# Tag Info

44

USB-C will use the Power Delivery specification, a first connexion is done at 5V, then "negotiate" whether it can use a higher profile to charge. There are 5 profiles available : Profile 1 : 5V@2A Profile 2 : 5V@2A or 12V@1.5A Profile 3 : 5V@2A or 12V@3A Profile 4 : 5V@2A or 12V@3A or 20V@3A Profile 5 : 5V@2A or 12V@5A or 20V@5A There are 4 connection ...

30

Phone chargers are indeed usually a 5 V regulated power supply. Here's an example of a simple circuit that is commonly used: Source. This is a flyback converter circuit. The output voltage is regulated even though it's not immediately obvious how that's done. But note the winding "Na" on the left, it is one of the transformer's windings. This ...

25

First make sure everything is working as intended. Point the solar panel at full sun and see what kind of current you can get at 5 V. Try a 5 Ω power resistor. That should draw 1 A, which takes 5 W of power at 5 V. You should be able to get at least that according to your specs. If that works, it may be that the phone is expecting a "smart" ...

24

The problem with these theoretical examples lies in the fact the current is assumed infinite for 0 seconds. Crudely substituting this in the conservation law: $$\frac {\partial \rho }{\partial t} +\nabla \cdot \mathbf {J} = 0$$ $$\frac { \rho }{ 0 }+ \infty \neq 0$$ Since charge is conserved, the assumption of infinite current in zero time is wrong. ...

21

You're hooked up wrong. The meter's big rotary switch has a legend around the outside indicating range. Obviously, there are as many range markings as there are switch positions. Only two of them have the "20A" icon, which indicates you should use the 20A socket instead of the V/ma/ohm socket. You have not selected one of those positions, yet you ...

21

To be compatible with the original standard, USB devices should not draw more than 100mA (which is plenty to power the logic interface), until they have negotiated with the host, to find out what it can supply. After successful negotiation, they can draw up to 500mA. This is to protect the operation of a 4 port hub, should it be plugged into a PC with all ...

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

Historically: really old mainboards connect USB power pins to the 5V power rail, with no protection power on by keypress was added, which added a jumper or a BIOS setting that decided whether USB ports would be powered from the standby power or from the regular 5V rail. Since standby power was introduced in ATX, this does not exist on AT mainboards. USB ...

15

An AA cell is not the same as an 18650 cell. 18650 designates lithium-ion batteries of nominal voltage 3.6 Volts each. These typially consist of the actual lithium-ion battery and some circuitry, as shown in this image: (source: WikiPedia) Primary (non-rechargeable) AA cells are typically around 1.5 Volts each, such as the classic Zinc-Carbon batteries, ...

15

There are two additions to the USB specification that allow for more than 500mA current. usb battery charging specification 1.1. Allows for up to 1.3A. usb battery charging specification 1.2 (and this). Allows for up to 5A. Summary: USB 2.0 - BCS 1.1: 1.3A current, no data transmission. USB 2.0 - BCS 1.2: 5A current with data. USB 3.0 - BCS 1.2: 5A ...

14

LiFePO4 vs LiIon vs LiPo Some people have commented on LiIon batteries, but the question and this answer are about Lithium Ferro Phosphate batteries / LiFePO4 which I'll abbreviate in places as LFP4. . These are related to LiIon and LiPo batteries but have major differences. Notable, compared to LiIon and LiPo (which are chemically similar) LFP4 has an ...

14

You could do the entire discharge at the lower rate but then it would take a lot more time. When discharging at a high rate the voltage may collapse prematurely so the battery seems discharged before it really is. By combining the two discharge rates you can discharge the battery in a reasonable time but be confident that it is fully discharged. The lead-...

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

When masses collide in an inelastic manner, momentum is conserved but energy has to be lost. It's the same with the two-capacitor paradox; charge is always conserved but, energy is lost in heat and EM waves. Our schematic model of the simple circuit isn't sufficient to show the subtler mechanisms at play such as interconnection resistance. An elastic ...

13

It is correct. You normally see PMOS connected like this to act as a reverse-polarity "diode". simulate this circuit – Schematic created using CircuitLab It has much less voltage drop than an actual diode and will protect currents from flowing the wrong way when the voltage is connected between the battery terminals are connected in reverse. ...

