Installing Battery Isolation Manager - Grounding Question

[Kevin H]

When I built my Sprinter van I did the house electrical completely separate from the chassis.  I did not want any possibility of a chassis electrical problem being blamed on my house system.  The system works great.

I want to install a Li-BIM from Battleborn.

Because the BIM will tie the two systems on the positive side, should I run a ground from the Battleborn batteries to the chassis?  If so, what gauge wire do you recommend?  The run will be about 6 feet.

Here are my specs:
3 Battleborn 100AH batteries
650 watts solar - 2 X 325 watt, 65v panels
Victron Smart Controller 150/60tr
Aims Charger 2000w Pure Sine inverter/charger

[jcussen]

A lot of people are using dc-dc chargers. This what I used on my Sprinter Class C with lithium house batteries. Easy to wire, I used 10 gauge for the ground. Just alternator/start battery positive on one terminal, and house battery positive on the other one.

https://www.solar-electric.com/victron-energy-12-12-30a-orion-tr-non-isolated-dc-dc-charger.html?msclkid=a882440e914d150c3a3a240a2da19c56&utm_source=bing&utm_medium=cpc&utm_campaign=Shopping - Brand - Victron Energy&utm_term=4588399462083300&utm_content=Brand - Victron Energy

Edited January 17, 2021 by jcussen

[oldjohnt]

On 1/17/2021 at 5:31 PM, Kevin H said:

I want to install a Li-BIM from Battleborn.

Because the BIM will tie the two systems on the positive side, should I run a ground from the Battleborn batteries to the chassis?  If so, what gauge wire do you recommend?  The run will be about 6 feet.

Kevin, obviously the ONLY way to transfer current to your Battleborn Lithium DC batteries is to use TWO Conductors, Pos and Neg, so if you use cable for the POS current conductor you could use EITHER cable    orrrrrrrrrrrrrrrr     sure in theory the RV's conductive iron frame for the NEG current carrier.

 Personally I prefer use of two matched copper cables instead of copper cable for one and the RV iron frame as the other, even though the iron frame could serve as the NEG current conductor BUT THATS JUST ME (retired electrical engineer).

To your specific question

"should I run a ground from the Battleborn batteries to the chassis?"

Welllllllllllll there needs to be a conductor for the NEG current and the frame could serve as such, but if you use a cable (my choice)     YESSSSSSSSSSSSS    I would do as their diagram seems to indicate (ask them however) and also bond it to the RV frame/ground.  

The Li BIM wiring diagram  BIM-LI225-Quick Guide.pdf (netdna-ssl.com) shows its two main POS connector post/terminals connect to the Chassis and Coach batteries respectively using presumed "cable" and it indicates the NEG of the Coach and Chassis batteries are connected using a presumed "cable" WHICH INCLUDES A GROUND SYMBOL so again YES run a ground wire.

WHAT SIZE OF CABLE YOU ASK

It appears the Li BIM is rated for 225 Amps THEREFORE I would recommend use of a conductor having a minimum ampacity of 125% of 225, or 281 Amps. NOTE while the 225 amp rated contacts and if 225 amp cable is used for BOTH POS and NEG conductors, any frame ground bonding jumper should  not be carrying very much current. 

CAVEATS:

1) While it appears from the diagram

BIM-LI225-Quick Guide.pdf (netdna-ssl.com)

the contacts are rated for 225 Amps and I don't envision anywhere near that amount of current flow

2) I DO NOT (Unless its one heavy duty high current unit which if a diesel it may be??) envision the engines alternator or engine battery and charging system (unless a bigger diesel RV) supplying that much (225) current into your Battleborn Lithium batteries

3) One OTHER method to use the engines alternator to help charge lithium house batteries WITHOUT DAMAGING THE ALTERNATOR  and  TO SUPPLY THE PROPER CHARGE FOR LITHIUM BATTEIRES is use of a DC to DC Charger suitable for Lithium battery charging 

SUMMARY if your engines alternator battery and charging system are suitable for supplying 225 charging amps into tour Battleborn Lithiums ???? it appears the Li BIM is well rated for that amount,,,,,,,,,,,,,,,Ifffffffffffff that much current is actually transferred (diagram indicates 225 amp contacts) I would use 281 amp rated copper cable for BOTH the POS and NEG conductors,,,,,,,,,,,The diagram includes a universal Grounding Symbol on the NEG cable so again yes I would do as they say.

I just don't envision your Sprinter Van alternator and charging system having that much current capacity but no harm in using that much higher rated isolation manager GO FOR IT !!!!!!!!!! Just be sure you do NOT overcurrent or overheat your alternator !!!!!!!!!!! If the Li BIM is designed to charge the Battleborn Lithiums PROPERLY and NOT damage a smaller alternator again GO FOR IT.       

