How to compare model ratings with other Combis
Watts vers / VA the truth
The most significant issue to be aware of is how output ratings are massaged to appear better than the competition. You might be excused for thinking that a unit with '3000' written on it, for example, means that it will deliver 3000 watts continuously. This is not necessarily the case when you look at the small print.
Have you never found it strange that the product you want to run (i.e. the hair dryer, washing machine, TV, etc) in their specification have the power consumption in watts, yet the inverter/ generator companies give you their rating in VA, and when you put your 1000 watt product on a 1000 VA inverter it does not work because in the small print you find out that the 1000 VA inverter is only 700 watts for 10 mins then it over heats, this simply cannot be right.
In the eyes of the unknowing consumer, rating a power product in VA is a simple way of using meaningless figures to confuse and make performance appear better that it really is. Unfortunately this practice is still allowed in Europe (European standards committees are looking into this practice) unlike the USA where there are recognised standards (eg ABYC) and you can be sued for publishing misleading information and incorrect ratings. The only true rating, without confusion, is in watts, using a simple resistive load with unity power factor, such as a electric heater / standard light bulb, etc. This method gives a lower correct figure, however it is not what the marketing teams involved in promoting power products want to see.
Take, for example a 3000 Victron Multi that is perceived by the public to be 3000 watts continuously rated. If, however, you read the Victron specification for watts at 40degC the actual power is 2000 watts. The Sterling 2500W Combi delivers 2500 watts which in fact makes it a more powerful unit. This distortion is not limited to Victron, unfortunately most, if not all, the European manufacturers push model figures to the realms of fantasy in spiralling competitiveness and in order to confuse and impress the public who believe that these figures are actual continuous power rating.
To ensure you are getting value for money you have to ensure compare the true continuous power in watts at 40degC. Companies like Mastervolt do not even publish this figure, I can only assume, is through embarrassment. (Not available on their specification sheet on 12 Aug 2008.)
Furthermore, the effects of temperature and the duration of duty (i.e. how long a load is maintained) can also be used to manipulate ratings. It is much harder for a unit working in 40degC ambient temperature than in 25degC, just as it is harder to run at a higher load for extended periods. So a unit rated for short periods at a cooler temperature will also appear more powerful.
To illustrate, taking data published by Victron Energy and Mastervolt, the following comparison can be made:
||Public perceived power
||Tru Cont. Watts @ 40degC
|Victron Phoenix MultiPlus 12/3000/120
|Mastervolt Mass Combi 12/2500-100
|Sterling Pro CombiS or Q 12/2500
|Victron Quatro 12/5000/120
||12 v 3000Watts
|Sterling 3500 combi
The simple truth of the matter is VA means nothing, if you want to know how much power your inverter is going to give you then ask for the rating in watts at 40degC , all the other ratings should be kept for the comic books where they belong. ProCombi has the lower value in the model name but, in fact, is the more powerful of the bunch when like for like ratings are compared making it even better value for money than you thought! With a Sterling unit you get what you think you should be getting, and it does what it says it does on the box.
The sooner ratings have a legally recognised standard like the U.S.A. then the better for everyone.