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Lifepo4 battery

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offgrid View Drop Down
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Post Options Post Options   Quote offgrid Quote  Post ReplyReply Direct Link To This Post Topic: Lifepo4 battery
    Posted: 13 Nov 2019 at 4:15am
Actually Li batteries are less finicky to charge and maintain than PbA’s. You can leave them at partial state of charge for long periods without damage. You don’t need a complex multistage charger. Just a simple max cutoff voltage is fine. No trickle charging needed. No water adding.

There are a couple of don’ts with Li. Do not overcharge, ever. Do not use them at cold temps. Warm them up first. Don’t discharge them 100% (that applies to PbA’s as well of course).

So they aren’t harder to manage, just different.

As for cost to convert from PbA to Li, the batteries themselves are close enough in cost now that you break even or come out ahead if you boondock and keep your trailer long enough to benefit from the much longer cycle life of the Li batteries. But all your charge control equipment needs to get changed too (a/c charger, tow vehicle charging, and solar). That significantly changes the cost equation.

Re energy vs power, let’s keep our measurement units straight. Amperes are units of electric current. Volts are units of electric potential. Volts x amps = watts which are units of power. Energy is power x time = watt hours. So watts = volts x amps x time.

Batteries are energy storage devices. But they are generally rated in terms of how long they can provide a given amount of current while being discharged. That is amp hours = amps x time. The reason for using amp hours and not watt hours is because the voltage delivered by the battery changes during discharge. So for our purposes it’s easier and more accurate to use amp hours to compare different batteries as long as you are comparing two nominal 12V batteries.



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Post Options Post Options   Quote Olddawgsrule Quote  Post ReplyReply Direct Link To This Post Posted: 13 Nov 2019 at 7:18am
Originally posted by TheBum

Originally posted by Olddawgsrule


Originally posted by TheBum

No, it's an energy thing, as in amp-hours.

Huh?? Care to elaborate a bit?


Power (e.g. wattage) is energy expended per unit time. It's only a rate, not a capacity. The same battery can output 10W or 100W, but the more watts it outputs, the less time it'll take to drain the battery. To look at it another way, a LA battery and a LiFePO4 battery can output the same wattage, but the amount of time it'll take to drain the batteries is dependent on the energy stored in the battery.

LiFePO4 batteries have a higher energy-to-weight ratio than LA batteries do and they can output a large amount of wattage, but they're a bit more finicky on how you charge them, i.e. they're only good for a limited number of charge cycles, so it's a bad idea to trickle charge them: it reduces the service life of the battery because it's essentially cycling continuously.

Well, now I have a clue as to what you were implying. I agree with Glue on this.. Wattage is 'power' and watt hours is power over a period of time. 
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Post Options Post Options   Quote Olddawgsrule Quote  Post ReplyReply Direct Link To This Post Posted: 13 Nov 2019 at 7:36am
Originally posted by offgrid

Actually Li batteries are less finicky to charge and maintain than PbA’s. You can leave them at partial state of charge for long periods without damage. You don’t need a complex multistage charger. Just a simple max cutoff voltage is fine. No trickle charging needed. No water adding.

There are a couple of don’ts with Li. Do not overcharge, ever. Do not use them at cold temps. Warm them up first. Don’t discharge them 100% (that applies to PbA’s as well of course).

So they aren’t harder to manage, just different.

As for cost to convert from PbA to Li, the batteries themselves are close enough in cost now that you break even or come out ahead if you boondock and keep your trailer long enough to benefit from the much longer cycle life of the Li batteries. But all your charge control equipment needs to get changed too (a/c charger, tow vehicle charging, and solar). That significantly changes the cost equation.

Re energy vs power, let’s keep our measurement units straight. Amperes are units of electric current. Volts are units of electric potential. Volts x amps = watts which are units of power. Energy is power x time = watt hours. So watts = volts x amps x time.

Batteries are energy storage devices. But they are generally rated in terms of how long they can provide a given amount of current while being discharged. That is amp hours = amps x time. The reason for using amp hours and not watt hours is because the voltage delivered by the battery changes during discharge. So for our purposes it’s easier and more accurate to use amp hours to compare different batteries as long as you are comparing two nominal 12V batteries.


