Solar panel help on amps needed

George25 · May 11, 2019

We have a two x 50 amp battery split charging system. From the leasure battery we plan to run an ARB type compressor fridge, around 40 litres which is said to draw 0.87 amph at 3'c
Nothing much else will drawer current from this battery a few LED lights etc
Mainly summer use UK and Southern Europe nothing excessive in terms of ambient temp probably Southern France so 30 ish and not looking to keep frozen goods just 3 to 5 c
SO any help deciding on panel output that we might need greatly appreciated

kermit_rr · May 11, 2019

Do you mean a 50ah vehicle battery and a 50ah leisure battery and alternating your solar charge between the 2?

George25 · May 11, 2019

kermit_rr said:
Do you mean a 50ah vehicle battery and a 50ah leisure battery and alternating your solar charge between the 2?

Hi Yes thats exactly what we have. All the solar sites say calculate your need to match against panel you buy. I understand mono /poly crystal and the need for shade protection diodes etc
We have a battery management system that shouldn't allow us to flatten the vehicle battery but if the vehicle battery is flat it will start off the leasure battery so getting it wrong is not the end of the world and if the butter goes runny hey ho ANY advice gratefully received

kermit_rr · May 11, 2019

I'm going thru a similar set of issues with my parents mobile home so i know your difficulties!

You want to match your panel output to your battery size, or vice versa. You already have the batteries, so that just leaves the panels

The ideal charging rate is 10% -15% of your battery amps, which works out nicely to around a 100w panel, assuming 36 cells to the panel

I'm not sure what you're planning to use the leisure battery for but it sounds quite small? Ideally you should only discharge to around 50%, meaning you can only use around 25ah

kermit_rr · May 11, 2019

Starting off a leisure battery isn't recommended

Turboman · May 11, 2019

kermit_rr said:
Starting off a leisure battery isn't recommended

Lot of dual purpose batteries are available now. Bit of stuff about the various types and their applications here.

https://www.shieldbatteries.co.uk/applications/leisure.html

Turboman · May 11, 2019

George25 said:
Hi Yes thats exactly what we have. All the solar sites say calculate your need to match against panel you buy. I understand mono /poly crystal and the need for shade protection diodes etc
We have a battery management system that shouldn't allow us to flatten the vehicle battery but if the vehicle battery is flat it will start off the leasure battery so getting it wrong is not the end of the world and if the butter goes runny hey ho ANY advice gratefully received

Guessing you will also be charging both leisures and starter from alternators?
It is not usual to charge the starter battery from the panels, that is usually charged by an alternator, and, because it is not wired into the leisure circuits, should never go flat. It will get ample recharging while the vehicle is running, like a normal vehicle battery.
Also, is the fridge you mention 12v, or 230v running off an inverter?

kermit_rr · May 11, 2019

My parents van has split charge over both batteries from the alternator and solar, I assume it's based on the fact many camper won't be started for long periods

George25 · May 11, 2019

kermit_rr said:
I'm going thru a similar set of issues with my parents mobile home so i know your difficulties!

You want to match your panel output to your battery size, or vice versa. You already have the batteries, so that just leaves the panels

The ideal charging rate is 10% -15% of your battery amps, which works out nicely to around a 100w panel, assuming 36 cells to the panel

I'm not sure what you're planning to use the leisure battery for but it sounds quite small? Ideally you should only discharge to around 50%, meaning you can only use around 25ah

Hi The manageme system displays the status so we should be able to prevent discharge below 50% . So it sounds like all things being equal we have a desirable max use of 25 amph. The probable fridge use is 0.87 amph at 3c SO it sounds like a 100 watt panel shiuld do us

Turboman · May 11, 2019

kermit_rr said:
My parents van has split charge over both batteries from the alternator and solar, I assume it's based on the fact many camper won't be started for long periods

Shouldn't really need it, a fully charged battery with no drain should hold it's charge for many months, and having completely separate circuits removes the possibility of draining the starter battery for leisure use.
Main concern about battery condition is on very cold weather anyway, and you won't get much off panels in winter in the UK.
If you are really concerned about the starter battery, you could always use one of the small temporary panels that just connect to the starter battery with crocodile clips, and are removed while the vehicle is in use.

kermit_rr · May 11, 2019

Turboman said:
Shouldn't really need it, a fully charged battery with no drain should hold it's charge for many months, and having completely separate circuits removes the possibility of draining the starter battery for leisure use.
Main concern about battery condition is on very cold weather anyway, and you won't get much off panels in winter in the UK.
If you are really concerned about the starter battery, you could always use one of the small temporary panels that just connect to the starter battery with crocodile clips, and are removed while the vehicle is in use.

