Hi everyone I am hoping to add a ultra sound sensor on a servo that does 180 movement the power will come from a polo dc/dc voltage booster that provides 5 volts at 600 Ma current. the server will have no load as such. Thanks for your wisdom
Hi @Richard198778 - it sounds like you’re making a robot with a swivelling distance sensor head!
I see no problem with what you’ve described - what exactly do you want help with? What steps have you already taken towards the project?
Hi I have raspberry pi pico board, and its setup with micro python. I love it I ca run code in thonny to test it before I move it over as main.py the board will be powered by 2 1.2volt rechargeable Ni Ma and a dc/dc voltage booster which provides 5volts and up too 600mA current. My plan is to do a step by step build first testing how the ultra sound sensor will work I will also need a H-bright to control 2 small dc motors, Needs tow work on 3.3 for logic and motor power more but I will see what I can setup. Yes I have been avoiding Lipo as it seems very unstable and dangerous compared to Ni Ma batteries. You are spot on with that I want to make. Oh yes I love using I2C I have aht2.0 temp sensor and oled, but I use a big 5volt lcd wit 4 lines and 20 chars per line is great and I keep the back light off as I don’t need it. my i2c goes through a logic power converter so my 3.3 and 5volt devices can talk and no blow up.
Does your 5V DC-DC have an EN(able) pin? This may allow you to disable the power to the servo when not needed - they will “hunt” even when still otherwise.
I don’t know how much you are going to run off this 5V but you do realise that (as an example) if you are using 600mA @ 5V via a booster that equates to 1.47A (1470mA) at 1.2V for each 1.2V cell irrespective of how they are connected (series or parallel). This is allowing for 85% conversion efficiency. So the NiMh (not NiMa) will need to be quite large to realise any useful operating time.
Another consideration the mAhr capacity of a cell is normally quoted at the 20hr rate. That is for a cell quoted at 1000mAhr that will be the capacity when discharged at 50mA. I don’t know what the graphs for a NiMh cell are but for a lead acid cell the reduction in capacity as the discharge rate increases can be quite drastic. Down to a few minutes at full discharge rate.
Just found this in an Energiser publication.
I think 1V is considered discharged.
Note “0.2C” is 20hr rate. “C” equals the quoted mAhr capacity so you can see if the cell is discharged at the quoted rate the time to fall to 1V would be something less than 90% of 1hr, “2C” about 75% and the rate of reduction would get progressively worse. BUT they do seem to hold their voltage pretty well up to that point. Note the actual voltage is reducing also and I think 2C would be maximum discharge rate recommended.
The great thing about Mi Ma is they are easy to charge and safe. I also used them years ago for my avr robot projects and they have plenty of power an they hold it well. I don’t demand much current from my batteries. If I was into RC planes I would be using Lipos.
That is true and seems you are more comfortable with them (rightly so) so is a good choice.
In that case NiMH cells should be OK. I was just explaining that the current actually from the battery is far greater than what is supplied at 5V. You need to be aware of this to avoid disappointment in use.