Sorry to those who I might bore with this, but I need a little clarification on my thinking:-

I have a 2 year old caravan with all the bells and whistles in it and when I connect to mains it just passes 240v through all the systems and maintains the battery at 13.8v, fine.

I am thinking of installing a 100watt PV panel so I can go off grid and save around a £5 a night when touring but if I do, I won’t get any 240 volts to my microwave etc unless I fit an inverter. Well that is ok, they are not that costly, 1500watt should do fine to power microwave and charge my macbook which is all I really need at 240v.

Thing is, if my PV panel is generating 100watt and I plug into the mains, will that interfere with the PV panel?

My logic would suggest no as 100watt at 13.8v (float charge) would combine with the mains charger at 13.8v and the battery would be fine.

Also, would the white box of tricks that sorts out the electricity in the caravan complain if I used an inverter and simply output it into the box of tricks to give me 240v at all sockets, probably not, but then what if I plug in the mains, would I have to disconnect the inverter?

If any of you auto/electrical bods out there can give me some feedback I really would appreciate it as getting this kind of information is not altogether easy and while I am aware of normal electrical issues, I am just not confident in my thinking on this one.

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Ipanema Sand

MY10 TD4-e GS Manual
Lago Grey Now retired after 8 trouble free years

A 1500W inverter used flat out is 125 amps, the caravan does not have the cabling to take that load, at 600W for a microwave it's 50A, that is about twice as much as a mover and for a longer time, your panel would not be able to replace the power in the battery in a day. I suggest you buy a 350W inverter to run the TV and set top box if they are not 12v, there are plenty of 12v chargers for most tablets and phones.
You will be lucky to achieve 50W average from your panel so 4A x 12 hrs in summer equals 48A/H on a good sunny day. my PC is slightly to the right of Genghis
2012 HSE SD4 In Orkney Grey now gone, best car ever.

Regarding the PV panel, I understand they are normally used just to keep the battery topped-up when there is no mains available but ask on one of the caravan forums, try http://www.caravantalk.co.uk/community/forum/99-caravan-electric/

If you plan on running all your mains appliances from the battery via an inverter, just the microwave will use about 1,200W i.e. 100Amps at 12Volts, you seen the size of 100Amp cable ?

I wouldn't think that either the inverter or the caravan PSU would like 230V stuffed up their outputs, so you would need some sort of switching.

The standard caravan battery is 85 or 110 Ah, so if you use 50% of that before the voltage drops to something below the voltage required by the inverter, you would have less than 30 minutes use out of the battery, possibly a few minutes longer if the sun is shining and the PV panel is delivering the full 100W.

Also with good quality PV panels and regulators costing upwards of 200 quid, that's a lot of £5 per nights.

Look at the back of the microwave for power input, it is a lot more than the output, lots more! I have a 3kVA UPS with extra batteries & will keep my computers going for hours. I boiled a single cup (modest size mug) for tea, out of interest. 1 minute & 5% of my backup time was gone with a 2000 watt kettle. UPS is 90% efficient & it is a good quality UPS. That is about 185 amps at 12 volts.

So if the input for power is 1500 watts for the microwave, & 85% efficiency for the inverter. Plus add anything that is turned on at the same time. 147 amps with no drop in voltage with this current is the absolute bare minimum current. You will need some serious cable in the region of 50 mm2 minimum for 6 metres total length, so 152 amps with 3% drop in voltage due to resistance. Don't forget to double the length for resistance calculations. it is the total length of + & - (there & back so to speak).

& top quality connections that do not overheat from resistance. Procrastination, mankind's greatest labour saving device!

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scrimple wrote:

... they are not that costly, 1500watt should do fine....

Thanks for all the replies guys

Maybe you have all got a little er enthusiastic with the mains and microwave thingy, a microwave is not that important, but it is good for 20 seconds to soften the butter from the fridge!

The main issue was the 12volt side of things and PV and mains putting out 13.8volt float charge into the battery. I have posted on a caravan forum but so far, no one seems to know hence my question here .............

Thanks though guys, I was aware that 1500watts would need some hefty cable, but the inverter would only be about 18 inches from the battery so the cable/load issue would be less of a concern. Again that was secondary to the 12 volt issue.

Thanks for taking the time to contribute everyone, certainly got me thinking is it all worth it!  MY2014 SD4 XS
Ipanema Sand

MY10 TD4-e GS Manual
Lago Grey Now retired after 8 trouble free years

Check http://www.photonicuniverse.com/en/faq/#Ca...__vehicle_

Your caravan almost certainly has a specific connection for a solar panel, normally just behind the battery box RTFM.

Thanks for that, and yes it does, a 10amp cigar socket in the battery box, but there is no way I would connect a permanent connected 100watt PV through a 10 amp cigar socket, the cabling to it is also quite light.

I have in mind to update the socket to a marine 20amp and rewire with 4mmsq cable (each about 18inches long) with an in line 20amp fuse connected to the battery as my awning air pump is rated at 15amps but I still would not use that as a connection point. It really needs to be hard wired.  MY2014 SD4 XS
Ipanema Sand

MY10 TD4-e GS Manual
Lago Grey Now retired after 8 trouble free years

The cigar socket will be to power something rather than a PV input.

On our caravan the PV regulator output connects to a 2 pin Molex type of connector under the seat behind the battery box.

What make and model caravan is it?

The bailey handbook advises the cigar socket is for a PV panel.

Believe me, there is no cable large enough (6mmsq) for a PV connection to the battery.  MY2014 SD4 XS
Ipanema Sand

MY10 TD4-e GS Manual
Lago Grey Now retired after 8 trouble free years

Quote:

The bailey handbook advises the cigar socket is for a PV panel.

The 12v socket is just like all the others in the van (4 in total) each one is permanently wired 12v and individually fused at 10amp through the vans wiring.

A permanent 100watt PV (about 8.5 amps at 12volts) will need 6mm cable due to the length, about 2.5 meters each way, 5meters in total. I could probably just about get away with 4mm cable, but bearing in mind the temperature the van roof will get to in summer, I think 6mm would be a safer bet.  MY2014 SD4 XS
Ipanema Sand

MY10 TD4-e GS Manual
Lago Grey Now retired after 8 trouble free years

You should get a PV regulator with the panel this will produce the correct voltages for battery charging and blockers to eliminate reverse current at night, some of the regulators can be intelligent chargers and produce 14.4v for charging and reduce to 13.8 v to float, the PV panel could produce as much as 18v without a regulator and that is not friendly to a battery  my PC is slightly to the right of Genghis
2012 HSE SD4 In Orkney Grey now gone, best car ever.

yes thanks for this, I have a 10amp in mind though I had thought about going up to a 20amp due to likely temp issues under a bunk, as long as there is a reasonable airflow behind the unit it should be OK.

It will be mounted close to the battery to reduce cable losses.  MY2014 SD4 XS
Ipanema Sand

MY10 TD4-e GS Manual
Lago Grey Now retired after 8 trouble free years