We recently had a question from an audience member on EDN regarding how cordless/battery-operated power tools might behave at higher altitudes. This question came out of an article by Dave Norton at TDK-Lambda Americas, entitled, How does altitude affect AC-DC power supplies? Dave and I did some more research and here is what we found:
Dave Norton: The high altitude mining guys are concerned about getting dust out of drill holes apparently due to a reduced number of air molecules to carry the dust away.
I would say that since many portable power tools are now using brush-less DC motors the arcing of the brushes to the motor commutator will no longer be an issue. AC motors using brushes would certainly arc more and that would cause a shorter life of the brushes and commutator.
There is the issue of cooling the motor and the semiconductors in the motor control circuit, be it DC or AC which may have them run hotter and hence decrease the life of the bearings and the components. If they relied on grease-less bearings, like PTFE, that might change things a little.
So probably power tools would have a shorter life at high altitude.
I did notice some comments to the EDN article regarding vacuum being a better insulator.
Steve T.: I also delved deeper and found the following1,2:
It seems that the reduced air density at high altitudes and cosmic rays are the prime concerns for commercial-off-the-shelf or COTS electronic components. In Reference 1, a laptop was the object tested. In a laptop, the CPU and the memory, as well as the chipset between the CPU and the computer’s I/O devices are the prime ICs that were most affected. First, air density reduction affects the thermal management system which subsequently reduces the cooling of electronic devices. Secondly, Cosmic rays can cause soft failures in electronics. This study was done at 35,000 feet max altitude and 20 degrees C nominal.
Let’s look at the power supply. The main effect here at high altitude is reduced efficiency of convection-based heat-sinking architectures due to a decrease in air density which in turn reduces the mass flow of the forced air over the heat sinks. The CPU and some other elements will see an increase in temperature due to this. Thermal calculations must be done in the early design phase to account for this.
The battery is usually Lithium Ion and there may be safety concerns here. Right now there are problems with many of these batteries above 35,000 feet
Electrolytic capacitors will experience end seal bulge at high altitudes because the atmospheric pressure is lower than the internal capacitor pressure.
A Liquid Crystal Display (LCD) is affected by both the lower temperatures and air pressure changes at high altitudes. The liquid crystal itself will have lower viscosity at lower temperatures which leads to a longer response time in the display. The display may also exhibit lower contrast at lower temperatures and reduction of the backlight lifetime. Cells may short out and fire and explosion is possible and has happened.
Solutions here are usually redundant systems and/or Rad Hard ICs. See Reference 2
Image courtesy of Reference 2
Let’s look at Cosmic rays first. Cosmic Ray density increases in direct proportion to altitude increases. It was observed that flex cracking occurs as a root cause of failure here.
Also take a look at Jonathan Harris’ Space and Radiation blogs on Planet Analog, especially in References 3 through 9 below.
1 Failure Mechanisms in Electronic Products at High Altitudes, N. Blattau, C. Hillman, CALCE Electronic Products and Systems Center,
2 Deploying Commercial Electronics at High Altitude, Atrenne Integrated Solutions
3 A Quick Overview of Radiation Effects
4 Total Ionizing Dose (TID) Effects with High Speed ADCs
5 Single Event Effects (SEEs) with High Speed ADCs: Single Event Latch-up (SEL)
6 Single Event Effects (SEEs) with High Speed ADCs: Single Event Transient (SET)
7 Single Event Effects (SEEs) with High Speed ADCs: Single Event Transient (SET), Part 2
8 Single Event Effects (SEEs) with High Speed ADCs: Single Event Upset (SEU)
9 A Quick Overview of Radiation Effects