LiFePo vs Lead Acid - Knowledge and myths

[John in Michigan]

On two recent outings, I packed two Lion Energy UT 1300 lifepo4 batteries. These are 23 lbs. each. When packing, I put both of them in the TV, then installed one in the trailer at the campsite.

In preparation for each outing, I charged both batteries. To speed this up, I used two chargers:

1. Battery Tender 4.0 Amp Battery Charger & Maintainer Model 022-0209-BT-WH with a LIFEPO4 charging mode (EDIT: corrected charger name and model number)

2. CTEK MUS 4.3 (Part No. 56-864) charger with NO LIFEPO4 charging mode

I set the CTEK (no LIFEPO4 charging mode) to "normal battery program" which charges to 14.4 volts at 4.3 amps. I then charged one of the batteries. When the CTEK charger indicated it had reached float mode (e.g., charging complete), I then switched this battery to the Battery Tender charger in LIFEPO4 charging mode (and the other battery to the CTEK charger), and guess what? Within 20 seconds or so the Battery Tender charger indicated the battery was fully charged.

So both of these chargers fully charged these batteries.

[John in Michigan]

The CTEK MUS 4.3 (Part No. 56-864) charger with NO LIFEPO4 charging mode progressed past the desulphation step in less than a second, so no issues there.

[jwcolby123]

Originally Posted by FloridaNativeMike

Not being argumentative or picking nits here, but with PbA batteries, all you need for charging off the alternator is a high amperage relay (~$10). For a Li-ion or LiPo you need a DC-DC charger ($150-200) to make it work. So, you must factor that into the initial cost as well, but still with the 2-4x range originally quoted (but much closer to 4x).

-Mike

Mike, the issue is that a Lifepo4 battery can be charged at extremely high currents, well beyond what your alternator is designed to deliver and for long periods. Your alternator may be destroyed.

Yes a PbA house battery is easy.

[parmm]

Originally Posted by jwcolby123

Mike, the issue is that a Lifepo4 battery can be charged at extremely high currents, well beyond what your alternator is designed to deliver and for long periods. Your alternator may be destroyed.

Yes a PbA house battery is easy.

That is what they make 12 vdc to 12 vdc battery chargers for!!! You run a 4 or 6 gauge line from you tow vehicle battery to the front of your trailer where your house batteries are and locate the charger there. Make sure you get a isolated charger. No alternator problems!!!

[parmm]

Now that I've stated the extent of my knowledge above, I have questions on what accessories I need if I were to swap my Scamp 19 battery out for two LiFePo4 100 ah batteries? Not planning solar. We usually travel 300 miles a day with a couple stops during the day. We usually stop at a campground where we can use shore power. How large of a DC/DC charger would I need. I am thinking a Orion-TR Smart 12/12V-30Amp Isolated Charger should be adequate. And I know I am going to have to swap out my converter charger and wiring. Would the Progressive Dynamics 45Amp LiFePO4 Converter Charger be big enough? As to the batteries, I pretty much have my mind made up - Battleborn heated.


Oh, planning a 12 volt TV, 12 volt coffee maker, computer on 12 volt charger and other 12 volt chargers for phone, etc. Also thinking of change out the dying Dometic 3 way fridge for a 12 volt compressor fridge, and installing a Maxx Air roof fan. All the lights have been swapped out for LED. I have experience with the Dometic "Electric Portable Travel Coolers". They are compressor units which refrigerate or freeze I have been running one for 4+ years now in the back of my Honda Odyssey. It starts up every time I start the van. We use if on weekly grocery trips to keep frozen items frozen. We also use it to keep drinks and snacks cold. Saved a fortune when we took the grand kids to Yellowstone while we were RV less!! Has not affected the Honda's battery at all. Considering how I have mis-used the Dometic cooler I own, I would definitely consider a 12 volt fridge for the Scamp. Think it would be ideal.

[jwcolby123]

Originally Posted by thrifty bill

The cost difference is closer to 10X. If/when it gets down to 2X, its over. Group 27 marine/RV battery at Walmart = $81.




"2) Upfront costs are 2-4 times the cost of PbA"

Did you happen to read the very first link I placed in my large preliminary post. Comparing any PbA battery usage to LiFePo is... like apples to oranges. Yes the cost is $84 but what you are getting is a mess. There was a time when a mess was all that you could get. If a mess works for you then that is also fine. And in fact it does work for many people, I have already clearly expressed that.

To be clear, I have owned RVs for decades and I used PbA batteries. And I hated them. And I replaced them when I killed them. And I hated them. And I replaced them, over and over and over and over and over...

