[MrEnergyCzar]

Someone wants to know what he needs and if the following can be done: (My instincts are it can't be done with a regular 12v car battery?)

How long can I run a 1,000 Watts heater from a "regular" 12V car battery "fully charged". I am assuming it will have to go through an inverter.

Battery Specifications:

Amp Hours: 20
Cranking Amps: 850
Weight: 13.5 lbs.
Dimensions: 3"D x 7-1/2"W x 6-1/2"H


HEATER SPECIFICATIONS
SPEED WATTS AMPS BTUS
HIGH 1500 12.7 5118
LOW 750 6.5 2559

 

[timlange3]

20 amps seems small for a car battery. Anyway, Watts = Volts times Amps. so 1000w / 12v = 83.3a, then 20ah / 83.3a = 14 minutes.
Then you mentioned going through an inverter (some power loss there), so may I assume the heater is a 120v heater? If so, the time will be less for the inverter loss.

 

[jfkirk]

20 ah at 12 volts is 240 Wh Assuming reduced capacity at 4C, ~10 minutes.

 

[saghost]

Keep in mind most batteries are rated based on C/20 discharge (drain the battery in 20 hours) and have far less energy if drawn quickly.

As jfkirk says, you're looking at a 4C rate - so I think even his answer is optimistic. I'd guess 7-8 minutes.

20Ah is very small for a car battery - both the Volt and my Eos are 60 Ah I believe.

 

[Ladogaboy]

If you're doing what I think you're planning to do (have an extra battery to run an inverter and heater), I'd suggest a marine/RV deep cycle. Sure, it's going to weigh 80-100 lbs, but the difference in weight is going to have a minimal effect on mileage. However, the impact of deep cycling a non-deep-cycle battery can be pretty harsh.

But as others have stated, you can calculate the draw by A*V. You might experiment with the heater using a Kill-A-Watt meter so you can get a better idea of the draw. Also, most batteries, while rated on a C/20 discharge as Walter pointed out, will also have a discharge rate charge for other amperage draws.

 

[mortinsany]

You will have to tend with Perquets equasion wich states that durring a signifigantly higer rate of discharge or re charge the battery will be depleated signifigantly faster than at the advertised 20ah rate. Additionaly traditional car type lead acid batteries are rated at full capacity but one should never depleate them beyond 50%. So that 20 amper battery should really only be discharged 10 ampers before it reaches 50% or 12.2 volts / static (no load) additional discharging will signifigantly reduce overall battery life and durring heavy loading the low voltage received by the inverter after 50% discharge has been reached will probably shut the inverter down. My guess is that your inverter powering this heater on high (1500 watts) would shut off in 4 minutes or in other words dont try this it is stupid. Even on big yachts where people have 2000 amp hour battery banks (around the same size as a Nissan Leaf's 24 KW battery pack) we never suggest running resistive element type heaters off of inverters. Microwaves are generaly a good use for inverters due to the short operating durrations. Good luck!
P.s. we have been using Odyssey batteries almost exclusivly for 5 years now and even with their greater tolerance for discharge rates, we still would strongly recomend against this.

 

[kns]

Why not just use a 12v car heater. There are quite a few on the market. Some can be connected to a cigarette lighter and others, more powerful, require a higher amperage circuit. I just searched for "12v car heater" on Amazon and several of each type popped up.

KNS

 

[garyg]

this just looks like a conversion to kilowatt hours:

http://www.ehow.co.uk/how_5985435_calculate-battery-watt_hours.html

looks like 15 minutes (.240 kwh) if you could get it all and all at once.

but think of it another way: an average car starter might use about 100 amps on a cold engine. so at 12v* 100 a is about 1200 watts. Of course the battery voltage wont be 12 volts under load but...How many minutes do you think you crank your engine for before battery cant do it anymore? (assuming your starter motor doesnt fry first).

and you could use a couple of these (or may be bigger). They are gell pack lead acid. dont breath and can be mounted in any direction and are reasonably light wieght. use them in experimental planes alot but are used mostly in atvs.

http://shop.odysseybattery.com/p/pc680-p?pp=12&pp=12

7.15x3.00x6.65, 15 lbs.
20Hr Nominal Capacity (Ah) 16.

so this would have .192 kwatts total. you can sometimes buy them for about 110 or so.

 

[Cord]

at 400 BTU generated per person just put a few more people in the car

 

[Sparks The White Warrior]

Hi MrEnergyCzar,

With a conventional Pb battery I would NOT recommend to do this at all. Discharging such a battery severely shortens it's life time.
A conventional start motor will consume between 1 and 2 kW. Normally starting the engine takes seconds. After that, the battery in immediately re-charged. As a result, the charge of the battery will never go under 50%. Below 50%, you risk damage to the battery.
Discharging a conventional battery completely within minutes might cause high temperatures and even getting the electrodes to bend and short circuit.

So your instincts are correct. It can not be done with the described battery, or only a few times.

 

[Noel Park]

at 400 BTU generated per person just put a few more people in the car

Good idea! I had 2 extra people in the Volt this AM, one of whom was quite large, and it really was warmer. Probably a lot more efficient that this electric heater idea, LOL.

Although the windshield fogged up much faster so there was a tradeoff there from running the defroster - some people just can't grasp the concept of keeping the window open in the middle of winter, don't you know.

Our local LA Times columnist Steve Lopez said that he sometimes hired a day laborer at the Home Depot to ride in his car in the carpool lane when he needed to get downtown in a hurry, so maybe there's some potential there for keeping the car warm...............................

 

[Kevin from Canada]

I love these types of questions..
Ask someone who has an off grid solar system, they'll be able give you "real world" answers.

Although, I think the question could be rephrased to "What's the fastest way to discharge a 12V battery?" One benefit of doing this is that the battery will give off heat as well.