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Old 05-13-2024, 02:08 PM   #1
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Do I NEED a DC/DC charger?

So here is my deal / use-case.

My ordered rig has no solar; I didn't order solar b/c I've never boondocked, and don't really intend to. It's just not how we choose to camp. Also, for layovers between destinations we always find a KOA or some other place to spend the night; so we always have access to a pedestal.

So, given the above I don't 'need' lithium batts for my coach. 2 80AH AGMs should get me from stop to stop with capacity left over. Yes, I understand I'll only have 80AH total capacity (50% rule). However, as the dealer will have my coach for prep and other upgrades I'm still debating getting lithiums as I won't have to worry about replacing my batteries for a good length of time over the Lifeline AGMs I'm leaning towards.

If I go lithium, I'll have 200AH of battery capacity available to me, which is plenty to get me where I'm going. I don't really care if the tow vehicle is charging them or not; like I said at the end of every leg I'm at a campground.

What I really don't want to do is wire anything into my truck, and ideally I don't want to play around with the wiring on my trailer. I just want to plug the trailer into the truck like normal and get on with it.

Will I do any harm to my truck or trailer by doing it this way? I understand if I turn my truck off, it might be a good idea to unplug the 7-way so that my lithiums aren't back feeding to my truck's battery.

Thanks !
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Old 05-13-2024, 02:56 PM   #2
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I wouldn't worry about adding one, especially if you get the lithiums. You can get by with AGMs but especially with the 12V refrigerator there's just a whole lot more margin and they charge a lot faster. And it gives you the option of staying at a Cracker Barrel on the way instead of looking around for a place to plug in. A DC-DC charger is nice to have, but I'd see how things go first. With the lithiums, I'd disconnect the charging wire (it's in the DC box, not hard to do), so the batteries are being fed by the charger with the correct lithium charging profile.
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Old 05-14-2024, 04:54 PM   #3
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With the lithiums, I'd disconnect the charging wire (it's in the DC box, not hard to do), so the batteries are being fed by the charger with the correct lithium charging profile.
Do you mean to say so that the lithium batteries are only being charged by the converter, w/ the correct lithium charging profile?

When plugged into the pedestal or genny, obviously.
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Old 05-14-2024, 06:02 PM   #4
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Your signature shows "2023 F250 Lariat Supercab". My 2021 F150 has a relay that completely disconnects the 7-pin charge line when the truck is not running, I'm guessing your truck would act the same. In the beginning I left the 7-pin alone after I changed to lithium batteries, allowing whatever voltage in the 7-pin charge line to "feed" the lithiums (DC fridge) while underway. That configuration seemed to at least maintain the state of charge in the batteries but not recharge the lithiums.


Ultimately I added a Renogy DC-DC charger fed directly from the truck battery via an Anderson connector and used the 7-pin charge line to run a relay that would turn the DC-DC on or off.


Completely pleased with the performance of the DC-DC charger. We have 2ea 100A lithiums and in the winter loose about 60A daily with the DC fridge and furnace. Batteries get fully charged after a 2-3 hour drive.


I suggest you leave the 7-pin alone so while underway the truck will maintain the battery state of charge and at the end of the day you'll be on shore power to fully recharge for the next travel day.


Steve
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Old 05-14-2024, 06:12 PM   #5
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I suggest you leave the 7-pin alone so while underway the truck will maintain the battery state of charge and at the end of the day you'll be on shore power to fully recharge for the next travel day.
Steve
Thanks, I hate it when I give bad or misleading advice. Leaving the charging wire connected doesn't hurt. My knee jerk is that I was thinking in my case with solar the MPPT controller can get confused if there is sufficient voltage applied via the charging wire but in this case, there is no solar. I'll sit in a corner for a while.
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Old 05-14-2024, 06:31 PM   #6
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So ... am I hearing if I have no solar panels, and I just want to upgrade to Battleborns in the trailer, I can just have the dealer drop them in (w/ the shunt that reports out the lithium voltage since the AS onboard monitor is useless w/ lithiums) and get on with it like I had hoped?

I won't burn out my alternator, ruin my truck or camper batteries, etc.?

Too good to be true?
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Old 05-14-2024, 07:03 PM   #7
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For my 2, you'd be fine. Your biggest concern is if your converter will "see" that the batteries are lithiums and use the proper charging profile. We were lucky with our 2022 and it was delivered with the WFCO 8955LiS converter which has a physical switch to set to lithium profile. The WFCO 8955-AD seems to be problimatic (green light/blue light). I have no idea what converter you have.


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Old 05-14-2024, 07:10 PM   #8
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I have no idea what converter I'm going to end up with either. Mine starts getting built on Thursday (or so I've been told).
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Old 05-14-2024, 09:01 PM   #9
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Following as I too am confused. Have no solar, normally on pedastal. Just need the extended time of lithium for a couple of music festivals a year in the cooler months. My converter has a lithium setting I can put in place. Just don't want to mess with my umbilical for other towing purposes and really don't want to burn out my alternator.
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Old 05-14-2024, 09:12 PM   #10
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It sounds like you won't be relying on the truck to charge your batteries much, regardless of which setup you choose in the battery box.

My advice would be to do nothing to the 7-wire setup - just leave it be. The dealer can install the two Battleborn batteries, and as long as they also set up the converter/charger to properly charge them you should be fine.

In spite of all the talk of worry about burning up the alternator in the tow vehicle when connected to a trailer with lithium batteries, I don't recall reading of a report where this happened. You won't get much of a charge from the TV to the lithiums, but since you won't be depending on it you should be fine.
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Old 05-15-2024, 04:12 AM   #11
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Sounds like what I was hoping to hear !
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Old 05-15-2024, 09:11 PM   #12
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I apologize to be dense....but am still confused. Why all the discussion of needing DC to DC or you will kill alternator, need a shunt, need this and that? I totally understand a converter/charger that is meant for lithium. But if not doing solar, not boon docking without a generator what should we do?

