I've got few questions regarding PSU's/Adapters

[playman]

Hello.
I have few questions I wanna ask you guy's/girl's

1. What is the difference on PSU (Power Supply Unit) and an Adapter?
I ask this because of language barrier.

2. I've noticed on some PSU's/Adapters they are said to be certain voltage
but when I measure them they show much higher voltage.
Example: I have a linksys adapter "Model:AD 12/0.5A" it say's that it's
supposed to give 12v output, but when I measure it, it gives me a reading of 17.6v
Is this normal? On other adapters I've measured the correct voltage.
I've noticed even for the higher voltage the appliance still works and shows
no symptom of malfunction.
Is it ok for me to use them even they are showing higher voltage then given up?
This is the adapter in the example http://azsurplus.com/index.php?main_...oducts_id=1911

3. Is it right that some adapters don't show any voltage when I measure them
with a multimeter because the multimeter does not drain any power from the adapter?
And the only way for me to measure them is to use a light bulb or anything like that so the adapter "knows" that it is connected. (something to drain power from the adapter)

4. Can I charge a battery by only connecting the bare wires from an adapter
to the poles of the battery? with out using any electronic equipment?
I'm talking about rechargeable batteries of course, like 1.5v or even 12v

With hope of detailed answers.

[mariushm]

Re: I've got few questions regarding PSU's/Adapters

1 and 2.

Adapters are also power supplies.

There are several types of power supplies, depending how the lower voltage is produced.

The easiest power supply is a linear power supply, which uses a simple transformer to lower the input AC voltage to a smaller AC voltage, then it rectifies it to DC voltage using a bridge rectifier and smooths out the output a bit using a capacitor.

By the nature of transformers, when there's nothing connected to this power supply, the voltage will be high. When something is connected to it, the output voltage goes down, closer to the specified voltage.

This is an unregulated power supply / adapter.

Your adapter could be this type of power supply. It shows 17v when you have nothing connected to it. The moment you plug the cable in your device and that device starts using some power, the voltage will be less, closer to 12v.

The device either doesn't need very accurate input voltage, or has its own internal voltage converter to convert that 12v DC to some lower voltages like 2.5v or 5v, so accurate input voltage is not important.

From this type of unregulated power supply, a step up is a regulated linear power supply

What happens inside is that there is a chip that monitors the output voltage and if it's above a particular value, it lowers it using some method (linear regulators for example, pass transistors)

These power supplies still use a large transformer, but the output voltage is usually much better, and stays within a very small range of the wanted voltage.

These two types of power supply are very easy to make but they require bigger, heavier transformers compared to other power supply and all the copper in the transformer is expensive

The lightweight power supplies are called "switching power supplies" ... these no longer use a heavy transformer, they use a small high frequency transformer.

The AC voltage is converted to DC and then a chip inside these power supply turn off and on the power going to the transformer 50-100 thousand times a second.

These pulses cause power to appear on the secondary side of the transformer and this is how you get output voltage. By adjusting the number of pulses sent each second to the transformer, there's more energy, more power present on the secondary side, so the output voltage changes.

The simplest switching power supplies don't have feedback, so they're designed from start to always use a number of pulses that would output 12v at 0.5A, for example.
But if your device doesn't use that much current, the transformer receives so many pulses that the voltage on output is higher, maybe at 17v.
This may happen on your adapter.

On most switching power supplies, there's a chip on the secondary side that monitors the output voltage and sends to the other side a signal through an optical isolator which tells the IC to increase or decrease the number of pulses depending on how much power a device connected to it uses, and this way the voltage is always within a small range.


So to keep it short.

An adapter is usually a power supply that outputs only one voltage, and that's either unregulated (higher voltage with no load, closer to specified voltage when has load) or regulated (keeps voltage steady no matter what)

A power supply is usually a switching power supply that is also regulated to a degree, and it's capable of several voltages. For example, the ATX computer power supply outputs 3.3v, 5v and 12v and these are kept steady for a wide range of current.

3.

Generally no. There are devices like Apple's iphone, ipod etc that use some tricks to detect if the adapter or charger are genuine and refuse to take power from them or take a very small amount of power if they think they're no genuine.

Dell laptops for a while had adapters with a special jack with an extra pin inside, which sent a sort of password (a series of pulses) to the laptop when the jack was plugged in. If the password was not right, the Dell laptop would refuse to use the adapter.

Apple uses USB jacks to charge, which have two wires for power and two wires for data. The trick Apple uses is to send through each of those 2 data wires a voltage of a particular value. If the phone doesn't see that voltage, it won't use the charger, or will only charge slowly.

4. No, you normally can't charge a rechargeable AA battery just by connecting it to a power supply.

Batteries have a charging curve and they have to receive limited power while charging... the current has to be limited, otherwise the batteries overheat and can be damaged or explode.

Battery chargers send a burst of power to the batteries, stop for a bit, and repeat the process and constantly check the voltage on the battery and at some points they increase the current.

[playman]

Re: I've got few questions regarding PSU's/Adapters

Man thank you so much for this information.
That was way better response then I hoped for

4. No, you normally can't charge a rechargeable AA battery just by connecting it to a power supply.

Batteries have a charging curve and they have to receive limited power while charging... the current has to be limited, otherwise the batteries overheat and can be damaged or explode.

Battery chargers send a burst of power to the batteries, stop for a bit, and repeat the process and constantly check the voltage on the battery and at some points they increase the current.

Tell me, how can I spot if the item, let's say I have a kid electronic car, the kinds you buy in toy's R' us,
how can I know it has a inbuilt battery charger, and not in the adapter?
I have the car but not the adapter.
And do adapters have battery charger inbuilt in them, is there any way to know that, that is if they have it.
Or are maybe never battery charger in adapters?

I hope you understand my question

[ben7]

Re: I've got few questions regarding PSU's/Adapters

Man thank you so much for this information.
That was way better response then I hoped for



Tell me, how can I spot if the item, let's say I have a kid electronic car, the kinds you buy in toy's R' us,
how can I know it has a inbuilt battery charger, and not in the adapter?
I have the car but not the adapter.
And do adapters have battery charger inbuilt in them, is there any way to know that, that is if they have it.
Or are maybe never battery charger in adapters?

I hope you understand my question

Usually they will say that they have a current limited output, or that they are actually a battery charger.

[Behemot]

Re: I've got few questions regarding PSU's/Adapters

You can use resistor to limit the current while charging.

Anyway, for some types of acumulators it does not matter at all. For example lead batteries can be charged directly, they have low internal resistance, but as the charging is chemical process, it can only happen at some speed. The battery regulates itself; the current is high at the beginning (but not incredibly high, couple amperes usually) and than drops as the battery charges and the voltage difference lowers also.

Definitelly don't charge Li-On cells just like that, they are very sensitive to overcharge and like to explode.

[ben7]

Re: I've got few questions regarding PSU's/Adapters

The kiddie gocart is very likely to have an SLA battery inside. (SLA = Sealed Lead Acid, very similar to a car battery). However it could have a gel battery too.

Almost all batteries (NiMH, SLA, LA, Gel, NiCd) can be trickle charged at a constant current, and even when the battery is charged, the built up gases inside from the overcharging will be converted back to electrolyte by some chemical conversion. This allows these batteries to be charged by a 'dumb' charger, although quite slowly! A smart charger usually charges with a much higher current, but it detects the charge level (the 'smart' part) and shuts off or drastically decreases the charge current to avoid damaging the battery.

-Ben