Hi Guys

The length of the battery cables needs to be exactly the same length.

What about the length of the positive and negative solar cables? They are also DC

Don't think it matters for the PV side. For one, you don't have the same problem where one string deteriorates faster than the other even of it works a little less hard, but also, if you have an mppt on there and the panels are all similar it will park the voltage at a point where it gets the best overall power out of the parallel strings, which means a longer cable on one string will cause it to pick a voltage that will also make the other strings work less hard.

Basically, with an mppt on there, your PV modules always run at max current and therefore the idea that one string works harder is not true.

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Of course it's still advisable to keep the overall resistance similar, but you really don't have to match them to the centimeter :-)

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11 hours ago, plonkster said:

Of course it's still advisable to keep the overall resistance similar, but you really don't have to match them to the centimeter :-)

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While it's  advisable to keep the PV cables to the same length, it's almost impossible to achieve. if you can pre-measure the longest cable run and cut all the cables to the same length, it would be possible, but in many cases it would mean a lot of cable wastage, i.e. if your MPPT connection is to the far side of your PV array, the closest panels would use up a lot of cable in order to have the same lenght cable as the farthest panels.

PV panels also have bypass diodes and stuff, so in partial-shading situations they are dissimilar anyway. Bird droppings on one and not the other? Etc etc... :-)

thanks guys

 

On 12/12/2016 at 6:56 AM, Chris Rossouw said:

HI SilverNodashi

The vertical brackets manufactured and powder coated = R 60 each = 30x 60 = R 1800.00

14 x 3m purlines @ R130 + powder coating @ R150.00 = 280 x 14 = R 3 920.00

16 x 41 x 1.6mm Unistruts @ 195.00 each = 16 x 195 = R 3 120.00

100 M8x60 Stainless steel Security Torx screws = 100 X 9.70 = R 970.0

100 x M8 30mm square stainless steel washers = 100 x 2.41 = R 241.00

Total cost excluding labour = R 10 051.00

 

Cheers

PS. The structure is for fitting of 2 sets of 20 panels each, one facing Northwest and one South east.

Interesting. Using "commercial" aluminium solar panel mounts, I could have supplied a kit for R 9783.90

Hi Guys

A quick question about batteries and battery cables.

But first, I hope 2017 is going to be a wonderfull year for every member of this forum!

Now for all the experts out there. 2 strings of 4 x 12 v batteries > 48 v. ( 4 x 180ah) x2 ) In every string, the serial connections will be done with copper plates, thus being all exactly the same length. From the positive and negative to the busbar, I understand that the cable lengths must be exactly the same length, and from there to the inverter the same will apply. My question is, how important is the actual cable lengths? Would it make a big difference whether it is 1.5m or 3.0 m long? I will be using 35mil  welding cables and would also want to know whether you agree on the type of cabling? What is your suggestions on this. I am planning to start-up my system on Friday and this is still one of the last items to be completed.

Thanks Guys !

 

7 hours ago, Chris Rossouw said:

Hi Guys

A quick question about batteries and battery cables.

But first, I hope 2017 is going to be a wonderfull year for every member of this forum!

Now for all the experts out there. 2 strings of 4 x 12 v batteries > 48 v. ( 4 x 180ah) x2 ) In every string, the serial connections will be done with copper plates, thus being all exactly the same length. From the positive and negative to the busbar, I understand that the cable lengths must be exactly the same length, and from there to the inverter the same will apply. My question is, how important is the actual cable lengths? Would it make a big difference whether it is 1.5m or 3.0 m long? I will be using 35mil  welding cables and would also want to know whether you agree on the type of cabling? What is your suggestions on this. I am planning to start-up my system on Friday and this is still one of the last items to be completed.

Thanks Guys !

 

Shorter cables have less volt drop. The main question is, how many Ampere will be drawn from the batteries - that will determine your volt drop. And, with volt drop you will have increased Ampere. Too high and the cables could get hot, very hot, or even too hot - and you don't want that. I assume your battery bank capacity was calculated to run 180Ah max at 50% DOD? IF you use a 4KW inverter, your max draw will be about 95-100A. If you start with 54V and draw 100A, the volt drop over 3m will be 0.15V. Not much, but the ampere will go up slightly to compensate as the inverter will draw enough Volt + Ampere to fulfill it's wattage "needs". 

 

In general, 3m is the max recommended cable length by most manufactures. But, in theory / reality you can go longer as long as you compensate for everything in between. IMO, 35mm is bare minimum but many people will argue that it's too thick for this application. According to Aberdere (large cable manufacturer), you could use a 16mm cable for this application. It can handle 131 Ampere. I'm not sure if that is satisfactory in a solar setup. I would rather go as thick as I can afford, and the installation allows (i.e. how big are the terminals that the cable has to go into) and you will always know that a melt cable won't be the cause of fire. 

Hi SilverNodashi

I would like to not go over 70% DOD. Will put excess power during the day back into the grid and use that power during night times. Hope I will be able to balance my load like that.

The batteries will be there for times of grid failure only. The max discharge current = 200 amp and max charging current = 160 amp. Lets already cater for he max current and rather be on the safe side. I should be able to get max total length just under 2.5 meter, whilst catering for another set of 4 batteries if required. Does this answer your questions?

200A? What inverter do you have? 8KW? 10KW? I would have gone 75mm on those inverters. Check the link I provided from Aberdere. It's probably just a guideline and I assume those ratings / limits are a combination of the copper strand capabilities + insulation heat retention. 

