I know this is probably something simple, but it is not something I’ve ever needed to learn.
We were having some problems in the lab, we had received a spectrometer but no power suplies for it. So we looked around for some power supplies that seemed to fit. And we picked up some AC adapters (that is all that is written on them) and to cut a long story short (involving motorcycle batteries and magnets) we managed to get all the power supplies we needed. Then we proceeded to blow part of the spectrometer (when the smell of burning and smoke starts coming out, that is a problem).
So after all this my question is : How do AC adapters work? Do they convert AC to AC; or AC to DC? I have seen some adapters that say ‘AC/AC Adapter’, and I know that AC/DC adapters do exist, I have one for my CD player. So how do I tell the difference between the adapters?
Also, on the adapters was a metal block, what does this do? It wasn’t magnetic and just sat there. Any ideas?
And all this was in Sweden. I would take responsibility but I am a Chemical Engineer, and the computer/electronics people here are worse than useless. They know the software but have not got a clue about the hardware.
Usually, AC adaptors convert AC voltage from the wall outlet into DC voltage. This is a simple 2 step process where the voltage is first dropped to a usable level with a small transformer, and then rectified into DC.
The transformer is the heavy-ish thing encased in plastic that has the prongs sticking out of it which plug into the wall outlet. Transformers can be wound differently, to produce different DC voltages at the end of the cable, and the cable terminations are (usually) a standard size for a given voltage. Often though, lab equipment manufacturers will avoid using standard sizes in favor of their own “proprietary” designs, to that you must deal with them and them only.
Probably the easiest way to see what you need is to look for markings or symbols on the instrument right next to where the power cord plugs in.
And AC/AC adapters exist also, but they’re a different animal. They are little adaptor plugs that have slots on one side to accommodate your American made 120 volt hair dryer, and chubby prongs on the other side to fit into the standard 240 volt outlets.
And your spectrometer, is it a benchtop device or a handheld unit? If you already think it’s destroyed, don’t be afraid to open up the case and try to find a blown fuse. It would be the first thing to melt (hopefully) if you applied the wrong voltage. Often they’re easily replaceable. Just make surre it is not connected to any power source at all, including your motorcycle battery and magnet contraption.
Thank you very much honkytonkwillie. That was very informative.
Just clarification on one point, the metal black was hanging on the cable, about 50cm from the adapter (in the wall) and closer to the spectrometer (which is just a small device). Does this negate the heatsink idea? Or will the heat be transmitted along the cable? Or is it more to stop any unwanted magnetic pertubations?
And what is an RFI shield? See I told you I have no idea about this stuff. Give me Bernouilli’s equation anyday.
Smoke probably means it wasn’t a fuse that blew. Smoke is bad.
Usually, the AC->DC transformers will have markings which describe what they do. Something like, “Input: 120V AC, Output: 9V DC, 750mA”. Often, the device being powered by the transformer will have markings saying what it wants as input. Something like “Input: 9V DC 750mA”. This should match the output of the transformer.
Usually, if you match the output voltage of the transformer to the input voltage of the device, and the output amperage of the device is close to the input amperage of the device, it’ll work fine.
Another thing to worry about is polarity (i.e. the plug going into the device is coaxial, and sometimes the outer contact is positive, with the inner contact negative, and sometimes it’s the other way around). As far as I know, the polarity for most devices is the same, although I don’t have anything handy to check which way it is. Most of the time, the polarity isn’t indicated on either the transformer or the device, but if it is, it will look something like:
–o)-- -
(except imagine the curved part going most of the way around the dot, in a nearly-complete circle). This indicates that the center pin is positive (+) and the outer contact (the “ring”) is negative.
I think most devices are idiot-proof enough that they don’t care in small variations in amperage, and they don’t care about the polarity. I experiment with the “wrong” transformers all the time when I can’t find the right one, but then again, the equipment I do this with is generally not expensive lab equipment.
Your mileage may vary. Don’t blow up much more stuff.
