Solar Panel Battery Charging

[andyp1]

Hi , I am sure this has been done many times before - just hard to search.

so... Can anyone advise on the best Solar panel to get for using the 'van off hookup for long weekends and to keep battery charged when in storage.

Dont want to spend a fortune - but it obviously needs to work

Thanks

 

[Parksy]

A lot depends on how much power you are likely to consume during the long weekends Andy.

Have a look Here to calculate approximately how much battery power you use on a day without e.h.u.

Choose a panel with a blocking diode to avoid the leisure battery becoming completely discharged during the hours of darkness. (the panel would drain the battery)

Monocrystaline panels (as opposed to Polycrystalline)are more efficient and you will need a charge controller to avoid too much power cooking the leisure battery.

I recently bought an 80 watt solar panel from Greener Electric a UK based company. The charge controller supplied with the panel wasn't much good in my opinion so I bought a 16 amp model with better terminals from Maplins

Most of those who go on C&CC rallies with our local d.a. use panels of 40 watts or over depending on their requirements.

It's vital to use the correct sized cable to avoid voltage drop, connect an inline fuse holder with a blade type fuse on the + cable between the solar panel and the charge controller. The connections need to be tight for all cables, connect the battery first whilst the panel is not exposed to light, then connect the panel to the controller and expose it to daylight and your leisure battery will be charging.

 

[andyp1]

Many thanks for your help - link is useful

Cheers

Andy

 

[ChrisUK]

Thanks Parksy, I also found your post useful. We are currently in the middle of a 6 week hol in Scotland without EHU, and this year I am using the "aux car battery / inverter / mains battery charger method, but it is a bit of a faff monitoring battery volts. Weight and size are a problem for me, I might try to get away with a 40W or even a 20W panel as we have no radio / TV (no reception) and we can read by daylight till gone 10. The panel that was refered to does not give any indication of installation. Do you prop it up against the van, or did you make a frame ?? I assume that they are fully weatherproof?

 

[Parksy]

The panels are weatherproof and can be mounted on the caravan roof using designated mounting brackets or you can make a stand for the panel to be free-standing so that it can be turned towards the sun (or light) for greater charging efficiency.

I haven't made a frame yet, up to now I propped mine against the fire bucket but now that I've connected it properly and tried it out (it works!) I'll use some spare timber that's in my shed to make a stand to bolt on either side of the solar panel frame.

As far as the wattage of the panel is concerned it depends on your power requirements and whether you use the caravan during the darker months. It's best to work on a 'worst case scenario' basis, a panel with lower capacity will supply a charge but this is dependent on the available light. Obviously direct sunlight would be ideal but on dull overcast days during the dark months I will still need to charge the battery which is why I opted for an 80 watt panel. I'm considering using two 110 amp hour leisure batteries wired in parallel to increase the power storage capacity because the Maplins 16 watt charge controller supports the charging of two batteries connected in this way.

 

[Parksy]

I forgot to add that solar panels weigh very little and 40 or 50 watt panels are reasonably compact.

 

[ChrisUK]

Thanks, looks like this is my next years project before coming back for our extended Isle of Mull stay.

Can say two 20W panels be connected in parallel if one proves not enought. currently we are getting 18 hours of daylight and very little rain although it is often overcast, this is why I was hoping to get away with much less than the generally recommended 80W panel.

 

[Mikey1]

The problem with fitting to the roof on the van is you never get the best angle to the sun and also the possibility of being in the shade whereas loose you can turn etc.

Aire and Sun sell a study frame which isnt cheap but will last for years.

The problem with fitting batteries in parallel is the batteries will drain down together,this is great if batts are of equal discharge state but if one dicharges quicker than the other this will pull current from the other batt when not being charged.

I have a similar controller but have my tv wired to the second batt.

 

[EmmanuelMuldoon]

You can usually connect several solar panels in parallel as they have internal series diodes. It is bad practice to connect (car) batteries in parallel, as, if one then develops a faulty cell & its terminal voltage drops, then the other one tries to charge it. Depending upon the exact conditions, large currents can flow!.

When you get your system, a series regulator (perhaps the Sunsei cc10000) is much preferable to the shunt type, as they generate minimal heat.

 

[Parksy]

Thanks for the good advice guys, I won't be connecting the leisure batteries after reading posts on this topic.

I made a solar panel stand for under

 

[Gafferbill]

..batteries have been connected in parallel for years without trouble.

When towing your car charges your caravan battery by connecting your caravan battery to your car battery in parallel.

