mcs/mc4 solar panel palugs and the new 'phoolery strain - Page 1
Forum section: electronics / general

author: Simon
author_rank: Unknown
timestamp: February 19, 2011, 10:38:09 am
content: As with audio stuff and what we affectionately call audiophoolery (the beleive in mystical audio products by audiophiles that have little technical understanding) I believe a new strain of the 'phoolery pandemic is emerging in the form of solarphoolery or solar panel phoolery.I see many panels advertised on ebay with MC4 plugs that meet the MCS standards ? what is this all about, and oh yes we already have special "solar cable" being supplied as a bonus with panels.I've just bought a 50W panel from Germany for £ 103 deliveredhttp://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&item=200561996580&ssPageName=STRK:MEWNX:IT(£2.06/W compared to the £3.25/W I paid 18 months ago and I've aready spotted panels at £1.97/W if you in for getting 160W in one go). This comes with some heafty cable - reminds me a bit of car sparkplug cables and are claimed to be 4 sqmm far in excess for carrying 3 amps max the 80cm length of the cable. they are fitted with these plugs, actually quite nice plugs they certainly look waterproof but really are they and the "solar cable" needed ? I mean you just connect a wire straight into the panel in the connection box and run it right into your main box or the dry area housing the batteries or other equipment.Are we looking at a new hype over so called special stuff in solar technology as we have in audio technlogy (special cable, gold plugs etc)I'm not criticising the plugs they really do look waterproof in fact I like them but at £5+ a set (different ones for - and + just to make it fool proof for the solarphiles who really won't know what they are doing and will blow something up connecting a panel backwards) I'm not going to go buying them, geeze that's money I'll put into more solar panel "real estate".On the plus side I'm quite exited at the price drop in panel prices, electric has just gone up here and no doubt will go up further.

author: the_raptor
author_rank: Regular Contributor
timestamp: February 19, 2011, 10:54:39 am
content: There doesn't seem to be any magical claims made about "solar cable". It just looks to be designed for high UV resistance and easy routing for the unskilled. As is appropriate for a self-installed product that needs to live in the open environment.

author: Simon
author_rank: Unknown
timestamp: February 19, 2011, 11:01:01 am
content: yes i expect cable for solar panel does need to survive in the sun but 4 sqmm for 3 amps ?The plugs for negative and positive are different so they cannot be puged in the wrong way round, fairly good idea, why not use white cable ? I've just taken down a couple of panel from my dads house that I used white mains cable for and after 18 months the cable looks like it did the day I put it up.I'd also add if you don't know what you doing don't do it. Connecting up solar panel is not rocket science, if you need specific cables and plus to get it right then you should not be doing it at all. Of course having a universal plug system - thats if these plugs become the standard will make it quike and easy to setup but like i said at over £5 a pair I'd solder them together if need be

author: Bored@Work
author_rank: Super Contributor
timestamp: February 19, 2011, 11:01:48 am
content: If you deck out your whole roof with solar panels you want something that lasts and something that can be installed by roofers. The later are, in my neck of the wood, strong, but, well, not exactly Einsteins. So the plugs need to withstand some physical abuse already when mounted, need to be water proof, dust proof, temperature range proof and whatnot.And you want a one-plug-fits-all system, to not overload the roofers with decisions on what type of plug and cable to use when stringing together a bunch of them.

author: Simon
author_rank: Unknown
timestamp: February 19, 2011, 11:11:25 am
content: yes that's true, are roofers allowed to install panels with no electrical training ? that will sound like a joke in the UK, I cannot even change a light bulb for myself yet an electrically untrained roofer could be plugging in KW of panels ? I mean are they going in series or parallel ? after seeing what a council contractor did on my wiring system I'd not put it past a roofer to connect a load of panels in series instead of parallel which you can easily do with thse plugs as the "-" fits into the "+". Anyway like i said my main complaint is the price, for £5 I can buy another 2.5W of panel, in the case of a 20W panel the plugs that will connect it to the rest of the sysetem will cost me 10% of the panel priceAt 12-24V providing the connections are not being rained on plain unwaterproffed connector blocks will do the job

author: Bored@Work
author_rank: Super Contributor
timestamp: February 19, 2011, 11:47:10 am
content: Try to find an electrician to install solar panels on a 45° or even 60° gable roof. Good luck with that. Occupational health and safety rules might even prohibit an electrician doing it. And you want the mechanical installation to be solid. Good luck with an electrician :-) Thats where the roofers come into play. An electrician is then supposed to measure and inspect the installation and do the final connection.

