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Old 05-03-2021, 12:53 PM   #1
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Switch to LiFePo without DC-DC Charger?

Hello. What are the risks if I do not get a DC to DC charger between the truck and the trailer if I switch to LiFePo batteries? I'm thinking it will be a non-issue since the new solar panels on the roof will be charging the batteries at the correct voltages while driving down the road (and maybe even the truck battery). The truck is always unplugged from the trailer while camping too.
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Old 05-03-2021, 01:02 PM   #2
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maybe no problem

I recently installed a DC to DC charger in part to prevent what some, but not all, LiFePo users reported as a drain of TV batteries. Might not be an issue depending on your TV circuitry, and certainly not an issue if unplugged while camping.

There are some what-ifs: if your TV doesn't isolate when the ignition is off and you are in Walmart reprovisioning and it has been rainy and overcast for a while... might not be happy for the TV battery.

Browse the DC-DC treads for more detailed what ifs, as well. Part of the reason I installed the Victron in spite of the other options available was the bluetooth monitoring and its capability to condition the flow of electrons according to the app.
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Old 05-04-2021, 02:35 PM   #3
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Thank you for the reply. i read some of the DC-DC threads, makes me want to get one, but I think I will go without for now and see how it goes.
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Old 05-04-2021, 02:42 PM   #4
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Thank you for the reply. i read some of the DC-DC threads, makes me want to get one, but I think I will go without for now and see how it goes.
I passed on the DC to DC charger as well. To isolate the truck I just lifted the 7-pin charge wire off the battery bus bar.
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Old 05-04-2021, 02:44 PM   #5
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Suggest that without the DC-DC charger you just disable charging from your tow vehicles and rely on solar.--Frank
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Old 05-04-2021, 03:01 PM   #6
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you need a dc-dc THE CHARGE FROM tv TO as

The TV voltage is not high enough to charge the Lion. as well , The Dc-DC prevents back feed power to drain the battery
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Old 05-04-2021, 03:06 PM   #7
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Yeah, I've thought about that too. I think I will just leave it for now, that way, the solar can trickle charge my truck battery too. I am not worried about either battery (truck or trailer) being depleted (like when it is dark out), the voltage potential between the two types of battery is around one or two volts.
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Old 05-11-2021, 05:11 PM   #8
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Opted for intelligent relay

Instead of a DC-DC charger, I installed a Victron Cyrix-Li-ct relay that disconnects the lithium batteries from the tow vehicle based on the voltage sensed at the TV. It works fine.
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Old 05-11-2021, 05:52 PM   #9
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I have two Battleborn LiFePo batteries and solar charging on the roof, but have never gotten around to installing a DC-DC charger or other isolation device. Knock on wood, I have never had any problem with TV battery discharge, in spite of the fact that we often don't disconnect when stopping in route for just a night. Maybe just lucky, or perhaps some unique situation with wiring of the TV or trailer.
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Old 05-11-2021, 08:23 PM   #10
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I simply pulled the 30A fuse in my truck for the trailer 12v power line in the 7-way. I have enough solar and batteries so I don't need additional charging source.
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Old 05-12-2021, 06:51 AM   #11
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Originally Posted by jmickow View Post
I have two Battleborn LiFePo batteries and solar charging on the roof, but have never gotten around to installing a DC-DC charger or other isolation device. Knock on wood, I have never had any problem with TV battery discharge, in spite of the fact that we often don't disconnect when stopping in route for just a night. Maybe just lucky, or perhaps some unique situation with wiring of the TV or trailer.
I donít understand why there would be an issue discharging the TV batteries since theyíre going to be at 12.7v and the trailer batteries are at a higher voltage (13.5?). It seems the issue would be discharge of the trailer batteries into the TV.
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Old 05-12-2021, 09:23 AM   #12
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I don’t understand why there would be an issue discharging the TV batteries since they’re going to be at 12.7v and the trailer batteries are at a higher voltage (13.5?). It seems the issue would be discharge of the trailer batteries into the TV.
Lithium batteries have a very low resistance to charging (unlike LA). If they are below full charge (even a small amount), they will pull power from the lead acid battery in your TV. If they are significantly "empty" they will very quickly pull your TV battery down to the point that TV battery can be damaged. The DC-DC charger isolates the two systems. Or, you can simply disconnect the positive side from your TV to the trailer.

