Solar panel install, help needed.

[Anseo]

At present I am putting together a DIY 200w solar suitcase.

2 X 100w panels wired in series, and using 14 AWG (approx) supply cable, actually I am utilising one of my EHU cables that has 2.5mm positive and negative conductor wires.
I have made up connector cables to my EHU cable using MC4 connectors; the earth wire in the existing EHU cable is not utilised at any point in the solar set-up.

I will be fitting a 30 Amp MPPT controller close to the battery (mounted internally in the caravan).

Caravan battery is 110 Amp, I have a spare 100 Amp battery that I may use as a backup.

Using both panels I understand that 200w is around 16 Amps.

So to my question; should I install fuse(s) in the system, I read that a fuse between the controller and battery is recommended (I'm not sure what else should be fused).

If I should fit fuse(s), what amperage(s) should I fit?

Cheers for staying with me this far, and I hope it all makes sense.

EDIT, 11 AWG changed to 14 AWG

Thank you,
John

 

[Guzzilazz]

I think 2.5 sq.mm is a bit on the thin side... You will get a bit of voltage drop between the panels and the controller, and with MPPT, you want the highest voltage possible. Better to go bigger. AWG 11 = 4.16 mm2, I'd go for 6mm2. Your MPPT output is a max of 30A is too big for your solution, because at 40v (series connected) the current would be 200/40 = 5A... So, you could go for a 20A controller, and then get a 20A fuse on the battery terminal to protect the wiring between the controller and battery. Your current flow is based on parallel wiring (200/12 which should be 200/20 - the voltage output (max) by the panels) so way over the top...

 

[JTQ]

At present I am putting together a DIY 200w solar suitcase.

2 X 100w panels wired in series, and using 11 AWG (approx) supply cable, actually I am utilising one of my EHU cables that has 2.5mm positive and negative conductor wires.
I have made up connector cables to my EHU cable using MC4 connectors; the earth wire in the existing EHU cable is not utilised at any point in the solar set-up.

John

I similarly utilise my 10 and 15 metres EHU cables for connecting my solar panel, sometimes just one occassionally both if the shadows force the panel further away.
However, I don't waste the potential of the earth core, my "adaptors" place the negative onto both the return and earth cores, ie in parallel, as any drop in the circuit resistance can be beneficial. Mine is an 85 Watt panel feeding a Duo controler with 90 & 60 Ah batteries.

Whilst voltage drop at high current is important for optimum efficiency, the real life situation with as large an array as 200 Watts will not require optimisation at high yields.
Then the battery will be very quickly charged [if not wrecked!].
By far the more relevant time will be during the low light periods where the current and therefore the voltage drop will be way down, so core size is not too critical, low current low voltage drop.

The high charging current potential of a 200 Watt set up is in itself not good news for a 110 Ah battery, the more so if a true deep cycling battery as off EHU users would normally fit. A "starter" battery will suffer less abuse by these exceedingly high charging currents than a proper deep cycling battery.
Therefore, a bit of loss from voltage drop here is not unwelcome, it will help mitigate that abuse.

 

[Dodger524]

The output from solar panels is about 20 volts, so volt drop calculations may be based on that value if the controller is situated close to the battery that is being charged as it is only the circuit between the battery and controller that will be reduced to around 13 volt.

With regard to fusing, yes it is essential to protect the circuit.

 

[ProfJohnL]

I can't help thinking that Guzzilazz's response is overkill for your situation.

With low voltage systems running high currents, cable resistance is certainly something to consider, but in the context of your system 6mm csa is massive, costly and heavy and more difficult to handle.

For what it's worth, if you are running the two panels in series, then you are effectively going to double the panels output voltage. But you are not doubling the output current, so the current is unlikely to exceed about 8 Amps, perhaps 10Amps on a super sunny day. That is well within the current handling capability of 2.5mm csa cable (like EHU cable).

Voltage drop is caused by the inherent resistance of a conductor R measured in Ohms. For any given piece of cable the resistance is determined by the material the conductors are made off, it's cross sectional area csa, and its length. BS standard 2.5csa mains cables have a resistance of 7.41Ohms or less per 1000m that is 7.41milliOhms per meter.

If we assume you are using 5m of cable that gives a resistance 37mOhms per conductor. If your panels are producing 10Amps of current, the voltage loss in the cable would be 10A x 0.037Ohms = 0.37V per conductor.

