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Old 02-19-2024, 06:29 PM   #1
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2014 DX3 Conversion to LiFePO4 and Protection of Alternator

Hi people: I'm just about to convert to a 24V LiFePO4 system in my 2014 DX3, and I've got the batteries, a new 3000W 24V inverter, and a DC-DC 24/12 converter ready to install (I've got a Midnight solar charge controller that will handle 24V, and 1.53 KW solar panels).

Question- what is the best/simplest/least expensive way to protect my chassis alternator? I know these may not all be the same answer. Thanks.

Steve
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Old 02-20-2024, 01:17 AM   #2
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I did the same concept (except used 48V) once before. The one thing I overlooked was the capability of the DC-DC converter. I used a 70A converter by the math and everything worked fine EXCEPT for the auto-leveling. The amount of surge current for the auto-leveling motors sucked-down the 12V DC-DC output so low that it reset the auto-leveling controller. Just thought I'd throw-in my experience in case it helps...

With respect to protecting the alternator, you would use a DC-DC converter (Victron or Renogy have them--Victron has a new one coming out in a month--programmable up to 50A). One might use the Li-BIM if it was a 12V battery, but your 24 volt won't cut it. You'll loose the ability to jump your chassis battery from your coach battery; but probably not a big deal. Good luck. Tom.
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Old 02-20-2024, 06:11 AM   #3
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I did the same concept (except used 48V) once before. The one thing I overlooked was the capability of the DC-DC converter. I used a 70A converter by the math and everything worked fine EXCEPT for the auto-leveling. The amount of surge current for the auto-leveling motors sucked-down the 12V DC-DC output so low that it reset the auto-leveling controller. Just thought I'd throw-in my experience in case it helps...

With respect to protecting the alternator, you would use a DC-DC converter (Victron or Renogy have them--Victron has a new one coming out in a month--programmable up to 50A). One might use the Li-BIM if it was a 12V battery, but your 24 volt won't cut it. You'll loose the ability to jump your chassis battery from your coach battery; but probably not a big deal. Good luck. Tom.
Great info- thanks Tom. I hadn’t thought about the auto- leveling issue (other than believing 70 A was enough)- my DC/DC is also 70 A.
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Old 02-20-2024, 11:25 AM   #4
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If you don't have auto-leveling, you're good. If you do, you might try and measure the surge current it draws off the current setup. Mine was a huge 5th wheel, so there was a lot of mass. Perhaps if it were lighter, the 70amp DC-DC would have worked. Just a thought. Remember that they are rated for 70 amps continuous, but the surge capability is pretty terrible. That would be OK for a motor-only; but if their controller dies during the operation, you're screwed.
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Old 02-20-2024, 11:58 AM   #5
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If you don't have auto-leveling, you're good. If you do, you might try and measure the surge current it draws off the current setup. Mine was a huge 5th wheel, so there was a lot of mass. Perhaps if it were lighter, the 70amp DC-DC would have worked. Just a thought. Remember that they are rated for 70 amps continuous, but the surge capability is pretty terrible. That would be OK for a motor-only; but if their controller dies during the operation, you're screwed.
I DO have auto-leveling, on my 2014 DX, GVWR 33,000 lb, so it sounds like it will be an issue. I reached out to Power Gear to ask if they have an idea what the surge would be, so we'll see if they come back.
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Old 02-20-2024, 12:15 PM   #6
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I never did find a solution. We ended up keeping one of the 12V batteries (connected to the hitch-electrical for charging) JUST to drive the auto-leveling. Luckily, the 5th wheel had a lot of room and weight.
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Old 02-20-2024, 01:25 PM   #7
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I never did find a solution. We ended up keeping one of the 12V batteries (connected to the hitch-electrical for charging) JUST to drive the auto-leveling. Luckily, the 5th wheel had a lot of room and weight.
Yes- gotta love the big 5ers. Now I'm thinking I could just route the auto-leveler power to the chassis batteries.
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Old 02-20-2024, 01:54 PM   #8
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24V?
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Old 02-20-2024, 01:56 PM   #9
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Oh, sorry, no I get it. You'd use the 12V from the chassis. Not the 24V from the coach. Yep, that would probably work fine.
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Old 02-20-2024, 02:02 PM   #10
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Oh, sorry, no I get it. You'd use the 12V from the chassis. Not the 24V from the coach. Yep, that would probably work fine.
Actually- I need to check that. I know I've got two 12V chassis batteries, but I haven't checked to see if they're in series or parallel. They're starting a 8.9 Cummins diesel.
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Old 02-21-2024, 05:51 PM   #11
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If you don't have auto-leveling, you're good. If you do, you might try and measure the surge current it draws off the current setup. Mine was a huge 5th wheel, so there was a lot of mass. Perhaps if it were lighter, the 70amp DC-DC would have worked. Just a thought. Remember that they are rated for 70 amps continuous, but the surge capability is pretty terrible. That would be OK for a motor-only; but if their controller dies during the operation, you're screwed.
Tom- or others- got another glitch in my understanding. My RV service was out today to look at the installation of the new system- 3000W 24V inverter/charger, two 270AH LiFePO4 batteries, and the 24/12 converter (70A) that I thought might do the job. However, RV guy inspects current set-up, and says that he sees breakers/fuses to 150 A for some 12V lines going into the coach, so I need a DC/DC 24/12 converter with a rating of 150 A or more. Wow- these are not readily available, and the only ones I found were around $650. Does this sound right? My RV guy and I don't know why the POs used such big 12V breakers- maybe just used what they had on hand??
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Old 02-21-2024, 06:27 PM   #12
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Do a energy audit to see what may actually draw the amps.

