Can I use a charger that provides the same voltage but a different amperage?

Chargers and power supplies come in a wide variety of configurations. Choosing the right one is important. I'll look at a few of the parameters.

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I’d like to know if it is okay to use a different power charger for my netbook. Originally, the charger specs are 19v and 1.58A. This charger is not available anymore and I can only find a 19v and 2.15A. Can I use this as a replacement?

Yes.

With a couple of caveats, of course.

Getting the right power supply – if it’s not made specifically for your particular model of computer – involves matching voltage, amperage, and polarity.

And each have different constraints.

Voltage

Let’s start with the simplest.

The voltage output by your charger/power supply should match as closely as possible. In your case, you’ve got that covered: you had 19 volts before and your replacement candidate is also 19 volts.

When replacing an external charger for a battery-based device like a laptop or netbook, it’s important to get the right voltage. The device may work with voltages that are close, but often at the cost of shortening the lifespan of the batteries being recharged.

When replacing an external power supply, the same rule applies – except that you may be shortening the lifespan of the device by not getting the same voltage.

Or you may not.

Some devices are quite tolerant of voltage variations and will work just fine. Others, not so much.

Because there’s no easy way to know which category your device falls into, it’s best to simply get the right voltage from the start, if at all possible.

Amperage

Many people are confused by amperage ratings and what they mean when it comes to power supplies and replacements.

One easy way to look at it is this:

  • Voltage is provided by (or pushed) by the power supply.
  • Amperage is taken by (or pulled) by the device being powered.

In other words, while the voltage is a constant and should match, the amperage is something that varies based on the devices need. Your computer will “pull” more amps when it’s working hard than when it’s not. The voltage will remain the same regardless.

The amperage rating of a power supply is the maximum number of amps that it’s able to provide if needed.

Thus, as long as you replace your power supply with one that is capable of providing as much or more amps than the previous supply, you’ll be fine.

If you replace the power supply for some reason with one that has a maximum amperage rating that is less than the previous and less than what your device actually requires, then you may end up with a burnt out or (at least) overheating power supply, and the device itself may not function, or may not do so well.

Polarity

This one catches many people by surprise, especially when replacing simple or small power supplies with generic replacements.

Most power supplies provide DC (direct current) power via two wires labeled positive and negative. Polarity refers to which wire is which.

Just because the physical plug into your device matches doesn’t mean that the positive and negative connections are hooked up the right way. In fact, there’s often no real standard.

Particularly when it comes to popular circular power connectors, make sure that the expectations match: if the device expects the center connector to be positive and the outer ring to be negative, your power supply’s connector must match. If the device expects it the other way, the connectors must still match. There’s no getting around this.

Often, you’ll see some kind of indication on the power supply that will show which connector is negative or positive.

If you’re replacing a power supply that uses a custom connector used only by one manufacturer, then typically you don’t have to worry. Similarly, if the device is powered over a USB connector, that standardizes the connection, too.

Summary

In short, when replacing an external power supply or charger:

  • Make sure that the voltage matches as closely as possible.
  • Make sure that the new supply is rated to provide the same amperage or more.
  • Make sure that the connectors match, both in physical form and in polarity.

There are 32 comments:

  1. Robert R Reply

    Interesting analogy for volts vs amps. I’d always heard the water hose comparison, voltage is the water pressure, amperage is the amount of water flowing through the hose.

  2. David Price Reply

    Very well said (sound electrical opinion) I agree completely. David (Australia).

  3. Dan Reply

    Just be careful with some laptops. I know that with my Dell laptops, if the chip in the charger goes bad (the chip that tells the Dell laptop that this charger is the correct charger for the computer), it will no longer charge the battery, and the laptop will draw less power (or amps – but Amps times Volts gives you Watts – or power) – thus slower laptop. Their reasoning, is so you don’t plug a charger in that isn’t rated for your laptop and damage it, but it forces you to only buy the correct Dell chargers, and when that chip goes, even if the charger is working – you no longer can charge, and you have a slower system (even my USB ports wouldn’t produce the correct power output when the Dell isn’t able to read the charger’s chip.)

  4. Steven Reply

    You mentioned “most” are DC currents. I think you should caveat that with most “U.S.” I may have missed it, but I didn’t see that mentioned.

    The output of most power supplies and chargers is DC world-wide. The input is typically AC world wide, but with voltages that differ depending on where you are.

