Current Setting on a Portable Charger: What Are the Six Steps For?

When people choose a portable charger they mostly look at power: how many kW? Yet in daily use the feature that really does the work usually sits somewhere else — being able to set, step by step, the current the unit will draw. Thanks to it the same unit works both on a household socket with a weak fuse and on a three-phase industrial socket. Below we have gathered what the steps mean, how many kW each one gives, and when you should step down.

What does current setting mean?

In AC charging it is not the car but the charger that decides how much current will be drawn. The unit keeps sending the car a signal saying "you may draw at most this many amps from this run", and the car obeys that ceiling. The current setting lets you change that ceiling. Lowering the power does not break charging, it only slows it down — and in most situations that is exactly the right thing to do.

How many kW do the six steps give?

On the Pro Mobile 2 the charging current is set in six steps: 6, 10, 16, 20, 25 and 32 amps. On a three-phase socket each step corresponds roughly to the following (it can move by a few hundred watts with the grid voltage):

On a single-phase run the same current gives roughly one third of the power: 16 amps on a single phase makes 3.7 kW and 32 amps makes 7.4 kW. That is why Mini Mobile works between 2.3 – 3.7 kW with its two steps of 10A/16A, and Mono Mobile between 3.7 – 7.4 kW with its two steps of 16A/32A.

Why would you step down?

Stepping down is not a shortcoming, it is a tool. It is used most often in these situations:

• The wiring is weak or old: the cross-section and the fuse of the run cannot carry a high current continuously.
• The run is long: once an extension cable comes in, resistance rises, voltage drops and the cable heats up.
• The socket is shared: if a heater, an oven or workshop equipment sits on the same run, the total load can trip the fuse.
• Hotels, campsites, holiday resorts: when you do not know the capacity of someone else's installation, starting on a low step is the safest approach.
• Charging from solar: by limiting the current to match production you can reduce what you draw from the grid.
• The plug is getting warm: heat you can feel by hand is the clearest sign that the run cannot carry that current continuously.

Why would you step up?

The only reason to go up is time. Once you are on a suitable industrial socket, moving to the full step shortens charging noticeably; that is what lets one unit serve several vehicles from morning to evening in site, fleet and service use. But the ceiling is not only in the unit: the real limit is whichever is lower, the capacity of the run or the car's own AC charger. A car whose onboard charger is 11 kW takes 11 kW even on a 32 amp socket.

How do you choose the right step?

• Find out the fuse rating of the run that feeds the socket; the step must stay below that value.
• Check whether other loads sit on the same run; if they do, go one step further down.
• Start the first charge on a low step and check the plug and the cable by hand after half an hour.
• If there is no heating, move up one step and repeat the same check.
• If you need a permanent answer, think of a fixed unit rather than patching the run; a dedicated circuit is the safest route.

The relationship between the fuse and the step

Charging differs from the other loads in a house at one point: it lasts hours rather than minutes, and the current stays almost constant throughout. That is why the number written on the fuse is not the current that can be drawn continuously; choosing a step close to it makes the fuse trip over time. The practical rule is to stay one step below the fuse rating of the run — on a 16 amp run you pick the 10 amp step rather than 16.

How many steps does each Bemis model have?

This is what makes the Pro Mobile 2 the flagship of the portable range: six steps make fine adjustment to the capacity of the run possible, and because the setting can also be made from the phone you do not have to walk over to the unit. So the same unit can run at 10 amps on a weak socket at home during the week and at 32 amps on an industrial socket on site at the weekend.

How much longer does charging take on a lower step?

Taking a 60 kWh battery from 20% to 80% needs roughly 36 kWh of energy. On a three-phase run that job takes about 1 hour 40 minutes at 32 amps, about 3 hours 15 minutes at 16 amps and about 5 hours 15 minutes at 10 amps; once losses are counted in, these times stretch somewhat. If you park the car overnight, a lower step costs you nothing in practice — the car is full again in the morning.

In short

• The current setting changes the current ceiling the unit reports to the car; it does not break charging, it slows it.
• You step down on weak runs, long extensions, shared sockets and unknown installations.
• The step should stay one notch below the fuse rating of the run.
• The real ceiling is set not by the unit but by whichever is lower, the capacity of the run or the car's AC charger.
• The Pro Mobile 2 offers six steps and can also be set from the app; Mini Mobile and Mono Mobile have two steps each.