My plan is to put in a new converter from Best Convertor that has lithium capability and just want to buy the lifepro, set the toggle connector and live off campground or generator to charge without changing anything on my 7 wire umbilical. Will I burn out my alternator or screw something up in the trailer?
So much science and black magic floating around this topic. And I an functional, not an experiment and play person. I want to do it right and have it work.
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Old 05-16-2024, 09:50 AM   #13
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Quote:
Originally Posted by bweybright View Post
I apologize to be dense....but am still confused. Why all the discussion of needing DC to DC or you will kill alternator, need a shunt, need this and that? I totally understand a converter/charger that is meant for lithium. But if not doing solar, not boon docking without a generator what should we do?

My plan is to put in a new converter from Best Convertor that has lithium capability and just want to buy the lifepro, set the toggle connector and live off campground or generator to charge without changing anything on my 7 wire umbilical. Will I burn out my alternator or screw something up in the trailer?
So much science and black magic floating around this topic. And I an functional, not an experiment and play person. I want to do it right and have it work.
Like I said earlier, despite all the talk about alternators dying an early death if a lithium-equipped trailer is pulled behind the tow vehicle I don't see a large number of reports of this actually happening. Can't even remember any reports, actually.

Likely what will happen is nothing other than a slower-than-desired charging of the lithium batteries from the tow vehicle, or possibly no charging of the trailer batteries at all.

If the trailer were to suddenly draw more current than the tow vehicle could handle the fuse will blow.
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Old 05-16-2024, 11:59 AM   #14
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Battleborn says you do not need to disconnect your 7 pin charge wire.



I went more simple. I bought batteries with bluetooth that show state of charge so I could avoid installing a smart shunt. LiTime smart Group 24 100AH. Just installed them and have not used them so I can't vouch for them yet. Much cheaper than Battleborn. I elected not to disconnect my charge wire, but have only done one short tow in that configuration. Happily no drama in that initial tow.
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Old 05-17-2024, 11:06 AM   #15
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Interestingly enough, I emailed Battleborn Wednesday morning to ask this question to no avail. So I've tried calling their 800 number but nobody picks up.

I left a message. Maybe they'll call. *now the Joe Walsh song is stuck in my head*
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Old 05-17-2024, 11:18 AM   #16
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Maybe I should talk about winning the lottery and see if it happens.

Battleborn just called me back and confirmed that plugging in the 7-way will have no negative affect on my alternator. The wire gauge and run length will not support pulling too hard on the truck.

Sounds like I'm having my dealer install Battleborns.
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Old 05-22-2024, 09:05 PM   #17
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Soooo, if the current consensus if doing a simple lithium drop in with the proper converter and not using solar, just shore power via converter to charge there is no chance of burning out your alternator.....how did the red flag of burn out get started?
Who started the burnout the alternator theory that has many of us freaked out?
Just a curious question.
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Old 05-22-2024, 09:38 PM   #18
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You can find some alternator bench testing on Youtube where they overload alternators until they smoke. I'm guessing that's the beginning of it.


I have a Renogy DC-DC 40A and ran 4 GA wire from the battery through an Anderson connector to the trailer and charger. When I first tested it I saw a bit better than 50A load from the battery. I used the charge line from the 7-pin to power a wireless switch which turns the DC-DC ON or OFF. I wait until I'm on the road before I turn on the DC-DC and I know I have plenty of cooling for the alternator. If I run into a traffic jam... switch it off.



Works for me.
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Old 05-22-2024, 10:05 PM   #19
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Originally Posted by bweybright View Post
Soooo, if the current consensus if doing a simple lithium drop in with the proper converter and not using solar, just shore power via converter to charge there is no chance of burning out your alternator.....how did the red flag of burn out get started?
Who started the burnout the alternator theory that has many of us freaked out?
Just a curious question.
Bob
It is theoretically possible to overload an alternator. When I was involved in the bus conversion world it happened even to guy running the huge alternators that buses carry which can put out over 400 amps - they were trying to power two rooftop a/c units via a large inverter and powering everything by the bus's alternator. It could do it, but the extra load generates enormous heat which causes early alternator failure.

On our rigs, if you had adequate wiring and large enough fusing for the lithium to draw all they wanted from the tow vehicle, it is possible to do the same unless your alternator has been upgraded. On stock wiring with stock fusing, it would be highly unlikely.

Where did the rumor start? Some guy doing back-of-the-envelop calculations is my guess, looking at the potential draw of lithium batteries and comparing it to the ability of the alternator to power things.

It is important to keep in mind how much of an electrical demand a modern vehicle makes on the alternator, even without the trailer behind it. It's not just the truck's a/c unit and headlights - much of a modern vehicle is electrically powered, including power steering, air pumps for suspension, rear a/c units, etc.
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Old 05-23-2024, 09:33 AM   #20
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Soooo, if the current consensus if doing a simple lithium drop in with the proper converter and not using solar, just shore power via converter to charge there is no chance of burning out your alternator.....how did the red flag of burn out get started?
Who started the burnout the alternator theory that has many of us freaked out?
Just a curious question.
Bob
My conclusion is that the concern is real for anyone wanting to charge the Lifepo4 batteries from their alternator and simply connects a big wire from the alternator to the charger. Think boat or motorhome. Some alternators may have protection for this, but some do not. It appears that the 7 pin or a DC - DC connection is not going to cause this issue.
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