12

In practice, 'smart' chargers use a special chip called a Dedicated Charge Port Controller. A DCP controller can act like different chargers, and picks the mode which seems to work best. That's because regular ('dumb') wall chargers use USB's data connections to signal in a static, analog way what they are capable of. 'Smart' chargers can do the same, ...

12

Typically: It just monitors the voltage of the power supply. If that drops too far (typically, for USB chargers, below 4.8 V), it reduces the current sink into the battery. A smarter charger might "scan" the "tolerable" input voltage range and find the sweet spot where most power can be drawn from the supply, but really, supplies are designed to be low ...

11

No, that’s perfectly normal. See the charge curve for NiMH below. It’s about 1.45 V / cell fully charged. NiMH are tolerant to overvoltage as long as the current is kept low enough. This is commonly referred to as slow charging where the cells stay hot when fully charged until you remove them. Medium solution is higher charge current and thermal cutout. Any ...

11

Complementary to main answers: It is crucial to note that attempting to charge a Li-ion cell by simply applying 4.2 V (or whatever maximum voltage is required) is an extremely bad idea because: One normal charging method is to use CCCV (constant current / constant voltage) charging where a constant current is applied while Vbat is under 4.2 V and then a ...

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

simulate this circuit – Schematic created using CircuitLab The current is determined by the voltage across the resistor, which is V1-Vc. As the capacitor charges, Vc increases while V1 stays the same, so the current decreases. The rate at which a capacitor charges is directly proportional to the current, so the rate at which it charges decreases ...

9

These kind of AC to DC converter will always consumme a small amout of power to maintain the control IC alive. I do not see a way around that unless your USB port has some sort of mechanical switch to flip on the converter when you connect a device. I recommend you to look around as I found this wall plug (for US 120V unfortunatly for you) that only turn on ...

9

It doesn't matter what voltage your power source is, as long as the capacitor is not subjected to a higher voltage than it is rated for. You could, for example, charge the capacitor from a 12 V source with a resistance in series with it. That will start the capacitor charging exponentially towards 12 V. You have to monitor the capacitor voltage and ...

8

The in-battery protection circuitry is usually intended to act as a gross fault protector and it is strongly recommended that it not be relied on as a means of charging control. As a means of gross short circuit protection it may be suitable as long as the values they choose for max Iout are acceptable to you. For charging, use of one of the large number of ...

8

Those batteries do have built-in protections, but not the kind of ones you see on sparkfun batteries. They have thermal protection required for charging the battery and sometimes low charge cutout device which prevents discharging too much the battery. However, there is no overcurrent protection, overvoltage and noob-proof abuse protections... You have ...

8

A device (phone) gets charged at optimal (high) rate only when it recognizes "charging port signature" on charger side. For Type-A port, there are several DIFFERENT port signatures that a charger port can provide: USB Battery Charging v1.2 Dedicated Charging Port, where D+ and D- are floating but tied together; USB Battery Charging v1.2 Charging Downstream ...

8

No, this won't work. You can't simply daisy chain chargers but drive them off the same 5V supply. Your charger needs to be able to define both the out+ and out- rails (chances are, out- is directly connected to in-, anyway). Same goes for b+ and b-. So, by doing this, you're shorting battery + to 5V -. That's a way to start a fire.

8

The USB wires D+ and D- have attached resistors for coding the nominal current of the adapter - 500mA, 1.5A, .... This is detected by the charging IC that will sink just the nominal current of the adapter.

8

...use a LC network to store small amount of electrical energy (500 mWHr or less) You might think that 0.5 WHr is "small" but for an LC tank, it is HUGE. So what is 0.5 WHr? 0.5 Watt = 0.5 Joule / second One hour is 3600 seconds so that gives a total energy of 0.5 J/s * 3600 s = 1800 Joule You want to use an LC resonator. In an LC resonator the energy ...

8

A reason to do this would be to get a quicker assessment of the charge capacity at a constant 5A drain. Another may be because that more closely simulated the actual battery drain on the Llama farm 75 years ago. All batteries tend to have a characteristic open-circuit voltage to which they'll recover under no load. For some chemistries (NiCd, dry cells), ...

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