Word of warning for LiFePO4 battery conversions (Battle Born)

[DannyClark]

Thanks a ton Trout. When i figure out the BMV712 I’ll move forward on the Orion via your advice, and probably a better charger. My OEM unit isn’t getting the BB’s past around 13.7volts.

[larry9000]

Originally Posted by SCOTTinNJ

Can you tell me what voltage your BB batteries sit at generally? Say at night with no large loads and fully charged? Thanks.

Sorry for the delay in reporting back. I started too late in recording Voltage vs. Capacity Remaining on my recent boon docking adventure, so never recorded the fully charged value. I was taking out 30Ah a day, and putting back 20Ah each day, so it never got fully charged in the latter days. What I did find was little correlation between voltage and % remaining. This shows the value of the battery monitor.

So I ran an experiment this morning at the RV park. The battery monitor said fully charged, so I disconnected AC to the trailer, and waited until the solar charge in was equal to the power being drained- that is, exactly 0 current into or out of the battery. Voltage was 13.53. I'm not sure this is peak voltage, but a reasonable value for fully charged. I have a hunch I could have gotten a higher value if I temporarily put the 14.4v from the converter onto the battery.

[larry9000]

Originally Posted by larry9000

So I ran an experiment this morning at the RV park. The battery monitor said fully charged, so I disconnected AC to the trailer, and waited until the solar charge in was equal to the power being drained- that is, exactly 0 current into or out of the battery. Voltage was 13.53. I'm not sure this is peak voltage, but a reasonable value for fully charged. I have a hunch I could have gotten a higher value if I temporarily put the 14.4v from the converter onto the battery.

I ran one more experiment- I turned on the PD converter into Boost mode. That placed 14.4 v (actually, a bit more than 14.5v) onto the battery. It charged at 30A in for a few moments and quickly declined to 0, fully charged. I then disconnected from AC, watching the battery voltage with a 2.2A load (solar was in float mode, not adding power). The voltage started at 14.35v, but declined to 13.5v over 10 minutes or so. I didn't measure beyond that.

So my conclusion is that 13.5v is a full charged battery with little load on it. I have noted that when drawing or charging significant current that voltage will change due to internal resistance of battery. That is, the voltage will read higher when charging, and read lower when discharging.

[Tincampers]

Originally Posted by larry9000

I ran one more experiment- I turned on the PD converter into Boost mode. That placed 14.4 v (actually, a bit more than 14.5v) onto the battery. It charged at 30A in for a few moments and quickly declined to 0, fully charged. I then disconnected from AC, watching the battery voltage with a 2.2A load (solar was in float mode, not adding power). The voltage started at 14.35v, but declined to 13.5v over 10 minutes or so. I didn't measure beyond that.

So my conclusion is that 13.5v is a full charged battery with little load on it. I have noted that when drawing or charging significant current that voltage will change due to internal resistance of battery. That is, the voltage will read higher when charging, and read lower when discharging.

I’ve read that you cannot rely on voltage readings of a freshly charged battery.

[larry9000]

Originally Posted by Tincampers

I’ve read that you cannot rely on voltage readings of a freshly charged battery.

I think this is true. I recorded V vs % Capacity remaining and found little correlation. Also, the amount of charging or discharging influences the voltage reading too. I attained the same 13.5v as fully charged when actually at 79% of capacity. However I had 8A of charging current going into it. I eyeballed the results, and the battery acts as if it has a 0.03 ohm impedance. That is, 3A of charging current will raise the voltage approximately 0.1v.

[uncle_bob]

Hi

As you charge a battery it heats up. As you let it sit, it cools down. If you heavily discharge a battery, it heats up again. Battery voltage changes with temperature. With some chemistries, it changes more with small temperature changes (5 or 10 degrees) than it does for a modest amount (20 or 30%) of change in charge.