author: Simon
author_rank: Unknown
timestamp: February 19, 2011, 11:59:21 am
content: either way the roofer has to have some minimal electrical ability, the universal plug system is a good idea proving it has a reasonable cost. However I'm not sure why I got a panel with 80cm of wire on it. It would make much more sense to have a couple of sockets on the panel's connection box that the wire going all the way from the panel to the point of connection would plug directly into. As it stands 80cm is not long enough so I'd have to connect another peice of wire. So twice the amount of plugs have been used an an extra unneccesary connection that could be a weak link later. Of course in my case I'll probably just remove the "solar cable", with the price of it I may even be ablw to resell it !If you have a whole roof load of panels and a few are connected wrong i bet it could get past test, but then I don't know how the panels are connected together on large systems. Again, if UV is a problem why black wire ?Yea health and safety, all good fun in stoppig stuff being done properly to ensure it is safe. If an electrician wants to climb a roof that's his problem providing he has been trained etc. Aren't solar systems installed by specific installers though ?None of these cables and plugs were around a year ago. Has some sort of recognised standard been established for solar panel hookups ?

author: bill.rowland
author_rank: Contributor
timestamp: February 19, 2011, 12:12:08 pm
content: simon try this guyhttp://www.southwestsolarsolutions.co.uk/bill

author: Simon
author_rank: Unknown
timestamp: February 19, 2011, 12:18:53 pm
content: ah a "proper" solar installer, versed in both roof scrambling and electrics (I hope) as it happens in my case I'm just "lopping" 3 panels onto my shed roof, however my main point of discussion was that it looks as though as fast as the panels become affordable the related "hardware" to install the panels suddenly becomes "a thing" and it's price starts to eat into your budget should you care to follow the "standard"

author: Sionyn
author_rank: Frequent Contributor
timestamp: February 19, 2011, 01:35:30 pm
content: yep looks like marketing department again

author: bill.rowland
author_rank: Contributor
timestamp: February 19, 2011, 03:08:19 pm
content: Quote from: Simon on February 19, 2011, 12:18:53 pmSimon did you look at his generator lorry? It has a 6kw solar generator and 2 x 3kw outback inverters to give the ac output the lorry is parked next door to mebill

author: Simon
author_rank: Unknown
timestamp: February 19, 2011, 03:13:26 pm
content: no I didn't look much at the website but from the little I read it looks like he specializes in making the best of whats available for power.Say do me a favour: nip next door and ask him if he has heard of MCS standards and MC4 plugs. In fact invite him to the forum sounds like a guy who would be great to have around

author: Zero999
author_rank: Super Contributor
timestamp: February 19, 2011, 04:01:45 pm
content: The cable is also thick because it's probably double insulated for use at 600V or more as solar cells are often connected in series and connected to grid tie inverters rather than a <48V battery pack.As far as I'm aware, solar installations have to be inspected and signed of as with the rest of the building's electrical system. A roofer may lay the panels and hook them up but I don't see why anyone would need any electrical training just to plug a few panels in.

author: bill.rowland
author_rank: Contributor
timestamp: February 19, 2011, 04:12:22 pm
content: Quote from: Simon on February 19, 2011, 03:13:26 pmSimon the lorry is parked next door Tony do's not live there he is away at the moment he also has a mobile stage he uses for eco gigswhen i see him i will ask him for the info you requested but looking at the truck the panels have heavy cable with plugs which look like thy only fit one way so may be what you are talking about the truck has a armered cable reel on the side looks like 64amp which conects to a consumer box with rcd, mcbs with voltage , ampage meters it has 4x16a 2x32a outlets avery nice set upbill

author: Simon
author_rank: Unknown
timestamp: February 19, 2011, 04:23:35 pm
content: Bill bear in mindl that 6 KW will require some amperage so yea they will be hefty cables, I just question 4 sqmm to carry 3 amps on a 50W panel, I mean thats thicker than house cableHero, the cables are not marked and really I can't see why too much insulation is required, even for 600 V I mean that's only less than twice the mains peak voltage and is DC. sure good insulation is required for external setups more for mechanical endurance than anything, but I still don't buy 4 sqmm for 3A and these special expensive plugs (I can get 7 mains plugs for the price of a pair of these things)