I would go along with most of Galt’s excellent advice, and I am impressed with the very creative ASCII representation of the polarity markings on the transformer. (Note: IANA Electrical Engineer)
A few points:
An “AC adapter” is probably for transforming 110V AC to 220V AC, or vice versa. An AC output will usually be a socket (think about it), while a low-voltage DC output will often be in the form of a round “jack plug”.
The smoke effects sound like you fed the spectrometer with the wrong mains voltage rather than a slightly wrong DC voltage. If so, the spectrometer power supply will need to be replaced.
The rated current of the transformer should be greater than the current drawn by the device, not “roughly the same”.
With DC outputs, polarity varies a lot, and the range of voltage outputs is wide enough to destroy electronic equipment.
There are better ways of checking the voltage at the output of a transformer than connecting it to expensive equipment.
The thing hanging on the cable is most likely a “ferrite choke” and is, as you guessed, designed to reduce or eliminate interference from traveling on the power lead.
And your spectrometer is probably not toast. If you can find any 2nd semester electronics student, they should be able to replace the burned components in the device, so long as the board is not double sided or uses silver solder.
Most of the time there is a protection diode fixed to the DC input jack, the purpose of which is to blow the fuse in the power supply by drawing excessively high current in the event that it is connected with reversed polarity.
There are AC/AC transformers out there and they generally look just like AC/DC trasnformers to the average consumer. The trick is to read the markings and determine what the expected input and output values are.
AC/AC transformers for consumer products most commonly used for external modems these days. The ones I’ve used have mostly been 110VAC>9VAC and 110VAC>20VAC.
How to tell AC/AC from AC/DC transformers if there is no lettering to say so: DC types will often have a little symbol with two parallel lines, one of which is dashed and one is solid (Sometimes there is a humped line
nnnnn
sperating them. This represents the coils in the transformer). The dashed line represents AC, the solid line means DC.
When all else fails, get out an oscilloscope or multimeter.
A note on current ratings: If you have a device that requires, say, 200mA@9VDC, and you are looking for a transformer, You need a transformer with a current rating equal to * or greater than* the max required current. I don’t know how many times I’ve heard “I can’t use that 1A transformer, my device only needs 150mA.” [oversimplification] You cannot force current down a line. It flows only as much as the voltage of the supply and the resistance of the load allow. [/oversimplification]
Well, still don’t know what is wrong with the spectrometer, but as this was the first time we tried to use it, they are sending us a replacement under warranty. We didn’t mention the whole battery cutting up wires and stuff. So this works for us. Just curious how they worked.
And the information provided by all of you has been very helpful. And I understand more now. This just goes under the useless information folder in my head. Not something I’m ever going to be asked to do.
Feel free to continue discussing this. The AC/AC adapters that I saw looked just like the AC/DC adapters, which was why I asked. We use them for web cameras.
Just looking around, the first adapter that we used was possibly an AC/AC adapter. Think we found the problem. Hey one little bit of ignorance defeated today. That’ll teach them not to send power supplies with the equipment.
FloChi
Sewalk has the best answer for telling the difference between AC/AC and AC/DC plug-in adapters (AKA “wall warts”). Sometimes, the labelling is not easy to read without very bright light, as it will be etched into the casing.
Two things for using different adapters with not-their-original devices :
1.DO NOT use the wrong voltage adapter – this is what will cause more problems than anything. If the voltage is too low, it simply won’t work. If it’s too high, you’re liable to blow a fuse or worse.
You may notice that some devices will use a slightly higher voltage (within 1-2 Volts) adapter than what the device is rated for. This is okay (it means they take care of the slight mismatch inside the device). I’m only referring to products that come with such adapters. Don’t try it with anything else, since most devices won’t take care of the mismatch.
2.Using an adapter with a higher current rating will always work, though there is one warning that applies to rechargeable devices.
These are run on rechargeable batteries; the battery is often connected directly to the adapter. If you use an adapter with a much higher current rating than the recommended, you are liable to greatly shorten the lifetime of the battery. These are the one kind of device for which, if you’re stuck with nothing else, you can use a lower current rating (with matching voltage, of course). Most likely it will take a much much longer time to charge the device than normal.
panama jack
