Posted by kaffelogic on August 6, 2021

“The Kaffelogic Nano 7e is the same product as the Nano 7. The only difference is that it comes fitted ex-factory with a 220-240v element and with CE certification.”

What does this actually mean?

Ok, we’re going to get just a wee bit technical here. If you remember Ohms law from high school physics class you will know that the power delivered by an element is V2/R. This means that the power delivered by a heating element is very dependent on the supply voltage V, R of course being the resistance, a constant property of the element.

Normally the precise amount of power doesn’t matter. When you put an electric kettle on to boil you don’t stand there with a stop watch timing it. But when you put your Kaffelogic on to roast it does keep time to the second. Coffee is sensitive to the last second when it comes to heat. So let’s look at some numbers.

The Nano 7 is fitted with a 40Ω element (that’s R in the above equation). It was designed for the Australian-New Zealand market where the typical mains supply voltage is 237-240V. This means power between 2372/40 = 1,404 Watts and 2402/40 = 1,440 Watts. Depending on where you plug it in, whether you use an extension cord or not, how far the plug outlet is from the main board, and so on, the voltage you actually get in Australia and New Zealand can be as low as 228V. That’s 2282/40 = 1,300 Watts. This explains why the Nano 7 is rated at 1300-1400 Watts. The maximum amount of power that it will draw is somewhere in that range depending on supply voltage. Most of the time it draws less, but the absolute maximum will be in that range so long as the supply voltage stays in the range 228V to 240V.

When you roast coffee, the Nano 7 draws as much power as required to keep the temperature following the profile.  Often this is between 900 Watts and 1,100 Watts. However, if it needs more it will take it – up to a point. That upper limit is V2/R. Once that limit is reached the temperature will no longer follow the profile. Also the power being delivered will sit at the maximum.  This is noticeable on the power log as a totally flat line. We call this flat lining. Here is an example of flat lining at 1,506 Watts on the black line (power line).

In moderate cases the roast finishes a little late and the coffee still tastes great. In more severe cases the roast never reaches target temperature, times out early or late depending on the profile, and the coffee tastes terrible. It’s pretty important that roasts do not flat line, which is why profile designers need to pay attention to how much power the roaster is drawing in order to follow the profile line.

There are other things going on too. Cold air uses more power to heat than warm. Air pressure also makes a difference, so does humidity. So any one person roasting on a profile might see a difference in power used when comparing to another person roasting in potentially a different climate or season. (Reported power is adjusted for ambient air temperature, which is why in warmer environments more power is reported. When starting from a higher temperature the beans can be got hotter with the same amount of electricity and the Nano 7 adjusts for this. The above example is a roast that took place at an ambient temperature of 7 deg C above the profile's 18 deg C starting point, and the power has been normalised from 1,450W to 1,506W accordingly. The roaster is actually drawing 1,450W from the supply.) 

All that leads to one very important number: all official Kaffelogic profiles are designed to need no more than 1,200 Watts in typical conditions. This gives us a ‘spare’ 100 Watts beneath the 1,300 Watts lower rating figure. Without this 'spare' variations in ambient temperature and/or humidity would sometimes cause roasts to fail.

If you are confident that your power supply is good you can usually get away with things like really cranking up the fan speed or significantly increasing the rate of rise. In some parts of Australia people are typically getting 245V-250V at their plugs, which pushes the power available from the element up to 1,500 Watts or more (before normalisation). Potentially this enables the Nano 7 to be pushed beyond its rated design limits and follow what we would call ‘extreme’ profiles. More about that later.

Enter the Nano 7e.

Different countries have different voltages. It’s a historical thing – a tale of colonization and the spread of technology. To keep a long story short (a book could be written about it) some countries have a typical voltage of 240V, many European countries have 230V, and a small number of countries have 220V. It’s only a small number of countries, but let’s do the math: 2202/40 = 1,210 Watts. At 220V we have only 1,200W and so have lost that 100W buffer. In reality some roasts will flat line for our customers in these countries.

The solution is to switch to a 35Ω element. This boosts the available power at the bottom end of the voltage range to 2202/35 = 1,383 Watts.

The only change is the length of the element wire. Nothing else is different.

With a 35Ω element you have a Nano 7e. The Nano 7e continues to draw as much power as it needs to follow the profile, but when supply voltage sinks low it will have extra buffer before it flat lines. It will roast successfully and consistently in 220V countries. This explains why it is rated for 220V when the Nano 7 is not rated for lower than 230V .

What about the top end? I have already explained that when supplied with 245V the Nano 7 could be pushed to 1,500W. The Nano 7e with the same supply voltage could be pushed to over 1,700 Watts. Now we are melting plastic and burning out elements. This is why the firmware that runs both the Nano 7 and 7e stops drawing more power when it gets to 1,450 Watts (just over the rated maximum). This keeps the roaster safe and within its rated power. It prevents the Nano 7 being pushed to 1,500W and the Nano 7e being pushed to 1,700 Watts.

To summarize, if you have a supply voltage of 230V or 240V both Nano 7 and 7e will behave identically. Neither model has any advantage or disadvantage over the other at these voltages. If your supply voltage is 220V the Nano 7 will sometimes flat line, whereas the Nano 7e will tolerate this lower voltage. An 'extreme' profile is always at risk of flat lining on either model depending on ambient conditions.

Converting a Nano 7 to a Nano 7e is simply a matter of changing over the element. Converting may be useful if you are moving to a county with 220V (or if you are experiencing flat lining at around 1,200W in a country with 230V). Neither element will enable more than 1,450W to be drawn, so converting will give no advantage in a 240V country, and usually no advantage in a 230V country.

Chris Hilder
CEO, director of product development
Kaffelogic Ltd

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