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Why choose solar panels to go off-EHU

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Posted

I'm currently researching options to allow us to go off-EHU so we can wild camp in Scotland (it's legal and acceptable there).

I can't get my head round the fact that most caravannere/motorhomers choose a solar panel solution costing many hundreds of £££ rather than the much cheaper extra battery in the tow-car boot which is charged up each day when out for the day.

I reckon that £150 for an extra 110AH leisure battery and heavy duty wiring and relay would give 40-50 Ah per day (1.5 hours driving/day) and allow me to run TV as well as lights, etc.

Just how much would I need to spend on a solar setup giving 480-600 whrs per day for spring/autumn use?

It seems a no-brainer to me in favour of the boot battery solution but the vast majority have taken the other option - what have I missed?

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49 answers to this question

Posted

The car-boot battery ideas doesn't really qualify as a gadget, does it?

I think that's part of the idea with solar panels - the boy's toy factor. I can see the point with caravans because the caravan is not moving for much of the holiday and, if you choose not to go out in the car, then there's no way of charging the second battery. With a motorhome it's less logical because, as you travel around in the m/home, you will be charging both the cab and leisure batteries, albeit not to the extent that migth be required.

What if you weren't taking the towcar / motorhome out, but needed a way of charging the battery? For some people a solar system will be the way forward but, as with all things, they may not suit everyone.

I'd love one. ::):

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Posted

The car-boot battery ideas doesn't really qualify as a gadget, does it?

It will the way I plan to wire it - I'll match the car cabling from alternator to starter battery with the run down to the boot battery - in the style of chavs with stupidly high-powered stereos but used for a good purpose!

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Posted

Solar gives you more options. Having a battery that needs to be topped upped is ok if you go out everyday for a 3 hour drive. Or you just leave the engine running for 3 hours but then you have extra fuel costs.

Solar for some people is more practical. Requires no extra energy to charge the batteries just what you get from the sun, so you don't have to run the car engine just to top the battery up. And you get a warm fuzzy feeling because you have gone green with solar.

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Posted

if you go out everyday for a 3 hour drive.

Solar setups have to cope with cloudy low output days interspersed with brighter days - no different to variablle amount of daily car use - in our case 1.5 hours / day on average.

you get a warm fuzzy feeling

Two things give me a warm fuzzy feeling - malt whisky ........

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Posted

You wouldn't be able to charge both at the same time.... You'd have to have them switched..... One charging one not.... Otherwise you will have 24 volts running wild in your electrics.....

Also your altenator might not be up to charging a leisure battery also...

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Posted

You wouldn't be able to charge both at the same time.... You'd have to have them switched..... One charging one not.... Otherwise you will have 24 volts running wild in your electrics.....

Also your altenator might not be up to charging a leisure battery also...

Wiring in parallel should see to that.

The starter battery is 90AH so an additional 110AH should be ok as long as the cabling is right.

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Posted

I had an ammeter on the 12S circuit on one car and used it to monitor the battery charging in the boot. A completely flat battery would draw about 15A, but that soon dropped to less than 10 (typically about 7.) That car was wired with 27A cable (don't ask me the gauge, it's just whatever Halfords sell to people who want massive halogen spotlights stuck on their front bumper.) 1.5 hours of driving would have done well to put 10Ah into the battery, though if you go for meatier cable, then the charge rate should be better.

A boot install will never match the under-bonnet one. The resistance of the cable relates to the length as well as the thickness, and the run from the alternator to the starting battery will always be a lot shorter than a run to the boot. Having said that, there are a number of cars that manage to function and charge batteries that are mounted either in the boot or under the back seat.

Just as an aside: How do you plan to use this second battery? I always used to swap the two over, but that was in the days before inverters were cheap. Nowadays, I think I'd avoid the hassle and use the boot installed battery to power a 12V charger via an inverter. Not 100% efficient, but it will successfully charge one lead acid battery from another. I tried it once just to test. Another tempting option is to hook the inverter output up to the caravan's 240V input. You'd be able to use the other mains sockets for low current loads, as well as run the caravan battery charger.

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Posted

I had an ammeter on the 12S circuit on one car and used it to monitor the battery charging in the boot. A completely flat battery would draw about 15A, but that soon dropped to less than 10 (typically about 7.) That car was wired with 27A cable (don't ask me the gauge, it's just whatever Halfords sell to people who want massive halogen spotlights stuck on their front bumper.) 1.5 hours of driving would have done well to put 10Ah into the battery, though if you go for meatier cable, then the charge rate should be better.

