Posted by Peter Kennedy on 10/7/2022 to Battery Chargers
We get asked the question all the time: "Do we need an isolated or a non-isolated DC DC charger?" Well here is the scoop:
The example above shows a non-isolated charger. An example of this kind is the Victron Energy ORI121236140 Orion-Tr Smart 12/12-30A Non-Isolated DC-DC charger. It has three connections, one for the input positive, one for the output positive, and one for the common negative. To use this both the source and destination battery must share the same negative. On boats it is mandatory for all the batteries to share the same negative. In a van or RV it is normal for both batteries to share the chassis as the common negative. So for most applications non-isolated is the one to use.
The example below shows an isolated charger. This could be the Victron Energy ORI121236120 Orion-Tr Smart 12/12-30A Isolated DC-DC charger. There are four connections, two in and two out. The negatives are not common. This is a fairly specialized application and for most purposes there is no need to use an isolated charger. One place where it might be useful is in a vehicle being towed. Because of voltage drop at the connection between the two vehicles the towing vehicle chassis may not be exactly at the same potential as the one being towed, so they are not sharing exactly the same negative. In this case the isolated charger is appropriate.
Not all of the chargers are available in both isolated and non-isolated. What happens if all you want is a non-isolated one but all that is available in your size is an isolated one? An example is the Victron Energy ORI121222120 Orion-Tr Smart 12/12-18A Isolated DC-DC charger which only comes in an isolated version. Well it is easy to convert to non-isolated by wiring the two negatives together as shown below.
Why do they make the isolated ones anyway? It doesn't seem like the example of the towed vehicle would be of enough importance to be worth the trouble. Well they have another application for use as isolated power supplies. If you want to power something from a totally clean power supply that doesn't vary in voltage and doesn't carry electrical noise through from the source and where the voltage can be controlled very precisely then the isolated chargers do a great job. In the programming you can set them up as power supplies instead of chargers. Then they can be used to power sensitive equipment like medical or scientific apparatus or Hi Fi audio systems. The screenshot from the app shown below shows where you can change it from a charger into a power supply. This screenshot is taken from the Victron Connect App.
And finally here is a comparison sheet between two units: