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Discussion Starter #42
Hi all, 1st time posting to ask a question.

TDIwyse:

What is the watt rating of the resistors you used?
Would +/-2% tolerance work? You used +/-5% tolerance, no?

And thanks for your libertarian, with a small "l", perspective :)

Thanks.

Based on other GM heated seat module schematics (here's a Cruze one for example that is kinda close to the Bolt's, but not exactly the same: https://www.cruzetalk.com/forum/attachments/gen1-audio-electronics/11993d1363628331-adding-heated-seat-question-seat-heat-electrical-diagram.jpg) I believe the thermistor path, and thus the resistors I added, have 5V applied to it. At worst case if the thermistor shorts out then the 2.2k resistors I'm using would have V^2/R = 5*5/2.2k=11mW. Or if its actually 12V instead of 5V, then worst case would be 12^2/2.2k=65mW. I believe the resistors I used are physically large and rated at 1/2W=500mW which has lots of margin on what it would ever see.

I didn't use high tolerance resistors. These were from my undergrad lab kit from many years ago :)

The seat heating elements were less than 2 ohms as I recall based on my multimeter measurement and their paths would have the 12V switched on/off via the switching FETs to modulate the power going to them to regulate the heat. V^2/R for the seat heating elements is pretty high power when the FET switches are "on", but the thermistor path is low power.

Here is an example "theory of operation" for the cruze seat heater:

Temperature Regulation
When the engine ON, the heated seats will initialize in the OFF state. With each activation of the heated seat switch, the seat heating control module will cycle the temperature setting in the following manner: HIGH, MEDIUM, LOW, and OFF.
The seat heating control module monitors the seat temperature through the temperature sensor signal circuit and the temperature sensor (thermistor) that is located in the seat cushion. The temperature sensor is a variable resistor, it's resistance changes as the temperature of the seat changes. When the temperature sensor resistance indicates to the seat heating control module that the seat has reached the desired temperature, the module opens the ground path of the seat heating elements through the heated seat element control circuit. The module will then cycle the element control circuit open and closed in order to maintain the desired temperature.
 

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@TDIwyse, I have data for you

I used an Omega HH82 dual thermocouple digital thermometer, one thermocouple measured interior ambient, one measured the A** Interface Temperature, typically abbreviated as AIT.

The type of thermocouples used were fast read film type, (Type K), pictured, very low thermal mass for minimal error contribution.

Why not use a thermal camera? Because a thermal image has no relevance to the desired measurement, with a thermal camera you are measuring the surface temperature of a poor thermal conductor being convection cooled. By using the thermocouple and placing it in the back jeans pocket, at the optimal A** to Seat contact position, we can measure the interface temperature or AIT, directly perceived by the driver occupant.

Test conditions and measurements:
The Bolt drivers side seat heater was turned on to high and the temperature was allowed to stabilize for the duration of 2.5 radio airplay rock songs, or about 10 minutes.

Outdoor ambient as reported on Bolt display 40F
AIT = 107.5
Internal cabin ambient 70.5
Subject was a 165Lb male wearing levi 505 jeans.

And yes, I can only run my stock Bolt LT seat heater on high for a very short duration before I need to reduce the power level to avoid the dreaded "seat heater swamp A**" condition that would result. ;)
 

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Discussion Starter #45
@TDIwyse , I have data for you

I used an Omega HH82 dual thermocouple digital thermometer, one thermocouple measured interior ambient, one measured the A** Interface Temperature, typically abbreviated as AIT.

The type of thermocouples used were fast read film type, (Type K), pictured, very low thermal mass for minimal error contribution.

Why not use a thermal camera? Because a thermal image has no relevance to the desired measurement, with a thermal camera you are measuring the surface temperature of a poor thermal conductor being convection cooled. By using the thermocouple and placing it in the back jeans pocket, at the optimal A** to Seat contact position, we can measure the interface temperature or AIT, directly perceived by the driver occupant.

Test conditions and measurements:
The Bolt drivers side seat heater was turned on to high and the temperature was allowed to stabilize for the duration of 2.5 radio airplay rock songs, or about 10 minutes.

Outdoor ambient as reported on Bolt display 40F
AIT = 107.5
Internal cabin ambient 70.5
Subject was a 165Lb male wearing levi 505 jeans.

And yes, I can only run my stock Bolt LT seat heater on high for a very short duration before I need to reduce the power level to avoid the dreaded "seat heater swamp A**" condition that would result. ;)

Thanks for taking the time to do this and reporting.



I don't agree with your assessment about the lack of accuracy with the thermal gun/camera for the condition of extended "on time" of the seat heater and a human sitting in the seat. The temperatures will stabilize even though the seat material is a poor conductor. 25 minutes of riding in the seat with the seat heater on is more than enough time to fully "saturate" the thin leather material and have a stabilized temperature. However, you do need to have an emissivity close to 1 for the thermal gun/camera to give an accurate result. Your LT seat material is likely too far below 1 to give an accurate result based on the emissivity chart link I posted earlier. But leather, as with the seat of the Premiere, is very close to 1, and will thus give an accurate reading.


But I will test this additional measurement approach with a similar method you used to compare to the results I got with the thermal gun and report back.
 

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Discussion Starter #46
...
But I will test this additional measurement approach with a similar method you used to compare to the results I got with the thermal gun and report back.

Just added pics to the photo link showing the same (<0.5 deg off) measured temperature with a thermometer probe placed between my back and the seat and with the heat gun (when done on roughly the same location and immediately after getting out of the seat). Both were between 98 and 99F. I've got to leave in 5 minutes, so I didn't have time to let the seat get up to full temp, but this shows that the heat gun on the Premiere leather seats gives the same results as a thermometer probe...
 

