Hi
I have 2 x 14500 batteries, wemos d1 mini v1.0 , max7219
Till now I powered using USB. But I want it portable and away from sockets. So supplying 2x 3.7 = approx 8v
This is provided to pin 5v. I think Wemos is ok with this. But I need to use same 5v pin for max7219
battery +ve, 5v wemos, vcc of max7219 are all connected.
Is this going to fry? or is it ok?
The voltage of 8 volts is beyond the specifications of the Wemos D1 mini so I think that you are just lucky. Eight volts is also beyond the specifications of a Max 7219 so my answer would be "fry" but maybe you will get lucky here too.
Also keep in mind the maximum voltage capability is NOT a threshold. i.e. the Max7219 is OK at 6.00 Volts in but a 6.100 it will fail. This is not the case.
The higher the voltage the more stress in put on the device. So with 8 volts applied it will likely not fail immediately. However it would not be expected to last for a long period of time. Maybe a day, a month, a year or 10 minutes. Also know that any other stressor (like temperature) could aggravate the system.
So the answer is.... you will fry it, however it is unknow how long that will take.
vaj4088:
The voltage of 8 volts is beyond the specifications of the Wemos D1 mini so I think that you are just lucky.oo.
Indeed. The RT9013 regulator used in a genuine WeMOS D1 mini is actually rated to only 6 V.
Remember that many USB "power banks" uses a single 18650 cell and a boost converter to derive regulated 5 V. That would probably be the simplest approach to obtaining 5 V for both the WeMOS and the MAX7219.
OK . thanks for inputs.
I am using this for this GitHub - Qrome/marquee-scroller: Marquee Scroller Clock News Weather and More
I updated my connections - using buck boost converter for 5v
Problem: when the voltage came down to 4.9v etc, Wemos struggled and flickered.
Starting voltage - approx 6v. After some time..1 hour or so it started having the issue.
Any suggestions to run longer on batteries...(though planning to reduce brightness, not accessing services every minutes...but may be 15mins or so)
krisferrari:
Problem: when the voltage came down to 4.9v etc, Wemos struggled and flickered.
Starting voltage - approx 6v. After some time..1 hour or so it started having the issue.
It is not clear what you are connecting to what here, but if a "buck/ boost" converter fails to maintain a 5 V output from 4.9 V, it clearly is not functioning as a buck/ boost converter. 
If that converter can't keep to 5V under load you're overloading it. You need a better buck/boost converter. This assuming that the input voltage and current do stay up.
You measuring 4.9V doesn't mean it's a stable 4.9V. It may be "flickering" (having short dips in the voltage that average out to 4.9V as it struggles to keep up), as you say you observe this on the WeMOS.
Paul__B:
It is not clear what you are connecting to what here, but if a "buck/ boost" converter fails to maintain a 5 V output from 4.9 V, it clearly is not functioning as a buck/ boost converter.
Apologies, its a step down converter.
But main concern is - how to use battery efficiently
krisferrari:
Apologies, its a step down converter.
krisferrari:
Problem: when the voltage came down to 4.9v etc, Wemos struggled and flickered.
Starting voltage - approx 6v.
You are feeding the buck convertor from 2x li-ion cells in series? The starting voltage should be around 8.4V and drop to 6V when the cells are empty. The convertor should be able to maintain 5V output for all or nearly all that range. So what are these 4.9V, 6V voltages you measured? It's time for you to post a schematic.
ok
please see diagram
Question: Should I use 3,3v? ofcourse using step down to 3.3 instead of 5v
ABout voltage - Batteries are not fully charged...so not saying 2x 4.2 max = 8.4v ( though these ate 3.7 was told that they can hold upto 4.2)
SO 6v when I tested power in batteries...and getting drained to 4.x and dying
For a 5V system 4x NiMH is a great option, nominally 5.2V(*). If you have 2S lipo power you
need to use a 5V regulator, either linear or a switch-mode (buck) converter.
Most 5V chips quote something like 6V or 6.5V as "absolute maximum never exceed" - you
can check in the datasheets for your chips - for instance the regulator (ME6211) in the Wemos
mini has a limit of 6.5V and the MAX7219 has a limit of 6.0V - you may well have degraded
these devices, leading to premature sudden failure or other problems.
(*) NiMH is 1.3V per cell in practice, (not 1.2V as often quoted, that's the voltage for NiCd,
the chemistry that NiMH replaced). Thus 4x NiMH is a little over 5V, typically safe for most
logic uses.
MarkT:
For a 5V system 4x NiMH is a great option, nominally 5.2V(*). If you have 2S lipo power you
need to use a 5V regulator, either linear or a switch-mode (buck) converter.Most 5V chips quote something like 6V or 6.5V as "absolute maximum never exceed" - you
can check in the datasheets for your chips - for instance the regulator (ME6211) in the Wemos
mini has a limit of 6.5V and the MAX7219 has a limit of 6.0V - you may well have degraded
these devices, leading to premature sudden failure or other problems.(*) NiMH is 1.3V per cell in practice, (not 1.2V as often quoted, that's the voltage for NiCd,
the chemistry that NiMH replaced). Thus 4x NiMH is a little over 5V, typically safe for most
logic uses.
