Just got a great deal on a little system

mcgivor · July 2018

Personally I've never understood the single pole approach in a fixed ground mounted array, looks nice yes, but four legs along with some triangulation adds ridgity, lighter gauge steel can be used to provide a space frame which is way stronger.

BB. · July 2018

I do worry about the diameter/thickness of the "mono-pole" here too.

-Bill

Thick8 · July 2018

I'm not worried about the pipe bending as it is filled with high strength concrete. I have the same concrete filled poles holding up my pool shade and have had no worries from them in 10 years even with 6" of snow cover it's 12' x 24' size.

There is no weldment where the clamps attach. The 110 lbs of panels and frame are being held up by the angle resting on the top of the pole. The clamps are pretty much keeping it from twisting.

The panels are bolted together at 2 locations wherever they join another panel. The lader is bolted to the panels and the rungs bolted to the ladder. Also the u-bolts the mount the pipe to the ladder rungs extend through the lip of the panels and now have a nut added to help maintain rigidity.

I plan on adding a couple of braces that extend to the pipe. Just had to get it up to decide how to do it while being able to change the angle through the seasons.I think I have it figured out. I'll post a pic of what i come up with later.

One benefit is that the array is near the corner of an 8' privacy fence so hopefully the fence will offer a bit of a wind break.

Image: https://us.v-cdn.net/6024911/uploads/editor/fr/gjm60osm9c59.jpg

My plan is to motorize the array on 2 planes; hence the single pole configuration. I built a 2DOF flight simulator platform (prior to going VR) and plan on using the knowledge gained from that on this. I already have 2 wheelchair motors, an Arduino Mega, and a sketch written that will follow the sun acurrately and reset to the morning position at sunset each day.

mike95490 · July 2018

Filling a pipe with concrete only adds mass, not much strength, unless it has rebar embedded in it.

Photowhit · July 2018

So I've had a couple EZ ups, this isn't very heavy metal. And bolting the panels together makes for a nice fulcrum. Looks like the EZ up frame material is also strapped together... Looks too fragile to me!

Ever try to pass a sheet of plywood onto a roof on a windy day? Doesn't take much wind to make it an effective sail!

Thick8 · July 2018

mike95490 said:

Filling a pipe with concrete only adds mass, not much strength, unless it has rebar embedded in it.

I researched this pretty thoroughly when I put the sunshade over the pool. It makes quite a difference.

http://www.ctsee.org.tw/出版品/200310/ee0401-05.pdf

mike95490 · July 2018

OK, I'm not a mech engineer. As I understand it, plain steel pipe is not good. If it's chewed up/roughed up on the inside so the concrete can attach/bind to the pipe, then it gets stronger. But just plain water pipe, not a big improvement.

https://www.eng-tips.com/viewthread.cfm?qid=264916 gives this quote from some body on the internet

It is my understanding that flexural strength of the composite section is not increased much by the addition of concrete, at least not as much as axial capacity. However, your stiffness is increased so deflections can be smaller.

Thick8 · July 2018

Did you read the document that is referenced a couple posts below that opinion? It's quite interesting. The gist is that in order for a metal cylinder to bend it must deform or tear. When filled with concrete it can't deform without the concrete being removed. it can tear but I'm not putting those kind of stresses on the pole.

Estragon · July 2018

Do you do the math from the linked-to paper?

There's a point load at the base of the pole where it's imbedded in the concrete base, and a long lever arm relative to pole diameter. The concrete will stiffen the pole along its entire above-ground length, putting almost all the bending stress at the base. Over time, the repeated stress makes a concrete crack most likely there, further limiting the point load to the base, and weakening it at that point It's a bit like a stiff tree growing in rock. Less give in the trunk puts more stress on the base in a wind.

The paper shows ways of dealing with these kinds of loads (eg reinforcing sleeves at beam-column connections) and the math to define when it's needed.

It looks like the trees and fence should be a pretty good windbreak for you though, so it may not matter.

Thick8 · July 2018

Trial by storm today. 45 mph winds with heavy gusts followed by 2.53” of rain in less than an hour with run and hide tornado advisories. Still solidly pointing south with a 68 degree tilt. My wife said it looked like a waterfall when she could still see out to the yard from the kitchen window.
So would it be best to hook up the panels in a 80v/5.5a or 40v/11a to feed the mppt controller? 8 or 10 gauge wire is the same cost. I was looking at another post here where it is recommended to have the array supply only 30% more voltage than the battery to keep heat down.

