Lithium battery upgrade questions

[alanmalk]

Originally Posted by John in Santa Cruz

...
Interpreting the graph you posted, If you use a safe 3.0V per cell minimum as your discharge cutoff point, the 3.4V charged cell of a 100AH LiFePO would have about 91 AH, while a 3.5V charge would give 94 AH, and a full 4.2V charge would be 95.5 AH. So if I was designing the charger, I'd target about 3.6-3.8V

First, for anyone following...
The "typical" Lithium RV 100AH battery has 4 cells, so multiply the numbers in this conversation by 4 to view charging voltages. So, targeting "about 3.6" would be a charge voltage of 14.4V. And for a charge of 91AH you need 3.4 X 4 = 13.6V.


Keeping those numbers in mind, I looked at a GoPower manual - slightly newer than the charger in my 2015 Escape. The voltages seem reasonable assuming I don't need the full 100AH of my LiFePO4 BattleBorn battery. But if there are flaws in my logic, kindly follow up with your comments. Thanks, Alan

[Semievolved]

Originally Posted by alanmalk

First, for anyone following...
The "typical" Lithium RV 100AH battery has 4 cells, so multiply the numbers in this conversation by 4 to view charging voltages. So, targeting "about 3.6" would be a charge voltage of 14.4V. And for a charge of 91AH you need 3.4 X 4 = 13.6V.


Keeping those numbers in mind, I looked at a GoPower manual - slightly newer than the charger in my 2015 Escape. The voltages seem reasonable assuming I don't need the full 100AH of my LiFePO4 BattleBorn battery. But if there are flaws in my logic, kindly follow up with your comments. Thanks, Alan

Absolutely Alan! 3.4V/cell (at a slow charge rate) gets you a bit past 90% SOC and many people use that because that leaves them enough capacity and removes any risk of overcharge damage.

[MVA]

Originally Posted by richardr

Jon, Instead of a DC to DC converter, why not disconnect the TV power going to the trailer and only use the solar panels for charging the battery while traveling? If you think that would work, where do you recommend disconnecting it?

You can disconnect the TV charging wire. So interestedly, we toured the Oliver trailer plant while traveling though TN this summer. When I asked the tour/sales person if they install a DC/DC converter when installing their Li package, he stated that they do not connect the charging wire on the 7-pin due to the need to not backfeed current to the TV. Oliver is currently looking at installing a DC-DC converter to allow the TV to charge the LI battery(s).

We did install the DC-DC converter (per Jon's recommendation) so we can charge Li battery while driving at night, on very cloudy days, etc. Works great.

[Centex]

Originally Posted by richardr

Jon, Instead of a DC to DC converter, why not disconnect the TV power going to the trailer and only use the solar panels for charging the battery while traveling? If you think that would work, where do you recommend disconnecting it?

That's the plan for my trailer upon completion of my Solar mods. I intend to simply disconnect the +12VDC 'battery' feed to the trailer at the inside of the junction box on the trailer-end of the umbilical cord.

It's easily accessible, is an easy to R&R 'nut-on-post' connection with a ring terminal, and can be readily restored if I find I don't like it and want to install a DC-DC charger. Carefully insulate the disconnected "hot" side of course, and just leave it tucked-aside in the box. The 7-pin connector on the vehicle will remain fully-functional for use with other trailers.

[Vermilye]

Originally Posted by richardr

Jon, Instead of a DC to DC converter, why not disconnect the TV power going to the trailer and only use the solar panels for charging the battery while traveling? If you think that would work, where do you recommend disconnecting it?

I have a switch on the input to the DC to DC converter so I can disconnect it if the batteries are fully charged. Most of the time I leave it on when I make a long drive with the batteries down & don't have much sun.

I primarily use it to increase the voltage from the truck alternator to better match the lithium battery requirements. A secondary reason it to prevent the lithium batteries attempting to charge the truck battery and to limit the charging current to prevent blowing the 25 amp fuse in the truck's charge line.

If you have enough solar, disconnecting the truck to trailer charging system would work. I'd do it at the truck since Escape uses the charge line to power the breakaway switch. Disconnecting the charge line anywhere between the 7 pin junction block & the batteries would shut of the power to the breakaway switch (and the power tongue jack if you have one).

[Vermilye]

Originally Posted by alanmalk

First, for anyone following...
The "typical" Lithium RV 100AH battery has 4 cells, so multiply the numbers in this conversation by 4 to view charging voltages. So, targeting "about 3.6" would be a charge voltage of 14.4V. And for a charge of 91AH you need 3.4 X 4 = 13.6V.


Keeping those numbers in mind, I looked at a GoPower manual - slightly newer than the charger in my 2015 Escape. The voltages seem reasonable assuming I don't need the full 100AH of my LiFePO4 BattleBorn battery. But if there are flaws in my logic, kindly follow up with your comments. Thanks, Alan

Two concerns I would have with the non lithium GoPower solar controller.

