Replacing OEM batteries with LiFePO4's

OrioN

2008 2500 170" EXT
I can't tell you much about solar charger settings - I don't have solar and haven't researched it too much. But what does your battery company say about charging? Mine says that the battery rest voltage at full charge is around 13.4, and they recommend CCCV chargers with a charge voltage of 14.6. So setting your absorption mode to 14.2 is similar to charging from the alternator (mine puts out about 14.2) - won't get the battery to quite 100% SOC but will get it close. It also makes sense to turn float off - I haven't read anything that recommends float for lith batteries. More detail than this - I can't even begin to guess.
Incorrect... a charging source of 14.2V and like an alternator will get LI's to 100% SOC, and as efficiently as a source of 14.6V due to their very low internal resistance as compared to lead acid batteries.


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OrioN

2008 2500 170" EXT
Thanks Peter ! that's helpful. I'll take a look at my settings and confirm but I think that's pretty much what I'm working with.

I'm still confused on how to determine the true SOC when running on alternator and it's feeding the lifepo4 when my battery switch is closed. the voltage shoots up to 14.2v then sits there. How do I know when the battery truly hits 13.6v with the BMV ? is the fact that I'm using a simple battery switch vs an intelligent relay the issue ?
Let me try one more time.

Use the the monitor's aH reading to determine SOC, and to trigger 'points'. NOT VOLTAGE and especially under a non-regulated charge source like an alternator.

The only thing keeping the alternator from being 'smart' is exactly what you are or should be using the Victron for...a brain.

Li's which do not require a Peukert Law will charge and discharge many times and a calibrated monitor that senses a batteries charge algorithm will keep extremely accurate, so there will be negligible margin of error.


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Peter Tourin

2020 Unity RL, ex 2012 Unity MB
OrioN - would you talk to me more about this? I got that from a very long thread either on the Class B Forum or the cruising forum - don't remember which - but I took away that charging at 14.2 would get you near to full charge, but not entirely there - thus the CCCV 14.6 charger recommendation. The general idea was that the differential wasn't enough, and after the surface charge dropped off the resting voltage wouldn't be quite as high - not a big issue with lith charging, but that was what they were explaining. I remember it surprising me, but I just accepted it. So maybe I'm the victim of Bad Internet Info? <g>... It seems to me that if the rest voltage is 13.4, any voltage somewhat higher than that would bring the battery to full charge - sooner or later, depending on how much higher - that's why I was surprised.

So - what happens if you provide around 14.2 charging voltage instead of 14.6? Will it be the same routine, with current dropping as the voltages equalize? Will it take longer with lower voltage? And once the surface charge drops off, will it really drop to the same ~13.4? I will happily stand corrected if I can understand better what's happening as the system approaches full charge.
 

casmith32

Member
Incorrect... a charging source of 14.2V and like an alternator will get LI's to 100% SOC, and as efficiently as a source of 14.6V due to their very low internal resistance as compared to lead acid batteries.


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That's what I thought based on all the research I've done...seems like even 13.8v would do the job, just not quite as fast, but easier on the batteries ?

What I'm trying to understand the relationship between the bulk charge voltage, and the absorption charge voltage specifically for my LifePO4s. As Peter suggested, our batteries have a resting charged voltage of 13.4v. So for my solar charger I'm trying to make sure I've got proper settings.

My blue sky 3000i charger has a few settings I'm trying to make sure I've got set properly to maximize charging and life of the battery. I've put in what I *think* is right, but not sure...

AbS - absorption charge voltage - 13.4v
Abt - absorption charge time - .5 hrs (should be set already)
uPr - max setpoint limit - 14.2v
FLt - off (should already be set)

my understanding is that no matter what, no setting will be able to exceed the uPr parameter of 14.2v. And that Bulk charging would shoot up to the uPr limit, deliver as much current as possible to the batteries. As the battery voltage rises to AbS (13.4v as the fully charged voltage), the current is backed off, and voltage maintained for 30 mins. Then since I have float charging turned off, charging just stops until battery voltage drops below the AbS voltage of 13.4v, and re-enters bulk charging, shooting up to 14.2v if possible to bring back to AbS voltage, and repeat.

