Replacing OEM batteries with LiFePO4's

Peter Tourin

2020 Unity RL, ex 2012 Unity MB
I got some info from Progresive Dynamics today. Their lith chargers charge at their rated current until the battery is nearly fully charged, then they hold 14.6 volts and the supplied current drops as the battery voltage climbs, until the charger is basically delivering no current. The charger does NOT switch off when the current drops below a preset point. I'm trying to figure out what this implies - it seems that once the battery is charged, the charger acts sort of like a float charger - as the battery goes down a bit, the charger starts supplying current (but always at 14.6v).

I'm no engineer, and I'm not sure whether the batteries mind being treated this way. I don't think the charger can overcharge the batteries - if there's no voltage differential I don't think the charger will supply any current. But I have a memory of reading a white paper indicating that it might not be good to keep pushing li-po batteries right up to full charge. Once I have the new charger in place and watch it for awhile, I could handle that - the Victron monitor has a set of relay contacts that can be made to close at a preset high voltage and open at a lower voltage - I could use that relay to feed a 2nd relay that opens the 120vac to the charger. More complexity and current drain of course. But not hard to do.
 

Charlie

2008 2500 170 Diesel
Peter,

I have been looking into this and I think you will be OK without the added complexity of an automatic charging disconnect.

From what I have read, LFP cells should not be floated long term at the final charging voltage (3.65v per cell or 14.6v for 4) but the research on this is not clear. There are lots of people tossing out opinions but the only rigorous paper I found in a quick search was this one. A bit dated but still interesting.

https://www.jstage.jst.go.jp/article/electrochemistry/78/5/78_5_342/_article

Note that in this test, they floated at 4.0 volts per cell, higher than you would. At normal temperatures (77F), it took over a year before there was much capacity loss. At higher temps, things got worse.

You would not be floating "long term" i.e. weeks or months. Plug in at a campsite, charge up, maybe float for a day or two, then leave. If you happen to notice a full charge, you could switch the charger off manually, but probably not a big deal. At home, just don't plug in.

For alternator charging, things are even better since the max voltage is 14.2 (3.55 per cell) and you typically only drive so many hours a day.

I think the case to watch out for is a solar system that is always on when the rig is not in use. A great approach for lead batteries but not needed for LFP. Depending on the controller, you could float every day at too high a level, especially if you are in a cold climate and the controller has temperature compensation. A simple switch for driveway use would seem the solution.

As far as using the battery monitor SOC signal for a disconnect, be careful. Monitors are great (I have one) but they can exhibit cumulative error. What you really want for disconnect is a voltage trigger.

Of course it is easy for me to say this since the expensive batteries are not mine, but I think it is decent advice. If anyone else has studied this in detail, please chime in.
 
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Peter Tourin

2020 Unity RL, ex 2012 Unity MB
I'm hoping you're right on all these counts. No question about the alternator - that should work fine! I don't even have the Progressive Dynamics charger in hand yet, so we'll see how it works. The monitor can be set to react to high/low SOC, voltage or a combination of both - all settable. It can display a visible alarm or that plus a buzzer, and in addition it can trigger a relay - all settable via independent parameters. That having been said - I hope I don't have to use them for anything as elaborate as controlling the charger.
 
I just started to look at this thread so I may repeat a prior suggestion. The problem of charging batteries of any type is constantly discussed on the Airstream forum because they use Parallax converter/chargers most of the time. The fix usually involves replacing it with another brand that has a multistage charger or remove the converter/charger and use a good inverter/charger. It seems that the inverter/charger method has more benefits of better technology and adjustable charging to meet battery requirements, but costs more. You might want to look at a recent discussion (http://www.airforums.com/forums/f449/new-inverter-what-brand-135268.html) and the comments from the person with the handle of lewster. He is very helpful and installs systems in rvs and trailers.
 

