Engine block heater in fall, spring & Summer

[TXwaterdog]

I was just reading a report titled "Reduced Air Pollution and Fuel Consumption with Preheated Car Engines by Paul G Hoglund and Anders Ydstedt" It's very apparent that preheating the engine at below 20C / 68F is better all around. So everyone here is saying Solar is out.. What about using a deep cycle battery to keep the engine warm while at work, etc.. Has anyone used something like this for the B side?

[brucepick]

I've also wondered about using a spare battery (marine or automotive) to run the engine heater via an inverter. I ran a series of calculations and came up with...

The bottom line:
Using an a/c inverter: Assuming a 90 minute reserve capacity specification in my car battery, my 125 Watt (AC) heater would run about 3 hours before running the battery down to 10.5 volts. The battery capacity spec is rated at 80 ºF so it would be less in cold weather. If your heater is 2x my wattage, the battery will run about 1.5 hours (less in cold weather).

I have a spare battery that is a larger size, might do the job. If you have a larger heater, 300 watts or more you might want two batteries in parallel to run the heater. In any case, use a SPARE battery, not the one that needs to start your car! Charge up the spare(s) at home, of course.

Whenever I junk an old car I keep the battery. Those spares have come in handy for various purposes; I recommend you do it if you have room to keep the spare(s).

Calculations:
Please, someone with an electrical engineering degree, double check these calcs!

First I converted the heater's watt rating to amps of current.

Ohms Law says: Watts = Amps * Volts, or thus Amps = Watts / Volts. So a 100 Watt preheater draws about 0.83 Amps, assuming 120 Volts. A 200 W heater will draw double that, etc. My 125W heater draws just over 1 amp.

Powering the heater from 12 volts DC, you need about 11 amps of 12V DC to generate 1 amp of 120 volt AC (my source; see section "DC load"). Working strictly from Ohm's Law you'd need 10 amps but the AC inverter is not perfectly efficient, thus 11 amps DC per each amp AC. So for my 125W heater (1A) * 11 = 11 amps when running off 12V.

How long will the battery hold up driving that load?

Batteries for my Civic have a reserve capacity specification of about 90 minutes. That will vary by battery size and model but it's a decent starting point.

Here's the definition of Reserve Capacity for automotive batteries: The number of minutes a battery at 80 degrees F can be discharged at 25 amps and maintain a voltage of 10.5 volts for a 12 volt battery.

So with 90-minute "reserve" you could run a 25A load for 90 minutes. My load is about 11A so I could run it for a bit more than 180 minutes, three hours. But if you need an engine preheater, it's likely not 80 degrees outside. So your capacity in winter would be less than that.

[TXwaterdog]

Originally Posted by brucepick

I've also wondered about using a spare battery (marine or automotive) to run the engine heater via an inverter... If your heater is 2x my wattage, the battery will run about 1.5 hours (less in cold weather).

... In any case, use a SPARE battery, not the one that needs to start your car! Charge up the spare(s) at home, of course.

Calculations:
So with 90-minute "reserve" you could run a 25A load for 90 minutes. My load is about 11A so I could run it for a bit more than 180 minutes, three hours. But if you need an engine preheater, it's likely not 80 degrees outside. So your capacity in winter would be less than that.

Suggestions on buying a battery that will be kept inside the passenger cabin (hatchback trunk)- AGM Group 27-4D=?