mcgivor · July 2018

The rule of thumb is to have at least 30-50% over the nominal battery voltage for the MPPT to take advantage of the higher voltage, the efficiency of the controller will largely dictate how much loss, in the form of heat, there will be. Sometimes choosing a higher voltage to compensate for volt drop over distance is advantageous, in my case with 24V nominal I wired for 60V first then 90V, there was negligible difference in output, or difference in temperature of the controller, obviously this is comparing apples to oranges as the controllers are of a different make. For a 12V nominal system running 80V may be excessive, use a volt drop calculator to get an idea how each configuration would impact results, remembering the amount of voltage drop multiplied by the current will give the amount of power loss over the conductors. The controller losses will be reflected by the difference between watts in versus watts out, it's difficult to accurately monitor because of the dynamic nature of MPPT controllers, an IR thermometer is handy to monitor temperatures, my best suggestion is use the rule of thumb to start with.
https://www.calculator.net/voltage-drop-calculator.html

Photowhit · July 2018

Thick8 said:

I was looking at another post here where it is recommended to have the array supply only 30% more voltage than the battery to keep heat down.

It's a trade off, with a long distance you will either lose more in voltage drop, or have to run heavier wire for long distances. You will want to measure your distance of wire run and plug it into a voltage drop calculator.

For the record 30% above the charging voltage is the minimum, and about double is near ideal with many.

Your VMP is 36, so it is doubtful you will ever see more than that. If 8 and 10 gauge are the same cost somebody likely made a mistake go with heavier wire!

littleharbor2 · July 2018

Photowhit said:

Thick8 said:

I was looking at another post here where it is recommended to have the array supply only 30% more voltage than the battery to keep heat down.

You will want to measure your distance of wire run and plug it into a voltage drop calculator.

Remember, when measuring distance for DC voltage drop you need to figure round trip distance. 45 feet away is actually 90 feet round trip.

westbranch · July 2018

+2 on the 8 awg wire IF it is the same price for the right type. I always opt for the largest wire when the price is the same. For ease of mind check out the 6 AWG and 12 AWG.

mcgivor · July 2018

littleharbor2 said:

Photowhit said:

Thick8 said:

I was looking at another post here where it is recommended to have the array supply only 30% more voltage than the battery to keep heat down.

You will want to measure your distance of wire run and plug it into a voltage drop calculator.

Remember, when measuring distance for DC voltage drop you need to figure round trip distance. 45 feet away is actually 90 feet round trip.

Different calculator perhaps but the one I posted a link to, post 42, says use one way, not round trip.

Photowhit · July 2018

Yeah, most only want one way distance;

Thick8 · July 2018

My plan is to get everthing hooked up this weekend. I was able to trade out the 5000w and a 2500w modified sine wave inverter for 2 2000w Magum dimensions pure sine wave inverters. with the 1000w one that I already have that should give me enough power to run my garage and have emergency backup for th house.

below is the recommended battery configuration (thanks Photowhit) and below that is how I currently have my batteries hooked up. Is my way going to create too great of an imbalance? I'd have to go make new cables and don't have access to the cable reels at work over the weekend.

Image: https://us.v-cdn.net/6024911/uploads/editor/a7/pb9tzo8qh9bh.jpg

Thick8 · July 2018

I also didn’t know if the fact that using pretty heavy cabling negated some of the imbalance.

mcgivor · July 2018

The crimped terminals need attention, that's a fault waiting to happen, a fuse wouldn't be a bad idea between batteries and on the output, there are thousands of amps there looking for a short circuit, be safe.

Thick8 · July 2018

Yea they do look pretty crappy. They are not just crimped but soldered as well. The lugs are made for a smaller gauge of wire so the cable was trimmed around the outer circumference. The green is from flux.

I hooked everything up to get an idea of the output. a re-wire with circuit protection and disconnects will happen over the next couple of weeks before I put it into use. I broke down and spent some money on a more moblie platform than what I had. This way I can wheel it up to the house when power is out (about 4 times a year from a few days to a week).

mike95490 · July 2018

Thick8 said:

Yea they do look pretty crappy. They are not just crimped but soldered as well. The lugs are made for a smaller gauge of wire so the cable was trimmed around the outer circumference. The green is from flux. .......

You have pretty much ruined your cables.

1) poor crimps

2) soldered

3) green flux is usually plumbing based acid flux, it will dissolve fine wires in months.

So be prepared to do it right pretty soon.

Thick8 · July 2018

No it was a rosin core flux. Those hammer type crimpers don't do a great job is the reason for the solder. It was old 24 volt starter cables from a 99 Kenworth so the quality of the wire is suspect. I'm wondering if the green is because he battery pack was stored near my pool supplies; there is always a smell of clorine in that corner. It's been moved. I work for a company the outfits/modifies trucks for the power company so I'll have one of the guys make up a set of 2/0 cables.

Just got a great deal on a little system

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