Re-working my old system

[qrper]

Gang...

while I'm fighting with the electrical inspector on the new grid tie system, I had to pull the cable from the DC array. Out of sightâ€"out of mind. The DC cable was right across the trench being dug for the new conduit for the grid tie. The dc cable wasn't in any sort of conduit, and wasn't buried deep enough. Although the inspector should have blinders on, and only inspect the new system, why call attention to it?

So, with the cable out, I'm installing a MNDC175 so I can upgrade the circuit breakers. It's also large enough to handle the heavier gauge wire. I also added a whizbang JR and shunt inside the new box.

Right now, I have 4 ought cables from battery neg and battery pos going to a dc breaker located next to the inverter in the basement which is located right next to my electrical panel. Moving the inverter, it weighs almost 80 pounds, is not an option.

So, although there is no need to use the circuit breaker in the MNDC175, I thought I'd do so, that way I have two ways of discounting the inverter. One in the garage, the other in the basement.

Opinions? Leave it as it, except for the run of cable to the shunt in and out of the new box?

Or?

Run new cable between batteries and the new disconnect?

That being said, to run the cables to the new box would put in almost 20' of new cable! (12' from the battery + terminal to the disconnect inside the MNDC175 and then from the disconnect back to the + cable to the inverter which is another 5'.

Mike

[Vic]

Hi Mike,

It is hard to remember exactly what some members here are using in their power systems.

Would you please compose a Signature,  which details your batteries,  system voltage (unless the inverter model notes this),  inverter,  CC,  Solar,  the purpose of the system,   etc.  Your system is evolving,   but  this info,   would be helpful for the most  pertinent  replies,  to the extent that you can specify it.

Most inverter manufacturers give guidance on the maximum cable length twix the batteries and the inverter.   To me,  20 feet,   seems far too long.  12 feet is better,  but,  really too long.  (a number of manufacturers of inverters,  spec 10 feet max length).    Personally,  try to keep these cables to 5-6 feet. The issue is not just voltage drop in the cable,   but,  also stability of the inverter/charger.  Twisting these positive and negative cables,  should reduce cable inductance,   but   ...  just my opinion.

Just a drive-by,   FWIW,  Vic

[ClassicCrazy]

You battery negative goes to one side of the shunt - all the other negatives are on  the other side.

Larry

[qrper]

Right!

If I decided to run the positive battery cable into the disc, then I have to extend its length. Right now with the original disconnect in the basement next to the inverter, the wires are much shorter.

I have the shunt and the whizbang mounted in the box. I still need to extend the battery wires to get inside the MNDC175 to the shunt.

I've been playing with some of the online voltage drop calculators and it seems that even with 30 feet of cable (round trip) and at 125 A, I'd see only .3 V drop from battery to inverter. The other side of the coin is the cost of the 4ought cable. It's about $7 a foot here locally.

Mike

[Vic]

Hi Mike,

Thanks for the Signature.   Apologize if you had added it,  prior to my previous post,  here   ...  it does disappear while one is writing a reply   ...

However,  the primary issue with      l   o     n       g    inverter cables is STABILITY,  even with large cable sizes.    If the CC  is 12 - 20 feet from the batteries,   this is generally not good for voltage drop  OR  CC looking into that cable inductance.

Also,   there is a bit of voltage drop in each breaker (even Magnetic-Hydraulics used by MN),   so  try to take that into consideration.

As an aside,   noticed the reference to a SolarEdge Inverter.   Hope that you can avoid using SolarEdge Optimizers (or probably any other optimizers),    as they have a rep of creating quite a lot of HF RFI  (from the experiences  of Ham acquaintances/friends.

Just opinions.   Vic

[qrper]

Hi, Vic,

These pass few weeks have been one for the books.

Friday the electricians started to wire the grid tie.  Tomorrow, they should finish wiring and commission the inverter.
Yes, it's a SolarEdge and works with those optimizers. I hope I don't have RFI issues with them. Fingers crossed.

Okay on the inductance and voltage drop. According to one of the online calculators, at 125 A I'll drop .3V. THAT'S not including circuit breakers. As you know every connection is not perfect, so there are plenty of places to add extra voltage drop.

I think what I'm going to do is leave the inverter + cable to the battery as it is. Then extend the batt- and INV- so I can connect the shunt that's living inside the MNDC box.

That, by the way, was an issue. I had an extremely hard time getting the box to fit the Classic 150. I called the mother ship, and talked to Todd. He and I were on the phone for a while and after exchanging some photos, it seems that I have the "PLUS" version which does NOT have the same dimensions as the MNDC175 regular.

I sure wish the documentation was accurate. It's not.

mike

[ClassicCrazy]

That is a bummer about that plus model mndc box . I always used the regular ones and the holes on top match up with the holes on the bottom of Classic.

Larry

[qrper]

That is a bummer about that plus model mndc box . I always used the regular ones and the holes on top match up with the holes on the bottom of Classic.

Larry

Let me tell you I said some choice words! Nothing lined up. There is only one way to install the shunt 'cause there is that grounding bolt in the way. Holes on top don't aline with the Classic's hole pattern.

Had I known there was a difference between mounting holes between the regular box and the 'plus' I wouldn't have had all the problems. There is no where that I could find that says what if any difference there is between the two.

Mike

[Steve_S]

grper, don't feel bad...   remember that Murphy's Laws will always apply, whether your ready for it or not.

I have a Classic 200 (standard model) and bought an MNDC 125 box originally as I was running with a 3kw inverter/charger.  After deciding to upgrade to a 4kw Samlex Inverter/Charger and the required 4/0 cables, replacing the 125 with a 175 breaker was no fun !    Making it even worse, is that my C-200 is mounted on the Left Side of the box which is not how it was designed to go...  With a bit of customizing and using some good hardware, I made it a very nice & neat package.   You can see images from my link in my sig.  I had to "nudge" my shunt over & down to make it all fit nice & tidy but it is all quite "snug" in there.  Note that I put a BUS BAR on my shunt, that made it much easier.

Hang in there, it's all worth it in the end, even the occasional burst of "blue air" are ok.