Lifespans:

• Starting: 3-12 months
• Marine: 1-6 years
• Golf cart: 2-7 years
• AGM deep cycle: 4-7 years
• Gelled deep cycle: 2-5 years
• Deep cycle (L-16 type etc): 4-8 years
• Rolls-Surrette premium deep cycle: 7-15 years
• Industrial deep cycle (Crown and Rolls 4KS series): 10-20+ years
• Telephone (float): 2-20 years. These are usually special purpose "float service", but often appear on the surplus market as "deep cycle". They can vary considerably, depending on age, usage, care, and type.
• NiFe (alkaline): 5-35 years
• NiCad: 1-20 years

Some common battery size codes used are: (ratings are approximate)

U1 34 to 40 Amp hours 12 volts
Group 24 70-85 Amp hours 12 volts
Group 27 85-105 Amp hours 12 volts
Group 31 95-125 Amp hours 12 volts
4-D 180-215 Amp hours 12 volts
8-D 225-255 Amp hours 12 volts

http://www.windsun.com/Batteries/Bat... Battery Types


This one is around $75 from Autozone but it's not AGM
Duralast/685 CA marine deep cycle battery
Part Number: 24MD-DL
Alternate Part Number: 24MDP-DL



Part Number: 24MD-DL
Weight: 44.65 lbs
Warranty: 3 YR
Type: Marine
Category: Deep Cycle
Application: Marine
BCI Cold Cranking Amps Value: Tested to BCI Standard
Battery Height: 225 mm - 8 7/8 in
Battery Length: 260 mm - 10 1/4 in
Battery Width: 173 mm - 6 13/16 in
Cold Cranking Amps (CCA): 550
Core Charge Applicable: Yes
DIN Designation: BCI or EN Only
EN Designation: DIN or BCI Only
Right Or Left Hand Positive: Left
Post Location: Top Post
Reserve Capacity (Min): 140
Voltage: 12

[ConnClark]

Ummmm..... using a car alternator to charge a battery to pre heat an engine isn't a very efficient proposition.

Lets run some numbers.

Alternator is about 65% efficient at best.

A lead acid battery charging and discharging is about 80% efficient.

A good inverter is about 90% efficient.

so 0.65 x 0.8 x 0.9 = 0.468

Less than half the energy you expend is going to be used to preheat the engine.

Your far better off using the fuel to heat the engine by driving.

In a typical engine at operating temp 1/3 the energy goes to the cooling system. In a cold engine this would be higher. About 25% goes to moving your down the road. By just running the engine your almost getting the same amount of energy heating it plus your using energy to move you down the road for a net benefit of greater than 50%.

I know for diesels you can get a block heater that runs directly off the fuel by burning it thus reaping close to 100% of the fuel heating energy. Not sure about gas engines though.

[TXwaterdog]

ConnClark no-one said anything about charging two batteries.. I'd just charge the second one at home and use it to re-heat the car for a b side trip.

[ConnClark]

Originally Posted by SimonSellsAustin

ConnClark no-one said anything about charging two batteries.. I'd just charge the second one at home and use it to re-heat the car for a b side trip.

just get an oil fueled lantern and stick it in the engine bay and throw a blanket over the the hood. It will weigh less and cost less and you can use corn oil to fuel it.

Cheaper and more eco friendly

Edit : link https://www.vermontlanterns.com/cont...dietz-brass-10

[slowmover]

I know for diesels you can get a block heater that runs directly off the fuel by burning it thus reaping close to 100% of the fuel heating energy. Not sure about gas engines though.

In the recent past there has been this option (by either WEBASTO or ESPAR) though small cars are not the intended vehicles. A passenger van, pickup or similar would be more likely.

.

[TXwaterdog]

I like the blanket over the hood idea. I'm Planning on getting a car cover and that might be all I need. Afterall the enginebay is mostly sealed up from the bottom straight out of the factory.

[Diesel_Dave]

When I was a kid my dad had an air-cooled diesel tractor that would barely start if it was below frezzing. His solution was to throw and old blanket over the engine compartment, back up his truck, and run an old eavestrough between the truck tailpipe and run it under the engine compartment. It wasn't pretty (or fuel efficient), but after an hour or so with the truck idling, we could get the tractor started.

A word or warning, be very careful about getting heat near a flammable blanket.

[ConnClark]

Last year when my battery was dying and all but one of my glow plugs went out I used a blanket over the hood and grill with some success while at work. (Covering up the grill is the most important)