Replacing OEM batteries with LiFePO4's

[Peter Tourin]

My understanding as well. My OEM Parallax charger voltage varies from about 13.8 at no load to around 13. My understanding is also that the PD chargers sit at 14.6 all the time - the internal BMS in each battery decides when 1 of the 4 banks has reached a set voltage, and opens the battery relay - at that point, the RV's 12vdc system is being supplied by the charger and the battery is out of the circuit - it sits for awhile and the BMS equalizes the cells, then the relay connects the battery again for the next round of charging.

Mind you, this is just MY understanding, and I'm trying to figure all this out as fast as I can - so if I've missed something or not said it well, please chime in!

 

[smiller]

My OEM Parallax charger voltage varies from about 13.8 at no load to around 13.

Odd, should be better than that I would think. They're certainly not the best units around but I have mine set to 13.4 volts (it's used used as a float charger) and it regulates to within a few tenths of a volt under load. Are you measuring right at the terminals on the charger? If not maybe you are seeing some voltage drop in the wiring. Anyway, you want a better unit in any event.

 

[OrioN]

My understanding as well. My OEM Parallax charger voltage varies from about 13.8 at no load to around 13. My understanding is also that the PD chargers sit at 14.6 all the time - the internal BMS in each battery decides when 1 of the 4 banks has reached a set voltage, and opens the battery relay - at that point, the RV's 12vdc system is being supplied by the charger and the battery is out of the circuit - it sits for awhile and the BMS equalizes the cells, then the relay connects the battery again for the next round of charging.

Mind you, this is just MY understanding, and I'm trying to figure all this out as fast as I can - so if I've missed something or not said it well, please chime in!

Any charger above 13.8V will work fine. The 14.6V that Smart Battery states is a little bit of marketing (so folks could use their current installed equipment)... and a little bit of 'Maximum Voltage' (so folks don't get surprised when they apply a higher charge and the BMS opens the contactor).


Yes... Your OEM Parallax is on the 'weak' side of a good charge for sure, as it is hardly above the cell balancing volts point, but mostly from the fact that it is not capable of supplying constant voltage.




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[OrioN]

Odd, should be better than that I would think. They're certainly not the best units around but I have mine set to 13.4 volts (it's used used as a float charger) and it regulates to within a few tenths of a volt under load. Are you measuring right at the terminals on the charger? If not maybe you are seeing some voltage drop in the wiring. Anyway, you want a better unit in any event.

All due respect, Parallax is low hanging fruit in the RV world.



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[smiller]

All due respect, Parallax is low hanging fruit in the RV world.

Agree completely, mine has been relegated to a float charger and it's barely good enough for that. It should definitely be replaced with something better.

 

[Don Horner]

...
http://www.bestconverter.com/Lithium-Ion-Battery-Chargers_c_221.html

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Is it a bit too easy ??
What do you guys think?

I haven't put in the research and study as has Peter, but my opinion is that it's really that easy. I would think all the models would fit in the existing space if you completely remove the existing charger/converter and mount the new one directly to the floor. Here's a photo of my PowerMax converter screwed directly to the floor:

The PowerMax is 10.5" long, 7" wide and 3.5" tall. Notice how much space is around it. The PD9100 series 90 and 80 amp models are 11.15" long, 9" wide and 3.6" tall.

I forget the exact specs for the breaker, but if a 20A breaker in the same style is available, it should be a simple swap.

 

[Don Horner]

Peter -- now that you have the batteries, some questions. If you can really pull them down to 20%, your 200ah gives you 160ah -- right? This is a huge improvement over 2 Full River 6v, which can supply 110 @ 50%.

Next, they are 12V, correct? With banks of 6V batteries, they have to be installed in series-wired pairs to get 12V, which means that anything over 220A requires at least 4 batteries, which are heavy and require bracing of the compartment to support them. If I understand this correctly, one could add a third 12V lithium, providing 300ah, and able to draw 240ah from them to 20%. And, this increase only weighs 28 pounds, so should go into an unmodified compartment near the battery box, correct?

I assume they are similar to AGMs in the sense that they don't require venting? How about mounting -- any position, like an AGM?

If all my surmises are correct, it sounds like the only thing between me and 240ah, at less weight than my existing batteries, is cost :.

