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25mm2 cable


blackrose

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26 minutes ago, David Mack said:

And with 11A maximum from the panels you don't need a 32A breaker (although it will do no harm).

Best to leave it at 32a in case the panels are ever run in parallel.

I would size everything for that scenario, just in case

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2 hours ago, Jen-in-Wellies said:

You have the batteries connected in series, when they should be parallel, but aside from that 👍

 

Yes they're in parallel, sorry 

1 hour ago, Loddon said:

Best to leave it at 32a in case the panels are ever run in parallel.

I would size everything for that scenario, just in case

 

Well my cables from panels to controller aren't sized for parallel but if I ever did change the configuration it wouldn't be that difficult to change those cables.

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Someone else at my mooring is fitting two panels in parallel and his installer insists that if you double the amps going into the controller you'll get more amps out of the controller going to the batteries. 

 

Is he wrong? I thought it was watts x volts going into the controller, so if you connect the panels in series and get double the volts then won't watts x volts = the same amps going into the controller as if you connected in parallel and doubled the watts?

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12 minutes ago, blackrose said:

Someone else at my mooring is fitting two panels in parallel and his installer insists that if you double the amps going into the controller you'll get more amps out of the controller going to the batteries. 

 

Is he wrong?

Short answer. Yes.

13 minutes ago, blackrose said:

I thought it was watts x volts going into the controller, so if you connect the panels in series and get double the volts then won't watts x volts = the same amps going into the controller as if you connected in parallel and doubled the watts?

Watts = volts x amps

volts = Watts / amps

amps = Watts / volts

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Whilst we can most easily measure Volts and Amps at any point, what we are really dealing with is Power, measured in Watts.

 

Watts come from the sun, and some  are  caught by the  panels and sent down the cables, very slightly less Watts go into the controller, slightly less Watts come out again, very slightly less Watts go into the batteries.  Quite a lot less Watts are stored by the batteries.

 

All the Watts lost before the batteries go to heat up the cables and the controller.  The Watts lost in the battery go to making it gas and to warming it up.

 

Now, since Watts are Amps x Volts, while charging, the Watts before the controller can be either higher voltage, lower Amps ( series panels) or lower voltage, higher Amps (parallel panels.)  The Watts after the controller are at  battery charging voltage, and  the Amps are as necessary to make up the right number of Watts.

N

 

 

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1 hour ago, blackrose said:

Someone else at my mooring is fitting two panels in parallel and his installer insists that if you double the amps going into the controller you'll get more amps out of the controller going to the batteries. 

 

 

 

 

 

Already answered above. (NO !)

Edited by Alan de Enfield
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The clever electronics in the mppt controller probably have varying efficiency with input voltage and current, but the difference will be pretty small, otherwise the controller would overheat. Similarly the wiring between panels and controller will need to be fatter to carry the greater current in a parallel configuration but, but since in either case the required wire size will be rounded up to the next standard wire size, you can't say which will have the lower losses. In the bigger picture any difference will be trivial.

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1 hour ago, blackrose said:

Someone else at my mooring is fitting two panels in parallel and his installer insists that if you double the amps going into the controller you'll get more amps out of the controller going to the batteries. 

 

Is he wrong? I thought it was watts x volts going into the controller, so if you connect the panels in series and get double the volts then won't watts x volts = the same amps going into the controller as if you connected in parallel and doubled the watts?

Yes

However there are pros and cons

Series

Pro, voltage is higher, so less loss in cables and better regulation in winter with lower light levels

Con, have to be careful all panels are in the sun and none are shaded.

 

Parallel 

Pro no worries about any one panel being shaded.

Con not such good regulation in low light levels.

 

If it was me I would parallel the panels in summer and series in winter but then my cables are sized for parallel.

 

In reality they have been in parallel for 4 years as ICBA takes over and 40v is still high enough to get decent regulation in a 12v system.