Again, thank you and well said. 

I deal in wattage mainly to track what is used and what is replaced. Dis-charge/charge cycle. My meters track this for me as watt-hours. I would be close if I tracked amps, yet as you say, wattage changes according to solar in voltage and battery out voltage. Much prefer tracking with wattage.

Also much easier in a power audit when you have both AC & DC appliances. 
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Post Options Post Options   Quote GlueGuy Quote  Post ReplyReply Direct Link To This Post Posted: 13 Nov 2019 at 10:10am
Originally posted by offgrid

Re energy vs power, let’s keep our measurement units straight. Amperes are units of electric current. Volts are units of electric potential. Volts x amps = watts which are units of power. Energy is power x time = watt hours. So watts = volts x amps x time.
All the way up to the end you had me. watt-hours (energy) = volts x amps x time.

... and I still prefer using watts. Precisely because amps will vary by voltage. Unless the load is purely resistive, the amps will go up as the voltage goes down. This is particularly noticeable with lead-acid batteries because their voltage changes with their state of charge.
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Post Options Post Options   Quote offgrid Quote  Post ReplyReply Direct Link To This Post Posted: 13 Nov 2019 at 2:01pm
Originally posted by GlueGuy

 All the way up to the end you had me. watt-hours (energy) = volts x amps x time.

... and I still prefer using watts. Precisely because amps will vary by voltage. Unless the load is purely resistive, the amps will go up as the voltage goes down. This is particularly noticeable with lead-acid batteries because their voltage changes with their state of charge.

Thanks for the correction. Embarrassed

Which loads are constant power (current goes up as voltage goes down)? LED's aren't, water pumps aren't, fans aren't. Those are the main 12V loads in the trailer. 

The reason for working in amp hours is that it makes load calcs, battery sizing, and solar sizing easier, not that you can't do it either way. That's how the off grid solar industry does it and why. If you want to work in watt hours that's fine too, you just have to be careful to apply the correct conversion factors for battery round trip, charger, and solar array efficiencies. No need for a debate about it I don't think. 
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Post Options Post Options   Quote jato Quote  Post ReplyReply Direct Link To This Post Posted: 13 Nov 2019 at 6:49pm
There are a couple of don’ts with Li. Do not overcharge, ever. Do not use them at cold temps. Warm them up first. Don’t discharge them 100% (that applies to PbA’s as well of course).  posted by OFFGRID

Here I sit with my pair of nearly 9 year old 12v Interstate group size 24 deep cycles, considering the Lithium until I read the above post by Offgrid.  So . . . . do not use them at cold temps.  Hmmm, for the majority of the time we have camped with our 177 over the past nearly 9 years the bulk has been in the shoulder months (when it is colder) and where electricity is not available.  So if and when these give up the ghost it looks like I will go back the the LA style, but maybe look at a pair of golf cart batteries instead.  For the most part we change out each battery when it gets to 12.2 volts, hence that may be part of the reason they have lasted as long as they have.  Also regular cleaning on top with baking soda and keeping an eye on the water levels.  

Being in the golf industry for over 40 years I have found it interesting how Yamaha, about 6+ years ago went to the 48 volt system.  No, they do not use 4 12v batteries but 6  8v batteries.  Hopefully there will be enough demand for the 6v ones (like the old 36v electric carts had) so that they don't become discontinued.
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Post Options Post Options   Quote offgrid Quote  Post ReplyReply Direct Link To This Post Posted: 14 Nov 2019 at 7:09am
Keeping a Li battery warm shouldn't really be a show stopper if you would otherwise want to make the switch from PbA. In an rPod I would suggest placing the Li battery inside the heated part of the trailer somewhere. Since they don't outgas or need easy access for adding water that would be fine and the battery wouldn't be subject to extreme temperatures that way. 