Peter Tourin

2020 Unity RL, ex 2012 Unity MB
Thanks, I'll look him up - I'm definitely relying on the comments and advice of others who've gone down this path already. I do have a Parallax 7355, and though it's not very good at charging flooded cells, it at least won't hurt the Li-phospate batteries until I can replace it. I'm leaving the inverter alone and simply replacing the converter/charger from the Parallax with a Progressive Dynamics 60A charger that was designed for charging lithium batteries - I should have it today or Monday. It's simpler than changing the inverter, and cheaper also, since if I did an inverter change I'd want a larger inverter - that'd be another whole project, what with rewiring, etc. It's also what my battery supplier recommended - and the issue of lith battery chargers and how they should work has been pretty confusing so far, and I'm counting on their statement that they've tested their particular battery design with this model charger.
 

Unity Traveler

2013 LTV Unity Twin Bed
Thanks, I'll look him up - I'm definitely relying on the comments and advice of others who've gone down this path already. I do have a Parallax 7355, and though it's not very good at charging flooded cells, it at least won't hurt the Li-phospate batteries until I can replace it. I'm leaving the inverter alone and simply replacing the converter/charger from the Parallax with a Progressive Dynamics 60A charger that was designed for charging lithium batteries - I should have it today or Monday. It's simpler than changing the inverter, and cheaper also, since if I did an inverter change I'd want a larger inverter - that'd be another whole project, what with rewiring, etc. It's also what my battery supplier recommended - and the issue of lith battery chargers and how they should work has been pretty confusing so far, and I'm counting on their statement that they've tested their particular battery design with this model charger.
Peter - You may want to check the RV.Net Forum "wincrasher65" dtd 7/13/15 as he to is adding a Lithium batteries. You may want to compare notes with each other? Here is the link: http://www.rv.net/forum/index.cfm/fuseaction/thread/tid/28463455.cfm
 

Davydd

Well-known member
Peter - You may want to check the RV.Net Forum "wincrasher65" dtd 7/13/15 as he to is adding a Lithium batteries. You may want to compare notes with each other? Here is the link: http://www.rv.net/forum/index.cfm/fuseaction/thread/tid/28463455.cfm
More discussion on Wincrasher's Smart Battery install with the Progressive Dynamics converter can be found here on the Class B Forum.

http://www.classbforum.com/forums/f8/travato-lifepo4-battery-install-3664.html
 

Peter Tourin

2020 Unity RL, ex 2012 Unity MB
Thanks, I definitely want to go over there and join that thread - they're discussing just the things I'm trying to sort out, and it sounds like they've way ahead of me.
 

Peter Tourin

2020 Unity RL, ex 2012 Unity MB
I've finished the basic installation - posting a couple of pics of the Progressive Dynamics PD9160AL lithium charger - you can see that it's smaller than the OEM Parallax 7355 charger. The install went pretty smoothly - no surprises. I gutted the OEM charger chassis and mounted the new charger on it, as the chassis slides in and has bolt holes for the front cover.

I haven't really had much time to observer the system - going away tomorrow for 10 days, so I'll know more when I get back. But a few things I've noticed...
The batteries seem to rest around 13.4v at full charge. I did a charge from about 50% SOC - at first the charger put out about 45A (don't know why it didn't put out 60, but...) and the voltage started climbing from a start point of around 13.1 - as it climbed to perhaps 13.7, the charger current dropped to perhaps 32A. As the batteries approached full charge there was a rapid change - the voltage rose to around 14.5v and the current dropped, ending up at around 1.0A. Next day I used the batteries a little bit, then charged again - the voltage quickly rose to 14.55v and the current ended up at less than a half amp - don't have my notes with me and don't remember exactly.

So we'll now get to see what it's like to have almost double the original battery capacity and no worries about "running out of battery cycles" if we use the batteries hard between chargings. I don't yet have a handle on one thing - the debate about whether it harms these batteries to leave a CCCV charger running constantly once the batteries are at 100% SOC, or to do long drives with the alternator output feeding the batteries. I think there was a bit of discussion in this thread about this issue, and there more over on the Class B Forum on the link you guys showed me: http://www.classbforum.com/forums/f8/travato-lifepo4-battery-install-3664.html
 

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Peter Tourin

2020 Unity RL, ex 2012 Unity MB
So far this installation is working out very well. LOTS of battery capacity!! - I haven't dropped below 75% SOC yet. Voltage always around 13.2-13.4. When driving, the alternator charges the batteries to at or near 100%. I just posted over on the Class B forum, so this is a duplication of that post, but just in case anyone is interested....

