Solar Battery maintainer during storage

Until recently I have been using a system of two 110ah batteries (one inherited at no cost, nothing untoward mind-you) and either the battery charging facilities at non-EHU sites or a small unit (cost £5, the normal price at time of purchase being £15) that allows safe charging of a second battery carried in the car while out for the day. I have spent a max of 11 continuous day’s off-grid using this system and it has shown the potential to supply enough 12v power to meet my requirements for an indefinite period. So I have no need to change this system.  With regard to keeping the batteries charged during storage periods the van has been kept at home with easy access to 230v mains supply.  However as with all things in life circumstances have changed and storage is no longer viable at home and I now no longer have access to 230v mains supply.  Now with a couple of hours work and the price of some suitable cable I could link the two batteries together during these storage periods to give 220Ah capability but this would lead to extra work each time I stay off-grid, or it seems for about £35 I could simply buy a suitable plug-in ‘Solar battery- maintainer’.

None of the above diminishes my interest in understanding the technical details involved in generating 12v Solar Power or its useful application in the world of C&MH touring.

Looks like you have a system that works for you for of grid.  If a 6W battery maintener keeps the battery charged then that fine. The Halfords price seems a bit step but convenient.   For the record I have a 150W roof mounted panel and my battery definitely stays charged in storage. 

Yes Boff,  I do have a system that works but it has its beginnings in the somewhat dim (pun intended) & distant past when Solar Power was little more than a dream. It has come together and been refined over a number of years from equipment readily to hand but it now needs some further tweaking in order to meet my present day requirements.   I can see that my present situation presents me with the opportunity to invest in Solar Technology and create a system that requires far less management and labour so I will be giving some time to further research whether such a move is really what I desire.  

Thanks to all !!    

I didn't mean to be patronising.  In life I believe that there are two types of system those that work for you and those that don't.  The technological advance that I believe is a game changer is the advent of the led both for lighting and TVs.  This is allied to the collapse in price of solar panels makes it a real practical proposition.   Our first SP bought about 10 years ago was 43w and a real bargain at £156. The last one I bought about 18 months ago was £128 for a 150W panel. If you are serious about one  I would look on eBay or amazon for prices. But fitting one in truth is a simple DIY job.  Just takes a bit of nerve to drill a hole in the roof. 

I got the Aldi solar panel to keep the battery charged whilst stored.
It says it can be used inside and plugged into the 'cigarette lighter' socket. Just wondered does anyone do this and is it effective?

Alternatively, how much do they cost to have fitted on the roof?

Boff.   Re: "I didn't mean to be patronising"

I apologise   if by the wording of my last post it seemed that I was implying that you were being patronising towards me, I assure you that nothing was further from my mind. I was just trying to say that because something works it does not mean it is the most suitable means to achieving the desired end.  

JCB4x4

I think the fundamental questions for all owners are:

A. do you want to good off grid without EHU (for more than a weekend) 

B. If no to A. then is off-grid overwinter storage with alarm etc still powered needed.

For the former, a large freestanding or roof mounted powerful panel is needed with a regulator. (Caravan covers is a contentious subject, but if you like covers overwinter in storage and want solar then it may be an extra complicator).

But if you normally EHU or offgrid only for a night or 2 then but need to maintain your battery overwinter without regular visits to swap out the battery then a small solar maintainer as I bought will suffice. I suspect if I hunted around on mail order I may have saved a few pounds or up'ed the spec; I initially installed the £25 2.4W version but mid winter it didn't produce enough power. Halfords kindly swapped it (plus some cash) for the 6W £39 version which seems to have done a great job of maintaining the battery. The 6W was much bigger, nearly as big as the sunroof and the ease/convenience & security installing the panel on the inside of the caravan was fantastic.