That being said if there is no other compelling reason to make the change (reducing weight and or increasing capacity) then sticking with PbA and all your existing charging gear makes economic sense. The 6V configuration is common in the RV and off grid solar world too so I think there's not much worry it will get discontinued anytime soon. 
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Post Options Post Options   Quote Olddawgsrule Quote  Post ReplyReply Direct Link To This Post Posted: 14 Nov 2019 at 8:14am
Originally posted by jato

There are a couple of don’ts with Li. Do not overcharge, ever. Do not use them at cold temps. Warm them up first. Don’t discharge them 100% (that applies to PbA’s as well of course).  posted by OFFGRID


Well, you don't wish to over-charge a Pba either.. that's called boiling the battery. 

Li is more sensitive to cold where Pba is to heat. Both batteries types survive best at room temp, 68F or 20C. It is stated that every 8C or 46F increase you cut the life of the Pba in half (I assume same is true with decrease).
Lithium now has the advantage in warm weather climates.
It is also stated that a Pba will loose capacity in colder weather. Stated that at 32F or 0C you've lost 15% of your battery capacity. If your camping at 0F or 18C you've lost almost a 3rd of your battery capacity

Neither really likes cold weather.

The additional benefit to Li is it 'can' come into the living space and operate normally with no hazard. Again, it can come into the house and operate there as a UPS or Backup power.

Going Li is a choice to be made by ourselves and our own intentions. What works for me, may not for you. My hesitance was multiple: Cost being #1, verifying my power audit as to how we camp & what we actually use and finally weight. 
For me, it now makes sense. 
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Post Options Post Options   Quote offgrid Quote  Post ReplyReply Direct Link To This Post Posted: 14 Nov 2019 at 9:16am
Originally posted by Olddawgsrule


Well, you don't wish to over-charge a Pba either.. that's called boiling the battery. It won't really hurt anything if you overcharge a flooded PbA battery as long as you keep the plates covered with distilled water. OTOH, a Li battery could catch fire under the same conditions. A so-called "sealed" (actually valve regulated) PbA battery will also severely overheat under overcharge conditions, ask me how I know.Shocked

Li is more sensitive to cold where Pba is to heat. Both batteries types survive best at room temp, 68F or 20C. It is stated that every 8C or 46F increase you cut the life of the Pba in half (I assume same is true with decrease). There are two determining factors in battery life (both PbA, Li, and others), shelf life aka corrosion life and cycle life. Shelf life determines how long a battery can sit on a shelf not being cycled, and is very dependent on storage temperature, both below (longer life) and above (shorter life) normal room temp. Cycle life determines how many cycles to a given depth of discharge a battery can handle. The battery will reach its end of life, typically stated as having 80% of its original capacity, when the first of these two factors occurs. 
Lithium now has the advantage in warm weather climates. Not really. A Li battery's life is also determined by temperature, just ask folks in Phoenix who bought a first gen Nissan leaf EV. All the EV mfgs (I think) use active liquid battery cooling for this reason, except Nissan who is still doing air cooling for some reason. We don't need to do that with our batteries because the charge and discharge rates are much lower than in an EV. 
It is also stated that a Pba will loose capacity in colder weather. Stated that at 32F or 0C you've lost 15% of your battery capacity. If your camping at 0F or 18C you've lost almost a 3rd of your battery capacity The capacity is actually still there, you just can't get it out because the internal resistance of the battery is higher at low temps due to the slowed chemical reaction rates. If you warm up that battery the capacity will "magically" reappear. 

Neither really likes cold weather. But there is a big difference. If you try to recharge a Li battery at low temps it will undergo permanent damage because the chemical reaction occurring at the battery anodes changes. With PbA batteries everything is just slowed down, no long term harm done unless you leave them really discharged and allow the electrolyte to freeze. So, be sure you warm up your Li battery before trying to recharge it. 

The additional benefit to Li is it 'can' come into the living space and operate normally with no hazard. Again, it can come into the house and operate there as a UPS or Backup power. Yep, agreed. 

Going Li is a choice to be made by ourselves and our own intentions. What works for me, may not for you. My hesitance was multiple: Cost being #1, verifying my power audit as to how we camp & what we actually use and finally weight. 
For me, it now makes sense. For me too, I want to be able to run a/c off grid and need about 4kWh minimum useable capacity to do so. That would weigh in at about 400 lbs with PbA but only about 60 lbs with Li. 
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