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Discussion Starter · #1 · (Edited)
See Post #11, page 2, I think this graph is "wrong", an "alias" caused by the sample rate. More to follow -

Here is my first look at steering wheel heater current over 10 minutes (2018, Premier). Car temperature was about 33F, plugged in (L2), car turned on, heat off, steering wheel heat on. Current was measured by a home-made fuse tap loop through a DC current transformer, data taken once per second (600 points of which are shown here, 3600 points went on in a similar way). Did not measure voltage. Raw data was standard 4-20mA converted by equation to amperes (mA value-4mils)*(200/16mils) [200A unipolar full scale]. The relatively high start up current is interesting considering F26 is a 7.5A fuse. It was a 200A sensor, not sure if a 10A sensor would show less "noise", or if the tiny wiggles top and bottom are real. DMM is AG34410A, 1PLC integration time, 10mA scale (auto), data logger function.
 

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I would assume that the nominal voltage is 12V, and a rough eye-ball estimate of the average current is 3.5A, so the heater is consuming about 40 to 45W. That's equivalent to a mile of drivable range for every 5 hours.
Thanks for doing the calculation (if you hadn't, I'd have had to satisfy my curiosity and do it). When something is drawing less than 0.05 kW, you can basically ignore it.

It'd be cool to measure the seat heaters too, but I suspect they are similarly little (even if the seats are double the steering wheel, it's still basically nothing).

The moral is, go ahead, turn on the heated seats and steering wheel, they use negligible power and add lots of comfort.
 

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I would assume that the nominal voltage is 12V, and a rough eye-ball estimate of the average current is 3.5A, so the heater is consuming about 40 to 45W. That's equivalent to a mile of drivable range for every 5 hours.

Telex reported voltage at 13V. It could be even less than 40-45W because it is a pulsed signal as shown in GreyBolt's data. Would have to integrate the area under that current waveform to know the true power consumption. Very sophisticated method to minimize power producing the desired heating.
 

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Telex reported voltage at 13V. It could be even less than 40-45W because it is a pulsed signal as shown in GreyBolt's data. Would have to integrate the area under that current waveform to know the true power consumption. Very sophisticated method to minimize power producing the desired heating.
Telek said it was 13V x 3.6A = 47W, so it's more or less on spot on with GreyBolt's graph, given the higher actual voltage.
 

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Telex reported voltage at 13V. It could be even less than 40-45W because it is a pulsed signal as shown in GreyBolt's data. ... Very sophisticated method to minimize power producing the desired heating.
It's actually a very simple method, much simpler than trying to step the voltage down to a lower level to modulate the power level. It works well because the heating elements have a thermal mass that doesn't heat and cool instantaneously, but rather tends to heat proportional to the average power level sustained over several seconds.
 

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You can either:

1. Ignore this information, and use the heated items to drive comfortably
2. Worry about the power consumption, not use the heaters, and use extra layers of clothing and gloves to save energy.
3. Move south, never use that heater power, and get better range.

I did the third over fifty years ago, and now I need to buy my BEV.
 

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Discussion Starter · #10 · (Edited)
Rear seat driver's side heat

Now that we know what the wheel and front seats energy cost is, what about the heated rear seats? They are single setting, either on or off.

Keith
Rear seat driver's side (rear seat heater button on each rear door, 2018, Premier) Car is on, connected L2 EVSE (voltage not measured, probably 13V to 14V by the APM). Temps about 36F.

There was no easy way under the rear seat to place a relatively large clamp on DC current transformer. So, clamped on to the entire wire harness leaving the front compartment fuse box (turned off lights, heat, steering wheel heat, front seats heat).
used .365 second sample rate of 10ms samples (to avoid alias, because Telek describes seat heater on-off times on the order of seconds)
The baseline current is any number of other loads, so use the difference max - min

The first graph is the 10 minute test period, the second shows 1 second subdivisions from minute 8 to minute 9.

If anything is happening much faster than 1 second (e.g. a faster pulse width modulation (PWM) scheme, it would not show on these graphs)
 

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Discussion Starter · #11 · (Edited)
Steering Wheel heater current - Redone

I re-did the steering wheel heat measurement from the front wire harness as for the rear seat heater above (same settings)
It is clear the switching is happening much faster than minutes or tens of seconds as shown by the first graph in this thread, so that first graph is wrong as an alias, an artifact of the relatively slow sampling rate. This one may be the same, it will take a fast digitizer or an oscilloscope to investigate further.