Hi Chris

As @SilverNodashi already said, buy the thickest you can afford. OK, not really, but I would probably use at least 50mm² (or the next value up) for 200A on that length of cable. The thing about cable lengths is often misunderstood. The positive and negative cables running to the inverter does not have to be the same length, just as short as possible to have as little as possible resistance and losses.

The exact cable length thing is very important in parallel battery strings in order to utilize (charge and discharge) each string equally. So in your case you are going to use copper bars (obviously needs to be of the same length and cross-section) to link the batteries, which is perfectly fine. Equally important are the cables connecting the battery strings to the busbars. Here you should again use cable of the same type and thickness (which should then have the same resistance and other properties) - ensure that the total length of cable used per string is equal for each string - say you have 200mm of cable between the negative busbar and the battery pole in string 1 and 300mm of cable between the positive busbar and the battery pole in string 1, you will have a total length of 200 + 300 => 500mm of cable in string 1. In string 2 you must therefor also use exactly 500mm of cable in total, does not matter if you use pieces of 100mm & 400mm or 250mm & 250mm etc. etc. as long as the total length of cable used per string is equal in each string. Refer to the images below.

If you are however going to add a battery monitor with midpoint monitoring, you'll have to keep the cable length on each side of the midpoint exactly the same per string and on each side of the midpoint. Since you are going to make use of copper bars to link the batteries, you must ensure that you have equal lengths of cable between all the batteries and busbars. The best way to achieve that is to measure the longest piece of cable you'll need and to then cut all your cables to that length.

As matter of interest, at a (prospectus) client, their 6KW inverter was averaging on 105% and their 50mm battery cables were too hot to hold for a few minutes. I'm not sure if they changed it yet, as per my recommendation, but since the cables run through a metal battery case, of that insulation had to melt, their shop would burn down to the ground. 

It's interesting when the check the specification of wire. The 4mm solar cable I use can apparently go up to 50A in "open air". Now I have to tell you, above around 35A it starts to feel warm to the touch, so what I take from that is a warm cable in itself isn't necessarily a sign that you're out of spec, though it certainty hints that you're getting close. If it's too hot to touch though?! That certainly is a sign :-)

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I have the Imeon 9.12 - 3 phase hybrid inverter. Thanks for the link. I checked it and agree that 70mm will most probably be safest. I hope I will get this in Bloem in cut lengths. What is this possibility in Jhb  for cut lengths of this type of cable? Any idea or could you possibly supply?

Thanks - Chris

9 minutes ago, Chris Rossouw said:

... agree that 70mm will most probably be safest.

My 2 cents. If you can, have the cables made, with lugs, to your specification.

 

Very interesting TTT. Have you got any recommendation where I could have these cables made up? I looked at the movie and phoned Cabac, but unfortunately they do not make up cables themselves.

Thanks

9 minutes ago, Chris Rossouw said:

... where I could have these cables made up?

Nope. Best I can suggest is asking the cable supplier.

I went and bought a crimping tool a while back, for I did a lot of cables for UPS'es.

But even thought it can do up to 50mm2, man it made me uncomfortable. So for 35mm2 and bigger, when I need them, I will have to find a company myself to do it.

Bought one similar to this one: http://www.hellermanntyton.co.za/site/products/crimp-tools/ht0650/911-00246

And I try and buy only Hellemanntyton lugs, blerrie expensive per lug, because the ACDC ones are getting thinner by the batch. Even flimsy at times compared to HellermanTyton lugs.

 

EDIT: And I do not use solder resin nor that nice looking heat shrink.

28 minutes ago, Chris Rossouw said:

Very interesting TTT. Have you got any recommendation where I could have these cables made up? I looked at the movie and phoned Cabac, but unfortunately they do not make up cables themselves.

Thanks

Some auto electricians will do it for you and also try Afrox, if they have the cable and lugs they will do it.

Thanks Downtime

12 hours ago, Chris Rossouw said:

I have the Imeon 9.12 - 3 phase hybrid inverter. Thanks for the link. I checked it and agree that 70mm will most probably be safest. I hope I will get this in Bloem in cut lengths. What is this possibility in Jhb  for cut lengths of this type of cable? Any idea or could you possibly supply?

Thanks - Chris

I can get you any length of cable. Or you can join 2x 35mm cables. Just make sure the bolts and washers are tight enough and it will be fine, though possibly a bit bulky to bolt onto the batteries. 

I found this to be a very useful site to do DC cabling calculations.

http://www.solar-wind.co.uk/cable-sizing-DC-cables.html

 

@Chris Rossouw I wonder if you would be so kind as to supply the web address of the supplier from whom you aquired the HA02 balancers as one looks for a reliable source and it seems you found one. Alternatively if you intend to order more yourself for resale, do jou have availability date and price estimates. From the post above, it would seem that SolarNoob needs 1 and I need 5 as I would need four to install and have at least 1 as a spare. Your help will be much appreciated.

Hi Guys,

I have just completed the installation and just can't believe its done! Unfortunately it is already dark and I will thus only be able to switch on tomorrow morning. I can't wait and just had to share this with all you wonderful oaks out there. I have attached a few pictures to give you an idea of what I have done with the installation. I also have to thank everyone on the forum for all your assistance and support, all the good advice and just for being available at all times!!!! Without the forum I really don't think I would have been able to do it alone!  THANKS GUYS !!!!!!!!

Amazing.  GREAT WORK! How about reposting this in the member installation showcase thread,  im sure the new commers would love to see.

Great work once again!