DC to DC Charger with MPPT controller + lithium iron phosphate batteries - Page 2 - Fiberglass RV


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Old 12-01-2020, 03:44 PM   #21
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Trailer: LiL Hauley
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Just one more thing. I'm starting to sound like Columbo. Don't over torque the screws on the battery terminals. I have heard of people twisting the terminals inside the battery. One of the reasons I like the Battleborn is they have terminals that stick out of the top and you fasten your wires with a nut and bolt. You won't damage the battery if you over torque them.
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Old 12-01-2020, 06:10 PM   #22
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Name: Ian
Trailer: Escape
British Columbia
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DC-DC Charger and Wiring

Thanks for the input. A friend had also made this suggestion, so in moving from deep cycle lead/acid batteries to LiFePo4 I moved the batteries off the back bumper and put one on either side, at the back of the trailer, under the bench seats. Today I also added the LC line to the charger so I have that 50% option available. Thanks again for putting in the effort to help me, I really appreciate it.
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Old 12-13-2020, 08:15 PM   #23
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Name: Ian
Trailer: Escape
British Columbia
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DC-DC Charger and Wiring

So I have installed the Renogy 20Amp DC-DC charger, and the Renogy 20Amp
Rover MPPT Controller. (as outlined above) But I found out something the hard way that may be helpful to someone else. I initially wired the D+ line and the
LC line from a 12V source in my trailer as that is where the DC-DC charger is.
I couldn't figure out why the charger would not turn on. Then I rewired the D+
(activation wire) and the LC wire to the positive terminal on the input side of the charger; each with their own switch mounted in the trailer. Now everything works perfectly. Seems the D+ and LC lines need the higher voltage of the input positive; vs. the lower voltage of the trailer. So it goes.. hope this helps someone else.
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Old 02-03-2021, 08:36 PM   #24
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Name: Ian
Trailer: Escape
British Columbia
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The Wiring

One final note: I disconnected the 12V line from the trailer plug in to the vehicle.
Because I have the 20Amp DC to DC charger and an MPPT solar controller which are both set for LiFePo4 batteries I did not want this original 12V line to keep sending 4-5 amps to these batteries.
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Old 02-04-2021, 06:27 AM   #25
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Name: Mel
Trailer: aliner
Texas
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DC-DC LFP charging disconnect

Disconnect from TowV or use of on/off switch is good practice I always install to:
-- Avoid depleting TowV battery on the many/most 7-way TowV installs that do not turn off TowV power when engine not running.
-- Avoid continuous LFP charging voltage even when battery is full -- a concern many have
-- Allow other 'smart' charging systems to gradually reduce charging as battery filled.
IMHA, this is a good catch and good practice.
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Old 02-04-2021, 07:03 AM   #26
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One more detail of my system might be of interest. The shore-power-connected chargers in the trailer are a PD 60 amp and a no-name Amazon 3 amp. I have them plugged into switched outlets so I can easily select either one or neither one from the power console.

Addressing Mel's advice to not routinely charge to 100%, I typically run the Battle Born batteries between 60 and 80 percent SOC when I have shore power. When they start getting a little low, I switch on the 3 amp charger, which generally keeps up with the Truck Fridge and lights.

Then, if we are headed out to boondock, I fully charge with the 60 amp charger and keep SOC as high as possible with the TV, solar, and DC/DC converter when towing.

Not as hassle-free as Raspy's system but it works.
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Old 02-04-2021, 09:58 AM   #27
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Trailer: scamp
New Mexico
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Hoping for a little tutoring but worried you folks are way beyond me. Current set up is a Scamp with 170W solar and Sunsaver MPPT charge controller. I disconnected the Scamp electrical feed from the TV so as not to worry about potentially draining the TV. My next trailer will come equipped with a DC-DC charger and I am not sure what its purpose is. Is it to allow the TV to charge from the trailer system when the trailer is on shore power and to allow the TV to charge the trailer when towing?
At any rate, I am installing a LFP battery in the new trailer and I don't want issues with the different charge profiles of the LFP and the lead AGM in the TV and am planning on installing a disconnect between the TV and trailer again.
Is there any downside to this other than the TV won't be charged from the trailer solar or when plugged into shore power; i.e. the TV is on its own just like in the real world?
I appreciate any help here. The new system will be much more complicated than what I have now and I am trying to be ready when it arrives.
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Old 02-04-2021, 11:32 AM   #28
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Name: Mel
Trailer: aliner
Texas
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DC-DC converters can be used to:
A. --(most common) Increase the TowV voltage to 14.1-14.6vdc to properly charge the LFP battery.
B. --Increase the existing RV converter output voltage from lower lead-acid battery charging voltages to the 14.1-14.6vdc needed for LFPs. It's better and more common to replace original converter with a made-for-LFP converter for reliability.
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Old 02-04-2021, 11:42 AM   #29
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Originally Posted by MelH View Post
DC-DC converters can be used to:
A. --(most common) Increase the TowV voltage to 14.1-14.6vdc to properly charge the LFP battery.
B. --Increase the existing RV converter output voltage from lower lead-acid battery charging voltages to the 14.1-14.6vdc needed for LFPs. It's better and more common to replace original converter with a made-for-LFP converter for reliability.

