Block heater.
 

As the overnight temperatures start to tumble (it isn't even officially autumn yet) I think a block heater would make a lot of sense. This morning I drove my wife to her work, two miles there, two miles back, and the car didn't get up to even approaching operating temperature.
My question is, could I run a block heater off an auxiliary battery and inverter?
I would take the battery into the house during the day, and charge it from the mains, then return it to the garage at night, to run the block heater. I would require some sort of battery operated timer (run from the car battery to avoid having to constantly reset it), but that, the inverter and the block heater would be a permanent fixture on the car. I would just need to connect the battery to a plug on the car.
My garage is provided by the county, is remote from my flat, and has no provision for power.
What do you guys think? Any better suggestions? All ideas welcome.

That's a lot of power. Most block heaters are only 400 to 600 watts.
Do a warm air intake using exhaust heat or any of my fast warm up ideas.

If you are going to battery power it, might aswell go with a 12V heater.

Do some power calculations, and then determine the Ah of the battery. Look up lead acid battery weight and then ask yourself are you willing to transport that much lead to gain x £.


If you do decide to go that route, there are some neat internet enabled relays, then you could switch it on and off with your mobile phone.

My intention is only to use the block heater overnight, while the car is in the garage. I wouldn't need to carry it in the car. What I would need to do is carry it the 70 yards from the garage and up the 48 steps to my flat.
The mobile phone would work fine as I am up an hour before I use the car. Any longer for heating the block would need a timer, as 05:20 is the earliest I intend getting up!
A 50AH battery is big and heavy.

I really think you should consider insulating your engine bay as much as possible. Full grill block with a section you can open, belly pan and insulation around engine. Check out my album on my echo mods. You could maybe
do what your suggesting, but not with a 50ah battery.

The block heater is very light. And removing it would be a pain.

You stated that you do not have power where you park, so you would need to carry all the power in a battery.

To run it the whole night you need even more power, because heat loss is a function of delta T. The hotter the engine is the faster it loses heat. So switching it on just before starting your car is the energetically optimal way of doing it.

My thoughts were to switch the block heater on an hour before I need the car. It is in a garage, and because we are near the sea the outside temperature here seldom drops below 0°C. A 400 watt heater running on 12v would draw 34A. Leaving on an hour would need 34AH, hence a minimum of 50 AH battery. It would only be used for first trip of the morning, then on my return the battery would be taken into the house and charged up until the evening, when it would be reconnected to the car. The block heater would be fitted to the car and never removed.
An electronic timer, powered by the car battery would switch on the auxiliary battery/block heater an hour before I need the car.
I intend manufacturing a grill block, which for the 4 mile morning trip, would be closed completely, and opened up for my longer journeys.
There is insulation on the underside of the bonnet at present. Not very thick, but it is there. There is also a factory fitted undertray, which is reasonably full. For me to do any more is really beyond the tools and facilities I have access to.

It's good you have some protection already. You could let some reflective insulation in the existing under tray and some over top of the engine. I think it would help and be cheap and easy. As for your battery calculations, in theory you are right about the AH and amps required, but nothing is 100% efficient. Batteries are rated at a 20 hour rate. The 1 hour rate is about half that. Also, you don't want to discharge below half capacity or you will get very few cycles out of it. Do you already have a block heater in the car or do you have to buy one? The inverter will have a percentage of losses as well.

Just a note, this applies mainly to lead acid batteries. High-draw and deep cycles also hurt other chemistries, but not nearly as much. On the downside, most of the alternatives like lithium-based batteries would be fairly expensive.

I had been looking at using a deep draw battery. I don't have a block heater so would try and get a 12v one, if they are available, so I would not need the inverter.
The garage itself is fairly well insulated in that the door is the only outside surface and that faces away from the prevailing wind. The roof is a heavy concrete plinth, with a heated house on top of it.
This is a picture of my old car outside the garage, to give you an idea of the set up. I now have a new door without windows in it!

http://i.imgur.com/5hEukVz.jpg