hello!
im in the designing process of making a teardrop caravan for the back of the locost, and in need to fit into the 'eco' theme of the course, im going to fit solar panels to the top of it. as i will be using power at night when there is no light i plan to store it in a motorbike battery (or if fund allow an aeroplane battery). this is mainly because it needs to be as light as possible, as im going bec. ive been trawling through ebay for flexible solar panels, but i cannot work out what kind of wattage i need. as i put it needs to charge the battery, run a small air conditioning unit/heating unit, run a 15" lcd tv, and charge my laptop, maybe whilst im using it. i shouldnt be using both the tv and laptop at the same time, so that should cut down the power used at one time. i would only need the tv for at most a few hours each night, and probably a similar time for the laptop (lets hope i dont get a rainy day when i go away).

id like anyone who knows their electricicals (or solar panels) to tell me how i can work out how to work out if it will work !?! i could also do with some help on what inverters i need to change the power from 12v motorcycle.

so what do you think- would it work and could i do it without spending crazy amounts of money? any input would be greatly appreciated!!

pic if anyones interested: (hopefully will work)
Rescued attachment cravan prnt screen.jpg

try again:
Rescued attachment trailer prnt scrn.jpg

Whilst I don't know a great deal about solar panels, If you planning on going some distance with it, could you not charge the battery, or a small bank of batteries from the engine? Would it be poss to fit a bigger (car?) alternator and go this route? This should be enough to last for a day or two.

why dont you upgrade the battery in the tow car and use that and its got a built in charger

On campers you can have a spare battery and a relay that will only charge when your alternator reaches a certain voltage. (go to your local camping/caravan shop).
You may have to uprate your alternator though.
Solar panels would have to be very large to charge your battery, especially if you are going to drain it daily.
Click here for 175W panel cost!
Ever thought of wind turbine ?
You could even charge it on the move!
Combined with the alternator method it should be good.
Why do you need inverters?
Most of your kit can be run from 12v (with voltage converters) and again inverters can be expensive and introduce more power losses to your problem.

[Edited on 18/6/2006 by nitram38]

I wouldn't even consider ac invertors as they are usually very inefficient. If you use 12V equipment it will be much easier. You can convert 12V to higher or lower dc voltages by using dc/dc convertors if required.

As previously mentioned, make max use of your tow car's electrical charging system as it is already available to you.

You'll need a poo load of panels and a bigger battery to run your TV / Laptop off it for a reasonable time.

i wasnt going to use the car alternator as im using a bike battery in that, and i thought that it has to work pretty hard anyway, without the power being used elsewhere as well. i was looking at some 80w solar panels, but do you think thats definately not going to cut it? that battery relay alternator cut off thingy nitram said, where could i get one/how would i make one?
the problem i see with using the car alternator is that i may stay in one place for a few days, and i wouldnt be getting any power in that time. a turbines a good alternative but i didnt want to compromise the looks, and make it look a little like a hippy wagon(lol).
i didnt really want a bank of batteries as im trying to keep the whole caravan under 100kg's, and batteries would take up quite a portion of that, not including the space that they would take up......

thanks for the replies, if anyone has any more dont hesitate to put them on, i want to have a lot to consider!!

I think you'd be better off having a car alternator and a big car battery in the tow car. If/when you take the caravan you could have a removable boot box with an extra battery set up in it. This could then give you the extra batteries, but keep the weight down in the caravan. Or put a removable tray in the bottom of the caravan. This could be the same thing so you have a choice of where to put it. Whilst it may add a little weight, it'll be nice and low, so should aid stability a bit too.

For solar panel info and a calculator try HERE
Also as the others said, you could split charge the battery from the tow car using a self switching relay, that does not require connections to the alternator as it senses the higher voltage when the alternator is charging.
LINKY
The other thing I have used in the past is a battery cut out regulator which allows you to run the battery down to a preset voltage. It then cuts out and a switch resets it and allows you to start the vehicle. I've only used it on 24volt vehicle but I assume a 12volt version is available.

quote:

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Originally posted by peterriley2
i wasnt going to use the car alternator as im using a bike battery in that, and i thought that it has to work pretty hard anyway, without the power being used elsewhere as well. i was looking at some 80w solar panels, but do you think thats definately not going to cut it? that battery relay alternator cut off thingy nitram said, where could i get one/how would i make one?
the problem i see with using the car alternator is that i may stay in one place for a few days, and i wouldnt be getting any power in that time. a turbines a good alternative but i didnt want to compromise the looks, and make it look a little like a hippy wagon(lol).
i didnt really want a bank of batteries as im trying to keep the whole caravan under 100kg's, and batteries would take up quite a portion of that, not including the space that they would take up......

thanks for the replies, if anyone has any more dont hesitate to put them on, i want to have a lot to consider!!