Thanks MelH, I was planning on replacing the converter with a unit compatible with LFP so that would negate the need for the converter under your "B", right? In fact, I am wondering since I want to have the TV isolated from the trailer, if I even need or want a DC-DC converter in there?


Since the DC-DC would be acting on power between the TV and trailer and also on the output of the converter, that would seem to involve a fair amount of wiring. Is that true and would it be crazy to pull that out if I don't need it just to simplify the system and remove parasitic losses?
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Old 02-04-2021, 12:13 PM   #30
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Trailer: Xplore X22
Smith Valley, Nevada
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It sounds like you may not need a DC-DC converter.

Some modern TVs, such as Ram, have a "smart" charging logic in the charging system that will charge Battle Born lithiums just fine. A good way to get significant amps from the TV to the trailer, is to use an Anderson plug near the seven pin plug. This is fed with a pair of #6 wires from the TV battery to the rear bumper, with a 50 amp breaker near the TV battery. Unplug the Anderson if you are concerned about draining your TV battery while parked.

Here is a quote from Battle Born about the charging needs of their lithium batteries. You can see how well it matches the bulk and float voltages of a modern system, and that they say it is fine. You could take some voltage readings from your TV, during bulk and float, to see if it matches. My Ram does.


Battle Born says:

"There is a wide variation among values for charging algorithms for lead acid batteries. The bulk and absorption voltages typically vary between 14.0 and 14.8 V, and the float can vary between 13.2 and 13.8 V. The 12 V Battle Born batteries sit comfortably right in the middle of these ranges. We recommend a bulk and absorption voltage of 14.4 V. A float is unnecessary, since li-ion batteries do not leak charge, but a floating voltage under 13.6 V is fine."
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Old 02-04-2021, 03:41 PM   #31
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Name: Mel
Trailer: aliner
Texas
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Originally Posted by semievolved View Post
Thanks MelH, I was planning on replacing the converter with a unit compatible with LFP so that would negate the need for the converter under your "B", right? In fact, I am wondering since I want to have the TV isolated from the trailer, if I even need or want a DC-DC converter in there?

Since the DC-DC would be acting on power between the TV and trailer and also on the output of the converter, that would seem to involve a fair amount of wiring. Is that true and would it be crazy to pull that out if I don't need it just to simplify the system and remove parasitic losses?
MelH:
I'd delay putting in the DC-DC converter until you find you'd like charging while driving.

Most RV 7-way wiring ends near the power panel. If so, adding a DC-DC converter is usually not hard hard -- it needs TowV external power (Black 10 guage) and Ground (White 10 guage) and you'll usually get about 12-12.9v between them.

I just checked my system with TowV running (I'm getting ready to travel).
Result: It puts out 8.6A at 14.2vdc to the LFP battery using 10AWG 7-way wiring. For a 100Ah, this will charge 8.6%%/hour of drive time. For my 150Ah, I'll get 5.7%/hour. My DC-DC is a Victron Orion-Tr 12/12-9 (about $80 and very robust).

Challenge: After-market 7-way installs seldom disconnect RV external power when engine is off. Disconnect RV plug or switch power off during long stops to avoid depleting TowV battery.
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Old 02-04-2021, 03:53 PM   #32
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Trailer: scamp
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Originally Posted by MelH View Post
MelH:
I'd delay putting in the DC-DC converter until you find you'd like charging while driving.

Most RV 7-way wiring ends near the power panel. If so, adding a DC-DC converter is usually not hard hard -- it needs TowV external power (Black 10 guage) and Ground (White 10 guage) and you'll usually get about 12-12.9v between them.

I just checked my system with TowV running (I'm getting ready to travel).
Result: It puts out 8.6A at 14.2vdc to the LFP battery using 10AWG 7-way wiring. For a 100Ah, this will charge 8.6%%/hour of drive time. For my 150Ah, I'll get 5.7%/hour. My DC-DC is a Victron Orion-Tr 12/12-9 (about $80 and very robust).

Challenge: After-market 7-way installs seldom disconnect RV external power when engine is off. Disconnect RV plug or switch power off during long stops to avoid depleting TowV battery.

