What mm2 wire thickness for Solar Regulator to leisure batteries?

[Hagstrom]

I have 2 x 150 watt solar panels, to be connected in parallel to a Votronic 350 Duo charge regulator but need to use the correct (safe) guage of wire to connect the regulator to the batteries.

The panels are rated at 9amps max output each at around 21volts so there's around 18amps going to the regulator. So the Votronic would be outputting up to 18 amps at at maximum of 14.7 volts (2 x 95amp AGMs with the "AGM2" regulator selector dip switch selected). I am not connecting through the EBL119.

How do I calculate the safe wire thickness for the regulator to leisure batteries over a distance of 12 inches? I realise that thicker is better. The connections will not be fused.

 

[Bobby-gg]

What is the maximum size cable that you can fit into the solar controller connections?

I'd go with that

 

[Lenny HB]

4 mm sq will be fine over that distance. Don't make the mistake of buying thin walled auto cable they include the insulation thickness in the sizing.

Cable calculator on this page.

Cable Size Calculator - Cable sizing and selection | 12 Volt Planet

Cable Size Calculator - Read our guide to selecting cable of the correct type and size for your automotive, marine or leisure wiring application. Auto and Marine Electrical Components from 12 Volt Planet

www.12voltplanet.co.uk

 

[Tombola]

6mm will be fine.
flexible will do.
You say you arent fusing it? why. And while you are at it add a switch or trip fuse that can isolate it in case you need to work on it at some point.
similar to this

Amazon product ASIN B074RK2DZB

 

[Lenny HB]

6mm will be fine.
flexible will do.
You say you arent fusing it? why. And while you are at it add a switch or trip fuse that can isolate it in case you need to work on it at some point.
similar to this

Amazon product ASIN B074RK2DZB

The Votronic regulator has a fuse in it, although it is useful to have a fuse on the input side of the regulator.

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[Richard n Ann]

I just put a 60a trip in the panel cable so it can be switched off.

 

[Raul]

I have 2 x 150 watt solar panels, to be connected in parallel to a Votronic 350 Duo charge regulator but need to use the correct (safe) guage of wire to connect the regulator to the batteries.

The panels are rated at 9amps max output each at around 21volts so there's around 18amps going to the regulator. So the Votronic would be outputting up to 18 amps at at maximum of 14.7 volts (2 x 95amp AGMs with the "AGM2" regulator selector dip switch selected). I am not connecting through the EBL119.

How do I calculate the safe wire thickness for the regulator to leisure batteries over a distance of 12 inches? I realise that thicker is better. The connections will not be fused.

Assuming this is a mppt regulator, the amps out are always more than the amps in. Mppt is power in power out. If 300w going in, 300w coming out. So 300w divided by 12v, the max output will be 25A. The regulator should be fused and wired by its max power , I think 350w as te name implies. But since you only hooking up 300w of panels, you will only see 25-26a out max. From regulator to battery you should have no voltage drop, otherwise the parameters set on controller will not reach the battery terminals. In a nut she’ll, personally I would wire from controller to battery with 10mm2 and 30a fuse. From panels to controller does not matter if you get a bit of voltage drop, it will get converted anyways before it goes to the battery.

 

[sallylillian]

I have 2 x 150 watt solar panels, to be connected in parallel to a Votronic 350 Duo charge regulator but need to use the correct (safe) guage of wire to connect the regulator to the batteries.

The panels are rated at 9amps max output each at around 21volts so there's around 18amps going to the regulator. So the Votronic would be outputting up to 18 amps at at maximum of 14.7 volts (2 x 95amp AGMs with the "AGM2" regulator selector dip switch selected). I am not connecting through the EBL119.

How do I calculate the safe wire thickness for the regulator to leisure batteries over a distance of 12 inches? I realise that thicker is better. The connections will not be fused.

Your amps to the battery will be higher than arriving from the panels as the regulator drops the voltage to your selected 12vdc charging algorithm, so between 13v and 14. something. Therefore if you were getting 18 amps from the panel at 21v that would ball park be 24amps to the battery at circa 14vdc.

 

[Hagstrom]

I've taken wise advice above to check with the 12v Planet wire size calculation website.

I've fed in the numbers using a working voltage of 14v, a cable run of 0.3m, an assumed current draw of 25 amps (gleaned from advice above) and three wire sizes which I have mulled over.

The calculations are below. 12v Planet suggest that wire should be sized to allow for a voltage drop of well under 3%.

Using 2.5mm2 cable appears to result in a drop of 0.11v or 0.8%. Using 4mm cable results in a voltage drop of 0.07v/or 0.5% and using 6mm results in a voltage drop of 0.05v or 0.34%.

Unless I am using the calculator wrongly (and I accept that this may well be the case) the Wire Size calculator would seem to suggest that 2.5mm2 wiring would be appropriate? Experts please, have I used the calculator wrongly?

