32
votes
Accepted
How to safely discharge oneself
The best way is to use an ESD strap, that is connected to earth via a 1MOhm resistor. This slowly but continuously discharges you without creating high currents. This way it does not hurt or damage ...
- 9,599
25
votes
Accepted
Capacitor discharging theory vs experiment doesnt match
You should check the datasheet to be sure, but the usual cause would be that ultracaps are often quite limited in terms of current they can provide. You're trying to draw about 100 mA, while most ...
- 25.8k
17
votes
Accepted
Do we need a resistor to discharge capacitor of MOSFETs while connected to MCU?
One good reason is to have this resistor to keep the gate low if the MCU pin is in high impedance state (e.g. during reset or after reset until the port is initialized).
(Otherwise during high ...
- 16.3k
17
votes
Accepted
Discharge time of 12 V 8.4 Ah at 5 mA
I have a motorcycle battery rated as 8.4Ah (20HR). It also says 8Ah (10HR) and I am not sure what´s the difference.
The capacity decreases at higher discharge rates. The figures are telling you that ...
- 176k
16
votes
How to safely discharge oneself
You can use a ESD mat, which is directly connected to the electrical ground. Just place it under your electronics and wear the connected bracelet when you are working with them. Touching the mat when ...
- 356
14
votes
How much do lithium polymer batteries expand in volume?
This paper measured a cell, they reported a max of 0.5% expansion over a charge cycle:
Source: Expansion of Lithium Ion Pouch Cell Batteries:
Observations from Neutron Imaging Figure 7
Over the ...
- 82.3k
14
votes
Accepted
What is the point of a high discharge rate Li-ion battery if the wire gauge is too low?
AWG 10 is 1 Ω per 1,000 feet. So, 1 foot of wire (305 mm) will be 1 mΩ (that's 1 milli ohm). I don't know how much wire is needed to wire up a battery pack but it's going to be less than 305 mm.
So, ...
- 457k
12
votes
Is it healthier for a capacitor to be discharged to itself or to "ground"?
The only GUARANTEED safe answer is to discharge the capacitor, through a suitable resistor, across the capacitor terminals.
It is true that in most cases one side of the capacitor will be grounded ...
- 46.7k
12
votes
Do we need a resistor to discharge capacitor of MOSFETs while connected to MCU?
During normal operation there is no need for the resistor.
However you may want it to put the FET into a known state during power up and reset. Otherwise on power up before the MCU starts to drive ...
- 6,902
12
votes
Accepted
Shorting a high voltage electrolytic - damaging?
The possibility certainly exists, depending on how the current distributes within the cap and how much energy is suddenly converted to heat inside the cap- and there are capacitors designed for pulse ...
- 398k
11
votes
Accepted
How to fully discharge supercapacitor?
The energy stored in a capacitor is given by :
$$E= \frac{CV^2}{2}$$
Fill in the numbers for both 2.7 V and 900mV:
$$E_{\text{full}} = \frac{100 \text{F} \cdot 2.7 \text{V}^2}{2}\approx365 \text{J}...
- 12.5k
11
votes
Accepted
Current limiter circuit is damaging MOSFETs
Safe operating area. Repeat after me "look at the safe operating area graph": -
According to the data sheet SOA graph for the IRF630 it would survive less than 1 ms with 5 amps and 160 ...
- 457k
10
votes
Accepted
Diagnose battery drain in small appliance
Short story
Clean the optical reflector and/or remove cat hairs from the tunnel around the optical sense head.
Long-story
My cat flap has an IR diode and reflector back to a sensor. This is pulsed at ...
- 457k
10
votes
Accepted
When discharging a capacitor, why would a resistor make a difference if it is situated after ground?
Two concepts that you are missing: "ground" is arbitrary and voltage is relative. And one more: current flows in loops.
In the first example, R2 is shorted by SW1. This also shorts the ...
- 3,060
9
votes
why is RC= exactly 63.2% full charge, and how is 5RC considered 100%?
Take a look how a capacitor charges through a resistor: -
Capacitor charging follows this exponential relationship: -
Where Vs is the target "supply" voltage and, if you let t=CR you find that Vc/Vs ...
- 457k
9
votes
Accepted
What happens to the energy stored in a short-circuited capacitor?
You have specified a superconducting shunt, with zero resistance. What you have not done is to specify its inductance. And you cannot force inductance to zero.
So your circuit looks like
simulate ...
- 60.6k
8
votes
Accepted
How does voltage progress during discharge of a battery?
Battery discharge curves and you
Batteries indeed vary in voltage as they are discharged. This is a function of the chemistry of the battery, and specified by the battery maker as a discharge curve, ...
- 8,978
8
votes
Battery balancing circuit
Charging one battery from the other will result in overall drop in efficiency and run time. Consider that energy will be lost in the charging circuit and in heat losses of both the battery powering ...
- 176k
8
votes
Is it safe to discharge Li-Ion to 0V?
Storing them "discharged" to ~3V with the device they were used in
still preserves lots of energy in the battery.
At 3V a Li-ion battery has almost no capacity left.
In this graph two 800mAh ...
- 56.4k
8
votes
Why do most battery protection circuits have 2.5V discharge cap?
This may not be a definitive answer, but a couple of points to note when choosing the threshold voltage.
The output voltage of a cell while discharging is lower than its quiescent voltage and the ...
- 352
8
votes
discharging capacitor through led
No. To quote a famous actor "It's physics Jim". Your formula has already told you that it is not possible There is nothing we can say which changes that.
You can gain a bit by using a more sensitive ...
- 14.4k
8
votes
Accepted
What difference between two discharge resistors in two circuits?
Circuit 1 will light the LED on one half cycle only. This may result in some visible flicker. Circuit 2 improves on this by using a full-wave bridge recifier to light the LED on both half-cycles.
...
- 54.1k
7
votes
Is it healthier for a capacitor to be discharged to itself or to "ground"?
To discharge a capacitor there must be a circuit, a loop, that passes through both terminals of the capacitor. Whether there is also a connection to some "ground" makes no difference to the process.
...
- 7,524
7
votes
Accepted
Smoothing a Full-Wave rectifier voltage
The diodes only conduct briefly, when the source voltage is greater than the capacitor voltage (by two diode drops) as shown below:
When the magnitude of the source voltage is less than the ...
- 398k
7
votes
How to safely discharge oneself
Carry around a 1MOhm resistor and touch one end to something grounded while holding the other end, or just get an ESD bracelet and wear it.
- 864
6
votes
Accepted
Super capacitor directly on the power supply
You can use them like that. The only drawback is the self-discharge of them internally. For a battery application this can be disastrous. For a mains powered application it's probably neglectable.
If ...
- 14.7k
6
votes
Can an external defibrillator deliver a continuous charge?
An external defibrillator will deliver a biphasic waveform usually. This would look like something like this:
The waveform can also be monophasic or triphasic. So we are not talking about ...
- 1,401
6
votes
High voltage capacitor discharge tool
Any sane designs that use high voltage capacitors have bleed resistors across them. So as a precaution let the device under test sit without power for a while before probing, then proceed with your "...
- 1,831
Only top scored, non community-wiki answers of a minimum length are eligible