# Tagged Questions

146 views

This battery is rated at 12V, and it says it provides 7Ah of power. Does that mean that it can provide 12V at the terminals for 1 hour if 7 amps are being drawn from it? Also, what does it mean when ...
100 views

### Will a 12v 2000mAh battery overpower(and damage) a 1.2a DC motor?

Sorry if this is Electrical Engineering pre-school. I'm a software guy that hasn't taken a class involving voltages for 10+ years. I'm working on an Arduino project that will have to be fairly ...
121 views

### Charging batteries directly from 117 volt wall socket

It has occurred to me that almost no battery charger would be required if the battery pack was of the same voltage as grid supplied power. I build electric bikes, and the voltage on these has been ...
193 views

### What's the relationship between volts and amperes in batteries?

I recently bought a bag of 100 5mw 4.5V laser diodes (the spec said they have "driver: out"). My idea was to connect two and two of these in series to get something that needs 9V, and then connect ...
127 views

### How do I go about building a charger circuit?

I am working on robot, and I want it completely automated. Everything I can tackle, except for when it comes with power. (Pretty big problem, I know.) I want to know how I can make a charger circuit ...
44 views

### Cells capacity and current max draw

Can you draw 12mA from a CR2032 cell for long time ? and from RL44 ? the data sheets says ~240mAH means about 24 hours to 2v, ...
335 views

### Stabilize 12V to 12V

How can I stabilize a 12V input to a 12V stabilized output voltage? I have a battery that supplies 12V but not regulated and a device that uses 12V regulated, how can I supply power to that device ...
116 views

### Safe Discharge Rate of Alkaline Batteries

I am working on a portable project. I need to pull 3,500mA average with 10,500mA peak at 3.6v-4.5v. I see that "D" Alkaline Batteries are rated for 1.2-1.5v and 12,000mAh. So I am looking at using a 3 ...
116 views

### Typical Power circuit for smartphones? Correct energy measurement? (Nexus 4, iPhone.. etc)

I am trying to perform some energy measurements using smartphone. And to make sure that I am performing my calculations correctly, I been trying to find any examples of typical power circuit in ...
154 views

### Attempting to determine power consumption

So I am attempting to determine if the battery I choose can power the devices I need. This is my first day doing anything with ohms and current and such. So go easy. I have: 2000mAh battery 45mA ...
45 views

So if I have a batter that says it can produce a max of 2000mAh and a device that says it uses 3.6 mA does that mean I can run the device for 2000mAh / 3.6mA ? How does the voltage get factored into ...
119 views

### Replacing a 12v battery (model A23) with power pack

I have a fan RF remote which runs using the a small 12v A23 battery. Note this is not 23 Amps but the battery model. They can provide something like 50mAh and are quite small. I am hacking the remote ...
522 views

### What is this white stuff inside this circuit board?

I'm having problem getting any output from this universal adapter for my older laptop, so I opened it up to see this rubber-like white substance inside, on top of the big 68uF 400V capacitor. A ...
171 views

### What do I need to power a 20V 3A device using “D” or “AA” batteries?

I'm going to try and build my own battery pack for a portable speaker. It uses 20 volts and 3 ampere as input. I realize I will burn through quite a few batteries if trying to power it with just AA or ...
127 views

### Can wet-cell and gel-cell batteries be mixed?

Given the same power ratings, can a (lead-acid/deep-cycle) gel-cell battery be paired together with a wet-cell battery in use? For example, with a motorized/electric wheelchair, would one be able to ...
240 views

### Could I double the batteries for double the usage time?

If I were to double the exact same battery of a particular device (noted below), could/would that effectively ~double the device's usage time (more or less)? For reference -- There's a motorized ...
279 views

### Why is it bad to mix new and old batteries?

I've seen warnings that it's bad to mix new and old batteries -- why? Is it a matter of a battery's age or a battery's voltage/current (remaining)?
148 views

### Building a High Current Power Supply? (Odd Voltage)

I'm working on a project involving some custom LiFePO4 battery modules. They can take a very high current charge, and I'd like to take advantage of that. I have battery management and charge ...
811 views

### How to get high current from 9 volt batteries

I am planning to make a solenoid.. Which should be so powerful as to lift up about 600N force. I have thought about it, and I have a doubt. How can I get DC currents up to 20-30 A using a 9 V battery? ...
118 views

### What are the possible causes of sudden extremely high internal resistances in Lithium batteries?

Not a duplicate, just to separated a good question from Does a crude Li-ion 18650 battery have internal thermal (mechanic?) protection? Short history long: I extracted 6 18650 (Sanyo) batteries from ...
141 views

### What's a simpler way to switch between power sources?

I want to make a device that allows the user to switch between two different power sources (a wall mount and batteries). I could perform this circuit using two DPDT switches, but I would need to ...
73 views

### Multiple power supplies in series: Negative voltage on one of them possible?

It is common practice to connect multiple power supplies in series to obtain a higher voltage; examples: 1, 2, 3, 4. Many power supplies are designed to handle this application well. However, users ...
56 views

### Clarification regarding batteries and ups

I am planning to setup a ups with 2 100ah/4h batteries next to my server setup. Is it safe to work to work next to such high load batteries. Are there any health concerns that comes with working ...
94 views

### Running 7V motors with 2x 3.7v batteries

We're really enthusiastic to build a homemade quad-copter with almost no knowledge about such things. We will probably use Arduino and Bluetooth to control it, but we have a question about the motor ...
67 views

