My dad has dozens of tools and electronics and the charge adapters are all mixed up or lost. So I was looking into getting a universal AC adapter that can be adjusted to work on various products.
Most of his things say the chargers are 1500mah or less, usually much less (300-900mah) and voltage of 12V or less. The universal chargers I’m seeing adjust the voltage usually around 3-4.5-6-7.5-9-12 and they come with various charging tips, but they don’t seem to adjust the amps (the amps are listed as constant on some). Do the amps automatically adjust on any, and how important is that? what happens if something calls for 7.5V and 800mah but the charger is 7.5V and a constant 500mah? Will it damage the product or just charge slower? I don’t know a lot about electronics.
I see lots for $10-15 on amazon, but I want to buy a good one since I figure a bad one could be a fire hazard or damage the products to charge.
Amperage is a capacity, not something you need to match precisely; it doesn’t need to be adjusted. Your device will draw as much as it needs and no more (hopefully, at or near the amperage listed on the old adapter). So all else being equal, a 2 amp adapter can safely power devices from the smallest 300mA widget up to (and slightly over, for most devices and adapters) the full 2000mA.
It’s more or less the same in AC. Your 75 Watt light bulb is desgined to run on 120V @ 60 cycles. It DRAWS 75 watts, it doesn’t need to be wired up specially for 75 Watts.
Radioshack sells a variety of replacement adapters including universals and a variety of tips to fit your particular widget’s coaxial power jack. They’re expensive, though, sometimes more expensive than just replacing the device. I’m in the habit of keeping a stash of AC adapters around. If you have enough of them saved it’s pretty easy to find the right voltage and sufficient current and you can cut and splice the right tip on from another adapter you have laying around.
Storebought or home re-made, one thing to watch out for: check the polarity! Convention is tip positive ring negative, but I’ve seen plenty that apparently missed the memo which can lead to anything from just not working to spitzensparken puffensmoken.
Having established that an excess of current capacity is fine, as to your specific question: can you feed too little current into a device? It depends, what’s the device? Could work but slower or could draw more current than the adapter wants to put out and start making wires toasty. What are you working on?
The ones that I have seen (opened up) just have a transformer with multiple taps on the secondary and a switch to select them. The current rating is dependent on the transformer itself and is limited by the size of the wire used; they could make one that can supply twice as much current at half the voltage (power limited by the size of the transformer) and so on but it would cost more.
Newer models probably use a switch-mode power supply design, which has similar restrictions on output current, although both types may be able to supply more current at lower voltages, but not peak output power (SMPS designs are better since they use a single winding transformer and regulate the output based on the selection, a good design can output full power at any voltage, except perhaps the lowest voltages).
Also, current is determined solely by how much current the device requires - you won’t blow anything up if it needs 100 mA and the adapter supplies 500 mA, just as a 15 amp wall outlet won’t try to supply 15 amps to anything you plug into it unless it draws that much (of course the other way around will lead to blown fuses or overheating of the adapter, many of which don’t have fuses or only a non-replaceable thermal fuse, although SMPS adapters usually have overload/short circuit protection).
Finally, a nitpick: mAh refers to battery capacity, not the current drawn by the charger, which may be much less depending how how fast it charges.
Here is an adapter which looks good, with a maximum output current of 1.5 amps (output power is stated as 10 watts, so presumably it is limited to 0.83 amps at 12 volts, 1.1 at 9 and 1.33 at 7.5) and a pretty favorable rating, 4.3/5 (also a SMPS design, so overloads/shorts won’t/shouldn’t burn it out). Note: I have no experience with Velleman products, so take this for what’s it worth (a few bad reviews, one saying it burned out their equipment, although perhaps they forgot to check the tip polarity).
The universals can adjust the voltage, there’s no need to adjust current. Usually there’s a simple slide switch to change the voltage. Sometimes there 3 pronged connector with different connector sizes. Sometimes there’s a replaceable connector so you pick your size, put the rest away in a safe place, and you won’t be able to find them when you need them. But they will turn up when you are looking for something else that you can’t find.
Phillips makes a good multi voltage, multi tip switchable polarity DC adapter that goes from 3VDC to 12VDC and has a 1 amp capacity.
You need to be careful with some stuff like digital cameras as some (even tiny ones) will want 2-3 amps even though they are small and will throw the internal breaker on the adapter if you try to use them. Yes, I speak from experience.
As others have said, voltage is the important figure, amperage is just a capacity. It is fine if the charger has a higher rated amperage than what your device calls for; this just means the charger is capable of providing more power than your device needs.
However, anything that lists a specification in “mAh” is likely to be a battery, since mAh (milliampere-hours) is a measure of battery capacity. The voltage listed next to this is almost certainly the nominal output voltage of the battery, not the design input voltage for the power plug. It is at least conceivable that you could come across a device that requires a different power supply voltage than battery voltage.
The specification for the power supply will be expressed in volts and amps or milliamps (A or mA), without the “h” indicating hours. Be careful not to mix things up.
That is the model I was looking at because it runs at up to 1.5 amps and the reviews say it is voltage regulated to stay close to the voltage you pick. I have no idea how common it is for AC adapters to provide 9V when you select something like 6V, but supposedly the margin of error is smaller on that model. snowmaster my dad has chargers for battery powered drills, a cheap android tablet, electric screwdrivers, portable DVD players, etc. He didn’t keep the AC chargers identified and connected, so I don’t know which is which.
can you elaborate more on what you mean by
Like I said, I don’t know alot about electronics. I have seen some devices with this diagram, I assume this is what you are referencing.
How would I find that info if it isn’t on the product to charge though? Would the manual contain that info, or do most default to positive polarity (I assume that is what you mean by tip positive ring negative).
Quite common, actually. I just picked up an AC adaptor yesterday which claimed to provide 12V, but actually provides 14V when unloaded - in order to save costs, cheap AC adaptors use the load to lower the voltage, which means that when unloaded or loaded to less than rated power, the voltage is higher than it says.
It shouldn’t make much difference for most applications, but just be aware that it happens - don’t blindly trust a cheap 12V 2A adaptor on something which needs 12V 100ma.
In addition to what Tabby_Cat said, cheap transformer-based adapters, consisting of a transformer, switch, rectifier and filter capacitor (no regulator, which is true with many of them, universal or not), may not have a bleeder resistor across the output, so if you set it to 12 volts, it will charge the capacitor to 12 volts (or more) and it will remain charged at 12 volts even when you set it to a lower voltage, which can be enough to damage sensitive devices (this can also happen in SMPS based designs, but is less likely since the regulation loop will stop switching until the voltage drops to the specified, and even without a bleeder the feedback loop itself uses resistors to divide the voltage down to the feedback circuitry; SMPSs are regulated pretty much by design, although a few cheap designs don’t directly sense the output voltage, which can drift up without a load).
