How to buy a 9V 3A AC Adapter

[bobcat2000]

Hello All,

I am looking for a 9V 3A ac adapter.  Reading reviews from Amazon by itself is an exercise.

I see 2 of these.  Is it bigger the better?

Thanks!

[ledtester]

What are you going to use it for?

The second one has a display and a knob for adjusting the voltage which is convenient but it also means the voltage could be changed if it gets accidentally bumped.

The first one is better for an unattended, permanent installation - the second one would be better as a power supply for testing things out.

[bob91343]

I am very suspicious that these have poor, if any, regulation.  You would be better off with an old CB 3 A power supply with an added regulator.

Plus, I never buy from Amazon.  Prices too high.  Try ebay or Aliexpress.  Maybe All Electronics has what you want.

[bdunham7]

Those are DC adapters.  Which is it that you want and what will it be powering? (it all matters quite a bit)

[rsjsouza]

These adjustable models might be very sketchy when operating at their extreme capacity.

I would trust a fixed output voltage from a good brand - for example, this 30W CUI SDI36-9-UD-P5 is one of them.

[mariush]

Do you actually need AC output  or DC output ?  It's two totally different things.

You can buy an adapter rated for higher current than 3A, that value is just the maximum the adapter can provide.

Distributors of electronic components like Digikey Mouser Newark/Farnell have tons of such adapters
For example, here's Digikey's selection of 9v DC adapters with current rating equal or higher than 3A  (up to 100w, around 11a) : https://www.digikey.com/short/rvtf20vf

[james_s]

The term "AC adapter" is commonly used to mean any power adapter that takes in line voltage AC and outputs some lower, isolated voltage, whether AC or DC.

I would look at Mouser or Digikey instead of Amazon. Real electronics suppliers tend to carry better quality stuff like this, with more reliable specs. 

[bobcat2000]

Thanks guys!  I can see that there are many options.

I need one for a dehumidifier that comes with a 9V 2.5A ac adapter.  The cap inside bursted.  It was running 24/7.  Maybe that was why.  The power brick ran quite hot drawing 2+ amp.

The cost is the primary factor.  Buying from Mouser may not be possible.  The ac adapter is like $20 plus another $10 for shipping.  That is $30+ expense.  I can save the shipping if I add up $25 buck from Amazon.

I also agree that the one with a dial is not idea.

Amazon also has a bigger one with the selector.  Is a longer one better than the small one?

The dial or the selector is just there for changing the resistance to the switching circuit.  Correct?

[Gyro]

Thanks guys!  I can see that there are many options.

I need one for a dehumidifier that comes with a 9V 2.5A ac adapter.  The cap inside bursted.  It was running 24/7.  Maybe that was why.  The power brick ran quite hot drawing 2+ amp.

The cost is the primary factor.  Buying from Mouser may not be possible.  The ac adapter is like $20 plus another $10 for shipping.  That is $30+ expense.  I can save the shipping if I add up $25 buck from Amazon.

I also agree that the one with a dial is not idea.

Amazon also has a bigger one with the selector.  Is a longer one better than the small one?

The dial or the selector is just there for changing the resistance to the switching circuit.  Correct?

Ok that clarifies - you want a 9V DC output mains adapter with a minimum output current of 2.5A.

I would definitely go for one without a voltage selector for the reasons previously discussed. (the knob adjusts regulated output voltage, not resistance btw). I would also go for a rectangular laptop style rater than a 'wall wart' due to the weight - particularly with US outlets.

If you want it to run cooler and with longer life then there's no harm in going for one with a higher current capability, for instance, 5A.


P.S. Double check that the output connector polarity is correct (centre +ve etc). It's easy to screw up with those multi-plug kits.

[ledtester]

The dial or the selector is just there for changing the resistance to the switching circuit.  Correct?

It is likely the adapter uses a switch-mode power supply inside and the dial/selector changes a feedback resistor to adjust the output voltage.

[bob91343]

If the original one has a bad capacitor, why not do a repair job?

[bobcat2000]

I thought about fixing it.  But that will be another $10 to buy a bag of cap.  The AC adapter looks well made.  The board looks burned front and back though.

I would rather spend the money to just buy a new one for like $40 if I had to spend $10 here and there.  Driving to the place to buy a parts will cost a lot of gas.  The cost will add up.

[james_s]

How about this? https://www.ebay.com/itm/164138851093?hash=item2637701b15:g:txkAAOSwN~Vee~rv

Do check the output connector, most are center-positive but some are center negative, there is no standard and if you get it wrong it will usually damage your device.

[Gyro]

Yeah, that's been running too hot, the board is delaminating. Caps wouldn't fix that.

[james_s]

It may have been running hot due to failing caps, which of course will fail faster when it's hot. Replacing the caps probably would fix it, but whether it's worth it is certainly debatable.

[bobcat2000]

Come to think about this.  Those dehumidifiers use Peltier chip inside.  Can I just use a 12V 3A AC adapter instead of the 9V one that come with the unit?

I have a bunch of 12V 3A adapters.

Thanks!

[james_s]

Maybe.

The higher voltage will cause it to draw more power, so the cold side will get colder and may ice up, more importantly the hot side will get hotter. If it were mine and it was not some kind of valuable heirloom I would try it while monitoring carefully.

[perieanuo]

Hello All,

I am looking for a 9V 3A ac adapter.  Reading reviews from Amazon by itself is an exercise.

I see 2 of these.  Is it bigger the better?

Thanks!

hi, i guess you mean DC adapter
not bigger, heavier is better. buy second one

[Zero999]

Come to think about this.  Those dehumidifiers use Peltier chip inside.  Can I just use a 12V 3A AC adapter instead of the 9V one that come with the unit?

I have a bunch of 12V 3A adapters.

Thanks!

Assuming it's just a resistive load, the power will go up by a factor of nealry 1.8, as P = V²/R.

How often do you use the dehumidifier? Is it on continiously? If so, you probably won't like my suggestion, but your best bet is to toss it and buy a more expensive compressor based one. Peltier coolers are cheap, but very inefficent and cost a lot to run, for the same cooling power, compared to a compressor refrigeration unit. If you use it a lot, you'll save money in the long run, by investing in a more efficient dehumidifier.

[bobcat2000]

That was what I was wondering.  I run the thing 24/7.  It draws 9V 2.5A.  So, it is about 23W/h.  23W/h x 24h x 30 days. = 17KW/month.

Is my calculation correct?

[james_s]

KWh per month, but otherwise yes.

[bobcat2000]

Hmmm... The compressor types use close to 800W/h.  Not cheap.  I think I will continue to look for a 9V 3A adapter instead.  Cheaper.

[bdunham7]

Hmmm... The compressor types use close to 800W/h.  Not cheap.  I think I will continue to look for a 9V 3A adapter instead.  Cheaper.

How much water does it extract from the air in a day?

[james_s]

They don't have to be run continuously. If you look at it on a basis of energy consumed per quantity of water removed, the compressor type is much more efficient.

[rsjsouza]

Indeed. I have a few small Peltier models and have been considering changing to a larger one. You run the smaller ones 24/7 and the bigger one for one hour or so. I had a borrowed one and it extracts much more water, which most probably saves you energy in the long run.