kid to battery question

[Kommy]

Hi, I'm new at this and in a process of installing solar panel run with kid mppt marine version.
Seems pretty straightforward but I'm starting to doubt myself.
I'm planning for now to use kid mppt to charge a house bank of 2 batteries in parallel connections 12v system.
Of course I'm reading all the information on internet and starting to question the distance from mppt to battery.
I know you should mount mppt as close as possible but the closest I can do is about 9 feet of wire distance from mppt to a battery bank.
From what I can see, it is a 10 gauge wire from mppt to batteries. When I use calculators online, it's showing potential voltage drop of 5%. Is that normal, or is charge controller aware of this voltage drop? Anything I can do about it?
I know if I had higher voltage bank, it would not be an issue but this is your normal sailboat 12v deep cycle system.
Eventually I will be taking out diesel engine and putting in electric motor and installing 48v battery bank, so at that point I will rewire mppt for 48v bank but for now I have to stick with existing setup.
Again, I can't place it any closer to battery bank since it is hidden in a tight space and 9ft of distance is the best I can do, though in a perfect world I would place it even further with the rest of my dc/ac panels but that would be close to 12' distance.
Please let me know if I'm over thinking this and if these distances are ok.
Thank you

[ClassicCrazy]

9 feet isn't so bad a distance.
You can just go with a larger diameter cable like 8 or 6 gauge.
I don't remember on the Kid what the largest size wire it will accept. Since it has a 40 amp fuse in it I think it must be at least 8 gauge and may take 6 no problem.
This is for 12 feet of 8 gauge  on southwire volt drop calculator
40
Amps Rated ampacity of selected conductor
0.7421
Ohms Resistance (Ohms per 1000 feet)
0.052
Ohms Reactance (Ohms per 1000 feet)
0.9
Power Factor
0.6
Maximum allowable voltage drop at 5%
0.497
Actual voltage drop loss at 4.14% for the circuit

If it was me I would use 6 gauge wire - drop will be even less.

Larry

[ClassicCrazy]

Also if those voltage drops are calculated for the maximum current.  If your system was even less current ( not the Kids full charging potential of 30 amps) then the drop would be even less.  I think you asked what happens when the voltage drop is higher- you loose some of your power heating up the wires a bit  ( higher resistance ) .  But yes you want to keep the resistance low as possible.

Larry

[Vic]

Hi Kommy,   welcome to the Forum.

As Larry said,  9 foot long cables between the battery and KID,   is not so bad.

Think that the largest cables that the KID terminals will accept is #10 AWG (and NOT Fine-Stranded).

Since input and output breakers will be needed,   often the breakers can be mounted near the KID.  So,   in increase in the cable size can be made on the battery side of the output breaker.

FWIW,   Vic

[ClassicCrazy]

Hi Kommy,   welcome to the Forum.

As Larry said,  9 foot long cables between the battery and KID,   is not so bad.

Think that the largest cables that the KID terminals will accept is #10 AWG (and NOT Fine-Stranded).

Since input and output breakers will be needed,   often the breakers can be mounted near the KID.  So,   in increase in the cable size can be made on the battery side of the output breaker.

FWIW,   Vic

So what kind of solution do you have for the negative side ?  I can think of something like a short piece of buss bar made for grounding . those have holes for larger wires.   I would do other approaches for myself too like maybe putting a crimp ring to splice the larger wire to short piece of 10 gauge  and then use  something like a propane torch to solder them together , and layers of quality electrical tape for insulation on the splice.

Larry

[Vic]

Hi Larry,

Good point,   some just leave the negative battery cable #10 AWG,  for example.

Personally,  for the KID would  generally run all cables through a small cast AL outlet box.   And splice the negative battery cable there,   OR,  might use the BigBaby box,  which has room for DIN breakers,   and a place to mount a short busbar  (MN Short Busbars that include insulators)   â€¦   depends.

MNBigBaby Box:
http://www.midnitesolar.com/productPhoto.php?product_ID=122&productCatName=Small%20Breaker%20Boxes&productCat_ID=10&sortOrder=2&act=p

MN Short Busbar:
http://www.midnitesolar.com/productPhoto.php?product_ID=587&productCatName=Busbars&productCat_ID=17&sortOrder=4&act=p

Thanks for noting that,  Larry.   (73)   be safe,    Vic

.

[ClassicCrazy]

And just to be sure Vic - are you thinking of the original Kid connections ? They did change to a new connector add on a few years back but I couldn't find any specs in the literature of what size those take  . I know it probably isn't recommended but wouldn't just clipping off a few strands of a larger cable to fit into the terminals on the Kid be the same thing electrically as going from a larger to smaller size wire ?

