12v heater

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atelford

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I have a 17foot boat currently in a marina for the winter. To attempt to get some use out of it to justify the cost I intend to spend some weekends staying over. The boat has a 75 amp/h leisure battery. Can anyone recommend a 12v heater that would inject a bit of heat into the cabin but not take all the power out of the battery. The outboard charges the battery and I also have a mains battery which is kept at home 10 mins drive from the marina so getting power into the battery will not be an issue. All the same I would like to have something that wouldnt drain the lot in 1 hour. Any recommendations ?
 
Not from 12v - there just isn't enough capacity in a battery - the only way to get heat will be from gas or diesel heaters. (or mains electricity)
 
As said there is not enough capacity in the battery. To put some numbers on it though.

You should not take your battery below 50% charged, and even that would be pushing a leisure battery if you did it more than just a few times. For the sake of the argument suppose you have 40Ah available at 12 volts that is equivalent to 480 watt hours, a bit less than half a "unit". If you could find such a thing you could run a 12volt , 0.5 kilowatt heater for a bit less less than an hour!

You can get 200watt 12 volt fan heaters SEE HERE, OR HERE

You could run run of those for a bit less than 2½ hours. Might be worth a try!

Recharging with the outboard probably 5amp max will take 8 hours minimum in theory, but longer in practice as you probably won't maintain the 5 amps continuously.
 
[ QUOTE ]
if I got a 75 Watt Heater

[/ QUOTE ] yes but is 75 watts going to be enough power to make any significant difference?

I suggest you spend a cold evening in your garden shed with a 75 watt light bulb and see if you feel warm enough

2 or 3 other people will help enormously. Hopefully a heating engineer will be allow shortly to quantify that.
 
Both you and Vic are wrong. The quoted capacity of a battery is usually stated at the 20-hour rate - so, for example, your 75Ah battery could theoretically supply 3.75A for 20 hours. If the battery is discharged at a faster rate, its practical capacity is severely reduced. This is an effect discovered by a man called Peukert many years ago (Google for more info).

Vic's example of a 500watt heater running for about an hour is roughly 100% optimistic - it would actually only run for about 30 minutes before the battery was 50% discharged. Similarly, the 200watt heater would really only run for about 1.5 hours. And your 75watt heater would discharge the battery to 50% in about 5 hours.
 
Agreed. I was trying to keep things simple. Too simple perhaps. I thought I was putting a pessimistic enough slant on the idea as it was.
 
OK. Prob wont work then. The cabin in a Leisure 17 however is about the came size as the inside of a car. With blankets etc I was hoping to not need alot of extra heat piped in. I dont want to use a gas burner or anything like that as the cabin will quickly fill with monoxide. Any other ideas ?
 
When winter sailing charter boats in the UK, we used to bring a 2kw fan heater to plug into the shore power.

We only needed warming when we got to destinations (cuppa soups & T doing the rest).

Means you're forced to stay in marinas but after a cold day on teh water you won't want to miss out on a warm shower, and at least you're getting the most for your marina fee.
 
If you get a couple of paraffin lamps, and keep those on the winter they will not only give you a nice warm glow in the evening but will provide a surprising amount of heat. The downside is that they pump out a lot of water as well, so you will need to provide ventilation
 
[ QUOTE ]
In a marina but not paying for shore power /forums/images/graemlins/frown.gif.

[/ QUOTE ]

I would suggest that fr the £3 a day, it would make snese to pay for the day(s) your there, like a visitor.

Personally we bit the bullet for eberspacher and haven't looked back.

you're goign to kill service batteries with any heater that generates any useable heat and need to run your engine for long periods to get the charge back.

Just a pragmatic thought - i hate spending more money than i need to.
 
[ QUOTE ]
Why not consider a girlfriend ?-could keep you warm & happy but perhaps not cheaply,
Jim

[/ QUOTE ]

I believe that 1 live body is approx 100W 'at rest'.

That puts a 75W heater into perspective.
 
Put the kettle on & have a cup of hot chocolate. Cooking soon warms up a small cabin. I have heard that an old pottery plant pot upside down over a gas hob will radiate a decent amount of heat. Cheap & simple, what else do you need?

Don't forget you NEED ventilation when burning a propane/butane flame as a LOT of water is produced and there is also a risk of oxygen depletion or even CO poisoning if the blame is not burning properly. I've never had a problem, but I wouldn't leave on once I started to feel at all sleepy! Great for getting undressed & into bed, but then turn it off!!!
 
Just before you waste money on one of those dashboard heater things from the car accessory shop, don't!

I bought one when my Citroën cabin heater stopped working.. what an absolute waste of time that was! The heater not the car.
 
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