Hey all,
A pretty basic question here: Should I put my combiner box on array pole or in the house? MNPV6 manual says on the pole if over 30 feet from batts. I'm at 75 feet. I think I would prefer to have all the equipment in the house though.
System description: Two solar world 285 watt panels, 37 Voc, wired in parallel, 12 volt battery bank, Outback Flexmax 60 amp CC, 1/0 home run cables, 2000 Watt Samlex inverter, TruCharge 40 amp battery charger, with 1000 Watt Honda generator (I'm stuck with 12 volt system due to legacy install and $$$ limits)
I'm guessing they suggest the combiner on the pole bc of voltage loss? but with my 1/0 cable, that voltage drop should be minor. I thought I would just put a pass-through box on the pole and connect the array strings to home run cables and then put the combiner in the electrical closet.
Suggestions?
thank you very much
well 12 v is a bit of a pain, as you could run the PV's in series and really reduce the losses, though with 1/0 you should have minimal losses in parallel or series.
The Series advantage is that you only need one CB as a shut down when you want to do system work etc... with 2 parallel you would want 2 CBs though you could do it with only 1 CB for shut down, at 3 panels you NEED 3 CBs for backfeed protection...
go here and use the calculator... http://forum.solar-electric.com/discussion/60/voltage-drop-calculator/p1
to test the various options you may have
hth
Thanks HTH. I was instructed to go 12-24 volts over system voltage for max efficiency of MPPT charger. Thus my decision to wire in parallel.
So given this decision, where should I put the combiner box? (I am at around 2% voltage drop with my configuration)
I don't really understand system shut down. Why would I need two combiners? I can't really afford to purchase another one...
thank you!
CB is Circuit Breaker not combiner box...
the higher the voltage the less loss in a given length of wire.... so lower voltage /higher Anps over 75 feet will loose more Volts than higher voltage/lower Amperage.... use the calculator to see the impact on your setup.
my suggestion is to use the heavy wire , 1/0, and go to 74v from the in-series PV, no combiner box needed and lower line losses, but higher losses in the down conversion from 74v to 12 v....
or go 2 in parallel, @ 37 v, use the combiner box and have more line losses by having parallel PV panels and lower voltage but higher Amperage from the combiner to Charge controller.....there will also be down conversion losses, 37v to 12v but less than the in-series option,
your choice, different losses in each scenario, that is why you need to compare the losses in each scenario and the additional or lower costs of each....
hope this helps
Ah, thanks. This has been like learning a new language for me.
I understand voltage loss over distance versus wire gauge and have made those calculations. However, won't the voltage loss be the same regardless of where my combiner box is located? (the distance and the wire gauge don't change, but I know the loss will be less if I wire in series)
How do I calculate the voltage loss or efficiency loss at the charge controller due to the big step-down if I wire in series? I'm assuming this loss is due to something internal in the charge controller?
Why would I NOT need a combiner box if I wire in series? Don't I still need a place to make all of these connections and for breakers?
And back to my original question, where should I put the combiner box?
Lot's of design decisions here. Thanks for bearing with me.
And back to my original question, where should I put the combiner box?
There is no set answer to that question, since each system is a bit different it is a decision you need to make BASED ON THE LOSSES THAT ARE ACCEPTABLE TO YOU ( my system has some higher than normal losses due to some temporary PV locations as we are waiting for a deck to be built...but need solar input)
So you can have it in either place,as the calculator will show you, the place that will give you the lowest losses is nearest the Charge Controller and the batteries...
I recommend that you input both scenarios and compare the total losses, series and parallel, and you should see the resistance loss jump after the combiner ...
Hi pablo,
You do not need a Combiner for one or two PVs in parallel. If you were to run strings of PVs in series, you would only need a Combiner is there were three or more strings of PVs. So, with two PVs either in series, or in Parallel, you will not need the Combiner.
For troubleshooting, having a Combiner can be convenient, although not necessary.
The SW 285 PVs have an Open Circuit voltage of about 39.7 Volts. But for calculating the voltage drop in a cable, I would use the Imp of the PV, and for estimating any conversion losses in a Charge Controller (CC), you can just use the Vmp. For the SW 285, the Imp is 9.2 amps, the Vmp is 31.3 volts.