For the circuit to work you will use two conductors so the total voltage lost will be 0.74V.
That would be a peak power loss of 0.74V x 10A = 7.4Watts out of 200 or 3.7%.

Most of the time the panels will be running at rather less output, so the losses will be proportionally less.

If you went for 6mm csa cable the cable resistance is down to 3mOhms per m, and your losses on a 5m length would reduce to about .3V or 3W or 1.5%.

In my view the loss of performance by using 2.5csa cable easily offsets the cost and inconvenience of using 6csa cable for your situation.

If you were to use EHU type cable, you could use the brown for +ve, Blue for -ve, and the green with yellow stripe, could be run in with the blue to reduce the resistance of the. -ve side just a bit more to reduce losses from 3.7 to about 2.9%

 

[Anseo]

I'm learning lots, thank you all.

Can I have suggestions for what size of fuse I should fit between my controller and the battery? (main battery is 110 amp deep cycle type, spare battery is 100amp deep cycle);
Should there be any additional fuse protection added to my set-up ?

I accept that my 30 amp MPPT controller has a greater capacity than I need for a 200 watt panel array, is there any downside to having a greater capacity controller ?

JTQ, I thought that the MPPT solar charge controller would take care of protecting my 110 amp battery from any overcharging etc.
You state " a 200 Watt set up is in itself not good news for a 110 Ah battery, the more so if a true deep cycling battery as off EHU users would normally fit" you have me worried now hmy:

Thanks for the replies folks

 

[ProfJohnL]

....

I accept that my 30 amp MPPT controller has a greater capacity than I need for a 200 watt panel array, is there any downside to having a greater capacity controller ?

JTQ, I thought that the MPPT solar charge controller would take care of protecting my 110 amp battery from any overcharging etc.
Why is " a 200 Watt set up is in itself not good news for a 110 Ah battery, the more so if a true deep cycling battery as off EHU users would normally fit" you have me worried now hmy: ...

I'm not sure on this one, We have to make a comparison to what often already fitted to caravans-
The largest power supplies normally fitted to caravans a standard will have a 16A output capacity. As far as I know this does not cause any significant detrimental effect to normal caravan Leisure Batteries.

A charging current of 16A at 13.8V equates to 220Watts which is very similar to your 200W solar panel capacity on a bright day.

BUT as the charge in the battery increases the charging current it will accept diminishes, so it would only be putting that much power into a battery if the battery was all but fully depleted. Most of the time the charging current will be perhaps 3 to 4A.

I think we have to accept that batteries will not last for ever, even those that are used in the most optimal way possible will eventually fail, so there will be an ongoing replacement cost. If a leisure battery costs say £80 and super duper deep cycle battery may cost twice as much or more, it would have to last at least twice as long to make economic sense. I have no life figures to compare so I don't know for sure but I suspect the life expectancy in a caravan would not be enough to make it viable

I would welcome any verifiable evidence to the contrary.

 

[Guzzilazz]

The high charging current potential of a 200 Watt set up is in itself not good news for a 110 Ah battery, the more so if a true deep cycling battery as off EHU users would normally fit. A "starter" battery will suffer less abuse by these exceedingly high charging currents than a proper deep cycling battery.
Therefore, a bit of loss from voltage drop here is not unwelcome, it will help mitigate that abuse.

This is absolutely wrong. The only time it would be correct is if there was no controller, but here there patently is, and indeed it's absolutely the point of a controller to keep batteries in optimum condition. The MPPT will dump power from the panels (usually as heat - see the finning on MPPT controllers), My MPPT on the boat delivers 7 stage charging just like a CTEK, starting afresh each day.

 

[Percyprod]

I may have missed something, but shouldn't they be connected in parallel? Series doubles the voltage for same current, parallel gives same voltage double current?

 

[ProfJohnL]

I may have missed something, but shouldn't they be connected in parallel? Series doubles the voltage for same current, parallel gives same voltage double current?

Hello Percy,

You are correct about the relation ship of current vs voltage and it relation ship to series or parallel connection. But the size of panels being considered (200W) here could damage a battery by over charging, so that is why they need a charge controller.

Modern charge controllers can accept a wide range of input voltages, and can convert power more efficiently to match the needs of the storage battery. Not only do they maximise power conversion for optimal charging, the also monitor teh batteries and will prevent over charging.