This is a non-technical answer. I am sure there are others here that can give you a more technical explanation.
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Old 05-12-2021, 09:56 AM   #13
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Lithium batteries have a very low resistance to charging (unlike LA). If they are below full charge (even a small amount), they will pull power from the lead acid battery in your TV. If they are significantly "empty" they will very quickly pull your TV battery down to the point that TV battery can be damaged. The DC-DC charger isolates the two systems. Or, you can simply disconnect the positive side from your TV to the trailer.

This is a non-technical answer. I am sure there are others here that can give you a more technical explanation.

This is true. Lithium batteries can charge or discharge at a ferocious rate, and if connected directly to the tow vehicle's charging system they not only can discharge the TV's batteries quickly enough to damage them, but the alternator on the TV will work its absolute hardest to recharge the TV batteries at essentially a 100% duty cycle, overheating the alternator and potentially damaging it too. Some alternators on large luxury cars are water cooled to try to prevent damage, and some pickups have two alternators as an option to charge trailer batteries, but even these water cooled alternators and dual alternators can be damaged by the ferocious charge rate of a bank of Lithium Ion batteries. The DC-to-DC charger can protect the TV's battery and alternators from damage.


Also, remember that "dumb" Lithium batteries can charge quickly enough to catch fire, something that just can't happen on lead-acid batteries. Be careful with Lithium batteries.


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Old 05-12-2021, 04:39 PM   #14
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Originally Posted by DaveP View Post
Lithium batteries have a very low resistance to charging (unlike LA). If they are below full charge (even a small amount), they will pull power from the lead acid battery in your TV. If they are significantly "empty" they will very quickly pull your TV battery down to the point that TV battery can be damaged. The DC-DC charger isolates the two systems. Or, you can simply disconnect the positive side from your TV to the trailer.

This is a non-technical answer. I am sure there are others here that can give you a more technical explanation.
Got it. Thanks!
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Old 05-12-2021, 04:57 PM   #15
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I installed a Renogy 20 amp DC-DC charger as part of my LiFePo upgrade. I do not have solar installed, though I do have a 100W Renogy suitcase.

I went with the 20 amp as I wanted to use the existing 10AWG wires from the 7-pin plug.

Just returned from a trip to Utah and can now report on how it performed.

We camped for 4 days at Lake Powell and drained the batteries to about 66% of 210 AH. This was taking two showers a day, running the fans, lights, invertor to power a 750w hair dryer, coffee grinder, etc.

Then drove about 2-hours to Capital Reef. The batteries re-charged to about 88%. We camped there for three days and drained the batteries to about 75%.

We drove home, but by Green River, the batteries were fully re-charged.

The DC-DC charger worked as hoped it that it would help maintain the batteries when traveling while using 10 AWG. I did install a 30amp fuse as protection.
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Old 05-12-2021, 07:18 PM   #16
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Steamy,

We are taking our first trip with the 20 A DC-DC Renogy next week. I am looking forward to observing their performance with our new Renogy lithium batteries. I have already measured 24 amps to the batteries at idle in the driveway. Should work well for charging!
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Old 05-13-2021, 08:13 AM   #17
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Steamy,

We are taking our first trip with the 20 A DC-DC Renogy next week. I am looking forward to observing their performance with our new Renogy lithium batteries. I have already measured 24 amps to the batteries at idle in the driveway. Should work well for charging!
Hi Dave,
did you use the existing 10AWG wires? It seems to work just fine in my configuration.

I considered a RADARC unit or a higher amp Renogy, but did not really want to run separate cables from the vehicle battery to the trailer. It seems like the 20amp unit is a good compromise and value for the money.

I am please with it so far. Good luck on your trip!
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Old 05-13-2021, 05:51 PM   #18
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Hi Dave,
did you use the existing 10AWG wires? It seems to work just fine in my configuration.

I considered a RADARC unit or a higher amp Renogy, but did not really want to run separate cables from the vehicle battery to the trailer. It seems like the 20amp unit is a good compromise and value for the money.

I am please with it so far. Good luck on your trip!
Hi Steamy,

I decided to run new 4 gauge wire with a 30 A fuse. But I come from the overkill department of electrical engineering. Seems like your 10 gauge and my 4 gauge work just fine! I'll let you know how it works out on my trip.
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Old 05-13-2021, 06:46 PM   #19
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I simply pulled the 30A fuse in my truck for the trailer 12v power line in the 7-way. I have enough solar and batteries so I don't need additional charging source.
X2. I did the same. Cost =$0.00.
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Old 05-27-2021, 06:43 AM   #20
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Steamy,

On our trip this last week, the DC-DC generator worked great. We left the campground Monday morning with a 70% SOC. When we arrived home 1 1/2 hours later, the SOC was 83%. Very pleased!
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