I know several of you have done quick checks on the temperature a V1 reaches under normal circumstances. However, I wanted to determine just how bad things can get. Saturday I instrumented an old Valentine 1 and left it in a closed vehicle parked in direct sunlight for the day. It got way hotter than I expected. By the way, the V1 was not powered up.
Testing Details
I moved the vehicle into the sun around 9:10am, placed the detector on the windhield, positioned the cabin temperature thermocouple and then closed the windows and doors. The weater stripping was flexible enough to route the thermocouple leads between the window frame and roof. The test was stopped at 15:30 due to shade from nearby trees. However, maximum temperatures had already been reached by that time.
Results and Discussion
The TC location inside the V1 case reached a max of 175F, the bottom of the case reached 171F and the air in the car near the roof reached 145F. A graph showing the temperature variations with time is included below.
The V1 maximum temperatures were significantly higher than I expected and, recall, this was for a white vehicle. Note, the interior temperature of the V1 reached a value 30F higher than the interior temperature of the car. Of course, the V1 is in “direct” sunlight (the windshield absorbs some of the solar radiation) and sees the solar radiation heat load. The V1 heat loss will be primarily due to convective cooling of the case by the 145F cabin air and infrared radiation to the surroundings. Please note, the V1 uses a case that is roughly sealed. There are no ventilation slots to promote cooling of the interior like in some other brands. Of course, even higher temps may be expected in a hotter location.
A word of caution, if you try a similar test don’t attempt to take the V1 off of the windshield barehanded when it’s this hot.
I realize there may be concerns about the accuracy of these results, so I’ve included a discussion of possible sources of error (at least those I thought of) in a section below.
Technical Stuff in case Anyone is Interested
The thermocouples used were fine-gage (30 AWG) type K. A fine gage thermocouple is best here to minimize the “heat sink” effect that can lead to false readings when thermocouple wire is used that is too thick. The thick wire can essentially conduct heat away from the junction. In addition, Special Limits of Error thermocouple wire was used that is accurate within +/- 2.0F. (More on this later.)
Temperature measurements were taken using the thermocouple input on a Fluke 189 true RMS multimeter. Assuming a stable ambient temperature within +/- 1.8F for the multimeter, the accuracy for this input is +/- 1% of the reading plus 1.8F. This accuracy limitation could lead to a temperature reading error of up to 3.5F just from the multimeter alone.
I was uncomfortable with the potential error imposed by the thermocouple accuracy limits combined with the multimeter accuracy limits so I checked the accuracy of the multimeter/thermocouple system for each of the thermocouples using a boiling water bath and an ice bath. Compensating the National Weather Service barometric pressure for altitude gave a predicted boiling point temperature of 209.9F. Of course, the temperature of an ice bath should be 32.0F.
The table below compares the correct boiling and freezing temperatures with the values obtained from the thermocouples used in the above testing. Thermocouple I = Inside the Case TC, C = Case Bottom TC, and A = Air temp in the cabin TC. All temperatures are within 1F so I’m not going to worry about thermocouple or meter inaccuracies.
Another inaccuracy can come from the cold-junction-compensation circuitry within the multimeter. For this circuit to work properly the multimeter temperature should remain fairly constant. In my case I kept the multimeter outside in the shade. When making a measurement I tried to keep the meter shaded from the sun as best I could. Even so, this effect may have led to an inaccuracy of a degree or two. All in all, I’m confident the values presented above are easily within 3F of the actual temperatures reached.
Testing Details
- Date was 7/11/2020, location central Alabama, elevation 1,000 feet and the car was parked on grass. Parking in an asphalt parking lot may have given higher temps, but I didn’t want to suffer that much.
- The weather was sunny with a slight haze. There was a 15 mph breeze and the ambient temperature reached a high of 91F.
- Vehicle was an 2014 Audi Q5, Ibis White with Pistachio Beige interior (who comes up with these names?), panoramic sunroof with shade not pulled.
