New Member with New system questions Magnum 4448 and Midnite 150

67chevelle

Hello all, my 1st post here, but have been lurking for a while.

        I'm 2 years into building a 500 sf off-grid cabin in the central Idaho mountains. I've got a small 12v solar setup that we've been using

for lights, that I'm going to replace with a larger setup. I have many questions that I'd like input on.

Here's the Specs on the starting point for the new system.

Panels 6-305 W panels wired 3s2p

Midnite prewired MS4448PAE with the Classic 150 CC

8-T105 6V Trojan 225ah batteries in series for a 48v bank.

1st question: Do I need any additional monitoring hardware besides what comes with the prewired setup? Do I need to add a Trimetric?

2nd question: I know my battery bank is on the small side for this system, but I already have these batteries and they're only a year old.

Can I set up the Midnite Classic 150 so that it doesn't overcharge this battery bank?

Thanks in advance, Mark

here's a pic of the cabin.

Estragon

Nice cabin!

The classic has a setting to limit output.  You're unlikely to hit it often, but you might want to limit at 30a or so.  It also has a "skip days" setting, so if you're not using the system daily it will go straight to float for 'X' number of skip days.  This prevents daily absorb cycles, which are hard on the battery and not really helpful on an idle bank.  I set mine for ~7 days.

Not really needed with two strings, but a combiner with a breaker for each string would be handy as a string disconnect for troubleshooting, and for possible future expansion.

A trimetric isn't really a necessity, as midnite "local app" and or the android phone app give lots of monitoring info.  The TM is handy as a sanity check on the classic data, and to see what's happening at a glance though.  

Midnite also has a web monitoring site which works well for remote monitoring, but requires a decent internet connection.

67chevelle

Thanks for the info Estragon.

 Do you have any recommendations on combiner boxes as far as brand goes?

Mark

Estragon

I use midnite combiners & breakers, but some here have used some from amazon which apparently work well.

littleharbor2

Are your 305 watt panels 60 or 72 cell panels?  Being in the northern regions you will get cold in the winter. If your panels are 72 cell panels you may be pushing the 150 Voc. limit of your controller. if you haven't already purchased your controller you might consider a Classic 200. You can use the midnight string configuration calculator to check your configuration's compatibility.

BB.

Per Lilttleharbor2 advise,

Here is the link for the Midnite classic string sizing tool:

http://www.midnitesolar.com/sizingTool/index.php

-Bill

Estragon

Note that the classics have "hypervoc" - essentially a buffer zone in which max voltage can be exceeded.  In this voltage range, the controller won't produce power, but won't be damaged.  IIRC, it's classic max + nominal bank voltage, so 150+48v = 198v in this case.

If it's a close-ish call at 150v at record low temps, it may make more sense to stick with the 150 and accept the few minutes of no power before the panel warms up on really cold days.  Closer to the higher end of the range, a 200 might make more sense though, rather than risking exceeding the top of the range.

67chevelle

The panels are 60 cell.

I did run the sizing tool ( I've attached the results. It says I'm good to -58F, which is colder than it's ever gotten in the area our cabin is in, although -40ish is possible .

i don't yet have the charge controller or inverter. My current plan is to get one of these.

http://www.midnitesolar.com/productPhoto.php?product_ID=242&productCatName=Inverter Systems, Pre Wired - Off Grid&productCat_ID=20&sortOrder=8&act=p

Estragon

I used similar epanels for Outbacks and they worked well.  I didn't get the prewired version though for easier/cheaper shipping.  All assembled, they're pretty bulky and heavy.

67chevelle

Next Question:

        3 of the 6 solar panels will be ~100 feet from the charge controller (set 1) and the other 3 (set 2) will be ~35 feet from the charge controller.

Set 1 will be wired in series, and then I will need to run the output wires from this set ~65 feet to set 2's location. The 3 panels in set 2 will also be wired in series.

