electric heater

Been thinking about some sort of (better?) heater for my 90 and came across this:

How will a 240v heater element work off of 12 volts?

Any thoughts?

Richard

it do not use 240v the wire has to be made to length to work on 12v

How do work out what length?

Richard

Work out the power you can allow yourself to use in the heater. Find the resistance per unit length of your heater wire. (RPUL)

Power = V^2/R >>R=V^2/Power

Length = R/RPUL.

Wire must be insulated !

Steve

>>

Well if the element is rated at 240v and you want to run at the same amount of 'glow' (wire temperature) on 12v you need 12/240 of the length ie one twentieth. However you will also only have 1/20th of the power, so unwind the element, cut it into 20 pieces, and parallel connect as many as you want to give you the power you want.

Looking at our toaster - it is 1400 watts which would draw 117 amps at

12v - far far too much for that design which is fused at 30 amps. Lets assume a fair consumption would be 24 amps = 288 watts. Each 1/20th piece of my toaster wire would give 1400/20 watts ie 70 watts, so for 288 I would need 288/70 = 4.1 lengths so use four lengths and expect 4 x 70 = 280 watts.

Don't forget to re-work the figures if the toaster that you pull apart is not 1400 watts. Also a used toaster will have very brittle nichrome element wire whereas a new one will be soft in comparison.

AWEM

and a new toaster can be bought for as little as £5 to £7 uk

tesco value toaster 700w. £4.44 Might be worth a go

Richard

"> Work out the power you can allow yourself to use in the heater.

I don't think so!!!!....... It won't work very well as a heating element if it is insulated, and will produce lots of toxic fumes as it burns off.

Regards Jeff

Google for "12v hair drier" and you'll find lots of them for peanuts, only up to about 180W but you could build in a couple without overloading your alternator. A lot easier and safer than trying to bodge it from a toaster and PC power supply!. Greg

We use insulated Nichrome wire in heaters I designed at work, for expanding a precision mechanical stop- its designed for the job, and its rated to 200C.

It can be wound into much more intimate contact than non-insulated wire, so it works much better.

Steve

I don't think it would be much use in this application, you want the wire in the air flow and as hot as possible, so 200C would be well short of producing any effective o/p. Somewhere just short of red heat with the fan running I guess would be optimum; just like a normal mains fan heater. Any insulation would add thermal lag to the system and make the core temperature of the wire higher without any benefit.

Regards Jeff

Yep.

er no.

R = V^2/P = 230 * 230 / 1400 = 38 ohms.

at 12v

I = V/R = 12/38 = 0.31A

The stated conditions of same wire temp mean that the resistance is constant.

Not sure and I have a bathroom to tile rather than do the maths...

snipped-for-privacy@howhill.com

Dave, you have totally missed the point that the entire element has been cut into 20 pieces which are then connected in parallel to draw

117 amps !!!!!!!!! Obviously if left intact it would draw the lower current you indicate and be useless in the application.

AWEM

only be used with the engine running. The wires will get pretty hot and may be a fire risk if something gets in there like leaves or paper. Otherwise it looks like a good cheap heater. TonyB

Yep, the little electric car heaters are rated at about 140 watts so two of those wired to the battery would give 280 w at around

25 amps, and the fan is built in. TonyB

On or around 12 Dec 2006 04:30:28 -0800, "Greg" enlightened us thusly:

good call. lot cheaper than those heaters we had in "demisting...", which in any case were out of stock when I tried to order 'em.

Mind you... check out this page and tell me what you think is the difference between the 2 hair dryers on offer, other than the price.

The other easy thing is to make a little manifold to install in the water heater inlet hose, this manifold needs about 4 bosses on it to screw in Diesel engine heater glow plugs.

At least one modern Diesel car has such a device as standard, it helps 'kick-start' the heater on cold mornings.

Julian.

Sorry, should read heater matrix inlet hose, I've been up since 04.30!

Or you could buy a block heater, routinely used in the generating set industey, they are mains heaters that fit inline with a suitable coolant pipe and maintain the whole block at a decent temperature by convection so the engine can go on load within seconds of being started. A suitable mains inlet hidden under the bonnet and a caravan hook up should do it, not sure about the safety aspects with a vehicle but for stationary engines it's very common. Greg