Battery charging using solar power and an inverter.

[crinklystarfish]

Would anyone with the requisite technical knowledge care to advise on the following please?

 

I have a 2003 Knaus Traveller and spend a lot of time wild camping. I don’t use the mains hook-up, but this does connect to a transformer and split charger that allows both leisure (85 amp hr) and starter battery charging. I would like to use a solar panel to charge both batteries but am out of my depth when faced with precisely how this would be achieved safely and efficiently. I’d like to charge the starter battery as well as the leisure battery because I often sit in the cab with cab lights and CD player on.

 

Which brings me to this; which may, I accept, be absurd. Could I install a further ‘stand alone’ deep cycle battery fed directly from a solar panel and then use an inverter coupled to this stand alone battery to feed 230v ac into my existing Knaus transformer / charger? In effect self generated mains power without the hook-up, but used solely to power the dc circuits and components.

 

This, if technically plausible, would seem to be a neat solution to providing the charging functions I want, whilst maintaining the protection and integrity of the on-board electronics. Knaus have seemingly made a good job of them and I don’t really want to meddle.

 

If feasible, would anyone have any idea what capacity solar panel, ‘stand alone’ battery and inverter might pull this off? I have purposefully chosen low wattage components in my van with only the blown air heating still drawing any significant power.

 

I suspect the inefficiency of the inverter and lack of solar charging on dull days might prohibit the proposal, but hey, nothing ventured…

 

Thanks in advance to anyone willing to comment.

[Clive]

Hello Steve,

I have risen to the bait on this.

 

You need to change a few things around in your van first. If you like to sit in the cab and play then you need to get those items in the cab that you use re-connected to run from the leisure battery. Internal Cab lights and the Radio come to mind as prime contenders for re-connection. Then you only need to be concerned about keeping the leisure battery charged when wild camping. If you are not competant to do this yourself then there are people who are, and some are frequent contributors on this forum. This problem of the radio and cab lights running from the starter battery is quite common, most converters do not re-connect them to the leisure battery purely to save their time and money - but it needs doing.

 

Having removed the need to solar charge your starter battery during season you arguement to justify an inverter has dissapeared. The solar panel you might get should be as big as you can mount/afford. Always connect this to the leisure battery via an intelligent regulator. Again if not confident then use someone who is. Probably that same person you have identified to re-connect your cab lights and radio.

 

If you have need for further leisure battery capacity and have the space and weight capacity available then for sure get another battery and connect it in parallel with your existing battery. If however you wild camping is never more than say 4 days at a time you may just consider more leisure battery capacity and forget the solar panel. Solar charging is quite satisfying when you can see the free amps on the ammeter though!

 

If you have need for AC mains when wild camping then that is an arguement for an inverter, but its not a good way of powering the vans charger, too many losses, too many bits etc. It will work but not very efficiently.

 

 

Lastly, if you want to charge your starter battery from the solar panel when the vehicle might be laid up for the winter then a simple "bridging fuse" is a simple low cost way of doing this. "Battery Mate" is another more expensive way of doing this.

 

 

Hopefully Dave Newell will pop up next with his thoughts!

 

Have a browse around my primitive web site for a few ideas.

 

http://www.motts.dsl.pipex.com/MOTORHOMES.htm

 

 

Good luck

 

Clive

 

 

 

[Dave Newell]

Hi, this is not a good way of acchieving your goal. The simple solution would be to fit the biggest solar panel (array if necessary) you can afford/fit on your roof and connect it to your existing leisure battery via a regulator. Then connect a battery master (or similar device) to trickle some surplus charge to the engine battery.

 

D.

[Brian Kirby]

Steven

Just a thought, but you may find some advantage to transferring the power feeds to your cab lights and CD to your habitation battery.

If your charger unit is by EBL and is under the passenger's seat, a half decent car entertainment fitter should be able to find a spare live feed for the radio CD.  If the Knaus set up is similar to Hymer/Burstner/Dethleplease models, there is probably a fuse panel on the charger unit with a number of spare/unused ways.  Some of the spares remain live whether the 12V supply is switched on or off, others are switched with the 12V supply.  Wiring the radio CD to the latter will cause it to dump its memory when you switch off the 12V electrics, but it will also prevent the live feed to the preset station memory draining the battery when the van is left static - say during the winter.  Wire the cab lighting to a permanently on feed. 

If you have one of these charger units, you may also find there is provision for connecting solar panels built in.  However, you'll need someone familiar with the Knaus set up to be sure it is done right.

Be a bit cautious with assumptions about the charging of the starter battery.  Although present, this facility is frequently only a maintenance, or float, charge rather than a full re-charging current.  If you do run down the starter battery, I don't think this can be relied upon to reinstate the full charge.  Hence my suggestion that you get the radio CD and cab lights switched to the habitation battery, which does get the full charge.

Hope this helps.

[Mel E]

Steve,

 

As Clive says, step 1 - and much cheaper than a solar panel - is to fit a second and, if you can find space, a third leisure battery. Connect them in parallel with the existing leisure battery and they will charge automatically when you drive. But make sure that you get 85 amp hour batteries so the 2 or 3 batteries are the same size.

 

A couple of reasonable leisure batteries will cost you about £70 at any motorhome show. If you have room, change the existing leisure battery for a 110/120 amp hour battery and get a second one, then 2 batteries will give you the same as 3 85s.

 

Step 2 MAY be to fit a solar panel or two. But even one modest 75 watt panel with regulator will set you back over £500. And don't be fooled by the 75 watt (=75/16.5amps output or 4.5 amps). You only get that when the panel is at right angles to the sun on a clear summer day. Mounted flat on the roof, that only happens in the Tropics. On an English cloudy day, output will be a good deal less than an amp. And even in summer you'll be lucky to get more than 10 or 12 amps into your battery when it's cloudy. Even in the south of Spain, you'll do well to get more than about 45 amps over the course of a sunny day. Compared with your boosted battery capacity of some 240 amps (say, 180 amps usable), that's peanuts.

 

So solar energy is far from free!

 

Mel

[crinklystarfish]

Thanks gents, I will get on with rewiring the offending cab items to a suitable free 'leisure' circuit, and thereafter consider which way to go. I'm coming down on the side of bigger / additional leisure batteries at the moment. I use the 'van year round and probably don't need to worry about starter battery charging once I've rearranged my wiring. Very helpful advice, thanks once again.

[colin]

A lot of it comes down to how you use van, for us most of time we would expect to drive van each day (or maybe every other day) when on holiday, so bateries get charged from engine, but for 1 week of year I go to favorite site, park up and don't start van for a week, solar panel is essential for this.

[Brian Kirby]

colin - 2006-12-04 7:59 PM A lot of it comes down to how you use van, for us most of time we would expect to drive van each day (or maybe every other day) when on holiday, so bateries get charged from engine, but for 1 week of year I go to favorite site, park up and don't start van for a week, solar panel is essential for this.

Well, it may not be a feasible option on your favourite site, but a hook up for a week would be streets cheaper than a solar panel.

[colin]

Don't think they'll ever get hook ups, no caravans and I can only remember seeing one other VW, here's view a few yards away from site first thing in morning, when I used to go to shop for paper, unfortunaly shop is now shut and I have to cycle to get paper in other direction.