# Tag Info

32

It's marketing, like PMPO watts. Big numbers sell! If the battery is 1.2V nominal, there won't be a big difference between W.h and A.h numbers. But if the battery is 3.6V nominal, the W.h number will be 3.6 times more bigger than the A.h number! So a 1200 mWh 3.6V battery sounds a lot better than a 330 mAh battery... even though it's the same battery of ...

18

cIt's complex, and some of the answers are "soft" and some of you assumptions are (reasonably enough) inexact. Li-ion are measured in mWh LiIon cells are frequently measured in mAh capacity. LiIon batteries (1 or more cells) often have mWh and mAh markings. Neither is a certain measure of what a user will receive. Both are useful. (cf George Box's "All ...

13

An Estes rocket engine squib looks about like this: (The above picture comes from a document I wrote on the topic.) Estes provides very clear all-fire specifications for their squibs: $\frac12\:\text{J}$ within $50\:\text{ms}$ into a resistance that is spec'd at $\frac23\:\Omega$. This implies an average of \\$\sqrt{\frac{\left[\frac{\frac12\:\text{...

13

If you "forget about" internal resistance, then the maximum current is infinite. An "ideal" component, non-existent in the real world, can provide mathematically "pure" infinite or zero amounts of resistance, voltage, current, and all the rest. Different battery compositions will have different amounts of real-world "impure" limitations. Internal resistance,...

12

Google "laptop battery pinout". Typically you'll have: Plus and Minus power terminals (maybe several contacts each for higher current) Some form of communication like I2C Temperature sensing (for example a thermistor) Your typical laptop battery has several cells in series, so it requires balancing which is usually implemented in the battery management ...

11

It's possible, using a heavy-duty DPDT switch.

9

Figure 1. There are two current-loops in the circuit: control and power. Notice that provided the transistor's ratings are not exceeded that no current flows from the power circuit back into the control circuit. The control circuit turns on the transistor and allows current to flow from V2 through the R3 - Q1 loop. In this circuit the base of Q1 will be ...

8

How about the following? simulate this circuit – Schematic created using CircuitLab Close SW1 to charge, or deliver, 24 V. Open SW1 to deliver 12 V, less a diode drop. For Schottky diodes, this need not be more than 400 mV or so.

8

Yes, the output voltage of a battery decreases (roughly) in proportion to the current drawn from it. This behavior is usually characterized as an internal resistance of the battery, although its actual physical origin may be related more to the chemical properties of the battery than to the actual resistance of any conductive part of the battery. For the ...

7

I can see a few issues: The UltraFire batteries shown in your photo (and in your calculations) are fake. It is impossible to have 12,800 mAh capacity 26650 batteries. This is similar to my answer here about 18650 batteries. The largest capacity 26650 batteries currently available are less than 6000 mAh. For example: UltraFire BRC26650 7800mAh (Red) - test ...

7

simulate this circuit – Schematic created using CircuitLab Figure 1. A very simplified schematic. How a battery is being charged and used as the same time? It can't. Either current is flowing into the battery (it's being charged) or current is flowing out (it's being discharged). You can't have current flowing both ways in the one wire. This is ...

7

At 1.6A you're shorting the battery. Maximum load is about 500mA, this is already <1 hour. Internal resistance is about 0.3 Ohm, at 1.6A sets you back half a volt per cell. So, for one pack with 4.5V (real 4.2V ) you go down to 2.7V in real conditions. If equally divided over 4 packs this 1.6A is maybe fine (0.4A per pack), but if one cell fails, your ...

6

When using an AC input to the device a transformer with two seperate windings (or one winding with a tap in the middle) can be used to create a postive and a negative rail. Source: https://www.quora.com/What-is-a-dual-polarity-power-supply-using-a-transformer-a-full-wave-bridge-and-a-Zener-diode With only one DC input you typically use a DC/DC converter, ...

