Hi All,

Currently I'm planning to build a battery pack to power my dashcam when parked. The concept is once I start the car, the alternator should charge the battery pack. I can both charge using cigarette socket or directly tap to car fuse box.

The question is what is the best way to regulate the voltage from the car to 14.4V (4s lifepo4 charging voltage), Im thinking of using buck boost converter but its not very efficient and can only support low current. My target is 14.4V 6A charging current and voltage.

 

If you used a lead-acid battery, the car would already know how to charge it.

 

Welcome to AAC!
Can't you run the dashcam from a fused/switched direct connection to the car battery?

 

Hi All,

Currently I'm planning to build a battery pack to power my dashcam when parked. The concept is once I start the car, the alternator should charge the battery pack. I can both charge using cigarette socket or directly tap to car fuse box.

The question is what is the best way to regulate the voltage from the car to 14.4V (4s lifepo4 charging voltage), Im thinking of using buck boost converter but its not very efficient and can only support low current. My target is 14.4V 6A charging current and voltage.

Hi,

You should thoroughly read up on how to charge this kind of battery. There are certain parameters that have to be addressed and if you don't you could run in to some very big problems. It is not that good of an idea to just use a power supply to charge it unless you are there to monitor it during the whole charging phase.
Some simple questions come up though for which the answers could help greatly with this project.

What current does the dash cam draw from the car battery when connected like that?

Also, why charge the LiFePO4 battery with 6 amps of current?

I could guess that you would only have to charge at 6 amps if the cam was running for a long time with the car off and you only drive for short trips.

 

Welcome to AAC!
Can't you run the dashcam from a fused/switched direct connection to the car battery?

Hi,

I ran into this issue with my automobile telemetry. If you take it off the battery, you drain the car battery, then the car potentially doesn't start.
It's true though it depends on a number of factors:
1. How much current is being drawn.
2. How long is the current drawn with the car engine off.
3. How long does the engine run when you go on trips to different places like the store, relatives, etc.

If the current is small, you can get away with it, as long as the time between engine runs is not too long.
What i did was i reduced the total current draw to around 1ma and that solved that problem. I could easily see using a separate battery though so that there is no chance the car won't start one day. If the secondary battery runs down, you only lose the telemetry, which would be detected right away anyway by the receiver and computer and software.

 

Welcome to AAC.

How did you determine you need 6A of churning current?

 

If you used a lead-acid battery, the car would already know how to charge it.

I want to store the battery on the glove box compartment, so lead acid will not do for my application.

Welcome to AAC!
Can't you run the dashcam from a fused/switched direct connection to the car battery?

Thank you.
Yes, I can but to preserve my car battery I don't want to use my car battery while the dashcam is on parking mode.

Hi,

You should thoroughly read up on how to charge this kind of battery. There are certain parameters that have to be addressed and if you don't you could run in to some very big problems. It is not that good of an idea to just use a power supply to charge it unless you are there to monitor it during the whole charging phase.
Some simple questions come up though for which the answers could help greatly with this project.

What current does the dash cam draw from the car battery when connected like that?

Also, why charge the LiFePO4 battery with 6 amps of current?

I could guess that you would only have to charge at 6 amps if the cam was running for a long time with the car off and you only drive for short trips.

The dash cam is drawing around 0.2 ~ 0.4A The plan is when the car is running the dashcam is drawing its power from the car alternator while the battery pack is charging.
Based on the datasheet of my prospect LiFePo4 battery it can charge up to 1C. Its capacity is 6AH, the battery pack will be on 4S1P configuration so I would have around 6AH capacity. charging at 6A gives me roughly 1hour to fully charge the battery pack, any lower would prolong the charging time which is not ideal as I usually drive for 1hour trip to work.

Hi,

I ran into this issue with my automobile telemetry. If you take it off the battery, you drain the car battery, then the car potentially doesn't start.
It's true though it depends on a number of factors:
1. How much current is being drawn.
2. How long is the current drawn with the car engine off.
3. How long does the engine run when you go on trips to different places like the store, relatives, etc.