 

[smiller]

If all my surmises are correct, it sounds like the only thing between me and 240ah, at less weight than my existing batteries, is cost :.

Same boat here, the technology is very tempting, not only for the higher capacity and lower weight but the excellent charge/discharge characteristics as well. It's just difficult to justify the cost at current pricing. The lithium battery industry is scaling rapidly and I expect we might start to see some significant price reductions in the next few years, or at least I hope so.

 

[Charlie]

Is it a bit too easy ??
What do you guys think?

It can be that easy but there are some things to look out for.

Many companies are packaging up LiFePO4 cells with some electronics and selling them as Lead-Acid drop in replacements. Price per amp hour tends to be high but the simplicity is great. Since the electronics are fairly cheap to make, I would expect prices to come down as the market grows and we move past the early adopters.

The details of "some electronics" matter. In particular, look for low voltage cutoff. Discharging LiFePO4 cells too far will ruin them. No second chances. Even with low voltage cutoff in the spec sheet, look a little deeper. Is it per cell or per battery?. If the battery has no low voltage cutoff, consider adding it (starting to get less simple) Or just monitor it and don't screw up. (simple but a PITA to use and stressful) If present, is the low voltage system just a detector or is there a high current relay bundled with it. Adding a relay is not hard but is less simple. Is the low voltage cutoff adjustable?

At the high voltage end, just monitoring the battery voltage is pretty safe if the maximum charger voltage is correct. Cell level monitoring (4 of them) is better but may be overkill. Depends a lot on how well the cells are balanced.

Does the "some electronics" include cell balancing. Opinions on the need for this vary, but be aware of it. There are some lengthy discussions about this online, especially in boating forums. Get ready for an earful.

I think that the market will eventually converge on the right configuration and price point for these products but in my view, it is not quite there yet.

 

[Peter Tourin]

Here's what I can find about the SmartBattery's that I used:

Low voltage disconnect: 8v - it doesn't specify whether that's a battery level 8v or an internal level of some sort
Over voltage disconnect: 15.8v
Short circuit and reverse polarity protection: instant

Batteries are built of 4 sections, each 3.2v @ 100 ah - each section is built of enough individual cells to reach 100 ah
BMS system opens relay and cuts power to terminal post when it detects over/under voltage, short or reverse polarity
BMS system balances during charging by providing balancing current to any 3.2v section that has lower voltage than other sections

That's as much as I can get from the website without talking to one of their engineers. I don't know if the batteries in conjunction with the PD charger series that they recommend disconnects the batteries periodically to allow balancing with the battery offline, though that's the process that PD describes in their BMS discussion.

 

[OrioN]

Here's what I can find about the SmartBattery's that I used:

Low voltage disconnect: 8v - it doesn't specify whether that's a battery level 8v or an internal level of some sort
Over voltage disconnect: 15.8v
Short circuit and reverse polarity protection: instant

Batteries are built of 4 sections, each 3.2v @ 100 ah - each section is built of enough individual cells to reach 100 ah
BMS system opens relay and cuts power to terminal post when it detects over/under voltage, short or reverse polarity
BMS system balances during charging by providing balancing current to any 3.2v section that has lower voltage than other sections

That's as much as I can get from the website without talking to one of their engineers. I don't know if the batteries in conjunction with the PD charger series that they recommend disconnects the batteries periodically to allow balancing with the battery offline, though that's the process that PD describes in their BMS discussion.

Not sure where you heard/read cell balancing is or needs to be done when battery is offline. Can you provide links, pdf's, etc? Cell balancing is done via a BMS and is independent of or non reliant on the charger except to provide the requisite current/voltage.

Cell balancing is done during the last stages of charging when the pack voltage is above 13.8V.

When a charger is removed, and either when a load is applied or the pack rest a bit, the voltage will drop to the nominal of 13.4-13.5V (or less if a large enough load is on), and all cell balancing will have ceased (in actuality at the 13.8V point really).


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[Peter Tourin]

No, I haven't measured at all yet. I called and talked with one of their engineers, who said that's how the charger behaves.

Odd, should be better than that I would think. They're certainly not the best units around but I have mine set to 13.4 volts (it's used used as a float charger) and it regulates to within a few tenths of a volt under load. Are you measuring right at the terminals on the charger? If not maybe you are seeing some voltage drop in the wiring. Anyway, you want a better unit in any event.

