Block Heater Power Consumption

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Originally Posted by CR94
Originally Posted by StevieC
... At 1000 watts for 7 hours a day for 30 days = $21 Canadian, ...
Why run it that long, every day? Reasonable usage with a timer should be much lower in cost.

I find I can't get the coolant temperature to 100F (38C) if I don't set it for that long when temperatures are at -10c (14F) and lower. I have played with it in 1/2 hour increments and found that 7 hours is what is required to get it to the maximum temperature of 100F (38C).

It's on a default schedule in case I forget to modify it however, I usually set it the night before depending on what the weather is going to be overnight and when I intend to leave. So when temperatures are more mild, I put let time on it, and the opposite when it's going to be frigid.

In case anyone is wondering this is the Outdoor Smart-Plug I have and it has its own app as well as being compatible with Google Home, Amazon Alexa, Wink & Nest:
https://www.ihomeaudio.com/iSP100BC/

120V Volts AC, 60Hz
15A General use
1800W Resistive
 
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In my experience, some diesels only have trouble starting if they get below 50. I would say if you could get it to 75 or so you should be fine.
 
Originally Posted by Rand
Originally Posted by StevieC
I have mine on an outdoor smart plug. It has a default schedule of 1am to 8am (Monday-Friday) but I usually leave well before 8am, and then 2am to 10am on weekends. I just modify the schedule from my Smart Phone if I'm leaving at a different time or if it's going to be mild. It's also nice that I can ask Google to turn on/off the Block Heater. The smart plug I have is rated for a full 15 amps which gives me a buffer over the approximately 8-13 amps the heater draws (1000-1500 watt)

That said running it every night for 7 hours or so puts up my electricity bill about $15-25 CDN for the month. (We have expensive power here when you factor in all the costs)



I think you are underestimating its cost.. or overestimating the power draw.

At my relatively normal cost of 16c/kwh (that is all in pricing with distribution charges etc) that would be around $33

You can determine the wattage of the block heater easily, by measuring its resistance using an ohmmeter on the hot and neutral prongs of the block heater cord. For example, let's say you measure 10 Ohms. What's the wattage of the block heater?

Power (in Watts) = I (current) x E (voltage) = I^2 (current squared) x R (resistance). You know the voltage (nominal 120 VAC) and the resistance which you've just measured (in this example, 10 Ohms). You also need to determine the current to calculate the power consumption. Ohm's Law: I (current) = E (voltage)/R (resistance). I = 120 V/10 Ohms = 12 A (Amperes)

Now you have the current and the resistance. Plug them both into the I^2*R formula: I = (12^2)*10 = 144*10 = 1440 W

Seven hours/day x 30 days per month (rough average November through March) would yield 210 hours of block heater use/month. Let's use the 1440 Watts for the block heater as calculated above.

1440 W = 1.44 kW

1.44 kW x 210 hrs/month = 302.4 kW-hrs/month

Now plug in your marginal cost per kW-hr. (You don't have to count your basic costs, because they're fixed. We're interested in the cost of each additional kW-hr. Let's use $0.10 as an example. (That's high for here, but might be low for Ontario.) In any case, 302.4 kW-hr/month * $0.10/kW-hr = $30.24/month.

Charts of coolant temperature vs. block heater time show a natural logarithmic curve, in which the temperature climbs quickly at first and then starts to level out as the rate of change decreases. In other words, you get a lot of gain in the first hour (taking the coolant temperature up to perhaps 60% of the maximum it will reach), the 2nd hour is typically worthwhile (taking the temperature up to perhaps 80%), the third hour takes the temperature up to approximately 90%, and there's no gain after 4 hours. It's the same curve as exhibited by a charging capacitor (or the improvement in return for an investment as the interest is calculated on increasingly-small increments).

If using a timer, I would not bother with setting it to work for more than 3 hours before you want to start the engine.

Depending on the specifics of the engine and the block heater, on my vehicles (per the coolant temperature readout on the ScanGauge) the coolant temperature will peak and stabilize at around 23 C. (Which is great compared to, for instance, - 30 C ambient.)

You can cut your electricity cost way down by running the block heater for only 3 hours a day. Regardless, it's still way cheaper to use the block heater - there's way less wear and tear on the engine, the starter, the battery, the alternator ... and you get way better mileage and comfort by having the engine come up to temperature more quickly.
 
