solar panels and battery chargers

[Lonesome-Whizkid]

My question for this thread is... If you have a solar panel on the roof of your caravan, how handy does it come in, can you do multiple things with it like draw power from it to charge mobile phones and charge laptop batteries and does it defeat the purpose of having a leisure battery charger or am I getting myself mixed up, starting to think I've been told in another thread that the leisure battery takes its charge from the towing vehicle when hitched up and in tow. Is that correct or not? or is there an on board leisure battery charger aswell that charges your leisure battery when hooked up to a ehu.

 

[ProfJohnL]

The caravan will come with a mains charging circuit already built in, so if your using a mains hook up you can easily throw a switch and keep the battery topped up.

When you are towing, provided the wiring has been installed properly, when the cars alternator is producing enough power , the caravans habitation relay should switch over and allow it to charge the battery.

If you have a Solar Array, its best to fit a charge regulator to prevent, which will allow the panels to charge the battery but not over charge it.

I cant give you specifics about the switches and positions because they're designed be each manufacturer.

 

[Lonesome-Whizkid]

So there's three ways the leisure battery can get charged? by towing vehicle, by solar panel and also ehu on site?

Mentioning the caravan habitation relay, how do you know its charging the leisure battery, Is there a gauge to go by or a LED?

I know I'm asking a lot of questions but I'm starting to get an understanding of such a complex little house on wheels.

 

[ProfJohnL]

So there's three ways the leisure battery can get charged? by towing vehicle, by solar panel and also ehu on site?

Not usually- there are many ways you can charge a battery, but only the mains hook up with built in charger and the habitation relay usually come as standard in most caravans. I mentioned solar power as this has gained in popularity over the last few years and is quiet and pollution free. Several people who contribute to this forum have fitted solar panels, including Parksy who has become a bit of guru on fitting solar panels

Some of the other ways of charging the caravan battery can include , petrol generators (Which despite being marketed as silent do produce an annoying noise and fumes and are very inefficient). wind turbines, (free energy but you need wind, and they do pose a hazard because if the rotating vanes, and they can be noisy) Fuels cells (silent, and a bit space age and have a considerable cost to purchase and run). given time and a river, I could produce hydro electric power.

Mentioning the caravan habitation relay, how do you know its charging the leisure battery, Is there a gauge to go by or a LED?.

Most caravans will have some form of battery monitor, either a guage or LED's or LCD meter panel which type depends on the caravan manufacturer. This will sow the increase in battery voltage when its charging - However as the habitation relay senses the power coming from the car and only switches over when the cars alternator (Generator/dynamo) is producing enough voltage, you are likley to be towing when that occurs. You can check it by when the outfit is stationary by having someone in the car to press the accelerator (in neutral) and you can watch the display change.

You may need to set some switches in the caravan to allow the car to charge the battery. _ see your users manual.

 

[Lonesome-Whizkid]

Thanks all who have taken the time out to reply, It's most appreciated.

 

[mfdaustrey]

Just picked up my new Elddis Affinity 550 fitted with two solar panels. We are planning on not using ehu as much as before and would like to keep a careful check on the state of the battery.

The van has a meter which it'd at present reading 13.8v. An I right in believing that I should not let the battery drop to much as it is trickle charged?

Reading other sources 50% seems to be about a reading of 12v. Does this seem a reasonable value to strive for? Our am I mixing up everything?

 

[Gozza]

My caravan control panel has a little voltmeter - it's not hugely accurate, it shows the battery voltage as just over 12 when the "real" voltmeter puts it at 13.8, but it's good enough to give an indication. I can definitely tell from it when the battery is charging from the EHU and when it isn't, and that's about as much as I use it for.

One question which may contribute to the original poster's pool of knowledge, and will certainly help me...I've started to physically disconnect the mains charger from the battery whenever it's not charging on EHU, as someone told me that you can get some backward current drain through the charger - and it seems to me that the battery self-discharges more slowly since I've started doing this. Does that make sense or am I imagining things?

 

[ProfJohnL]

Hello Gozza,

A properly designed and manufactured charger should not drain a battery. If yours is draining the battery then it suggests its faulty.

In most modern caravans, the charger/psu is fully integrated into the 12V wiring, so I'm puzzled as to what you are actually disconnecting or unplugging.

 

[Lonesome-Whizkid]

So, is the charger that's integrated into the 12 volt system hidden under a seat or in a confined space? And can it be forgotten about if you have a display to inform you what the current condition is of the battery onboard? Is this outwith the solar panels control display? And a seperate entity altogether?

 

[Gozza]

My caravan is quite old (2005)

The charger is under a bed, mounted next to the fuse box on the back of the battery compartment. There is a two lead wire (quite heavy duty looking) which runs from the charger into the battery box, with a plug and socket in the middle which is what I unplug. I've checked the lead and the non-charger end has 12v on it when it's unplugged (but the battery is connected!), and I use this point to connect a solar panel (not permanently installed) when the 'van is going to be on the storage site for any length of time. The panel isn't enough to charge the battery, it was only a cheapy from Maplin, but it balances the self-discharge.

 

[ProfJohnL]

So, is the charger that's integrated into the 12 volt system hidden under a seat or in a confined space? And can it be forgotten about if you have a display to inform you what the current condition is of the battery onboard? Is this outwith the solar panels control display? And a seperate entity altogether?

Each caravan manufacture will decide where to mount the charger, and it could be different in each model of van they produce, Certainly the concept teh manufacturers will be working on is fit and forget, but as you will havfe seen in several treads some makes of charger seem prone to failing.
Also how the condition of the battery is displayed is also different, so you need to know your specific caravan for any specific advice to be offered on location of charger etc.

 

[waffler]

If your Elddis comes with a fixed solar panel i assume it is quite modern. It will probably have a built in digital volt meter. It will read to a tenth of a degree. We have this system and i have found the meter to be reasonably accurate. A normal full charge is 12.7 volts. Flat is 12 volts. However these are reduced if things are running. I have found the 23 watt tv reduces the voltage by 0.2 volts. The Truma combi boiler 0.1 when running. As soon a they stop running or being watched the voltage rises. So take the measurements with nothing on. Our panel is 80 watts and we do a lot without ehu. 5 days at Easter and a week now. We watch tv about 4 hours a day, have all led lights and our battery has always been recharged by lunch time.

 

[ProfJohnL]

Hello Wafler,

Just because your caravan is fitted with a digital meter , there is a temptation to think it will be accurate. In fact they can be surprisingly inaccurate, unless they have been calibrated (with a certificate ) or at least compared to a meter of know performance. Most cheap meters will have a claimed accuracy of 5% +/- 1 LSB that equates to about+/- 0.6V on a 12 V measurement with 1 decimal

Let me give you some examples of digital meters where it is well documented they are frequently not accurate and you should not implicitly trust their readings:-
Digital speedometers found in many cars, (Always set up to read faster than you are actually travelling)
Digital tyre pressure gauges.
Digital bathroom scales