charging from car outlet?

[RiverOfRationality]

I'd like to be able to charge my battery (12v LiPO4) from the standard 12v outlet in my car on cloudy days. What kind of equipment do I need to do this safely? I'd like to avoid running new wires directly to the car's battery, as I think the 150w that comes out of the outlet should be adequate.

 

[Supervstech]

I charge my power station's all the time this way.
As long as the voltages aren't too far off, it should work.

 

[RiverOfRationality]

How far is too far? I don't have a power station, just a battery, and I don't know what kind of equipment power stations include to do this.

 

[Lt.Dan]

How far is too far? I don't have a power station, just a battery, and I don't know what kind of equipment power stations include to do this.

Power stations have their own dedicated battery chargers. You will need a battery charger with a dedicated 12v input, and an output that matches your battery's charge chemistry

 

[Hedges]

It may depend on the weather.
Freezing, your automotive regulator ought to raise charge voltage.
3.5V to 3.65V per cell is reasonable for LiFePO4, 14V to 14.6V for a "12V" battery.

https://axleaddict.com/auto-repair/Alternator-Voltage-Regulator-Test

"Most voltage regulators are calibrated to output between 13.5 and 15.5 charging volts on a fully charged battery at normal temperature with no accessories or lights on."

Here's a link for a particular Trojan FLA that calls for 2.45V per cell (14.7V for 12V battery) at 25 degrees C. goes up when colder. So it is already a but above what you want. Maybe we can count on BMS to disconnect when charged. Maybe it would be nice to have a low drop out linear regulator.

Trojan Battery | Battery Maintenance

The key to achieving optimum performance and long battery life is to follow a regular care and maintenance program. Read our tips for high performance battery maintenance.

www.trojanbattery.com

 

[mikefitz]

charge my battery (12v LiPO4) from the standard 12v outlet in my car on cloudy days

The outlet is good for around 12 amps, even then there is a chance of overheating. You will need some sort of charger with current limiting to ensure the current taken from the vehicle is limited to a safe value.
What is the capacity of your battery?
I suggest you seriously consider connecting a dc to dc charger to the vehicle battery. For modest charging current a Victron Orion 12 12 18 would be suitable. This gives a correct charge profile for lithium and will auto start charging when the engine is running an power down when the engine stops.

Victron Energy Orion Tr Smart DC-DC Chargers | Inverters R US

Victron Orion Tr Smart DC-DC Chargers provide DC to DC charging where the alternator and the start battery charge the service battery.

invertersrus.com

An alternative is to use a dc to dc converter set to a safe output voltage, say 14.0 volts, and manually disconnect once the battery is charger. The low power Victron unit may just operate from the accessory socket, 12 12 9

Victron Orion-Tr IP43 DC to DC Converters – Non-Bluetooth

Victron Orion Tr DC to DC Converters Chargers IP43 Non-Bluetooth are high efficiency & can also be used as a battery charger.

invertersrus.com

As I pointed out earlier the vehicle sockets are not designed for continious high power use and you may get local overheating and perhap damage.

Mike

 

[Supervstech]

I'd like to be able to charge my battery (12v LiPO4) from the standard 12v outlet in my car on cloudy days. What kind of equipment do I need to do this safely? I'd like to avoid running new wires directly to the car's battery, as I think the 150w that comes out of the outlet should be adequate.

How do you charge the battery now?

 

[RiverOfRationality]

The battery is 40 Ah.

Here's a crazy idea. What would happen if I took a 5 or 10 A solar mppt charger, and connected the car's 12v outlet to the mppt charger's input? A solar charger is designed to be DC to DC, to safely charge a LiPO4 battery, and the charger has no way of knowing if the power it's getting comes from a solar panel or an outlet, does it?