6

A multimeter in ampmeter mode is basically a short. If you're lucky, the multimeter has a fuse that instantly burned when you connected the battery – a charged, a shorted car battery can easily source > 80 A, and that just vaporizes a lot of on-board conductor traces. So, what you might have been feeling is the electromotive force due to wires with very ...

6

Back when I was into model rockets I had a commercially made launch controller. That used 4 D cells in series. These have a much higher capacity than the small 9 volt cells do. Push the button and the igniter in the rocket motor would burst into flames the instant I pushed the button. I have no idea how much current it actually drew. The igniters were ...

6

The full chemistry-level explanation is beyond me, but the short consumer-level answer is to do with self-discharge. This is, as the name suggests, how much the battery discharges itself while not in use or in low-drain uses. Some rechargeable batteries are marketed as "low self discharge" for these use cases. However, personally I wouldn't bother using ...

6

The protection circuitry on a Li technology battery is not a charging profile controller. The protection circuit only tries to protect the battery from over voltage, too deep of discharge and over temperature detection in some cases. The web page that you linked to specifically specifies the protection features and applicable parameteric limit. Protection ...

5

It is hard to answer your exact question, since you want information on a scenario that has no commercial relevance, so companies are not going to test almost drained batteries just to know how much energy can be harvested from them. Those discharge curves they publish are used to design battery-powered products: the curves allow to estimate how long a ...

5

If the two cells are in series but one has significantly less capacity that the other, it can discharge first. The other cell will then discharge the expired cell even below zero as you have seen. If cells are in series you should ensure they are in the same condition, do not pair a new cell with a partly used one. This same effect can occur with ...

5

how I would calculate every stage together Using $$1 \text{ mAh} = 1 \text{ mA} \cdot 3600 \text{ sec}$$ you can calculate the average as: $$0.05 \text{ mA} \cdot 3473 \text{ sec} + 56 \text{ mA} \cdot 120 \text{ sec} + 0.44 \text{ mA} \cdot 6 \text{ sec} = 1.9 \text{ mAh}$$ get an accurate calculation of how long the battery would last You can ...

5

Alkaline battery capacity depends too much on load, it's too complex for the average consumer to understand and the difference between brands is small. Primary (non-rechargeable) lithium AA cells have more stable capacity but they are oriented to the same market. Capacity for NIMH batteries actually is quite stable under load. There is a trade-off between ...

5

All the stuff happening inside batteries is a bit complicated, even if we greatly simplify everything. After all, a battery is actually two batteries back to back, each one composed of a water-metal junction. The water, the electrolyte, is a conductor that connects the two. They're in series, so they both have to produce exactly equal current (if a ...

5

It would be somewhat ugly, but I would say tape to bulk the battery up to the correct width, so that the holders / enclosures keep it in place. For the length, I would use a generic 6mm nut Its 5.2mm long which makes up for the length difference in most cases, while having enough width to not move too much, and will make reliable contact with a number of ...

5

Even theoretically ignoring the temperature restrictions and internal resistance, this seems obviously impossible. Where am I going wrong? The answer is right there in your question summary. You're overlooking the fact that while in theory, theory and practice are the same, in actual practice, they're not. You can't ignore the internal resistance (actually,...

5

TP4056 is a charger chip for one (1) cell. If you plan to charge multiple cells simultaneously, each charging slot for a cell needs it's own TP4056. Please don't even think about connecting a 5V 3A power supply directly to a lithium cell. Even though the cell has built in protection, it is not a charger. It is the last line of protection to prevent ...

5

This is a major annoyance with "smart" chargers in that they follow certain recommendations and refuse to charge a battery that is too dead. You can probably revive the battery with a bench power supply to the point where the charger will work. Old fashioned chargers, which consist of little more than a transformer and rectifier, will also work. ...

5

Batteries don't often fail low voltage or short circuit, but if they do, then a 'very parallel' arrangement could be bad as all the good batteries gang up on the bad one to force a high current through it. Protect each battery with a fuse in series. Before connecting them in parallel, make sure one or more of them aren't duds, check each individually into a ...

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