I feel I have forgotten some basic principles of circuit design/protection here.
Please tear apart my design and tell me what i've done wrong/right.
So the local cats have been fouling in my veg garden, digging up baby plants and leaving their distinct packages. I like cats but they are making a right mess and I'd rather deter them from coming back to the veg plot with a motion detection garden hose sprayer.
I have loads of modules from old projects laying around and wanted to put them to good use instead of collecting dust in my drawers. So that's why I’m asking the rather weird question about dual TP4056, I really don't want to buy more modules when I have loads unused.
Realistically the relay and solenoid are only ever going to be turned on for a few seconds a day at the most. And if I change the PIR sensor to a Digital I/O then I could run the Arduino using the low power library to cut an extra 50/100mA off the draw.
Updated image above. I believe I've put them where they should go. I think it's called a flyback diode and prevents voltage spikes when coils are de-energised.
(The buck converters also have coils in them but I imagine the module design already has them incorporated.)
How would I calculate the max current draw from each? They are adjustable with a potentiometer so that complicates it in my brain.
TP4056 - Input Voltage: 4.5V to 5.5V
I can't find any references to if these modules have leakage protection, but in a few example circuits I have seen, people are using diodes on the Solar-PV live wire.
Nothing to do with increasing battery charge rate.
The TP4056 are heating up rather quickly; Either from charging or the battery to boost converter transfer (They have low voltage battery protection and I was thinking they might be overheating due to this.)
The circuit will be in a air/water tight unit so I want to reduce their thermal gain by sharing the load across two. These are what I have available to me so I don't mind using an extra one if it lowers their thermal gain enough to keep it sealed.
(Would this also be possible with the MT3608 boards? I know from past experience they also can get hot.)
The link to the circuit has more details on component information. I did activate labels but they failed to export into the image...
Here is a list of components.
5V-10W solar panel, TP4056 Charge Controller, MT3608 Booster, Relay Module, HC-SR501 PIR, Li-on Battery,
Solenoid - (12V / 10mA to 460mA / 26 Ω) ,
Check the new image to see values.
I did a test on drain time of the circuit with no solar panel connected running idle and not triggered. Battery lost 0.06V per hour.
You use boost converters, not buck.
Converters don't draw anything, your loads draw.
Your relay trigger is absolute no-sense, it's directly connected to 3v3 pin! What are you looking for here??
I did that to stabilise the signal using the 3.3v pin, similar to how a ground wire+resistor can be used to ground a signal wire to prevent floating.
The D4 output signal doesn't seem to be clean or stable due to voltage fluctuations. So this works to keep it stable enough for the relay to trigger properly.
That can't work. Connect D4 to relay and remove that 3v3.
You're telling me it doesn't work. But i'm looking at it working right in front of me...
The relay is a low level trigger if that helps you understand what is happening here.
@pathogenex Actually they do draw something. They have a quiescent current, and it can be quite high, maybe a few milliamps. They will drain the battery more than the a Nano when the Nano is in sleep mode.
If you want to reduce this, use a boost converter with an enable input for the solenoid. This will prevent it from wasting current when not needed, and remove the need for the relay module also.
Also consider switching to a Pro Mini or Pro Micro which runs at 3.3V, and a sensor that also runs at 3.3V, so the other boost converter is not needed.
Interesting, could you provide me a link to a boost converter with enable pin?
I had no idea these existed and I can't seem to find any online.
Found this one but i don't think I trust that link.
Found this one seems like it's fit for purpose.
Much appreciate the help.
Agree, I wrote according to OP's post. If energy saving optimization is target, better alternatives can be found.
Low or high, it cant work if wired like your image presents.
Not quite. A boost converter lets input voltage through when disabled.
So the solenoid will constantly see 3.7volt when the boost converter is off.
A relay has an additional drain of 75-80mA
A mosfet module (not an IRF520) instead reduces that to zero.
A switched boost converter and a mosfet module is the best choice.
The mosfet module can switch boost converter ground, so you don't need a boost converter with enable pin.
Good choice:
It's called a level shifter. I've used them before for projects. Works a charm.
The 10Kohm resistor and the D4 form a simple voltage-divider / level-shifter that makes the relay’s coil-driver input see a low enough voltage to be recognized as a logic LOW when D4 is driven low, and a high enough voltage (5V-ish) when D4 is high‑impedance or pulled high.
I was having issues running D4 due to system instability brought through from batteries/Solar and the back voltage spike from the relay. Hence why I went with this solution.
So i want to get a DC-DC boost converter with an explicit output disconnect and an enable pin
No, get the mosfet module of post#13.
Not one with opto coupler, not one with an IRF520 (bad).
Then connect the solenoid (with kickback diode) directly to your boost converter.
Then switch ground of the above setup with the mosfet module.
That will turn on/off both, so you don't need a boost with enable pin.
The 5volt boost converter for the Nano must be connected to the 5volt pin, not the Vin pin.