There is no way the block heater is 1440 watts with the thin gauge cord they are using on the plug for my vehicle. I will measure the wattage and get back to you. At best it's most likely 500-1000 watts.
 
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Originally Posted by StevieC
There is no way the block heater is 1440 watts with the thin gauge cord they are using on the plug for my vehicle. I will measure the wattage and get back to you. At best it's most likely 500-1000 watts.
Agreed, 1440 W is unrealistic - I made up the resistance (10 Ohms) and calculated the (theoretical) block heater's wattage from that.

For what it's worth, I just measured the resistance of the Kia's block heater - it's 30 Ohms.

I = E/R = 120 V/30 Ohms = 4 A

P = IV = (4 A) * 120 V = 480 W

That's way more realistic for a block heater for a gasoline engine.
 
I could have sworn mine said it was 480 watts as well but I didn't want to put that here and someone call me on it. (PentaStar Dry type block heater).

I'll have to measure it when I get a minute.
 
Funny thing ... I tried to the measure the resistance of the Mazda 5 first - and found it to be open. It's almost certainly the plug on the end. I'll cut it off tomorrow, and measure the resistance between the hot and neutral on the cord. If the cords good, I'll replace the 10-year-old plug.

Wouldn't have discovered this before it got cold without this thread!
 
grin2.gif
I'll measure my resistance when I get a chance later today. It's just so dark when I get home it's hard to see anything. (Super dark in the driveway where the van parks)
 
Resistance of a conductor, which a heating element would be, increases with temperature fellows. I don't remember roughly by how much off the top of my head, but you need to know the metal type as well. So if you are measuring the resistance, measure it while the element is hot.
 
Originally Posted by KrisZ
Resistance of a conductor, which a heating element would be, increases with temperature fellows. I don't remember roughly by how much off the top of my head, but you need to know the metal type as well. So if you are measuring the resistance, measure it while the element is hot.

Excellent point - when the conductor is cold, its resistance is relatively low, and there will be an inrush current before it warms up. In the winter here we flirt with superconductivity.
wink.gif


In any case, I've just replaced the plug on the Mazda's block heater cord, and the resistance now measures 36.0 Ohms (cold), which will determine the maximum current flow.

As before, I = E/R = 120 V/36 Ohms = 3.33 A

P = I * V = (3.33 A) * (120 V) = 400 W
or
P = I^2 * R = (3.33 A)^2 * 36 Ohms = 400 W

The resistance will rise, and the current and power consumption will drop as the block heater element warms up. In fact, I just tried this. After 10 - 15 minutes of being plugged in, the resistance had increased only 0.5 Ohms, to 36.5 Ohms. I expect it would have risen much higher in open air, but remember it started out being surrounded by coolant @ 0 degrees C. That cooling effect will diminish as the coolant heats, but the coolant will never get hot - it will peak at around 23 C after 3 - 4 hours. Therefore, I think we can consider the reduced current due to the element heating to be minor in effect.

Let's say that the resistance would rise, if given long enough, to 38 Ohms:

120 V/38 Ohms = 3.16 A

P = (3.16 A) * (120 V) = 379 W; measurable but not highly significant - still at around 95% of the maximum power consumption.
 
The best I can find for the PentaStar engine for information is between 450-600 watts depending on the vehicle.

I just looked through the last couple of days of electricity and it's more or less the same with the same devices running. Here is what it looks like with the block heater running and without it running. About $0.02/KwHr to run it (without taxes and delivery added on that)

Green = Off Peak smart metered power usage
Yellow = Mid-Peak smart metered power usage
Red = On-Peak smart metered power usage



Block Heater Power.png
 
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I wonder if the coolant heater/circulators you can plumb into the heater core hoses are any more efficient than a regular block heater? One place I worked at had these installed in the trucks. Start the truck up at -20 and it was like it had already been running for a while, instant heat!
 
Originally Posted by Number_35
Originally Posted by KrisZ
Resistance of a conductor, which a heating element would be, increases with temperature fellows. I don't remember roughly by how much off the top of my head, but you need to know the metal type as well. So if you are measuring the resistance, measure it while the element is hot.

Excellent point - when the conductor is cold, its resistance is relatively low, and there will be an inrush current before it warms up. In the winter here we flirt with superconductivity.
wink.gif


In any case, I've just replaced the plug on the Mazda's block heater cord, and the resistance now measures 36.0 Ohms (cold), which will determine the maximum current flow.