 

John T

 

Edited January 18, 2021 by oldjohnt

[jcussen]

26 minutes ago, oldjohnt said:

Kevin, obviously the ONLY way to transfer current to your Battleborn Lithium DC batteries is to use TWO Conductors, Pos and Neg, so if you use cable for the POS current conductor you could use EITHER cable    orrrrrrrrrrrrrrrr     sure the RV's conductive iron frame for the NEG current carrier.

 Personally I prefer use of two matched copper cables instead of copper cable for one and the RV iron frame as the other, even though the iron frame could serve as the NEG current conductor BUT THATS JUST ME (retired electrical engineer).

To your specific question

"should I run a ground from the Battleborn batteries to the chassis?"

Welllllllllllll there needs to be a conductor for the NEG current and the frame could serve as such, but if you use a cable (my choice)  YESSSSSSSSSSSSS I would do as their diagram seems to indicate and also bond it to the RV frame/ground.  

The Li BIM wiring diagram  BIM-LI225-Quick Guide.pdf (netdna-ssl.com) shows its two main POS connector post/terminals connect to the Chassis and Coach batteries respectively using presumed "cable" and it indicates the NEG of the Coach and Chassis batteries are connected using a presumed "cable" WHICH INCLUDES A GROUND SYMBOL.

WHAT SIZE OF CABLE YOU ASK

It appears the Li BIM is rated for 225 Amps THEREFORE I would recommend use of a conductor having a minimum ampacity of 125% of 225, or 281 Amps. 

CAVEATS:

1) While it appears from the diagram

BIM-LI225-Quick Guide.pdf (netdna-ssl.com)

the contacts are rated for 225 Amps and I don't envision anywhere near that amount of current flow

2) I DO NOT (Unless its one heavy duty high current unit which if a diesel it may be??) envision the engines alternator or engine battery and charging system (unless a bigger diesel RV) supplying that much (225) current into your Battleborn Lithium batteries

3) One OTHER method to use the engines alternator to help charge lithium house batteries WITHOUT DAMAGING THE ALTERNATOR  and  TO SUPPLY THE PROPER CHARGE FOR LITHIUM BATTEIRES is use of a DC to DC Charger suitable for Lithium battery charging 

SUMMARY if your engines alternator battery and charging system are suitable for supplying 225 charging amps into tour Battleborn Lithiums it appears the Li BIM is rated for that amount,,,,,,,,,,,,,,,If that much current is transferred (diagram indicates 225 amp contacts) I would use 281 amp rated copper cable for BOTH the POS and NEG conductors,,,,,,,,,,,The diagram includes a universal Grounding Symbol on the NEG cable so do as they say.

I just don't envision your Sprinter Van alternator and charging system having that much current capacity but no harm in using that much higher rated isolation manager GO FOR IT !!!!!!!!!! Just be sure you do NOT overcurrent or overheat your alternator !!!!!!!!!!! If the Li BIM is designed to charge the Battleborn Lithiums PROPERLY and NOT damage a smaller alternator again GO FOR IT.       

 

John T

 

Not sure why Kevin seperate's his two 12 volt systems, every van conversion and motorhome I have seen use a common ground for house and start systems. My sprinter van alternator puts out 160 amps,  his three battleborn's could conceivably take an 300 amp charge, The BIM will connect for 15 minutes and disconnect for 20 minutes to let alternator cool. The problem I had with a BIM, is that at idle, the alternator gets very little cooling because of the alternator fan running at low speed. I measured my alternator temp with engine idling with direct connection from alternator to lithium batteries, and alternator casing went from ambient to 250F in less than 5 minutes, and of course, the lithiums will never fully charge on the 13.2 to 13.7 volts the alternator puts out. The DC-DC charger will limit the amps going to your lithiums, to protect the alternator, but more importantly, will provide the necessary 14.4 volts to bring your batteries to 100% SOC.

Believe AM Solar  uses DC-DC chargers exclusively for all its big solar conversions. Good video  

https://www.victronenergy.com/blog/2019/10/07/careful-alternator-charging-lithium/

[oldjohnt]

22 minutes ago, jcussen said:

Not sure why Kevin seperate's his two 12 volt systems, every van conversion and motorhome I have seen use a common ground for house and start systems. My sprinter van alternator puts out 160 amps,  

JC, when Kevin indicates he separates his two 12 volt systems I wouldn't bet my life BOTH still don't have their NEG bonded to the frame somewhere somehow  BUT I CANT SAY SITTING HERE.  There's no need UNLESS the house batteries actually use the frame as the NEG current return path for some load or another ??? (I have seen gensets use frame as the NEG conductor) 

Obviously if the two are connected for charging the engine battery is already frame grounded SO THE HOUSE BATTERIES ARE ALSO !!!!!!!!!!  They are NOT isolated !!!!!!!!!!!!!! 

