[Chhanda Das]

How to charge a 12v DIY power bank from a car ?

Recently, my son made a portable DIY lithium power bank with a 50 watt rated solar panel and a 130 watt rated PWM-based solar charge controller and this setup is working fine. However, we also want this power bank to be able to get recharged from the 12v sockets in my car.

And here lies the issue. The sockets in my car are rated at 180 watts at 12 volts DC. When the engine is on, its battery voltage is around 14.2 volts and the solar charge controller has no issues handling that. But the problem lies with the amount of current. From what we have seen, anything above 5 amperes at 14.2 volts causes the power bank's batteries to become warm with the added risk of the charge controller getting damaged since the car's 12v sockets can put out way more power. We obviously do not want any untoward incidents to happen. In case it was not obvious, we want to use the solar panel's input port on the charge controller to work as the input from the car's 12v socket when the solar panel is not connected to the charge controller. I am assuming that a 5 ampere DC fuse is going to be blown almost instantly when the 12v sockets in my car are connected to the solar panel's port on the solar charge controller.

So my question is that is there a way to restrict the flow of current to below 5 amperes irrespective of the voltage ? If yes and if there are multiple ways to do this then what would be the best approach ?

I request my fellow knowledgeable BHPians to please help and guide me. I have an Arts background and hence I am not too familiar with electronics even though I have spent a very large portion of my life fixing and maintaining our cars by ourselves. On the other hand, my son has a Science background with a specialization in Mathematics but even he is not too familiar with the nitty-gritty of electronics.

Waiting for your knowledgeable assistance

[Indian2003]

Originally Posted by Chhanda Das

How to charge a 12v DIY power bank from a car ?

And here lies the issue. The sockets in my car are rated at 180 watts at 12 volts DC.

I dont see a problem. Your sockets are rated at 180W and that is 15A. Your alternator gives much more than that.
Just use your standard car cellphone charger and you should be fine.
My car has a 120A alternator and that is 1440W. I run all sorts of things from the sockets.

I also have a 100A Lithium battery under the seat that permanently powers my Blackvue dashcam and freezer box. The socket is wired directly to this battery of 1200W. I have charged my GoPro, my cellphone and GPS and never had a problem. This battery is charged with a DC-Dc charger of 360W, connected to the alternator.

The plug you use decides what the current output will be. You can get a plug rated at 1 or 2,1A and you should be fine.

[Chhanda Das]

Originally Posted by Indian2003

I dont see a problem. Your sockets are rated at 180W and that is 15A. Your alternator gives much more than that.

Thank you very much for replying. I believe that I have not been able to explain the issue properly. I have no issues with the maximum power output of the sockets since our requirements are well within less than half of their maximum capacity. We just need to restrict the current output of a socket to approximately less than 5 amperes.

Originally Posted by Indian2003

Just use your standard car cellphone charger and you should be fine.

We tried a standard 10 watt (5v 2A) charger as well as a Qualcomm Quick Charge compatible 18 watt fast charger in conjunction with a DC-DC boost converter to boost the voltage to 13 volts. This is because the solar charge controller only accepts charging from the solar panel if the panel's output voltage is higher than 13 volts but less than around 18 volts. However, much to our dismay, both the chargers got overheated and shut down after a few minutes of use since they were being run at their maximum capacity and more.

Originally Posted by Indian2003

The plug you use decides what the current output will be. You can get a plug rated at 1 or 2,1A and you should be fine.

We tried wiring a connection (with proper polarity) from the 12v car sockets to the solar input on the charge controller through a 5 ampere blade fuse but this fuse got blown within a few seconds obviously due to excessive current flow since the charge controller can accept upto 130 watts before it gets damaged.

We were thinking along the lines of adding resistors or current limiting diodes to the wire between the 12v sockets and the solar input for the charge controller but we are unsure as to how to approach it. We do not want to mess with the voltage put out by the alternator as well. I feel like we have hit a wall