Thread: Camper trailer solar set up

Hi folks and Landy, for a starter, providing you have run suitably sized cabling between the cranking battery and your house batteries, you will have no need nor benefit from fitting any form of DC/DC device.

If your house batteries are in a low state at the beginning of the days drive, neither your alternator or a DC/DC device will fully charge your batteries, but your alternator will replace far more of the used capacity of your house batteries that a DC/DC device could do.

Next and this may be a bit confusing if you are not use to working with watts, but watts measurements are far more relevant when working with solar power supplies.

So keeping the above in mind, when calculating the power available at the house batteries, you need to know the total watt output of the panels and the total watts being supplied, via a solar regulator, to the house batteries.

The thin cable causes heat lose, heat uses watts to create the heat, and thats lost watts.

If you have 150 watts coming from the solar panels but you use thin cabling between the panels and the regulator, it doesn't matter if the regulator is mounted on top of the battery, if there is a reduction in the amount of watts available at the input of the regulator, then there is going to be a reduction in the current ( watts ) at the batteries.

Best suggestion Landy, as others have posted, get a good quality MPPT regulator and some decent cabling to connect the solar panels to the house batteries, via the regulator.

Tim. I know that this type of stuff is your specialty, but the bloke I purchased my solar panels from also had a very broad knowledge of solar and electronics.

He owned a Jaycar store which he ultimately closed and took a job in a mine doing solar installations.
This was pre Kevin Rudd, so was long before the solar craze took off, where every one can easily become a solar installer, not necessarily an expert in the field.

Now this bloke told me what I posted in post nine, that being a small voltage drop through long cables does not matter.(if reg is close to the battery)

Obviously you would not want to use phone cable.

In my situation I have two 80 watt panels. One for the car with Engle, and one for the caravan house battery.

Each of these is fed by a 20 metre 6mm auto cable, which from memory is a bees dick over 4mm squared.

If we get a couple of cloudy days, I put the two panels to the fridge and have at times to get them out of the shade, join the two cables together to make a 40 metre run.

Using my Plasmatronics regulator which measures input, there is no measurable difference whether the cable is 20 or 40 metres..

Hi Dave and in your case, you are not charging low batteries, you are simply supplying energy for a set current load.

If for example, say your fridge draws 3 amps and your panels, on a cloudy a day, produce 2 amps each at each panel's output, then loose an amp over the cable length, but you still get your 3 amps.

If on the other hand, your were trying to recharge a low battery, your are more likely to have 2 amps coming from each panel, at the panels but because of the "ATTEMPTED" high current draw of the low battery, which will cause a greater voltage drop, you might be lucky to get 1.5 to 2 amps at the battery.

Thats the same setup but different results because of the different current loads.

NOTE, I did this in amps, not watts but you would actually see better figures if you were doing a watt count rather than an amp count.

The higher current draw of the low battery will cause a far greater voltage drop and that means wattage lose because of the heat generated in the cable.

Your mate was right but he didn't stipulate the size of the cable and in your case, the loses in the 6mm is fine for your fridge, but would cause a totally unacceptable loss when trying to charge a low battery.

In the caravan industry most solar stuff ups are caused by the van builder using to small a cabling from the panels to the regulator and that is over very short distances compared to the long runs used with mobile fold up panels.

Having decent sized good quality cabling is one of the more important parts of any good solar system if you want to get the most out of it.

We only have 2 x 100 amp AGM's in our 18 foot van and two very good quality 135 w panels plus a good quality regulator. We use heaps of power, with a 60 litre chest fridge going 24/7, fans on all day, stereo going all day, plenty of lights on inside and outside the van and usually TV at night. In the warmer months no matter how much power we use in a day the next morning the regulator is usually on float by 8.00 am to 9.00 am (ish). Meaning all day while the sun is up we are only using the excess power the solar provides on fully charged battery's, most of our friends we camp with take advantage of that even though they have their own various mobile solar set ups. After a day or two of camping when their battery's start to run down each day or two between them they carry over their chest fridges and plug them into our vans batterys hoping to let their systems get half a chance to get enough power to keep their fridges going overnight. This happens all the time and with many different friends.

If you have to rely on running your vehicle or a genie to keep your battery's up with a decent charge in them then your solar system is inadequate for your power needs. Of course weather can and does make a difference but few of us sit in one spot for days and days on end if its bucketing down.

