Lifepo4 Battery pack installation

[Philzter888]

I also did some further research to determine the discharge efficiency of my planned setup with a LiFePo4 battery. As you know, you might get a large battery rated for so many amp hours, but that will depend on the type of battery, the load, and the efficiency. I found information that says this difference in efficiency is due to the Peukert Effect, which describes the inefficiencies in the charge and discharge of batteries. To quote this web site, Battery University.

Peukert Law​ The Peukert Law expresses the efficiency factor of a battery on discharge. W. Peukert, a German scientist (1855–1932), was aware that the available capacity of a battery decreases with increasing discharge rate and he devised a formula to calculate the losses in numbers. The law is applied mostly to lead acid and help estimate the runtime under different discharge loads. The Peukert Law takes into account the internal resistance and recovery rate of a battery. A value close to one (1) indicates a well-performing battery with good efficiency and minimal loss; a higher number reflects a less efficient battery. Peukert’s law is exponential; the readings for lead acid are between 1.3 and 1.5 and increase with age. Temperature also affects the readings. Figure 1 illustrates the available capacity as a function of amperes drawn with different Peukert ratings. As example, a 120Ah lead acid battery being discharged at 15A should last 8 hours (120Ah divided by 15A). Inefficiency caused by the Peukert effect reduces the discharge time. To calculate the actual discharge duration, divide the time with the Peukert exponent that in our example is 1.3. Dividing the discharge time by 1.3 reduces the duration from 8h to 6.15h.

As for the Peukert Exponent that applies to LiFePo4 batteries, I found this web site which suggest it to be between 1.01 an 1.03.

Bottom line is that you'll get close to the rated capacity of the battery in discharge. About 97%.

Edit: So I did some battery life calculations using an online battery calculator.
Camera power use during parking mode. Using the front and rear camera. Measured on the 5v input: 2.23W.
2.23W into amps at 12V = 0.185 amps.
12V to 5V conversion overhead: 10% to 15%.
12V power draw including overheads 0.185*1.15=0.21275 amps.
100 amp hour battery
1.03 Peukert exponent

Here's the results
View attachment 56211

Considering that the safe acceptable depth of discharge for a LiFePo4 battery is around 99%, we can get close to the full discharge time of 491.778 hours or 20.5 days. Is this wrong?

I did research on this with regards to lithium cells but to some extent it applies to lifepo4.

Its best to discharge to 15% of capacity and charge to 70-85% of capacity if your objective is longevity. Most cells are really rated to 80% of the capacity, and the remaining is a kind of overcharged state with higher heat. Your cycle life may increase up to 200% if you charge only up to these levels and it’s well ventilated. From memory cycle life may go from 300-500 all the way to 800+.

The good thing about running a dash cam is that the discharge is very gentle and so starting the constant recharging is not at all hard on the battery. I am running only a small 38A pack (144whr) with around 8-10 hrs driving with a lot of short trips and the battery has never gotten flat in 9 months with 3-4w constant load. Your battery has 8x more capacity since it’s rated at 12v and mine is rated at 3.7v.

One benefit with your setup is the dash cam is always powered even after an accident. I had a rear end recently and I had to keep the car running to make sure to capture the actions of the other drivers. Some cars just shutdown completely if it’s a big crash just in case oil and coolant is leaking or the car is turned over and ignition is not left on. Night use for parked recording is going to be of limited use - it’s pretty much impossible to get plates at night so you may not need as much recording as u think.
With such an old car and a huge battery with small load, there is no need for really any aggressive charging. So make sure the controller has some adjustment in it. Your car wiring is old and fragile so as Indian said this is the only way for you to go with such a large battery. Guys have melted wiring just from installing aftermarket LED bulbs, so they don’t over engineer the wires...

 

[SawMaster]

The various Lithium technologies behave differently, so you can't apply 'rules' or 'best practices' for one type to another. The charging practices mentioned above seem to be aimed toward LiIon types, and are different that what applies to LiFePO4 or LTO types, which can be discharged more deeply and charged more fully without being detrimental to their usable lifespan.