Thanks MelH and Raspy, good advice and information. Yeah, it's a new trailer and the DC-DC converter I think comes installed. But, with good solar on the trailer, I won't need the TV to charge the trailer and I don't want power flowing to the TV so I'll almost certainly want to remove teh converter and install a 12V disconnect switch instead. Hopefully, after a couple hours and enough coffee I'll be able to sort out where the switch will need to go! Alternately, I could just cap off the power wire in the trailer to terminate it before it goes to the coupling to the truck or put an in-line fuse there and remove the fuse.
Thanks again, great help!
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Old 02-04-2021, 09:09 PM   #33
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DC/DC converter is also isolater?

I am confused by the worry about being sure the tow vehicle battery is disconnected from the house system. I expect that most decent DC/DC converters isolate the two systems and only allow flow from the starter battery to the house battery and for example, on my Sterling, only when the ignition is on and when the starter battery is above a preset voltage. There is no backwards "leaking" at all. Maybe other units aren't like this? I just assumed they all had the isolation built in.

One other clarification, the words equalize and equalization was used to talk about the cell balancing that the BMS does when above a certain voltage on a LiFePO4 battery equipped with a BMS. It's a little confusing since equalization already has a meaning with respect to battery charging and the BMS cell balancing is not that. This cell balancing only needs to happening once in a while, unless you have very large current flows in either or both directions frequently. With moderate current, LiFePO4 batteries that start out with balanced cells will mostly stay that way, only drifting a little bit as time passes.
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Old 02-04-2021, 10:09 PM   #34
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To Glenn's point, equalizing/equalization applies only to lead acid batteries, not LIFEPO4 batteries:

"An equalizing charge is nothing more than a deliberate overcharge to remove sulfate crystals that build up on the plates over time. ... An equalizing charge also reverses acid stratification, a condition where acid concentration is greater at the bottom of the battery than at the top."

Cell balancing pertains to LIFEPO4 batteries. For "drop in" LIFEPO4 batteries with built-in BMS's such as BattleBorn, Lion Energy, etc, balancing is done by the BMS. Also, generally it is NOT advised to charge a drop in LIFEPO4 battery with a battery charger that has an equalizing cycle unless the equalizing cycle can be switched off/disabled. The reason is that many battery charger equalizing cycles apply a voltage higher than the maximum specified LIFEPO4 battery charge voltage which is typically 14.6 volts. When this happens the BMS in the LIFEPO4 battery will shut the battery down, and charging will stop.
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Old 02-05-2021, 11:12 AM   #35
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Trailer: scamp
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Originally Posted by gtinseth View Post
I am confused by the worry about being sure the tow vehicle battery is disconnected from the house system. I expect that most decent DC/DC converters isolate the two systems and only allow flow from the starter battery to the house battery and for example, on my Sterling, only when the ignition is on and when the starter battery is above a preset voltage. There is no backwards "leaking" at all. Maybe other units aren't like this? I just assumed they all had the isolation built in.

One other clarification, the words equalize and equalization was used to talk about the cell balancing that the BMS does when above a certain voltage on a LiFePO4 battery equipped with a BMS. It's a little confusing since equalization already has a meaning with respect to battery charging and the BMS cell balancing is not that. This cell balancing only needs to happening once in a while, unless you have very large current flows in either or both directions frequently. With moderate current, LiFePO4 batteries that start out with balanced cells will mostly stay that way, only drifting a little bit as time passes.

my worry is probably mostly caused by my ignorance about what the dc-dc converter does and doesn't do. but, the fundamental issue is that my TV has an AGM whereas the trailer will have a LFP and I don't want to try to use the same charging parameters for both. Neither AGM nor LFP should be equalized but there are other differences in terms of absorb (boost) voltages and duration as well as Float that need to be different to maximize capacity and lifespan. I am aware of the confusing crossover in the use of the term "equalize" for lead acid vs LFP. I don't recall mentioning that earlier so maybe you were referring to a different poster? I like to use the term "balancing" for the process of making individual cells that are in series in an LFP battery equal in voltage, and just use "equalize" for the use of above-absorb voltages in flooded lead acid batteries to burn off the sulfates and restore the batteries to where their internal cells are more equal.
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Old 02-05-2021, 11:53 AM   #36
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my worry is probably mostly caused by my ignorance about what the dc-dc converter does and doesn't do. but, the fundamental issue is that my TV has an AGM whereas the trailer will have a LFP and I don't want to try to use the same charging parameters for both. Neither AGM nor LFP should be equalized but there are other differences in terms of absorb (boost) voltages and duration as well as Float that need to be different to maximize capacity and lifespan.
The AGM starter battery should be handled by the alternator alone and won't involve the DC/DC. I set the Sterling BB1230 I use to LiFePO4 parameters (actually I use the Custom setting because I only charge to 14v, not the 14.4 it chooses and I turn equalization off and float at a much lower voltage). I think there are dual battery DC/DC convertors that can handle two different sets of house batteries, but I am not familiar with those. My starter battery is hooked directly to the alternator and the starter receiving whatever the alternator gives it and the house batteries are behind the Sterling being fed by its custom settings.

