Good Sam Club Open Roads Forum: Isolating TT's Lithium from TV's Lead Acid Batteries
Open Roads Forum Already a member? Login here.   If not, Register Today!  |  Help

Newest  |  Active  |  Popular  |  RVing FAQ Forum Rules  |  Forum Posting Help and Support  |  Contact  

Search:   Advanced Search

Search only in Tech Issues

Open Roads Forum  >  Tech Issues

 > Isolating TT's Lithium from TV's Lead Acid Batteries

Reply to Topic  |  Subscribe  |  Print Topic  |  Post New Topic  | 
Page of 3  
Prev
grizzzman

salt lake city, Utah

Senior Member

Joined: 12/07/2014

View Profile


Offline
Posted: 08/24/19 01:11pm Link  |  Quote  |  Print  |  Notify Moderator

BFL13 wrote:

Do you really have to isolate the Lis from the TV batteries? Why? Going down the road, you might be getting 13.9 volts from the TV and 14.x from solar, so in that case the solar will do the charging.

If no sunshine, who cares if the Lis are charged at 13.9 volts for a while? When you get there, you unplug the 7-pin and now you are isolated anyway.

I can see it if the 7-pin were charging at a higher voltage than the Li spec calls for, but who cares if they are getting less voltage than they can handle?

You can overcharge a LFP at 13.9 volts.


2019 Ford F150 EcoBoost SuperCrew
2016 Rockwood Mini Lite 2504S. TM2030 SC2030
640 Watts Solar. Costco CG2 208 AH and Lifepo4 3P4S 150 AH
Renolgy 40amp DC to DC charger 400 Watt and 2000 Watt Inverter's hard wired.
Boondocking is my Deal

BFL13

Victoria, BC

Senior Member

Joined: 02/15/2006

View Profile



Posted: 08/24/19 01:32pm Link  |  Quote  |  Print  |  Notify Moderator

If they take bulk at 14.4 but can be overcharged at 13.9, I assume that is after they are full and charging should be cut off?

What was that about the Lis having some sort of protection attached so they can't be overcharged that is part of that balancing thing? Or (very possible) I got that all wrong from the other thread on Li batts?

If they are that close to full before heading down the road, why charge them up at all? They like to be at 80% SOC

My problem with the premise of this thread's OP post is the idea that the Lis in the trailer will be supplying current to the truck while driving down the road and thus lose some AH. I find that notion peculiar.

If charging is wanted driving down the road, and the 7-pin isn't enough (I don't see how it can be too much, but waiting to hear more about that), then the DC-DC gizmo is known to work. We have had other threads on those by guys who have them.


1. 1991 Oakland 28DB Class C
on Ford E350-460-7.5 Gas EFI
See Profile for House electronics set-up.
2. 1991 Bighorn 9.5ft Truck Camper on 2003 Chev 2500HD 6.0 Gas

time2roll

Southern California

Senior Member

Joined: 03/21/2005

View Profile



Good Sam RV Club Member


Posted: 08/24/19 01:50pm Link  |  Quote  |  Print  |  Notify Moderator

Need to review battery specs to know if 13.9 float will overcharge the specific lithium battery. If the lithium is charged to 14.4 to 14.6 range like most I have my doubts 13.9 would be an issue. Lithium resting voltage does not drop like lead-acid from 14.8 to 12.7 just for resting.


2001 F150 SuperCrew
2006 Keystone Springdale 249FWBHLS
675w Solar pictures back up

cruz-in

Southern Maryland

Senior Member

Joined: 02/15/2009

View Profile



Good Sam RV Club Member

Offline
Posted: 08/24/19 03:27pm Link  |  Quote  |  Print  |  Notify Moderator

Below is a link to an extensive thread on this subject. Includes real world measurements and acknowledgement from Sean of Battle Borne of the issue.

If you want to cut to the chase, after reading the OP, go to post number 70 & 81. A gentleman used his BVW Battery monitor and bluetooth to monitor current flow while driving. He saw 1 to 2 amps going from the TT to the TV.

Then go to post 84 where Sean from Battle Borne says:

"Dear SilverHouseDreams (the OP of the thread)

Your observation of the problem with keeping your Li-ion trailer batteries hooked in parallel with your tow vehicle starter battery is spot on. The Li-ion battery operates on a higher and flatter voltage curve and therefore will continue leak charge into your lead acid starter. That is why a battery isolator is imperative in this situation."

