Using RF coax cable as DC Solar PV cable
 

Warning, if you are not trained to handle high DC voltages,
please do not attempt any of the experiments discussed below.
The DC voltage from series-configured solar panels can seriously burn and/or kill you.



At work, I've had success using RF coaxial cable as a high voltage DC cable.

Because of the small diameter of the center conductors of coax cables,
the are not suitable for high current applications.

Specs for the cable I've been testing (RG-214U) shows 6 ohms/km in the center conductor,
and 3.1 ohms/km on outer (shielding) conductors.
(RG-8u is more common and has similar specs).

My goal was to test surplus RG-214U cable for currents under 10A,
so the power losses at 100 feet would be minimal. (Around 0.2 to 0.4 ohms).
I'm using a negative ground system. + voltage is on the center pin.
RG-214U is direct burial cable. But beware of using old network cable, underground.
Since some network RG8 type cables have tiny pin-holes in the plastic jacket. Not waterproof.

The aim of these tests is to confirm the utility of the Coax PV power method of power transfer.
If this method is found safe & effective, for use in temporary/emergency installations,
it could be useful to provide power for communications equipment,
using existing (and available) RF coax cables.

~~~


By using panels in series, peak amperage would always remain near the
max amperes rating for a single panel.
So, using four panels in series increases the voltage, but not the amperage.
Power Loss= Amps squared x Resistance.
For 8A panels, using a 100 run, the losses should be less than 5 or 6 watts.

http://www.universal-radio.com/catal...le/2929lrg.jpg
What worried me is the connections. Crimping and soldering large terminals
at the ends of the cables works okay. But, I wanted to use standard 'N' type coax connectors
(since I also use them for Ham Radio).

Some Type N connectors are difficult to install, but sometimes,
you can get cables with factory installed connectors..

The center pin of N connectors is tiny. But, I've only had one get blasted.
I think it was installed off-center or it wasn't really gold plated.

The water heater experiment, uses N connectors at both ends (100')
and no heat (losses) can be detected from the connectors.

Typical high power is 600 to 800 watts. With voltages between 60 & 100vdc,
with currents under 8.5 peak amps.

The cable (left) is connected to a N type Bulkhead or chassis connector,
which is wired to the water heater load. (Scan shows 45deg F).
http://ecorenovator.org/forum/attach...1&d=1360945191

This is the outdoor side. PV comes in the bottom wires.
The + side is switched and fused before going to the center conductor of a very short coax cable..
Which is connected to a double female N bulkhead.
http://i46.photobucket.com/albums/f1...Solar/CCPV.jpg

Warning, just like the MC-4 or other Solar panel connectors,
these can NEVER be unplugged or plugged in while the sun is on the panels..
The power will arc weld/melt the center pin. It will have to be replaced.

This flexible cable has an OD is 0.405" and can be quickly buried a few inches underground,
just by parting the sod with a spade blade.

So far, my results have been good. I've also been using this same setup
on my 500W back-up system without any problems.

Of course, since this is a temporary Ham Radio related research project, (I hold an Extra Class FFC license) :rolleyes:
and can be quickly uninstalled, I'm not worried about meeting code requirements for buried cables etc.

Edit:
I have not yet tested the low-cost version of this method, which will use the PL-259 / SO-239 type connectors.
These are a bit easier to install and have a larger center pin, which might make it less lossy.
I might try these (cheaper) connectors this summer..

Why not just use regular wire? Is coax cheaper, or did you just have it on hand?

Could a surge protector help protect the system during plugging unplugging ? or is it not surge, only flow ?

I had a three 100 ft sections with N connectors, purchased cheap at a Ham fea-market.

IIRC you can find 100 ft sections (w/ PL-259 connectors) on Ebay for 20 to 30 bucks.
Much cheaper without connectors.

I wanted to use this type of direct burial cable for my testing, but other cable could be used.
I've actually used regular 120Vac extension cords for short tests.
They are easy to use, and the connectors are pretty cheap.
