32

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 anything. But I also want to mention one "trick", when you dont want to use special equipment like an ESD strap. Discharging at the earth connection of mains ...


25

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 ultracaps are rated at 1-10 mA discharge current. BTW, I suggest you stop your experiments if you need that cap later on. You can easily damage an ultracap by an ...


17

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 discharge current of \$ \frac {8.4 \ \text {Ah}}{20 \ \text h} = 0.42 \ \text A \$ will last 20 h and \$ \frac {8.0 \ \text {Ah}}{10 \ \text h} = 0.8 \ \text A \...


16

Capacitors and (rechargeable) batteries can both be used to store and retrieve electrical energy, and both are used for this purpose. But the way they store electrical energy (charge) is different, which leads to different characteristics and hence different use cases. A capacitor directly stores charge on what is essentially two plates of conductors. The ...


16

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 impedance state it could act as an antenna and pick up some voltage that turns it on)


16

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 you arrive at your desk would also discharge the static charge without affecting your PC. Image source


15

Ideally the manufacturer supplies the discharge rates on the battery datasheet. A quick point: You mention you have a 12 V 2.4 A SLA (sealed lead acid) battery, but batteries are rated in amp-hours not amperes. Therefore I suspect you have a 12 V 2.4 Ah battery. Now that we have that out of the way, a 12 V 2.5 Ah SLA battery from Power Sonic, as an example ...


14

You are much better off making ideal diodes using MOSFETs Replaces a Power Schottky Diode Internal 20mΩ N-Channel MOSFET 0.5μs Turn-Off Time Limits Peak Fault Current Operating Voltage Range: 9V to 26.5V Smooth Switchover without Oscillation No Reverse DC Current But the simplest solution is a better Schottky Diode Array $6 with a heatsink These are ...


13

An easy rule-of-thumb for determining the slow/intermediate/fast rates for charging/discharging a rechargeable chemical battery, mostly independent of the actual manufacturing technology: lead acid, NiCd, NiMH, Li... We will call C (unitless) to the numerical value of the capacity of our battery, measured in Ah (Ampere-hour). In your question, the capacity ...


13

Actually SLA batteries have a vent... so the name "sealed" is a bit of a misnomer. VRLA (valve-regulated lead-acid battery) is actually a name for the same tech. Practically every UPS (uninterruptible power supply) I know of has one [or more] SLA[s] inside, so it's generally safe for indoor use. Here's a snippet from an APC white paper on the issue: ...


13

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 lifetime of the battery, it swelled more than 1.5% Source: Expansion of Lithium Ion Pouch Cell Batteries: Observations from Neutron Imaging Figure 9 One could ...


12

My quick look into it: The lifetime of lithium batteries decreases with the depth of discharge, looking like the following (this curve is for lead-acid batteries, but Lithium is stated as following a similar curve): (source) If the 100% DoD value is taken as a reference, one can plot what I call the "isoenergy" curve (I gave it a 2sec thought) which is ...


12

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 the pin the FET could turn on. This could cause glitches on the output or worst case (and this is very unlikely) depending upon what other current surges happen ...


12

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 discharge applications, such as photoflash, but even there there is some series resistance and inductance to limit the current. The place to look would be in ...


11

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 and the other attached to some rail, HOWEVER this is NOT TRUE in all designs. There is no guarantee that grounding either pin of the capacitor to frame ground ...


10

First, 'The "22Ah" implies a discharge rate of 1.1A over 20 hours.' Only if the manufacturer says so. It might as well mean 22A over 1 hour, or any other combination that multiplies to 22Ah. C is generally the capacity divided by 1 hour, so for your battery it would be 22A. Hence eg. 'charge at 1C' can be stated, independent from the capacity of a battery....


10

Wouter's answer is quite good. I would add this chart: Energy density is how much energy can be stored in a given weight of product. Power density is how quickly you can get that energy out. So you can see that aluminum electrolytic caps can deliver orders of magnitude more power than any battery technology on the chart, and the energy stored by batteries ...


10

The best conditions for static generation and discharge are; dry air, neoprene soled shoes nylon seat cover, nylon carpet. and holding a metal key or pen to discharge to another metal object. So reducing these effects comes from using; leather shoes (sweat) or better, ESD approved heel straps or best, ESD shoes paid for by your employer ($) with ...


10

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: $$E_{\text{full}} = \frac{100 \text{F} \cdot 2.7 \text{V}^2}{2}\approx365 \text{J}$$ $$E_{\text{end}} = \frac{100 \text{F} \cdot 0.9 \text{V}^2}{2}\approx41 \text{J}$$ In other words, we have \$41/365\approx 11\% \$ of the full capacity ...


10

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 volts across it. Looks like it managed to survive 3 ms though: - What´s is going on here? It's called operating the device below its zero temperature coefficient ...


9

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 this circuit – Schematic created using CircuitLab Let's say the cap is at some voltage V0. When you close the switch, the cap is at full voltage, and the ...


8

I know... old post... still... LOL at the criticisms of the wisdom of putting these in series. While completely accurate when expressing the ideal, there is middle ground. Say hello to my '06 Honda Civic Hybrid battery pack - 132 D cells in series comprised of eleven 12-cell welded assemblies. No cell voltage monitoring capability. Following an 18 hour C/...


8

This is based on UK/European practices: - Firstly you need to decide what category zone and group you are likely to be working in. From memory Zone 0 is the most onerous and again, from memory, only Ex i (intrinsically safe) equipment is allowed. More than likely you are in group 2 because group 1 is reserved for mining environments. I think these days you ...


8

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, characteristic of the chemistry of the battery but also varying with the discharge rate and a few other parameters (such as temperature). For instance, a 12V ...


8

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 the charger and the battery being charged. The most efficient is to take power from the 'good' battery. As its voltage drops to the level of the battery with ...


8

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 LED, some work good at 0.5mA (I thought you 15mA was way over the top anyway). But that is where it stops.


8

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. There's no real effective difference for the R1 connection. In Circuit 1, C1 is discharging through the load, and in Circuit 2, it's discharging across the cap ...


7

In a Rayovac Application Note entitled "OEM Application Notes & Product Data Sheet -- Primary Batteries—Alkaline, & Heavy Duty", there is a graph on page 4 which lists the expected service life for various continuous mA drains of the battery. For the #815 AA Alkaline battery (dotted red line), the graph shows that you should be able to draw 1.5A for ...


7

That's because the material between the plate is a good, but not perfect insulator and it has a non-infinite resistance. Therefore it acts as a very high resistance across the terminals of the capacitor, leading to slow self-discharge. Of course using better insulator materials could lead to lower self-discharge rate, as it is exploited in FLASH memory ...


Only top voted, non community-wiki answers of a minimum length are eligible