are lifepo4 batteries worth it?

[shmick82 Junior Member Find all posts View Profile Close shmick82]

Hi,Im doing a new setup in the car and am after an outside point of view.
I sold my thumper due to size of it (height) and was going to buy a 200ah deep cycle agm. This would be permanently mounted in boot, to run fridge. Car is usually driven daily so at most if it sits 2 days the fridge might drain 40-50ah (75%). so the agm will be close to full charge all the time (well its off isolator in 120 grande, so probably 13.5-13.8V?), hopefully getting long life. it might from time to time (like once a year) get LEDs attached for camping, but will probably never discharge more than 50%. This battery is a f@#king tank. 600mm long (not too much issue) but 65kg!!!!!
other option is to pay nearly double for a 50-60ah lifepo4 which weighs less than a quarter (im not too fussed on size, just weight, as my draws alone are 60-70kg, plus fridge). so the lifepo4 battery would quite regularly be discharged over 50%, sometimes closer to 80%. plus im not sure my projecta electronic isolator will charge it (so more money).
The way im planning to use the batteries, which battery would be better off?
Any other things im missing?
im thinking even if i get half the life out of the agm, in 3-4 yrs the lifepo4 might be heaps cheaper so not much point getting it now.

[Symo Advanced Member Find all posts View Profile Close Symo]

I only run a 55AH optima under the bonnet and it runs the 60L waeco for 3 days, and because the optima battery can actually be drained 100% (its actually a 70AH battery really so once yo have used 55A its at 20% SOC) - and it will recharge to 90% in 40mins.

Stuff having 70kg permanently in the boot, that's like dragging around an extra 90L of fuel for no reason!!

[D4Dforme Senior Member Find all posts View Profile Close D4Dforme]

http://www.thebackshed.com/basiclyna...s/logotext.gif


Talk to these guys

[photoprado Avid PP Poster! Find all posts View Profile Close photoprado]

Um...

Lithium batteries are a lot lighter Symo

Have a look at this diagram and see if you can tell the difference:


(Never heard of this mob before, but the graphic is relevant)

They do cost more, but they are longer lasting and have a wider drain tolerance compared to traditional batteries.

[Symo Advanced Member Find all posts View Profile Close Symo]

Um...

Lithium batteries are a lot lighter Symo

Have a look at this diagram and see if you can tell the difference:


(Never heard of this mob before, but the graphic is relevant)

They do cost more, but they are longer lasting and have a wider drain tolerance compared to traditional batteries.

The original post quoted 65kg, go figure...

[photoprado Avid PP Poster! Find all posts View Profile Close photoprado]

The original post quoted 65kg, go figure...

He was talking about a 200ah AGM and was wondering about going LiPo:

other option is to pay nearly double for a 50-60ah lifepo4 which weighs less than a quarter

[shmick82 Junior Member Find all posts View Profile Close shmick82]

He was talking about a 200ah AGM and was wondering about going LiPo:

lol, LiPo, i need some of that too. after some research and looking at charts, it seems id get similar amount of cycles from discharging an AGM 20% (looks like AGM life tumbles massively after 20%) comparable to LiPo at 80%.

(NOTE I have decided on LiPo as I found them at amazing prices (hopefully not duds, not sure if im allowed to list shop so i wont, but below is my reasoning)

So a $400 200ah AGM will theoretically get 3000 cycles if only 40ah are used. At a weight of around 65kg.
So a $448 60ah LiPo will theoretically get 3000 cycles if only 48ah are used. At a weight of around 11kg.

So its settled. Now I have to figure out if I need a new charger.

Oh, the 60ah is on backorder, so I ordered a 90ah for $672. Which at 50% discharge (45ah) should theoretically get around 5000 cycles. Which in a perfect world will see me through almost 2 decades, which comes down to $33/yr. I'll report back in 20 yrs

Oh, and the LiPo could also be called portable, so I can take it in the tent, or hiking in my backpack with an inverter so my wife can watch TV because walking is "boring"

[t303 Senior Member Find all posts View Profile Close t303]

I have a LiFePO4 60ah in the back, it charges perfectly off the standard alt (I have 6 B&S twin cable to the rear, about .3v drop at 15A charge rate)
The benefits: 60ah Li vs 100ah AGM
9.5kg vs 22kg (don't need massive battery tray, can strap it to the side of the drawers) and about 1/2 to 1/3 the size
will accept whatever charge rate you can feed it, and the rate does not drop off as the battery tops up, thus charges faster
13.8 volts will still charge the battery to close to full (95+%), AGM will need to be taken to 14.4 and held there for some time
13.4 volts will still get within a few% of full in the same amount of time
an almost flat discharge curve, ie you will have 12+v for most of it's capacity, unlike AGM
3000+ cycles to 80% DOD, compared to (lots) less than 1000 for AGM
It ends up being somewhere about (ah available over it's life) 4 times as economical as AGM
The only other thing needed is a low voltage cutout set at around 11.5v

My ideal would be to fit a 120w solar panel to the roofrack with a PWM solar controller set to 13.8v, fire up the fridge then forget about it if the car is parked outside all day.