Having a good solar set up for me makes the difference between a great camping experience and a pain in the arse trip.

I invited Tim (Drivesafe) to this thread after reading it because I knew he would explain solar and what's needed better than me.

Originally Posted by TerryO

In the caravan industry most solar stuff ups are caused by the van builder using to small a cabling from the panels to the regulator and that is over very short distances compared to the long runs used with mobile fold up panels.

Having decent sized good quality cabling is one of the more important parts of any good solar system if you want to get the most out of it.

We only have 2 x 100 amp AGM's in our 18 foot van and two very good quality 135 w panels plus a good quality regulator. We use heaps of power, with a 60 litre chest fridge going 24/7, fans on all day, stereo going all day, plenty of lights on inside and outside the van and usually TV at night. In the warmer months no matter how much power we use in a day the next morning the regulator is usually on float by 8.00 am to 9.00 am (ish). Meaning all day while the sun is up we are only using the excess power the solar provides on fully charged battery's, most of our friends we camp with take advantage of that even though they have their own various mobile solar set ups. After a day or two of camping when their battery's start to run down each day or two between them they carry over their chest fridges and plug them into our vans batterys hoping to let their systems get half a chance to get enough power to keep their fridges going overnight. This happens all the time and with many different friends.

If you have to rely on running your vehicle or a genie to keep your battery's up with a decent charge in them then your solar system is inadequate for your power needs. Of course weather can and does make a difference but few of us sit in one spot for days and days on end if its bucketing down.

Having a good solar set up for me makes the difference between a great camping experience and a pain in the arse trip.

I invited Tim (Drivesafe) to this thread after reading it because I knew he would explain solar and what's needed better than me.

Sounds like you have a good setup Terry. Where did you source your kit?

Originally Posted by fraser130

Dave, I agree 100% that the reg should be next to the batteries, I was just meaning that if you put the panels in series, you will halve the loss for the same power. Or you can double the length of the cable or use cable half the size and have the same loss.

Fraser

Actually the power loss will be quartered.

Doubling the voltage halves the current and halving the current halves the voltage drop across the cable. As Power (loss) = Voltage (drop) X Current, ie. 1/2 X 1/2 = 1/4 , so in fact you can use quadruple the length of cable or use cable a quarter the size and have the same loss.

Just be very sure the solar reg used is capable of running '24 volt' in for a '12 volt' output if running a 12 volt aux battery. Not all regs are capable of doing this properly.


Deano

Hi Deano and 24v solar setups for 12v battery systems are only an advantage where there is a necessity for a long run of wiring between the solar panels and the battery.

If you are setting up a system where the panels are 15-20 metres or more from the battery, then the over all cost can be reduced by using a 48v solar set up and thinner wire/cabling, but there is still a wattage lose.

As most RV solar setups require 10 or less meters of cabling between the solar panels and the battery, the cost of thicker cabling is validated by the lower wattage loses and the simpler system setup.

So if you know you are always going to have to have a long run of cable between your solar panels and your battery, then specifically setup for a 24v system.

But as above, with most RV type solar setups, a 12v solar array with thick cabling is a better and simpler way to go, even if on occasions, you fined you need to use a long ( but temporary ) extension cable, where you will, on those occasions, loose wattage while using the extension cable.

Hi Tim, as you say a 48 volt system can be more trouble than it's worth. I'm not advocating this as a solution but highlighting the common misconception that doubling the voltage halves the (transmission) loss when in fact it quarters the loss in the 24 volt example described by fraser130. For a' 48 volt' system the loss would be quartered again for a loss of 1/16 that of a 12 volt system. Very significant for a remote panel stationary installation but, as you say .............. "Best suggestion Landy, as others have posted, get a good quality MPPT regulator and some decent cabling to connect the solar panels to the house batteries, via the regulator".

I have series connected '12 volt' panels to overcome problems with some cheap ebay '12 volt' panels that have too low an output voltage to be much practical use on their own. A tip for the unwary, a '12 volt' panel should have a Voc of around 21 volts and a Vmp of around 18 volts.
A couple of my mates bought these for the same application as the OP and got caught out. The eBay add selling these panels had a big yellow sunflower or daisy in the add so beware as they were not much use used singly or paralleled as a 12 volt source, which IMO should have been pointed out in the add.

Deano