I've got a simple circuit powered by one 18650 LIon battery. Now i want to light up a LED when the battery voltage drops under a specified value (e.g. 3,4V) I know it would be easy with a ...
239 views

### How do I measure ripple current in a battery charger? [closed]

Minimizing ripple voltage is major factor to avoid failure of equipment such as digital axle counters. (Eldyne) How do I measure ripple voltage in a battery charger with a 230 VAC input and a 24 VDC ...
316 views

### Convert 9v of battery into 5v at 3.5watt

I want to run Raspberry Pi using a general non-rechargeable 9v battery. Raspberry Pi needs 3.5W and 5V input. Questions: Which LDO should i use ? For what amount of time general 9V battery is able ...
588 views

### What types of batteries are typically used in UPS (uninterruptible power supply) and why?

They definitely need to be safe for indoor use so they can't vent, they should probably support deep cycling due to the nature of backup power supplies, and I imagine they should have relatively long ...
532 views

### How do I determine the maximum amp output of a battery pack?

How can I determine the maximum amp output of a battery pack? Some background: I've got a 5-AA battery pack hooked up to a microcontroller and some continuous rotation servos, but there's current ...
165 views

### Voltage regulation on the high side of a Darlington array?

I'm looking to build an 3.3V Arduino Pro Mini based LED driver that drives 3 (possibly 6) super bright 10mm LEDs (R, G and B). I intend to use this 3.7V LiPo battery and these LEDs. The LEDs have the ...
110 views

### Best and safest supply for 12 standard servos or more?

I am building an hexapod 2DOF robot, and I had planned a Power supply (5V/5A) for all devices, like this : Would that work and be safe? I have another plan , to seperate the power between servos ...
154 views

### Getting a higher voltage from a battery than specified

This may be a totally stupid question, but say I have a battery that supplies power at 7.5 V. Is there any way to boost its voltage to provide 9 V? I know you can step down voltages in many ways ...
147 views

### How to connect a DC socket to a switch

I have a basic flip switch that I want to use to control whether a DC power socket is providing energy (from a connected battery pack). The power socket has three prongs, the switch has three, and ...
80 views

### Possible to determine a device's power requirements based on the batteries it takes?

I have a magnifying glass LED lamp that I lost the power adapter to. There are no power requirement markings anywhere on the device, nor do I have the box/manual. Short of trying to find the ...
932 views

### Battery powered portable wall outlet?

For a college competition we aren't given any wall outlets to power our devices. We are purchasing (we don't have it yet) the wireless camera kit in the following link and we need to rig up a portable ...
527 views

### Can we connect battery negative terminal to oscilloscope ground?

I want to test my setup with 200Ah battery and check the outputs on oscilloscope. While testing can I connect battery ground to the oscilloscope ground? Is there any safety risk, as oscilloscope ...
267 views

### What is the proper name or part number of a 12V DC female car adapter with leads?

I've searched hobby sites like SparkFun, Digikey, BGMicro, and Jameco. I'm starting to wonder if I'm calling this item by the wrong name. What I'm looking for, exactly, is a 12V female car adapter ...
77 views

### Why is it only one of four batteries (Li Ion) is drained?

I have a programmable TV remote control ( a Marantz I've had since 1999 or longer if it matters), it uses 4 AA batteries. I often find (at least when I use Li-Ion, non-rechargeables) that when the ...
163 views

### How to protect an electronic construction kit (a toy) from damages?

As I child, I had this electronic construction kit called Elektronik 1. It was manufectured in former Czechoslovakia, based on resistors, diodes, bjt transistors, capacitors, an LW+SW radio antenna ...
592 views

### Arduino and Backup Battery Power

I have a very simple project that is working off of an external "wall wart" power supply and I would like to add a back up battery in case of power failure. I have breadboarded a backup power supply ...
173 views

### Tapping the battery from an UPS to feed low voltage devices

My UPS powers one 120V AC device and a whole bunch of small 'bricks' that end up rectifying things down to 5-12V DC. Instead of using the 'bricks', my idea is to tap the battery directly, and use ...
623 views

### Common ground between battery and AC/DC adapter

Is it possible to connect an AC/DC power adapter's ground (-) to a battery's negative side? I am powering a car radio with a 12V AC adapter. That works fine. However, if the radio loses power, it ...
138 views

### Need chargeable momentary 15 watt regulated voltage source

I'm working on a RF telemetry side-project that requires an amplifier IC to be run for about 5 seconds bursts between charges. The system is portable and runs off of a 3.3V battery that can supply ...
2k views

### How is wristwatch with 10 years battery life possible?

Turns out Casio offers a handful of wristwatches with "10 year battery life". The claim is that thanks to "an advanced technology" the battery life in those watches is extended to ten years. Now if ...
349 views

### Battery in parallel with main power source

I have a system that is powered by a main voltage supply and I want to connect it to a battery for backup, in case of power outage. I need to know what would happen if I connect the system with the ...
241 views

### How to best estimate power consumption for a system?

I'm not an engineer, I'm a software guy getting into hardware - so bear with my ignorance! I'm in the process of building a system with many components (e.g. a computer, many sensors, a few motors, a ...
2k views

### Least expensive way to plug in a microcontroller into 120V (without wall wart or batteries)

I need to be able to power a Atmega168 by plugging it into a wall. The circuit is a little bit more complex but not too much. The Atmega168 needs between 1.8V and 5V at 200mA. The ideal solution ...
785 views

### Charging affects battery life?

I wish to understand how a battery charger may best be designed in order to maximise the life of Lithium Ion batteries. I have specified Lithium Ion batteries as they are what is used in most laptops ...