window demister 12v -> 6v

[tortron]

He guys, a while ago i was browsing through this site and came across a picture of a minor with a stick on type demister on the inside drivers screen (not like the heated screen variety, it was sort of a cylinder with suction cups)

anyway i said to my self, i said myself you need to find one of these gadgets

Anyway i have found one - the problem being that it is 6v rather than 12.

my question is - is there a way i can modify it, or use some sort of stepdown to run it?

[teenoes]

as far as i know you just have to measure the resistance of that thing and put an three times as big resistor in line with it
then the total possible power uptake of the demister is the same as when run on 6v
this only applies to items that are not incorporating any kind of motor as these as far as i know will rev faster with increasing voltage and can get quite hot
in this case there is a device on the market called dc/dc-converter which converts your 12v to 6v
costs for the resistor variant are under half a quid and for the converter are about 10 to 15 pound for appliances with an current uptake of around 1 amp
there are heavier converters on the markets but i have no idea of prices but these can easily be found via google
i am actually interested in a picture of what you have got there

[bmcecosse]

Well - it would need to be an 'equal' resistance (3 times reistance would give almost nothing in the demister!) - and that resistance would then also give off the same heat as the 'demister'. Best would be 2 of these 6volt demisters -wired in series. But honestly - these thing are useless anyway - just make sure your heater vent pipes are connected up properly - and open the quarter lights slightly in extremis.

[tortron]

thanks for the reply's, i think i have found a suitable means of dropping the voltage

plugs into a cigar lighter (which i don't have, however i am going to install a small aux fuse box - which i will connect to)


this is the unit (it hasn't actually arrived yet)

Airflow Defroster - made in England

i cant remember what car i saw a similar defroster on here - i think it was a traveler[/img]

[tortron]

Well - it would need to be an 'equal' resistance (3 times reistance would give almost nothing in the demister!) - and that resistance would then also give off the same heat as the 'demister'. Best would be 2 of these 6volt demisters -wired in series. But honestly - these thing are useless anyway - just make sure your heater vent pipes are connected up properly - and open the quarter lights slightly in extremis.

For my sidevalve - i have recently installed a "heater" it is basicly a fan unit that ducts air from behind the radiator.
in anycase im a glutton for period accessories

[paulhumphries]

thanks for the reply's, i think i have found a suitable means of dropping the voltage

plugs into a cigar lighter (which i don't have, however i am going to install a small aux fuse box - which i will connect to)

I don't think that'll work.
Max power, according to the label, is 800Ma. That means max output is going to be no more than 10 watts ! Imagine two 5 watt sidelight bulbs to get an idea of what sort of output the dropper will handle.
To be honest I had a 12v version from new and total waste of time for demisting anything other than a couple of inches above the heater.
Regard as a period accessory but not something that is actually useful and therefore don't worry about it not working. You could spend ages / money getting a dropepr that will carry sufficient amperage only to find, like I did, that not worth the effort.

Paul Humphries

[bmcecosse]

Aye -'period accesory' - but it was useless in it's day, and still will be !

[tortron]

and a sidevalve engine in a minor is the same

[mike.perry]

A side valve engine may be a little slower than an A Series but it is a much smoother and more pleasant engine to drive. I have both engines so I am in a position to compare. Are you?

[bigginger]

I think he(?) was being a little light hearted...

[bmcecosse]

The side valve engines in my old Morris 8 Series E cars used to sing along very nicely thank you!

[tortron]

yes, was being light hearted. seeing as though the mm's were a new car, but with predated performance
my sidevalve will purr along all day (albeit newer cars tend to purr a bit faster)
really needs a 3.5th gear but

[teenoes]

Well - it would need to be an 'equal' resistance

yes that is right for the current to be the same as when running it on 6v
and i wanted to post it that way as well
but you would then still have doubled the heat from the demister as it would now be run on 12v

(3 times reistance would give almost nothing in the demister!)

but enough to have it running with the same output of heat

- and that resistance would then also give off the same heat as the 'demister'.

that is right
and a three times as big resistor would only produce one third of the heat
of the demister

Best would be 2 of these 6volt demisters -wired in series.

as above heat output of both would be double

But honestly - these thing are useless anyway - just make sure your heater vent pipes are connected up properly - and open the quarter lights slightly in extremis.

agreed

[bmcecosse]

Sorry -don't agree. If you put a resistor 3 times the value of the element 'in line' with it - and connect to 12 volts, the overall current flow will be pathetic - it will NOT be running on 12 volts ! It would need to be as I said earlier -to split the 12 volts into two equal loads, each with 6 volts across.