question

death2allchavs avatar image
death2allchavs asked

Non Isolated DC - DC Charger Cable Sizing

Hi Guys,


I'm converting a Mercedes Vario 814D bus into our dream camper. I have a question regarding wire sizing for Non-Isolated 24-12 DC Charger.

When sizing cable for the isolated version im assuming you need to account for the entire cable run from Starter Battery to Orion and back to the Starter battery. Which would be around 14m for the bus.

As I am using the Non Isolated version, there is only going to be a positive from Starter Battery to Orion as the ground will be connected to the Lynx Distributor.

How would I size the cable gauge taking this into account?

Also what's the max amps I have to account for when sizing the cable, is it the continuous output current (30A), maximum output current (45A) or the short circuit output current (60A).

The manual states to use a 60A fuse as near to the Starter Battery as possible and also I will be using a 60A fuse where it connects to the Lynx.


Any advise would be great.

Paul

battery chargingorion-tr smart
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3 Answers
mvas avatar image
mvas answered ·

Add together ...
A) The red cable length from the 12v Starter Battery to your Charger PLUS
B) The red cable length from your 24v Battery Bank to your Charger.
Then see the "Minimum Cable Gauge" chart chart your manual.
The wire must be sized per the amps of the fuse.
The continuous, maximum and short circuit amps are irrelevant there.
You are allowed to use a larger size for wire vs the fuse amps rating.
A larger size wire can reduce the voltage drop, if needed.

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kevgermany avatar image
kevgermany answered ·

Is this a 12V starter and 24V leisure setup? Your Orion description suggests 24V starter/12V leisure.

Fuses are for cable protection.

Size cables according to the individual currents. Also aim for a voltage drop of less than 3% at max current. Fuse must blow before cable current rating is exceeded.

Although you're earthing the neg through the leisure battery, the current still needs to return through to the starter/alternator, so base voltage drop on 14m.

Input cable to Orion must be sized for max input current, not output current.

Both cables to leisure battery should be sized for max output current and voltage drop.

If there's a conflict between sizes for current and voltage drop, use the larger size.

Fuse the output positive cable to the leisure battery at the leisure battery.

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death2allchavs avatar image
death2allchavs answered ·

Good morning,

The Mercedes Vario has a 24V starter battery system and alternator so the Orion is a 24/12 to drop the voltage down to the 12V leisure battery for charging.

The + cable from starter battery's to the Orion would be carrying 24V for approx 7M.

There would be a short run then off less than 0.5m to the Lynx.

The starter battery system is comprised of two 12v 140ah batteries connected in series. Would a 60amp fuse be sufficient at the starter?

I could work it out if both batteries systems were 12v and I was using a isolated Orion with two cables going to each battery. But this 24v to 12v is confusing me.


Any help is appreciated


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