You're right, but don't forget all the electronics on a modern van, every time you operate the central locking everything wakes up etc

George25 · May 11, 2019

Turboman said:
Guessing you will also be charging both leisures and starter from alternators?
It is not usual to charge the starter battery from the panels, that is usually charged by an alternator, and, because it is not wired into the leisure circuits, should never go flat. It will get ample recharging while the vehicle is running, like a normal vehicle battery.
Also, is the fridge you mention 12v, or 230v running off an inverter?

Hi 12 v but if available it can run off an electric hook up. .The alternator gives a preferential charge to the vehicle battery and once fully charge then charges the leasure battery which is why we want to suppliment the system with a solar panel which will give a preferential charge to the leasure battery (fingers crossed)

Turboman · May 11, 2019

kermit_rr said:
You're right, but don't forget all the electronics on a modern van, every time you operate the central locking everything wakes up etc

I hear what you are saying. But it doesn't seem to be a problem on a regular car or van, with no solar at all.they simply up the battery size to allow a bit for the electronics.

The issues mostly seem to occur due to drain from the leisure side, which is why I was asking him about the fridge. Fridges are the main cause of flat leisure batteries on boats, which use a similar system to camper vans.

George25 · May 11, 2019

kermit_rr said:
You're right, but don't forget all the electronics on a modern van, every time you operate the central locking everything wakes up etc

Hi We have tried to keep things simple so our vehicle doesn't have central locking, climate control, electric windows, electric door mirrors or puddle lights and such stuff. We have changed bulbs to LED but you are right there can be lots of stuff secretly draining the battery.(some dash cams for instance) .

Turboman · May 11, 2019

George25 said:
Hi 12 v but if available it can run off an electric hook up. .The alternator gives a preferential charge to the vehicle battery and once fully charge then charges the leasure battery which is why we want to suppliment the system with a solar panel which will give a preferential charge to the leasure battery (fingers crossed)

That sounds like a good system, provided you will be running the vehicle most days. If you are intending to be parked up for long periods of time, without mains hook-up, your leisure battery capacity sounds on the low side.

Panels are useful for top up, but modern power usage is surprisingly high, water pumps, charging computers and phones, TVs, stereos, and the fridge chugging away all the time.

I have 600W of panels, 4x110ah leisure batteries, one same for starting, which is charged by a 45A alternator, there is a separate 130A alternator that charges the leisures.
I still turn the 230v fridge off at night, though, so as not to run the battery bank down too much while the panels and engine are not charging the leisure batteries.

George25 · May 11, 2019

Turboman said:
I hear what you are saying. But it doesn't seem to be a problem on a regular car or van, with no solar at all.they simply up the battery size to allow a bit for the electronics.

The issues mostly seem to occur due to drain from the leisure side, which is why I was asking him about the fridge. Fridges are the main cause of flat leisure batteries on boats, which us a similar system to camper vans.

Hi Yep the fridge is my main concern ARB compressor fridge 0.87 amph at 3c. We have even thought to go to powder milk etc

steve2286w · May 11, 2019

so fridge takes 20a in 24 hours, our 120w panels give about 6a when in full sun pointing directly at it,
Assume 6 hours of full sun and no cloud with a smaller panel giving 4a there’s 24A in total so would run fridge without any additional charge from alternator or hook up. For max amps you would need to move panel towards sun through the day , if you are travelling it’s getting charged up anyway but if camping for a week without hookup it would draw the battteries down with smaller panels

Turboman · May 11, 2019

George25 said:
Hi Yep the fridge is my main concern ARB compressor fridge 0.87 amph at 3c. We have even thought to go to powder milk etc

If you will be using the van in Souther Europe, you will get a much better charge on the panels than in the UK. But all the same, 100W is only 100W, and that only during daylight hours.
If you have room, I would try and squeeze in another leisure battery, and another 100W panel, be on the safe side.
The fridges are a problem, 12v draw a lot of battery power, and run almost all the time. Mains fridges off an inverter don't run so much, but the inverter burns power in itself.

Turboman · May 11, 2019

steve2286w said:
so fridge takes 20a in 24 hours, our 120w panels give about 6a when in full sun pointing directly at it,
Assume 6 hours of full sun and no cloud with a smaller panel giving 4a there’s 24A in total so would run fridge without any additional charge from alternator or hook up. For max amps you would need to move panel towards sun through the day , if you are travelling it’s getting charged up anyway but if camping for a week without hookup it would draw the battteries down with smaller panels

True.
But don't forget all the other drains on the leisure side, that often occur during darkness, and when the engine isn't running.
Shower pumps, domestic water pumps, entertainment systems, phone charging, etc.

There really isn't any substitute for decent battery bank capacity.

In practice, you get a decent charge off flat mounted panels, but only around midsummer in the UK.

kermit_rr · May 11, 2019

Don't forget your charge controller isn't 100% efficient and PWM controllers are less efficient than MPPT controllers, but MPPT are much more expensive.
Also remember to keep your panel clean and shade free. Because of the way solar cells are wired internally, covering 10% of your panel will reduce output significantly more than 10%

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