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It might be worth looking at the lighter racing batteries - I was amazed at the small size of my Oddysey battery which is big enough to crank over a 7 litre V8!

solar panels are very inefficent, even the best ones only manage at best 20% efficency. so as people are saying u would need a lot of them to power ur laptop or tv etc.

Also u have to take into account that it may not be sunny! this is england after all. Solar panels may work, but u will deffo want another option that provides power, i would imagine its best to have serveral ways of powering ur caravan, maybe even setting it up so u can plug it in, like normal vans at camping sites. as well as solar panels and wind turbines.

As people have mentioned upgrading ur BEC's charging system is probally the easiest way of doing it.

ive just done the solar calculator, putting in-
19" tv for 2 hours
portable heater for 2 hours
stereofor 2 hours (thought it might be close to the laptop)
and what it advised me was this

im sure this cant be right can it?
anyway thaks for the links and stuff, ill fully investigate when i get the time, hopefully later tonight. where would i find oddysey batteries, and how much do they cost?
i didnt want to plug it in, as id like to take it off road to places where there are no plugs handy, so want it to be prettymuch self sustaining.
the other option is to have a generator, which could be home made with an alternator. this is not particularly eco, but may solve my problem. i could do this with a small engine, attaching an alternator. this isnt particularly light however, and i dont like the way that energy could be wasted if the generator is too big and over powered my appliances. this is also coupled by the cost of petrol.

ive just been looking at some oddysey batteries like this, and id just like to know how much better this would be than a normal bike battery, eg r1 or fireblade, how much lighter would it be, and would it store more or less charge? on its own fully charged, how long would this battery run a tv or laptop for, on average would you guess? its just that i dont have a clue- i dont know if it would be 5 minutes or 10 hours. cheers,

that can't be right, that solar charger would never be able to power ur electrical items for very long. an electric heater is the main drain, a laptop wouldn't take much to power it, not sure about the LCD tv tho.

to be honest i was expecting u to need to have pretty much the whole roof in solar panels to charge the battery powering ur caravan.

my housemate is an electrical engineer, or in the process of becoming one! so will ask him when i next see him for u if u like?

a generator would be a waste of time i would think, if u go down that route u may as well set the BEC up to be the generator.

not sure how long a fully charged battery would last, if its just the laptop, it would last for ages, and the tv would prob be ok too, especially if u got a 12 volt one, i am assuming u can get 12v lcd's? the heater will be the main power eater, if its an average one, say a 2kilowatt heater, it will exhaust a battery pretty quickly.

that would be great if you could ask your mate, and what do you mean when you say it will drain pretty quickly- around how much time? i wasnt going to use the car as the generator as i can guess that the petrol would be a great deal more than a small generator unit. as the heater will take the most power, ill look at different ways to go about it- i know there are diesel units, but dont really fancy carbon dioxide poisoning!

Would you really need a heater? If you're planning on going off into the wilderness, can't you just take a lighter and find some dead wood lying about? Or just buy a bigger sleeping bag? Another option could be to have solar water heaters in the roof and use hot water to heat it up. A bit like central heating. Or if you're feeling really brave, you could use the bike engine to provide hot water heating. Ie pull up some where, attach some houses to the back of the bec and transfer heat to the caravan. Kind of like using the caravan as a radiator. Might need a fair bit of water though.

The laptop is no great problem, the tv is a bigger current draw, but still not impossible - but heating??? No chance, just think about it even a tiddly 1kw heater (pretty useless given the losses from a caravan) at 12v would be drawing over 80 amps!!!! (W = Volts x Amps)
If you rethink & use portable throw away gaz cylinders - cheap & light then the rest of it could besolar powered without too much problem.