So, for two SW 285s in series the String Vmp is about 62.6 volts, which is for the solar cells in the PVs at only 25 degrees C, which seldom occurs, so, in full sun, the actual Vmp will be reduced by the heating of the PV solar cells, from the sun, plus any effect from the ambient temperature of the air, etc.
There IS also a consideration of the effect of lightly loaded PV modules (with the PV voltage into the CC increasing due to this light loading). But, this is a secondary effect.
In the initial post, you mentioned, "1/0 home run cables". I assume that there is a single home run, comprised of one positive, and one negative 1/0 AWG Copper cable. If you have already bought the cable, especially if it has been run in conduit, would suggest that you run the two PVs in parallel, and not have use a Combiner. You really should have one circuit breaker on the cable that feeds the FM-60 PV input. It would be best to place this breaker (MidNite MNEPV breaker highly recommended for this) in a box, like the Big Baby Box also from MidNite (MN) close to the FM CC. You could also have the REQUIRED DC breaker for the FM's output-to-battery cable in this box. This can also be an MNEPV breaker, if this output cable is large enough. There are tradeoffs on cable size, and distance from the this breaker to the battery, plus any thoughts that you might have concerning future additions of PV modules to this system, etc.
You are probably familiar with the MNEPV breakers, which are also used in the MNPV Combiners:
http://www.solar-electric.com/installation-parts-and-equipment/midnite/cipr1/stfubr1/mnepv.html
May we ask what is the approximate location of this system. Assume that this is an off-grid, or Grid Backup system, and that it will probably not need any Inspection for compliance to local Codes/standards (?).
EDIT: Just looked at your Profile, and do see your location.
AND, here is a Voltage Drop Calculator that is easy to use, and seems good:
http://www.calculator.net/voltage-drop-calculator.html
FWIW, Vic
My solar contractor left me with a very nice MNPV6 combiner box so I should probably use it even though it's not necessary. Also left with, AL 1/0 direct burial cable, 2 conductors plus a 4 AWG AL direct burial ground conductor (we were trying to reduce cost) already buried and ready to go. Contractor also left me with one polarized 15 amp circuit breaker for the array (says "made is Lesotho" on the the CB) and one polarized 63 amp CB for the battery charger which I have currently installed a couple of inches from the positive terminal on the battery bank (positive side towards battery!). Tangential question: i was instructed to install the 63 Amp CB very close (within 6 inches) to battery terminal so does that mean I should not put it in the combiner box? It looks kinda sketchy just hanging in the air next to the battery positive. If it's supposed to be so close, what is proper way to install?
Yes, it is an off-grid system for my yurt which will not be subject to inspection. My location is in the Columbia River Gorge near Lyle, WA. (profile updated)
I am currently working on a 3-line diagram of my system progressing about 1/4 inch per week. Is it acceptable to post the diagram and get feedback?
A little history. My 25 year old system started biting the dust this last year. I started replacing components one at a time as they died instead of having a comprehensive overall plan. So right now, I have nice new batteries and a sweet inverter, but I am using an old Siemens 75 Watt panel and an Evergreen solar 115 Watt panel WITHOUT a charge controller in the loop (bit dust). The panels are wired direct to my batteries. We rotate the panels out of the sun when the batteries get close to charged up. I know...
Thanks again for all the help and for spelling out some of the abbreviations!
For long cable runs, I use aluminum wire, you just increase the gauge 2 sizes (if #6 cu works, #4 alu is replacement) and save the $ difference, quite a bit of savings on the 900' to the water tanks.
Just be sure you use the anti-ox goop on Al rated connections (most everything IS cu/al rated)
Hi pablo,
Thanks for the added detail.
For now, you could use the MNPV6 Combiner inside, near your CC, for the PV input breaker (PV input to the FM-60), and also for the breaker for the FM-60 to battery connection (FM-60 output). Assume that you have the CBI DIN breakers that the contractor left with you -- the 15 A and 63 A. The CBI DIN rail breakers have a small yellow tang, on the lower part of the breaker that allows the breaker to latch into the lower part of the DIN rail. Usually these are MidNite supplied, and will have a very small sticker of the top of the front of the breaker that notes that it is rated for 150 VDC, as opposed to the more customary 125 VDC rating. The Outback breakers also have a similar tag, IIRC.