According to the chart, it only goes into the 14.4V bulk/absorption stage for 30 minutes each morning. This is not long enough to do much charging, let alone provide 14.4V for the length of time necessary for the BMS to do cell balancing. According to Battleborn, balancing takes place after the batteries are charged to 98% SOC and should be at 14.4V - 14.6V for 20 minutes per battery. The battery needs to get down to 12.3V for it to go into the bulk/absorption stage to run 2 hours. The problem with this is that a lithium battery voltage will stay above 12.3V even down to 20% SOC. Will the GoPower controller ever go into bulk/absorption, and if it does, will it stay in bulk/absorption long enough to go from 12.3V - full?

The second problem is the float is a bit high for lithium at 13.7V. Battleborn recommends 13.6V or none.

[alanmalk]

Originally Posted by Vermilye

Two concerns I would have with the non lithium GoPower solar controller.

According to the chart, it only goes into the 14.4V bulk/absorption stage for 30 minutes each morning. This is not long enough to do much charging, let alone provide 14.4V for the length of time necessary for the BMS to do cell balancing. According to Battleborn, balancing takes place after the batteries are charged to 98% SOC and should be at 14.4V - 14.6V for 20 minutes per battery. The battery needs to get down to 12.3V for it to go into the bulk/absorption stage to run 2 hours. The problem with this is that a lithium battery voltage will stay above 12.3V even down to 20% SOC. Will the GoPower controller ever go into bulk/absorption, and if it does, will it stay in bulk/absorption long enough to go from 12.3V - full?

The second problem is the float is a bit high for lithium at 13.7V. Battleborn recommends 13.6V or none.

Points worthy of consideration, for sure.

It is unlikely that the batteries will reach the 98% SOC required for balancing while in daily use. But I am thinking that while the trailer is sitting unused the solar will eventually get them up to 100%. Another option is using a DC-DC converter set at 14.4V while under tow. The unknown at this point is "how often do LiFePO4 batteries need balancing"?

Regarding the question of the voltage dropping below the 12.3V threshold to trigger the Bulk&Absorption cycle - my guess is "highly unlikely" given the lithium voltage curve. Which brings us to point #3, the float voltage. 13.7V float is actually a charging voltage for LiFePO4, but at the low current (?) provided by the GoPower. It will eventually bring the battery up to 90-94% SOC at which time it is a "true float" situation (battery stops accepting much current). But given our average daily withdrawal from the batteries, it is likely to reach that true float at the end of the sunlight charging period (aka, evening). For long term storage when the batteries remain above 90%+ SOC we might have to disconnect the solar.

All-in-all, it is really a tricky decision to go to lithium. Lead-acid technology has been around a lot longer and most of the questions regarding lead-acid have been answered. We are the guinea pigs for lithium RV battery usage. But there is no denying the weight advantage and the flat voltage curve (I'm in my second year of using a LiFePO4-100AH battery for fishing). Whether we all get those 5000 cycles and the $$$ savings in the long run - time will tell. Will the battery companies be around in 10 years to honor their warranties? Will I be RVing? Time will tell...

[AllanEdie]

I also installed a dc-dc charger on our E21, but I used the TV charge wire to turn on the charger when the TV is running, and turn it off otherwise. The charger is only turned on when it sees charging voltage on the control wire which is now supplied by either the TV alternator or the shore power charger. I use the shore power charger only to supply the DC-DC charger because the latter has better charge control.

I installed a completely separate battery cable circuit between the alternator and the DC-DC charger, with a plug at the TV bumper which allows a disconnect between TV ad trailer. The standard charge wiring, at least on my truck, is useless over that distance - far too much voltage drop at charging amperages because the wires are too small.

[alanmalk]

Originally Posted by AllanEdie

...
I use the shore power charger only to supply the DC-DC charger because the latter has better charge control.
... far too much voltage drop at charging amperages because the wires are too small.

Not a bad option to use a high quality DC-DC converter with a lithium charging algorithm in place of the stock WFCO. Solar, WFCO and TV alternator can all function as inputs since the heart of the device is similar to the innards of an MPPT solar charger. It will also - within reason - compensate for wimpy wiring between the alternator and the back of the trailer. (On my Tacoma just using the 'fridge on DC will drop more than 1 volt. A 30 amp charger might cause a 3 volt drop.) Thanks for the suggestion.

[AllanEdie]

That voltage drop will defeat any attempt to charge deep cycle batteries in the E21 from the TV due to the length of the run. A dedicated charger near the batteries is the only way an effective charge can be delivered to the batteries. It can be a DC-DC which was my choice, or it could be 120 volt charger fed by an inverter on the TV. If the DC_DC option is used, the charger must be capable of raising the input DC voltage as needed to proper charge voltages. IMO this setup also requires a dedicated charge circuit between the TV alternator and the DC-DC, the ones standard in most trailer wiring are inadequate.

