Combiner box

[fblevins1]

Hi Guys/Gals,

I have a solar set up on the rooftop lab and I need to combine the outputs of my three charge controllers into one output that goes to the test batteries. I can get cheap and easy combiners/splitters at Home Depot, But I notice that there are pretty nice ECO-WORTHY PV combiners but the problem with using them is the maximum rated current for each PV input is 10 amps and I guess in a perfect world, each of my charge controllers put out 30 Amps so what I need is a good DC combiner that has most of what I would need all inside the box, only requiring the wire hook ups, heck, I don't even mind some built in protection, If the ECO-WORTHY could handle more current for each input, it would be perfect. Some of you folks do this for living or even an active hobby, so I defer to your experience and knowledge. Minimum 3 inputs at 30 amps and of course the combiner would need to pass up to 90 amps on the output but that is a job for the AWG rating of the cables....the box just needs to accept the conductor dimensions. (it has to fit) I am going up to the roof to verify my grand claims of 30 amps each, if I find the information is different, I will edit. Thanks a heap guys, got to help the military officers get their microgrid thesis lab set up...what they do with is up to them.

 

[chrisski]

I almost bought the ecoworthy.

If you need to modify anything in that box because it does not fit your specs, I recommend you build your own combiner. It’s not that hard.

For example, changing to 30 amp circuit breakers will require at least 10 AWG wire, so if there is not, that would need to be replaced.

Midnite Solar makes official combiner boxes you add components to up to the max specs, or you get a project box that fits the bus and breakers that combine. I have done both.

 

[fblevins1]

I almost bought the ecoworthy.

If you need to modify anything in that box because it does not fit your specs, I recommend you build your own combiner. It’s not that hard.

For example, changing to 30 amp circuit breakers will require at least 10 AWG wire, so if there is not, that would need to be replaced.

Midnite Solar makes official combiner boxes you add components to up to the max specs, or you get a project box that fits the bus and breakers that combine. I have done both.

Yea, the Ecoworthy box just won't handle the potential 40 amps per charge controller. My boss is warming up to the simple high current combiner that are small and have a safety lid you just snap into place. I think I may wind up buying a good heat resistant plastic box with knock out holes and just mount the combiners and safety breakers all inside the box., which is pretty much how the Ecoworthy boxes are set up.

 

[TomC4306]

Combiner boxes go between the solar panels and the charge controller. What you need to combine the output of charge controllers are bus bars

 

[chrisski]

Combiner boxes go between the solar panels and the charge controller. What you need to combine the output of charge controllers are bus bars

I missed that this was from SCCs. Yes a busbar is what you need. Disregard what I said earlier.

 

[fblevins1]

I think you guys are right. I found one at Home Depot that has a snap on plastic guard, not complicated and provides a safety factor not present with standard bus bars although I did present them for consideration. I like the one with the plastic guard because it also has two flush mounts I can use tile underneath for heat resistance and possibly electrical insulation between the set up and the old beat up work benches. I like the Eco-Worthy because it had all the concerns addressed, fused, circuit breaker and surge protection and of course a couple of bus bars already where needed. But without the ability to carry more than 10 amps per input, that is a no-go. So simple and effective wins. Thanks guys, and if any of you do run across a good combiner box with built in whatchamacallits and wingdingers that would be awesome.

 

[featherlite]

I found one at Home Depot that has a snap on plastic guard,

Could you please post a link to the Home Depot bus bar? Thank you

 

[TomC4306]

I was thinking something like this

300A 4-Stud Bus Bars - Distribution Block w/Cover - Red/Black

Designed to streamline and organize electrical connections, our high-performance 300A 4-Stud Bus Bars are suitable for a wide range of applications!

www.currentconnected.com

 

[fblevins1]

I was thinking something like this

300A 4-Stud Bus Bars - Distribution Block w/Cover - Red/Black

Designed to streamline and organize electrical connections, our high-performance 300A 4-Stud Bus Bars are suitable for a wide range of applications!

www.currentconnected.com

I ordered two sets of those from Ebay, not exactly that MFR but same color coded design only 200 Amps instead of 300 but they will work. I don't normally spend my own money but if these work, they will definitely work at home for my own distribution, especially when I retire and really get my solar mojo on. I don't suppose you happen to know a good supplier of a plastic distribution box? My boss not only want's a better way to split 3 dc sources into on (that block you linked me to) but he also wants to install the three PV switches and the 3 circuit breakers into a box and have the associated wires coming in and out. Not sure if I agree with his lid mount for the tops of the breakers and switches, but we have to start somewhere.

 

[fblevins1]

Why do people who sell wire always high ball the amount of current that their cables can take? I just don't understand it. It's like they went to an AWG chart, and took their fingers and went along the AWG line of interest and they take the highest value, usually at some ridiculously high temperature and they state that as the maximum ampacity, which is a load of crap. So far because I usually safe side the requirements the wires I bought were good enough. I mean who operates at near the surface temperature of the sun? (standard exaggeration rates apply) seriously, our microgrid lab might see 30 C in the summer but nowhere near 105 C? Ugggg OK, pointless rant over.