    Leo
    01-May-2012

  5. Mike Reply

    Very good explanation. Two other problems arise, though. The TYPE of voltage. While most chargers are DC, some are AC or pulsating DC, which just will NOT work place of the correct one. AC chargers are usually represented by a tilde (~), and pulsating DC chargers are indicated by a solid line over a dotted line, kind of like highway dividers where there’s no passing in one direction.

    The other problem is size of the coaxial connector, and the combinations are nearly endless. There is the I.D. or Inside Diameter, which is what size the pin will fit into, and then there is the O.D. or Outside Diameter, which is the outside ring that plugs into the device to be charged.

    Nothing more frustrating than to spend $10 – $25 on a replacement charger and find that it doesn’t fit at all. And often, none of the adapter fittings work, either.

  6. Jim Cooper Reply

    Dell Laptops have that center pin, I forget what the interface is called, but it makes it likely that other chargers won’t work. I bought a higher amp Dell charger to replace my busted one, and it works great, but I had a Dell parts expert guide me to the right choice

  7. Yeppers Reply

    Leo, what are the voltage and amperage ratings of a USB 2.0 port on a PC? I’m looking to purchase a USB recharger that plugs into the wall for use with a MP3 player when traveling without a PC. Do the rules you list in the Summary section apply to a USB wall recharger? (By the way, does the voltage and amperage output for each USB port decrease when you are using more than one USB ports at the same time? And are the power ratings for a USB 3.0 port different from a USB 2.0 port?) Thanks…

    I believe that USB provides 5 volts at 0.5 amps maxium per connection (that’s often whil you’ll find some devices that connec to two USB ports, because they need more than 0.5 amps but less than 1.0). Remember what the article said: the voltage remains constant, and the amperage is dependant on the device’s needs, regardless how many are connected. USB wall chargers have to provide the same voltage (like the article said, it’s fixed), but some are capable of providing higher amperage for those devices that can use it.

    Leo
    01-May-2012
  8. Andrew Keir Reply

    “Amperage
    Many people are confused by amperage ratings and what they mean when it comes to power supplies and replacements.
    One easy way to look at it is this:

    Voltage is provided by (or pushed) by the power supply.
    Amperage is taken by (or pulled) by the device being powered.”

    - facepalm -
    [rant]
    Oh Leo, you’re a great IT guy but not so hot at getting electronics across to beginners. I could agree with your definition of Voltage – the ‘push’ on the electrons that tries to make them move and make a current, but not your definition of Current. The load / laptop / whatever does NOT pull – it lets the current through; faster if the resistance is low, slower if it’s high. Current is how fast the electrons (that carry the charge) are moving.
    [/rant]
    But I thoroughly agree with your working rules; get the voltage exactly right, and only substitute a higher current power pack where a lower current one used to be.
    And if you use a different size plug you’ll be sorreee…

    I stand by the analogy (or is is a metaphor?). Of course it’s not technically correct, analogies rarely are. But in terms of making the concepts usefully understandable to people who don’t care about Ohm’s law I think it works.

    Leo
    01-May-2012
  9. Steve Reply

    For Mr. Keir. I prefer to think of current as volumn and voltage as pressure. An example being a water pipe with a pressure/voltage of 10psi and a diameter(volumn)/current of 1 inch allows so much water through. Increase the volumn/current to 2 inches and it lets 4 times as much volumn through. aka available wattage. ( I think I got that right) Its been a long time….

  10. Peter Mackin Reply

    Leo, I agree with your analogy re power supplies. However, your statement that voltage is constant is not correct. If you load up a power supply, you will have losses in the wire that connects the supply (wall wart) to the device. Engineers like to refer to this as I^2R (I squared R) losses. The losses increase a the square of the current so a doubling in load will more than quadruple the I^2R losses in the wire. These losses cause a voltage drop in the connecting wire so that the voltage seen at the load drops when the current increases.

    As you said, if you get a supply rated at the same voltage as the one being replaced and with a current rating at least equal to your device’s requirements you will be fine with respect to I^2R because these losses will already be accounted for in the design of the power supply. I just couldn’t resist picking a nit. :-)

    Peter

    Yep. And for the audience and use for which this article is targeted that nit is just unnecessary distraction. :-) (My degree is actually Electrical Engineering, so I do have a clue about how complex this can get. However my audience isn’t nor should they need to be. Smile)

