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Old Dec 23, 2014, 12:32 AM
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Power Supply Voltage

Why would you choose a 24v power supply over a 12v? Wouldn't the wattage really be the important variable? For example, would a 1000w-12v supply be the equal of a 500w-24v supply? They would both supply the same max current, right? Am I thinking this correctly at all?
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Old Dec 23, 2014, 02:59 AM
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You're right that wattage is important. A 24v supply that can deliver 20A, for example, will deliver twice as much power (watts) as a 12v one delivering 20A.

I'm afraid your numbers are wrong; a 1000W 12v supply will be running at 83A at full output, whereas a 500W 24v supply will only be running at 20A. If that 24v supply were to run at 1000W though (i.e. the same power), it would be 41A.

Amps is usually what kills an electric or electronic circuit, so it's often advantageous to keep them low by building a circuit that can use a higher voltage.
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Old Dec 23, 2014, 03:25 AM
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All of the above.

Plus, some chargers are limited by max power or max input amps, whichever comes first, and can't output full power with 12V input.
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Old Dec 23, 2014, 07:01 AM
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Originally Posted by jkettu View Post
All of the above.

Plus, some chargers are limited by max power or max input amps, whichever comes first, and can't output full power with 12V input.
+1
This is true for all higher power chargers. To realise their full power output potential you need to supply them with a higher voltage DC supply, over 30V in some cases.
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Old Dec 23, 2014, 07:14 AM
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Lets say from the I Charger 106b 250 watts down are rated 12-18 volts,so a 24v PS is useless for small chargers,you have to get into the mid range and up for chargers to be spec'ed 24volts and up.So it's also relative to what power bracket you are in.
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Old Dec 23, 2014, 07:58 PM
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Originally Posted by go_hercules View Post
Why would you choose a 24v power supply over a 12v? Wouldn't the wattage really be the important variable? For example, would a 1000w-12v supply be the equal of a 500w-24v supply? They would both supply the same max current, right? Am I thinking this correctly at all?
Many power supplies are rated for maximum watts capability. They also come in a range of voltage outputs. Standard voltages are 5, 12, 24, 48 and 120 Volts DC output.

Since watts equals volts times amps, Amps will equal watts/volts.

So, your 500 Watt power supply will put out 500 W/5 V or 100 Amps at 5 Volts. Or 500/12 or 41.6 Amps at 12 Volts, or 20.5 Amps at 24 Volts.

The higher powered chargers such as the Cellpro Powerlab 8 charger is rated at 1344 Watts, but only with a 24 Volt DC input voltage. (I've got two of the '8 chargers)

Also be aware that not all LiPo chargers can handle a 24 Volt DC input. If you apply 24 Volts to a unit rated at a maximum 15 Volt DC input, you'll blow the charger. And it won't be covered under warranty.
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Old Dec 23, 2014, 09:03 PM
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Amps is usually what kills an electric or electronic circuit, so it's often advantageous to keep them low by building a circuit that can use a higher voltage.
That's kind of misleading. Excess Amps, excess Volts, and excess Watts will all kill electronic circuits, if any one of them exceeds the ratings of the devices.
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Old Dec 24, 2014, 12:04 AM
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That's kind of misleading. Excess Amps, excess Volts, and excess Watts will all kill electronic circuits, if any one of them exceeds the ratings of the devices.
Add to that static discharge. Just walking across a carpet, and drawing s spark can easily create a voltage well over 20,000 Volts. The current is very low, but damage can result to electronic equipment. They even have a ESD (Electronic Static Discharge) test for making certain your TV, DVD player, all electronic equipment can handle this.

So when reaching inside your desk top computer with its side panels off, touch its metal frame first.
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Old Dec 24, 2014, 02:47 AM
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That's kind of misleading. Excess Amps, excess Volts, and excess Watts will all kill electronic circuits, if any one of them exceeds the ratings of the devices.
It's a generalisation, I know, but I don't think it's misleading in the context of this discussion, namely model aircraft systems.

But you're right, almost anything can kill an electronic circuit if it exceeds the circuit's spec -- we need to include temperature, humidity, vibration, etc. if we want a complete list
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Old Dec 24, 2014, 07:15 PM
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It's not likely a charger will draw excess Amps; sure, there will be a bit more loss when charging a battery with a higher Voltage than the input, but not that much. And, most 'smart' chargers will shut down when the input Voltage drops too low, so that leaves Voltage that is too high. I'd sooner run a charger rated for up to 24V input at something less than that, if only to avoid any damage if the power supply rose above it's normal range when the current shuts off.

As for static discharge - Volts is Volts, and you can't always feel the discharge that can kill electronics. Before touching any unprotected device, safely grounding oneself to a common point is always recommended.
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Old Dec 27, 2014, 12:52 PM
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Ohms Law

Quote:
Originally Posted by go_hercules View Post
Why would you choose a 24v power supply over a 12v? Wouldn't the wattage really be the important variable? For example, would a 1000w-12v supply be the equal of a 500w-24v supply? They would both supply the same max current, right? Am I thinking this correctly at all?
Just use Ohms Law Wheel to find your answer:

http://www.ohmslawcalculator.com/ohms_law_wheel.php
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