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

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cruz-in

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Posted: 08/23/19 04:38pm Link  |  Quote  |  Print  |  Notify Moderator

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


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pianotuna

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Posted: 08/23/19 05:34pm Link  |  Quote  |  Print  |  Notify Moderator

Dan,

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


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CA Traveler

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Posted: 08/23/19 05:38pm Link  |  Quote  |  Print  |  Notify Moderator

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* This post was edited 08/23/19 06:04pm by CA Traveler *


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garym114

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Posted: 08/23/19 05:45pm Link  |  Quote  |  Print  |  Notify Moderator

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


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Posted: 08/23/19 05:50pm Link  |  Quote  |  Print  |  Notify Moderator

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?

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Posted: 08/23/19 06:10pm Link  |  Quote  |  Print  |  Notify Moderator

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.

BFL13

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Posted: 08/23/19 06:18pm Link  |  Quote  |  Print  |  Notify Moderator

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.)


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grizzzman

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Posted: 08/23/19 06:32pm Link  |  Quote  |  Print  |  Notify Moderator

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?


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Posted: 08/23/19 06:35pm Link  |  Quote  |  Print  |  Notify Moderator

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.

NRALIFR

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Posted: 08/23/19 06:48pm Link  |  Quote  |  Print  |  Notify Moderator

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.

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