Is it hazardous to use a 3.7 V output adapter to power a 7.5V.DC electronic item?

Question

I lost the original adapter and this one fits, so can I?
Will there be electrical fire or soething bad?

Please verify that you are an expert in this field if you can.

Answer 1

If you are using 3.7V to power a 7.5V item, it may not work in the first place because the voltage is too low.

However, if the tolerance of the electronic device is very wide (unlikely), then there might be a chance that it may work. Typically for non-motor driven devices such as a radio.

Make sure that the polarity of the (+) and (-) is correct. You are unlikely to damage the item with an under voltage.

Under very special situation:

If your electronic device requires only very little current. There is a chance that your 3.7V adapter may appear as 3.7V x 1.414 in some cases, converting to peak voltage, which means it is 5.328V.

But there is still a difference of 2.172V. Additionally, if your device has a wide operating voltage, then it may work. But the chances are slim.

So, in conclusion, it will not likely to destroy your device and it is not likely to work either.

Answer 2

Firstly, so long as the adapter will provide as much current as needed or more current then it will not catch fire or do anything dangerous. Neither will the device take more current because it's being run at a lower voltage (despite the earlier answer stating this). Electronic devices take less current when run at a lower voltage, not more. I presume they were thinking that to keep the same power at lower voltages you need more current, but that isn't what is happening here. You can consider your device to be a resistor, as the voltage is dropped so the current taken is dropped as well.

Secondly, unless it's a regulated 3.7v output it might be giving more. Lots of (unregulated) adapters are designed to give the stated voltage at the stated load.

Thirdly, although it's important to run the connector in the right polarity for the device to work as stated by an earlier answer, I have yet to blow up something by putting such a low voltage onto it the wrong way. In fact, I have often used the following method to work out the correct polarity and voltage of a device when I've not got the info:
1) Using a variable voltage adapter, set it on it's lowest voltage. If the device works, great, you've got the voltage and polarity right.
If not, change the polarity and re-power up. Does it work yet?
If not, increase to the next voltage and repeat 1)

I have never ever blown anything up using this and most equipment has a blocking diode so that even if it is incorrectly driven it can't be damaged anyway.

3.7v is hardly enough to damage anything which is rated at 7.5v though even if the wrong way around.

What about if the current is too low from the adapter? Firstly, it will either have an internal fuse which it will blow or it will warm up. It's not likely to catch fire (it's pop before it explodes!) if you just turn it on and just keep an eye on it for 10-15 minutes to see it doesn't get overly warm.

At such low voltages, I'd plug it in and see if it works, then change the polarity if it doesn't. If it then doesn't work, hard luck but you won't have blown up your device nor probably your PSU. If the voltages were higher, I'd use the previous method.

I'll leave you with a final question: How do you verify I'm an expert in this field and how do you know I'm telling the truth?

PS If you do follow my advice, e-mail me and let me know how you get on.

Answer 3

Without knowing what kind of device that is, I can only speculate things here.

Let's do an assumption first. That is your adapter has enough power to provide to the electronic item.
With that settle aside, here is my analysis.

If you device is a relatively low tech or el cheapo item, I will say there is a very slight chance it may get damage.
I consider a good design will incorporate a brown out protection that will stop any activity going when the input voltage is not
correct. On poor and el cheapo designs, all bets are off.

Even it is not damaged, your input is 1/2 of what requires. i doubt the design will allow input to go that low.

I don't encounter devices that uses 7.5Vdc. Most of them are either 12V, 9V or 6V. There must be some reason why they select a 7.5Vdc adapter.

What is your current on the adapter, if that is a lot, then don't bother. Go find yourself a replacement.

If the current demands is 2A or less, I would try to find a 9V adapter and then put several power diodes to drop the voltage down.

In some case, there are some 6V adapter that will have voltage in the 7V range at the output.

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In short, I am 99 % sure that the adapter will not work. the voltage supply is less than 1/2 of the nominal input voltage. The only thing I am not sure is whether it may have irreversible damages.

To salvage the situation, I would go to electronic surplus store and pick some available adapter to play with, if you are handy with electonics.

Hope it helps!

Answer 4

Not very smart at all to try for several reasons. First under voltage, as well as over voltage, can damage your electronic item. Second when you decrease the voltage your current will rise which most likely will cause your adapter to burn out. Last there is the issue of polarity which may be different on the other adapter you try. Just because the plug is the same size doesn't mean it will work. If you reverse polarity + or - to the tip then you also can destroy your electronic device. My suggestion is check and see the polarity of the plug first. Is it a positive (+) to the center or a negative. Next find the current rating of the 7.5VDC adapter. With that information go to a Radio Shack who sales replacement adapters that will work on most devices. You can even try it while in the store to make sure it's going to work. WalMart and other stores also sell the same things in their electronics department but don't go substituting devices into your electronic equipment just because the plug will fit. Hope that helps.

Answer 5

What a lot of different opinions!
Yes, I do this a lot. But an expert would tell you to buy a proper power supply.
On the other hand, I think it's OK to try it, because there is a good chance that, lightly loaded, you power supply of 3.7 may actually generate 5 volts, and your 7.5 V device may actually work down at 5 V.

MOST IMPORTANT is current. Read the lables if you can.
Look for how many mA (miliamps) the power supply can give, and the 7.5 V device needs. As long as the power supply is greater than (or almost equalt to) the 7.5 V device then you are probably OK. To be sure,try it, see if it runs, and then check if the power supply gets hot. That's bad. Power supply getting hot is a sure sign that it does not have enough current (mA or amps)

Answer 6

Depending on what you are powering, yes, it can be hazardous.

If the equipment has any motors in them, by powering 7.5V motor with 3.7V power supply will cause it to either turn very slowly or not turn at all. Motors will present near dead short when it is not turning. This is because by turning, the coils get switched on and off reducing the average current. If it doesn't turn, it will be continuously on. It could overheat and possibly cause fire. (although unlikely)

If the equipment contain any TTL digital circuits, 5V minimum is required. When it is supplied with under voltage, the results are unpredictable.

Hazardous or otherwise, it will be ill advised as whatever the equipment you will be powering won't work anyway with as much as 50% lower voltage.

I don't know if I would call myself an expert but I have few years of experience as a prototype and small quantity production engineer in mostly small signal equipment.

Answer 7

No it is not hazardous to use a 3.7V adapter on a circuit requiring 7.5 Vdc. It just will not work because there is not enough voltage to power the circuit.

Answer 8

A fire nearly broke out when my daughter used the adapter to a drill on her scooter... I would call the manufacturer to get another adapter!

Answer 9

Don't do it.

Take the adapter that fits to Radio Shack and tell them you need an end just like that one on a 7.5 VDC adapter.

Answer 10

i would advise against it the last time i did something like that I shorted out the electronic item and had to get a new 1