So just mulling this idea about at the moment.

After having to sit around in the car in that freezing weather we had a few weeks back, I was thinking that I could do with a heater that works when the engine is off.

After doing a bit of research it doesn't look like it would be to hard to fit a second auxiliary battery with a voltage sensitive relay, and run the auxiliary electric heater from this second battery. (Obviously using this type of system stops the cars main battery from being drained)

So is it as simple as it looks to install this type of system?

In every topic I've looked at so far they all deal with this system being used with the engine off, but I would like the auxiliary heater to work when the engine is first started to quickly build up the cars temperature on a cold morning. Can this be done with this sort of dual battery system?

I'm guessing that people who go camping/have a motorhome will have more experience with this type of system.

The car I'm thinking of fitting it to is a 99 skoda Felicia.

What auxiliary electric heater? A 12 volt one? Is your vehicle equipped with one?

No heater currently installed.

I was thinking just a small 12v aftermarket heater.

 

11 hours ago, R_U_AFA said:

In every topic I've looked at so far they all deal with this system being used with the engine off, but I would like the auxiliary heater to work when the engine is first started to quickly build up the cars temperature on a cold morning. Can this be done with this sort of dual battery system?

As well as the voltage sensitive relay to charge the auxiliary battery it sounds like you need a time delay relay triggered by ignition to enable the auxiliary heater for a timed period after the ignition turns on.

5 hours ago, PetrolDave said:

As well as the voltage sensitive relay to charge the auxiliary battery it sounds like you need a time delay relay triggered by ignition to enable the auxiliary heater for a timed period after the ignition turns on.

I don't suppose you could recommend one?

I found these

https://www.ebay.co.uk/itm/315013660143

 

https://www.ebay.co.uk/itm/134785535193

 

I was just worried about issues being caused with the cars current electric systems with the switched live active

18 hours ago, R_U_AFA said:

No heater currently installed.

I was thinking just a small 12v aftermarket heater.

 

 

How many watts?

 

There is a reason why most pre-heaters are either mains or carburant powered.

 

The alternator on your older vehicle will definitely not be up to the job of keeping up with the discharge of the 12v heater, the reason I asked how many watts, if your normal journeys will be many miles after the engine coolant heater has taken over then maybe you will get away with your alternator.

 

So I should ask as well as how many watts will the heater be what is the output of your alternator?

25 minutes ago, J.R. said:

I should ask as well as how many watts will the heater be what is the output of your alternator?

Not 100% sure but;

Aux heater 1250w

Felicia Alternator 1000w

 

Are you saying that with the engine running it could damage the alternator, or just that the auxiliary battery would be quickly drained and need long journeys to recharge?

The auxiliary heater would only be needed for 5 mins with engine running until the cars engine coolant heating system comes up to temp. (If I've calculated properly 105watts needed)

 

Although after doing some calculations (if correct) assuming a 60Ah battery I would only have 36mins of auxiliary heat anyhow (with engine switched off) As seen as I was sat in my car for 6 hours the other week that doesn't seem a lot.

 

But that is what the VSR is for isn't it, so there still is power left in the cars main battery.

 

To be able to sit in the vehicle with heat for 6 hours without the engine running i think you would need an aux heater that used fuel.

What form is the energy transfer of this heater?

 

Does it heat the coolant water like an immersion element?

 

Is it a radiant or convector heater?

 

Is it a fan assisted radiant heater?

 

I doubt with any of these that you would feel much effect from 1.25kw within 5 minutes of driving off in a cold car.

 

I have a 5kw diesel heater intended for heating lorry cabs overnight while the driver is sleeping, it is sufficient to heat my workshop but to get any warmth from it in the first 5 minutes you have to stand right in front of it and that is blown warm air.

 

 

1 hour ago, J.R. said:

Is it a fan assisted radiant heater?

 

Yes, just mounts to the dash

 

But I have just seen an element type that heats the coolant.

 

I'm not looking to heat the car to some steamy 30°C heat and be wearing no clothes, just enough to bring the temp up a little, so I'm not freezing cold whilst sat there 5-7° would probably be enough on a freezing day.

 

6 hours was an extreme case, and any how even then i would be cycling it on off not constantly running it.

 

Looking at a campervan forum 30mins would be good from a standard lead-acid battery.

  ?

When you can be near home or a 3 pin socket / extension lead then a Green House heater is all that is needed.

 

 

Edited 26 December, 20232 yr by Rooted

10 minutes ago, Rooted said:

When you can be near home or a 3 pin socket / extension lead then a Green House heater is all that is needed.

 

 

 

That's how i defrost my car whilst having breakfast in the winter

Good for keeping mildew at bay and condensation all winter or all year in cars, campers, vans, caravans.

Set to above freezing and can use very little electricity firing up as when needed as long as there is some ventilation as well.

I would not want cables carrying 105 amps draped across my dashboard, that is the same current as a starter motor, I bet it comes with  bell wire cable and a plug for the cigarette lighter 🤣

 

Your auxiliary battery would have to be fitted in the boot, the volt drop over that distance would mean that the cables to your heater would have to be larger than your existing battery & starter cables.

 

What sort of battery size do you think you would need to crank your engine for 30 minutes or even 5 minutes and what state would that leave it in?

 

14 hours ago, J.R. said:

There is a reason why most pre-heaters are either mains or carburant powered.

 

Edited 26 December, 20232 yr by J.R.

Most common with diesel's, or the heater runs on diesel.   As to the UK very low temperatures even Anyone and Braemar has many a motorist / driver / vehicle owner that just de-ices and drives the vehicles there have as they come from a dealership.  Often just on the tyres they come on.  15 miles or so til Diesels up to temp and maybe 10 with a petrol.