solar panels

Ozboc,
you say-> " So with this - I actually carry 4 batteries - 2 for car (one isolated via Redark solenoid) one in the the Jayco and one spare"

why not add the 'spare' in parallel to the battery powering the fridge ?

Mainey . . .

Have a look here

http://www.campertrailers.org/solar_spreadsheet.htm

This is an excell spread sheet that allows you to change the parameters and see what come out the other end, solar wise.
Its been done by one of the guys on campertrailers.org, look under tech tips.

Cheers

Mainey
All that is good advice but the main one is Buy The Best performance you can afford.
I think the best preformance does not in this instance include fast charging AGM batteries if the charging is only minimal solar or low power chargers and would be an over expense.
I agree low internal resistance batteries are the best for fast charging but you need the capacity of charging to utilise this facit to get the benefit and that is also not cheap although extremely efficient.
Ian

What Mainey said, and as a rule of thumb take the number of litres of your fridge then add 100 to get the minimum number of watts you will need to keep it going.

Ie

40L needs 140Watts
60L needs 160Watts
80L needs 180Watts

Fridge has to be a compressor type, this will work anywhere in Australia for a good PWM regulator. Add 20W for lights or safety margin. You can reduce the number of watts by 20% for a MPPT regulator.

Ian,
yes, I suggest AGM's because they charge much faster and higher than wetcell batteries in the same, short time period, remembering often you only have a small time frame for efficient charging ( ~6 hours? )
__ __ __ __ __ __ __ __ __ __ __ __ __ __ __ __ __

You just can't have too much Solar power or a battery bank that's too large !!

BUT... you can have a Solar system that's too small
then it becomes very inefficient and costly ($$$) to maintain batteries and replace or add extra panels to increase capacity, so do it right the first time.

With the Solar system set up (with a 'efficient' Solar reg) so the fridge runs direct from the Solar reg, the Solar system will power the fridge direct (during the day) and the excess power produced will then be run into the battery system, if it is needed at all, as can be seen on my 'profile' Solar pics & information.
With this system the battery bank will never get the chance to go below 12v !!

Mainey . . .

Mainey
With a small amp input a flooded wet cell battery accepting 14.7V will charge faster than than an AGM at a lower voltage .

The high recombination of the AGM batteries comes into play just that way High recombination or low resistance where you can belt high AMPS in and you cannot get a solar system on a car that can give you high enough amps to get the benefit of High Recombination.

Solar is always too small because you are restricted by the footprint size against the average vehicle roof and thats a pity.

A battery bank can be too large if you cant charge it efficiently.

Smart charging vehicle equipment combined with solar is very efficent and the more efficent the charging is the smaller the battery bank that is needed.

The battery size is a problem with weight.

Ian

Ian,
we are talking about "Solar" power charging a battery
we have to compare apples with apples, yes if you compare a flooded wet cell battery accepting 14.7v it will charge faster than than an AGM at a "lower" voltage, however the Voltages & current for comparison purposes must be identical.

When you have a large battery bank you never get to use most of it anyway, it's just a matter of 'topping up' the battery system daily, however when a smaller battery is used they most often get run down to low conditions daily causing sulphation and if the Solar system is small capacity and inefficient it may not fully charge the battery system in the few hours available daily.

Yes, a Solar system has to be a matched system, the battery bank has to be suitable for the Solar system and vice versa.

It's a case of size does matters :-))

Mainey . . .

Yes that correct we have two scenarios
One is a 100AH FWC
One is a 100AH AGM
Lets assume the FWC can accept 20A before resistance limits the charge.
Lets assume we have 4 solar panels at 5A each giving 20A connected to the 100AH FWC.
Lets assume we have 4 Solar panels at 5A each giving 20A connected to the 100AH AGM.

Then we have what can be called comparing apples with apples as the FWC will charge faster than the AGM due to a higher acceptance voltage.

Now to do this we would more than likely need maybe 80W panels so does anyone think they can get more than 4x 80W panels on their vehicle roof.