'N' connectors are very water resistant, which helps on the outdoor side.

There isn't any device, that I know of that will inhibit arcing of connectors.
If there was, they would be used on PV cables.

If plugging in, the instant first contact is made (or very close to contact),
a large current will melt the (small) point-of-contact,
causing the contact surface to blow open or melt into a dead short.
If the voltage is 60 or more volts, an arc will form (like an arc welder),
melting & pitting the surfaces of both sides of the contact.

The same thing can happen when unplugging under power.
That last (tiny) point of contact melts, starts an arc, that damages the contact surfaces.

If you had enough panels, I'll bet you could arc weld steel..

That wouldn't help. The reality is that all you need to do is block the sun from them so they can't produce power. Cover the entire surface of the panel with a black garbage bag, cardboard, or something like that would do the trick while you plug or unplug the panel.

Actually nevermind. With panels in series you would need to cover the whole set.
Also since this isn't UL listed, it isn't to code and can't be integrated to the grid unless the panels and interconnects are UL listed.

When I'm out messing with the panels on a sunny day, I'll take a sheet of cardboard
with me to block off the bottom of one of the panels..
That way, I can use the cut-off toggle switch to kill the power out, without toasting the switch contacts..
It's actually much safer to just do the work after the sun goes down.. :)

I was thinking about one of these Contactors for controlling the power going into the hotwater heater element..
White Rodgers 120 114751 6 Coil 24V DC 120 904 Heavy Duty Contactor New | eBay
But, maybe a big MOSFET would be better.. Only need to handle 10A max..

This is an Off-Grid experiment. Any inverter that can take 122 volts is out of my price range anyways.. :)

Wow - this discussion takes me way, way back to the '60s. I knew well that RG-8 could handle 2,000 watts with ease and had friends that were trying to wire up a "shack" for late night CW contests (ham radio stuff where you are up all night).

The RG-8 was already in the ground - in fact in conduit (to a defunct antenna tower), so we used it to pipe out 120 V ac. I think it was about 150-200 feet.

We tested it by putting on 1200 W electric space heaters until we saw a voltage drop. If I recall, we put on 4-5 of them before we saw any voltage drop. The cable was not even warm.

We also hooked up an intercom system from the house to the "shack" that used the old wired intercoms on AC systems.

Later on - and in an arena that was completely different I recalled this and used RG-8 to multiplex signals when we used burst communication in very short pulses. The pulse (20 msec) was about 20-30 kW in ERP and only used once or twice a day. The burst was also in Rg-8 coax that was used on a 240 V system drawing about 40 amps. No code inspectors were present, not even thought of . . .

Coax is used in a lot of undeveloped countries for household power as it is readily available and cheap. Some people even use it to wire their homes. The center conductor looks about like AWG #10 or so and the braid must have the equivalent cross section.

Steve
ex WA1LHT

Wouldn't a circuit breaker solve the problem of a arc at disconnect ?

I think I got it .. :)

Is that labeled as a 220v~ 3,000 amps??
That's not really going to work with a 0.66 megawatt load is it? :eek:

What uses that much power??

~~~

An AC~ breaker that had large self-wiping contacts and
a good air-gap when open might to the job on DC.
You could try it.

On any kind of switch for DC power switching,
one thing you want is speed. It's going to arc anyways,
but if you minimize the time it's arcing, the contacts will last longer.

Hey Steve, I would never try to feed AC neutral anywhere on a coax shield.
That's just too dangerous.
In 1968, I purchased 6 meter rec converter from an old Ham.
It came with a DIY power supply. It was a plain metal box with a transformer on top.
It worked fine, so I never opened the box.. It had a non-polarized AC plug.

After a near disaster, I opened the box and found the transformer was only
6.3vac for the tube's filaments! The 170VDC B+ for the tube plates
was directly rectified right off the grid!!

The neutral side of the plug was the box ground.
The hot line connected to a big diode and a cap.

