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

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time2roll

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Posted: 08/23/19 06:57pm Link  |  Quote  |  Print  |  Notify Moderator

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.


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BFL13

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Posted: 08/23/19 07:37pm Link  |  Quote  |  Print  |  Notify Moderator

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?


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cruz-in

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Posted: 08/23/19 07:51pm Link  |  Quote  |  Print  |  Notify Moderator

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...


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cruz-in

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Posted: 08/23/19 07:56pm Link  |  Quote  |  Print  |  Notify Moderator

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

BFL13

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Posted: 08/23/19 08:30pm Link  |  Quote  |  Print  |  Notify Moderator

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 [emoticon] 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/fusea........d/tid/29894388/srt/pa/pging/1/page/1.cfm

* This post was edited 08/23/19 08:39pm by BFL13 *

cruz-in

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Posted: 08/24/19 05:16am Link  |  Quote  |  Print  |  Notify Moderator

I think the point is two fold:
1) When driving the TV/TT combo, current will flow from the higher voltage LI battery (assuming it is fully charged) to the lower voltage Lead Acid system.
2) Having a DC to DC charger for the LI batteries will allow the TV to charge the LI batteries (albeit in limited fashion) when traveling down the road.

BFL13

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Posted: 08/24/19 08:00am Link  |  Quote  |  Print  |  Notify Moderator

cruz-in wrote:

I think the point is two fold:
1) When driving the TV/TT combo, current will flow from the higher voltage LI battery (assuming it is fully charged) to the lower voltage Lead Acid system.
2) Having a DC to DC charger for the LI batteries will allow the TV to charge the LI batteries (albeit in limited fashion) when traveling down the road.


1. The resting voltage of a full 12v Battleborn is about 13v and it wants 14.4v for bulk charging, 13.2 for float if I have that right. So when can the TT battery be higher in voltage?

Any alternator charging will be above that 13v, starting at 14.x when the vehicle engine is turned on and tapering quickly to 13.8 or so soon after, once the alternator warms up and the vehicle battery is recharged.

When parked, if the TV is a Chev, just disconnect the 7-pin. With a Ford you have the relay, so no worries.

2. You just want one of those DC-DC gizmos! (And why not?) [emoticon]

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Posted: 08/24/19 09:06am Link  |  Quote  |  Print  |  Notify Moderator

IHMO High dollar lithium batteries should be properly charged and a flooded battery alternator does not do that. Plus the TV battery/alternator voltage is not the voltage at the end TT end of the wires. Often TV and TT wiring is adequate for small loads like a propane refer and inadequate charging.

Typically the starting battery is quickly charged and the voltage drops to 13.6V or so regardless of the TT battery charge on the end of those long wires.


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Posted: 08/24/19 09:18am Link  |  Quote  |  Print  |  Notify Moderator

OP,

Your linked Renogy manual seems short on Li battery information to me. It may be adequate for you. I'd want to better understand the Li charging.

1. Does it time out after 4 hours?
2. Or does it sense the charging voltage and stop charging when the current drops to the right amount? Apparently not since I didn't see any mention of a shunt since otherwise it could only detect house + battery amps.

3. What about low temperature charging restrictions?

And likely more questions if I dug deeper as I saw other information like an ignition wire to the charger - ie another wire from the TV to TT, etc.

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Posted: 08/24/19 09:25am Link  |  Quote  |  Print  |  Notify Moderator

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?

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