 

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4 hours ago, blackrose said:

Someone else at my mooring is fitting two panels in parallel and his installer insists that if you double the amps going into the controller you'll get more amps out of the controller going to the batteries. 

 

Is he wrong? I thought it was watts x volts going into the controller, so if you connect the panels in series and get double the volts then won't watts x volts = the same amps going into the controller as if you connected in parallel and doubled the watts?

He is wrong, unless it's a PWM controller? But why would you use one of those?

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8 minutes ago, peterboat said:

He is wrong, unless it's a PWM controller? But why would you use one of those?

 

I looked at the controller. A Victron 50 amp unit. I just assumed it was MPPT.

 

I'm just amazed that people tasked with installing this stuff don't know the basics. What I've learned about solar I've only learned in the last few weeks on here and I knew he was wrong.

 

Let them get on with it...

Edited by blackrose
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2 minutes ago, blackrose said:

 

I looked at the controller. A Victron 50 amp unit. I just assumed it was MPPT.

 

I'm just amazed that people tasked with installing this stuff don't know the basics. What I've learned about solar I've only learned in the last few weeks on here and I knew he was wrong.

 

Let them get on with it...

Correct it's a MPPT, I have played with my panels recently and for me series is winning with output in amps, I have a 24 volt system for domestic and had at one point 4 in parallel, then 2 in parallel then series and finally 4 in series, the series gave power earlier and later with slight  improvements over the other 2, all parallel was worse. I have no shading however, I also now have 5 panels in series now.

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This isolator I've bought is enormous. I know it's over-specified at 32 amps but 16 amp versions seemed harder to find and weren't any smaller or cheaper. I'm surprised it has to be so big. A 32 amp breaker is tiny in comparison.

 

Does anyone know how the cables go in and out? There's not much in the way of instructions. If you take the screw on caps off you just get left with a hole. It's meant to be 1P66 waterproof so I don't really get it.

 

IMG_20220922_215549.jpg

IMG_20220922_220038.jpg

Edited by blackrose
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1 minute ago, blackrose said:

This isolator I've bought is enormous. I know it's over-specified at 32 amps but 16 amp versions seemed harder to find and weren't any smaller or cheaper.

 

Does anyone know how the cables go in and out? There's not much in the way of instructions. If you take the screw on caps off you just get left with a hole. It's meant to be 1P66 waterproof so I don't really get it.

IMG_20220922_215549.jpg

IMG_20220922_220038.jpg

You're meant to fit waterproof glands in those holes.

  • Greenie 2
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On 13/09/2022 at 10:29, cuthound said:

 

If I got one of these instead why would I need a 63A version? The panels are only going to output about 11 amps or 22 amps in parallel.

Edited by blackrose
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5 hours ago, David Mack said:

Why not this which I suggested in another thread a couple of weeks ago?

 

You mean this? Are they rated for frequent use to be used as a manual switch? I can't tell if they're dual pole? Which one should I choose?

 

Screenshot_2022-09-23-05-50-49-960_com.ebay.mobile.jpg

Edited by blackrose
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To be honest I'm struggling to understand the point of fitting an automatic breaker since the panels can never produce more than their rated output? In what circumstances is the breaker ever going to trip? So surely the only isolator you would want to fit is one rated for frequent manual use? Or is that wrong?

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9 hours ago, blackrose said:

 

If I got one of these instead why would I need a 63A version? The panels are only going to output about 11 amps or 22 amps in parallel.

 

What is the current rating of the cable?

 

Fuses and circuit breakers should be rated to protect the cable, not the devices connected to them 

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2 hours ago, blackrose said:

 

You mean this? Are they rated for frequent use to be used as a manual switch? I can't tell if they're dual pole? Which one should I choose?

 

Screenshot_2022-09-23-05-50-49-960_com.ebay.mobile.jpg

No. They are single pole - that's what the "1P" on the description refers to.

Why would you need "frequent use" capability. Solar panels are a fit-and-forget solution and you will hardly ever be switching them off.

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