I am done with that. And I truly do not care what anyone else does. But to do a simple "it is X times more" misses the entire point and isn't true anyway. At this very point in time, LiFePo batteries, when taken over the life of the RV are several times cheaper than PbA batteries. And zero maintenance.

That point in time is long since past.

And yes, up front cost is still marginally larger. I paid $500 for a real 100ah usable for at least 3000 charge cycles. I will never again pay $84 for a PbA battery. I'm done with that.

[jwcolby123]

Originally Posted by parmm

Now that I've stated the extent of my knowledge above, I have questions on what accessories I need if I were to swap my Scamp 19 battery out for two LiFePo4 100 ah batteries?

Let's start with this. Given what I am seeing in the rest of your post I think that two batteries are overkill. BTW Battleborn will do a (free I believe) system plan for you. Send them an email with this post included and see what they say.

If you are staying in campgrounds with shore power, there is no way that you will drain even one LIFePo4 battery down very far. The big advantage of LiFePo chemistry.

Not planning solar. We usually travel 300 miles a day with a couple stops during the day. We usually stop at a campground where we can use shore power. How large of a DC/DC charger would I need.

A LiFePo battery charges at whatever rate you give it. It really doesn't matter whether you have one or a dozen 100ah batteries, it is how much amp hour you actually use that matters. So...

assume that you drive for awhile and then stop for an hour. You use the coffee maker at your first stop of the day. Assume it uses 1100 watts for 10 minutes. That is 1100 / 6 = 180 watt hours total, i.e. about 14 amp hours total draw. You have 86 remaining. You fire up the laptop while you are waiting for your coffee. 110 watts for .5 hours is 55 watts hours or about 4 amp hours. You have 82 amp hours left. Those compressor fridges use about 40-60 watts. Let's say it actually runs the whole time you are stopped, That is 60 watt hours or 4.5 amp hours. You have about 77.5 amp hours remaining.

You understand how I am running this calculation.

Now you fire up the rig and drive down the road. The Dc-Dc converter has to push about 22.5 amp hours back into the battery. Which means that given the 30ah charger you are considering it is going to take it about 45 minutes to recharge your battery.

I am thinking a Orion-TR Smart 12/12V-30Amp Isolated Charger should be adequate. And I know I am going to have to swap out my converter charger and wiring. Would the Progressive Dynamics 45Amp LiFePO4 Converter Charger be big enough? As to the batteries, I pretty much have my mind made up - Battleborn heated.


Oh, planning a 12 volt TV, 12 volt coffee maker, computer on 12 volt charger and other 12 volt chargers for phone, etc. Also thinking of change out the dying Dometic 3 way fridge for a 12 volt compressor fridge, and installing a Maxx Air roof fan. All the lights have been swapped out for LED. I have experience with the Dometic "Electric Portable Travel Coolers". They are compressor units which refrigerate or freeze I have been running one for 4+ years now in the back of my Honda Odyssey. It starts up every time I start the van. We use if on weekly grocery trips to keep frozen items frozen. We also use it to keep drinks and snacks cold. Saved a fortune when we took the grand kids to Yellowstone while we were RV less!! Has not affected the Honda's battery at all. Considering how I have mis-used the Dometic cooler I own, I would definitely consider a 12 volt fridge for the Scamp. Think it would be ideal.

I love those DC driven compressor fridges. Very efficient and low power draw.

The only way you will need more than a single battery is if you see yourself being off grid for a day or two once in awhile. Even then if you can charge at 30 amps from the alternator just take a drive looking at the scenery.

I know that you say no solar, but they make little units that fold up and give as much as 200 watts. A perfect match for your use case and your battle born battery. And cost way less than that second battle born battery!

Just my opinions of course.

[Raspy]

jwcolby123

John,

I disagree with this paragraph:

"Connecting a LiFePo4 to the tow vehicle battery is not recommended. The biggest reason is that the LiFePo4 can accept enormous charge currents, and can easily burn out the tow vehicle alternator. If you want to charge from the alternator, you should use a Dc-DC converter which is sized to the alternator."

Before you promote that statement, please go to the Battle Born website and read their recommendations. Second, the charge rate is determined by many factors. Generalizing that an alternator will be "easily burned out" is not true. Victron did a test that showed a smoking alternator, but it was set up in a controlled setting that had nothing to do with an automotive application and was designed to make the alternator fail. It was a sales pitch and misleading. I tested one of my alternators with a dead short form the output to ground and it did not burn out. DC-DC chargers are fine, but not always needed. The lithium batteries have a BMS controller inside to protect them and the typical automotive voltages are within the specs of Lithium batteries, according to Battle Born. Lithiums do not need a float voltage, but as long as it is below a certain voltage, it will not hurt them in an automotive setting. Rams, for instance, have a smart charging system that drops the voltage to a float level when the battery is charged.

