Isolated vs Non-Isolated? What DC DC Charger to get.

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:

7 Comments

Bill

Date 11/3/2022

Great information, I now have a much better understanding. Time to verify my installation. Cheers

Ross Lukeman

Date 11/6/2022

Thanks Peter, this is indeed a common question! I think a lot of people get the isolated version because it just sounds better. This includes my students building vans, I show them non-isolated and I see in the photos they have isolated. I'm going to make a bigger deal about this going forward. Great article, thanks.

alan

Date 4/2/2023

Good knowledge here. Thank you! I would like to add that the isolated version can be important for galvanic corrosion. For example a bow thruster in a boat may be isolated from the rest of the dc system with it's own battery in order to reduce the risk of galvanic and also stray current corrosion. In that case an isolated charger would be needed.

Kim Albee

Date 4/24/2023

Peter - thanks for the article. I would love more information about this sentence: On boats it is mandatory for all the batteries to share the same negative. Why is it mandatory on boats? Because they ground to the engine? I initially bought a Renogy DC-DC charger, then found out about the “non-isolated” vs “isolated” and Renogy only makes isolated DC-DC chargers, yet are a pretty big name in battery systems. It’s unclear to me why on boats it is mandatory and what issues arise from using isolated DC-DC charger between starter and house battery bank. Thanks!

Peter Kennedy

Date 4/25/2023

I believe the ABYC requirement to have all the batteries share the same ground is to do with lightning. If you get hit by lightning you want different parts of the boat to already be electrically connected so you don't get lightning within the boat from one part to another.

Henry Stage

Date 5/19/2023

This was very helpful. I have an off-road adventure trailer with lithium house batteries which need a DC-DC charger to protect the truck's alternator from killing itself trying to charge them. But I could not get a good answer on if I needed an isolated or non-isolated one. And you stated very clearly that in a towed application you might need an isolated one. Many thanks!

Andrew Panckhurst

Date 8/20/2023

Thank you, nice and simple, short and sweet explanation.

Doy Lane

Date 8/24/2024

I inherited solar setup in a Nissan NV 2500 that I bought. As far as I tell, neither the starter battery nor the house battery (solar charged only at the moment) are connected to the chassis. I would either need to first connect them both and get a non isolated, or get an isolated, right? Thanks

Date 8/27/2024

In a motor vehicle, the start battery negative is almost certainly already connected to the chassis. I don't see any reason not to also connect the negative of the house battery to the chassis also.

Isolated vs Non-Isolated DC DC Charger?

7 Comments

Bill

Ross Lukeman

alan

Kim Albee

Peter Kennedy

Henry Stage

Andrew Panckhurst

Doy Lane

Peter Kennedy

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