Larry

[Vic]

Hi Larry,

OK,   yes,   there is that Wall Terminal adaptation for the KID.   But it is not clear just who and who does not have this  --   yes,   the KID here does NOT have this option/accessory.

From the latest KID manual,  that I can find is the following:

"   â€¦   The KID wall mount terminals will hold a maximum wire size of #8, the internal terminals will accept a maximum wire size of #10. If your wire run requires wire larger than #10, the best place to transition down to #10 is inside the Big Baby Box. The circuit breakers can accept up to a #6 wire. There are several handy online wire sizing calculators available      …   ".

Am not certain when this wall mount was added   â€¦   guess that it became standard issue at some point   â€¦

Thanks for the reminder.  Our KID is a very early Beta unit.

73,  Vic

[Kommy]

Wow, thank you for all the answers. Guess cheaper way is to upsize to 6 gauge right outside of MPPT or splurge and get the mini big box and just do all the connections via that. I was going to have a shut off switch right next to the MPPT and connect 10 gauge from KID to switch and 6 gauge from KID to battery on negative run but positive I guess I can do inline upsizing to 6 guage, this way I can avoid buying the box for just 2 connections.
Also, I noticed that you said no fine stranded wire, so this is for marine application and marine wire is bigger in diameter, so am I forced to use a regular household wire with solid copper instead of stranded?

[Vic]

Hi Kommy,

The BigBaby Box is designed to accommodate up to four  DC circuit breakers,  like this:
https://www.solar-electric.com/midnite-solar-mnepv-30-amps-circuit-breaker.html

These are DIN Rail breakers,  and have screw terminals for the cable connections.  Generally these screw terminals are designed to receive coarse stand cable (and in some cases solid cable).   Building wire,  like THHN,   and similar usually has a few dozen individual strands.   Fine strand cable that is common in Marine environments is often not compatible with these screw terminal connections.

There is a different small MidNite box  --  the DC Quad  --  that accepts Panel Mount (PM) breakers.  These breakers have threaded stud connections at the rear of the breaker,  allowing crimp terminals to be used on connecting cables.   This box/breaker combo should allow use of fine-strand cable.

DC Quad box:
https://www.solar-electric.com/mnedc-quad.html

MN PM circuit breaker:
https://www.solar-electric.com/midnite-solar-150-volts-30-amps-dc-panel-mount-circuit-breaker.html

Later,   FWIW,  VIc

[Resthome]

While Vic is correct about the terminal using screw connections.  Be aware if you ever need or have to have a marine inspection for insurance or other purposes they will write up use of non marine wire.  Go with panel mount breakers that have studs that the wires can use ring terminal that can be crimped on.

[ClassicCrazy]

Hi Larry,

OK,   yes,   there is that Wall Terminal adaptation for the KID.   But it is not clear just who and who does not have this  --   yes,   the KID here does NOT have this option/accessory.

From the latest KID manual,  that I can find is the following:

"   â€¦   The KID wall mount terminals will hold a maximum wire size of #8, the internal terminals will accept a maximum wire size of #10. If your wire run requires wire larger than #10, the best place to transition down to #10 is inside the Big Baby Box. The circuit breakers can accept up to a #6 wire. There are several handy online wire sizing calculators available      …   ".

Am not certain when this wall mount was added   â€¦   guess that it became standard issue at some point   â€¦

Thanks for the reminder.  Our KID is a very early Beta unit.

73,  Vic

Vic , they changed to that wall mount awhile back now because it used to be a major pain to try and wire the Kid the way it used to come .  Midnite in the past had offered all us early Kid owners to send us one free - I took advantage so if you have an older Kid talk to Midnite and they may still get you the upgrade box.

Larry

[Vic]

Hi Larry,

Yes,  do recall that MN did offer that Wall Mount to Beta KiD owners,   but I did not want to ask MN for one of those,   as I had already mounted the KID using my means (which was a bit tortured - needed to transition from 1/2" fittings to 3/4 & 1" fittings,  too many times).   But,  this approach was RFI Tight,   and so on   â€¦

It was great that MidNite went to the trouble of making the wall mount,   and offering  it to the installed-base of users !

FWIW,   Thanks,  73   Vic

[ClassicCrazy]

Wow that is a pro install there Vic.
I bet you have some tin foil lining that pvc junction - wouldn't want the RFI sneaking out there after all that other nice metal work !

Larry

[Vic]

Hi Larry,

Thanks.    All of the pipe is EMT,   and all fittings are cast Zinc.   You might be referring to the short radius 90 fitting,   it IS cast Zin,   but it is difficult to see in that pic   â€¦   like this one:
https://www.amazon.com/Halex-19007-Degree-Short-Radius/dp/B010PSKCNG

The KID is a great performer !

73,  Thanks,   Vic