electric cabin interior heater

[ade61]

does anyone have any experience with the 600 Watt electric heaters sold by DT and others : anyone know if they could be the sole source of heat in a small coupe,.....or, maybe with the addition of some mains-voltage pre-start warm-up

[Penelope Stopit]

Are you able to post a link to one?

Ohms Law - Watts = Volts x Amps

600 = 12 x 50

50 Amps is a big current draw and there are bigger heaters on the market
The thing is I don't know the product until you post a link

Edited by Penelope Stopit on Friday 30th March 19:04

[ade61]

here we are https://www.demon-tweeks.co.uk/motorsport/cockpit-...

[PositronicRay]

ade61 said:

here we are https://www.demon-tweeks.co.uk/motorsport/cockpit-...

DT says ' this lightweight heater is perfect for camper vans, light trucks or commercial vehicles'


Is your battery/alternator/harness up to it?

[Penelope Stopit]

2 x 60 Watt Main Beam Headlights = 10 Amps
Heated Rear Window Guesstimate = 15 Amps
Blower Full Speed Guesstimate = 10 AMPS
Wipers Full Speed Guesstimate = 10 AMPS

Total 45 Amps

With the car being driven at reasonable speed the alternator will easily cover a 45 Amp discharge on the battery and very likely more

With the 600 Watt 50 Amp heater running we can now switch off the Heated Rear Window and Blower

We now have

2 x 60 Watt Main Beam Headlights = 10 Amps
Wipers Full Speed Guesstimate = 10 AMPS
600 Watt Element = 50 Amps

Total 70 Amps

During a day with poor light you would be on dip more than main but that only saves you just under 1 Amp
Wipers will not be running all the time on fast speed so going over to slow speed could save you 5 Amps

Say 64 Amps current draw on a rainy day with poor visibility
You have to allow for the above during the day

As long as you have an alternator to cover approx 70 amps you will be charging the battery a little while running those above circuits
You may need to fit a smaller alternator pulley to up the output at lowish revs - Trial and error with what you've got to begin with but lots of slow moving traffic won't help

Edited by Penelope Stopit on Friday 30th March 21:23

[Penelope Stopit]

Regarding mains pre-start warm up - keep it simple and use a mains blower heater to achieve this

[227bhp]

Why?

[ade61]

it will be in a Porsche 356 and i want clean air, that's the reason for it....and it will have LED lamps, so very low power draw there......and i will be fitting a 75A alternator......and, if its raining, i'll just have to make do with less heat.

But, if i have 50A available, will that 600W heater heat the interior comfortably in winter?

Also, does a (high output) alternator always "waste" the same amount of engine HP, irrespective of how much electric power it is supplying?

[Penelope Stopit]

ade61 said:

Also, does a (high output) alternator always "waste" the same amount of engine HP, irrespective of how much electric power it is supplying?

The alternator load on the engine varies depending on how much current it is required to output to the battery, an alternator with a 75 Amp output will place roughly the same load on the engine as a 50 Amp alternator until its is output goes above 50 Amps and then it will place a higher load on the engine than a 50 Amp alternator does at maximum output

I am interested to know how this pans out as I have a vehicle with a leaking heater matrix that I have considered replacing with a heating element, my main concern is not getting enough heat from an element, demisting is one thing, keeping warm is another. I don't have the knowledge to calculate the heat output of a heater matrix so as to compare it with an element

[ade61]

thanks....so, i assume that the output of an alternator is in no way related to the speed it is turning but purely the current which it is required to output....what i'm getting at, is i dont want to rob the engine of HP unnecesarily

anyone else out there used one of these heaters?

[Penelope Stopit]

ade61 said:

thanks....so, i assume that the output of an alternator is in no way related to the speed it is turning but purely the current which it is required to output....what i'm getting at, is i dont want to rob the engine of HP unnecesarily

anyone else out there used one of these heaters?

Alternator output is very much dependant on speed, this is why I mentioned in my earlier post (Yesterday 21:09) about slow moving traffic and a possible smaller alternator pulley

[ade61]

but, if output is dependent on speed, what happens to all that power when the alternator is running fast and when there's no or little call for electrical energy (i.e. a fully charged battery, no lights on etc)....it can't all be dissipated in heat, can it?

my car originally had a 40A generator and not much power/torque (ancient air-cooled flat four). If fitting a 75A alternator is going to reduce the usable output of the engine by 0.5 HP (a guess) ALL of the time, then i might as well fit a Webasto petrol-fired heater, at least it'll only use power when i need it

[AW111]

Alternator power draw from the engine is roughly proportional to the current it's supplying.
So in daylight with no heater / wipers / lights and a fully charged battery, it will supply 5-10 amps, and require little engine power to do so.

[ade61]

yes, potential output is dependent on speed but actual output is dependent on electric loading, thats where i got confused....but i'm still not totally sure if engine power loss will be virtually the same with either a 75A or a 40A alternator, when both are putting out say 7A. Maybe, it comes down more to mechanical losses.

Even if i fit a 75A-rated alternator, chances are that is a max output and the output at , say, 2000rpm is only 30A....that won't be enough to power my 600W heater and a few LED lights.

So, petrol-fired Webasto heater looks like its the only option