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

[cruz-in]

Hi Team,

I am installing Lithium batteries on our TT. To provide isolation between TT's Lithium and TV's Lead Acid batteries, I plan to install a Renogy DC-to-DC converter. It is kind of neat. Has three stage charging and supports Lithium. Here is a link to them:

20 Amp and 40 Amp DC-to-DC charger

TV has 30 AMP fuse for the power line to the Trailer Plug. I assume I need to stay below 30 Amps so am I stuck with the 20 Amp Model?

Would be nice to use the whole available 30 amps.

Thanks
Dan

[BFL13]

cruz-in wrote:

BFL13 wrote:
Do you really have to isolate the Lis from the TV batteries? Why?

check out this thread...many others on the subject..

Interaction Between LI and TV's Lead Acid

OK, I read the OP's post in that before the whole thing started to eat my computer 😞 After a restart, I have escaped from whatever that was about.

Anyway, the OP there has some weird notions, plus he seems to have been talking about staying parked with the 7-pin left connected, NOT about when driving down the road.

IMO this "problem" is not a valid concern, and if you have a Ford with a relay instead of a Chev that stays live even with the engine off, you don't care--the relay isolates you. If you have a Chev, just unplug the 7-pin.

Non-problem! Meanwhile, enjoy the Lis. Another member here was trying to adjust his ways for Lis, and ran into some interesting issues. Might apply to your situation, don't know.

https://www.rv.net/forum/index.cfm/fuseaction/thread/tid/29894388/srt/pa/pging/1/page/1.cfm

[cruz-in]

BFL13 wrote:
Do you really have to isolate the Lis from the TV batteries? Why?

check out this thread...many others on the subject..

Interaction Between LI and TV's Lead Acid

[cruz-in]

time2roll wrote:
Stick with the 20 amp. This thing boosts voltage so you need more than the rated amps protecting the circuit. You would need a 50 amp circuit to go to the 40 amp level. Solid 20 amps is still a significant charge.

concur....this will work fine....and in time, when I upgrade the TV wiring, all the better...

[BFL13]

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?

[time2roll]

Stick with the 20 amp. This thing boosts voltage so you need more than the rated amps protecting the circuit. You would need a 50 amp circuit to go to the 40 amp level. Solid 20 amps is still a significant charge.

[NRALIFR]

If the OP will invest the time and effort into providing the DC-DC charger with the proper sized wires, it won’t be just a “little bit of charging”. It will be 20 or 40 amps of multi-stage lithium optimized charging. I have a Redarc 25 amp DC-DC charger in my TC, and I think it’s great. I installed it according to the mfgr’s specs, including the recommended wire size for my circuit length.

OP, don’t use the tow vehicle or trailer wiring or the 7-way plug for this. You will probably need wires of about 4 awg, and either an Andersen power pole connector or a Pollak 2-pin lift gate plug. The DC-DC charger should be installed as close to the trailer batteries as possible. The wires on the tow vehicle side should connect to the TV batteries, not the alternator. I recommend using Temco fine strand welding cable for this.

:):)

[CA_Traveler]

Charging is important for boondock to boondock travel and very important for the trailer battery for the brakes to work correctly . I'd want adequate charging availability while driving.

[grizzzman]

I have the 40 amp DC to DC charger. With 20 foot of 4 awg copper wire
I still see a bit of a voltage drop. To get 40 amps out it takes 50 amps from the truck. I would advise at least 6 awg from the tow rig to the trailer. Here is my post on it

What type lfp? How are you going to shut off the charger when the bank is full?

[BFL13]

You don't need the little bit of charging you get from the TV to the TT while driving.

Just pull the truck's fuse for pin #4 (Chev it is Stud 1--whatever for other trucks--Ford has a relay to disconnect.)

[CA_Traveler]

The 30A TV fuse is to protect the TV wiring. The TT wiring may not be adequate for 30A, hopefully for the 20A model.

Consider new wiring, connector and fuses for the 40A model. Plus is the TV alternator adequate for an additional 40A load? Likely more than 40A due to wiring losses.

[CA_Traveler]

pianotuna wrote:
Dan,

Think about beefing up the charging wire to meet the 40 amp requirement?

X2 Wire length, amps and volts all factor into what size wire to use. Maybe the manual has some guidelines?

[garym114]

You are going to need a larger gauge wire from the TV battery to the TT converter.
The 12 gauge wire in the 7 way and probably the other wire in the trip is not large enough for even a 5 amp load.
See the voltage drop calculator at the bottom of this page.
http://www.powerstream.com/Wire_Size.htm

[CA_Traveler]

Deleted

[pianotuna]

Dan,

Think about beefing up the charging wire to meet the 40 amp requirement?