?

Hi everybody!

I completed the wiring of the Mini-DC and the Pentametric this weekend. It was quite a bit of work but I completed most of the internal wiring in the Mini-DC on my kitchen table. Below are a few pictures of the system. I will replace the cables to the 12V loads with thicker ones the next time I visit my cabin.

EDIT: I regret that I removed the lower, big cutout where the 12V leaves the mini-DC. I should have used one of the smaller ones or the cutout to the inverter cables. I guess it is too late now or is there something I can plug the hole with?

Regards,
Ole

icarus

Re: 12V DC disconnect recommendation?

Very nice, Ole',

T