Is this correct ? should my AbS voltage setting be higher? or am I right in setting the absorption voltage to be the 100% charged voltage of 13.4v ?
 

casmith32

Member
OrioN - would you talk to me more about this? I got that from a very long thread either on the Class B Forum or the cruising forum - don't remember which - but I took away that charging at 14.2 would get you near to full charge, but not entirely there - thus the CCCV 14.6 charger recommendation. The general idea was that the differential wasn't enough, and after the surface charge dropped off the resting voltage wouldn't be quite as high - not a big issue with lith charging, but that was what they were explaining. I remember it surprising me, but I just accepted it. So maybe I'm the victim of Bad Internet Info? <g>... It seems to me that if the rest voltage is 13.4, any voltage somewhat higher than that would bring the battery to full charge - sooner or later, depending on how much higher - that's why I was surprised.

So - what happens if you provide around 14.2 charging voltage instead of 14.6? Will it be the same routine, with current dropping as the voltages equalize? Will it take longer with lower voltage? And once the surface charge drops off, will it really drop to the same ~13.4? I will happily stand corrected if I can understand better what's happening as the system approaches full charge.
DITTO - what he said :thumbup: ; seems like the 14.6 recommendation is just to get the charge up as fast as possible ? but likely harsh on the batteries over time ?
 

OrioN

2008 2500 170" EXT
DITTO - what he said :thumbup: ; seems like the 14.6 recommendation is just to get the charge up as fast as possible ? but likely harsh on the batteries over time ?
14.6V is within the charging volts range and will not lead to any significant degradation of the cells. Considering the low internal resistance, there isn't going to be any significant difference in charging time either.



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OrioN

2008 2500 170" EXT
That's what I thought based on all the research I've done...seems like even 13.8v would do the job, just not quite as fast, but easier on the batteries ?

What I'm trying to understand the relationship between the bulk charge voltage, and the absorption charge voltage specifically for my LifePO4s. As Peter suggested, our batteries have a resting charged voltage of 13.4v. So for my solar charger I'm trying to make sure I've got proper settings.

My blue sky 3000i charger has a few settings I'm trying to make sure I've got set properly to maximize charging and life of the battery. I've put in what I *think* is right, but not sure...

AbS - absorption charge voltage - 13.4v
Abt - absorption charge time - .5 hrs (should be set already)
uPr - max setpoint limit - 14.2v
FLt - off (should already be set)

my understanding is that no matter what, no setting will be able to exceed the uPr parameter of 14.2v. And that Bulk charging would shoot up to the uPr limit, deliver as much current as possible to the batteries. As the battery voltage rises to AbS (13.4v as the fully charged voltage), the current is backed off, and voltage maintained for 30 mins. Then since I have float charging turned off, charging just stops until battery voltage drops below the AbS voltage of 13.4v, and re-enters bulk charging, shooting up to 14.2v if possible to bring back to AbS voltage, and repeat.

Is this correct ? should my AbS voltage setting be higher? or am I right in setting the absorption voltage to be the 100% charged voltage of 13.4v ?
Set the AbS to 14.1v.

0.5 hrs is OK for the absorption charge time. Keep in mind that this is only the time the charger stays in absorption mode AFTER it the SOC is 100%. This is the CV state of a CCCV charger so that the last aH can get into the bank.

I float with my Solar charger. Why? Since I draw significant current during the day for work, floating is like a constant current flow into my inverter. No point in consuming 'cycles'.

I set the float v's to 13.3V which is the resting v's of my bank.

If I'm not inverting, I turn of the charger.


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casmith32

Member
Set the AbS to 14.1v.

0.5 hrs is OK for the absorption charge time. Keep in mind that this is only the time the charger stays in absorption mode AFTER it the SOC is 100%. This is the CV state of a CCCV charger so that the last aH can get into the bank.

I float with my Solar charger. Why? Since I draw significant current during the day for work, floating is like a constant current flow into my inverter. No point in consuming 'cycles'.

I set the float v's to 13.3V which is the resting v's of my bank.

