I'm shopping for batteries and it's easy to find a 48V lithium ion battery that has like 30A max continuous discharge rating. However, I know that the battery supply has a variable voltage from 54V - 42V depending on how much energy has been drained.

I'm using a 48V to 24V buck converter to power many of my electronics for a stable 24V power supply. However, I still have some 48V motors that takes 10A max for my robotics application. I can't figure out a way to power my 48V motors with a stable power supply.

I found a 36V to 48V step up converter but it only outputs 5A.

  • $\begingroup$ -48 volts is what the telephony industry runs on. With so much happening in the technical industries perhaps it would be worth your while to check if any surplus power supplies are available in your area. $\endgroup$
    – st2000
    Apr 21 '19 at 19:56

Edit: I'm not sure if a 48V - 48V boost converter will work because it won't step down my voltage when the input is over 48V. I will continue looking into this and keep you updated.

From the looks of things, this a boost Voltage Regulator DC 8-60V to 10-120V 15A Boost Converter might work.

I found 2 on amazon that seems to fit the bill. I would go for the 96% conversion efficiency one since the other one is 85% efficient. In addition, it seems like I will need to add a fan/heat dissipation solution to the 96% efficient one.

(I am no way affiliated with these amazon links, sellers, and links are only provided for convenience for people with the same problem).

96% efficiency: https://www.amazon.com/Aideepen-Converter-Step-up-Supply-Module/dp/B01MSYVMAL/

85% efficiency: https://www.amazon.com/dp/B01GFVI6R6/

  • $\begingroup$ yes, I'm trying to answer my own question. I'm ordering a 96% efficiency boost converter to see if it can regulate my 48V battery supply when it has full charge (~54V). If it can't, I think I will need to make my battery supply 36V. $\endgroup$
    – aztrorisk
    Mar 20 '19 at 19:35
  • 1
    $\begingroup$ you can "accept" your own answer $\endgroup$
    – jsotola
    Mar 21 '19 at 15:47
  • $\begingroup$ Motors usually allow for some overvoltage. Another thing you want to consider for a converter is the amperage that it can handle. Is 20 amps enough for your motors? $\endgroup$
    – NomadMaker
    Mar 1 '20 at 9:53

Usually, motors in robots are speed controlled, for example using PWM.

Design your system so it meets the spec at the speed you get when the motors are running at 42V.

With the supply above 42V, your motor speed feedback reduces the PWM duty cycle and the motor speed is maintained.

  • $\begingroup$ I feel like altering the PWM to support a constant speed with variable voltage is more difficult than just using a voltage regulator. $\endgroup$
    – aztrorisk
    Mar 24 '19 at 1:15
  • $\begingroup$ @aztrorisk Yes, it's more difficult. But even with a constant voltage the speed will vary dependent on load, which is usually something that robots care about. If you don't care about the speed, why do you care that the speed varies when the batteries drain? $\endgroup$ Mar 24 '19 at 16:33
  • $\begingroup$ The goal of the voltage regulator is to make my robot perform more predictably rather than controlling a constant speed. As long as the robot behaves predictably, I can fine tune the algorithm that controls it vs controlling a motor whose performance is more variable. $\endgroup$
    – aztrorisk
    Mar 25 '19 at 17:41
  • $\begingroup$ @aztrorisk I'm not sure what 'perform more predictably' could mean if not consistent speed under varying load. There are only two useful things a motor outputs - speed and torque - and you won't control torque by applying a constant voltage. If your algorithm can cope with a wheel skidding or bogging, then it can cope with the difference between 42V and 48V. If it can't, then you need to control the motors. $\endgroup$ Mar 25 '19 at 17:47
  • $\begingroup$ By predictably, I mean the motor should rotate same speed under the same amount of load. Let's say I have a 100 lb load, the speed will change depending on the voltage if I don't have a voltage regulator. Even worse, the speed will drop as the battery is continually drained. If I do have a voltage regulator, the speed will stay the same with the 100 lb load as the battery is continually drained. $\endgroup$
    – aztrorisk
    Mar 25 '19 at 19:08

You indicate the need to have both a stable 24V and a stable 48V power supply from a single battery. And that you are already using a 48V to 24V buck converter to meet the stable 24V need.

If you intend to continue with this design, you may need to choose a battery voltage between 24V and 48V. Then continue using a buck converter to get the 24V, while adding a boost converter (in parallel from the battery) to get a second line with 48V.

Most DC-DC converters have a fairly wide range of input. So if you switch to a 40V battery, you may be able to continue using the same buck converter. Search for "20A boost converter" or "30A boost converter" to see several options for your 48V line.

Be sure to confirm the input voltage of your converters includes 33V through 46V if you use a 40V lithium ion battery.

Good luck!


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