A boot install will never match the under-bonnet one. The resistance of the cable relates to the length as well as the thickness, and the run from the alternator to the starting battery will always be a lot shorter than a run to the boot. Having said that, there are a number of cars that manage to function and charge batteries that are mounted either in the boot or under the back seat.

Just as an aside: How do you plan to use this second battery? I always used to swap the two over, but that was in the days before inverters were cheap. Nowadays, I think I'd avoid the hassle and use the boot installed battery to power a 12V charger via an inverter. Not 100% efficient, but it will successfully charge one lead acid battery from another. I tried it once just to test. Another tempting option is to hook the inverter output up to the caravan's 240V input. You'd be able to use the other mains sockets for low current loads, as well as run the caravan battery charger.

27A cable (2.5mm2) is the standard for the 12S and 13-pin circuits for fridge, permanent supply and caravan battery charging - not unreasonable as the 12S/13-pin system operates at around 10 amps. I'm planning to go way up on that from engine to boot battery, 150A for the cabling, 140A for the relay and probably 120A for the fuse. Because the starter battery is 90AH and auxilliary battery is 110AH, the maximum charge rates from a 150A alternator should be split 68A starter + 82A auxilliary but those are at high engine rpm so the real charge split will be more like 27A/33A

The second battery will be used through the 12S/13-pin connections as the consumption will be under 10A - it's only the charging side I plan very high power. I'll use a 100-150W inverter in the caravan.

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Posted

Generator

Solves all the problems and is easy

She can also use hair dryer / curlers etc etc

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Posted

Generator

Solves all the problems and is easy

She can also use hair dryer / curlers etc etc

Non-starter as far as we're concerned - it would mean running the generator from 6pm to 10pm which I regard as anti-social.

And the cost is more like solar panels - it's not down to my planned spend.

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Posted

Roger, Don't forget elf & safety - u need a holder/cage for the battery

We looked into this last year when we had the towbar fitted to the xc90. Reason behind our thoughts - we had a volvo 245 F reg many many years ago and it had a charging kit, complements of previous owner, worked great - but...... as with all things, not allowed anymore

Check with your local towbar fitter, our local guy is Redcap, been in the trade for years which is where we got our info from

Hope you sort out your problem

Just a thought, go back to origins - gas and candles - simples :laugh::laugh:

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Posted

Roger, Don't forget elf & safety - u need a holder/cage for the battery

We looked into this last year when we had the towbar fitted to the xc90. Reason behind our thoughts - we had a volvo 245 F reg many many years ago and it had a charging kit, complements of previous owner, worked great - but...... as with all things, not allowed anymore

Check with your local towbar fitter, our local guy is Redcap, been in the trade for years which is where we got our info from

Hope you sort out your problem

Just a thought, go back to origins - gas and candles - simples :laugh::laugh:

I take your point about H&S - the auxilliary battery will be in a battery box contained within a DIY locker fitted into the space where one of the 3rd-row seats currently is.

I don't accept "not allowed", well not in a non-commercial sense - but I won't anyway.

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Posted

Non-starter as far as we're concerned - it would mean running the generator from 6pm to 10pm which I regard as anti-social.

I find 6 - 10 pm very social...........down the pub :thumbsup: :thumbsup: :thumbsup:

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Posted

Sounds like a sound plan, the thought of relying on a solar panel in Scotland seems optomistic :laugh:

All the people saying no no to a battery in the boot obviously have never heard of BMW or Mini's you just have to use specially thick cable!!, good move to have a special, ventillated battery box in the seat well, even better if it is removable say for home charging/storage in the off season, dont forget a switch or better still some sort of relay to isolate the car battery, nothing like two flat batteries to start the morning especially before youve had your coffee :wine:

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Posted

Our spare battery lives in a prehistoric TP2 box. It gets charged from the car power point in the boot when we go out and has a mains charger in it if we need to blag some volts from e.g. the site owner. We don't stay off EHU for long enough to justify a solar installation, much as I would love to stick a flexible panel on the roof and wire in a controller.

Roger, if you need to look like you have a boy's toy solar panel, try some black lino on the van roof. No wiring necessary! :thumbsup:

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Posted

Our spare battery lives in a prehistoric TP2 box. It gets charged from the car power point in the boot when we go out and has a mains charger in it if we need to blag some volts from e.g. the site owner. We don't stay off EHU for long enough to justify a solar installation, much as I would love to stick a flexible panel on the roof and wire in a controller.