[shmick82 Junior Member Find all posts View Profile Close shmick82]

t303, I just started a new thread about charging, but you answered that here. Pretty much I have an existing isolator which cuts out at 12.8V, so my charge range is 12.8 to the max voltage the car pumps out. I'm also like yourself running 6B&S cable. LeighW mentioned looking into something to protect from those random rare events that may cause voltage spikes. I suppose you've had no problem, yet.

Couldn't the LiPo battery be used as stand alone crank and accessories battery? Provided you had a fail safe to make sure it always had enough to crank the car?

[Symo Advanced Member Find all posts View Profile Close Symo]

lol, LiPo, i need some of that too. after some research and looking at charts, it seems id get similar amount of cycles from discharging an AGM 20% (looks like AGM life tumbles massively after 20%) comparable to LiPo at 80%.

(NOTE I have decided on LiPo as I found them at amazing prices (hopefully not duds, not sure if im allowed to list shop so i wont, but below is my reasoning)

So a $400 200ah AGM will theoretically get 3000 cycles if only 40ah are used. At a weight of around 65kg.
So a $448 60ah LiPo will theoretically get 3000 cycles if only 48ah are used. At a weight of around 11kg.

So its settled. Now I have to figure out if I need a new charger.

Oh, the 60ah is on backorder, so I ordered a 90ah for $672. Which at 50% discharge (45ah) should theoretically get around 5000 cycles. Which in a perfect world will see me through almost 2 decades, which comes down to $33/yr. I'll report back in 20 yrs

Oh, and the LiPo could also be called portable, so I can take it in the tent, or hiking in my backpack with an inverter so my wife can watch TV because walking is "boring"

When you say LiPo you literally mean Lithium polymer? If so I would be very cautious. With our LiPo's at work they are small (2-3Ah) yet the risk of fire is so great we have to place them in a fire blanket for charging, and they can never be left unattended while charging.

LiPo batteries are notorious for bursting into flames as they have a thrmal run-away when the short, which happens alarmingly often.

The other issues is because they have such a high C rating, when they unload or short they burn hot enough to melt steel, so you won't stop it.

Also LiPo cells tend to fail if left charged, they are designed for compact rapid power release, not slow deep cycle, they will swell to twice their size and will either short and burnout (taking your car with it) or not hold any charge.

In other words, I'd be shit scared you're going to burn you car to the ground if that this has something go wrong with it bouncing around in the car. I treat the LiPos at work as little sticks of C4.

Also an AGM will get 5-10 years of use at 20% SOC, as 300 cycles is 1 every day for a year, so 3000 is 10 years. And I bet the AGM will still fail before then so running down to 20% is well worth it to get your moneys worth regardless.

I've been running my 120AH down to 11v 5 times a year for the last 5 years and it still holds 12.9v charged and just on easter ran my 60L and 4 LED lights for 4 days and was still at 12.1v.

[Tin175 Senior Member Find all posts View Profile Close Tin175]

I played with A123 Batteries over 5 years ago in my RC electric helicopters. A123 Batteries use the LiFePO4 chemistry which is much more stable than the LiPo chemistry. LiPo (lithium Polymer) are a lighter and a more energy dense battery but can catch fire and explode especially when they are physically damaged (crashed heli) or if they are overcharged.

LiFe batteries will not explode if overcharged and do not cause fire when damaged.

https://www.youtube.com/watch?v=rb_J2QQ0k-4

[t303 Senior Member Find all posts View Profile Close t303]

t303, I just started a new thread about charging, but you answered that here. Pretty much I have an existing isolator which cuts out at 12.8V, so my charge range is 12.8 to the max voltage the car pumps out. I'm also like yourself running 6B&S cable. LeighW mentioned looking into something to protect from those random rare events that may cause voltage spikes. I suppose you've had no problem, yet.

Couldn't the LiPo battery be used as stand alone crank and accessories battery? Provided you had a fail safe to make sure it always had enough to crank the car?

I have two separate hivolt alarms that will both be screaming their t*ts off if it goes high.
IMHO battery management systems are not required unless you are trying to push the limits on charge and discharge voltages. If you stay in the middle of the bell curve you are unlikely to have any problems. I check individual cell voltages (out of idle curiosity) occasionally and rarely have more than a couple of millivolts difference between cells. That is another advantage of the Li cell setup; if you were able to measure the individual cells in an AGM you would probably be somewhat alarmed at the different states of each, but you never know how they are until they drop the cell (as has been the failure mode of just about every LA battery I have owned).

[shmick82 Junior Member Find all posts View Profile Close shmick82]

by LiPo I meant LiFePO4, sorry, photoprado mentioned it and i went with it.
I might add a battery management system if I pick one up cheap, otherwise I'll wing it (im an optimist).

[photoprado Avid PP Poster! Find all posts View Profile Close photoprado]

Yep, I think we all knew you were talking about current standard Lithiums, LiFePO4.

Sorry if it went off track.