I posted earlier that Victor at SmartBattery told me that their batteries had only over- and under-voltage protection, no BMS. But in one of the PDF's on their site, I just found this: "Balancing: During charging the PCB board will provide up to 2A current through the lengthway circuitboard which is lower voltage than the other lengthway boards. Tests show that the cells are so precisely matches, batched together with high conformity and passive assembly design that the balancing function will remain inactive for most of the battery life." So it sounds like they top balance by bringing up the lowest bank.

I still would love to understand the issue of possible damage to the batteries from constant low-current charging at 14.6v once the battery is at/near 100% SOC. I'll probably call SmartBattery again and see if I can find out anything about why they DON'T discuss this when other battery suppliers do. I still can do it - build my own system using the Victron monitor's internal relay - but I don't want to if I don't have to! Simplest would be nice...
 

casmith32

Member
Very interested in your findings. I'm about to install 2 x 50Ah smartbatteries in parallel for my van. You may want to try and chat with the Canadian distributor to get more answers on the specifics around the BMS, etc...

www.totalbattery.com

So far this installation is working out very well. LOTS of battery capacity!! - I haven't dropped below 75% SOC yet. Voltage always around 13.2-13.4. When driving, the alternator charges the batteries to at or near 100%. I just posted over on the Class B forum, so this is a duplication of that post, but just in case anyone is interested....

I posted earlier that Victor at SmartBattery told me that their batteries had only over- and under-voltage protection, no BMS. But in one of the PDF's on their site, I just found this: "Balancing: During charging the PCB board will provide up to 2A current through the lengthway circuitboard which is lower voltage than the other lengthway boards. Tests show that the cells are so precisely matches, batched together with high conformity and passive assembly design that the balancing function will remain inactive for most of the battery life." So it sounds like they top balance by bringing up the lowest bank.

I still would love to understand the issue of possible damage to the batteries from constant low-current charging at 14.6v once the battery is at/near 100% SOC. I'll probably call SmartBattery again and see if I can find out anything about why they DON'T discuss this when other battery suppliers do. I still can do it - build my own system using the Victron monitor's internal relay - but I don't want to if I don't have to! Simplest would be nice...
 

Peter Tourin

2020 Unity RL, ex 2012 Unity MB
What did they recommend for a charger? I'm still trying to sort out how they best should be charged, and I've never gotten clear and consistent answers from SmartBattery. I'm curious whether Total Battery has anybody that really knows what's required.
 

Peter Tourin

2020 Unity RL, ex 2012 Unity MB
I finally reached a support engineer at SmartBattery today, and I'll put down what he said - with a big caveat at the end...

I asked about charging - specifically, charging their batteries with Progressive Dynamics lithium chargers, which are CCCV chargers that charge to 14.6 volts. I asked whether the charger could be left connected 24/7 without damaging the batteries from overcharging - the question that people on various forums are asking. His answer was that I could - that the charger would ramp up to 14.6v and the current would go down towards zero. He said that 14.6 volts would not overcharge the batteries, and in any event they have an internal over/under voltage relay that would open if the voltage got up to 16v. To me, that's a "party line" sort of statement - I consider a 16v relay opening more like disaster prevention than real battery management. I asked about the issue of small imbalances between banks allowing the better banks to overcharge while the charger tried to bring the weakest bank up to 100% SOC. He said it's not an issue with SmartBattery because the battery cells are so well matched at the factory that they're almost perfectly balanced, and they remain so - very little current drawn as the battery as a whole approaches 100% SOC. That's what he said...

That led to a discussion of balancing circuitry - their website is not clear about whether they have top balancing circuitry or not. He said their BMS doesn't have any balancing functionality, that their manufacturing process matches all cells, and therefore all banks, well enough so it's not needed. That's what he said...

