In this project the spider robot is controlled by at least 12x servos SG90 9G, and driven by an arduino nano
But as you can see the battery used is about like, what, max 3A output ( even 1A output with external power bank on the video I provide ) how is this even possible ?
Like the sg90 9g draw about 10mA at rest but can draw 500mA when stressed so even if we use a battery than can contain 10000mAh it still often provide max 3A at output for like power bank and is still not enough ( can damage the battery ? Even make it explose ? )
Maybe im lacking on power topic but I didnt understand
Also I saw people using 2x18650 battery in a holder ( with a DC - DC to stay at 5V ), is this a better solution to draw more current at time ?
But if yes, why power bank can't?
So many question that froze me, but I want to understand before making, I think its the point of making DIY project
Thanks for the help and at least for the read
Current rating are essentially thermal. That is, it is the increase in temperature which kills the device (or connector, wiring etc). Because it can take some time for the device to heat, a device can withstand short peaks above the rated current.
The rated current is the safe current for continuous operation, i.e. at that current, the heat increase above ambient should not damage the device. Typical ambient range may be up to 60 degrees, or more or less depending on the device.
With 12 servos in this bot, in typical use it is unlikely they will all be operating at or near peak load. For a "hobby" device, you probably don't need to worry about worst case.
Okay so if I understand so the servos are not running at peak and the battery can exceed the max output for a very short time ? Maybe like for only the calibration ( that will run all the motors at same time) ?
But actually in this robot the spider standing use current in stale no ?
I already mount it and he can stay stable (without the belly touching the ground ) if I balance the legs well
If you want to be sure to have enough current for all 12 servos stalling at the same time
use a 2S Lipo that is optimised for race-drones
75C means the maximum dis-charge current is 1 Ah * 75 1/h = 75A
even a cheaper 1000 mAh Lipo like used in rc-airplanes has 20C which means maximum dis-charge-current 1 Ah * 20 1/h = 20A
or if you take a 2S 2200 mAh 2.2Ah * 20 1/h = 44 A
So the limit will be the maximum current-rating of the DC-DC-stepdown regulator that transforms the 8.4V (fully charged to 7.7V total dis-charged) down to 5,0V
No problem I think I sent lot of link that contains other link
Yeah thats my actual think that it could not run except if all the servos aren't running at the same time ( so I suppose they don't )
But I'm not sure about that regarding the way the spider stay balanced on it legs and the way the belly stay above the ground ( when I say I belly I talk about the main body that will handle the PCB and the Arduino )
Also it can be dangerous if miss programmed no ?
Maybe the solution for me to stay calm in my mind is to use some kind of current limiter ( dont know if this exist ) or even a fuse that will shut the circuit if the battery exceed the continuons output recommanded ?
So with this kind of battery there is no output current formely speaking ?
Is about the C and the mAh ?
So using those battery with a regulator to keep them at 5V could help to output like around 20 - 40A at the same time and continuously if needed and without damaging the battery ?
what the difference between those battery and a classic battery pack or 2x18650 ?
Thanks a lot for the link I will take time to check deeper on the side
Most of the power banks have some kind of current limiting built in. A 1A power bank may turn off if you exceed say 1.25A
Also you don't want to use a big battery that may be too heavy to lift.
Don't understand what you want to say with that. "No output current" makes no sense. Of course each battery "outputs" current.
Yes this is what these batteries do if they were used in an RC-airplane like this one
The L200C can limit the current. But it is a linear regulator that has a low efficiency.
The too much voltage is dissipated as heat.
So a combination of a high efficiency DC-DC-step-down-converter with a fuse will be better.
chinese shops on aliexpress and ebay tell not the whole truth about the maximum current
of the offered DC-DC-step-down-converters.
They are advertising them as example "5A" converter. Where this 5A is the maximum short-pulse current of less than a second.
I have tested different types. One was rated 3A and did get too hot on only 1,5A
So you better lookup a serious online-shop that has detailed technical data that the number for maximum continious current
Oh okay thats rassuring ! Did you think that adding an extra fuse could be overkill ? Or it could be a solution to protect the circuit if the battery is from a bad manufacturer ?
Okay so fuse of 5x20mm can be suitable for my need ? Did you have a link I saw some fuse ( like one we put in the electrical central at home) but they are marked for 250v ( or maybe they work with 5V but juste they can't exceed 250v , but it will be triggered if I exceed the current supported even with 5V ? )
Okay so its better to use a DC-DC and a fuse ( and in fact only a fuse if I use a battery providing the right amount of Voltage am I right ? )
Yeah I totally agree with AliExpress and shop like that I will check on market like Conrad I think
Also for the "no current output" what I mean is that in the link of battery you provide I could not find the output current data
Only capacity in mAh and the discharge current in C ( dont know what C mean in Electronic for now )
So unlike power bank marked with a specific output current from connector provided ( like 2A output in USB etc ) I didnt find the information
My overcurrent reference was only for USB type battery banks/power banks not plain batteries.
You can also use a fuse if you want, it can't hurt.
Personally I wouldn't buy a batery bank if the manufacturer did not specify if it had overcurrent proection.
Yes they do work with any voltage. Safe to use is up to a voltage of 250V
Yes. Because the thing that triggers the fuse is only the current.
You could trigger fuses with a voltage of 0,01V if the powersupply is able to deliver enough current.
You really should learn the basics about electricity and electronics
Is english your native language?
