What I would like to do is warm a greenhouse or just some seed trays. Not to tropical temperatures, obviously, but I'd be interested to see what can be done.
First thoughts are... one of these
Alternatively what about a 12v heat mat powered by the same means?
Si
The smaller the area (volume) you're heating - the higher the temperature rise you'll be able to achieve.
If you're looking at raising seedlings in seed trays then you could construct a simple sand bed with a heating cable running through it - and put the car battery across the cable.
Trouble is - standard car batteries don't like being fully discharged
- 'leisure' batteries (caravan batteries) work better in this mode.
If you're stuck with a car battery then it might be an idea to design some sort of circuit that disconnects the battery when its voltage drops - to avoid completely flattening it...
In the 'It's hard being green' series they built a heat-store into a greenhouse, by blowing warm air from the top of the greenhouse through a rock store in the floor of the greenhouse - this heat was then released overnight - keeping the greenhouse warmer overall...
Another way round would be to build a mini-solar-water system - and use that to heat a decent volume of water stored in the greenhouse
- seed-trays could sit on top of the water tank, maybe....
In its simplest form, black-painted oil drums, placed in the greenhouse & filled with water will absorb heat in the daytime and release it at night....
All depends on what you're trying to achieve......
You'll get losses as you convert wind energy to electrical energy - and then convert that again to heat... will be less efficient than a simple water-based system
Adrian
Is it? I've never understood why people want it.
Si
'Ello Ade,
Yup.
It's mainly for chilli seeds, some of which need the soil to be at around 90 degrees F before they'll germinate.
As it's very often windy here I was thinking/hoping that a fan-powered car alternator, running through a voltage regulator, might be able to keep the battery happy and charged as I'd have thought a heat mat or two would be less demanding than a car's electrical equipment.
I saw that - I think it's a bit late to build one now as the greenhouse is on decking and I'm buggered if I'm taking that up or cutting holes in it :o)
I did see a couple of radiators offered on Freecycle and considered a water system but that wouldn't work when I need it most - now. Chillies need as long a growing season as possible and it's starting germination that's the problem so electrical or paraffin is probably the way to go, but I wondered if I could make use of wind power as there's quite a lot of that.
But it would be easier to build and install... probably.
I've just found a 240v heatmat under the stairs that we bought yonks ago and it's only 11-13w so if it heats the compost sufficiently I'm thinking a car battery should cope with a couple of 12v jobbies easily. Can't easily get mains to the greenhouse though.
Si
Of course, that means sourcing a suitable fan. Fan? Impeller? Turbine! That's the fella! I wants a turbine! :o)
Si
HFM!?
I'll start them indoors on the 240v heat mat, eh?
Si
Cheeky !
Gosh - that's hot. I've got one of those electrically-heated propogators - the 'just smaller than 2 seed-trays' variety
Maybe. Many, many years ago (when I was in the Scouts!) - I set up a multiple-tent-lighting system with low-wattage bulbs and a car battery
- which lasted a surprisingly short time before it went completely flat. As I understand it - a car battery is designed to give a couple of really high-currrent blasts, and then be recharged, rather than suffer from a slow discharge.....(sounds nasty!)
Ah - I see your point !
Yes _ I get that effect with chillies Seriously though - how about starting them off indoors (where you do have mains) and then taking them out the the greenhouse once they're big enough ?
..... probably......
Hmm If it's 11w heating at 240V then that'll be .04A Same heating mat at 12v will give 9/10 of b-all - as in .03W
To get 11W out of 12v you're going to need an amp or so - only way to see how long it works for is to suck it & see
FWIW - I managed to flatten the little battery on my '64 moggie by leaving the interior light on for 5 hours or so while working on the front doors (doh!) - and I'd guess that the current drawn would be similar...
I guess the other option is a couple of batteries - one on mains charge inside the house and the other in use - but I sense a deep desire here to build a windmill..... am I right ??
Have fun ! Adrian
Mungo "Two Sheds" Toadfoot explained on 23/03/2008 :
The discharge would be much larger than the charge for most of the time. A 12v car battery could only keep the heater running for perhaps
2 hours and the battery would soon be damaged by such use.
Probably not by very much, the heat losses through the fabric would be too great.
Funny, aren't they? I'm using Poundland 6-for-a-pound ice cube trays and a squillion-for-a-pound polystyrene cups this year!
Heh! Yes, I just read that and was reminded that they're made to give lots of amps for a short period of time. I also read that forklift truck batteries are the things to have. I'll just nip out and get some...
Yes, that's what I'll have to do now that I'm thinking realistically! I might even build a frame to keep the warm in.
Dammit! I wanted a windmill! Ah well, as I haven't got an alternator, a battery, a fan, a pole, or a metal-working shop I suppose I'll just have to start my chillies indoors.
Buggrit.
'64 Moggie, eh? Same age as me. Is it as knackered?
Si
Thanks, Harry. I've pretty much given up on the idea of free 'letric now. It's a nice idea though, eh?
Si
What - cannabis or the halide bulb?
On the hot chillies, I suggest you stick 'em in the airing cupboard until they've poked their heads up. They won't care it's dark until then.
Andy
We recently had new central heating throughout and I was slightly miffed to find that the temp in the airing cupboard doesn't go above 65-70 now!
Bloody decent insulation!
Si
Mungo "Two Sheds" Toadfoot wrote: SNIP
Could you get ELV from the house to the greenhouse, or charge batteries in a wheelbarrow just ouside the house?
You saying that - I recently ran some 1mm t&e outside to where the bike lives so I could use a Lidl Optimate-style battery charger (the 1mm is carrying the 12v). I could get another one and do that again, I imagine. Hmmm...
Si
Probably just as effective ! Mum & Dad always used 'recycled' containers for their tomato seedlings
- all kind of yoghourt pots, cut-dwon fairy liquid bottles & whatnot...
You'll need the forklift truck to lift 'em with.
That'd work - expanded poly or somesuch
Ah - yes - you are missing one or two of the vital ingredients.
Millennium hand & shrimp...
I've got no idea or your condition, sirrah ! No - she's a good one. Odd bit of rust showing up on the bodywork - but mechanically pretty good. She's a Traveller - and does sterling service hauling my stained / fused glass around the local open-air markets. Not a weekend goes by without some person 'of a certain age' going all dewey-eyed and telling me that their Dad / formmaster / uncle had 'one of those', or that they had one and drove it across America / India / the continent, or that they learned to drive in one / lost their virginity on one / were conceived in one..... - what fun !
Adrian
Soil heating cable. Doesn't cost too much, running costs are much better than anything else.
Heating the airspace itself is to stop frost killing existing green growth. For seedlings, just warm the soil.
Poor old Terry. How fair's that?
You are Jack Hargreaves and I claim my five free phallic farming implements.
Heh! I never owned one, or knew anyone who did apart from my father-in-law but he crashed and killed it before I came along. Good for transporting stained glass, I hear. Moggies, not father-in-laws. I imagine it's handy being able to stand in the engine bay beside the engine to work on it too.
Si
Ta, but mains = pita.
Si
The voltage drop might kill that idea.
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