Hi all,
I am building a robot with a 5S Lipo battery pack.
I am having a hard time trying to figure out how to design (or buy a ready made component) which can charge the batteries while being charged at the same time. I see plenty of Lipo balanced chargers out there. But the basic principle behind them is that you need you power off your robot, remove the battery, and connect it to the LiPo charger.
What I am looking for is a way to keep the robot powered on and the battery connected yet only plug in the charging cable to charge the battery. Kindly of how a laptop works, many laptops have lips batteries, and you can just plug in your laptop and continue using it.
Its quite easy how this works with SLA batteries, any basic charge controller circuit will do the job. But I just cannot find any product or design online that would help me with a LiPo battery.
Could someone be so kind as to steer me in the right direction so I can educate myself about this topic or what kind of product I should be looking for.
Thank you!
P.S: I am planning to use a 5S Lipo battery with a 20AH capacity
Hi,
What you would need is a custom circuit to function as a power path for managing your battery/power in your robot.
The main reason why you cannot find these online is because these circuits are typically custom-made for the product they are used in. In the case of your laptop batteries, there is special circuitry both inside the battery pack and also the laptop to handle this. In the case of a cell phone, you have a single cell LiPo “battery pack” that is connected to a circuit that manages battery voltage, charging and load all at once (again a custom circuit).
Please note that charging, load balancing and use the current provided/battery simultaneously is not a simple task and would not be trivial to design.
Here is an example of a circuit from TI to create a power path management for a low power system with only 1 cell (i.e.: a “1S LiPo battery pack”):
Please note that is uses a special, custom chip, created for the exact purpose of doing voltage regulation, charging and power management. Doing the same for a 5S high-current application would be quite complex. Also, you would need a very high-capacity power supply to compensate for battery-use if you want to use the robot and charge at the same time.
It is most likely much more reasonable to change the batteries and charge them externally then have them charging while under use.
Sincerely,
Thank you so much for the reply. I think it is pretty clear that this topic is too time consuming due to its complexity for me to pursue as I need to put more time into other more important aspects of the project.
Would you be able to give me a recommendation other than LiPo (yet somewhat lightweight for a 20AH application) where I could buy a ready made charger which would fit my purpose? Or is this topic doomed to be “not so simple”?
Hi,
Indeed, you’ve just discovered the dirty secret of LiPo battery packs. While they do have great characteristics when it comes to power density, capacity, etc., their complexity for charging is the cost of this.
You can most certainly use other battery types, such as NiMH or SLA, but it will be most certainly heavier at the same capacity and discharge rate. If you project is stationary or on wheels/threads, this won’t matter too much.
If, on the other hand, your robot is instead on legs or other limbs that need to be powered, the extra weight might be detrimental. Try and place it as low as possible to reduce its impact on power consumption.
You can see our NiMH battery packs here. We do have one 10 Ah one, RB-Sta-11, but it only provides 6 V DC. Most robotics only require something around 6-12 V DC, therefore the NiMH battery packs that we carry follow those voltages, too.
We do offer some power supplies, such as the RB-Hit-162, which can provide up-to 50 A @ 15-30 V DC (we also have lower power versions available as special orders).
You can find our battery chargers here. Please note these are meant to charge batteries that are not under load (i.e.: not powering anything else).
As mentioned before, if you want to have both power coming in from a power supply simultaneously with a battery pack, you will need extra circuitry.
We hope this helps.
Sincerely,
Thank you so much for your advise I really appreciate it. I think NIMH might be more suitable for my application because it is less complex to handle that LiPo and I also do not have much of an issue with its extra size/weight.
I think for now, I will have to settle for a offline charging solution but I will eventually need to upgrade that by perhaps hiring someone who can design the custom circuitry for my application.
Many thanks!