Trust me you won't need a heater in a caravan that size, just eat a couple of cans of beans and you'll soon warm it up . Air conditioning will be an unnecessary luxury as well just put a vent in the door, I thought you were aiming for an all up weight of 100kg? You'll need a V8 to get it moving with all the stuff you're thinking of taking along there. Get all the stuff you are thinking of taking, put it in a box and weigh it, bear in mind that you can tow 50% of the vehicles kerbside weight with an unbraked trailer. Unless you are fitting a 1500 Goldwing engine you are asking for too much from the engine, you will never set off if you stop on a hill. I don't know if you've driven or towed but you'll realise what you are asking is not feasible when you pull the clutch out of the engine, towing needs torque even for the lightweight you are aiming for.

i burnt my clutch out today, and all i asked of it was to drive onto a transporter last week (you have no idea how much i had to slip to clutch to make it move up such a steep slope!) and set off in third today, when my gearlever broke. Setting of with a total of about 700kgs (lets say 450 in the car, 100 in the trailer and 150 in the passangers) would wipe it out within weeks of town driving.

As far as i can tell from the techincal specification on that solar panel, it only provides 2w at 15volts, hence you need 1000 of them to power the 2kw fan heater. A computer is about 400w isnt it? Memory takes a hell of a lot of power to maintain. That too is asking a lot from a battery.

I would strongly recommend using the normal bike generator with a heavy duty car battery, and a small odyssey as a backup, or the other way round. And dont forget the jump leads! In fact yeah, the other way round. Car has an odyssey, and a removable heavyduty battery in the passanger footwell.

[Edited on 18/6/06 by JoelP]

quote:

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As far as i can tell from the techincal specification on that solar panel, it only provides 2w at 15volts

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I am afraid that solar is not the way to go. Check out yacht chandlers for small wind turbines they are a better bet. While travelling you need to set up some mechanical charging, if you are not keen to use the engine alternator and a split charge system how about rigging up a drive off the caravan hub to a car alternator? A good source of compact high power batteries are the carryable boost systems though these are not good for deep discharge.

Heating is an issue depending on where yo plan to go camping. Insulation is the first starting point 75mm of styrofoam on floors walls and ceilings is a good start as long as the exterior shell is very waterproof, good windows, not necesarily caravan ones are important. Cheapest heatsource is a gas cooker and camping gaz bottle stored outside! and as has been said a good sleeping bag is a good thing, though if you are taking a friend get a double bag

Caber

I am afraid that solar is not the way to go. Check out yacht chandlers for small wind turbines they are a better bet. While travelling you need to set up some mechanical charging, if you are not keen to use the engine alternator and a split charge system how about rigging up a drive off the caravan hub to a car alternator? A good source of compact high power batteries are the carryable boost systems though these are not good for deep discharge.

Heating is an issue depending on where yo plan to go camping. Insulation is the first starting point 75mm of styrofoam on floors walls and ceilings is a good start as long as the exterior shell is very waterproof, good windows, not necesarily caravan ones are important. Cheapest heatsource is a gas cooker and camping gaz bottle stored outside! and as has been said a good sleeping bag is a good thing, though if you are taking a friend get a double bag

Caber

okay, this has all been a great help to get me thinking seriously, ive know realised that with the laptop i can get a tv reciever, and not bother with a tv at all. the laptop gives out heat which i hadnt thought of, and im now thinking that it would be a good idea to use the excess heat from the hob, by somehow making a cover for pots that go on it, moving the heat into the main compartment with a small pc fan. this would mean that the wasted heat from cooking is used, and also i could use it as a simple heater when weather gets cold. so, back to my question, as the laptop is really going to be the only electrical item (apart from the fan and anything else i think of), how long would i be able to use the laptop for, from a full chatge of a motorcycle battery,-standard or odyssey? i may still use a small solar panel, just to trickle charge the battery whilst at site. cheers,

As has been said, solar panels aren't efficient, the manufacturing process is extremely nonfriendly to the environment, so you'd be better off with traditional methods.

If camp site has plugin power, that's no 1 for pro environment.

Then batteries charged at home. Anything using your vehicle to produce power isn't "free", it just uses more fuel etc.

ATB

Simon

Of course the six foot satellite dish you are going to need to get the internet access for the Locost forums MIGHT slow you down a bit on windy days

if ur laptop is the only thing u plan to run it should last quite awhile depending what u do with it, sorry thats not really helpful but it depends what u do with the laptop and what make and model the laptop is, my laptop is a toshiba one thats really small with no disk drive etc which would be good as it will mean it will have a lower drain, however the bigger laptops with dvd drives and big screens will drain the battery quicker.

what u really need is to work out how much power the laptop will take from the battery then u can work it out. though i would of thought if u were using it for a few hours a day over an weekend, maybe a long weekend it would last ok, especially with an solar panel to top up the battery.

my housemate has gone home for awhile, had just missed him! so will ask when he comes back.

as mentioned above, good insulation will be the key in keeping ur self warm. if u have a good sleeping bag, with heat scavenged from the heater and maybe the laptop? u can keep warm. u could also take heating sachet things that could be used to keep u warm if all else fails. though with a good sleeping bag u can sleep putside in snow, so within a caravan u should be nice and toasty!