The tiny ripples commented on in the first graph were not noise, but an artifact of the alias error. This is a .365 second sample rate of 10ms samples.

The rough shapes here (second graph) may be just the relatively slow sample rate .365s considering the minor axis lines are 1 second divisions. Or, it could be aliasing again.

10 minutes of steering wheel heater (from the front harness, so other stuff in the base line), and minute 8-9 in more detail.
 

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Nice work GreyBolt!


It looks like they just running the steering wheel heater at full power for the first 2m45sec, then they modulate power at xx Hz after that.
Looks like the modulation is at a fixed frequency?


If you have the rig in place again... can you run the steering wheel heater for 7-8min, turn it off for 60 seconds then turn it back on again.
I'm curious if it will start on full power for 2min45sec or a shorter period or will it go straight to modulation since the wheel is still relatively warm?


Good stuff here!
 

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Discussion Starter · #13 ·
Nice work GreyBolt!


It looks like they just running the steering wheel heater at full power for the first 2m45sec, then they modulate power at xx Hz after that.
Looks like the modulation is at a fixed frequency?


If you have the rig in place again... can you run the steering wheel heater for 7-8min, turn it off for 60 seconds then turn it back on again.
I'm curious if it will start on full power for 2min45sec or a shorter period or will it go straight to modulation since the wheel is still relatively warm?


Good stuff here!
Thanks, will do.

I just called it a day for now. I took a quick look with a scope, and there is often a 5 Hz (200 ms) waveform, even leading into a step change for the front seat heater. So, that means my last waveforms are aliased too (.365s sample rate, too slow for a .2 second waveform).
 

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Is the steering wheel heater on a thermostat, or just dumb? I wish there was a bit more juice in it during steady-state.--- I like the initial / warmer heat level better. I suspect the seat heaters are dumb, but you can play with the 3-level setting to get what you want.
 

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^ That's one of the things we'd like to find out by running it till reaching a steady state, turning it off for 60 seconds and re-powering it.


If it's on a t-stat it should modulate almost instantly as it's got enough mass to keep warm for 60 seconds unpowered.
If it's just on a timer circuit it will again run for 2m45 sec at full power then modulate after that.
 

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Is the steering wheel heater on a thermostat, or just dumb? I wish there was a bit more juice in it during steady-state.--- I like the initial / warmer heat level better. I suspect the seat heaters are dumb, but you can play with the 3-level setting to get what you want.
I am pretty sure the seat heaters cut back after awhile too. On a recent drive, I had the driver's seat set to three. At some point I didn't feel as warm, and saw two LEDs. I thought perhaps I had bumped it while messing with the radio knob, so I put it back to three, but it did it again later.
 

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Thanks, will do.

I just called it a day for now. I took a quick look with a scope, and there is often a 5 Hz (200 ms) waveform, even leading into a step change for the front seat heater. So, that means my last waveforms are aliased too (.365s sample rate, too slow for a .2 second waveform).

So Nyquist was right?:nerd:


Sorry...I'm a "recovering" EE...
 

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Discussion Starter · #18 ·
So Nyquist was right?:nerd:


Sorry...I'm a "recovering" EE...
I'm a rusty EE, off on other things for some years. As much as I was not going to add to the lab gear, I'm afraid this project takes me over the edge to a new DMM. The 34410A I was using can digitize much faster, but not as a stand alone data logger. The design is almost 20 years old now with relatively slow internal memory.

The new Keithley DMM 6500 looks like it can self data log at much higher rates and even has a built in 10A current shunt for a 10A scale that I could use directly with my home made fuse tap loop, or with the DC current transformer in other places (4-20mA loop). Guess I'm going to have to buy one :) Here it is: DMM 6500
 

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I'm a rusty EE, off on other things for some years. As much as I was not going to add to the lab gear, I'm afraid this project takes me over the edge to a new DMM. The 34410A I was using can digitize much faster, but not as a stand alone data logger. The design is almost 20 years old now with relatively slow internal memory.

The new Keithley DMM 6500 looks like it can self data log at much higher rates and even has a built in 10A current shunt for a 10A scale that I could use directly with my home made fuse tap loop, or with the DC current transformer in other places (4-20mA loop). Guess I'm going to have to buy one :) Here it is: DMM 6500

I would first need to pass such a purchase through the "finance committee" for approval. The "justification stage" would be problematic. >:)
 

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I would first need to pass such a purchase through the "finance committee" for approval. The "justification stage" would be problematic. >:)
I found that if you purchase something of equal value for the "finance committee" it increases the approval chances of my purchase request dramatically :D
 
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