Appreciate your answer. I am using Li ion because of box size restriction. Not sure how long the rechargeable NiMh will last
Goal: I want my device to run longer on batteries
I am always failing in this area, why commercial products are so efficient, but I have to pay so much attention and check batteries. no satisfaction, ofcourse its lack of my own knowledge
Please help me. Should I use 3.3V ? which one is power hungry? Is the step down converter eating part of it?
ABout voltage - Batteries are not fully charged...so not saying 2x 4.2 max = 8.4v ( though these ate 3.7 was told that they can hold upto 4.2)
Li-ion batteries are 4.2V when fully charged, 3.7V when half charged and about 3.0V when discharged. If the voltage of a li-ion is significantly below this, like 2.0V, then it has been over-discharged and damaged. It would be dangerous to recharge it because it could explode or catch fire. I suggest you recycle those batteries and buy new ones.
5V buck converter should be fine for reducing 2S LiPo to 5V for both modules - if the Wemos is
unreliable at 5V that's either because you already fried it or some other issue not related to power.
Does stuff test out OK on a known good 5V supply?
MarkT:
5V buck converter should be fine for reducing 2S LiPo to 5V for both modules - if the Wemos is
unreliable at 5V that's either because you already fried it or some other issue not related to power.Does stuff test out OK on a known good 5V supply?
I've charged for some time and it worked for an hour or so. Hence the question - why it is so power hungry. How to know what percent is eaten up by max7219
Most current will go to the display. The Wemos will draw about 80mA. The display will draw up to 1.3A at maximum brightness with all leds on. Maybe 25% of that with typical text symbols, so 300~350mA.
PaulRB:
Most current will go to the display. The Wemos will draw about 80mA. The display will draw up to 1.3A at maximum brightness with all leds on. Maybe 25% of that with typical text symbols, so 300~350mA.
Thank you
Please can you help on my other question -
Use 3.3v or 5V?
Taking Nano as an example, In some youtube videos and articles, the suggestion was...remove the resistor or led, Avoid 5v pin or Vin pin, as one of them consumes more power etc.
So is there a similar thing with Wemos?
Yes, the 5V pin on the Wemos is equivalent to the Vin pin on Nano - it connects to the input of the on-board linear voltage regulator. The regulator outputs the 3.3V needed by the esp chip on the Wemos, and can do this with anninput voltage as low as around 3.5V, because it has a very low minimum voltage drop. Powering the Wemos with 3.3V direct to the 3V3 pin from a buck converter is probably more efficient because you are bypassing that regulator.
But in your case, you may need your buck converter to output 5V in order to power the display. Max7219 needs 4.0V absolute minimum.
So you could try adjusting your buck converter down to 4.5V. If the display still works ok (you will lose some brightness), that might give a little more battery life, but not much I think. You would still need to power the Wemos by the 5V pin because when powering via the 3V3 pin, even 4.0V could in theory fry the esp chip.
But as mentioned in previous posts, your poor battery life is probably caused by one or both batteries being faulty or damaged, as indicated by the voltage readings you measured before. Li-ion batteries can be permanently damaged by over-charging or over-discharging. Some of the larger li-ion batteries, 18650 size, have a built-in protection circuit that disconnects the battery before it becomes over discharged and damaged. Smaller li-ion batteries have no room for such a circuit and rely on the circuit they are connected to for this protection. Your buck converter won't give that protection to the batteries.
PaulRB:
Yes, the 5V pin on the Wemos is equivalent to the Vin pin on Nano
But with a very significant difference - it is actually useful!
On the WeMOS, it has to drop only 1.7 volts, and you rarely connect 3.3 V devices that require any substantial current at all.
The singularly unhelpful suggestion often made, of powering a UNO, Nano, Leonardo or Pro Mini via "Vin" or the "barrel jack" is problematic as at 7 V, the on-board regulator drops 2 V, 4 V at 9 V supply and of course, 7 V at 12 V supply. This heat burden is barely manageable supplying the CPU and USB chip alone plus a few indicator LEDs with 20 mA each, but connecting other devices to the "5V" pin or drawing a lot of current from many output pins is clearly going to run into trouble.
PaulRB:
Yes, the 5V pin on the Wemos is equivalent to the Vin pin on Nano
Not really, as I said it cannot tolerate even 6.5V, the ME6211 regulator is designed
only for dropping 3.7V LiPo to 3.3V, so the pin is marked "5V", not "Vin". [Its a chip
specifically targeted at mobile phones]
If it was marked "Vin" someone would come along and plug 8.4V into it thinking it
could handle that (oh, hang on, erm, they have anyway!)
