Lifepo4 Battery pack installation

That's awesome. I found a battery with an in-built BMS from a reputable retailer in Australia called Battery World. I think this would be awesome, as the camera is the only thing I want to power. It's just for a small hatchback car, so space is at a premium.

I found another thread on here which shows the measured draw of the Viofo A129 dual camera to be 2.23W using the front and rear camera at the low powered parking mode while parked. This low powered mode takes video at 5 frames per second (fps) as opposed to 30 or 60fps while driving. However, that's measured from a nominal 5V USB output. At 12V that would equate to 0.185AH, BUT.. Naturally, there's going to be overhead between the 12V to 5V conversion. Although I don't know how much... So, I think your allowance for 0.5AH gives some generous overhead for the 12V to 5V conversion overhead.

I've already hard-wired my Blackvue DR-750S 4G camera, so I had a little bit of experience with this already. Very disappointed to find out that the hardwire kit doesn't come with support for the manufacturer's battery pack, as this requires a 9 amp draw, and the cables that come with it are clearly too small for that kind of amperage. Edit: Getting rid of the Blackvue as it's event recording sucks - Best you can do is throw you hand across the camera and it'll manually save the last 5 seconds and the next minute.. I loved my previous Viofo A119 so much that I decided to upgrade to the A139.

Just wanted to say thanks for your advice. Been trying to figure out how this is going to work for weeks now.

Picture credit: Gabilondo77
 

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PS. When you talk about delivering excess current to the battery. Does that mean that I need to have said 100ah LifePO4 battery connected in parallel with the existing car starter battery for it to operate in the fashion of only delivering excess current to the battery? I was thinking about finding a high amperage accessories circuit so that it only charged the battery while the car is on. Is my way of thinking wrong/flawed?
 
The accessory circuit feed would be the way to go for charging. You may need to add a charging isolater or relay to prevent backfeeding from the battery into the accessory circuit when parked.

Phil
 
That's awesome. I found a battery with an in-built BMS from a reputable retailer in Australia called Battery World. I think this would be awesome, as the camera is the only thing I want to power. It's just for a small hatchback car, so space is at a premium.

I found another thread on here which shows the measured draw of the Viofo A129 dual camera to be 2.23W using the front and rear camera at the low powered parking mode while parked. This low powered mode takes video at 5 frames per second (fps) as opposed to 30 or 60fps while driving. However, that's measured from a nominal 5V USB output. At 12V that would equate to 0.185AH, BUT.. Naturally, there's going to be overhead between the 12V to 5V conversion. Although I don't know how much... So, I think your allowance for 0.5AH gives some generous overhead for the 12V to 5V conversion overhead.

I've already hard-wired my Blackvue DR-750S 4G camera, so I had a little bit of experience with this already. Very disappointed to find out that the hardwire kit doesn't come with support for the manufacturer's battery pack, as this requires a 9 amp draw, and the cables that come with it are clearly too small for that kind of amperage. Edit: Getting rid of the Blackvue as it's event recording sucks - Best you can do is throw you hand across the camera and it'll manually save the last 5 seconds and the next minute.. I loved my previous Viofo A119 so much that I decided to upgrade to the A139.

Just wanted to say thanks for your advice. Been trying to figure out how this is going to work for weeks now.

Picture credit: Gabilondo77
Why is there overhead conversion? It’s not like you are outputting to AC and then going back to DC. These cells are typically 3.7v cells. The loss is going from the AC and charging the battery, but once it’s stored it’s just DC to DC.
 
Why is there overhead conversion?
Not sure what you're speaking about here. The BMS is necessary as a means to regulate charging, reduce the input 12V to 3.7V for each cell, and prevent overcurrent in discharging which is needed with LiFePO4 or any other Li battery type. You can't just 'float' these like you can a12V AGM.

Phil
 
Not sure what you're speaking about here. The BMS is necessary as a means to regulate charging, reduce the input 12V to 3.7V for each cell, and prevent overcurrent in discharging which is needed with LiFePO4 or any other Li battery type. You can't just 'float' these like you can a12V AGM.

Phil
That’s not what the poster was referring to and not what I’m referring to. He seems to referring to the implied lower capacity as a result from conversion loss from the draw or the load and not the charging input. Capacity issues are not usually relevant/discussed in the charging or input phase except to prevent damage. The only time I would think the battery outputs constant 12v is via a direct connect cigarette port bypass that pulls all the cells. This is typically when max amp is available.
Unless lifepo4 must always output all cells in parallel and can’t output sequentially or independently I suppose is a possibility but that is a weird setup that require a tear down to confirm.
 
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Why is there overhead conversion? It’s not like you are outputting to AC and then going back to DC. These cells are typically 3.7v cells. The loss is going from the AC and charging the battery, but once it’s stored it’s just DC to DC.
There will be an inefficiency in the hardwire kit converting 12v to 5v of around 10 to 15%.