So in essence Low resistance High Recombination AGM batteries are an unwarranted expense for this exercise unless the charging capacity is increased.
Ian

Ian,
yes, just far too many 'assumptions'

However, some relevant facts are:
in my own Solar system my AGM's never get below 12v
(even when measured at first light b4 the sun hits the panels, when connected all night to a fridge that draws 10 Amps and also runs Inverter and lights etc etc)

I've 2 x Solar panels = ~2OO Watts Solar system (~12 Amps)
I've 2 x 100+ah AGM's = ~2OO ah AGM DC battery system

The Solar system only has to replace any power lost from the Battery system, it never has to charge a fully discharged battery system.
I had 2 x 8Oah wetcell Deep Cycle batteries (16Oah) before I changed to AGM's, they lasted (only) 6 years and then I used one of them for my Cranking battery for probably 12 months.

The picture gallery with-in 'my profile' shows in detail how my Solar system works, with detailed gauge pictures showing the battery SOC, charging voltage and total Amps available at the Solar system and charging the AGM battery system too.

I believe what people forget or maybe don't understand is the Solar system only has to replace in the Battery the power used, as it is used, if your putting in more than you take out you never will have a discharged battery, until the sun goes down, then you only loose what is used that night as it is replaced again by mid morning.

Mainey . . .

I believe people can see what I was getting at and you have now confirmed it yourself.
If you got 6 years out of 2 FWC batteries and then a further 12 months as a cranker I hope you are going to get 12 years plus out of the AGM ,s or you have confirmed my response as being correct.
Ian

Ian,
Yes, well I do expect to get at least 10 years, no joke, as my AGM's have an expected 10 year life span
(not warranty or guarantee)
Yes, if I get 12 years I will be even happier.

But as can be clearly seen my Solar system is not capable of anywhere near the 20 Amps you mentioned, as they are generally only showing as putting just 2 to 4 Amps into the AGM's, because they only have to maintain them, not Re-charge them from highly discharged low voltages.

The batteries (obviously) only last as long as they do because they are correctly maintained in a charged condition and not run down, only due to the equipment involved, definitely not intervention from me.

Mainey . . .

Mainey
The only reason I posted was not to try and make things look wrong but to emphasise that what suits one may not suit another and your system is fine but economically may not suit others and the initial costing may not be achievable using AGM but the end result can be similar with two sets of FWC and initial cost outlay less with two licks at it.

I will try a tell someone what should suit them the best even if I do not sell it because that is what I think forums and pr are about a helpful hint regardless if your commercially involved or not.

Ian

Ian,
yes, I agree
hence my initial post stating:

* Buy the best *performance* you can afford *

I definitely don't make any attempt to gain 'sales' from EO !!

As I'm sure you would know some technologies are superior to others in the field of Solar power.
Is no good telling someone asking for information to look at the lesser of the options available to them, they have to make up their own mind as to how much they can afford to spend.
After all they will be cursing when it's not living up to their expectations, hence the reason I pointed to my own Solar set-up pictures, it's just a guide to see what is achievable and without advertising tags :)
Image Could Not Be FoundMainey . . .

Hi Ian,

Tks for the discussion about the different ways of doing things. To put it in it's most basic form what I am looking at is:

Being able to free camp for up to 10 days, I have a 3 way fridge so can switch that to gas. I was looking at the panels to provide lighting, power for music and TV and with luck enough for the coffee machine (got have some comforts). At the moment we only charge up when plugged in at a park so I may need to look at getting a connection from the car so I can charge while travelling. I have a duel battery system in the car and a single battery in the van, should I consider putting in another battery to increase the van's capacity and use the solar panels to keep that topped up, or wont that work.


Regards
DA

Both power from your car while travelling and solar to your van battery would definately work for you.
As far as the size of the solar and putting in another battery it would be a suck it and see and that will come from you and yours learning from knowing how long you used things and does your existing system cope for you.
Grow with your requirements so start with a 40 or 60 watt panel and your existing battery and enlarge if needed.
Ian