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Old 2 Days Ago
rykiel575 rykiel575 is offline
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Default LifePO4 battery system.

Hi guys

So due to a hit and run yesterday when my pajero was parked I have decided to investigate further the use of a LiFePO4 battery back system which will be hard wired to feed two dedicated 24/7 dashcams - one in the front, and one in the rear.

Last year I bought 4x 200Ah 3.2V cells which I will wire in series to form a 12.8V 200Ah battery pack.

I am thinking of using half channel slotted uni strut with M10 threaded rod to clamp the 4 cells together. The batteries did come with a BMS which I will install also.

My question is what is the best way to charge the battery pack?

I've thought of a few options.

1. Remove the primary lead acid starter and replace with the 200Ah LiFoPO4 pack. The max discharge on the cells as I understand it is 3C. But even if it was 1C the 200Ah pack should be able to handle it as cranking amps is probably about 100Amps (apparently 250Amps after some research) for a few seconds.. If I go this option I would have to move the battery pack to the cabin and insulate the battery box to protect it from the heat. I would also have to get a Li-ion battery starter for use if my pack were to ever go flat.
If I go this route I am thinking of building a plywood box which would sit longitudinally directly against the 2nd row passenger seats, with the terminals/vents facing up, and long edge against the seat side by side so it'd end up being a longish box that is not very wide. I have heavy duty cable cutters and crimpers from my old jobs and a bit of thick cable to do the job. (Any suggestions for cable size? would 25mm2 solid copper be enough or should I go higher? I have 70mm2 cable which is way overkill but nothing in between those two (id have to go and buy something else)... might have some 35mm2.


2. Leave primary lead acid starter as is, and purchase a mains powered 240v charger, and then take out the LiFePO4 battery box and charge it in-house. From my calculations (200Ah x 12v = 2400W. Assuming draw of 4Ws for both dashcams, that would be 600 hours it would run for, which is 25 days but I don't want to go to 0% depth of discharge so I would probably have to charge is every fortnight).

3. Get a special car charger (DC-DC? BC-DC?) - and use LiFePO4 battery like a secondary lead acid battery - one of the issues i ran into when researching this last year was because of the different chemistry and voltage characteristics between lead acid and lifepo4, you can't parallel the two batteries together (so presumably can't use a voltage sensing relay to shut off)

4. Dedicated solar panel permanently mounted which feeds the LiFePO4 batteries


The purpose of the batteries would be for the dashcam for now but would be for a fridge and so forth down the line. I'd also probably take the battery out when it comes to reselling the pajero so no loss there.
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Last edited by rykiel575; 2 Days Ago at 09:17 PM. Reason: Starter current edit
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The install of these batteries for the use of a dash cam doesn't make sense. I have a dashcam and it runs for weeks without the need to add anything other than the century start battery. They only have minimal draw and most vehicles are driven several times a week. Just use the start battery and install a 40watt solar panel on the roof. Simple solution. Heaps of info online regarding making a battery system up....first decide why you need the system and build it around this need.ie.....portable for use in any vehicle, bolted into one vehicle, used for fridge, also will connect solar..etc.etc.
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rykiel575 rykiel575 is offline
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In my previous pajero i had a starter battery used as a secondary as the guy i bought it from wanted to keep the deep cycle for his new car.

It died within a few months with just the one dashcam.

Solar panel might be an idea though.

At the end of the day i still have the batteries sitting around so would like to make use of them.
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I have been running 2x 30Ah LiFePO4 batteries in the cargo area for 7 years, they have an integrated BMS on each cell, charge voltage is from the Challengers conventional NON SMART alternator via a solid state VSR on the input side and a low voltage cutoff set at 11.5vdc, on the fridge side of the circuit. At the time of installation there was a limited selection of 12vdc chargers suitable for lithium batteries so I knew that the alternator would not be able to get the batteries up to full charge when travelling for extended periods especially in hot weather so I accepted the reduced capacity.

The car is driven every week day for 2 periods of about 30 minutes each but every second or 3rd weekend the car is not driven. I do not run the 40 litre Engel all the time but I do find the parasitic draw of the car, VSR and LVCO is enough to drain the batteries down to 11.5vdc over about a month in the cooler weather and 3 weeks in the hot weather. So I give the batteries a fully recharge every month using a 24 hour duration 16vdc 4amp Max trickle charge. I haven't tried isolating the batteries when they are fully charged and removing all parasitic discharges to see what the standby life of the batteries are.

OJ.
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