Bob

[DryFly]

One thing I love about this forum is it's so easy to go into the weeds on a technical subject - I learn so much!
If I understand the original post by SilverHouseDreams, the concern is leaving the TV 7-pin connector hooked up over an extended period while using a BattleBorn LifePo battery as a house battery in the TT, especially if hooked to shore power.
I never leave my 7 pin connected after I back in and level the trailer. Ever. So I'm safe, right?
Re towing with the BattleBorn in the TT, the issue seems to be not a question of a problem between the two batteries while towing, but again leaving the TV hooked up after setting up for camping, right?
If both these interpretations are correct, then one answer to the problem is to avoid it by disconnecting the TV from the TT after the trailer is leveled. Am I wrong? I'm married, so I'm used to it.

[Twinkie59]

Lol my idea of rv'ing is not pulling into a place with power

[uncle_bob]

Hi

While towing, the voltage regulator in the TV will drop back to a low voltage. That will (to some degree) discharge the lithium pack. Pull over for lunch or a bio break and the voltage regulator in the TV goes to zero with the engine off. You then are in the same situation as any "parked" setup.

Bob

[larry9000]

Originally Posted by DryFly

One thing I love about this forum is it's so easy to go
If I understand the original post by SilverHouseDreams, the concern is leaving the TV 7-pin connector hooked up over an extended period while using a BattleBorn LifePo battery as a house battery in the TT, especially if hooked to shore power.
I never leave my 7 pin connected after I back in and level the trailer. Ever. So I'm safe, right?
Re towing with the BattleBorn in the TT, the issue seems to be not a question of a problem between the two batteries while towing, but again leaving the TV hooked up after setting up for camping, right?
If both these interpretations are correct, then one answer to the problem is to avoid it by disconnecting the TV from the TT after the trailer is leveled. Am I wrong? I'm married, so I'm used to it.

Hi Dry Fly,

I think that SiiverHouseDreams focused on the aspect that the TT battery would discharge into the TV battery while hooked up and parked to start this thread. If that was the only issue, I agree, you could just unhook the 7 pin plug. You may not even have to do that if, like my 4runner, it disconnects the 12V power going to the plug when the ignition is off.

Alas, I found current drain to be the case even when driving! I used the BMV battery monitor and a bluetooth connection to the BMV app to monitor while driving. For a few minutes, the high revving motor and alternator would charge the Battleborn battery, but it would settle into a low output mode while driving where 1 to 2 amps of current would flow the other way- from the TT battery to the TV battery. This is undoubtedly due to the Battleborn voltage being higher than the TV battery. I don't know how long this current drain would continue, but I assume until the batteries are equalized, which means an undercharged Lithium battery. The bottom line is that I disconnected 12v power completely coming from the TV after a 15 mile test run. (I actually disconnected the wire inside the TT).I can get away with this, because I have solar panels that will keep the Battleborn batteries topped off. The "right" way to do this would be to install a DC-DC converter that would charge the Battleborn from the TV, and not allow current to flow the other direction.

Charging the Battleborn when you have power hook ups is a separate issue, and not connected to the TT-TV current issue.

I hope this helps. (By the way, I like your pen name!)

[Troutboy]

Again, doesn’t an inexpensive dc/dc converter properly installed isolate the two and prevent all of this and other issues?

It’s not clear to me why someone would spend thousands on lithium batteries and not spend $180 to do it the right way and protect the investment.

[RankAm]

Originally Posted by Troutboy

Again, doesn’t an inexpensive dc/dc converter properly installed isolate the two and prevent all of this and other issues?

It’s not clear to me why someone would spend thousands on lithium batteries and not spend $180 to do it the right way and protect the investment.

Troutboy, I have purchased two of the Battle Born 100Ah 12V LiFePO4 batteries, and I do want to protect them. I am looking here for the right DC/DC converter. I need one of the "isolated" models, correct? Do I need technical help to decide which converter I need, or is one of the units a clear choice for use between the tow vehicle and my two trailer batteries?

Also, where do you recommend physical installation of the converter?

Thanks.