It does this through wiring 3 to 4 meters long and is achieved because the car battery is at a higher voltage than the caravan battery when the engine is running.

I have been running a system for 5 years where up to 3 batteries are connected in parallel when towing my caravan.

I have a leisure battery permanently fitted to and electrically wired to the tow car.

Under this system when the engine is running and charging is taking place, all three batteries are connected in parallel.

When it is not, just the leisure battery on the car and the one on the caravan are connected in parallel.

By the use of isolation relays only the car battery is used for engine starting.

I effectively have a 220-amp 12-volt caravan supply with the ability to charge half this capacity whenever I use my tow car without the caravan.

On return I can electrically connect the two leisure batteries with an extension cable (in my case 12S)

whereupon the charge will silently equalise and be readily available.

 

[marlot]

My landcruiser has twin batteries fitted as standard, wired in parallel.

 

[Sproket]

Hmm ! looks like i will have to have another dream & hope the wife picks the right numbers :O).......

 

[Mikey1]

The issue of connecting batteries in parallel is evident when they are discharging not charging.

The batteries will try and equalise and as pointed out the stronger battery will try and charge the weaker one,you may have done it for years but you cant argue with physics.

 

[Gafferbill]

....you are right and that is exactly what I want the higher charged battery to do.

The higher charged battery is mounted on the car and charges the lower charged caravan battery.

The wiring just has to be sufficient and you have to maintain and replace batteries if required.

My point was that there is an alternative to solar charging...

 

[Philspadders]

just make sure the batteries are of the same type and capacity.

 

[SteveP]

Parksy, you mention "It's vital to use the correct sized cable to avoid voltage drop, connect an inline fuse holder with a blade type fuse on the + cable between the solar panel and the charge controller."
What size cable & fuse would be advisable for a 80 w panel?

 

[ChrisUK]

After a lot of searching, I ordered a 50W kit from Amazon this morning. It seems that the standard for cables is 4mm. I would definately put an in line fuse in the cable between the battery + and the controller (near the battery), that where the biggest fault current will come from. I have one of the Maplins current measuring devices (unter a £tenner) which plugs into the blade type fuse holder, so I will be able to easily monitor how much current I am producing.

 

[SteveP]

Parksy, you mention "It's vital to use the correct sized cable to avoid voltage drop, connect an inline fuse holder with a blade type fuse on the + cable between the solar panel and the charge controller."
What size cable & fuse would be advisable for a 80 w panel?
[/quote

Question for Parksy?]

 

[ChrisUK]

The standard cable fitted seems to be 4mm sq, terminated with MC4 connectors. That size should be OK for almost all panel sizes. The 80W panel will only produce about 3 to 4 amps and 4mm cable is rated at 10s of amps, too lazy to look it up. The volt drop is IR (current times resistance) The current is low and the resistance of 5m of 4mm cable is very low.

 

[ChrisUK]

Just out of interest as I can not afford a LC, are the two batteries both under the bonnet with a charge controller (not a relay / split charge relay) between them? I have seen this arrangement on the Aussie forums but never seen the kit on sale in the UK.

 

[SteveP]

thanks Chris

 

[MichaelE]

The LC has the 2 batteries under the bonnet as it needs the extra amps for starting a cold diesel engine.
No sure if it has a split charger etc but i do know if one battery fails it drags the other down too.

 

[Parksy]

Parksy, you mention "It's vital to use the correct sized cable to avoid voltage drop, connect an inline fuse holder with a blade type fuse on the + cable between the solar panel and the charge controller."
What size cable & fuse would be advisable for a 80 w panel?

Hi Steve
Sorry for the late reply, I've been away.
The panel that I bought was fitted with3 metres of 6mm cable with two extra 3 metre lengths with the outdoor solar connectors to use as an extension for the free standing arrangement. I added a 10 amp blade type fuse and weatherproof fuse holder between the +tive battery terminal and the regulator.
I haven't installed the panel onto the roof of the caravan yet but when I do hopefully within the next couple of weeks I will use the original 6mm cable which should be sufficient to reach the front under-seat storage close to the battery where I will permanently fix the regulator which will then be wired directly into the charging circuit.
4mm cable should be fine for an 80 watt panel
http://cgi.ebay.co.uk/Solar-Cable-Multi-Contact-4mm-Black-per-metre-/180608518755?pt=UK_Gadgets&hash=item2a0d1b4a63

 

[SteveP]

Thank you Muchly!