Which DC to DC converter to use?

[Lauren8363]

I am designing my off-grid system for my RV. I’m not sure which DC to DC converters I should be considering, Isolated or Non-Isolated. This is Not a chassis battery (starter), so I am thinking that it should be non-isolated. Everything I have read so far just explains the difference between the 2 types, but the “why” still alludes me.

Any input will be greatly apprreciated

Lauren

 

[Checkthisout]

I am designing my off-grid system for my RV. I’m not sure which DC to DC converters I should be considering, Isolated or Non-Isolated. This is Not a chassis battery (starter), so I am thinking that it should be non-isolated. Everything I have read so far just explains the difference between the 2 types, but the “why” still alludes me.

Any input will be greatly apprreciated

Lauren

What do you need it for?

 

[BlindBadger]

I believe it has to do with whether or not you have a common ground connection between the two battery systems (which I believe acts as a sort of common negative terminal of sorts...a path back to the batteries).

Examples:

• For a Truck camper and it's truck (or a truck and trailer), they are grounded to separate chassis and so you need each side to ground to each side. Camper/Trailer stuff is grounded all back to the camper's battery, truck stuff is grounded all back to the truck's battery and the systems aren't really connected to the same ground chassis. This is where an isolated DC converter helps (each side has a negative that goes back to it's respective side and the two negatives are never really connected to each other directly (all passes through a little transformer I think, which also has a benefit of cleaning up power if you're worried one side or the other has dirty power).
• For something like a Class C or a Class A RV, the chassis is the same on both sides (house/vehicle) and while there's two separate battery systems, they're usually both grounded to the same frame/chassis and you can usually use a non-isolated converter since both sides ground to the same chassis (only one negative terminal on the dc-dc converter) and so you'll often see only a single ground or negative connection or a line that indicates both "negative cables" are connected directly.

Source of some of my info: https://community.victronenergy.com/questions/55727/non-isolated-vs-isolated-orion-tr.html

 

[Reed Cole]

(all passes through a little transformer I think, which also has a benefit of cleaning up power if you're worried one side or the other has dirty power).

What's dirty power? Isn't that only an issue with AC?

 

[BlindBadger]

What's dirty power? Isn't that only an issue with AC?

You’ll run into it sometimes with generators or campgrounds with poor quality connectors, where voltage may not be consistent or not be consistent. It can happen with a faulty alternator on DC as well but I don’t think it’s super common.

 

[12vDC]

I am designing my off-grid system for my RV. I’m not sure which DC to DC converters I should be considering, Isolated or Non-Isolated. This is Not a chassis battery (starter), so I am thinking that it should be non-isolated. Everything I have read so far just explains the difference between the 2 types, but the “why” still alludes me.

Any input will be greatly apprreciated

Lauren

I believe while DC to DC modules are by default converters, you might be referring to a charger instead?

My van battery systems are isolated. I ended up going that way once I finally figured out WTH I was doing. Now its a preference. If there is any one reason, its so that an issue in one system doesnt affect the other regardless of any safeguards.

I never thought I could be stupid enough to short my starter battery with a wrench. I was right, but I did it with a stray cable instead. Welded a washer to the post. I got off easy with no fried circuits. Fireworks were impressive though.

On a different note: The new OrionXS 50A looks like it will be offered only in a non-isolated version (if you study the form factor) if youre a fan of Victron products.

 

[mikefitz]

My van battery systems are isolated.

Where you have a metal body RV or van with multiple DC cable runs its possible faults could make the structure DC live. With an insulated system no fault protection would act. With a DC grounded system the main battery fuse would protect. Thus its best practice to have a house battery connected to vehicle body.

the systems aren't really connected to the same ground chassis

They are when you couple the units together.

As suggested the trailer battery should be connected to metal frame/structure for safety, so a non isolated converter is suitable.

 

[time2roll]

I thought isolation solved a galvanic corrosion issue for salt water boats. Doubt it matters for an RV.

Unless the system is monster consider 12v system. My 675w solar, 2000w inverter, 1200 Ah battery works fine at 12v.