That battery will have no voltage regulation so will be very efficient, but without using a charger it will put a heavy load on the alternator,
PS. When you talk about delivering excess current to the battery. Does that mean that I need to have said 100ah LifePO4 battery connected in parallel with the existing car starter battery for it to operate in the fashion of only delivering excess current to the battery? I was thinking about finding a high amperage accessories circuit so that it only charged the battery while the car is on. Is my way of thinking wrong/flawed?
I don’t know what charge rate you will get with it just connected in parallel, but I guess you should use 100A cable and the charge rate will be limited by the alternator. Alternatively you could connect it via a charger which will limit the charge rate to something more reasonable.
 
That’s not what the poster was referring to and not what I’m referring to. He seems to referring to the implied lower capacity as a result from conversion loss from the draw or the load and not the charging input. Capacity issues are not usually relevant/discussed in the charging or input phase except to prevent damage. The only time I would think the battery outputs constant 12v is via a direct connect cigarette port bypass that pulls all the cells. This is typically when max amp is available.
Unless lifepo4 must always output all cells in parallel and can’t output sequentially or independently I suppose is a possibility but that is a weird setup that require a tear down to confirm.
OK, we were speaking of 2 different things ;)

Yes, every electrical circuit and device has some loss involved. For most wiring it's so small as to be ignored, but 'buck converter' chargers which drop the nominal 12VDC from the car to the ~3.7VDC needed by the cells are usually only around 85% efficient. This is built into the batteries internal BMS. It does not affect the battery output, which determines runtime. There's also some loss in the HWK, but if you measure the current draw at it's input the resulting figures will be close to actual runtime. If you measure current draw at the cam you'll probably find runtimes about 10% shorter than expected.

Battery wear and charging characteristics will also come into play so if you absolutely need a certain runtime it's best to oversize the battery to ensure you always get it. With 100A available you'll almost certainly get 7 full days runtime and likely as much as 10 days according to how the cam is configured. By that point you may be overwriting the card if it's below 512GB according to the mode used so 100A is plenty and about all you can do in terms of runtime for parking.

You're welcome to purchase and test a 1TB card and share the results with us, a card size I'll never be able to afford :giggle:

Phil
 
but 'buck converter' chargers which drop the nominal 12VDC from the car to the ~3.7VDC needed by the cells are usually only around 85% efficient.
I would expect that battery to have cells connected in series so that it does not actually need to drop the voltage, making it around 99% efficient. The BMS will be balancing the cells and protecting against under/over voltage.
 
These do charge in series. The way a BMS works is by monitoring each cell (sometimes every other cell in higher voltage batteries) and if it senses an anomaly beyond design parameters it will stop charging the entire battery at that point. It limits the charge rate to a single level which is always safe for the battery in any conditions. When the cells are in spec, it will also 'balance' them by applying a very low charge beyond normal limits for a time once full charge has been reached, still monitoring the individual cells (called "top balancing") which ensures that all cells are fully charged equally. It prevents against over-temp in charging, and might also protect against under-temp charging. Most do not protect against over-discharging which can also destroy cells.

The best batteries now use "MPPT" (maximum power point technology) instead of a BMS. What this does is factor in the cell temps during charge using a variable charge rate instead of a single level rate, so that the maximum charge is always being applied in whatever the ambient temps are thus allowing the cells to be charged faster than a BMS does when that can be safely done. It will also 'top balance' and protect against over-temp/under-temp during both charging and discharging, actively limiting the discharge rate to a safe level which a simple BMS doesn't do. Costs more but you get more.

The newer LTO (lithium titanate) cells are interesting and are being tried in real-world off-grid use. These offer performance equal to or slightly better than LiFePO4, but are more tolerant in temp range limits by several degrees Celsius. They are also supposed to significantly increase the number of charge cycles possible before the cells wear out. I'm not seeing anything better in the realm of possibilities in the next few years- lithium batteries have fully matured and we're near the limit of what lithium can offer. Because of all this, LiFePO4 batteries are one of the best values around today for the total usable energy over their lifetime.

Phil
 
I bought a lifepo4 portable camping lamp, and it had weird 3.0v cells that could overcharge a bit but didn’t retain the overcharge state for very long. I think lifepo4 cells have lower energy density and so lower voltage, probably in the 3.0-3.2 range c.f. Lithium cells. Honestly trying to get that last 20-30% capacity in lifepo4 seems wasteful.
 
You should not connect the 2 batteries in paralell. Connect the Lithium in paralell through a VSR. Victron Cyrix Li-ct is a good and proven VSR. I had this setup before and my 120A alternator charged the lithium at 16A. I took it off before the winter and installed a DC-DC charger to prevent charging under 0 degrees.
Without the VSR, you will drain the battery with most charge.


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Wow. There's some awesome level of knowledge on this forum. Thanks for the robust discussion.

You may need to add a charging isolater or relay to prevent backfeeding from the battery into the accessory circuit when parked.
That's a good point. Especially as I'm trying to get the maximum run-time out of this camera.

