# Connecting solar panel to vehicle battery



## Gilroy (Oct 4, 2007)

I have a 4W briefcase solar panel. Can I just clip this to the vehicle battery without disconnecting the other battery connections? This is for topping up the starter battery when the motorhome doesn't get moved for a couple of months.


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## rosalan (Aug 24, 2009)

In theory you could do so I believe but when I tried doing this some time ago, my battery failed; twice. So, whether or not this was a coincidence or not I do not know. I now have a much more potent solar panel with a control unit which has been working perfectly for a long time.
So I would not connect it to the battery without some form of protection.

Alan


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## boringfrog (Sep 22, 2006)

I don't think these 4 watt panels are very good especially for a large motorhome battery.


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## philoaks (Sep 2, 2008)

I'd agree with Alan and would fit a fuse (1 amp) close to the battery to protect things. I would also ensure there is a blocking diode in the solar panel so that it doesn't end up draining your battery.

A 4w panel is very small and wouldn't need a regulator, it would however only provide a miniscule amount of charge even on a sunny day.


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## nicholsong (May 26, 2009)

I agree with 'frog' 4W is what they can theoretically produe i.e. on the equator in full su. 

We do not know where you are in Europe, but if UK then in winter it is unlikely to keep up with the internal battery loss, alarm system and radio on standby. I tried similar - useless.

Whatever you connect, make sure there is a blocking diode internally or fitted in-line as a minimum.

If you use a much bigger solar then a controller that prevents overcharging is necessary.

Geoff


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## listerdiesel (Aug 3, 2012)

4Watts is about 300mA, that is just not worth using on a decent size battery.

30W is a good starting point, but if there's a chance it will bring the battery up over it's rated float voltage, you'll need a controller fitted.

A 36-cell panel will give a nominal 17V output, but it will not give that if connected directly to a battery. If the battery gets to full charge and the panel continues to input power into it, the battery will start to go into overcharge.

Peter


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