Has anyone successfully done this? I keep thinking, is it possible to have a spare battery in the trunk properly wired for this? For the parking lot in January, when the only other option is a tow. Phil

I think there would be way to much mass to heat and just not enough amps. Injection line heaters might be of some benefit. Experience with my ready heater tells me that heated b100 makes a huge difference in it's ability to be ignited.

http://biodiesel.infopop.cc/eve/forums/a/tpc/f/15960555...431016172#2431016172

You could ask Pasotx if his diesels start better after turning on the injector lines for a minute or two. Problem is Texas is that it just doesn't get that cold at least not the kind of cold your talking about.

Most block heaters are about 10 amps at 120VAC or about 1200 watts for pickup block heater of course smaller cars may be half as much, but the problem is that the resistance is setup for 120VAC and not 12VDC. You would need a heating element that is 1/10 the resistance to get the same amount of heat. If you could find the right element you would also need a timer to have the heater come on for an hour or two before you start because one battery wouldn't be able to do the whole night. If you really need a block heater because of hard starts your might want to check out Webasto parking heaters.

Would an invertor work properly here. I'm thinking of an hour of 'on' time, just to raise the temp of a VW engine 20 or 30 degrees. I'd love to have a Webasto but I am hard-up. Phil

It won't work, there simply isn't enough energy in the battery. Get an extension cord - use plug-in preheating.

Dear John Galt. it's very easy to answer questions with out reading the questions or concerns is it not so.

Any ways. I've got a similar problem. Although my 82 Rabbit pickup starts fine on it's own glow plugs in the mornings and makes it to work, but on some of the colder days it starts a little hard, I do wonder whether it'll start when I'm wanting to go home from work.

You know, it sits in the lot with open cold air blowing though the engine keeping it cold for 10 hours... of course with no plug in sight to PLUG IT IN no matter how LONG the CORD I bring with me... If it doesn't start, I'm stranded.

So... what is the answer to our question my friend? I found that if I park further away where there is a sewer drain in the parking lot and If I park with my engine on it taking 2 spots. It starts easier. perhaps there is some warm air coming out of the sewer line in colder months. see if you have access to a sewer drain in your parking lot.

my 2 cents.

Hasan.

I'm in Canada too. In our region of the Great White North, parking lot plug-ins are SOP. If 10 hour cool down is too much, go warm it up at lunch break.

Personal references are unnecessary, this is a public forum, so stick to the subject.

quote:

it's very easy to answer questions with out reading the questions or concerns is it not so.

John is right regardless of your access to what you need or what concerns you. You cannot use the battery to warm your block. Physics is impartial to your personal preferences and situation.

If you want a block heater that doesn't need mains electric get a diesel or petrol fired block heater from webasto or eberspacher. They can be fitted with timers to warm your engine ready for when you need to start.

Yes, if you tried to use the block heater for 10-12 hours it would kill the battery, if you found a heating element that would work with 12VDC in the desired watt range, and did the math on how long you could run it and expect the battery to maintain it's charge, and then how long you would have to drive to get a reasonable recharge from the alternator it could be possible. You could also augement the re-charge at home with a trickle charger that you could wire in paralell with your stock block heater so when you are plugged into wall power then you are charging the deep cycle as well.

The key is not running the heater for a long time. In most cases 45 minutes - 2 hours is plenty to help a cold engine to start. DC timers aren't very expensive and could facilitate a shorter heating time.

I don't think I would advocate this course of action, but it is certainly not impossible, but the question is all the work worth it when you can just by a product like a Webasto. RVs use deep cycle batteries to run all sorts of things as do the mobile add trucks. It is just a matter of figuring it out, but again I think this would end up in a lot of work and expense when all is said and done.

Man, the park over the sewer idea is kind of slick.

How about putting a 25 watt Kats silicone pad heater on the bottom of your oil pan?

http://www.warehouseautoparts.com/Specials/Kat/Kat_heater_Specials.htm

They don't have it listed, but they have more than what they list on the site.

A typical car battery is rated at 60 amp-hours. If you use a big battery like the one's in most diesels it is probably rated at 100amp-hours. However, you don't want to use all the capacity the battery offers,it shortens the battery life. Let's do the math on 60 amp-hours.