If the current is small, you can get away with it, as long as the time between engine runs is not too long.
What i did was i reduced the total current draw to around 1ma and that solved that problem. I could easily see using a separate battery though so that there is no chance the car won't start one day. If the secondary battery runs down, you only lose the telemetry, which would be detected right away anyway by the receiver and computer and software.

Hello,
1. the current draw is around 0.2 ~ 0.4A.
2. I have WFH schedule so my car can be idle for 4days.
3. usually around 1hour or more

Welcome to AAC.

How did you determine you need 6A of churning current?

Base on the datasheet of the battery it can take 1C with 6AH capacity, I need the charging to be as fast as possible so when I parked the car I would have full charge of battery for my dash cam.

 

I want to store the battery on the glove box compartment, so lead acid will not do for my application.


Thank you.
Yes, I can but to preserve my car battery I don't want to use my car battery while the dashcam is on parking mode.


The dash cam is drawing around 0.2 ~ 0.4A The plan is when the car is running the dashcam is drawing its power from the car alternator while the battery pack is charging.
Based on the datasheet of my prospect LiFePo4 battery it can charge up to 1C. Its capacity is 6AH, the battery pack will be on 4S1P configuration so I would have around 6AH capacity. charging at 6A gives me roughly 1hour to fully charge the battery pack, any lower would prolong the charging time which is not ideal as I usually drive for 1hour trip to work.


Hello,
1. the current draw is around 0.2 ~ 0.4A.
2. I have WFH schedule so my car can be idle for 4days.
3. usually around 1hour or more




Base on the datasheet of the battery it can take 1C with 6AH capacity, I need the charging to be as fast as possible so when I parked the car I would have full charge of battery for my dash cam.

Hi,

You're going to need a bigger battery

Seriously though, if you run the cam for 4 days straight at worst case 0.4 amps, it's going to run down long before you get to run the car again 4 days later. Sorry to have to say this I know these problems can be a pain to work out I've had the same experiences in the past multiple times. I could show you some computer logs that show how the battery voltage decreases at night and recharges in the morning.
Maybe you need to get into some solar panel technology also, that's what I had to do. I had to go multiple weeks sometimes not just 4 days.

Now to the basics...
The ampere hour rating of the battery has to equal or exceed (mostly exceed) the ampere hours during the time when the cam is being used. The ampere hours using the cam for 1 day, best case, is:
0.2*24=4.8 Ahr
and worse case:
0.4*24=9.6 Ahr.

You see the problem already? If the battery is only 6 Ahr then it will only work for 'maybe' one day at the best-case current draw of 0.2 amps. To get four days out of it, it would have to be about a 24 Ahr battery, but it is wise to oversize by a decent factor like 1.5 or something like that. The more you oversize the longer the battery lasts over it's entire life. The type of battery you chose is not a bad idea I don't think though, because you can recharge them a lot of times. Worst-case however, you would need around a battery rated for 100Ahr or something like that. That's a big and very expensive battery.

One solution would be to limit the 'on' time of the cam. That means turning it on for maybe 1 second, then off for 1 second. That gets you down to about 1/2 the ampere hour usage. Now worst case 0.4 amps you might get a full day. To get four days though, you would have to turn on for 1 second and off for 8 seconds, worst case. That may not be good enough for your purposes.
Alternately, you may be able to find a cam that runs on less current.

While we are on the subject of batteries, you may not be able to use a lead acid battery anyway because it would have to be the same type as your car battery. You should not try to charge a sealed lead acid battery with the car alternator charging system. There may be a modification though that may allow it to work, but you should look into this carefully if you do ever decide to use a lead acid battery of some type instead.
Lead acid batteries will not be as good as your Li-type battery though because they can not be recharged as many times.

Note we did not yet talk about recharging times. To charge a bigger battery in one hour you would need to charge at a higher current. For a 100Ahr battery you would need to charge for over 1 hour at 100 amps. That's probably very hard to accomplish with a regular automobile with only one alternator.

All this, taken collectively, means you are going to have to rethink most of your plans and make some serious changes.