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Here is an example "theory of operation" for the cruze seat heater:
[/I]
It looks like there are two thermistors on the passenger side and one on the drivers side. Am I reading this correctly? If so, do you know why this is?
 

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Discussion Starter #49
It looks like there are two thermistors on the passenger side and one on the drivers side. Am I reading this correctly? If so, do you know why this is?

The schematic was for a Cruze and not a Bolt. I just linked that as an example GM configuration on one vehicle. There are many more examples out on the web for other heated seats from other makes/models, but I couldn't find one for the Bolt. But most of them share similarities with the control theory posted above.



The Bolt has 2 thermistors for each front seat based on my testing. I'm not sure why GM, with the Cruze implementation, would have taken a short cut and just used one thermistor for controlling temps of both heating elements on the driver seat, but I'm guessing it was for cost/simplicity reasons.
 

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Discussion Starter #50
Just added pics to the photo link showing the same (<0.5 deg off) measured temperature with a thermometer probe placed between my back and the seat and with the heat gun (when done on roughly the same location and immediately after getting out of the seat). Both were between 98 and 99F. I've got to leave in 5 minutes, so I didn't have time to let the seat get up to full temp, but this shows that the heat gun on the Premiere leather seats gives the same results as a thermometer probe...

Went out to the car this morning after its been sitting all night. Car's outside temp (garage temp) showed 44F. The thermometer probe inside laying on the seat showed 44.4F. Heat gun measured a very even 45.1F across all the seat surfaces for driver/passenger.


So testing at multiple temperatures has shown a very consistent measurement result with the heat gun method versus thermometer probe method on the leather Premiere Bolt seats.
 

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The Bolt has 2 thermistors for each front seat based on my testing. I'm not sure why GM, with the Cruze implementation, would have taken a short cut and just used one thermistor for controlling temps of both heating elements on the driver seat, but I'm guessing it was for cost/simplicity reasons.
Thanks. I realize the schematic is for the Cruze. I was just trying to understand what I was seeing (so that I can understand the system in general better). Thanks for your thoughts on the reasoning behind what is shown. That helps. :)
 
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Discussion Starter #52
Just added pics to the photo link showing the same (<0.5 deg off) measured temperature with a thermometer probe placed between my back and the seat and with the heat gun (when done on roughly the same location and immediately after getting out of the seat). Both were between 98 and 99F. I've got to leave in 5 minutes, so I didn't have time to let the seat get up to full temp, but this shows that the heat gun on the Premiere leather seats gives the same results as a thermometer probe...
Drove to work this morning so I had more than enough time to get the seat temps up to their steady state temp, and also used the thermometer probe to measure the temp. Added pic to the photo link. With the probe placed in the lower small of my back between my big fluffy winter parka and the seat surface, it was fluctuating between 117-118F max temps. This is very close to heat gun results, although they were a little lower because the surface will cool off quickly when getting out of the seat and turning around to start taking measurements... but if you're quick and accurate with your gun you can get good results :)

So far from 3 of us reporting measured seat temps, it appears the single LT measured result shows seat temps are ~10-15F higher than the 2 reported Premiere seat temps in OEM configuration.

If anyone else could find time to do some measurements, I at least would find it interesting to see if there's a significant variation in max seat heat temps, or if the Premiere's just have lower max heat from the factory.
 

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If anyone else could find time to do some measurements, I at least would find it interesting to see if there's a significant variation in max seat heat temps, or if the Premiere's just have lower max heat from the factory.
Our LT should be out of the body shop today or tomorrow. I’ll do some tests when we have it back.
 
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I’m jumping in late here, but just to add a data point:
17 Primier.
Automatic mode during pre conditions just about removes the ice cube feeling.
Automatic mode during use - useless
3 light manual mode - take about 20 min to really feel warm if the weather is cold enough to want heated seats in the first place.

I previously had a 12 Cruze LTZ and the heated seats in it would indeed become uncomfortably hot after 5 minutes on high in anything but the coldest VA weather (say aroun 0deg F). I miss those seats!

I hadn’t looked at this post before because I can’t really picture myself doing the mod, but now I’m thinking I just might!
 

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Oh, one more thing, about seats not getting hotter for liability reasons. The seatin my wife’s 18 Volt get much hotter than my 17 Bolt. When you precondition that car the seats are noticeably warm when you get in, unlike my 17 Bolt.
 

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Discussion Starter #56
...
3 light manual mode - take about 20 min to really feel warm if the weather is cold enough to want heated seats in the first place.
...
This would be the mode I'm most interested in. Would you be able to take some temperature measurements and reply back? I think we're to the point where we don't need pics, although please add those if you can. However it would be good if at least some discussion of how the measurement was taken, what was the measurement device, and waiting long enough so the seat has time to stabilize at its max temperature.
 

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Discussion Starter #58
Yeah, it kinda looks like that with a very small sample size. But its a VERY small sample size right now.
 

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I would propose that the pattern starting to develop is: Premier = not hot enough seats, LT = hot seats, yes?
I don't have any hard data like temperature measurements to share, but in manual "3-dot" mode the seats in my 2017 Premiere become too hot for me within 5 to 10 minutes and I have to turn them down to the "2-dot" level. I agree that automatic mode is completely inadequate.
 

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2017 Premier on 3 dots. Measured after ~15 mins. Ambient temp was about 28°F.
Seat back = 108°F (42°C)
Seat bottom = 100°F (38°C)

It occurs to me that I took the measurements with a thermal camera, so that's the hottest spot. The average temp would be lower.

Subjectively, I've been ok with "Auto" mode - particularly if I've remembered to precondition. It's like sitting in a seat someone else recently got up from.
The 3 dot setting was noticeably warm, but I wouldn't say hot. After 15 mins there was no need to turn it down.
 
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