If I'm not inverting, I turn of the charger.


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Interesting - thanks that's the feedback I needed! I did get a similar suggestion from the guys at AMSolar about the Float charging piece...just very confusing with all the folks saying, "don't float charge lifepo4"; I'll make those changes!
 

Peter Tourin

2020 Unity RL, ex 2012 Unity MB
I'm on vacation, and have time to cruise the web <g>...
I just ran into several web pages written in January 2016 by PowerStream that are interesting. OrioN, their testing agrees with you about reaching 100% SOC or coming very close with lower charging voltages - they tested several different cells, and most got to 100% at 3.6 and nearly there at 3.5. Their discussion article is very readable and covers lots of interesting territory.

http://www.powerstream.com/LLLF.htm (charging discussion)
http://www.powerstream.com/lithium-phosphate-charge-voltage.htm (charge tests)
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Also - I might have posted these links may be posted earlier in this thread, but just in case - there are 2 threads on the Class B Forum that have a lot of LiFePO4 info.

http://www.classbforum.com/forums/f8/travato-lifepo4-battery-install-3664-21.html#post34449
This is an earlier thread on lith batteries, and I joined in.

http://www.classbforum.com/forums/f8/lifepo4-charging-the-overcharging-question-3877-7.html
I posted this one specifically on charging. Yesterday I asked about some of the questions that recently came up in this thread. Booster, the guy who answered, is the main mover and groover on this forum - and I was interested to find that he was also somewhat confused about the incomplete and sometimes inconsistent information that's available. Both good threads - a lot of information in there if you have the patience to wade through them.

There's also a cruiser forum (power & sail boats) that has a good very big thread on lith batteries. The boating people seem to have gone further into this than the RV people have - lots of good info - I can post that link if anybody is interested.
 
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Peter Tourin

2020 Unity RL, ex 2012 Unity MB
I just added a temperature sensor and a bluetooth dongle to my BMV 702 battery monitor. There's a Victron Connect app for Apple and Android smartphones. I'm in my house about 100' from the RV and I can connect with the monitor. It displays the basic info very nicely on a single screen - battery voltage & current, SOC, consumed Ah, time remaining, temperature and history. So my house thermometer is at 28 this morning and the battery is showing 35 - very handy.

History is accumulated date like deepest discharge, max and min battery voltage, etc. - it can be cleared by the app just like clearing it at the monitor.

Settings are grouped by function instead of listed by parameter number: Battery, Relay, Alarm, Display and Misc. They're much quicker and easier to understand and to set from the app than on the monitor.

So this turns out to be a very useful addition.
 

wade5979

New member
OrioN,
I think I follow what you are saying about monitoring amp hours instead of volts. Just returned from a 4 day stay in Key West and tracked SOC, Volts and Amp Hours out. Here's my results starting at our arrival. ME charger/inverter on shore power in sleep mode, solar disabled.

SOC Volts Amp Hours
89% 13.31 -43
84% 13.30 -62
75% 13.23 -101
64% 13.14 -130
62% 13.13 -151
60% 13.12 -158
56% 13.11 -175
48% 13.08 -208

As you can see Amp Hours Out differential seems much more measurable. Voltages are just so close.

Peter,
Now how do we measure Amp Hours In/Out with the Victron Monitors? The closest I can see is SOC readings.
 
Peter, same advice I give to everyone when the subject of charger/converters and inverters is raised. Talk to Randy at bestconverter.com. Click here to see his page about Lithium Ion charger/converters...
Any suggestion on a good voltmeter? Never owned one before and want to keep one on board to check batteries, etc.
 

Peter Tourin

2020 Unity RL, ex 2012 Unity MB
If you just want to measure voltages, you can get some very inexpensive meters. Go to Radio Shack and look up "multimeter" - they have several for $30 to $70. You don't need anything very expensive if all you want to do is measure DC and AC voltages. You can also check Home Depot - for $15 you can get a meter that's fine for measuring voltages - http://www.homedepot.com/p/GE-Digital-Multimeter-50953/203735809.