If your breakers are CBI (made in South Africa, or Lesotho), and they are DIN rail types, those would fit into your combiner. If you chose to use the MNPV6 for your two breakers, you would need to NOT use the included busbar. Would just tape this busbar inside the MNPV6, somewhere out of the way, so you can find it, if you should want to add more PVs later, and move the MNPV6 outside to Combine multiple strings of PVs.
You should not need to place the 63 A output breaker very, very close to the battery, if you protect, in conduit, the cable that will connect the output of the FM CC.
Please DO post your diagram, here, when you get the chance.
Would strongly suggest that you place the 15 A breaker near the battery, for now, to protect the cable that connects your present PVs to the battery, this can be a careful kludge, just as a temporary measure for safety. Assuming that the 115 and 75 watt PVs will not have more than about 12 - 13 amps maximum output, and that the cable connecting those PVs can safely handle this current -- normally #14 AWG Copper would handle this current.
Sorry to hear of the failures in your system, but it does sound like the system has given good service.
AL cable is fine, just am a Copper guy, and the longest run of large cable here is 225 feet of #2 for 240 VAC to the cabin, and that was run in 2005, when copper was relatively inexpensive. AND, copper building cable has become less expensive in the past 18 months, or so, as the demand from Asia has fallen ...
As Mike mentioned, use connectors for the AL cable that are rated for CU/AL, use NoALox (r) or similar anti-oxidant compound at all connections to/from the AL cable. You will want to transition to smaller copper cable at the PV end, and at the CC end of the AL PV cable run. These transitions need to be done with a means that is Rated (stamped on the connector - usually) CU/AL. With solid AL cable, it might be difficult to find an appropriate connector. AND, really should also be rated for solid AL conductors.
FWIW, Good Luck. Vic
I can't thank you enough for your time Vic.
Yes, the CBs do slide onto my DIN rail.
What would happen if I used the busbar?
Appreciate the suggestion to kludge the 15 amp CB into my system. Will do!
Was thinking of something like this to splice cables together:
http://www.galco.com/buy/Marathon-Special-Products/1321572
Although I like the products from Polaris. These are cool:
Quote from: pablo on June 20, 2016, 09:08:09 PM
.. Yes, the CBs do slide onto my DIN rail.
What would happen if I used the busbar?
Appreciate the suggestion to kludge the 15 amp CB into my system. Will do!
Was thinking of something like this to splice cables together:
http://www.galco.com/buy/Marathon-Special-Products/1321572
Although I like the products from Polaris. These are cool:
Hi pablo,
Most Combiners have a positive output busbar, a PV negative busbar, and a ground lug, or busbar. I should have noted, that you do not want to use the Combiner upper busbar, that connects the top breaker terminal connections of each PV breaker together. You do not want this, if you use the MNPV6 as a box for one input breaker and one output breaker, as it would connect two circuits together that you do not want to be connected.
The upper busbar does add some mechanical rigidity, but this is not essential for use as a simple breaker box.
The connector that you linked to, may be just fine for making the transition from solid AL to Cu cable.. Would suggest that this transition occur in a steel junction box, that has an easily-removable cover for periodic inspection. The steel box should be good protection if these transitions overheat.
Have used the Polaris, or similar splice blocks, and they work well.
These are just my opinions, and am not a professional electrician, with experience working with solid Aluminum cable, and connectors for transition to Cu cable.
FWIW, Good Luck, Vic
I see what you mean about combining the wrong two circuits together. I think the problem is that I'm designing my system based around this MNPV6 box. Instead of designing my system first and then purchasing the correct solution. I'm not sure why my contractor had me buy this box. Perhaps he had something different in mind. Her referred to it as a "DC breaker box" rather than as a combiner box.
I'm trying to get the box to do something like the attached (from my Flexmax manual). But with the upper DIN rail where the switches attach it would combine the circuits.
