Current control for a battery charge

Thread Starter

jesortsan

Joined Oct 17, 2020
1
How can I control the current that is supplied to a battery? I need to balance current consumption to avoid some parts of the system run out of power.

My system is described in the attached file. I have a 12V input which goes into a Boost regulator to get 48V. Those 48V are used to feed a battery and the rest of electronic as well. I need to limit the current injected to the baterry depending on the power consumption of the rest of the system (which I am monitoring), in order to avoid that battery charge takes all the power and the rest of the electronic doesn't work properly.

02.png

The battery is a complete commercial solution. I mean it has its own charge controller, protection, etc.

I have thought about a power mosfet working as a switch and controlling it by a PWM signal, but I don't know if it's a good practise or not, since I am not experienced in woking with batteries.

Another possible solution I was thinking about is the one you can see in 03.png attached file. The approach consists of dividing the 2A maximum current in several 250 mA limited branches, controlled by a mosfet switch. In this case, the current would be controlled in 250 mA "jumps", but it could be a solution. The problem here is the PCB area required for this and the heat the resistors will generate.
03.png
I appreciate any help on this issue, since I'm a bit lost right now. I'm sure there should be any other workaround to get my aim, but I don't know what.

Regards and thanks in advance

Jesús O.
 

KeithWalker

Joined Jul 10, 2017
1,305
It is difficult to offer a specific answer to your question because there is not enough information available.
What is the purpose of the system?
How much current is available from the 12V to 48V converter?
What is the type, nominal voltage and capacity of the battery?
What are the maximum and average charge currents?
What are the maximum and average load currents?
Regards,
Keith
 
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Alec_t

Joined Sep 17, 2013
11,752
Welcome to AAC!
I need to limit the current injected to the baterry depending on the power consumption of the rest of the system
The battery is a complete commercial solution. I mean it has its own charge controller, protection, etc.
:confused: Those two statements seem mutually inconsistent. Moreover, messing with a charge controller can have a severe risk of fire or explosion if the battery is a lithium-based one.

Boosting the voltage from 12V to 48V then bucking it back down to 12V is going to be inefficient. Why do you want to do that?
 

Irving

Joined Jan 30, 2016
1,070
If you have to limit the charge current to meet the load requirement then your solution is flawed as your battery will never charge fully whilst the system is on load. A UPS (for that is essentally what this is) with offline charging (battery disconnected from load) needs a power input >load requirement + charge requirement unless you have specific known times when you can charge the battery because the load requirement is low. In any case the battery charging has to be integrated at a low level with the overall system. Having a black-box charger means you have no visibility of the battery SoC and therefore fine control is unlikely.

Having said that, the use of resistors is wrong, thats just burning energy as heat.
You need to separate the charge and supply routes.... why do you need 48v? Can you simplify to just a 12v system and reconfigure the battery bank?

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