I have no doubt that there may have been some dull days where the panel allowed the battery to deplete slightly but I know my 110ah battery can survive a few weeks so on average over numerous days, even in the winter, the 6W panel produced enough juice. And regarding buying better/cheaper from another retailer - £39 isn't a fortune and the convenience of a Halfords branch 10 mins from the COSSOA site and confidence in that Halford won't quibble if it fails to perform in anyway so I wasn't inclined to bargain hunt. The SP that Aldi sells looks identical, exactly the same dimensions  - I suspect they are identical and £9 cheaper at Aldi

I hope the recommendation is useful to others with similar requirements

It is my understanding:

1)That in order to fully charge a 12v battery set the charging unit needs to be able to supply 14.7v (pulsed) at not <10% of the battery-set’s Ah rating.

 Eg.: 220Ah requires 22Amp input and 110Ah requires 11Amp input.

2) That in order to protect the battery-set from damage during use and charging, the charging unit must be able to detect and meet the battery-set’s required charging needs throughout its use, particularly if the battery-set and the charging unit are to be left connected and un-monitored.

I know this is achievable using mains 230v Smart-chargers.

My question is- are Solar Panels with Controls able to meet these requirements?

JCB4x4 regarding the info you've posted - some is, as far as I know, true but some I do not believe is correct.

Certainly the voltage of the charge must be greater than the voltage state of the battery. Although these batteries are nominally 12V, my  brand new Numax DC31MF 105ah when seriously depleted will be 11V but after a long charge (i.e. its 100% full) then left to stand for a couple of days, then a volt meter across the terminals shows approx 13V.

When I connect my charger to this full battery the charger puts out a voltage of approx 14.5V (the key thing is it has to be greater than the battery in order to "push" the charge and "overcome" the batteries voltage state.

But I think your amperage info is very off. Figures like 105ah; 110ah even 220ah is amperage over a period of time - hours. To understand what kind of amperage a caravan battery might normally sustain, for comparison, according to my owners manual, the typical site ECU supply is typically 10amp and often 5amps on the continent.   So, apologies but your "Charger must be capable of 22amps" calculation isn't realistic - the plug in the charger will be a 13amp fuse - so no - that isn't right.

Many typical battery smart chargers will initiate charging a flattish battery at 12V and perhaps 8 - 10amps. But as the charge state rises the voltage of the charger must similarly increase up to your 14.7V but the amperage from the charger will drop to <1amp. My Trickle charge is similar in terms of voltage profile, but it only puts out a fraction of an amp. Charger that are smart are able to monitor the charge state and in effect they temporally switch themselves off then either wake themselves up and charge until 100% again because the monitored charge state has dropped or perhaps a time based. Some smart smart chargers are also capable of attempting to de-sulphate a battery whose internal plates have sulphated (due to being left discharged for too long) - to do this chargers deliver a pulse charge. As far as I am aware chargers do not normally need to deliver a pulse charge.

So back to my solar maintainer - it also produces approx 14V, even in dull sunshine (this voltage ought not to fluctuate with sunshine, but the amperage will - until there just isn't enough sun and it shuts down). It is rated at 6W so I would expect in ideal sunshine with ideal panel point then it should produce 0.43amps. When I measured the amperage during a dull January day when I first connected it to a semi-depleted battery it output about 0.25amps if memory serves. So in the short winter days, the solar maintainer  might only deliver 2amps/day.  But my GPS/GSM tracker consumes <2ma - and I suspect that the OEM alarm system consumes similar - so I would expect the daily consumption to be <1amp/day.  In comparison, from experience without the solar maintainer, the battery was still functioning but pretty run down (30%) after 2 months which suggests consumption was around 1.5amp/day.  So my conclusion is 6W is clearly sufficient, but I only - the smaller one I initially installed (2.4W) didn't cut it (probably because it will only deliver about 1.25amp of charge during a winters day)

I am quite surprised that a 6 Watt panel will keep the battery fully topped up. Much depends on how much power the alarm/Tracker takes, how much sunshine their is etc. No doubt this is covered in detail on the other thread but if it works then fine. Since this is really just a top-up charge it would certainly be advisable to fully recharge the battery with a leisure battery charger at the end of the storage period. 

To recharge a sealed battery you need 14.4 volts and a multi-stage charger.