So, I would then position 1 combiner box at set 2's location and run wires from set 1 and set 2 into it and through a breaker for each string. The output wires would run from the combiner box to the shed and into the charge controller.

Do I have this right?

The combiner box will have a surge protector device installed in it, will this also protect set 1, or do I need to do something else?

I'll have ground rods driven at both panel locations and the frames of the panels will be tied to those grounds.

thanks

Mark

Photowhit

With just 2 strings, you don't need and aren't required to have a combiner box, just grab a set of 'Y' connectors and you should be fine. 

Also your battery bank is NOT under sized for your array. 48 volt 225ah battery bank should charge at a maximum of 13%, Your 1830 watt array, on a good crisp cold day with clear skys might produce their panel rating of 305 watts but it will be rare. 1830 watts ÷ 58 volts(charging voltage for a 48 volt battery bank) =31.5 amps or about 14% you will have enough losses to make this a non-issues and in normal system operating you will likely never see more than 13%, The sun doesn't pop into the sky and your batteries will begin to charge and likely be out of Bulk charging and naturally accepting less current in absorb when the sun is at an angle to produce maximum power.

Photowhit

If the prewired system included a Whiz Bang junior, you have pretty much the same information from the 150 Classic as the Trimetric. The only tricks are being sure to set it up correctly and running any DC loads through the shunt.

Estragon

As mentioned earlier and Photowhit notes, the combiner is optional (but handy IMHO).  'Y' connectors would also work.  Be careful to never make/break connections under load though, as arcing can damage the contacts.  It's a good idea to avoid this with breakers too, but proper DC rated breakers are designed to extinguish arcs.

My understanding of the surge (lightning) protection is to protect inside electronics (controllers etc), not panels.

I have my panels & racking grounded to a plate near the array, much as you plan. 

I should really have this plate also connected to the cabin ground plates, but rocky conditions make doing so difficult.  Without this connection, some faults (eg pv positive to frame) probably won't open a breaker.

67chevelle

Hello again, ,

I've been doing a bunch of reading on grounding and bonding on this site as well as others. It's not completely

clear to me what I need to do. The attached diagram shows what I have so far. The cabin and shed are built, and there are ground rods

driven at the locations indicated.

1) Do I need to connect the sets of ground rods together ? They're about 30 feet apart

2) PV1 is ~ 80 feet from the ground rods near the cabin, is the dashed green line the proper path to take to ground the panels?

3) The AC load center in the shed is currently connected to the ground rods near the shed and the cabin's AC sub panel is connected

to the ground rods near the cabin. If the answer to #1 is yes, have I created a "ground loop"? If so how do I correct it.

4) Have read several times that bonding neutral to ground should occur in only one place, given my diagram, where should this be done?

really appreciate your help

Mark

solar ground.jpg

BB.

Mark,

I would highly suggest that all of the ground rods be tie together.

There are two major reasons for ground. The first is to provide a current path from "remote loads" back to the power source/power shed.

So, in your case, the power shed to the home ground rods need to be tied together. The ground rod itself, can have 25 Ohms resistance to earth. At 120 VAC, that is less than 5 amps of current (V=I*R; I=V/R) and not enough to trip your 15 amp (minimum) power supply breakers) if there is a short from "AC Hot" to grounded metal at the home. Running a minimum 6 AWG cable between the two ground rods (power shed and home) provides that reliable safety ground current path.

The other (major) reason is lightning. You want anything metal+electrical to be earth grounded with a short and direct connection to the ground rod. Again, I suggest 6 AWG cable minimum. Note that lightning is not DC current (it is "radio frequency") and short runs/rounded corners, and there is special woven lightning cables, are used to get the lightning energy to earth, and not flow through your other electrical connections. (higher frequency AC and radio frequency energy/current has a whole different set of rules it follows for wiring/best conduction paths).

Some links to read:

https://forum.solar-electric.com/discussion/comment/84242#Comment_84242

-Bill