author: bill.rowland
author_rank: Contributor
timestamp: February 19, 2011, 04:42:13 pm
content: Simon my 3KW inverter has i think 80mmsq cable but this is 12v in so high ampage but i see what you mean 3amp draw 4mmsq cable is a bit over the top the lorry has a 48v system 2 ton of 1.2v batterys to power the 6KV output which is charged from the sunbill

author: Simon
author_rank: Unknown
timestamp: February 19, 2011, 05:09:06 pm
content: you have a 3KW inverter at 12V ? your nutsthat's 250 amps so yea you sure need 80sqmm, that's just over 3A/sqmm which is about right, now tell me that's not all hooked up on MC4 plugs is it? why not 24V at least or even 48V it would be much more efficientThe 6KW lorry system @ 48V requires 125 A capacity so yea your looking at around 40sqmm cabling, I suspect each panel is in parallel so that's about 4.5sqmm per panel, you might just get those MC4 connectors to work on them.To be honest the MC4 connectors are laughable, we use some fairly robust connectors at work that handle up to 10A which also are water proof and they cost a lot less than those MC4 connectors, they are used on a lot of stuff particularly military intended stuff, I think each plug/socket assembly works out about 50 pence although granted we buy them in quantities of 20-100, of course they are meant for indoor use although they still have seals and take smaller cable that is not so heavily insulated (which none the less carries 10A @ 24V)Of course new plugs: new crimp tools, the crimpers for MC4 plugs are £70 - quite an investment for a DIYer

author: ianryeng
author_rank: Contributor
timestamp: February 19, 2011, 05:28:35 pm
content: Quote from: Simon on February 19, 2011, 04:23:35 pmThe losses over DC are considerably higher than AC (especially on larger installations) and that loss is potentially lost revenue.There are regulations for the plugs that interconnect the DC on solar panels that require they be sealed and have a secondary mechanical locking mechanism. I doubt your mains plugs meet these requirements. If you don't like the price buy the knock-off's out of china.

author: bill.rowland
author_rank: Contributor
timestamp: February 19, 2011, 05:35:54 pm
content: stright conection from battery to inverter cable is 1 meter to stop voltage drop this is used on a bank of 1.2v forklift batterys which is charged by mains i did find out about solar but the workshop needs and my home the instaltion would be around £25,000 we have 3 phase in the workshop and it would still need to be conected to the grid we can kick in a 100kva diesel set if we got a power cutbill

author: ziq8tsi
author_rank: Regular Contributor
timestamp: February 19, 2011, 05:43:45 pm
content: Quote from: Simon on February 19, 2011, 04:23:35 pmSurely one would expect cables in low voltage systems to be thicker than mains cables at the same current. An IR drop of 1V in your mains wiring at full load is insignificant, but a drop of 1V from a single 12V panel would be wasting 8% of the power.Admittedly, by my calculation you would need 80m of cable per panel, not 80cm, for this to be an issue.

author: Simon
author_rank: Unknown
timestamp: February 19, 2011, 05:45:08 pm
content: Quote from: ianryeng on February 19, 2011, 05:28:35 pmI was just pointing out the stupidity of the price, not suggesting mains plugs for external solar connections !

author: Simon
author_rank: Unknown
timestamp: February 19, 2011, 05:47:57 pm
content: Quote from: ziq8tsi on February 19, 2011, 05:43:45 pmmy point is that prefittig an 80cm cable to a panel is a joke, you can't do anything with 80cm of cable so will have to plug an extension into it, the connection will add resistance, yes looses at lower voltages are felt more but as you say over 80cm it's a non issue.Like i said previously I'd expect to see some sockets in the connection box that my fancy plugs and cable plug straight into minimising plug use and redundant connections.

author: Zero999
author_rank: Super Contributor
timestamp: February 19, 2011, 05:57:07 pm
content: Quote from: ianryeng on February 19, 2011, 05:28:35 pmTo be picky, the losses are actually lower for DC than AC at the same voltage due to the lack of the skin effect. It's just because DC installations normally run at very low voltages so more current is required for the same power level. Designers like to keep voltages very low for DC for historical reasons (automotive and telecommunication equipment run from 12V to 48V is often cheaper because it's widely available) and for safety reasons: batteries are permanently live which makes higher voltages more hazardous than mains, even though the same DC current generally presents less of a shock hazard than mains frequency AC.I once worked at a company which made UPS systems with DC voltages up to 600V. I would rather not work with battery packs with voltages much over 100V because they can't be made safe easily, for example if you have eight 12V SLAs in series making 96V, as soon as you can disconnect them in the middle you only have low risk 48V, go much above this and you're at risk of a nasty shock.