Now it gets a bit less clear - I asked him about the temperature/performance data on their website. He said that the graph of temperature vs. usable capacity referred to ambient temp, but he waffled a lot about whether it was ambient or battery temp - he finally chose ambient, and pointed out that in cold weather the battery temp is always going to be the same or higher than the ambient temp (I was asking about low temp issues, as their high temp end doesn't worry me as much). So he said that I can discharge way down below zero F or even -20F without damaging the batteries as long as I understand how the low temp will affect usable capacity. He also pointed out that their internal BMS has low voltage disconnect as well as overvoltage, so the battery will disconnect if it drops below 8v. He pointed out that in winter outside storage, you simply charge the battery to near 100% before storage and you disconnect it - since they don't self-discharge much when disconnected, they can sit all winter with no damage and lose a lot of capacity - and I believe that from everything I've read.

Then I asked him what their "Operating Temp. -4F to +175F" meant. He said that it meant that although I could discharge below -4F, I shouldn't charge below that temp. I asked him several times whether he was sure that I could safely charge below freezing, and he said yes. He pointed out that in almost all RV use, the temp is well above -4F when you'd be charging - and that's certainly true for me. Maybe not if it were a car, but it's an RV. That's what he said...

I do need to add a caveat here. I didn't get the sense that I was talking to an engineer, not even a Tier 1 support engineer type - he sounded more like a battery technician. At first he wanted to convince me that I hadn't paid attention to their specs, and he pushed pretty hard trying to get me to say I hadn't studied the data on their website - he was a bit condescending at first. I pushed back pretty hard on this, saying that the data was incomplete and in places very unclear, and that's why I was on the phone. In the process I found that he could quote what was on the site quite well, but that he was pretty unsure when I pressed for detailed info. So I'm still not sure how much more I know than before I called. As I said before, Caveat Emptor! I've taken the plunge - we'll see if I burn, freeze or come out OK <g>...
 

casmith32

Member
Any ideas on whether or not a battery temp. monitor is at all useful with LifePO4s ? I've got two 50ah from smart battery that I'll hook up in parallel - wanting to know if I should bother with the temp sensor for my solar controller/charger... and my inverter charger

I talked with Victor at SmartBattery yesterday. Here's some info from the call - some of this pertains only to SmartBatteries, some to LiFePO4 in general:

Most surprising: SmartBatteries have no BMS, only under- and over-voltage protection via internal relay. Victor claims no balancing is needed because all 80 cells are very closely matched at factory. We'll see what that implies for long-term battery health...

The Progressive Dynamics series of lithium chargers are Constant Voltage Constant Current chargers. As the battery gets near 100% SOC the charger maintains 14.6 volts and current drops down to zero. This is Victor's description; I still don't have any detailed info from PD about what the chargers do as the battery gets fully charged.

Victor suggested setting 0% SOC to 12.5–12.8v (I'm installing a Victron BMV-702 monitor). He suggested that 12.5 is safe if draws are low, but 12.8 is safer if draws are high – these voltages are at the knuckle of the curve, and there’s very little battery capacity left by the time the voltage drops this low. Like OrioN said <g>...

He said that 100% SOC is 13.3 – 13.4v - again, like OrioN said. He said that this voltage would be as measured after charger is off and battery sits 1-2 hours. So apparently there’s a surface charge effect or something similar - I asked for an explanation but didn't get one.

I have a phone message this afternoon from Master Tech in Michigan that I can order a PD9160AL charger. I'm hoping that when I call and order, they can pry loose some tech info for me - we'll see.

The Victron BMV-702 is very nice - simple, easy to use display (once you go through about 60 setup parameters). Installation took much longer than I expected, mainly because of mounting the shunt and running the data cable from the shunt up to the display.
 