Hi pablo,
Here is a Brochure on the small MN breaker boxes:
http://www.midnitesolar.com/pdfs/smallEnclosure_front-back.pdf
You could use the Big Baby box for the DIN PV input and the DIN output breakers. If you needed a negative busbar, you could add a short MN insulated busbar.
You could use the MNPV6 to do the same thing, as described before. That busbar at the top of the PV breakers is a separate piece. It just slides into the top terminals on the PV breakers, and is held in place when these terminals are torqued.
You already own the MNPV6, and just thought that you could use instead of buying an additional breaker box.
MN Big Baby box:
http://www.solar-electric.com/installation-parts-and-equipment/midnite/elenanddcdi/misobigbabox.html
MN Short busbar (in black) for negative connections:
http://www.solar-electric.com/installation-parts-and-equipment/midnite/brbusbatebus/mnsbb.html
You could even use a wire nut fr the negative connections instead of any negative busbar.
More later, Vic
Ohhhh, lightbulb moment. I think I need to hire a translator.
I hadn't thought of the comb thing as a busbar and did not realize it was optional! That changes everything. Ok I'm back in the game.
I have been looking and looking at different MN wire layouts and configurations for my box but they always had the upper busbar in play. Is what I am doing so completely unusual or am I just using the somewhat wrong box for the job? After all, it is a "combiner" box...
Thanks again.
Hi pablo,
YES! You have the nature of that top busbar correct.
We do not know the nature of your inverter, and any electrical boxes that you are using that are from the original system. So you may only need to use the MNPV6 as the breaker box for the FM CC.
MidNite does make some boxes for dealing with the cables and breakers for inverters, plus CC DC breakers, etc ... plus some breakers for AC in and out cables. These start as the MiniDC, and go up to a series of e-Panels, if you really need a way to deal with additional breakers and cables. Will add some Links later.
It is possible that your now-absent electrician was thinking that you were going to add quite a lot of additional PVs, later, and that is why you have the 1/0 cable from the PV field, as well as the MNPV6 Combiner. This combiner should do fine, for now as a breaker box.
Later, Vic
pablo,
You may have seen the MidNite Mini DC boxes, but here is a Link:
http://www.solar-electric.com/installation-parts-and-equipment/midnite/elenanddcdi/midcdipoce.html
The MidNite e-Panels are usually made for a specific inverter, if you need a new way to manage all of the breakers and cables these can centralize all of this at a fairly low price, if you have nothing that is doing this job at this point:
http://www.solar-electric.com/installation-parts-and-equipment/midnite/misoe.html
FWIW, Vic
Attached is my design for my small off-grid 12 Volt system for my yurt (cross posted) Hopefully self-explanatory. Page 1 of the design is my proposed system, components are already purchased and installed, but just need to be wired together. My existing 12 Volt system includes the batteries on page 1 and everything on page 2 (did not include existing solar panels which are hard-wired to my batteries w/o charge controller).
Questions:
1. I'm using my combiner box as a DC disconnect box. Does the PV minus bar also serve as a battery minus bar? If not, where does the negative feed from the charge controller go to? I'm trying to get away from connecting everything directly to batteries!
2. Do I integrate my inverter with the disconnect box or just leave it as-is, directly wired to the battery? Same question for my Genny charger.
3. I have a lot of connections direct to my battery. Is that proper? Seems like a lot of connection stacked on top of each other makes for bad connections.
4. Do I need a fuse between the inverter and the AC panel?
I wish I would have bought a proper DC box as everybody has mentioned, but these are the components I have and am stuck with because I am out of money. :P
thank you!
page 2 of my diagram
Quote from: pablo on July 08, 2016, 11:45:47 AM
Attached is my design for my small off-grid 12 Volt system for my yurt (cross posted) Hopefully self-explanatory. Page 1 of the design is my proposed system, components are already purchased and installed, but just need to be wired together. My existing 12 Volt system includes the batteries on page 1 and everything on page 2 (did not include existing solar panels which are hard-wired to my batteries w/o charge controller).