One reason to go for higher voltage over current, is to minimise transmission losses through cables, and generally it is easier to use buck downward converters to to reduce voltage but maintain power than to try and do boost conversions, though these days its not so very different.

 

[JTQ]

I'm learning lots, thank you all.

JTQ, I thought that the MPPT solar charge controller would take care of protecting my 110 amp battery from any overcharging etc.
You state " a 200 Watt set up is in itself not good news for a 110 Ah battery, the more so if a true deep cycling battery as off EHU users would normally fit" you have me worried now hmy:

Thanks for the replies folks

The reason is simply that your system has the potential to exceed the "recommended" bulk phase charging current of 10% of Ah rating, which for example a Varta LFD series battery should be exposed to.. The 200 Watt has a possible ability at a charging voltage of 14.4 of a current of about 14 amps, whereas the recommended for a decent battery of your size is 11 Amps. Basically, there is a miss balance here between storage capacity and panel capacity. If your consumption is modest enough not to require the charger to delve into "bulk" charging to rechage what you used the night before the issue is mitigated, as it is if the next day it is overcast and the panel performance is down.
This is not a death knell situation but neither is it as I said "good news"; it is part and parcel of true deep cycling batteries I have used that modest charging rates are "recommended". Typically starter technology batteries are better capable of standing higher percentage charging rates than with the thick plates in deep cycling batteries.
Others believe the controller will identify the battery capacity and know the characteristics its build technology requires, I personnally doubt controllers in our market sector have that level of refinement.

 

[Guzzilazz]

I'm learning lots, thank you all.

JTQ, I thought that the MPPT solar charge controller would take care of protecting my 110 amp battery from any overcharging etc.
You state " a 200 Watt set up is in itself not good news for a 110 Ah battery, the more so if a true deep cycling battery as off EHU users would normally fit" you have me worried now hmy:

Thanks for the replies folks

The reason is simply that your system has the potential to exceed the "recommended" bulk phase charging current of 10% of Ah rating, which for example a Varta LFD series battery should be exposed to.. The 200 Watt has a possible ability at a charging voltage of 14.4 of a current of about 14 amps, whereas the recommended for a decent battery of your size is 11 Amps. Basically, there is a miss balance here between storage capacity and panel capacity. If your consumption is modest enough not to require the charger to delve into "bulk" charging to rechage what you used the night before the issue is mitigated, as it is if the next day it is overcast and the panel performance is down.
This is not a death knell situation but neither is it as I said "good news"; it is part and parcel of true deep cycling batteries I have used that modest charging rates are "recommended". Typically starter technology batteries are better capable of standing higher percentage charging rates than with the thick plates in deep cycling batteries.
Others believe the controller will identify the battery capacity and know the characteristics its build technology requires, I personnally doubt controllers in our market sector have that level of refinement.

Your completely misleading.... I give up. I've been using solar on more complicated 12v systems for over ten years, and even that time ago, the controllers worked with the sophistication that meant they wouldn't overcharge... My last response in this thread

 

[Guzzilazz]

Deleted

 

[Anseo]

I will be sorry to be without your input Guzzilazz.

Your comments have helped me, thank you, I'm hoping that you might reconsider and continue to share your knowledge

 

[Guzzilazz]

I'm just ignoring JTQ's comments

 

[Parksy]

Anseo, Here's a guide to solar controllers and how they work.
If correctly rated solar controllers (often known as regulators) allowed batteries to be 'over charged' why has my leisure battery survived being charged via the caravan system when using ehu on sunny days when the solar array would also be producing power?
It's because even my simple cheapo PWM controller can determine when the battery is fully charged so it switches itself off to avoid cooking the battery in effect.

For a 200 watt array, go for a good MPPT model like the Morningstar, which allows you to set the controller for sealed or flooded batteries.

 

[JTQ]

[

Your completely misleading.... I give up. I've been using solar on more complicated 12v systems for over ten years, and even that time ago, the controllers worked with the sophistication that meant they wouldn't overcharge... My last response in this thread

I made no mention of "over charging", indeed I very specifically only discussed an issue encountered in the "bulk charging phase", which is a phase well before we get anywhere near fully charged, let alone over charged.

I don't think any of us are suggesting a decent solar controller is going to over charge the battery, but in installations where the size of the panels installed overwhelm the capacity of the battery fitted, then excessive charge rates can become involved.