Roger, if you need to look like you have a boy's toy solar panel, try some black lino on the van roof. No wiring necessary! :thumbsup:

Solar panels have come down significantly in price, see this thread -

http://www.touringandtenting.com/forums/index.php?/topic/41737-really-pleased/page__p__491622__fromsearch__1#entry491622

..........ebt

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Posted

It is easier to steal a £300 solar panel than it is to steal a battery locked in car boot. Doubt if insurance would pay out on a stolen solar panel that was not secured with anti theft devices.

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Posted

They'd have trouble stealing mine. Screwed and also fixed with Sikaflex.

No different to a status aerial which could be nicked. My guess is that insurance would cover that too...ebt

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Posted

ebt - good point

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Posted

It will the way I plan to wire it - I'll match the car cabling from alternator to starter battery with the run down to the boot battery - in the style of chavs with stupidly high-powered stereos but used for a good purpose!

Just get an S plug, a piece of 2 core cable of sufficient capacity and a pair of quick relaes battery terminals. Connect the quick releases to the cable, wire the s plug so that the positive is connected to pin 6 and the earth is connected to pin 7 ( these are the fridge terminals but they are the only ones that are live only when the engine is running ) and plug the plug into the s socket and pass the cable into the boot then connect to the battery and whenever you are driving along the battery will charge, you do not need fancy wiring in the car to achieve this just as long as you only wish to charge one battery at a time.

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Posted

This is an interesting read and not surprisingly over-complication is playing a part !

Recipe is simple, so keep it simple;

1. Decent battery (eg Elecsol 110 or similar)

2. Decent Charger (Ring 16AMP digital)

Charge battery properly, not just over night. Don't take 2nd battery in boot, OR rewire caravan or set up a bizarre system.

The set up you see above powers in full my whole caravan. In addition I have upgraded to LED lighting through the whole caravan. But I no longer have a solar panel, generator or 2nd battery and I used to have all three.

Trust me on this, you don't need it. I run a TV, charge phone, charge kids PSP/DS games etc and light the whole caravan...and I did this for 10 days at the national rally and follow on...

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Posted

:wine:

Sound advice Nick - but I'll lay odds that you switch stuff off as soon as you've finished using it ! I somehow suspect that the 'doubters' wouldn't do that ... :laugh:

:wine::wine::wine:

:England:

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Posted

This is an interesting read and not surprisingly over-complication is playing a part !

Recipe is simple, so keep it simple;

1. Decent battery (eg Elecsol 110 or similar)

2. Decent Charger (Ring 16AMP digital)

Charge battery properly, not just over night. Don't take 2nd battery in boot, OR rewire caravan or set up a bizarre system.

The set up you see above powers in full my whole caravan. In addition I have upgraded to LED lighting through the whole caravan. But I no longer have a solar panel, generator or 2nd battery and I used to have all three.

Trust me on this, you don't need it. I run a TV, charge phone, charge kids PSP/DS games etc and light the whole caravan...and I did this for 10 days at the national rally and follow on...

I don't understand the arithmetic - a 110Ah battery lasting 10 days would draw 11Ah/day if was discharged completely flat - that's only 132Wh/day - so presumably it's a small number of hours/day?

I do like simplification - but we do go away for 30-40 days at a time !!

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Posted

I dont do all the fancy maths, it works or it doesnt in my book.

Ive done the generator thing to death. Until i realised, quite obviously, the most effective generator i could buy was the one pulling the caravan. Why would i be stupid enough to put a second one in the boot and carry fuel, leads etc etc. Just plain dumb if its for battery charging only.

So utilizing what is always with you, e.g the car.

Ive now got a solar panel fitted on my van, but ONLY because i no longer can keep the van at home, its in storage, and its a bit of a faff removing battery. So solar panel is nailed to roof.

But taking a step back to the second battery option, this then means your actually carrying 3 batteries, one which has its own effective charging system already in place, but you want to replicate this system on battery number 2. So why not do away with the 3rd battery and use the second, e.g your cars.

My preferred method which i swore by and used for years was an inverter. Big enough to power most things i needed. And i could run the inverter from my car battery to run my caravan charger or my secondary charger to charge caravan battery. A decent inverter will have a cut out so as not to run down the car battery to a critical level.

Also a lead made up (or bought) to run from the 12s plug to use the car battery as secondary power when needed works well.

If ive needed to really boost my caravan battery ive left my car on tickover for a few hours whilst inverter/smart charger charges the battery in van. Its also far more cost effective than a generator (dumb idea IMHO).

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Posted

Incidently, as i said i dont do maths, but Nicks method above works well. He runs a twin axle, and has 2 energy efficient kids......so to be honest if he was struggling fair enough, but he doesnt. Ive known him for a fair few years to know if it doesnt work right on go number one, its changed, altered or set fire to and onto plan b.

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