Extensive Thread on Isolating LI Batteri........ confirmation from Sean at Battle Born.

* This post was edited 08/24/19 03:45pm by cruz-in *


2011 Monaco Vesta
Interesting Coach
This particular one was the prototype.

cruz-in

Southern Maryland

Senior Member

Joined: 02/15/2009

View Profile



Good Sam RV Club Member

Offline
Posted: 08/24/19 04:26pm Link  |  Quote  |  Print  |  Notify Moderator

CA Traveler wrote:

OP,

I don't recall your intended battery size or usage. A 100Ah discharged battery needs up to 80A charging when driving - ie 20A for 4 hours. Double that for 200Ah.

Since your interested in the Renogy that suggests that you are not a pedestal to pedestal camper starting with a fully charged battery.

Are you planning on any TT charger changes for Li when plugged in?


It is two 100AH LI batteries with plans to add a 3rd.

In addition to the Renogy 20 Amp DC to DC LI Isolation/charger (referenced in the OP), I have also changed to a Renogy LI compatible solar controller/charger and a Progressive Dynamics LI compatible converter.

The LI batteries are situated in a compartment where they will be more/less the same temps as the interior of the TT.

Should be done with the mod tomorrow.

BFL13

Victoria, BC

Senior Member

Joined: 02/15/2006

View Profile



Posted: 08/24/19 06:38pm Link  |  Quote  |  Print  |  Notify Moderator

I will get to that later, no time right now. I trust cruz-in from before when he had the twin L15 (ISTR) set-up, which I learned from, so I expect to learn something here despite my doubts.

NRALIFR

Truck Camping Out West

Senior Member

Joined: 11/27/2005

View Profile



Posted: 08/24/19 07:22pm Link  |  Quote  |  Print  |  Notify Moderator

I can’t speak for the Renogy DC-DC charger, but my Redarc unit does not back feed voltage from the TC house battery to the truck starter battery. It effectively functions as an battery isolator as well. I also have a isolation solenoid on the truck that is only energized when the engine is running to keep the charger from running the starting battery down when the engine is not running.

[emoticon][emoticon]


2001 Lance 1121 on a 2016 F450


CA Traveler

The Western States

Senior Member

Joined: 01/03/2004

View Profile


Offline
Posted: 08/24/19 08:03pm Link  |  Quote  |  Print  |  Notify Moderator

OP,

300Ah is a potential 240Ah at 20% charge needed from the TV to full charge. Solar helps when there is sun of course. My 220Ah discharge at 50% is handled by the nearby 200A alternator.


2009 Holiday Rambler 42' Scepter with ISL 400 Cummins
750 Watts Solar Morningstar MPPT 60 Controller
2014 Grand Cherokee Overland

Bob


grizzzman

salt lake city, Utah

Senior Member

Joined: 12/07/2014

View Profile


Offline
Posted: 08/24/19 08:30pm Link  |  Quote  |  Print  |  Notify Moderator

BFL13 wrote:

If they take bulk at 14.4 but can be overcharged at 13.9, I assume that is after they are full and charging should be cut off?

What was that about the Lis having some sort of protection attached so they can't be overcharged that is part of that balancing thing? Or (very possible) I got that all wrong from the other thread on Li batts?

If they are that close to full before heading down the road, why charge them up at all? They like to be at 80% SOC

My problem with the premise of this thread's OP post is the idea that the Lis in the trailer will be supplying current to the truck while driving down the road and thus lose some AH. I find that notion peculiar.

If charging is wanted driving down the road, and the 7-pin isn't enough (I don't see how it can be too much, but waiting to hear more about that), then the DC-DC gizmo is known to work. We have had other threads on those by guys who have them.


Time at voltage plays a real roll when it comes to overcharging LFP.

Reply to Topic  |  Subscribe  |  Print Topic  |  Post New Topic  | 
Page of 3  
Prev

Open Roads Forum  >  Tech Issues

 > Isolating TT's Lithium from TV's Lead Acid Batteries
Search:   Advanced Search

Search only in Tech Issues


New posts No new posts
Closed, new posts Closed, no new posts
Moved, new posts Moved, no new posts

Adjust text size:




© 2020 CWI, Inc. © 2020 Good Sam Enterprises, LLC. All Rights Reserved.