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batteries and efficiency


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#1 Jerry Holway

Jerry Holway

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Posted 04 April 2007 - 05:58 PM

On another forum topic, far far away, I made some errors or incomplete statements about batteries and converters, and I felt less than thrilled about it, did a tad of research... so here's what I learned.

Probably (he hedges) all electronic devices we use on the Steadicam have internal regulation of power. If the device accepts 11-30 volts, then inside it regulates the incoming voltage down to some voltage lower than 11 volts (usually 1.5 or so volts lower) and uses that constant voltage to work.

Many complex electronic devices (such as monitors and cameras and receiver amps and, well, pretty much everything we use) have several regulators to provide different voltages - 5 and 3.3 volts for the microprocessors, for instance.

Every regulator has power losses - part of the trade off in vastly increased and stable performance. The best regulators work at between 85 to 95 percent efficiency. It's inconsequential if the device or circuit needs only a few milliwatts or tenths of a watt, but gets more serious (in terms of battery power being wasted) if the device draws a lot of power (LCD monitor backlights, tube monitors, and cameras).

And aside: Lights also draw a lot of power (and incandescents waste most of it in heat), but many of these are not electronic and have no regulators.

A regulator works better - more efficiently - if the incoming voltage is nearly at the highest possible voltage it wants to regulate - but it's only a few percentage points, like 92% efficient vs. 88%.

"Pre-regulating" your battery's higher voltage to the voltage "required" by a device rated at "x" volts, therefore, wastes 8 to 12% of the battery power before it delivers the power to the device, and it makes the internal regulator of the device slightly less efficent as well.

The only good reason to pre-regulate a battery powered system is to bring a battery's (or a multiple battery system's) voltage into a range that a specific device's regulator can handle. A nominal 28 volt battery system will not work with (or it will destroy) a "12 volt" device that has an input range of 16 to 11 volts, so a regulator of 14 volts is needed, and indeed, loses some power.

Would that every battery had a constant voltage and no voltage drop, and every battery chemistry the same voltage, and we could be far more efficient and have fewer regulators...

Hope this helps.

Jerry
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