Circuit Breaker Connections

hemmjo

Several of you have been assisting me with the planning of a solar water pumping system for the mission I work with in the Dominican Republic. Thank you with your assistance so far. Attached is a sketch of all the components as I see them connected.

Right now I have all of the components in my garage hooking them up to be sure I have all the little things I will need. I have hit a little speed bump. I have 2 Midnite Solar MNEPV 10 Amp, 150 volt DC circuit breakers. I have never used a breaker where polarity mattered. These have + marked on one connection and it says on the side of the breaker, "Polarity Sensitive, Do Not Reverse Feed". I can understand this may make a difference. However, in the + wire between the charge controller and the battery I am a bit perplexed. When the sun is up, the pump is not running, and the batteries are charging the most Positive point is + on the charge controller. Whenever the pump is running, the most Positive point is + on the batteries. How do I connect this breaker... + toward the battery, or + toward the controller? OR do I forget the breaker and put a plain ole fuse in that line?

Maybe I should just use fuses in place of both breakers?

Your thoughts are appreciated.

John
http://villagemountainmission.org/

westbranch

Re: Circuit Breaker Connections

best to use CB's when you need to disconnect, like on the battery Pos. others can use an automotive fuse. You should havea way to disconnect the PVs too. there the + side would go to the PV.

QO circuit breakers are rated to 48 v DC, no more so you can use Square D stuff to build a cheap disconnect.
see reply 37 here http://midnitesolar.com/smf_forum/index.php?topic=581.msg4077#msg4077


hth

BB.

Re: Circuit Breaker Connections

assuming a negative ground battery system point the positive of the breaker towards the battery bank. That is the only source of large amounts of current in the system.

-Bill

westbranch

Re: Circuit Breaker Connections

there are a bunch of postings by Ywhic like this one where he made his own combiner box and other stuff from readily available off the shelf materials
http://forum.solar-electric.com/showthread.php?15793-Using-a-Square-D-QO-Load-Center-for-Combiner-Box-pics-and-video

Photowhit

Re: Circuit Breaker Connections

BB. wrote: »

assuming a negative ground battery system point the positive of the breaker towards the battery bank. That is the only source of large amounts of current in the system.

Actually this has been discussed a good bit over at the Midnite forum and here, but since these are small breakers I would assume they are for solar panels pos output?

The rule of thumb is put the pos toward the battery on the battery side of the charge controller and toward the solar panels on the solar input side.

Here is a link to the forum of the people who sell the breakers.

...ooops I just opened your pdf, yes for your system both are on the battery side of the charge controller so + toward the battery.

BB.

Re: Circuit Breaker Connections

The combiner box has solar panels on both sides... So to clarify, the + on the breaker should point to the combined solar panel outputs going to the charge controller (i.e., a single shorted string would be feed too much current from the rest of the paralleled arrays).

So, even though you are not protecting against the battery short circuit current, the rule still works (combined current from the balance of the solar array).

-Bill

Photowhit

Re: Circuit Breaker Connections

BB. wrote: »

The combiner box has solar panels on both sides...

This makes no sense to me, on one side of the combiner box you have panels and on the other side you have a combined output going to charge controller.

BB. wrote: »

So to clarify, the + on the breaker should point to the combined solar panel outputs going to the charge controller (i.e., a single shorted string would be feed too much current from the rest of the paralleled arrays)

Maybe you should tell the people at Midnite this, as their boxes are setup with the '+' toward individual panels;

Attachment not found.Attachment not found.

Your description, at least to me, appears you would want the combiner box to be the divider with pos toward the "combined solar outputs" this at least in practice has not been the case.

Muskoka

Re: Circuit Breaker Connections

I don't own the box, but from an outsiders perspective, and following the instructions and posted link, you have them installed the recommended way Photowhit.

The positive (+) on the breaker should be "receiving" the (+) current from the panels. The negative (-) side of the breaker is connected to the combined buss, which then goes to the CC.

So, (+) positive current from each panel / string of panels is connected to the (+) positive side of the breaker, correct? The (-) negative side of the breaker connects to the combined buss bar. This is the way they describe it / show it in the pictures, just as you have it.

Glen

Photowhit

Re: Circuit Breaker Connections

I actually have a nice homemade fused combiner boxes on both of my systems. I just thought Bill's reply was either confusing, or misleading.

Muskoka

Re: Circuit Breaker Connections

Photowhit wrote: »

I actually have a nice homemade fused combiner boxes on both of my systems. I just thought Bill's reply was either confusing, or misleading.

Me too, yes it was confusing / contradicts their recommendation, as far as I can tell.

BB.

Re: Circuit Breaker Connections

The normal current from is from the solar panel string through the breaker to the combined bus, then to the charge controller (aka battery bank). During any sort of normal operation, there is no physical way that a solar string can output more than Isc. So, the breaker will always operate with "reverse current flow" during normal operation but will never have to interrupt excessive fault current. Yes, if the breaker is turned off during the day (say for servicing), it will interrupt the reverse current flow (how bad that even is--I do not know).

The breakers otherwise are there to protect a shorted solar panel string from the rest of the solar panels supplying combined current from the rest of the array to the solar charge controller (aka towards the battery bank).

In reality, you have two different failure modes (initial miss-wiring and a short to earth or sorted panel during normal operation). The two failure modes still have the excess current being supplied from the combined output of the array--Which would be in the "correct direction" for fault current interruption.

Otherwise there is no other source of energy/current that could reverse the fault current direction in the breaker, that I can see (using the single failure model). Because, the job of the breaker is to open during excessive current--That is the only valid configuration, as I understand it:

The battery positive terminal is the highest potential! Make sure that the plus (line) of the breaker is connected to the battery plus terminal. If the breaker is connected backwards, it can fuse in the closed position as it attempts to open. That could ruin your entire day!

The highest current potential is the combined solar array bus, after the combiner box.

I may be wrong, and I may disagree with Midnite. What more can I say.

-Bill