 

[sallylillian]

I tend to overkill all components to squeeze every last drop of sunshine. Not very scientific

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[Raul]

I just did a quick calc for you, 0,3m 300w load at 12v, not 14v. You calculate at lowest possible voltage incurred during use.
With 6mm2 conductor you will have a voltage loss of 0.1v 0,51%. That means if your controller is set absorb at 14,4v, the battery will only get 14,3v and rising towards the end charge cycle. Not bad.
But few pennies extra 1 meter ( will be enough for two runs) of 10mm2 you will have a voltage loss of 0,03v 0,248%.
I would not consider anything below 6mm, a 4mm would be temporary for me.

 

[Hagstrom]

Oh, I see. I had previously imagined that the Votronic regulator continuously monitored battery voltage and if it was only measuring 14.3v at the battery during absorption phase, it would compensate by increasing voltage of its supply to result in a voltage at the battery of 14.4v. I had thought that that was the point of an intelligent regulator.

(This is doin' me 'ead in, Sarge...)

 

[Tombola]

Just stick 6 or 10 in...job done

 

[autorouter]

I had previously imagined that the Votronic regulator continuously monitored battery voltage and if it was only measuring 14.3v at the battery during absorption phase, it would compensate by increasing voltage of its supply to result in a voltage at the battery of 14.4v. I had thought that that was the point of an intelligent regulator.

It doesn't have a separate voltage sense wire connected to the battery positive, so it doesn't know the actual voltage at the battery terminals. So it can't compensate for voltage drop by boosting the output voltage a bit. It does have a connection for a temperature sensor, so it can optimise the charge as the temperature varies.

If you want that, you can use a Victron MPPT. You could even use a SmartSense Module, which sticks on the side of the battery, measures voltage and temperature, and sends the data to the SmartSolar MPPT by Bluetooth.

 

[steveh57]

Question about the Victron smart sense module- with 2 batteries is it ok to connect accross the battery bank or should it be isolated to the battery it's attached to.

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[autorouter]

with 2 batteries is it ok to connect accross the battery bank or should it be isolated to the battery it's attached to.

You connect it wherever you want the voltage measurement. It's usual if you have more than one battery to connect the main power positive and negative on different batteries. That's where you'd connect the solar controller, and it's where you connect the SmartSense too.

 

[steveh57]

^^ Thanks, That's how I have it setup.

 

[Off da Grid]

The Votronic 350 duo mppt Will output 14.4 v for lead acid it has multiple settings for which ever type of battery you have works extremely well. A true fit and forget solution.
Don’t bother with the additional screen thing it’s not really necessary but interesting if you like that sort of thing.

 

[Ian60]

You say you will wire the 2 panels in parallel. Why not in series... lower current less voltage drop and/or thinner wire, and the higher voltage should make the mppt reg more efficient?

 

[Lenny HB]

You say you will wire the 2 panels in parallel. Why not in series... lower current less voltage drop and/or thinner wire, and the higher voltage should make the mppt reg more efficient?

Because if one panel is in shade you will lose the output from both panels.

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[sallylillian]

You say you will wire the 2 panels in parallel. Why not in series... lower current less voltage drop and/or thinner wire, and the higher voltage should make the mppt reg more efficient?

I read a very good comparison test which in summary convinced me that for us mobiles users there is questionable benefit. Cannot remember where before you ask. The series advantage of higher voltage delivering earlier and later harvesting, due to the 5v differential of panel voltage over battery voltage required by the regulator, did not deliver a significant extra charge to justify the risk of losses with shading. This is really only an issue for us mobile solar users where the position of the panels is in constant flux and optimum siting cannot be guaranteed. A static system at home presents the ability to overcome the shading issue. Of course there is the option on say a six panel installation like mine of pairing 3 x 2 in series and parallel the resultant 3 pairs. I decided against the option although for me it is a simple wiring change at the bus.

 

[steveh57]

On a smallish van does it often occur that one panel is shaded and the other not?

 

[Raul]

I have a portable two panels folding up and they are series connected. I can control the shade. On the roof I have two in parallel. You can put them in parallel if you have no obstructions. But, as you move, or relocate all the time, you will not have the ability to see if you have a shade and move to correct the position, unless you get up there with the ladder and have a look. There are advantages for series, but shade also is really bad. It’s really down to user and roof configuration, if the roof has vents skylights or other potential obstructions, the parallel is a better option.

 

[berni109]

300w on the roof with the same controller and 6mm works fine.

 

[Raul]

I have a portable two panels folding up and they are series connected. I can control the shade. On the roof I have two in parallel. You can put them in parallel if you have no obstructions. But, as you move, or relocate all the time, you will not have the ability to see if you have a shade and move to correct the position, unless you get up there with the ladder and have a look. There are advantages for series, but shade also is really bad. It’s really down to user and roof configuration, if the roof has vents skylights or other potential obstructions, the parallel is a better option.

Oops, should of read “ You can put them in series if you have no obstruction” instead parallel. But I think you guys got it. I should read it before posting, note to self.

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