Check with the 24 to 12 converter manufacture to see if you can just double up the 70 amp one you have.

The generator may use a 150 breaker. Move it to the chassis battery, but Mahe sure your charging it while it's running.
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Old 02-21-2024, 08:47 PM   #13
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The large 12V current draws in a motor home will be the inverter (which you'll power off of 24V now) and the jacks/pop-out motors. Its this second one that gets you. Especially for your weight. When I did this, I considered doubling up the 70A power supplies (using two large diodes to isolate them from each other), but I ended up not doing that. I probably should have. In truth, the leveling jacks "almost" worked, so I expect a second 70A supply would have made it work. This was a large 5th wheel, and I think your setup might be 2X the weight. You might clip a current/voltage meter on your battery and see what happens today when you use your leveling jacks.

There is a forward voltage drop going through the diode that you'd want to consider as well. Ideally, your 12V supply might be tuned-up just a bit (e.g. 12.5V) allowing your post diode values to be 11.5V or so. Just a thought.

Time for some experimenting....

p.s. I do have some experience with connecting the output of the 70A DC-Dc converter to the alternator charging voltage (it was a mistake). This caused SMOKE from the converter--interestingly, it continued to work, but cooked the capacitors inside. Lucky it was low cost

I too did not see a cost-effective DC-DC converter at the higher amperage (although I was looking for 48->12.
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Old 02-22-2024, 12:28 PM   #14
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I remember working on 12/24 volt systems on over the road trucks years ago. They were not fun to keep working that is why you do not see them anymore. Good luck getting it to work, hope you don't open up a can of worms. I would just switch the house Batties to 6 volts if you are looking for more amps.
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Old 02-22-2024, 06:34 PM   #15
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I've read through all the posts and perhaps I missed something but why 24V? Two 12 v batteries wired in parallel are the norm and with two 270 AH LifePo4 batteries, you've got a total of 540 usable or at least 90% of that. Most likely the batteries you replaced were rated at 200 AH each but you only have 50% of that usable so you increased your total usable AH from 200 to 540.


What requires 24V in the coach?
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Old 02-22-2024, 08:20 PM   #16
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Investigate if ..... is it possible to leave a separate 12v battery on the 12v side, that battery can handle any normal 12v loads. (slides, levelers etc etc)


keep the 24v separate and only use it to power the inverter

shorepower... Leave the original 12v converter in place to charge the 12v
add a separate 120v 24v charger for the big bank.

if/when you add solar you can charge the 24v battery side with the solar + the 24/12 to top up the 12v?
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Old 02-22-2024, 09:22 PM   #17
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Why 24V? Wire size and choice of 2 batteries (8 LiFePO4 cells). Taken to its logical (affordable) extreme, is to use 48V (16 cells)--That's what I did. There are very nice all-in-one boxes that provide 3.6KW DC-AC converters, 48V charger, MPPT controller and AC transfers switch with intelligent switching for $650. They make the same for 24V (just thicker wire and some other current limits). I had a 48V to 12V 70A DC-DC converter to run any legacy 12V loads.

I ended up using a separate 12V AGM battery (that I had left over) to run the levelers (not needed for the slides) and charged it off the trailer hitch connection just to keep it topped-off. A lot of extra weight, though. Not ideal, but it worked. This was on my brother-in-law's 5th wheel and he loves. He can run his AC for 9 hours off batteries. I put 1Kw solar on the roof and 600 W "roaming" solar where he deploys some folding panels to a sunny location and runs a regular green 12 or 14 Ga power cord (with custom adapters to MC4) to capture more sun in shady campsights.
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Old 02-26-2024, 11:42 PM   #18
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The new Renogy DC-DC charger I can recommend. It has buck and boost so you can go from 12v to charge 24v, vice versa, or 12v-12v or 24v-24v. That versatility was the main reason I bought it, but I've found it's easy to install and weatherproof, recognizes when to shut off without a starter sense wire, you can adjust charge from 10-50amps on the fly via Bluetooth, etc. Oh, and it has an mppt charger built in too. RENOGY 12V/24V IP67 50A DC-DC Battery Charger with MPPT
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Old 02-27-2024, 12:49 PM   #19
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I love Renogy's concept here. It also trickle charges your chassis battery from solar if available. One drawback is that the maximum charging current is 50A (from both sources). Alternatively, if you had a large battery and solar array and separate MPPT charger and DC-DC Alternator charger, you could run them both in parallel and get 100A of charging while driving down the road. That may be overkill for smaller batteries.
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