Solar panel cable size
Submitted: Wednesday, Mar 19, 2008 at 20:15
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GOM
From previous posts, I probably need 15 metres of cable between my solar panels (2 x Uni-solar 64W) and my (shaded) 4WD with the regulator Plasmatronic PL-20 in the 4WD.
I can buy twin-core 6-mm cable for $4.50 per metre, which seems to have a cross-sectional area of 4.65 sq. mm. According to Collyn Rivers' formula, the voltage loss at maximum amps (7.8A) would equal (30 x 7.8 x 0.017)/4.65 equals 0.86 volts.
If I lash out nearly $200 for twin-core 6 gauge cable (cross-sectional area 13.56 sq. mm) for $12.95 per metre, the voltage loss would be (30 x 7.8 x 0.017)/13.56 equals 0.29 volts.
Is this difference worth the cost? in a previous post, (followup 495854) Russ n Sue advised using the 13 sq.mm cable. However, brett suggested that if the panels are putting out say 18V, then if the cables lose even 3V, there will still be sufficient volts left to charge the battery.
Would it be the case that at midday there would be little advantage to the thicker cable, as the regulator would just chop off any excess volts? Or does the regulator squirt in more amps to the battery if it has more volts available?
Or would the main advantage of thicker cable be at morning and evening, when the volts from the panels may be only, say, 14V, and if the cable loses an extra half volt, there may not be enough volts left to charge the battery at all.
Any thoughts?
Reply By: titl4 - Wednesday, Mar 19, 2008 at 20:42
Wednesday, Mar 19, 2008 at 20:42
If it were me I'd go for a slightly heavier cable. Actual 6mm2 twin was about $7 / metre when I last bought some a few months ago. With the likely maximum current from those panels I'd calculate a voltage drop of about 0.6 - a big improvement for th extra $40.
Cheers ............. Alan
AnswerID:
293665
Follow Up By: GOM - Friday, Mar 21, 2008 at 17:11
Friday, Mar 21, 2008 at 17:11
Alan,
Can you remember where you got the cable at that price? Carac in
Melbourne sell 10mm2 twin for $10.65/m.
Cheers,
GOM
FollowupID:
559747
Follow Up By: titl4 - Friday, Mar 21, 2008 at 21:09
Friday, Mar 21, 2008 at 21:09
Haymans I think but I've bought it from other such stores as
well. Its industrial twinflex so not quite as flexible as that designed specially for low voltage applications (heavier insulation and fewer, thicker, copper wires in each cable). If Springers now have twin 6 mm2 for $4.50 - as reported below - I'd go there but I've found the electrical wholesalers generally cheaper for cable. The problem is I'm no longer sure of the price as I bought some 14 mm2 twinflex at the same time. Try a local wholesaler for price - they sell by the metre and usually have twinflex in 2 mm2 increments up to 16.
Cheers ............. Alan
FollowupID:
559809
Reply By: Mainey (wa) - Wednesday, Mar 19, 2008 at 21:23
Wednesday, Mar 19, 2008 at 21:23
For some comparison I used 10mm sq. twin core cable
The good thing is you only have to pay for it once.
Mainey . . .
AnswerID:
293678
Follow Up By: jeepthing - Thursday, Mar 20, 2008 at 18:21
Thursday, Mar 20, 2008 at 18:21
Yes I agree with you Mainey I use 110amp Tinned Solar Grade twin core which is 10mm so you must be using the same amperage cable? I've found that there is no voltage drop over 6m that's why I went big.
FollowupID:
559516
Reply By: oldtrack123 - Wednesday, Mar 19, 2008 at 22:02
Wednesday, Mar 19, 2008 at 22:02
Hi
Voltage loss in the cablle before the reg will simply reduce the max charge rate [current]available for that lighting condition & will mean the charge will cease sooner with poor light.
If you need as much input as possible then get the biggest cable you can sensibly afford.
AnswerID:
293699
Follow Up By: oldtrack123 - Wednesday, Mar 19, 2008 at 22:10
Wednesday, Mar 19, 2008 at 22:10
The higher the voltage being put out by panels & available at the battery,using your words, the more amps the solar PANELS WILL SQUIRT IN.