If you are actually in the market, I have had great service and excellent chargers from Sterling Electric. I have owned several of them, all worked perfectly.

[dstreight]

FWIW, some have discussed physically isolating the TV battery from the trailer side via the DC-DC charger; however my Sterling BB1260 serves as an isolator too. My only gripe with the Sterling: Its definitely not intuitive to set-up the charge profile setting; would be super nice if it had a Bluetooth interface. Otherwise it works as advertised.

I'm using a pair of Anderson SB175 connectors with the environmental boots...one on the trailer side and one on the TV side to connect properly sized cable from the battery to the bumper of the TV; ditto the trailer side.

[AllanEdie]

Agreed on the Sterling programming, that is the one area that they might improve their product. OTOH, if one wants full programming flexibility to individual battery preferences, some complexity is hard to avoid. Perhaps there are equally effective chargers out there with easier charge setups, but I could not find one when I was in the market. The good news on the programming issue is that Sterling actually answers their phone and provides immediate access to someone who is technically able to help. In my experience, that is pretty rare these days.

[alanmalk]

Originally Posted by AllanEdie

...
If the DC_DC option is used, the charger must be capable of raising the input DC voltage as needed to proper charge voltages. IMO this setup also requires a dedicated charge circuit between the TV alternator and the DC-DC, the ones standard in most trailer wiring are inadequate.

If you are actually in the market, I have had great service and excellent chargers from Sterling Electric. I have owned several of them, all worked perfectly.

Raising the tow vehicle voltage is indeed the main function of a DC-DC charger. The Victron brand of chargers specifies an input voltage as low as 10V, and a lithium-compatible output voltage.

Originally Posted by dstreight

FWIW, some have discussed physically isolating the TV battery from the trailer side via the DC-DC charger; however my Sterling BB1260 serves as an isolator too. My only gripe with the Sterling: Its definitely not intuitive to set-up the charge profile setting; would be super nice if it had a Bluetooth interface. Otherwise it works as advertised.

I'm using a pair of Anderson SB175 connectors with the environmental boots...one on the trailer side and one on the TV side to connect properly sized cable from the battery to the bumper of the TV; ditto the trailer side.

Love the Anderson connectors. I've standardized my boat connections to use SB50s and am moving trailer connections for my ham radio and 400 Watt inverter to SB50s.

Sterling products seem robust enough but the minimum input voltage that I can find with 5 minutes of research is 12.2V, which would indeed require a rewire of the tow vehicle and probably the Escape. On the other hand, Victron doesn't appear to have a 60 Amp DC-DC charger with a lithium profile.

Clearly this project will require much investigation. At least as of this morning I am leaning towards a pair of Victron chargers, one for each battery. Subject to change of course as more input is gathered.

[dstreight]

The BB series, including my BB1260, has a LFP profile. Additionally, one can program a complete custom profile if needed/wanted.

[alanmalk]

Got to run...
Off to a 4 day camping (fishing) trip.
Thanks for all the input, will look for more on my return.

[AllanEdie]

I use the Andersons as well. They work fine.

FWIW, I don't think there is much advantage in going to a 60 amp charger, at least not with AGM batteries. Maybe Lithiums would accept higher amperages for longer, but AGM's of the size of the standard 6 volters in and E21 will only accept more than 30 amps for a short while, most of the charge cycle will be at lower amperages than that no matter what the capability of the charger. Flooded batteries are even worse. It is the battery that determines acceptance rates. The charger controls voltage - it only limits amperage if the battery tries to accept more amps than the charger can deliver. I find the 20 amp Sterling that I use lots of charge capacity in combination with solar. We spend almost all of our time off grid.

[AllanEdie]

Two chargers? Not sure I understand why you need two of them.

[rubicon327]

Originally Posted by alanmalk

Sterling products seem robust enough but the minimum input voltage that I can find with 5 minutes of research is 12.2V, which would indeed require a rewire of the tow vehicle and probably the Escape. On the other hand, Victron doesn't appear to have a 60 Amp DC-DC charger with a lithium profile.

Clearly this project will require much investigation. At least as of this morning I am leaning towards a pair of Victron chargers, one for each battery. Subject to change of course as more input is gathered.

Not exactly sure what you are trying to accomplish but if you are aiming for 60A you may be able to wire two Victron 30A units in parallel.

[richardr]

Originally Posted by Vermilye

If you have enough solar, disconnecting the truck to trailer charging system would work. I'd do it at the truck since Escape uses the charge line to power the breakaway switch. Disconnecting the charge line anywhere between the 7 pin junction block & the batteries would shut of the power to the breakaway switch (and the power tongue jack if you have one).

Thanks for this advise. I will look into pulling the fuse in the TV instead. It's a 2017 Tundra and fuse 37 is 40A labeled "Trailer Towing".

[oldwave]

Hope that doesn’t deactivate your brakes .