As before, I = E/R = 120 V/36 Ohms = 3.33 A

P = I * V = (3.33 A) * (120 V) = 400 W
or
P = I^2 * R = (3.33 A)^2 * 36 Ohms = 400 W

The resistance will rise, and the current and power consumption will drop as the block heater element warms up. In fact, I just tried this. After 10 - 15 minutes of being plugged in, the resistance had increased only 0.5 Ohms, to 36.5 Ohms. I expect it would have risen much higher in open air, but remember it started out being surrounded by coolant @ 0 degrees C. That cooling effect will diminish as the coolant heats, but the coolant will never get hot - it will peak at around 23 C after 3 - 4 hours. Therefore, I think we can consider the reduced current due to the element heating to be minor in effect.

Let's say that the resistance would rise, if given long enough, to 38 Ohms:

120 V/38 Ohms = 3.16 A

P = (3.16 A) * (120 V) = 379 W; measurable but not highly significant - still at around 95% of the maximum power consumption.



Nice work
thumbsup2.gif

The power consumption may drop a little more as the coolant warms up, but this is probably pretty close. The heating element will always be hotter than the coolant anyways.
 
The OP could also wire up an outside line voltage thermostat to turn the power on , to the plug , below a specific outside air temperature . Along with the timer .
 
I have my block heater on a timer. Comes on at 4:30 AM and the truck moves at 7:15 AM and the timer is done by 7:30 AM. How much does that cost?

Answer: It doesn't matter, I need it when I need it.
 
Originally Posted by KrisZ
Originally Posted by Number_35
Originally Posted by KrisZ
Resistance of a conductor, which a heating element would be, increases with temperature fellows. I don't remember roughly by how much off the top of my head, but you need to know the metal type as well. So if you are measuring the resistance, measure it while the element is hot.

Excellent point - when the conductor is cold, its resistance is relatively low, and there will be an inrush current before it warms up. In the winter here we flirt with superconductivity.
wink.gif


In any case, I've just replaced the plug on the Mazda's block heater cord, and the resistance now measures 36.0 Ohms (cold), which will determine the maximum current flow.

As before, I = E/R = 120 V/36 Ohms = 3.33 A

P = I * V = (3.33 A) * (120 V) = 400 W
or
P = I^2 * R = (3.33 A)^2 * 36 Ohms = 400 W

The resistance will rise, and the current and power consumption will drop as the block heater element warms up. In fact, I just tried this. After 10 - 15 minutes of being plugged in, the resistance had increased only 0.5 Ohms, to 36.5 Ohms. I expect it would have risen much higher in open air, but remember it started out being surrounded by coolant @ 0 degrees C. That cooling effect will diminish as the coolant heats, but the coolant will never get hot - it will peak at around 23 C after 3 - 4 hours. Therefore, I think we can consider the reduced current due to the element heating to be minor in effect.

Let's say that the resistance would rise, if given long enough, to 38 Ohms:

120 V/38 Ohms = 3.16 A

P = (3.16 A) * (120 V) = 379 W; measurable but not highly significant - still at around 95% of the maximum power consumption.



Nice work
thumbsup2.gif

The power consumption may drop a little more as the coolant warms up, but this is probably pretty close. The heating element will always be hotter than the coolant anyways.
Hey, I thought I'd dig in a bit more, to try to determine how much the resistance does increase as the element heats up.

As we'd discussed, it's not a major factor with a car's immersed block heater, where the surrounding coolant doesn't get very hot. (+25 C at best in my vehicles.)

But anyway, I found an old electric kettle, the type that does not detach from the inductive base.

At 20 C its resistance was 14.7 Ohms (15.2 Ohms measured - 0.5 Ohms indicated with the probes shorted). 120 V/14.7 Ohms = 8.16 A. 8.16 A * 120 V = 980 W

At 100 C (right after the water had boiled) its resistance was 16.1 Ohms (16.6 indicated). 120 V/16.1 Ohms = 7.45 A. 7.45 A * 120 V = 894 W.

The current dropped from 8.16 A to 7.45 A (a decrease of 8.7 %). If the kettle were mine, I'd leave it out for a few hours @ -30 C and then check the resistance. Then we'd have three points to plot on a graph - it would be interesting to see if the result was a straight line.

But in any case, I think we can conclude that decrease in current draw as the block heater warms is measurable but not highly significant.
 
FWIW, the factory block heater on my Ford Focus 1.0 EcoBoost is reading 433 watts currently on my P3 Kill A Watt.
 
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