 While I discussed the worst case scenario above I still don't see his Sprinter alternator pumping anywhere near 200 charging amps into his Battleborns (needing such huge 200 amp cables), maybe 100 max or even 50 or 60 subject to how the BIM functions  IE  he may get by with 50 or 60 amp rated cables from the batteries  ??

 Regardless if it were mine (instead of the 225 Amp rated BIM) Id go with a 40 (or maybe 60) Amp DC to DC Lithium Charger between his engine and Battleborn batteries which

1) Provides the isolation he seeks EXCPET when charging PLUS

2) Protects his Alternator PLUS

3) Provides the correct Lithium charging profile without the on off cycling etc.

4) ONLY requires the two + and - cables in and out of the DC to DC charger   EASY PEASEY plus provides ISOLATION expect when charging   He also has the solar panels providing charge lessening the load on the alternator or BIM

A pleasure sparky chatting with you JC, looks like were on the same page ????????

John T  Long retired n rusty EE but still enjoy helping

[jcussen]

Agree John, just trying to see any benefit of a isolated house system {like you say, if he truly has one}. Seems like using a heavy steel frame equivalent  to a 100/0 cable , would be easier than running separate  negative  cables...When I did my second alternator output test with two 50% SOC battleborn's, amprobe measured 130 amps on the alternator positive lead, this is probably 30 amp chassis load and 100 amp battery charging load. 130 amps out of a 160 amp alternator at idle speed just seems a little excessive to me. Might work for a year or two, but sprinter alternators are expensive.

[Kevin H]

Thanks everyone.  Great responses.  To clarify, my house system is completely separate from the chassis.  There are NO connections whatsoever between the house system and the chassis. The chassis remains completely stock Mercedes.

After reading all your responses and other sources as well, I decided to return the BIM and order a DC2DC 30 amp charger.  Battleborn treated me extremely well and I am anxious to get the new unit.

I'll run POS and NEG cables from the chassis battery to the charger and then POS and NEG cables to the house batteries.  I am adding a ground from the house batteries to the chassis as well.

I may have some technical questions when it comes to installation time.  If so, I'll again tap into your expertise.
Again, thanks to everyone for your valuable input.

[oldjohnt]

1 hour ago, Kevin H said:

After reading all your responses and other sources as well, I decided to return the BIM and order a DC2DC 30 amp charger.  Battleborn treated me extremely well and I am anxious to get the new unit.

Sounds like a good plan so long as it suits YOUR needs and wishes. I would prefer a true DC to DC Charger suited specifically for your Lithium battery charging requirements (voltage and current) versus the less precise perhaps ??? On Off cycling of the Li BIM. That unit should (versus the BIM) better protect your expensive alternator (with its 30 Amp max output I doubt it will require much over 32 + amps out of the alternator subject to design and efficiency) and it coupled with your Solar will hopefully supply all your charging needs, ESPECIALLY ON CLOUDY DRIVING DAYS

ROUGH NON EXACT EXAMPLE:  If you were in decent sunlight (subject to intensity time and angle) your 650 solar watts might harvest say somewhere around 200 Amp Hours of energy in a day, and if you were to drive four hours charging at 30 amps that (but less efficiency and charging losses) may yield an additional  100+ Amp Hours totaling 300+ Amp Hours of replacement charging into your Battleborns

I like the idea of  dedicated + and - cables from the charger to both batteries versus using the frame as the NEG conductor and subject to length Id probably use at least 8 better yet 6 Gauge (50 amp rated) even if sure its overkill for only 30 amps to reduce line voltage drop. Your engine battery is of course already tied to frame ground so you may or may not have two perfectly "isolated" systems when charging (depends on the electronics and functioning of the charger).

NICE PLAN you did your homework, congratulations. I look forward to JC and others comments 

John T 

 

[jcussen]

Agree with John, I went with the Victron dc-dc charger, nice thing about it is , auto disconnect, will seperate your banks at 13.2 alternator output voltage, so pretty much hands free and the ability to set up your output voltage.  I used 14.4 constant voltage as per Battleborn specs.

My 30 amp charger will actually output [according to my Victron battery monitor] about 32 amps. As John said, that is a real 30 amps until the batteries are full. No more bulk, absorption, float etc, When batteries full, it just disconnects. On my sprinter, use the dc-dc charger and 390 watts of solar, and seldom have to turn the converter on to charge the batteries. 

[Kevin H]

Thanks again.  I'll let you know how the project goes.  Probably won't get to it for a few weeks.