- Detector: Old Valentine 1 Gen 1, last 4 digits in SN 0430. This is the “thick” model with lidar diode receiver below the rear horn. Hardware version 1.7. (I didn’t want to use a current model for this test.)
- Detector location. Mid-height on windshield in direct sunlight.
- Temperatures were measured in three locations:
- Inside the V1 case. I opened the case, fed a fine-gage thermocouple through the RJ11 socket and attached it to an integrated circuit beneath the horn using Kapton tape. (See photo below.) Of course, I closed the case back up before the test.
- Bottom center of the case. A thermocouple was attached here using Kapton tape. (See photo.)
- Inside the car approximately 2 inches from roof but out of direct sunlight. Used to measure interior air temp in the car.
I moved the vehicle into the sun around 9:10am, placed the detector on the windhield, positioned the cabin temperature thermocouple and then closed the windows and doors. The weater stripping was flexible enough to route the thermocouple leads between the window frame and roof. The test was stopped at 15:30 due to shade from nearby trees. However, maximum temperatures had already been reached by that time.
Results and Discussion
The TC location inside the V1 case reached a max of 175F, the bottom of the case reached 171F and the air in the car near the roof reached 145F. A graph showing the temperature variations with time is included below.
The V1 maximum temperatures were significantly higher than I expected and, recall, this was for a white vehicle. Note, the interior temperature of the V1 reached a value 30F higher than the interior temperature of the car. Of course, the V1 is in “direct” sunlight (the windshield absorbs some of the solar radiation) and sees the solar radiation heat load. The V1 heat loss will be primarily due to convective cooling of the case by the 145F cabin air and infrared radiation to the surroundings. Please note, the V1 uses a case that is roughly sealed. There are no ventilation slots to promote cooling of the interior like in some other brands. Of course, even higher temps may be expected in a hotter location.
A word of caution, if you try a similar test don’t attempt to take the V1 off of the windshield barehanded when it’s this hot.
I realize there may be concerns about the accuracy of these results, so I’ve included a discussion of possible sources of error (at least those I thought of) in a section below.
Technical Stuff in case Anyone is Interested
The thermocouples used were fine-gage (30 AWG) type K. A fine gage thermocouple is best here to minimize the “heat sink” effect that can lead to false readings when thermocouple wire is used that is too thick. The thick wire can essentially conduct heat away from the junction. In addition, Special Limits of Error thermocouple wire was used that is accurate within +/- 2.0F. (More on this later.)
Temperature measurements were taken using the thermocouple input on a Fluke 189 true RMS multimeter. Assuming a stable ambient temperature within +/- 1.8F for the multimeter, the accuracy for this input is +/- 1% of the reading plus 1.8F. This accuracy limitation could lead to a temperature reading error of up to 3.5F just from the multimeter alone.
I was uncomfortable with the potential error imposed by the thermocouple accuracy limits combined with the multimeter accuracy limits so I checked the accuracy of the multimeter/thermocouple system for each of the thermocouples using a boiling water bath and an ice bath. Compensating the National Weather Service barometric pressure for altitude gave a predicted boiling point temperature of 209.9F. Of course, the temperature of an ice bath should be 32.0F.
The table below compares the correct boiling and freezing temperatures with the values obtained from the thermocouples used in the above testing. Thermocouple I = Inside the Case TC, C = Case Bottom TC, and A = Air temp in the cabin TC. All temperatures are within 1F so I’m not going to worry about thermocouple or meter inaccuracies.
| Correct Temp (F) | Reading from Thermocouple I (F) | Reading from Thermocouple C (F) | Reading from Thermocouple A (F) |
209.9 | 209.6 | 209.1 | 209.5 |
32.0 | 31.6 | 32.0 | 32.0 |
Another inaccuracy can come from the cold-junction-compensation circuitry within the multimeter. For this circuit to work properly the multimeter temperature should remain fairly constant. In my case I kept the multimeter outside in the shade. When making a measurement I tried to keep the meter shaded from the sun as best I could. Even so, this effect may have led to an inaccuracy of a degree or two. All in all, I’m confident the values presented above are easily within 3F of the actual temperatures reached.
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