author: Simon
author_rank: Unknown
timestamp: February 19, 2011, 06:07:43 pm
content: surely you treat a high DV voltage with the same regards as the mains ? of course if your dealing strictly in electronics you may not be used to such high voltages around which can become a risk

author: Zero999
author_rank: Super Contributor
timestamp: February 19, 2011, 07:02:38 pm
content: It depends on what you mean by respect?It depends on the voltage, 50VAC will whack you much harder than 50VDC will but a huge chunky 48V battery pack will hit you much harder when short circuited with a spanner than the mains.Of course I'd treat 240VDC with equal or greater caution than 240VAC 50Hz, even though I know the shock may not be so severe, such an installation won't have an RCD (GFCI in US), the short circuit current will be higher, the arc flash will be more severe and there won't be a breaker at the battery terminals.Different forms of electrical energy have different hazards, it's important to be aware of them and exercise caution when dealing with them.I suppose another thing that makes working with live batteries safer (at any voltage) than mains, in some respects, is you can easily isolate them from ground and other circuits, making a shock impossible unless you touch two terminals at a high enough potential difference. For example if you take a 600V installation composed of 50 12V SLAs connected in series, the shock hazard may be greater than 230VAC but if you remove the earth connection and open the main isolator, disconnecting it from the appliance, the only way to receive a nasty shock is to touch two terminals with more than five batteries in series so you should be fine assembling/disassembling the pack, providing you know what you're doing. Thiing about this makes me feel better about working with DC systems now.

author: RayJones
author_rank: Frequent Contributor
timestamp: February 19, 2011, 09:51:33 pm
content: I agree that the size of cables fitted to the sub 100W panels is truly absurd.As Simon has stated several times, 3-5A at the most will come from the panel, and the voltage drop over such a short 0.5m run is insignificant.

author: PetrosA
author_rank: Frequent Contributor
timestamp: February 20, 2011, 01:47:49 am
content: Ok, first off, you guys are thinking small. Most arrays are minimum 3kW up to hundreds of kW in commercial installations. Panels get daisy chained (series connected) in an array - usually 11 panels to a string which is why there are short leads from each panel. With a nominal voltage around 25VDC and max about 30VDC you usually get about 325VDC from a string of panels in decent sunlight. In a typical 3 string array for a 10kW installation, you have three strings either ground mounted or roof mounted and both the + and - ends come back to a combiner box. From the end of a string you'll have about 60' (18m) back to the combiner box. Panels generally output between 200 and 250 watts each.The connectors have to be hefty for a number of reasons. First, a solar array system in most western countries is treated as electrical production the same as a utility, especially when you tie into the grid to sell it back. Lots of safety and construction regulations come into play because of that like fences and other methods of limiting access to non-qualified persons and the parts used to assemble the array have to be of very high quality. When you have a string of panels in series, if you disconnect one connector under load, there's a lot of current to break. You have to use a dependable connector in case one of the panels needs to be replaced. Soldering is out of the question because there's no way to turn off power other than to work in the dark.I don't know the exact reason why UV resistant products are black, but they almost all are. Ty-wraps or zip-ties (for bundling wires) come in lots of colors, but only the black ones are UV resistant. White ones will degrade and get brittle enough to crack off within a few months outdoors.Edit to correct "22 panels" to "11 panels". Oops.

author: Unknown
author_rank: Unknown
timestamp: February 20, 2011, 02:15:21 am
content: Quote from: Simon on February 19, 2011, 04:23:35 pmSo is a lot of automotive cable. The difference being our old enemy volt drop. At 12Vdc resistance is a real killer. One of the reasons trucks run 24Vdc is to reduce the cable size for trailer lamps.If our transmission lines were all 240V we would need cables the diameter of tree stumps. Even at 3amps you do not have to run too far t experience significant volt drop. Have a look at the cable sizes for low voltage garden lights.With the solar connectors being designed for a Leggo type installation, the cables etc need to be over spec-ed for a variety of reasons including.Volt DropEnvironmental and UV protection of insulationPossible high OC voltages from series stringsMechanical protectionIf you check about a bit you will see Chinese manufacturing is already gearing up for the solar connector market. You can see the prices beginning to fall towards garden variety pricing as a result.

