Using skateboard power unit

Hi All,

I have an old electric skateboard power pack that I would like to use to power my robot. The robot has 24 servos so I use two x PCA9685 servo controllers. Before I connect the power pack up to the PCA’s and the Arduino mega, I can foresee a problem.

The battery nominal voltage is 25.9v DC with a rated capacity of 2.0Ah/51.8Wh

If I was to split the power output from the power pack to power the two PCA9685’s and the Arduino, would this just overload/burn out everything?

The PCA’s would be connect to the Arduino Mega using the 5v pin.

What voltage do the PCAs specify?

You could use a or multiple step down regulators, Pololu has a variety, something might fit your voltage and current requirements.

Also what is the max current you can draw from the pack?

a7

The PCA’s are 5v and I have no clue what the current from the pack is, sorry!

Hi,
I don’t know the servos you are using but the PCA9685 module should work not above 12 V (V+).
So you should buy a DC-DC Buck Coverter that can turn 25.9 V into 12 V stable. In order to chose the correct one you need to estimate how much current the pack of servos will draw.
If you don’t have loads attached to the arduino you can apply the 12 V to Vin (of the mega) but be careful about the wiring because you could fry everything. If the arduino has loads attached wich bring arduino to the current limit you shoudn’t supply 12 V to Vin because the mega voltage regulator heats up too much

The PCA’s are daisy chained, so master and slave. The Arduino has no servos attached to it, just the output from the master PCA, so SDA/SLC/GND and 5v

Ok
How many sevos do you have and what is the model?

There are 24 servos and they are MG996R’s

Servos you are using operate at 4,8 ÷ 7,2 V and have a stall current of 2,5 A. Operating current between 500 ÷ 900 mA. Be careful.

would this do the trick https://uk.rs-online.com/web/p/switching-regulators/1933984/?cm_mmc=UK-PLA-DS3A--google--CSS_UK_EN_Power_Supplies_%26_Transformers_Whoop--Switching+Regulators_Whoop--1933984&matchtype=&pla-327047415026&gclid=Cj0KCQjw4cOEBhDMARIsAA3XDRg2X06dWTjiuI_CgmptPLudFTEwRFfSuoSbuXlyCpSRg1EyNlsWXqQaAjm4EALw_wcB&gclsrc=aw.ds

You have 24 servos, each of them can take up to 2.5A. Do you really think that 0.5A will do the trick? That’s not even enough for 1 servo.

Steve

Right technology, wrong choice.

That is relatively low current output device, inadequate for one servo let alone 24.

Figure out the maximum current you expect your servos to need, and the voltage you want to run them at.

Then find the step-down regulator that will h due that current.

You may need multiple regulators.

Also I advise some tests; these inexpensive regulators often are sold with somewhat optimistic specifications, and you should always never run them at the limit they can handle.

You may have to deal with heat.

The current into the regulators adds up, too… that is why I ask what is the maximum current you can draw from you pack - that should be a figure you can find on the unit or on something that documents the unit’s capabilities.

And knowing all that you should, you can get an idea of how long the pack will last until it is exhausted.

You should have a way to know you pick is reaching its minimum voltage and be able to stop operations before you damage it or light up a fire or whatever.

a7

Hi, as you have probably guessed by now, I am very new to this. So just looking for suggestions, ie here’s a link, buy x amount of these and wire them up like this.

I dont know how to do that.

The spec of the battery is:

LiOn
24V
2 Ah
Max Output = 150W
Input voltage is AC100-240V
Output current = 1A

If you don’t know this kind of basic electronics, you may want to adjust your goal.

Find something online to learn about the relationships amongst voltage, current and power.

Proceeding step by step getting answers to these kinds of questions one at a time will be difficult.

And in the case of batteries at the kind of power levels you are talking, ignorant experimentation can be dangerous.

Out of context, the specs you list make no sense. It sound like you are talking about the pack itself and the charger you have that, one can only hope, it is meant to be used with.

a7

Thanks for all the helpful tips and info, I bought this Buck which should do the job :slight_smile:

That looks far too small to handle 20A, the wire on the inductor is puny. Unbranded cheap chinese units are usually grossly over-spec’d. Go for a good quality brand of power converter - it will not be cheap.

This topic was automatically closed 120 days after the last reply. New replies are no longer allowed.