It is these kinds of differences which can make one type better than another for a given application. I'm a big fan of LiIon technology, but in the case of dashcam use it's not the best type to go with even though it's usable here. LiFePO4 or AGM is much better suited to this purpose, with AGM being much the lesser, only easier to implement.

Phil

 

[Philzter888]

The various Lithium technologies behave differently, so you can't apply 'rules' or 'best practices' for one type to another. The charging practices mentioned above seem to be aimed toward LiIon types, and are different that what applies to LiFePO4 or LTO types, which can be discharged more deeply and charged more fully without being detrimental to their usable lifespan.

It is these kinds of differences which can make one type better than another for a given application. I'm a big fan of LiIon technology, but in the case of dashcam use it's not the best type to go with even though it's usable here. LiFePO4 or AGM is much better suited to this purpose, with AGM being much the lesser, only easier to implement.

Phil

I’m sorry these figures I’ve provided are not rules but taken from studies I’ve read on lithium and lifepo4 capacity loss, which is usually a function of depth of discharge (DoD) and State of Charge (SoC). The battery changes in internal resistance as well due to rate of discharge. The only general difference in technology is just usually the baseline number of cycles as a result of inherent chemistry. Can you show me the study where lifepo4 is not affected by these factors? The OP is discussing discharge depths of 99%.

 

[Indian]

During the covid period I hardly drive 4 hours a week. From filling 70 liters of diesel every 2 weeks I now fill up 70 liters every 8-10 weeks. I drive about once a week now for a total of about 20 km to the shop and back. The lithium battery has never dropped below 70% with only the dashcam connected.
Your Opel Corsa is a borderline case. If Euro5 you probably have a smart alternator and regenerative braking. Do you have space to fit a 60A charger in your car? I drive a Multivan and space was an issue when I went for the smaller 30A charger.

Sent from my iPhone using Tapatalk

 

[SawMaster]

@Philzter888 It's not that those things don't make a difference, for they do. But you're now dealing with something of a deceptive situation- here's why:

If you are wanting a given amount of current (as in runtime for a cam), then if a battery can deliver that by using all it's potential, to use it more gently requires a larger battery to get that same amount of current (runtime). That's an added cost. And since we're not going to be there to control the charge/discharge rates and times, we now need a device to do that (an adjustable MPPT instead of a simple fixed-rate BMS, of which the already mentioned "Victron" brand is a good one).

So the real question becomes whether that added cost and the longer battery life it may give offset the need to replace the smaller cheaper fully-used battery more often. As battery prices are variable and we can't know future pricing it's hard to figure accurately. I've seen reports of both short and long battery life based on how well the batteries were treated, but when you do the numbers as I've shown, any advantage becomes much smaller than it initially seems. And of the short life tales, sometimes it's cells which aren't as good as they were initially thought to be, and that occurs even with good care and treatment.

Given the usage being planned here and the harsh automotive environment, I don't see any part of the whole system reaching it's full life-span potential. So I don't see any pressing need to 'baby' the battery here- it will last sufficiently long, far longer than the camera, and by the time the battery needs replacing the chances are good that the user will have traded in for a newer vehicle anyway.

So agreed to try to treat the battery well- just don't think you're gaining a lot by doing that because you're not.

Phil

 

[Vanhalo]

Hi guys, I am planning to install a sealed Lifepo4 12Vx9AH (Aliant brand) in my car, but the car may be parked in such hot area (under sun light).
So my question is: how safe is it to install this battery inside the car´s trunk?

Thanks!

I have left a Dometic PLB40 (40Ah Lithium ion Phosphate) in the hot summer sun for several days in the back of my Jeep without issues.
Constant power to a 12v fridge powered with 100w solar.
It's rating is 122F.
I have used this battery 24/7 (2 years) whether in my Jeep or my office.