The day I plugged it in the wrong way, it was snowing and raining.
The hot side was on the outside coax shield. I never noticed anything.

Later I heard on the scanner, 'A power line has fallen on the fences'..
My neighbor told me that there was sparks when he closed the gate.
I then realized, The 6M antenna was on the fence!
I disconnected the converter and opened the box.. Dang!
I ran out and told the power company guys what happened.
They were glad to get out of the weather.
My wife heard on the scanner, "Some ham radio nut had power connected to his fence".
All the fences on the block were connected together. And, all the steel poles
were sitting in wet concrete blocks in the wet ground.

All that ground should have shorted and blown the 15A fuse in the basement.
I went down and checked it the next day. It was blown!
It had been blown before we moved in..
But, some other tenant had placed a penny behind it.. :eek:

I looked over both basement fuse boxes and found 4 more pennies!

I had thought the 3,000 amps would suffice , Lord knows what circuit that is for, industrial I suspect or another Chinese marketing exaggeration..

Yeah, at that size, it's likely 30A..

god saves idiots
 

God saves idiots and kids . . . I now know how dangerous it was, but at that time, most everything was non-polarized.

Funny too in developing couintries, they throw a clamp over an overhead line, connect it to a 120 v incandescent bulb and literally ground the other end. If it blows up it is 220. Then then put in a 220 bulb, if it blows then it is 440 . . .

When the "village expert" knows the voltage, he rigs a transformer to step it down to 120 and strings wires to the village. Primitive, but it works :confused:.

Another person (same village) put up an electric fence around his pasture. I knew he was in trouble when he asked me which of the two wires he should plug the "electric fence" wire into . . . :eek:

So what is wrong with pennies . . . . .!!

Pennies are 3,000 amp fuses! :p

When we moved in to that apartment in August of 1968, we had a nice GE toaster.
It was a wedding gift. It sat on our big metal sink for 5 years and worked perfectly.

It had a non-polarized AC plug.

In 1973 we moved into our current home. Within a few years,
I talked my wife into one of those newfangled microwave ovens. (300watts)!

After plugging in it's three pronged plug, I put my left hand on the left side
of the GE toaster and pushed it up next to the new Sears microwave.

There was a bright flash as a steel screw head on the oven's cover,
welded itself to side the chrome toaster. The fuse blew within milliseconds..

I broke the toaster off the screw head and took it apart.
One of the AC cable lugs was installed, twisted 90deg to one side..
The terminal screw was nice and tight from the factory.
I re-tightened that screw after correctly positioning the terminal lug
(removing the short to chassis) and we had many more years of toast..

That thing could have killed one us at any time.
Just one hand on a ground, and the other on the toaster.
Didn't even have to be burning the toast.

That new micro wave not only warmed up leftovers, it might have saved a life..

This is pretty interesting. I never thought of using Coax connections, but I have thought of using RCA's before. Considering the power that twisted pair cabling can handle through RCA connections, including the 60KW I've put through them [audio installations], I imagine they'd work out pretty well.

Keeping an eye on this.

Check out RG8 with PL-259 males and SO-239 female chassis-mount connectors.

http://dxavenue.com/155-512-large/so...uhf-female.jpg


'N' on top, and PL259 on bottom.. These are crimp. Solder type is better.
http://www.eham.net/data/articles/19257/index2.jpg

The PL259 looks a bit more 'robust' in the mid pin... am I seeing that right? Seems that would be the better choice if one were to attempt this?

It's not a fragile pin like the 'N' connector uses. Once you learn how to install them,
it's easy to make pretty good connections.
PL-259 Installation Made Easy for RG213 - YouTube

Note: Always remember to slip the screw-on outer shell onto the cable before soldering..
Otherwise you will have to start over..

http://www.radiobrandy.com/image/PL259_Install-335.jpg

For testing purposes, would it be sufficient to use, maybe, some prepared RG-6? I think that's what it is.

I understand that the wire is thin and the shielding is more like aluminum foil, but how well do you think it would fare for short term beta testing type stuff?

