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August 31, 2008
News - Why You Should De-Rate Ca… |
about 7 months ago
Tantalums can also explode with high dI/dt, even if the voltage rating is never approached. Battery power can be especially bad for that. Happened on a product I was working on, fortunately we had some prototypes go and redesigned it before it was released. Here’s a paper from AVX with plenty of information…
Product TOL-10951 |
about 2 years ago
I’ve done this with a different brand of the same stuff. I didn’t get super details like alginate or plaster of paris would give, but it was much easier, and it was definitely recognizable as a face.
Heat it up, roll it out to about 1/8 inch thick and about 10 inches in diameter, lean back and gently mold it to your face like a big pancake. Let it cool. Cold water helps if you’re up to that.
You might want to make a small hole over the mouth area, but I found the fit loose enough that wasn’t necessary. And of course in an emergency you can just peel it off and start over.
Product PRT-10471 |
about 3 years ago
Point well taken. I mostly speaking tonguke in cheek, and thinking back to Polaroid’s PolaPulse batteries. They were 6 volt flat battery packs designed to be built into film packages. Having a large surface area, they could put out a lot of current, and stories circulated that two in series could start a car.
For these batteries, they should be pretty rugged, but you’re right, don’t try this unless it’s the only way to start your truck while you’re fleeing the zombie hordes.
Yes it would. Hmm, two in series might be able to jump-start a car.
Without searching through all the other batteries, there are various reasons why the energy density varies. The batteries here can sustain a 30C discharge. Typical Lithium batteries are rated at far lower discharge rates, on the order of 1/2C to 2C. There is a compromise in order to do that safely, and energy density usually takes a hit.
News - Squishy Circuits |
about 3 years ago
The squishy circuits look fun, I’ll have to try this with my nephew.
I envision extruding rods of this with a Playdough Fun Factory ® and laying out multi-layer boards…
Product COM-10213 |
about 3 years ago
(I assume you’re talking about a 5 volt signal driving the gate, referenced to the source.)
Using i = C * dV/dt, rearrange so dt = C * dV/i, and using the input capacitance, your drive voltage minus the gate threshold voltage and gate leakage current you can get a rough idea.
But if you notice, the gate leakage current can be either positive or negative. Bottom line: don’t depend on simply removing the gate drive to turn it off.
100 Hertz is trivial for this part, it has a turn on time of 140 nanoseconds and turn off time of 100 nS, but you need to drive the gate properly. While the gate current is negligible, there’s a very large capacitance that needs to charge (look at the gate charge and input and output capacitance in the spec), and when it’s between all the way on and all the way off it will dissipate lots of power, so you usually want to make that transition quickly, though with a 100 Hertz rate that’s probably not going to too bad. Te transient thermal impedance spec will help you there.
Also, if you’re driving an electromagnet, that’s a big inductor, and when you switch current there will be large voltage spikes which can easily damage the part, so you need to clamp that.
If you’re new to this aspect of electronics, one great resource is the application notes manufacturers publish, they want to help you use (and buy) their parts. For example, if you go to http://www.fairchildsemi.com/apnotes/power_management.html#MOSFETs and download app note AN9010, there’s a good introduction to how MOSFETs work.
Hope this helps, and good luck with your project.
Product PRT-10319 |
about 3 years ago
The MAX1555 has a minimum of 100 mA charge current, or almost a 1C charge rate. You could do it, but the battery life will probably suffer. I don’t see any easy way to reduce the current.
A rule of thumb for most lithium batteries is that you should be safe with anything around 1/3 C or lower for charging and discharging. (C being the amp-hour rating of the battery.) So limit the current in or out of this one to about 37 mA or so. I’d recommend ½ C (55 mA) as a maximum. Any more and the overall charge discharge cycle life of the battery will suffer.
A typical charger will first check the battery condition by using a low value test current, then charge for a couple hours or more at a constant current until the voltage reaches the design limit (typically 4.2 Volts). At that point the voltage is held constant and the current is monitored. When it falls to 10% of the main charge current the current is turned off. You must not trickle charge lithium batteries. And usually the temperature of the battery is monitored while charging.
For SFE’s basic charger sku: PRT-10217 you’d want to change R4 from 2 kOhms to about 30 kOhms.
This is for plain vanilla lithium batteries.
There are batteries for RC cars and copters and such that can handle 10C, 20C or more, and folks are working on batteries for cars that can be charged at 100C (essentially taking the same amount of time it takes to fill a gas tank).
No public wish lists :(