[dleverton]

My day job is designing charge controllers for lifepo4. I think this post is excellent and well covered. A couple comments, lifepo4 can be charged well below freezing, but only if the charge rate is less than C/10, so a 50 AH pack should not be charged at a rate greater than 5A, below freezing. When multiple charge sources are connected to a battery (solar , dc to dc, ac charger etc.) each regulates to some maximum charge voltage (11.7 to 14.1V for nominal 12V packs); they will not fight with one another, but the pack will charge to the highest of the multiple charge source voltages. The only issue is that the currents add and could exceed the max current set by the protection module in the pack.

[CarlD]

[QUOTE=Raspy;821921]

John,

"I tested one of my alternators with a dead short form the output to ground and it did not burn out."

This is not really a good test of an alternator. A short circuit has no voltage but may have current. Since the power produced is the product of voltage and current then you have no power delivered. If you really want to exercise an alternator you need to do it at a point where the product of the voltage and current is maximized. Similar to the way an MPPT solar controller works.

Another thought: If you assume a very low internal resistance of a LFP, then the current delivered to the battery from the TV will be determined by the resistance of the circuit feeding the battery. For example, if the battery is at 12.5 volts and the TV is at 14, you have a 1.5 volt difference. To supply 50 amps the the battery would require a 1.5/50 = .030 ohm wire. There could easily be 60 feet of wire from source to load, which in this scenario would require a 7 awg wire. The problem with this is, as the battery voltage increases, the current drops which prolongs the charge cycle. You can certainly use this droop type of current control to charge a battery, but it a more reliable and predictable solution is to use a current limiting DC-DC converter, where the current is controlled to a maximum value until the voltage setpoint is reached.

[CarlD]

[QUOTE=dleverton;821938] A couple comments, lifepo4 can be charged well below freezing, but only if the charge rate is less than C/10, so a 50 AH pack should not be charged at a rate greater than 5A, below freezing.

Doug, This is the first time I have heard this. Are you, or your company, planning on implementing some kind of temperature dependent current limit in your chargers? In my mind I can't imagine it would be too difficult. You would just need to know the battery temperature and adjust your current limit setpoint. Or perhaps a smart connection the the battery BMS for input. A design like this would certainly remove one of the perceived drawbacks to LFP batteries.

[jwcolby123]

Originally Posted by Raspy

jwcolby123

John,

I disagree with this paragraph:

"Connecting a LiFePo4 to the tow vehicle battery is not recommended. The biggest reason is that the LiFePo4 can accept enormous charge currents, and can easily burn out the tow vehicle alternator. If you want to charge from the alternator, you should use a Dc-DC converter which is sized to the alternator."

Before you promote that statement, please go to the Battle Born website and read their recommendations. Second, the charge rate is determined by many factors. Generalizing that an alternator will be "easily burned out" is not true. Victron did a test that showed a smoking alternator, but it was set up in a controlled setting that had nothing to do with an automotive application and was designed to make the alternator fail. It was a sales pitch and misleading. I tested one of my alternators with a dead short form the output to ground and it did not burn out. DC-DC chargers are fine, but not always needed. The lithium batteries have a BMS controller inside to protect them and the typical automotive voltages are within the specs of Lithium batteries, according to Battle Born. Lithiums do not need a float voltage, but as long as it is below a certain voltage, it will not hurt them in an automotive setting. Rams, for instance, have a smart charging system that drops the voltage to a float level when the battery is charged.

OK. I am neither a mechanic nor an electrical engineer. I am not "promoting" anything, I am attempting to gather knowledge into a single thread, and encourage people to think for themselves and learn. There is a ton of misinformation out there. That knowledge includes whatever people who know more than I care to contribute.

I have to say that a victron test and "I tested one of my alternators" both fall into the realm of insufficient information to be useful. It always comes back to being responsible for your own system.

I know that Lithium batteries can sink and source so much current so quickly that they can be quite dangerous. And large lithium batteries are easy to build because they are so small and light. I can easily build a 50ah battery or a 1000 ah battery. Both can be dangerous but imagine a 1000 ah battery connected to an alternator over a double 00 cable because someone thought that would be a good idea.

You won't find me telling anyone that is a good idea, mostly because i don't think that would be a good idea.