25 watts / 12 Vdc = 2 amps.
60 amp-hours / 2 amps = 30 hours.

So you should be able to run a 25 watt heater off of a large battery for the time you are at work without really draining the battery down very badly. It will not beat the battery up too bad, so it should have a nice long life.

Or you could run a 50 watt heater off of that battery and still be within the range of the battery discharge range.

I have no idea how much that would help you in Canada...it's friggen cold up there.

http://www.overtons.com/modperl/product/details.cgi?r=view&i=31620

Add in a battery selector switch and you can charge both batteries while you are driving, and then select the spare while parked in the lot at work.

-Jim

A 25 or 50 watt heater on the pan would make near zero difference in starting in any climate.

A 1000 watt block heater run off an inverter would drain a large deep cycle RV battery in about 20 minutes, so its also not enough to make a difference.

Ok, so up the Watts and put it on a timer.

60% of 100 amp-hours is 60 amp-hours.

300 watts / 12Vdc = 25 amps
60 amp-hours / 25 amps = 2.4 hours.

600 watts would be 1.2 hours

Throwing an army blanket or two over the engine would help hold the heat in.

-Jim

quote:

Ok, so up the Watts and put it on a timer.

Sunwizard is right the idea is a non starter. A typical block heater is 3kw and anything you can run on a battery without killing it in 7mins is of no use.

Well, coming from Edmonton, I should also say that's ridiculous. BUT, what if you found a good quality deep-cycle marine battery, and one of these:
www.batterybrain.com

Also, my TDIHeater draws 900 watts, not 3kW. And it works pretty fast.

quote:

Originally posted by Jim D:
60% of 100 amp-hours is 60 amp-hours.

300 watts / 12Vdc = 25 amps
60 amp-hours / 25 amps = 2.4 hours.

600 watts would be 1.2 hours

Battery ratings go down quickly as the amps go up. A large RV battery rated at 110AH is at a 20 hour (tiny 5 amp) rate. At the 50 amp rate you chose (600w) the rating drops hugely. Which may not be enough with a small 600w heater. Typical block heaters are 2x that big, or 100 amps. At a 100 amp rate, the large RV batteries are good for 10 minutes (1000 cold cranking amps )

He lives in ontario so it gets very cold, way too cold for this idea as pointed out by many on this thread. And when its cold (0F) any battery only puts out half what its rated, so factor that in too. They will put out about 25% of their rating, half it due to cold, half it again due to the amp draw.

He could maybe carry a bank of several very heavy expensive deep cycle batteries plus an inverter in his VW. And they would last <1 year with this deep cycling.

A car battery (the thread title) will never work, even with several of the largest you can get hooked together. They are good for about 5 deep cycles before they are shot.

quote:

Originally posted by canuck7870:
Also, my TDIHeater draws 900 watts, not 3kW. And it works pretty fast.

Is 20 minutes of that block heater enough? And at what temps? That may answer the question if he also has a TDI and you live in a similar climate in canada.

SunWizard: Well, let's wait 'till January! I did use it last winter, and 2 hours was more than enough. But, 20 minutes? I don't know. I'd have to try it when it gets colder.

five to twenty minutes is all a battery would last on that load and then it would be too flat to start the car. The battery brain idea will just disconnect the battery from the heater even sooner and it will have done no good at all. It just won't work. No one is trying to be horrible or slag the idea off for the sake of it. We are just trying to inform you of the facts to help you and save you wasting money.

If you really need a block heater then get one that runs on diesel or petrol. They can be expensive new but second hand ones are not so bad and whatever the cost it is better to spend a larger amount well and get a result than keep spending smaller amounts on schemes that cannot work.

No matter how tempting it is to wish the scheme you would like to work will work you have to accept the physics of things.

As Sir Francis Bacon said several centuries ago:

To control nature first understand it and then obey it.

I'm really grateful for all the replies and the effort to work out the numbers.I failed to realize the damage done to a battery(s) also. Someone suggested, somewhere, that I might be better off putting a small portable generator in the truck. I'm not sure that even it would start at 0 degF. Phil