 

[Don Horner]

Same boat here, the technology is very tempting, not only for the higher capacity and lower weight but the excellent charge/discharge characteristics as well. It's just difficult to justify the cost at current pricing. The lithium battery industry is scaling rapidly and I expect we might start to see some significant price reductions in the next few years, or at least I hope so.

The one number I've seen bandied about that somewhat justifies the higher cost is the cost per discharge. Apparently lithium batteries will hand many more discharge/charge cycles than our current batteries, perhaps of an order of magnitude. Based on this, over time the costs will balance -- providing, in my case especially, I live long enough to get full use of them...but I can't stop thinking young...

 

[Peter Tourin]

I don't see a 90A charger on their site, but the 80A is 11.65" - basically, as the current capacity decreases, the models get smaller in this dimension. The 9" is a bit of a problem for me - I have some wiring and an LP heater duct supply in that area, but I think they can be persuaded to move over enough. My particular setup has a 15A/15A double breaker, and there are indeed 20A/15A breakers available - so it looks like it'd just take a different breaker and probably some heavier wiring from the charger to the battery bank.

I haven't put in the research and study as has Peter, but my opinion is that it's really that easy. I would think all the models would fit in the existing space if you completely remove the existing charger/converter and mount the new one directly to the floor.

 

[smiller]

Based on this, over time the costs will balance -- providing, in my case especially, I live long enough to get full use of them...

Or they live long enough. One thing that lithium battery vendors conveniently ignore in their cost comparisons is physical aging, which along with cycle life determines the ultimate longevity of the battery. If you are in an application (off-grid, frequent boondocking, etc.) where you cycle the battery daily then lithium far outperforms lead-acid, but more typical RV use involves long periods of float and relatively few discharges per unit of time and in this mode it's likely even lead-acid batteries would age-out before they cycle-out. It's difficult to determine lithium battery life because it is so dependent on charge level and operating temperature, but floating at full charge (particularly at warm temperatures) is severe duty for them, in fact capacity loss can be 20% per year at 100% charge at 77F, so if you used them relatively infrequently they wouldn't last much longer than lead-acid.

That's not mean to denigrate lithium batteries, let's face it, they're seriously cool. But it would take a somewhat unusual use case to ever get to SmartBattery's '5,000 cycles.' In my case I might fully cycle my batteries dozens of times per year, not hundreds or thousands, and the rest of the time (on the road or when connected to external power) they just float. Under those circumstances the additional capacity is nice (additional capacity is always nice), but it sure wouldn't be very cost effective. At half the current price or less the equation might change and I think we might be there sooner than we think, but in the meantime I will continue to lust after lithium but in practical terms I'll have to stick with lead-acid. YMMV of course.

As an aside it seems that it would be very beneficial for lithium battery management systems to have a mode where batteries are held at partial charge when not in heavy use to obtain a longer service life. My laptop does this, i.e. I can select the battery to be held at 60% charge while on AC power. This is a good idea because laptop batteries often sit in a warm docking station with batteries constantly fully charged (and one might easily see similar conditions in an RV), and this is a terrible operating environment for lithium cells. If such protection is worthwhile for a $100 battery it seems like it would certainly be a good idea for a $1,000 battery.

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[Normand]

May be if you could check with Pleasure Way, apparently they are ahead of the competition and already supply those Lithium battery.
They certainly use the right way to charge them.

 

[Peter Tourin]

I just saw a note on the PW forum that the XL can now be had with 3 solar panels and lith batteries - I just posted a question to one of the techie types on that forum, asking for more details.

I hadn't thought about the float charge thing - that's interesting - I'd like to hear more about that.

Can anybody who's running lith batteries now (OrioN, are you there?) tell me anything about voltage behavior? I'm trying to get a sense of what's normal. I've been on the road for 8 hours - 4 hours, Walmart campground, and another 4 hours. Batteries read about 13.4 when they arrived. When I started, I saw that my old Parallax charger was putting the batteries around 13.7, and the Sprinter alternator put them around 14.1, as I'd expect from this discussion. When I stopped the car the first evening, they read 13.5, and in the morning (fan and fridge electronics the only load overnight) they read 13.3v. At noon today they read 13.8 after I turned the engine off - after 90 minutes they were at 13.4. So it seems that running readings are indeed a lot higher than for flooded batteries!

