cable from solar controller to battery

Thanks All.

Thank you all for your feedback, I now have the info i need.




Please do not adjust your mind.....
there is a fault in reality......
 
Solar panel wiring

In low voltage application, the size of the cable is important to minimise voltage drop. I have 300 watts of solar panels on the roof of my motor home, use 4 mm to link the panels together and down to my MTTP Regulator, then 6 mm from reg to batteries. From panels to reg voltage around 17, from reg to batt, around 14.4 but higher amps. On a bright Sunny day clear sky, I can get up to 14 amps if the batteries are down, even this size cable with crimps terminals will get slightly warm. If a cable gets warm it is using power in the form of heat generation. If you have too smaller wire you will loose amps.
 
I've just fitted a 20amp controller with one 80w panel going into it (may expand later) and the instructions for the controller state that 'the cable from controller to battery should be no bigger than 4amp/MM2' any bigger than this will result in voltage drop. Also you should keep this cable as short as possible and incorporate an in-line 5amp fuse. So I just used 4amp twin white sheathed regular household cable. No probs, and battery is up to full charge in no time in good sunlight, and no overheating at battery terminals or the cable itself.
 
It's only a matter of time before criminals stop nicking lead off Church roofs and target motorhomes with solar panels fitted.

All that thick heavy cable will be a tempting target. :lol-049:
 
El Veterano said:
I've just fitted a 20amp controller with one 80w panel going into it (may expand later) and the instructions for the controller state that 'the cable from controller to battery should be no bigger than 4amp/MM2' any bigger than this will result in voltage drop. Also you should keep this cable as short as possible and incorporate an in-line 5amp fuse. So I just used 4amp twin white sheathed regular household cable. No probs, and battery is up to full charge in no time in good sunlight, and no overheating at battery terminals or the cable itself.
Click to expand...

the instructions for the controller state that 'the cable from controller to battery should be no bigger than 4amp/MM2' any bigger than this will result in voltage drop.
Click to expand...


That should read 4mm² - 4mm cross sectional area any smaller will result in volt drop

So I just used 4amp twin white sheathed regular household cable.
Click to expand...
You should not use twin and earth cable in a van it is too rigid and will eventually fail, they don't make 4amp cable in T&E the smallest is 1.0mm² which is good for a max of 15.5A in optimum conditions
 
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3mm2 cable maybe.

The higher the current, the more power loss.

The currents on the battery side of the regulator are higher as there is a voltage drop from typically 20v at the panels to 14v to charge the batteries and a corresponding increase of current.

I think I have 2mm2 on the panel side and 3mm2 on the battery side. But bigger cables will mean less power loss, no harm in 4, 5 or 6mm2.
 
sparrks said:
That should read 4mm² - 4mm cross sectional area any smaller will result in volt drop


You should not use twin and earth cable in a van it is too rigid and will eventually fail, they don't make 4amp cable in T&E the smallest is 1.0mm² which is good for a max of 15.5A in optimum conditions
Click to expand...

Hi thanks for your input, I was hoping that posting would shed some light on the black art of solar! No, it's not twin and earth it is white round sheathed cable and just twin, no earth and is very flexible. I was also concerned that a 5amp fuse was not correct as well?
 
Pulsing Regulator

Has anybody experienced a pulsing regulator. My 80w panels works fine but they pulse when sunlight is really strong ie my needle on the current gauge pulses between 4amps and 0 amps?
 
I would suspect this will only happen when the LB are fully charged??? The regulator will look at the battery and see it fully charged and switch off, 0 amps. After a preset time it will look again and if voltage down will switch back on resulting in 4 amps.

Experts can confirm, but not a problem.
 
MATS said:
Has anybody experienced a pulsing regulator. My 80w panels works fine but they pulse when sunlight is really strong ie my needle on the current gauge pulses between 4amps and 0 amps?
Click to expand...




P W M Regulators........ Pulse Width Modulation.......That`s what they do.
 
hmmm not quite, the pulse in PWM is the on/off fast switching that gives a certain current duty cycle by turning the fixed voltage supply on and off quickly.
Pulse-width modulation - Wikipedia, the free encyclopedia
The pulsing from the reg is as already mentioned - the LB's are on the very cusp of being fully charged and the controller may well cycle on and off a little as it over-corrects. More fancy controllers will have some PID control built in where they can predict the need for voltage or not from a feedback system to a microcontroller.
 