The reg is a voltage contol system ,it does not vary current but merely switchs the panels on/off at various stages of batterycharge
FollowupID:
559390
Follow Up By: Mainey (wa) - Thursday, Mar 20, 2008 at 18:41
Thursday, Mar 20, 2008 at 18:41
Basic ellcheapo Solar Regulators may work in this way... eg. on/off
BUT NOT "quality" Solar regulators
sure they may be ~$50 dearer but they work far more efficiently !!
The QUALITY Solar regulator is an Amps control device.
Mainey . . .
FollowupID:
559520
Reply By: Mogul - Wednesday, Mar 19, 2008 at 22:19
Wednesday, Mar 19, 2008 at 22:19
I have used cable from Jaycar part no.s are:
WH3060 - Red
WH3062 - Black
$2.95 / M
Link
AnswerID:
293706
Reply By: Member - Mike DID - Wednesday, Mar 19, 2008 at 22:23
Wednesday, Mar 19, 2008 at 22:23
Solar Panels are a constant-current source.
If they're in
bright sunlight and you conect them to a 16 volt battery they will put out 7 amps. If you connect them to an 11 volt battery they will put out 7.5 amps.
If you use cable which has 0.5 volt drop at 7 amps the voltage at the Solar will INCREASE - the voltage at the battery will not go down in good light.
Only in marginal light conditions, where there is barely enough light to charge the batteries, you will notice some reduction in current if using higher resistance wiring.
In terms of total amp-hours into your battery, you will get little benefit from using such expensive cable.
AnswerID:
293709
Follow Up By: Member - joc45 (WA) - Thursday, Mar 20, 2008 at 00:15
Thursday, Mar 20, 2008 at 00:15
Just make sure the regulator is wired in at the battery end of the cable, rather than the solar panel end. This will correct for any voltage drop.
Gerry
FollowupID:
559419
Follow Up By: Mainey (wa) - Thursday, Mar 20, 2008 at 19:13
Thursday, Mar 20, 2008 at 19:13
Mike,
with-out getting technical, the Solar Panel puts electrical current down the cable, to the Solar regulator, which will then "regulate" this current relevant to the battery requirements - ONLY if it's a quality "constant charge" Solar Reg and NOT an elcheapo on/off regulator, which operates very differently.
The Amps recieved by the battery are most usually different to those 'collected' or 'made' by the Solar Panel due to battery requirements and solar regulator.
( this can be seen in the Solar reg pics on "my profile" )
Yes, it's in these ""marginal light conditions, where there is barely enough light to charge the batteries, you WILL notice some reduction in current IF using higher resistance wiring"" hence the thicker, low resistance cable is recommended, and it's for this reason you will get more Amp Hours per day delivered to the battery.
Mainey . . .
FollowupID:
559538
Reply By: Axel [ the real one ] - Thursday, Mar 20, 2008 at 18:54
Thursday, Mar 20, 2008 at 18:54
The ugly dim and dark spectre of voltage drop rears its head again ,, when we set out on the
solar power journey we to worried about voltage loss , no longer is it a deep and dark science ,,,did our cable from Springers , 6mm tinned twin core $4.50 per mt which we bought in 10mt lengths with a 50amp Anderson plug at each end , now have 4 lengths so can place panels upto 40mt away in
bright sunshine while c/t remains in shade ,, Steca 2020 mounted close to batteries ,, never mind the voltage drop maths ,, system works and batts charge from sunrise to sunset ,, the advantage of having options of panel placement far outweigh any voltage drop percieved or mathematical.
AnswerID:
293827
Follow Up By: GOM - Friday, Mar 21, 2008 at 17:24
Friday, Mar 21, 2008 at 17:24
Axel,
You must have some serious panels at the nether end to be able to run a 40m length of 6mm cable!
That's a brilliant idea using Anderson plugs and several short lengths. If the nearest tree is a distant memory you can then optimise the system with just one length.
Cheers,
GOM
FollowupID:
559753