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Lifepo4 earthing advice

LifeIsADeam

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All loads will have a negative run to The bus bar, which will be ground to the negative terminal. This completes the currents circuit, right?

Im just getting clarification, ive always run an extra cable to the chassis in the past. Now correct me if this is wrong but, a cable run to the chassis is incase a positive comes into contact with the metal body of van, the chassis cable gives the positive current a way to complete the circuit?

But could this actually be dangerous and possibly create a current running through the van? Couldn't this also cause erosion and rust? Apart from devices that require a dedicated ground to chassis, such as a dc dc charger, why earth everything else to the chassis? Its my understanding that boats dont have a seperate earth for this reason. To clarify, the van is covered (wood etc) and no wires come into contact with metal body

-Do i need to run a cable from the negative bus bar to the chassis?

Any input is appreciated
 
There are debates about what is 'best' for vehicle system grounding/Earthing. In my designs I always ti DC negative to ground.

A few points:
  • If any of your loads use chassis as the return path you are pretty much forced to tie negative to chassis.

  • I am not sure where you live, so this may not be relevant, but in the US, the National Electric code would say that you should tie to chassis for any circuit that might go over 50 volts. Lower than 50 volts it is optional but recommended. The reason for the 50V cut-off is that they consider anything over 50V as dangerous and they want to make sure a short to chassis blows the fuse/breaker to 'clear the fault'. On the other hand, if the Negative is not tied to ground, if your positive hits chassis, it is not a short..

  • Tying negative to the Chassis prevents the DC circuit from 'floating' to a different voltage due to static or other imposed potentials. This may seem unlikely, but when you touch something and get a static shock it is because that something is floating at a different potential than you are. In a vehicle it seems unlikely this would be a safety issue unless your panels are hit by lightning. However, static buildup while you are driving could possibly create enough of a difference that there could be damage to electronics.

  • If you are using a non-isolated DC-DC charger from your alternator, you are forced to tie negative to chassis. (Victron makes an isolated charger)

You may want to review this:


It is the 4th in a 4 part series of papers. I recommend reviewing all 4.
 
Thank you very much. That was an informative paper. Just to clarify, if you dont mind. Option 1 - It may be best for me to have a dedicated common grounding bus bar, isolated from the negative bus bar, as i have the victron non isolated dc dc charger, and i could have the inverter, dc dc charger, scc on this common ground bar?
Or i could have the negative bus bar grounded to chassis and have the dc dc charger on it own individual ground? Would either be sufficient? I appreciate your time and advice.
 
Thank you very much. That was an informative paper. Just to clarify, if you dont mind. Option 1 - It may be best for me to have a dedicated common grounding bus bar, isolated from the negative bus bar, as i have the victron non isolated dc dc charger, and i could have the inverter, dc dc charger, scc on this common ground bar?
Or i could have the negative bus bar grounded to chassis and have the dc dc charger on it own individual ground? Would either be sufficient? I appreciate your time and advice.
I am not sure I am following. With the non-isolated DC-DC charger, The negative output is the same as the Negative input. Since the vehicle has Negative tied to chassis, then Negative for the battery is also tied to the chassis.... there is no getting around it. Which model DC-DC charger do you have?
 
So then having the charger ground cable running to the second battery neg bus which is ground to the chassis? Or is it best to run the neg to neg bus which is isolated from chassis and run a seperate green earth to chassis common ground bus? Its the victron orion tri smart non isolated.
 
Could you please send me some diagrams of what you are describing? I am not sure I am following.
 
So then having the charger ground cable running to the second battery neg bus which is ground to the chassis? Or is it best to run the neg to neg bus which is isolated from chassis and run a seperate green earth to chassis common ground buIts the victron orion tri smart non isolated.
 

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Option 1 goes to neg bus which is also earthed to chassis.
Option 2 has a dedicated ground wire to chassis and the neg bus isnt earthed.

Sorry this is my first time wiring this type of charger.
 
There is only one shared negative on the non-isolated DC-DC charger so #1 is closest to correct. However, I don't like to use Chassis for neg return of a high current circuit. Consequently, I would run the 'ground' wire from the Neg bus bar all the way back to the same place the starter battery is tied to Chassis. (Other folks use the chassis for the return.....If you do, make sure you pick a spot to tie to that does not have a lot of paint or other coatings that would prevent a good connection.

Also, How far from the starter battery is the Orion? A lot of RV conversions have a pretty long run so they need very heavy wire to avoid excessive voltage drop. I am currently helping a guy with a van conversion and we went with 2AWG....and I am even wondering if that was good enough. I don't know what model Orion you have but I will assume it is the 12/12-30. That means there will be times when there will be 30 amps or more across the cable. Now lets assume there is 15 ft from the Orion to the battery. That makes a round trip of 30ft. (When you do the calculations, make sure you include any extra length you need to rout the cable around things. (It is surprising how quickly the length can add up)

Looking at the Blue Seas Ampacity and Voltage Drop chart, we get 4AWG

1616714821328.png
 
I would run the ground wire from neg bus to the actual underbody chassis of the van so should be good connection. The positive from charger to second battery is no more than 2 metres, perhaps 3m if run under van. I was planning to use 6 awg as it looks as if 4awg will be a tough fit, which i thought may be sufficient as the length is not far. Thought? Yes correct the 12/12 30. I appreciate your help.
 
@FilterGuy...I'm planning on using your grounding diagram below as the starting point for my van electrical system. My question is if the negative wire running from the Starter Battery -> DC-DC Charger -> Negative Bus -> House Battery needs to be oversized for the entire system, or just big enough to cover the dc/dc charging load? Does it need to be 4/0 because it's the only bond between the house system negative bus and chassis ground? Or can it still just be 2awg to cover the 60-70 amps for 2 x Orion-TR Smart 12/12-30s in parallel? Thanks!
 