[Edited on 19/6/06 by trogdor]

ok so i need to work out out how much power my laptop uses on average use. cheers

well looking at my laptop it uses 75W and 4.3A of power, therefore with an 50Ah optima battery it will last approx 10 hours. though this is very simplified so hopefully someone can give u a better idea!

If you want to run AC/Heating, forget batteries and solar, and get a small petrol or diesel generator! It'll be the least trouble in the long run.

ok, i looked on the laptop, on the transformer it says output is 3.16A, doesnt say anything about watts, where would i find that out?

ok forget the last post, just found this:

19 VDC, 3.16A, 60 W output
Automatically adjusts for 100 to 240 VAC, 50 to 60 Hz power sources

thats the power specs for my lappy, how do i do the calculations for battery time etc?

oooh urs uses less power than mine, it depends on what battery u will use on the caravan. what battery are u planning to use? ie how much are u going to spend on the battery? u will want to the best u can afford!

i was thinking of one of the top 3 here, hopefully thryll cut the mustard cos i dont want to spend any more really. how much better will they be compared to 'standard' mororbike batteries? im also no sure as motorbike batteries arent supposed to be used till flat- theyre permanently being charged on a bike.

just had a quick look at the batteries and this one is prob the best, is hard to be sure though as they don't give much info!

cli cky

it can be deep cycled 500 times so will be ok if u completely discharge it. not sure how long ur laptop will work as they don't provide any Ahr info but this has the highest cranking amps so prob has the highest capcity too. so thats the one i would choose, it would be great if u could trial them out and see which one lasts the longest as its hard to tell!

[Edited on 19/6/06 by trogdor]

[Edited on 19/6/06 by trogdor]

forget heating but sleep with the lady in a warm bag... will be allot faster then a heating thing and solar panels.

i would also use the laptop.
i even can garantee you that there is even a voltage on the adapter wich would only maintain the battery at the same level but would't charge the batteries!!

sow test the application.

if i was you i would buy 2 odessies...

and daily swap the one in the car with the one you used.

in that way you have the best choice of haveing it full.

make a pic of the BEC towing hte caravan should be funny to see really..

Tks

have found this website on the web, which while is not completely related has some useful information.

http://www.powerstream.com/BPD.htm

reading through it i found this paragraph which explains how many amp hours u will need in ur battery depending on current drain and time wanted to use it.

How many amp-hours do I need?

Cell capacity is rated in amp-hours or milliamp hours. The symbol for capacity is C. This is amps times hours. Divide by hours and you get amps, divide by amps and you get hours. For example a 5 amp hour battery is the same as a 5000 milliamp-hour battery. If you want to discharge in 10 hours, you can get a current of 5/10 = 0.5 amps. If you need 100 milliamps current, then you can run for 5000/100 = 50 hours.

Often a discharge or charge rate is given proportional to C. So a discharge rate of C/5 means C/(5 hours), or the constant current to fully discharge the battery in 5 hours.

"The calculation of run time versus current is a rough estimate, but is accurate under the right conditions. The faster you discharge, the lower the capacity of a battery. This trade-off depends on the battery chemistry and construction. Usually the capacity of a battery is quoted at a C/20 discharge rate. So an 12 amp hour battery sealed lead acid battery will actually put out a steady 0.6 amps for 20 hours. However, if you discharge the same battery at 12 amps, you would expect to run an hour, but you will only last for 22 minutes. Also, if you wan to run at 10 milliamp you will get less than the expected 1200 days, since self-discharge of the battery will limit your run time.