Andy75 said:
hmmm not quite, the pulse in PWM is the on/off fast switching that gives a certain current duty cycle by turning the fixed voltage supply on and off quickly.
Pulse-width modulation - Wikipedia, the free encyclopedia
The pulsing from the reg is as already mentioned - the LB's are on the very cusp of being fully charged and the controller may well cycle on and off a little as it over-corrects. More fancy controllers will have some PID control built in where they can predict the need for voltage or not from a feedback system to a microcontroller.
Click to expand...
Ok makes sense - yes the LBs are normally near full charge as sometimes it is a steady 2-3a then the pulsing begins after about 3 hours on charge.
Cheers all
 
My controller is pretty basic so just has a few LED's, the 2nd one in line pulses slowly green when the battery is fully charged. The same thing I would imagine.
 
shortcircuit said:
Cables designed for domestic fixed wiring installation should not be used as they are too rigid which will result in cores breaking due to vibration. Cores should not be cut off in order to make a connection fit. The current capacity of a cable is with all cores terminated and used.
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Domestic wiring is not flexible enough agreed. as to reducing the number of strands to fit the regulator nothing wrong with that as the length involved is too short to exhibit any heating losses. Over a long distance the greater the dia of the cable the better overkill does no harm whatsoever, generating leccy in the winter when there are only milli amps charging a battery losses need to be absolute minimal. There is more than one right in this world. I think an HNC in electrical and electronic engineering
is sufficient for me to give an informed opinion.
 
Update:
After everybody's learn'd input, now replaced my flexible household cable from controller to LB with two 4mm solar cables courteously provided by my electrician mate who had some left over from an installation. Seems to to be working exactly the same as the household stuff so far, but there again if it's putting more oomph into the LB then I'm all for it:dog:
 
wildman said:
Domestic wiring is not flexible enough agreed. as to reducing the number of strands to fit the regulator nothing wrong with that as the length involved is too short to exhibit any heating losses. Over a long distance the greater the dia of the cable the better overkill does no harm whatsoever, generating leccy in the winter when there are only milli amps charging a battery losses need to be absolute minimal. There is more than one right in this world. I think an HNC in electrical and electronic engineering
is sufficient for me to give an informed opinion.
Click to expand...

I also have an HNC in electrical engineering which has no relevance to installation work. I was also an Approved Certifier for Electrical Installations which covers the nuts and bolts which does provide informed opinion. Cutting cores off reduces the current carrying capacity of a cable
 
shortcircuit said:
Cutting cores off reduces the current carrying capacity of a cable
Click to expand...

Scenario:

I have a 10A 12v load which requires a 4m long cable, 1.0mm² will suffice (fused 10A). To ensure minimal volt drop I choose, say, a 10mm² cable and because the cable ends will now not fit in the terminations I would fit bootlace ferrules or wire pin crimps. Now if not available, I could cut the end conductors down to say 4.0mm², this would still be 4 x larger than the original cable, and whilst the overall current carrying capacity of the cable is reduced it is still greater than the design current of the circuit.
So whilst it may not be the correct way to terminate the cable it can be done without reducing the current carrying capacity below the design current of the circuit.
 
sparrks said:
Scenario:

I have a 10A 12v load which requires a 4m long cable, 1.0mm² will suffice (fused 10A). To ensure minimal volt drop I choose, say, a 10mm² cable and because the cable ends will now not fit in the terminations I would fit bootlace ferrules or wire pin crimps. Now if not available, I could cut the end conductors down to say 4.0mm², this would still be 4 x larger than the original cable, and whilst the overall current carrying capacity of the cable is reduced it is still greater than the design current of the circuit.
So whilst it may not be the correct way to terminate the cable it can be done without reducing the current carrying capacity below the design current of the circuit.
Click to expand...

But is a waste of 6mm sq. of conductor. The whole 4m @ 4mm sq. would be best. Unless of course you have a spare 10mm sq. roll and just want to use it up.
Copper cable is expensive these days, vehicle manufacturers size their cables with only very small safety margins in the interests of economy, and they make savings by earthing runs to the vehicle body in situations where use of twin core earthed back to somewhere where you can see the earth point might be preferable.
 
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