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@FilterGuy...I'm planning on using your grounding diagram below as the starting point for my van electrical system. My question is if the negative wire running from the Starter Battery -> DC-DC Charger -> Negative Bus -> House Battery needs to be oversized for the entire system, or just big enough to cover the dc/dc charging load? Does it need to be 4/0 because it's the only bond between the house system negative bus and chassis ground? Or can it still just be 2awg to cover the 60-70 amps for 2 x Orion-TR Smart 12/12-30s in parallel? Thanks!
First.... just for clarity, the picture you referenced is conceptually correct but could be misleading depending on the non isolate DC-DC charger that is between the Alternator and the Battery. Some of the DC-DC chargers do not actually have a negative connection to both the House and Starter battery. Instead they just have one connection for both. I recently helped a guy with a Victron Orion Smart charger and what he did was run a 2AWG from the starter battery to the common negative Busbar. And then a 10AWG from the common neg busbar to the Orion TR Smart. The reason it was a 2 AWG was that it was a rather long run and we wanted to avoid voltage drops.

Even though the 2AWG was a lot smaller than the big 2/0 he had between the battery and the inverter, I felt the 2AWG was sufficent. Keep in mind, the purpose of tying to chassis is to make sure the system does not float to a significant voltage different than the chassis. You don't need a heavy wire to do that.

Bottom line: No. It does not need to be 4/0. It does need to be large enough to carry the charger current for the distance from the alternator to the house system.
 
First.... just for clarity, the picture you referenced is conceptually correct but could be misleading depending on the non isolate DC-DC charger that is between the Alternator and the Battery. Some of the DC-DC chargers do not actually have a negative connection to both the House and Starter battery. Instead they just have one connection for both. I recently helped a guy with a Victron Orion Smart charger and what he did was run a 2AWG from the starter battery to the common negative Busbar. And then a 10AWG from the common neg busbar to the Orion TR Smart. The reason it was a 2 AWG was that it was a rather long run and we wanted to avoid voltage drops.

Even though the 2AWG was a lot smaller than the big 2/0 he had between the battery and the inverter, I felt the 2AWG was sufficent. Keep in mind, the purpose of tying to chassis is to make sure the system does not float to a significant voltage different than the chassis. You don't need a heavy wire to do that.

Bottom line: No. It does not need to be 4/0. It does need to be large enough to carry the charger current for the distance from the alternator to the house system.

I would be using 2 of the Orion-TR Smart 12/12-30 non-isolated chargers. My plan was to run a 2awg from the starter battery back to my house negative bus bar, and then 6awg out to each Orion. Perhaps I should consider something a little larger than 2awg, since it is about 15'. But good to know I don't need to go 15' with 4/0.

One more question...I'll be using a Multiplus 12/3000/120 inverter/charger and also running a 50-60A 12V DC air conditioner - so pretty big possible loads. Planning on running 4/0 from house battery to positive bus, and 4/0 from positive bus to inverter/charger. Would you recommend 4/0 from the house grounding bus to chassis? Thanks!
 
since it is about 15'
Is that 15' one way or round trip?
I would be using 2 of the Orion-TR Smart 12/12-30 non-isolated chargers.
60A total is a lot of current. Do you know the rating on your alternator? The alternator rating is for best case conditions and you will not normally be able to get the full rating. My rule of thumb is that you should never go above 50% of the alternator rating. Also what amp-hour size is your battery bank? What charge rate are they rated for?
I'll be using a Multiplus 12/3000/120 inverter/charger and also running a 50-60A 12V DC air conditioner
Wow, if you Max out the inverter while you are running the AC you are looking at 300A coming off your batteries.!!! That is a LOT of current. What is the rated Discharge rate of your battery bank? What BMS are you using?

Would you recommend 4/0 from the house grounding bus to chassis?
No, just use some of the 2/0.
 
Is that 15' one way or round trip?

60A total is a lot of current. Do you know the rating on your alternator? The alternator rating is for best case conditions and you will not normally be able to get the full rating. My rule of thumb is that you should never go above 50% of the alternator rating. Also what amp-hour size is your battery bank? What charge rate are they rated for?

Wow, if you Max out the inverter while you are running the AC you are looking at 300A coming off your batteries.!!! That is a LOT of current. What is the rated Discharge rate of your battery bank? What BMS are you using?


No, just use some of the 2/0.

- Actually it's about 12-13' one way. So I'm thinking 1awg or 1/0awg would maybe be better. With the inefficiencies, it could be up to 80A for two 12/12-30 Orions I would think.

- It's a Ram Promaster with the Heavy Duty 220A alternator.

- Battery bank would be 3 x SOK 12V 206Ah. Max recommended charge rate is 50A each, 150A total.

- Of course I would never max out the inverter while running the A/C, but I definitely have to design for it just in case. Planning on 150A fuses on each positive battery terminal, 4/0 cable, 350A master on/off switch, and a 400A fuse to the positive bus.

- SOK batteries are rated for 100A max discharge (safe up to ~130A I believe), so 300A recommended max discharge for the battery bank.

I initially wanted to go with a 24V system to stay away from that possible 250-300A discharge, but the 12V A/C kind of kills it. I'd have to convert the 12V alternator power to 24V for charging, and then back down to 12V for the air conditioner & other 12V loads. All of which seems inefficient and wasteful.

Thank you again for taking the time to answer my questions :)
 
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