I would get a digital one, not an analog one. Since the difference between a full battery and a fairly discharged one isn't so big - you might be looking at 12.8 volts vs 12.0 volts - it's handy to have a digital meter that reads fractions of a volt.

If you also want to be able to measure current, you can get a different kind of meter - a clamp ammeter. You can clamp its jaws around a wire and find out how much current is flowing through it. For example, you can put it on your battery's positive lead and then turn your fridge onto DC and you'll find out how much current your fridge really uses. These are tremendously handy if you're trying to find out what items draw how much current and you don't have a battery monitor in your RV. I've had two Extech clamp multimeters and they've been very solid items. An example - look up model MA220, they sell for about $90.

A warning here: you want to make sure to buy a clamp meter that says "AC/DC ammeter" - some of them will measure AC current but not DC, and your battery loads are DC. Extech sells 2 models of the MA220 and one is AC only - much cheaper but much less useful!
 
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wade5979

New member
When it comes to charge cycles of lithiums is it better to wait for them to reach your low SOC set point before charging. The reason I ask is the Magnum MS 2000 goes into constant current and then constant voltage as soon it's plugger into shore power and brings battery right up to 100% SOC and goes into sleep mode until it reaches 30% SOC that seems fine. If I'm staying in one place for a long time one of my questions is do I allow the solar charger to put whatever amp hours it can back into the battery during the day or do I keep it turned off until the battery reaches the low SOC set point to make a complete cycle form high to low SOC. The same question would go for the alternator do I keep it from charging until battery reaches low SOC set point? In other words if the battery is down 50 amp hours and I return those amp hours is that one of the life cycles of the battery?
 

Peter Tourin

2020 Unity RL, ex 2012 Unity MB
This touches on an issue that's been widely discussed on the LiFePO4 forums, with no definite conclusions at this time. The question is: once you've charged your battery up to a set voltage and watched the charge current drop to near zero, does it hurt to keep charging? The Nay-Sayers basically say, "the current drops to near zero so who cares, no real charging is happening". The Yay-Sayers reply, "if it's non-zero, even though it's low current you keep forcing some charging to happen after the batteries are nearly topped up, and that's when you'll start having problems if cells aren't balanced perfectly - you may overcharge some strong cells as the charger keeps trying to top up a weak cell".

Since there's no consensus and the batteries don't mind not being charged all the way up, my solution is the chicken one: I'm going to stop charging via either charger or alternator once I get to some point that's near full charge - I'm going to cut the AC supply to my charger and open the isolation relay to accomplish these 2 things.

A question for you: how does Magnum define "sleep mode"? - is charging stopped, or is it like float charging? That'll be relevant to the issue I'm describing above.

I'm not sure of the answer to your question about counting life cycles, and it's interesting. If this just a matter of how much overall charging you apply, you'd assume that 100 cycles of 60% SOC to 100% SOC would be about the same thing as 50 cycles of 20% to 100%, in terms of life cycles. But I don't know if that's the case. It'd be good to know - I'd rather start charging via some charging system when I drop down to maybe 70% SOC rather than 30% - that way I can top up every time I take a short drive or plug in for a few hours. But if each of those count as a life cycle, then it makes sense not to start charging until the batteries are discharged pretty far down. I'll ask the question over on the Class B Forum and see if there's any wisdom to be had there...
 

wade5979

New member
I am doing exactly what you are saying so I also am taking the cautious way out. The MS2000 charges full current until the tail current is reached and then constant voltage until it reaches 100% SOC and the cuts completely off until it reaches recharge level currently set at 30%.

So that is where my questions come in about short cycles or capping off the charge. A 400ah bank pulled down to 30% would never be capped off with 500 watts of solar that doesn't average 10-15 amps of charge. Let's say it goes from 30% to 50% charge on solar is that a cycle or should the SOC floor for solar be Higher than the SOC floor for charger or alternator if so i'm seeing a second viltron in my future to control just the solar charger.
 

