Tuesday, October 05, 2010

What do these "specs" mean?

Power Inverter Specification Breakdown:

What do these “Specs” mean? This is a question that comes up quite often and quite frankly if you do not work in the industry or have some sort of electrical background, can make selecting the right inverter pretty confusing. So let’s talk about the terminology and work our way through the specifications. While reviewing and contrasting the specifications between multiple inverters you will come across some very specific terms as well as some broad ones. Here is a list of terms you may come across while shopping for an inverter.

  • Maximum Efficiency – This indicates how much battery power is lost during the power inversion process.

  • No Load Draw (Switch Off) – This indicates how much power while idle the inverter is drawing with the power switch off.

  • No Load Draw (Switch On) – This indicates how much power while idle the inverter is drawing with the power switch on.

  • Output Wave Form – This indicates what waveform the inverter is producing. Typically, Modified, Square, or True/Pure Sine.

  • Total Harmonic Distortion – Refers to how much “Noise” is emitted from the output of the inverter.

  • Input Voltage – Indicates what the rated input voltage is, or indicates the rated input voltage range.

  • Output Voltage – Indicates what the rated output voltage is and in some cases what the voltage is regulated at.

  • Low Voltage Alarm – Indicates the input voltage at which the audible alarm will sound.
  • Low Voltage Shut Down – Indicates the input voltage at which the unit will shut off.

  • Overload Shutdown – Indicates whether this protection is available. (Yes or No)

  • Thermal Shutdown - Indicates whether this protection is available. (Yes or No)
  • Short Circuit Shutdown - Indicates whether this protection is available. (Yes or No)

  • Reverse Polarity Protection - Indicates whether this protection is available. (Yes or No)
  • AC Back feed Protection - Indicates whether this protection is available. (Yes or No)

  • Transfer Relay Rating – Indicates the current rating for the transfer switch (Not applicable to most standalone inverters)

  • Transfer Relay Time – Indicates how quick the transfer occurs once voltage drops on the AC input.

  • Continuous Output Power – Indicates how much power the inverter will produce continuously.

  • Peak Output Power – Often referred to as “Surge”, Indicates how high the unit will surge for starting heavy inductive loads.

  • Frequency – Indicates how fast the output voltage is flipping and flopping. (in the US 60hz is the standard for all appliances)

  • AC Regulation – Indicates how much deviation from the rated output the unit is allowed.

  • Operating Temperature – Indicates the temperature range in which the unit will operate properly at maximum efficiency.

  • Regulatory Compliance – Lists the UL, ETL and CSA standards the unit meets or is certified to.

  • AC Receptacle Type – Indicates what type of receptacle is installed on the inverter.

    Now that we have identified the terms listed in the specifications of a standalone inverter we can break them down further by looking at an example product page of an inverter.

Product Page Comparison:


The Breakdown:

Maximum efficiency 88% - This is basically stating that the inverter will lose 12% through the process of inverting. In other words, the unit is using 12% of the available battery to operate while inverting. Ideally, you are looking for a unit that has a high efficiency rating. The highest this author has seen is 96%. This unit appears to be a touch below average (90%). You will also find that with higher efficiency comes higher cost.

No-load draw <0.6> – This figure represents that the Cobra 2500 uses less than .6 amps DC in idle with the switch on. You will find inverters that give ratings for the remote on as well as with the remote off. For the most part 99% of the inverters are listing this rating for no load draw while the switch is in the on position. Again, remember the lower the rating the better.

Output Wave Form Modified Sine Wave – This is telling us that the unit produces a modified sine wave.

Input Voltage Range 12V (10.4vdc – 14.4vdc) – The figure represented here indicates that this unit has a voltage input rating for the low end of 10.4 volts DC and a high end of 14.4 volts DC. When sizing your inverter for use with a vehicle you will need to take your vehicles alternator output into consideration when selecting a power inverter. This inverter would work for most vehicles. However, the newer GM vehicles (2007 – Present) produce up to 15.5 volts DC. Just something to keep in mind while sizing your inverter.

Output Voltage Range 115vac 60hz – This Specification is pretty much standard for all inverters used in the US with US appliances. You will not see any deviation from this except on European (230vac, 50hz) inverters.

Low Voltage Alarm 10.5 +/- 0.3vdc – This is when the alarm will sound indicating it is close to shutting down due to low battery. Notice the +/- voltage, this represents the deviation from 10.5vdc.

Low Voltage Shutdown 9.5 +/- 0.3vdc – This is the voltage at which the unit will shut down.

Overload Shutdown YES – This indicates the unit does protect against an overload fault condition.

Thermal Shutdown YES – This indicates the unit does protect against an over temperature fault condition

Short Circuit Shutdown YES – This indicates that the unit will not become damaged from a short circuit in the AC wiring.

Reverse Polarity YES – This indicates that the unit will not become damaged when the DC cables are hooked backwards. This believe it or not occurs fairly often and selecting a power inverter with this protection is a great idea.

AC Receptacles 3 –
This tells us that the unit has three AC receptacles. Also, note that it does not state GFCI. Some inverters will have GFCI protection. Typically this would be found on a marine grade inverter.

Warranty 2 Years – Length of warranty from manufacturer.

Inverter Weight 6.6 Lbs. – Weight of the unit without packaging materials.

Shipping Weight 9 Lbs. – Weight of the unit with all packaging from the manufacturer.

Product Dimensions 10.75"x 9.75"x 3.5" – Physical dimensions of the inverter.

This pretty much covers breaking down a basic inverter specifications chart. You should now have a general understanding of what some of these terms represent and the importance of the specifications. Don’t be intimidated by these terms and should you have any questions after reading this post, feel free to get in touch with me using any of the following methods:

Twitter: @donrowecom (Yes, I respond to our Twitter as well)
E-Mail: jon@donrowe.com
Toll Free: 1-800-367-3019

Important Links for Key Terms:

Inverter - http://en.wikipedia.org/wiki/Inverter_(electrical)
Pure Sine Wave - http://en.wikipedia.org/wiki/Sine_wave
Frequency - http://en.wikipedia.org/wiki/Utility_frequency
Short Circuit - http://en.wikipedia.org/wiki/Short_circuit
Electrical Efficiency - http://en.wikipedia.org/wiki/Electrical_efficiency
Total Harmonic Distortion - http://en.wikipedia.org/wiki/Total_harmonic_distortion