Hank

[wulfraat]

Posted earlier in this thread, here are your options:

https://www.victronenergy.com/upload...50-400W-EN.pdf

I am in the process of building my Victron install list for the spring.... I will be using a DC-DC converter no doubt... Either of these ones below should work just fine... Rich to confirm... or give AM Solar a call....

Victron Energy Orion-TR 12/12-30A (360W) Isolated DC-DC converter p/n ORI121236100

or

The Victron Energy Orion-TR 12/12-18A (220W) Isolated DC-DC converter p/n ORI121222110

[lewster]

wulfraat,

The Orion 12/12-30amp is the one for you....................

[wulfraat]

Sweet, thanks for the confirmation Lew.

[rmkrum]

Good data. Appreciate it

[gklott]

Originally Posted by lewster

The Orion 12/12-30amp is the one for you.

Agree, works well.

73/gus

[Troutboy]

Hank,

Sorry for delay, busy day.

I think you should contact battleborn, as I used Victron batteries. Victron has a separate BMS and the dc/dc converter ties into that. In my install, I placed the converter next to the trailer plug box. Red from trailer plug power to converter input, negative/black from the trailer plug went to the negative bus bar, and then from neg bus bar to input of converter.

The output from converter then goes black/neg to the BMS, and the red goes to the trailer positive bus bar.

I tuned the converter for higher output voltage to properly charge the lithiums. You should also contact battleborn and find out the optimum charge voltage and set the Orion to that.

Basically, you want to put the converter between the trailer plug box and your batteries. It might be as easy as disconnecting the negative/positive cables from the trailer plug box, inserting the Orion dc/dc in the middle. Go from trailer plug box, into the converter, then connect the old lines that went from trailer plug box to the output of the converter. You will have to adjust the output voltage first to whatever battleborn tells you.

The description and diagram of my install is at the link below, the diagram is post #5.

http://www.airforums.com/forums/f382...-162955-5.html

Feel free to PM me if you want and I can send files of the drawing to you that are easier to read.

Again, call battleborn and find out what they suggest. Also, I used the converter in Wulfs post, the one Lewster confirmed.

[JayTheCPA]

Agree with the comment that controlling the current is best to occur on the trailer side of the equation as opposed to the TV side. My perspective is that the trailer might / will get towed by another vehicle (example: tow service, rental, or borrowed) which will probably not have electrical rigging to account for the lithium's.


I have one open question in this discussion stemming from TV alternator health. I attended a short seminar about installing lithium's in a boat (in that case, it was a sailboat designed for extended battery use to include air conditioning powered by battery driven inverter), so I know enough at this point to ask questions. One of the discussion points was that something needed to monitor alternator temperature to keep it from overheating and disconnect the lithium battery when / as appropriate. Implication was that extended 100% output on the alternator would get it hotter than normal which in turn raised a question about how long it would operate. IIRC, something was added to the boat's alternator to monitor temperature which in turn fed into the BMS's functionality. Any application to a tow vehicle's alternator versus the sailboat's in terms of controlling the charge?

Maybe alternator temperature and output is something that a new-er tuck's computing systems are able to monitor and control, although this is not something where I have any expertise.



Or, did I miss something about the Orion DC-to-DC converter's functionality in terms of controlling the charge rate as it applied to the TV alternator?

If I did not miss anything and am 'on track' in terms of effects on the alternator, anybody with better expertise have inputs on some alternator regulators that I found (https://www.bruceschwab.com/high-out...-regulators/)? Only down-side I can see is that they are looking like a truck side solution which leaves any other vehicles at risk if they tow the trailer with the lithium battery(ies) in the circuit.

[wponder]

I read this entire thread and I am still trying to understand if I need to do something short term like disconnect the charge line from the bus bar. I tested my 2017 F350 today it has dual HD alt. and tow packages.

With the TT plugged in and tuck off the batteries report standby

With the TT Plugged in and truck on but not running the batteries report standby

With the TT Plugged in and Truck running the batteries report charging

It never seems like the batteries go into a discharging state sending voltage to the TV?

Thanks