Peter Tourin

2020 Unity RL, ex 2012 Unity MB
Yes, I know what you're getting at. I got comments from davydd and booster over on the Class B Forum, but nothing that really helps - here's the link -

http://www.classbforum.com/forums/f...e-overcharging-question-3877-9.html#post43513

Another link there actually talks about that Magnum inverter/charger: http://www.classbforum.com/forums/f8/travato-lifepo4-battery-install-3664-10.html

If I had to guess, I'd guess that a partial charge at low charge rate from solar is not going to shorten battery life as much as a full charge at a much higher charge rate - at least, I sure hope so! Are you sure it really matters? At the rate I'll use the RV, even after I retire, it's going to take a lotta years to get anywhere near 2000 cycles! But I expect we're not going to find any hard info on this, and we'll just have to see how it works over time.

You're lucky that the charger will fully shut down when it drops down to the tail current setpoint. My charger doesn't, so I have to rely on the Victron battery monitor to find the setpoint and turn off the charger. It's the same result in the end, but I have to install another relay and wire run over to the charger.
 

Peter Tourin

2020 Unity RL, ex 2012 Unity MB
FWIW - take a look here: https://en.wikipedia.org/wiki/Charge_cycle. This short article says that "Apple Inc. clarifies that a charge cycle means using all the battery's capacity, but not necessarily by full charge and discharge; e.g., using half the charge of a fully charged battery, charging it, and then using the same amount of charge again count as a single charge cycle." This answers the question about charging after a partial discharge, and it's the answer I hoped to find. I saw this same definition 2 other places - haven't done a lot of searching, but I'm hoping this is the generally accepted definition, as it means that doing a partial discharge/charge doesn't count as a full cycle.

Edit: Booster pointed out that this quote isn't about lith phosphate batteries, and he has some discussion that this isn't linear for lith phosphate batteries.
 
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wade5979

New member
I'm pretty much in agreement with the postings on the other forum and have witnessed much of what booster is saying. The MS 2000 is very customizable in CCCV mode and has been the easiest part of my setup. I have gone back and forth with the charge done setting between which is best "Charge Done Time" or "Charge Done Returned Amps". What I want to use is Returned Amps but I'm not sure how the Returned Amps reading is effected if there is DC current draw on the charger while charging. Magnum Energy says that the BMK keeps up with how many amps are going into the battery minus the amps being used on any DC load which is hard for me to get my hands around. Right now I am stoping my charge at 5% of bank size which would be 20 amps leaving me with a 380ah bank if I understand the manual.

As far as cycles go I feel better now about letting the solar charger cap of the bank everyday and starting the solar charger at say 80% SOC and maybe the alternator at something around 50% SOC and stopping the at either 90% or 95% SOC. At idle the alternator is throwing around 90 amps at the battery so it wouldn't take long to get it up to say 90% SOC. I'd like to stop all charging based on returned amps but don't know how to do that with solar and alternator at this point. I'll probably bite the bullet and add a second Victron so each charge source has it's own monitor and can have it's own unique start and stop points. Another $200 dollars to protect a $3000 battery is worth it to me.
 
Peter, switching to AGM batteries is smart. The battery charger has nothing to do with powering the microwave or anything else electrical in your couch. It only charges the battery. Since the Unity has a single 12v battery with a capacity of 220 Ah, and most charging occurs at lower amperage, a 4 stage regulated charger producing 50-75 amps is more than adequate. Check out the IOTA IQ4 Smart Charger (55A).
We currently have Exide Nautilus 27MDP (specs below) for house batteries, we'd like to switch to AGM batteries without switching to six volt batteries. Any suggestions on brand and model would be appreciated .
FULL SPECIFICATIONS
Part Number
27MDP
Description
EXIDE NAUTILUS DUAL PURPOSE
Details
Exide's Nautilus Dual Purpose combines deep cycle capability with starting power to deliver enough power to start a 350hp engine and provide 8 hours of continuous 10 amp 12 volt draw.
Warranty
12 Month Free Replacement Period
MCA
730
CCA
575
RC (25A)
160
Ah Capacity (20hr)
100
Volts
12
Group Size
27
Terminal Type
M (3/8P 5/16N)
Handle
Yes
Length
12 - 1/32 in.
Width
6 - 13/16 in.
Height
9 - 7/16 in.
Weight
52.3 lbs.
 

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