Different battery chemistries differ in this respect. Lead acid batteries are probably the worst at the rapid discharge end of the scale. NiCads and NiMH are much better."

therefore with ur laptop using 3.12 amps of current and u wanting serveral hours a night, if u are somewhere remote then lets say u want 20 hours of usage, this is quite alot i admit but will give u an Ahr figure of 62.4. i think one of the batteries u were considering had a 70Ahr capacity, the other two didn't supply the capcity. So with an 70 Ahr battery u should be able to run ur laptop for 20 hours, this is probally abit optimistic but u will prob get 15!

this should be enough for ur needs, especially with a solar panel to top up ur battery. however the fun part will be trying to connect the battery to the laptop, as ur normal adapter will be no good, u will need a 12volt version using convertors etc.

i was planning on getting an oddysey battery for the bec, so that is a very good idea. if i used the relay thing from the alternator i wouldnt have to swap them over at all (i think?).
on the pic thing, i started designing a locost a while ago, ill see how far i got and give ita ago at putting them together!
ps, thangs for all the replies so far, its been a great help!

trogdor- thankyou sooo much for the post, that is great info, 15 hours im sure will be ample, especially if i swap it with the car battery. im not a very antisocial guy, so i dont want to be cooped up in the caravan all day long, i may not even use it for 2hours a night, which means it should be pretty much self sustaining for around 10 days. i was designing the caravan for short weekend getaways, but realistically i love camping so this would be extended to at least week stays. with that kind of battery time i may think about fitting a few speakers and pumping out some tunes!....maybe!

ok i only got the chassis done but you get an idea
ps. im not sure if i made it to scale- caravan looks too much higher than the car- alloys are the only part that i know are the right size!
Rescued attachment caravan and car chassis.jpg

and...
Rescued attachment caravan and car chassis2.jpg

that does look pretty cool, what are u planning to make the caravan out off? fibreglass with a spaceframe chassis? have u decided what the interior is going to be like?

Whilst quite cool, that'll look damn strange at a kit show!

It'd flow a liitle better if the bec had a sizable roll bar. Help lift the topline a little before the caravan, if you get what I mean.

it would be great to take to a kit car show, the looks on peeps faces! but it does look good, it reminds me of the saab caravan that was designed for the 2 stroke 93's and 96's. that was a light weight caravan too. it was called the saabo and looks like this, is not quite as nice as ur design tho!

[Edited on 20/6/06 by trogdor]
Rescued attachment Saabo 4.jpg

That will be a horror to tow with a light car with the wheels that far back, you'll need some 600lb springs to keep it level. you need to do some research into noseweights and balance points to work out where the axle needs to go, usually near the centre of your load area.

its gonna be fully carbon fibre (hopefully) with a very light space frame chassis, from 25x25 box, with 5mm angle going through the middle. ive designed the suspension myself, and i was hoping that the load point would be where i wanted it, as my cargo (clothing etc) would rest above the axle (wherever that be), and balance out the weights. ive designed the interior, ill post a side pic where you can see later on, although its very basic!!

that sounds really trick! a carbon fibre caravan sounds really good, would be great to see it when u finish it. as an aside what software are u using to create those images? have a ambious project of my own and want to get some experience of using a 3D modeller.

if u had to pay for it is there any open source software thats any good?

i use sketchUp, its made to design houses and large structures, but i find if what your doing isnt getting too technical and intricate its fine. its much more user friendly than autocad and such, and has a very cool function that you can put the shadows onto things, depending on the time of year, and time of day you want (although very pointless for me). i wouldnt really want to try designing a whole locost, ill put the bodywork on but thats as far as ill get i think- no engine or running gear as im sure ill get very frustrated with it! i seem to remember you can download a freeware version, but mines from limewire (dont tell!). its a great program to get you into cad, at college we use prodesktop, and what would take me 2 minutes in sketchup would take around 2 hours in prodesktop(literally). its not hard to get used to, just make sure that you change the units (in preferances i think?) to cm, as the standing is inches which really really confused me when i started!!!

howdy again, have aquired sketch up, and have been playing about with it, and ur right its much easier to use than autocad or any other 3d package i have messed around with.

do u think i could model a spaceframe chassis on here ok? not sure if thats to technical for the program! otherwise i will have to learn how to use another 3d program that can.

well what ive done on the screenshots above was ok, took awile but woudnt tak so long next time. what you have to do is no pannick when it turns into a flat box, if you click on the box face where you want nothing then press delete it will leave you with jkust the frame around... im sure itll make sense once you start using it!

by the way what are you modelling? space frame saab???

have you thought of taking a tent and a decent sleeping bag? it would make things way easier!!!!!

The tiniest 'commercial' ready made caravan is at least 700kg+ you will be going some to make one at 100kg..... the wheels alone will be 30% or more of the weight,


nice idea for a project - just seems a tad ott to me

good luck

atb

steve