Setting undervoltage and overvoltage protection sensibly

Updated 9 October 2026AmpyLighty

Undervoltage protection (UVP) and overvoltage protection (OVP) switch off an output when the system voltage falls below or rises above a set limit. You set both limits on Ampy and Lighty per load, not as a blanket value for the whole vehicle.

What undervoltage protection does for you

Two things. First, it protects the battery from deep discharge. Second, it protects your devices: motors and compressors draw more current as the voltage drops, to deliver the same power. If you let the fridge keep running with an almost empty battery, you risk a hot compressor.

What overvoltage protection does for you

It keeps voltage spikes away from sensitive electronics. These occur, for example, when charging with a high charging voltage, during an equalising charge of lead batteries or when the alternator is faulty. Devices such as routers, audio systems, cameras or control units often cope with this worse than a simple incandescent bulb.

What happens when it trips

The affected output switches off, and you see the reason in the dashboard. A manual reset activates the output again.

The real trick: switching off in stages

Because you set the limit per load, you can define an order in which things are switched off. Unimportant things go early, important things stay on the longest. For example:

  • Switch off early: inverter, outdoor light, awning, comfort loads
  • Switch off later: fridge, ventilation
  • Keep on the longest: heating, interior lighting, everything that is safety-relevant at night

Instead of everything failing at the same time at some point, you lose what you need least first.

Important with lithium batteries: set the lower limit so that it trips before the battery management system shuts down. When the BMS shuts down, everything in the vehicle goes dark all at once, and the battery usually has to be charged again before it releases. The undervoltage protection is meant to prevent exactly that.

Guide values

The following values are a guide, not a rule. What counts is the data sheet of your battery.

  • 12V system: lower limit typically in the range of around 11.8V to 12.2V under load, upper limit well above the highest regular charging voltage
  • 24V system: double the values in each case

If in doubt, measure it yourself: Ampy shows you the voltage per output live. So you can watch how far it drops under load and set the limit accordingly.

Related questions

Does Ampy work on 12V and 24V?

Both. Ampy detects the vehicle's electrical system automatically, so there is nothing to change.

How is Ampy connected?

The supply goes onto two M6 threaded studs, the loads into lever terminals for up to 4mm²: open, insert, close, no tools needed. The push button wires go into removable spring terminals.

How much current can an Ampy output draw?

24A continuously, up to 32A for short periods, and 120A across all six outputs combined. So even a compressor fridge, an inverter and a parking heater fit on a single output.

Do I still need to buy fuses for Ampy?

Not for the loads connected to Ampy. Every output has an electronic fuse that you adjust instead of replacing.

What happens when a fuse on Ampy trips?

The output switches off and you see it in the dashboard, including the reason. Resetting takes a single tap. If the fuse trips several times in a row, Ampy enforces a short pause so that a genuine fault is not simply glossed over.

Fast, normal or slow: which tripping characteristic should I choose?

The characteristic determines how quickly the fuse cuts out when the current is too high. As a rule of thumb: slow for anything that briefly draws more when it switches on, fast for pure electronics, normal for everything in between. • Choose slow for motors and compressors: water pump, fridge, fan, awning, pop-top roof, inverter. These loads draw several times their continuous current at the moment they switch on, which is completely normal. A fast fuse would trip every time, even though nothing is wrong. • Choose fast for loads without inrush current, such as LED strips, sensors, control units or charging sockets. Here a sudden rise in current is almost always a fault, and then it should cut out quickly. • Normal is the safe choice if you are unsure. A practical tip: if the fuse only trips at switch-on while the continuous current is fine, set it one step slower. Raising the fuse rating instead would be the wrong approach, because the rating still has to match the cable cross-section.

See all questions

Still have questions? We'll help you personally.

Get in touch