Questions: Do they read high just after you remove charging voltage? - that is, is there a surface charge type phenomenon and will they drop when they sit with no load and no charge for awhile?

When fully charged and at rest, what approximate voltage are they likely to read?

And since I don't have a way of monitoring SOC - what method am I going to use to know roughly when I'm nearing discharge? Since they have a relatively flat voltage vs. SOC curve until nearly discharged, and then plummet down, and since the sharp bend of the curve is around 12v, can I safely pick a rule of thumb that if I ever see them drop to 12.0v I should consider them down as far as I want to go? I know that they have internal disconnect protection at 8v according to their literature, but I sure don't want to ever get low enough to have it kick in!

Any thoughts and experiences greatly appreciated!

 

[jostalli]

Or they live long enough. One thing that lithium battery vendors conveniently ignore in their cost comparisons is physical aging, which along with cycle life determines the ultimate longevity of the battery. If you are in an application (off-grid, frequent boondocking, etc.) where you cycle the battery daily then lithium far outperforms lead-acid, but more typical RV use involves long periods of float and relatively few discharges per unit of time and in this mode it's likely even lead-acid batteries would age-out before they cycle-out. It's difficult to determine lithium battery life because it is so dependent on charge level and operating temperature, but floating at full charge (particularly at warm temperatures) is severe duty for them, in fact capacity loss can be 20% per year at 100% charge at 77F, so if you used them relatively infrequently they wouldn't last much longer than lead-acid.

That's not mean to denigrate lithium batteries, let's face it, they're seriously cool. But it would take a somewhat unusual use case to ever get to SmartBattery's '5,000 cycles.' In my case I might fully cycle my batteries dozens of times per year, not hundreds or thousands, and the rest of the time (on the road or when connected to external power) they just float. Under those circumstances the additional capacity is nice (additional capacity is always nice), but it sure wouldn't be very cost effective. At half the current price or less the equation might change and I think we might be there sooner than we think, but in the meantime I will continue to lust after lithium but in practical terms I'll have to stick with lead-acid. YMMV of course.

As an aside it seems that it would be very beneficial for lithium battery management systems to have a mode where batteries are held at partial charge when not in heavy use to obtain a longer service life. My laptop does this, i.e. I can select the battery to be held at 60% charge while on AC power. This is a good idea because laptop batteries often sit in a warm docking station with batteries constantly fully charged (and one might easily see similar conditions in an RV), and this is a terrible operating environment for lithium cells. If such protection is worthwhile for a $100 battery it seems like it would certainly be a good idea for a $1,000 battery.

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There is a lot of misguided information in this thread. LiFePO4 batteries are NOT meant to float so don't use a charge profile for other battery types. The best charge profile is Bulk then Off. These batteries are not like FLA or AGM, which like to be held at 100% SOC.

 

[smiller]

These batteries are not like FLA or AGM, which like to be held at 100% SOC.

Well yes, that's exactly what I was saying. I probably should not have used the term 'floating' since it's not technically correct, but if the lithium BMS charges fully and then disconnects the cells will still be sitting at a high state of charge until they are used, even though not actually floating. If usage is infrequent and they are sitting in a warm battery compartment at a high SOC then that's not an ideal operating environment for long life.

Most sources I can find quote an average 5-7 year life for LiFePO4 cells. That's about the same service life as you'd get from properly used and maintained flooded cells. The LiFePO4 would provide a much better cycle life but that's the point... if you cycle the batteries every day then you'd likely be well ahead of the game in terms of cost per cycle with lithium, but if you cycle them once a week then you wouldn't. You would still have the increased energy density advantage, but that's it and it's harder to make that alone justify the nearly 10x cost difference for less frequent users who won't be able to enjoy the increased cycle life.

There are lots of other things to like about lithium batteries beyond cycle life and maybe those things are worth the premium, I'm only noting that vendors seem to make their cost-effectiveness argument based primarily on cycle life and that factor may or may not be beneficial in the real world to any particular user based on their own use case.

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[blk65brd]

The site below has some real world RV testing on lithium batteries
http://www.technomadia.com/lithium/