author: PetrosA
author_rank: Frequent Contributor
timestamp: February 20, 2011, 03:45:56 am
content: I'd say the bigger problem with the connectors is the crimper cost (there are male and female connectors). The crimp tool body costs a few hundred bucks, and each new iteration of crimp dies costs another $350 or so if you get good quality ones. Since the beginning of last summer when I did my first solar installation, we're now on our second set of dies because of changing standards/configurations. Argh.@Simon - I'm not sure whether it was clear from the figures in my last post, but the reason they series connect panels is to increase the voltage which decreases the amperage. Because of that they have to size the connecting cables based on the output of an entire string - not just an individual panel.

author: RayJones
author_rank: Frequent Contributor
timestamp: February 20, 2011, 05:41:27 am
content: Quote from: PetrosA on February 20, 2011, 03:45:56 amBah!If the panels are series, the current will still be the maximum that any one particular individual cell in the array is able to pass.ie if one is shadowed, there goes a heap of current.To prevent this ideally you have a reverse diode across each cell, but most panels only have this for each half of the panel, 18 cells.I don't care if you have 1000 panels in series, the current is still only in the 3A region for the panels being discussed.For sure there is a higher voltage across the array, and hence more energy available, but current is not reducing nor increasing as you add panels.Yes the long run back to the central point should be heavy cable, but 6mm stuff on each panel is extreme overkill.

author: Simon
author_rank: Unknown
timestamp: February 20, 2011, 08:33:51 am
content: well if we are looking at a standard then maybe the 4sqmm is a one size fits all for all panel sizes simplifying the universal plug scenario, but then havng ,ooked at the plugs I'd not rate them over 10 amps and knowing all the dodgy crap that come from china not more than 5, they are after all just banana plugs and sockets in waterproof housings, so that knocks the capacity on the head for the cable. So really the only justification for the 4sqmm cable is that in a universal one size fits all situation it could be used up to say 10 amps maybe 16 if we want to push it but of course we want the lower voltage drop for low voltage systems

author: Zero999
author_rank: Super Contributor
timestamp: February 20, 2011, 09:00:24 am
content: Quote from: PetrosA on February 20, 2011, 01:47:49 amUV resistant products a black for the same reason as UV resistant people are black: the dark pigment absorbs UV light.Quote from: Uncle Vernon on February 20, 2011, 02:15:21 amBut 4mm2wire has a resistance of just 4mOhm/m so a twin cored cable at 3A has a voltage drop of only 3*4*2 = 24mV/m, which won't be a problem unless the cable is >20m long.Quote from: Simon on February 20, 2011, 08:33:51 amI think it could be something to do with overcurrent protection.The manufacturer doesn't know what fuse is going to be connected in series with the solar panels so has chosen to use nice chunky cable, probably rated for 32A or more so they can be connected to a safely battery pack with a 32A fuse. Don't forget fuses are there to protect the cable which is often sized according to the fuse, rather than the current actually flowing through it. Have a look at the manufacturer's instructions for the recommended/maximum fuse rating when connecting them to batteries.

author: Simon
author_rank: Unknown
timestamp: February 20, 2011, 09:32:17 am
content: there should be a charging controller between the panels and battery (particularly for large instalations, it only takes 40W of panel to boil a car battery at 16V). Usually the controllers have the protection, a short burst of current in a decent cable will do no harm and the only way that may happen is shorting out the panel cabling.

author: Unknown
author_rank: Unknown
timestamp: February 20, 2011, 10:45:17 am
content: Quote from: Hero999 on February 20, 2011, 09:00:24 amMeasure the run from an ideal rooftop location to a convenient location in a garage or exterior wall. On the average home that 20 metres and often much more will be required.

author: Simon
author_rank: Unknown
timestamp: February 20, 2011, 10:48:45 am
content: and in view of that I make the point that an 80cm cable is stupid because it will require an extra connection to join and extension lead to that 80cm cable so why not just put sockets in the connector box and plug right in instead of adding a redundant connection