Questions:
1. I'm using my combiner box as a DC disconnect box. Does the PV minus bar also serve as a battery minus bar? If not, where does the negative feed from the charge controller go to? I'm trying to get away from connecting everything directly to batteries!
2. Do I integrate my inverter with the disconnect box or just leave it as-is, directly wired to the battery? Same question for my Genny charger.
3. I have a lot of connections direct to my battery. Is that proper? Seems like a lot of connection stacked on top of each other makes for bad connections.
4. Do I need a fuse between the inverter and the AC panel?
I wish I would have bought a proper DC box as everybody has mentioned, but these are the components I have and am stuck with because I am out of money. :P
thank you!
Hi pablo,
You can certainly use the Negative Busbar in the MNPV6 as the Negative for the PVs.
A breaker between the Inverter and the battery is very convenient, but not necessary, as you are using the Class T Fuse. Those fuses are expensive, so, later you may wish to go with a MN MiniDC, or e-panel.
If you wish to use the PV6 as a place for the inverter breaker, the largest breaker that is DIN rail, is the double-wide 100 A (MNPV100, IIRC).
It is better to have a proper box for the Inverter breaker, and all of the other connections to/from the battery there. Some say that a direct connection to the battery from the CC's output breaker is better than connecting the CC + battery connection to the inverter breaker's input from the battery positive (but, I do not do it that way).
Yes, your TC40 needs a DC breaker.
You are correct about all of the connections going directly to the battery. It can be messy, less safe (generally), and can result in connections that are a bit sketchy.
More later, off to a remote site.
FWIW, Vic
Well, everything is up and running. I only almost-electrocuted myself once but did not blow up any of my equipment or start any fires. I had left the 110 circuit live in order to provide good lighting in my electrical closet while working on my DC circuits. At some point I moved from DC work to AC work w/o turning off the 110! I actually had a screw driver inside the AC panel connecting ground wires etc when I realized what I was doing. Lucky. Lesson learned... just turn everything off...
The only significant error I made was sizing my PV breaker too small. Amperage increased with my parallel wiring and I think my supplier had assumed I was going to wire in serial (which I now am... :)
"Some say that a direct connection to the battery from the CC's output breaker is better than connecting the CC + battery connection to the inverter breaker's input from the battery positive (but, I do not do it that way)."
Vic, could you explain this to me again? I don't quite follow. I am using the former method. Can you connect the CC+ to the inverter's circuit breaker? Directly? or via a splice or something? It sure would be nice to reduce the number of direct connections to the battery. I wonder if I could do this when it is time to tie my battery charger into the system?
Also, my inverter cables are 4/0. Are there actually CBs that can manage a 4/0 cable?
Thank you!
Hi pablo,
Great that everything is up and running, congratulations! And congratulations on NOT electrocuting yourself, as well.
Regarding the connection from the CC's output breaker to battery, it can take place at the battery, or at the battery side of the Main DC breaker that powers the inverter's positive DC input. The battery side of the inverter breaker is usually where I place this connection.
Forget just what inverter you are using (cannot see the Signature while Posting). There are large frame DC breakers that are common in our battery-based systems. Normally, we would use a 125, 175, or 250 Amp breaker, depending on the Surge capability of the inverter, and the size of the cable. 4/0 cable often has lugs with a clearance hole for a 3/8" bolt, and these large breakers use 1/4" studs for the 125A, and 3/8" studs for the 175 and 250 A. Here are some large breakers, the first three in this link are probably what you are looking for:
http://www.solar-electric.com/catalogsearch/result/?q=Panel+Mount+DC+Circuit+Breaker%2C
Have mentioned the MN Mini DC box, and the MN e-Panels, previously. These usually include the Inverter breaker, in a size that you specify when ordering. Know that cash is tight, but you may wind up getting one or the other of these boxes later. These large frame DC breakers should really be mounted in a fairly large metal enclosure, and adapting some inexpensive box will take some time ...
OK see that you have a 12 V 2K Samlex inverter. More later, Have Fun with the new system.
Vic
Awesome. Thanks for the link. I'll put those CBs on my wish list and start saving.
Generated 1.3 KW today!