 

[chrisski]

Why do people who sell wire always high ball the amount of current that their cables can take? I just don't understand it. It's like they went to an AWG chart, and took their fingers and went along the AWG line of interest and they take the highest value, usually at some ridiculously high temperature and they state that as the maximum ampacity, which is a load of crap. So far because I usually safe side the requirements the wires I bought were good enough. I mean who operates at near the surface temperature of the sun? (standard exaggeration rates apply) seriously, our microgrid lab might see 30 C in the summer but nowhere near 105 C? Ugggg OK, pointless rant over.

I’m not sure I’ve seen this. The only wires I’ve seen that ampacity is above a NEC chart are welding wires.

Which wires do you see that are exaggerated?

 

[fblevins1]

I’m not sure I’ve seen this. The only wires I’ve seen that ampacity is above a NEC chart are welding wires.

Which wires do you see that are exaggerated?

I admit I do order from Ebay because the prices are cheaper, I have ordered 0 AWG and 2 AWG and both times they just say the wires can handle 210 amps for the 2 AWG and 285 amps for the 0 AWG. I think I wouldn't cry like a baby if they would just add a * and tell you where they pulled the value from. I don't always have time to immerse into charts and temperature and wire length to figure out how large a conductor wire I need. The wires I order are relatively short (around 3 feet) so I just look at the equipment specifications and order wire that I assume based on the selling information is sufficient and I guess at the end of the day, it is. But barely. I mean the wires I have going from the batteries to the inverter are huge, like and inch wide. And I admit I just take what information is in front of me. For example I have a 3000 watt inverter and 3000/120 VAC is 25 amps so I figure for a 12 volt battery system I need a 250 amp cable and I buy a 285 amp cable and then I learn that at the temperatures we operate at, that is just barely enough. I really need to stop posting after taking a wee bite of the creature.

 

[TomC4306]

I don't always have time to immerse into charts and temperature and wire length to figure out how large a conductor wire I need

Hmm.
Please don't invite me over to your place for lunch.
Doesn't take that much time and this is a subject that you really should make the time for.

 

[fblevins1]

Long winded counter edited. I will leave this with the concession that "I don't always have time" and I never have time are two different meanings. I suspect that what I am guilty of is over gauging. But 3 feet of 0 AWG and 3 feet of 2 AWG is not breaking the bank. But you did inadvertently dislodge one thought. Why didn't the 3000 watt inverters come with current appropriate wire? My 5000 watt inverter sure did. Hmmmm. Well, I spotted 3 unopened boxes over in the power lab so I am going to pop one open and see what the MFR supplies....if anything. Wish me luck.

 

[Hedges]

Inverter battery cables, need fuse and wire to handle max continuous inverter draw, but most of the time they don't. So designing around 90C or 105C cable seems reasonable. Except, I keep hearing that whatever the terminals and breaker are rated for, have to calculate ampacity based on that (often 75C.)

I would be inclined to use "single wire free air" ampacity for the 75C rating at lugs, and "up to 3 wires in a cable" at 90C for rest of the wire run. This would need the individual wires long enough to dissipate heat coming from cable.

PV leads and SCC wires to battery, those we know how much they will carry for hours on end, so that's a reason to oversize them so they remain cool. PV wires are already oversized to 1.56x Isc, so that is sufficient.

For your 3000W inverter, if I assume 90% efficient at full load and 10V low-voltage cutout for lead-acid battery, here's my calculation:

3000W / 10V / 90% x 1.25 margin x 1.12 ripple factor = 467A minimum fuse, and wire ampacity must be at least as great.

Adjust battery voltage according to your chemistry, and update efficiency if one is available. (Not "peak" efficiency.)
The extra 12% ripple factor is my contribution to the field. Decoupling capacitors in inverter only handle high frequency switching, are not big enough to smooth out 60 Hz pulses. Power delivered is voltage x mean current, but heating of fuse and wire goes as the square of current, calculated as RMS. That is 12% higher than mean.

 

[fblevins1]

Well folks, the wire has been ordered, the mounting plate constructed, the combiner boxes and bus bars ordered and received. I will post a picture of the finished academic set up. Basically I am running 2 gauge between the controllers and the batteries to include the battery jumpers and 0 gauge from the batteries to the inverter. Overkill but room for expansion, the distance from the controllers to the inverter though the batteries is only about 6 feet. There are switches and breakers located in the combiner boxes along with the bus bars. Thanks for letting me soundboard off you folks.

 

[fblevins1]

Just about done, but more to come. We have been helping students with their projects since 1951, hence some of the older equipment you see in the picture. Supporting the War Fighters.