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lundy asked

Orion-Tr Smart Charger 12-12 30 Isolated Input Negative Connection

Hi all, newbie here, I am currently attempting to install a 12-12 30 Orion-Tr Smart Charger Isolated into my 2012 Mercedes Sprinter Van, using the charger to take current from my van starter battery and pushing it to my 2 100AH Lithium Ion house/leisure batteries.

I am wondering if I need to be making my Input negative connection directly to the starter battery negative terminal or if I can be grounding it to the chassis, and if I can ground it to the chassis if it matters where that chassis ground is (closer or further from the starter battery). I am looking to minimize voltage drop in the circuit for best performance delivering a charge to my house/leisure batteries.


I called Dragonfly Energy (Battleborn) energy and they recommended connecting directly to the negative starter battery post, and this seems in accordance with the orion install instructions provided with the unit. They also mentioned grounding to the chassis instead of the starter battery stud could result in issues.


However, after some research on this form and others, I am getting conflicting information on the topic. There are other posts on this and on Sprinter Forum and this site that recommend either installing to the factory ground stud underneath the driver seat box or a separate ground.

Ex.

  1. https://sprinter-source.com/forums/index.php?threads/102362/
    1. Mentions Mercedes Upfitter guide recommends against connecting directly to negative post for interfering with other electronics. Action recommended: Ground to Chassis stud under seat post
  2. https://sprinter-source.com/forums/index.php?threads/86193/
    1. Battle Born Cited: "You are able to wire the isolated version with a chassis ground for the input negative"
      1. This one is interesting because this is different that what was recommended to me when I called Battleborn.
  3. https://community.victronenergy.com/questions/51355/common-ground-connection-with-isolated-dcdc-charge.html
    1. Cites grounding will work on isolated version

Given the above context, I find it confusing with the seemingly conflicting install guidance. Could anyone shed some light over why or why not I would connect the input negative for the orion to a ground vs connecting to starter battery stud. Tradeoffs grounding near my leisure batteries (I created a ground in the rear for this system) vs running cable back to the factory ground stud closer to the starter battery? If grounding to the rear, how does that affect my calculations for AWG sizing (if i can cut wire run by grounding to the rear, can I run smaller AWG since the "run length" is shorter?) Thanks so much for the consideration!


orion-tr smartGrounding
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Sarah avatar image
Sarah answered ·

My two questions would be: 1) was it a deliberate choice to purchase the isolated model - if so why; and 2) are the house batteries grounded to the chassis if so how and irrespective of the grounding what is the reasoning for this choice. (A valid answer to these questions is that you are not sure). Also it would help to know how you are currently charging the batteries and to what degree this is working for you. Lastly, I am assuming you have ‘drop-in’ batteries and thus do not require the use of an external BMS - please confirm.

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lundy avatar image lundy commented ·

@Sarah Answers to your questions below:

  1. It was not a deliberate choice. At the time when I purchased the charger I was mostly following the lead of someone who I was working with at Battleborn to set up the system. The isolated unit is what they tossed in my cart. It was also the same unit in a guide I have been following for my whole setup as my electrical understanding is minimal.
  2. The house batteries are grounded to the chassis on a 2-3ft. 2/0 wire going from the negative busbar (using a lynx distributor) side via a 5/16 hole I drilled in the side wall of the van with exposed metal and a star washer to dig into the metal. Reasoning for the choice was because it listed to do so in the guide I was following, but otherwise I do not know why I am grounding my house/leisure batteries (I know, probably not a great reason!): https://www.explorist.life/2000w-inverter-200-400ah-lithium-200-to-700w-solar-camper-wiring-diagram/
    my setup resembles the diagram there almost to a t.

I am not currently charging the batteries with the Orion, or any other source. What spurned this post was I realized I was going to need much bigger cable than 6awg to make the run from the starter battery to the orion (opposite corner of the van) as at the run length (approx. 40-50 ft. round trip, 20-25 one way) I would need closer to 1-2AWG to prevent significant voltage drop which got me thinking about if I am grounding at the front could I not just ground at the rear and get away with a smaller AWG on the positive lead.

I believe there are 'drop-in' as you say, they are Battleborn 100ah Lithium Ion Batteries with a BMS built in: https://battlebornbatteries.com/product/200ah-12v-lifepo4-heated-battery-kit-2-batteries/

Thanks so much for your consideration, I am trying to further my electrical understanding through this whole process so I greatly appreciate it :)


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Sarah avatar image Sarah lundy commented ·
I can understand the confusion. There are lots of variables depending on whether you have an isolated or non-isolated DC Charger (there are lots of posts on the community that discuss the differences between the two chargers and implicatons for installing them). All of the proposed solutions will work it is just a matter of finding the safest and most reliable solution. The diagram that you are working off looks like a solid solution.


In this instance, using the isolated charger, I would go with what @kevgermany suggested and use the chassis ground stud under the seat for the negative input connection. Unlike 'home made' grounding points which may be closer to the charger they can be problematic (as per Kevgermany's note). The ground stud is a fit-for-purpose fully welded connection.


As far as voltage drop is concerned a 12 volt, 15 metre (50 foot) round trip, using 16 mm cable with with 30 amps is approximately 1.0 volts (using the Victron toolkit calculator - sorry I am metric). Provided the charger is located near the house batteries it will compensate for this voltage drop to deliver the correct voltage to the batteries (this is what they are designed for). I am assuming you are in the States so this may mean using a 5 AWG cable as opposed to a 6 AWG cable on the input (positive and negative). 6 AWG will be fine on the output. I hope this helps.


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lundy avatar image lundy Sarah commented ·
Thanks @Sarah I really appreciate the responses. Super helpful!
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kevgermany avatar image
kevgermany answered ·

With high power chassis connections possible problems are resistance, unreliability and electrolytic corrosion due to high current. Good side is no earth loops. Sprinter has a proper connection, will take the current and should be fine.

House battery should also be grounded to chassis, this is for safety, stray currents and to keep both systems at the same base level, otherwise things like battery monitors don't work properly.

Isolated transformer is fine.

On the house side neg busbar from battery neg. One connection to ground from that. All house negs back to the busbar. Orion output neg to busbar. Then no ground loops.

If you add a BMV with shunt, it goes between battery neg and busbar.

Non isolated Orion will put the charge current through the chassis.

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lundy avatar image lundy commented ·
Thanks for the reply @kevgermany . Do you know if the resistance generally is lower the closer you ground to the starter battery vs grounding at the rear? This was the only reason I could think of to run a negative wire back to the driver seat ground stud vs grounding at the rear. How would that impact AWG calculation for my positive run from the starter battery to the orion, I assume if the resistance is lower/the path is easier for the return via the chassis vs a 1 or 2 awg wire.
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kevgermany avatar image
kevgermany answered ·

Can't help on resistance except to say you need to measure it, sorry.

For cable sizes/voltage drop, there's an online calculator in the Victron toolkit app. Rember to add the positive and negative legs together for length calcs.

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lundy avatar image lundy commented ·
Thanks @kevgermany I appreciate the responses! Very helpful!
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