[dleverton]

All true.
Keep in mind that the alternator likely has 40mohm to 80mohm and the MOSFETs in the BMS have likely 20mohm to 30 mohm.

[Defenestrator]

The charge rate problems with alternators and LFP are more of an issue for boats and maybe motor homes than travel trailers. The wiring back to the battery is so long and thin that the voltage drop limits the charge rate to well below the point that it would stress the alternator. You only really need the DC-DC charger if you skip the 7-pin power and run a dedicated line with bigger wires.

It's especially a problem on boats because you often have limited airflow plus a very short large wire run to a large battery bank, and can see charge rates over 100A instead of the 2-10A or so you'll get over the 7-pin.

[parmm]

John & John
I want to thank the both of you. A little info there that make me feel a little bit more comfortable concerning LiFePo4. Am still thinking of using two 100 ah batteries. I can think of a couple places were we might stay more that two days without shore power. And I will leave the DC to DC battery charger up to the boys at Battleborn.

[dleverton]

[QUOTE=CarlD;821941]

Originally Posted by dleverton

A couple comments, lifepo4 can be charged well below freezing, but only if the charge rate is less than C/10, so a 50 AH pack should not be charged at a rate greater than 5A, below freezing.



Doug, This is the first time I have heard this. Are you, or your company, planning on implementing some kind of temperature dependent current limit in your chargers? In my mind I can't imagine it would be too difficult. You would just need to know the battery temperature and adjust your current limit setpoint. Or perhaps a smart connection the the battery BMS for input. A design like this would certainly remove one of the perceived drawbacks to LFP batteries.

Hi Carl, we have some of our products in Northern Alberta and for standards compliance, we had to go back to the battery manufacturer for their recommendation. C/10 is what they said. We are charging from solar and C/10 wasn’t an issue for us so we did not need to alter our charge algorithm to accommodate it.

[Defenestrator]

As I understand it, there's a curve for safe charging rates below freezing that falls off pretty rapidly. I'm having trouble finding a lot of published information, but it looks like 0.3C at -10°C shortens battery life noticeably (~100 cycles to 84% capacity remaining). I found another mention of 0.02C being OK at -30°C. As far as I know, the curve actually extends above 0°C as well - rates higher than 1C may be OK as you get closer to 25°C or so.

Unfortunately, almost all the studies seem to focus either on degradation rates above 35C, or higher charge rate capabilities closer to 25C. I guess I can see why - partly for increased practical application, but partly because testing a bunch of batteries for 3000 cycles at 0.1C would take years. Possibly longer than the cooling system could hold a steady temperature.

[jwcolby123]

I for one don't think it is a safe practice. I simply mentioned it because folks are saying it can be done. This is another thing that the BMS should just handle. Sadly many BMSs don't provide cold temp charge cutoff.

What Battleborn did say is just charge the battery up (at above freezing temps) and then disconnect the battery for the cold spell. My plan exactly.

Of course their batteries have cold temp cutoff, another reason to spend the bucks. If I had it of course.

[jwcolby123]

Originally Posted by parmm

John & John
I want to thank the both of you. A little info there that make me feel a little bit more comfortable concerning LiFePo4. Am still thinking of using two 100 ah batteries. I can think of a couple places were we might stay more that two days without shore power. And I will leave the DC to DC battery charger up to the boys at Battleborn.

I have to tell you that I plan to add at least another 280ah battery (maybe 2) for exactly the reasons you provide. I plan on ordering Prismatic cells from China and building my own. I think I can build a 280ah battery for under 700 - $450 for the cells, $150 for the BMS + a few parts like connectors and a box.

I could just buy an assembled 300ah from AmpereTime but what fun is that?

https://www.amazon.com/Ampere-Time-P.../dp/B08K7HZ6KZ

The nice thing about LiFePO4 is that it is entirely safe to parallel batteries as long as each has a BMS.

[jwcolby123]

Originally Posted by Defenestrator

The charge rate problems with alternators and LFP are more of an issue for boats and maybe motor homes than travel trailers. The wiring back to the battery is so long and thin that the voltage drop limits the charge rate to well below the point that it would stress the alternator. You only really need the DC-DC charger if you skip the 7-pin power and run a dedicated line with bigger wires.

It's especially a problem on boats because you often have limited airflow plus a very short large wire run to a large battery bank, and can see charge rates over 100A instead of the 2-10A or so you'll get over the 7-pin.

I think all of the above is true. OTOH My truck was wired (aftermarket by orig owners) to tow and has large wires, at least back to the pigtail connector. Not from there into the Scamp of course.