Peter Tourin

2020 Unity RL, ex 2012 Unity MB
I'm not sensing temperature, but it's not a bad idea. I don't think it makes too much difference for the charger, since your batteries will almost surely be able to handle whatever your charger puts out. But if your battery monitor has a temp sensor and you can program it to correct its SOC calculations with changing temperature, that's worth doing. It's nowhere near as much correction as you'd use for flooded cell batteries, but it's still enough of a drop with colder weather so the correction would be worth having in place. I intend to do it. I don't have at hand the suggested figures that Victron publishes for LiFePO4's but I can look it up if you're interested.
 

l70000

New member
Peter - i just caught your thread and thinking about LiFePO4 to replace my AGM. You may find the info at this site useful about these batteries and there are now a few generations of LiFePO4. I found some info regarding these cells and their insides. Charging should always terminate. BMS probably cause more problems than they solve... don't charge below 32F / 0C - discharge is okay a wide range of temps. http://media3.ev-tv.me/cellcare.pdf
i have an etrek and keeping cabin temperature under control is important for health reasons so i was thinking of switching from agm to LiFePO4.
lee
good luck
 

Peter Tourin

2020 Unity RL, ex 2012 Unity MB
Thanks Lee - I hadn't seen that CALB paper and it's very interesting.
 

wade5979

New member
Peter, Have you reached a level of comfort with your Smart Batteries charging at a constant 14.6 volts and is there a need for the BMS other than what's built into the Smart Batteries.
Thanks for all the R&D you have done I'm picking up my 2016 MB first week of November and this is the first upgrade I want to do.
 

Peter Tourin

2020 Unity RL, ex 2012 Unity MB
I haven't had much access to the RV, as Jean has been living in it while doing a contract job in the Boston area. I have it back now, but in a few weeks I'm going to have to put it up for winter - it has to go into storage before the first real snowstorm, and we usually have one by Thanksgiving. The Progressive Dynamics lith charger works as we've discussed - I see it put out about 45A at first (it's a 60W charger and I've never had the batteries much below 50% yet) and the voltage climbs to the high 13's - then the current starts dropping, slowly at first, and very fast as the batteries approach full charge. I've been controlling the charging entirely manually - the capacity is almost double what I'm used to, so I always feel I have lots of time. But of course that's risky on the low end - if I were to go away for a few days and leave something connected by accident - even if I was plugged in, the charger wouldn't come on and I'd be in trouble.

As for the other questions... no conclusions yet. There's no question that SmartBattery has a battery protection system - an internal relay that opens at over- or under-voltage (15.8 and 8.0). But that's just disaster protection. Their website now implies that they have an internal battery management system that has "automatic internal cell balancing". But I've called them a number of times and can get no straight answer on this. I was told once that they do indeed have an internal BMS that does top balancing, but I was also told twice that they have no BMS, only the over- and under-voltage protection - that they don't need balancing because the cells are so perfectly matched during manufacture that they won't go out of balance. So that's worrisome - what can you say about a company that can't give you consistent answers about what's inside their batteries, even when you call with specific questions about the subject?

I also asked several times during my calls to SmartBattery whether they were positive that there was no overcharging issue if the Progressive Dynamics lith chargers were left connected after the battery was fully charged. Their answer has always been that there's no problem - that the battery banks are extremely well balanced and that therefore the charger will simply go down to 0 amps and not overcharge. But there's so much discussion and disagreement about this topic that it's hard to accept that answer from a company that either won't or can't tell me what's in their batteries and how well protected they are. So I'm going ahead with developing a means of turning off the charger at some point at or near 100% SOC and on again at some lower point, be it 40%, 20% or whatever. My battery monitor will do this - I'm working on a simple system that consists only of several relays, controlled by the monitor. I don't know that I'll get this done before Spring, since I'm going to be forced by snow to put the RV into the storage place pretty soon.

So in summary - I'm enjoying learning about all these issues, and I'm impressed with the batteries and their capacity. I have had no problems manually controlling the charger up till now but I haven't taken any longer trips where we dry camp a lot - that won't happen till Spring or Summer of next year. If I wanted to be safe now I'd be looking at high quality AGM's as they're much cheaper in purchase price and I believe they're comparable in cost over the lifetime of the battery, and there's much more knowledge about how to handle charging issues with them. But personally, I don't mind risking a bit in order to try something new - I'm trying to be really careful so I don't damage the considerable investment!
 

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