There will be an inefficiency in the hardwire kit converting 12v to 5v of around 10 to 15%.
Yup! That's what I was referring to in terms of conversion losses. Thanks. So, question here then... would it be worthwhile, or even possible, to use an equally large 5V battery for this use case instead? I tend to think it wouldn't be possible as the parking mode kits typically require 12V input. I would also hazard a guess that 5V batteries of such a size don't exist. Further, trying to charge such a battery would require a much heavier gauge cable as you're more than doubling the amps. You'd probably also lose some amount of the gains in transmission loss anyway.
I don’t know what charge rate you will get with it just connected in parallel, but I guess you should use 100A cable and the charge rate will be limited by the alternator. Alternatively you could connect it via a charger which will limit the charge rate to something more reasonable.
This is one thing that I kinda get stuck on. Is it ok to run the alternator at full capacity for up to what could be a few hours while the bulk of the charge goes through? On one hand, it's designed to provide that level of output. On the other hand, I don't want to blow up my alternator.

My understanding is that I have 2 methods.
1. Operate charging at full alternator output capacity. Do this with the following method: Connect it to the main battery circuit. Use a 14V cutoff/charging isolator to ensure that it only charges while the engine is on. From what I understand, alternator output is nominally 14.4v. I wonder if I would also need something in this plan to ensure that the main battery was sufficiently charged first.
Benefit: You get the full charging capacity.
Con: Could run the alternator too hard, if that's a thing.
2. Operate charging at a rate limited capacity. Do this with the following method: Connect it to the accessory circuit. Use a 14V cutoff/charging isolator to ensure that it doesn't backfeed into the accessory circuit when parked. But then I need to make sure that I don't draw too much current off the accessory circuit to avoid starving the operation of the other car electronics, right? Too little, and I might not get enough charge into the battery to keep it operating.
Benefit: Avoid overworking the alternator.
Con: May not charge the battery sufficiently.

The best batteries now use "MPPT" (maximum power point technology) instead of a BMS.
You should not connect the 2 batteries in paralell. Connect the Lithium in paralell through a VSR. Victron Cyrix Li-ct is a good and proven VSR.
Will take a look into this...
 
You should not connect the 2 batteries in paralell. Connect the Lithium in paralell through a VSR. Victron Cyrix Li-ct is a good and proven VSR. I had this setup before and my 120A alternator charged the lithium at 16A. I took it off before the winter and installed a DC-DC charger to prevent charging under 0 degrees.
Without the VSR, you will drain the battery with most charge.


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I think this is how the 4x4 guys do it with a second battery. Anything drawing more than 50w from auxiliary or accessories, that sounds kinda scary. Most installers I spoke to will only do a connection to the main battery. Probably for insurance and liability reasons since melted wiring from a failed fuse or circuit breaker is expensive replacement. Dealers will replace the entire wiring loom. I have mine hanging off a built in AC point which is rated up to 150W.
 
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Mine draws more than 50W quite often in thw summer months.
If you have a smart alternator, a DC-DC charger is your only bet.
There is not danger of a fried alternator in a car as the alternator hardly runs at full capacity.
That problem is common on boats where engines run on full revs for prolonged periods.


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If you have a smart alternator, a DC-DC charger is your only bet.
I have a standard alternator. So, I'm guessing that means that output voltage should be relatively constant.

I'm looking at a 60amp DC-DC charger, as that's the biggest I could find. How many amps can these LifePo4 batteries take? I will look into how many amps my small car uses during regular operation by using an amps clamp to get a better understanding of what my expected power budget is.
 
I have a standard alternator. So, I'm guessing that means that output voltage should be relatively constant.

I'm looking at a 60amp DC-DC charger, as that's the biggest I could find. How many amps can these LifePo4 batteries take? I will look into how many amps my small car uses during regular operation by using an amps clamp to get a better understanding of what my expected power budget is.

What year model is your car? The 60A DC-DC chargers are used to charge battery banks of about 400A.
I have a 30A Votronic charger. Mine takes a 60A charger and the battery will replenish in minutes. These are used for off grid camping.
My 30A charger cost under half the price of the bigger brother.
My battery is used heavily running a fridge, dashcam and a Eberspächer D2 air heater and I have never run out of juice. In the summer my fridge and dashcan is on 24/7.
If your car is after 2005 you have a smart alternator and you will need a DC-DC charger. The low charge will not trigger a VSR.
A 100A lithium battery can be charged with a 60A charger.


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What year model is your car?
It's a 2005 Opel Corsa.
Mine takes a 60A charger and the battery will replenish in minutes.
Great. I want to go for maximum charging speed, as I want to ensure that battery gets enough charge during what little driving that it gets. Approximately 4 hours a week. So, I wonder what the maximum charge current is for a 100AH LiFePo4 battery is? This particulary battery says that it's maximum charge current is 50 amps. However, I think that might be slightly overstated. I did some research and found out that there is a thing known as batteries "C Rate." To quote this page, "C-rate is defined as the charge / discharge current divided by the nominally rated battery capacity. For example, a 5,000 mA charge on a 2,500 mAh rated battery would be a 2C rate." Powersonic wrote an article about battery charging profiles, and state that LiFePo4 batteries have a characteristic of max charging current of 0.4C for the first hour. So, bottom line is that I'd probably top out at around 40amps charging current for a 100aH LiFePo4 battery.

Hope that helps those of you that are considering doing something similar.

Edit: I wonder how this battery can take a charge current of 100amps.
 
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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
1618277959866.png

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?
 
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