Fuel for Thought

Auxiliary Power

By Greg Huggins
Posted Mar 13th 2023 5:44AM

Not all trucks on the road have some type of APU (Auxiliary Power Unit). Those that do have an APU on their trucks use them to power appliances in the sleeper like microwave ovens or refrigerators. They also use them to charge devices such as laptops, tablets and cell phones or truck batteries. They are mainly used for creature comforts like climate control when taking a break. Having heat or air conditioning available when trying to rest is a definite bonus to having some sort of APU. 

APU or Auxiliary Power Unit does not mean only having a ThermoKing or Carrier Comfort Pro power unit. While there are several brands on the market these days, these two brands seem to dominate the truck market. They both have their pros and cons. While the ThermoKing unit is much quieter than the other (the Carrier unit is generally much louder than a ThermoKing (TK)), the Carrier unit has an actual generator built in where the TK unit uses an alternator and inverter. Another difference between the two are the way they handle heating and cooling. The Carrier uses a heat pump in the form of an HVAC box that is mounted under the bunk, while the TK unit has an A/C compressor mounted on the engine and the evaporator mounted under the bunk. The TK unit also uses a separate heater unit mounted under the bunk. Both units have a condenser and fan mounted externally. 

I would venture to guess that most trucks in the US that have an APU, use a diesel fueled APU like the two mentioned above.

There is a growing market for solar powered APU units. These utilize solar panels and battery banks (multiple batteries) to hold the power generated from the solar panels and then with the addition of an inverter, that battery power power is used for AC power for the sleeper appliances.

There is also a market for eAPU users. Electric APUs do not use a separate diesel engine to  provide power but rather they consist of a battery bank that charges when the truck’s main engine is running. Therefore, while you drive, your truck’s alternator charges the eAPU (batteries) for use when you park. 

These APUs noted above can range from $10,000 - over $16,000 when new (including installation), they can be expensive to repair and costly to maintain at times. Some parts can be found at local auto parts stores or online, but many parts are only available at their respective dealerships and can be quite expensive, especially if you have to factor in labor costs for installation (if you are unable to perform the work yourself), as well as the downtime while your truck is in the shop. 

Then there are the inventive, creative truck owners who seek alternatives to commercially available APUs. Their reasons for finding alternatives are as varied as the drivers themselves. It could be they were motivated by cost, past experience with an APU that was troublesome, or just to see if it could be done better in a different way.

For me, I sought a better alternative to a Carrier Comfort Pro APU. I currently have the unit installed on the truck, it works well and with regular maintenance, it has been relatively trouble free. Fuel filters, oil filters and air filters are easily sourced from just about any Napa store. The alternator/fan belt can also be found at most auto parts stores. The generator belt though, I have only found at the dealerships. My main reason for looking for an alternative to my APU is the noise level. As stated earlier, the Carrier unit can be quite loud. I was looking for a quiet(er) alternative and I have found it. I am not a fan of solar (yet) as it has its obvious limitations and I didn’t want to maintain a box full of batteries or idle the truck to supplement the solar charging system. The eAPU sounds good until you factor in that you will have to idle the truck when on extended rest breaks, especially in extreme heat or cold (that seems to defeat the purpose in my mind, if I still have to idle the truck) and there is still the battery maintenance and weight.

After much research, I decided fossil fuel was still the best choice for me. This is not revolutionary by any means, but as you will see in future articles, it definitely is a viable alternative to add to the list of APU options. More on my “new” APU coming soon.

Necessity... the mother of invention. 

- Plato

See you down the road,