RG-6 is cable TV cable. Mostly it uses the center conductor as it's center pin.
They call them 'F' connectors. Most are crimp type.
Aluminum shielding foil isn't the best conductor. Copper mesh is way better.
The wire gauge is small..The cable itself isn't real bad. It could handle a few amps..

But the female connectors have a very smallish contact area.
I don't think they can handle much power.

Awesome. I have a couple friends who work for cable and satellite TV companies and have to build direct burial line all the time. I might be able to snag some bits from them to use for panel interconnects, etc of the higher quality stuff.

Teh last time a sat installer came out here, they used double-line coax [DirecTV] and it had a mesh copper ground sleeve on it.... come to think of it, there's over 200ft of it coiled in the root cellar... I may have to look into that. I'll have to change the ends on it, I think... no center pin, just has the wire poking through.

I will only use proper solar cable because I might use strings of 13 panels which will be 500+vdc. It needs to be rated for 1000Vdc and UV rated. What is the co-ax rated for or is it even rated at all?

This is RF cable. It's not designed for DC use, therefore, there is no DC voltage or current spec.
But, people have used it at high DC & AC voltages. I've used RG8 at 2,000 volts DC @ 300 to 400 watts, with no problems.
Because of the center conductor's size, there is going to be a limitation on current.
(See the loss info above). It's current squared x R.

If you had a real long run of small size wire with 2 ohms of resistance,
the loss at 10A would be 100 x 2= 200 watts of wasted power..
But, if it was 20A, 400 x 2 = 800 watts of loss.
40A would be 3.2 kW of loss.. Those wires would be kinda warm! :eek:

Here's some RG8 info on higher voltages.

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RG8 is water proof and UV resistant. It's been used outdoors for decades (radio antenna connections).

BUT, I'm pretty sure that using any kind of coax for PV won't meet code around here..
www.senecass.com/NEC2000.pdf

I don't think any city electrical inspector would allow you to use anything
that didn't meet NEC and/or local codes.


One might use Coax for low current / high voltage for PV, during an emergency when no other cable is available.
Or, you might use it strictly for experimental research or testing to see if it
is really a safe temporary replacement for NEC approved cable.

So, how large was the fire, and did you get the coax disconnected fast ?

AC vs DC circuit breakers
 

Circuit breakers designed for breaking AC currents use the fact that AC current goes thru zero every half AC cycle. Thus arcing is short and less destructive allowing relatively small contact seperation.

Not so for DC contacters and circuit breakers. They normally use larger and faster contact seperation and often employ magnetic arc blow out devices and power factor correction.

Isn't DC capacity just based on resistance and gauge?

It's all about the resistance of the wire. More resistance = more power loss.

http://ecorenovator.org/forum/attach...1&d=1362891010

But, if you only have small gauge wire, using higher voltage allows it to
conduct more power.

My Coax has performed pretty well at 100V at 8A..
The heat dissipation is minimal. But if I were using really small wire,
with a lot of resistance, it could get hot and even melt in half.

Sun is getting higher!
 

Getting 800+ watts today. (from the 800w array) :) But, I noticed the sun is being reflected back into the house.

http://ecorenovator.org/forum/attach...1&d=1362938070

(Reflected sunlight should be pointed right back at the sun)..
That means I have to get on my snow shoes and go lower the angle of the array!
Wow, it's almost springtime! :D

For maximum /panel/ efficiency, it should reflect back at the sun... BUT, seems that if you're not using all the power you can generate, it doesn't hurt to point some solar heat gain into the walls. :P

I re-adjusted them yesterday (they were way off angle).. Working better now.
I'm getting a nice amount of power out of the 800w array, considering the conditions lately.
Today we had over-cast+hazy, but once in a while it would get thin and a little brighter.
I looked at the power a couple of times and was surprised to see peaks over 600w.
I like the idea of reflected solar, but it's too big and complicated..

4 Practical Solar heliostats (time-lapse video) - YouTube

Neat eh?