I think it was another thread that someone was calling cell balancing equalizing. I just mentioned it for clarification because this stuff is already confusing without added ambiguity.
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Old 02-06-2021, 08:40 AM   #37
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The AGM starter battery should be handled by the alternator alone and won't involve the DC/DC. I set the Sterling BB1230 I use to LiFePO4 parameters (actually I use the Custom setting because I only charge to 14v, not the 14.4 it chooses and I turn equalization off and float at a much lower voltage). I think there are dual battery DC/DC convertors that can handle two different sets of house batteries, but I am not familiar with those. My starter battery is hooked directly to the alternator and the starter receiving whatever the alternator gives it and the house batteries are behind the Sterling being fed by its custom settings.

I think it was another thread that someone was calling cell balancing equalizing. I just mentioned it for clarification because this stuff is already confusing without added ambiguity.

thanks for the clarifications. we're on the same page with charging LFP. 14V (3.5V per cell) is plenty, especially if the charge rate is slow, which it typically is with solar. And, if the charge rates are higher, like on shore power, 14V should still give enough headroom to protect against overcharging as long as the individual cells are balanced fairly well at the top end.
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Old 02-06-2021, 11:25 AM   #38
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Originally Posted by semievolved View Post
Yeah, it's a new trailer and the DC-DC converter I think comes installed. But, with good solar on the trailer, I won't need the TV to charge the trailer and I don't want power flowing to the TV so I'll almost certainly want to remove teh converter and install a 12V disconnect switch instead.
It would be nice to retain the ability to charge from the TV as well as the solar. This for bad weather and to top things off completely when driving. It seems too, that usage will always rise to meet supply. So more management, or power budgeting will be required if you only have solar vs solar and TV charging. Also, you may want an auxiliary suitcase system and will need a port to plug it into.

First, I had no solar with my Oliver, and only the seven pin to charge the trailer. That system didn't even work until I traced it out and fixed it. Then, I had a 100 watt suitcase, but camping in poor weather or in the shade limited that. My 2000 watt Yamaha got used more than I liked so I stopped taking it on trips. For a while, I hooked up jumper cables from the truck to the trailer batteries and that worked well for fast charging. But at North Rim, a ranger came by and told me that was not allowed! Hmmm. Then I got my Black Series with 300 watts of solar on the roof. Wonderful. An abundance of power. Then I added an electric coffee pot, charged my electric bike, and was casual about leaving the inverter on and lights on. Pretty soon, I found the limit, especially on cloudy days. An MPPT controller helped, but two more collectors are waiting in the garage to go on the roof. If I need a bit of charging, the Anderson plug brings in up to 50 amps from the truck straight to the batteries (AGMs for now). And that same plug up on the tongue can plug in my suitcase or run my electric/hydraulic jack, or my air compressor for airing back up after leaving the desert. Having a plug up front that can take power in from different sources, or feed power out to run equipment is very handy.
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Old 07-05-2021, 07:11 AM   #39
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Mel, I have a progressive dynamics, which Battleborn sells, in my camper. It is basically a constant current, constant voltage, 14.6 volt, 40 amp power supply. ...
I wonder how a constant current constant voltage power supply works. A load is a resistance, which in the case of a camper can change. Think turning on a pump or a light or a microwave. If I want the current to remain constant and the resistance goes u I have to drop the voltage and v.v.

I know that a LiFePO4 battery internal resistance varies as the charge state varies, as it gets closer to full the internal resistance goes up. If the resistance goes up and my voltage remains constant, the current will drop. If the resistance goes up and I want the current to remain constant, my voltage must go up.

Something has to give...
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Old 07-05-2021, 09:44 AM   #40
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I wonder how a constant current constant voltage power supply works. A load is a resistance, which in the case of a camper can change. Think turning on a pump or a light or a microwave. If I want the current to remain constant and the resistance goes u I have to drop the voltage and v.v.

I know that a LiFePO4 battery internal resistance varies as the charge state varies, as it gets closer to full the internal resistance goes up. If the resistance goes up and my voltage remains constant, the current will drop. If the resistance goes up and I want the current to remain constant, my voltage must go up.

Something has to give...
I assume it works like my bench power supply. While the battery voltage is below your selected voltage, give max current. When the voltage approaches the selected voltage, decrease current. Stop at some predetermined current at the selected voltage (small, but related to the AH capacity of your battery - I have to do this myself, but it could easily be automated). I am not sure why you want the current to be at a preset when you have ended up in constant voltage mode where it is normal for current to decrease.
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