What are the tiny PV panels on the bigger ones?

Each of those charges a 12V battery. Two are old car batteries in the house and the third, smaller battery that runs the tracker motor.
http://i46.photobucket.com/albums/f1...Solar/z010.jpg

http://i46.photobucket.com/albums/f1...kerbattery.jpg

Xringer,
The idea of using RF coax cable for solar panel DC is good (find new use for coax cable). There is plenty coax cable around the house. I was wondering is it safe to use existing coax cable for a low power solar panel rated 45W (12V about 4AMP)? I didn't understand you concern about arcing. Is arcing also an issue for 45W low power solar panels? I am thinking to use the exiting coax cable to connect the solar panel to the charger controller which is inside the house (about 50 feet). Any comments? Thanks.

Arcing is a serious problem with high voltage arrays, when switching the power on and off.
My 800W array can deliver 7 amps at about 114 volts.
That will not only kill you, but you could do a little welding with it..

If you are only using a single 45W Panel with 4A @ 12v, you shouldn't have any problems.
But, if you are using TV coax, with it's tiny center conductor, you should avoid
plugging or unplugging the cable while it's running power.
The arcing will be minimal, but can still cause contact point damage,
which can increase resistance, losses and maybe melting at the contact point.

There is almost zero shock hazard at 12V (just don't put the wires on your tongue) :p
and avoid holding small wires together with your fingers.
If the point of contact sees too much resistance, that contact point will heat up.
(Think about how hot a 45W soldering iron can get).

That's fantastic! Now I can reuse my existing satellite dish coax cable system for my solar panel (I was going to recycle it earlier). The voltage from the solar panel can be as high as 23v before going into the charge controller but I don't think it will make much difference.

The best part is that I don't have to drill holes on the wall to get the cable in because they are already there. I searched the internet for hours and I found that you are the only one who has experimented with coax cable for solar panels. I will cite your posting as reference. Thanks a lot!

My old C-band Satellite dish had coax cable and some 12 & 14 gauge cables out to the old dish mount. (For motor and servo wires).

I'm using that 20+ year old TVRO cable to charge up a couple of old 12v batteries,
from two 5w 12V panels, at the end of the 100 foot run..

http://i46.photobucket.com/albums/f1...Solar/z010.jpg

One battery powers our master bedroom reading light (LED) and
the other one is for my Ham Radio gear in the basement.

Been working for a couple of years IIRC..

That's inspiring. I will try with my cable and solar panel.

BTW, speaking of old batteries, have you tried to use a "desulfator" on them? Does it really work? I looked at a few schematics including Alastair Couper's original version and did some circuit simulations but couldn't get the voltage and amps they mentioned. Not sure it really works or not.

I use a Schumacher SEM-1562A charger 'Maintainer' for my SUV battery, but it doesn't have a desulfator function.
I don't drive it much anymore. If we don't need to haul big stuff, we take the wife's Prius C2.

We replace car batteries every 6 years, so I'm able to cycle out my old junk 12V basement batteries.
When I buy a new car battery (we have two cars), I turn in my oldest 'basement' battery.

My 12V solar controllers are simple voltage regulator junk from China.
They were cheap and they don't over-charge, so I'm happy.. :)

My next big battery problem is to replace my three year old 48v battery bank,
with real solar backup batteries..
http://ecorenovator.org/forum/solar-...r-project.html

I'm not sure, but I may have set the controller voltage too high and
lately the output performance has dropped off..

I have some cable that I bought from a cable installer. It has a thick black plastic outer shield, next a foil layer, next a braided wire layer, then another foil layer, and then a tough white plastic center, and finally the solid copper center. There are no markings anywhere. I gauged the center copper wire and got .042 to fit the size hole with the copper center wire. The cable tech. man said it was waterproof and I could bury it . My question is: can I use this to any purpose for 2 Harbor Freight Kits (45 watt each) equaling 90 watts. Connected together. Is it wise to use this type wire for solar ? Thanks for your expertise !