    Leo
    01-May-2012
  11. Hilary Reply

    This is a great and *necessary* question-and-answer. At the risk of seeming politically incorrect, it may be more helpful to female computer users than male. In 2007, my terrific but three-year-old Lenovo laptop was fried after a now defunct, major electronics dealer opened a Kensington “choose-your-AC-tip” package, stuck it into the power supply, and “told me” it was right. The laptop fried within a week, and I resignedly concluded that its age was the problem. Several months later, packing the otherwise new Kensington adapter set to sell, I read the Instructions that came with it. I also noticed that the little baggie that held the color tip I *should* have used was unopened. In short, I settled with the retailer’s insurance carrier on the eve of its bankruptcy. Otherwise, I would have been out not only an excellent machine, but the amount I paid for the tips. I’m making this comment to warn husbands with non-electronic-savvy wives not to allow any “expert” to tamper with equipment on the basis of the (stereotypical) assumption that because an “expert” is male, he knows all about electricity and how it works. (I hope I don’t offend anyone, but I have seen other cases where female computer users just assume that men understand all about electricity.)

  12. Allen Reply

    Very good article and comments. No mention was made about Lithium Ion batteries and their associated chargers. The little bit of reading I did on the topic scared me away from exploring substitute chargers for Lithium Ion batteries. Was I being too cautious?

  13. packrtz Reply

    I’m not sure your answer about current rating is truly “exact”. When you refer to replacing a charger with equal voltage with equal or greater current rating you are “sort of correct’ -BUT — the issue of current is a bit fuzzy. IF you want to run the device off the charger it MUST have a current rating equal #or greater# – however if you want to CHARGE a battery a lower current is permissable! The HIGHER the current rating of the CHARGER the faster the battery will charge.

  14. A. Orcan Reply

    Chargers come in many qualities. A 19V charger with lower quality may have 21-22V when no current is drawn. However, a charger intended for brand A with 1.6 Amp will have about 19V at full charge and operation simultaneously. With the battery charged, it will have about 19.5-20.5V output fed to a laptop and the battery will continue charging at a negligible trickle rate. When a more powerful charger with 2.5 Amp rating is used, intended for laptop B, with higher power consumption, its output with the laptop A maybe as high as 20-21V with full current drawn and higher after charging finishes. This will cause a higher charge to a battery, even after it is completely full and shorten its life and may even cause an explosion. The chargers are PWM regulated, and ideally such problems would be avoided, but to keep costs down, regulation is not 100% and compromises against costs are made. Exceptionally good chargers are not common and these cost very high. At home, I use a variable Voltage and current supply to monitor and adjust charging curve against time to match aging characteristics of the battery. Travelling, I use chargers with a display and Voltage adjustment slider to prevent overcharging at high levels for my two laptops.

  15. Sara Reply

    Hi Leo … I need some help out here …

    I have a Vaio laptop
    the original charger which is gone now has :
    19.5 V
    Input: 100-240 V ~1.6 A 50/60 Hz
    Output:19.5 V … 3.3 A

    No here is the new charger I got :
    19.5 V
    Input:100-240 V ~1.3 A (1,3A) 50-60Hz
    Output:19.5V(19.5v)…. 4.7A(4.7A)

    the Amperage in new one is less input but higher output !!! compared to the old one .which one counts?
    I am worried it burns my laptop …

    The original Model is VPCEA42EG E series
    The new one is for model VPCEB42EG E series

    I am confused by this input output thing … the original model is not available since am in Iran n there is sanction… Is it safe I use the new one ? or I should ask someone bring me the original model from another country?
    Dear Leo plz email me your response …

    Regards,
    Sara

    It’s only the output amperage you care about. The new one can supply MORE, which is perfect.

    Leo
    11-Nov-2012

  16. Mark J Reply

    @Sara
    As long as the output voltage is the same and the output amperage is the same or higher you should be good to go.

  17. Cletus Reply

    Your explanation is correct. However would still like to know whether an original charger supplied with a new laptop does charging such that the charging current decreases as the battery attains its full voltage. I have a sony fz series. The ac adapter has an output voltage of 19.5 volts, 3.9 amps. The battery is li ion 11.1 volts, 4800 mAh. I have a regulated series power supply 0 to 30 volts adjustable to 19.5 volts and can supply 0 to 5 amps. Can I use this safely after setting the correct voltage.

  18. jay Reply

    Thank you! This article provided me with exactly the info I needed (with a bunch of device-specific USB chargers at 5V, choose the one with the highest amperage to charge them universally), from a trustworthy source, in exactly the amount of technical detail needed for someone with only vague memories of highschool physics.

    I’m a bit miffed at google for not ranking this higher in the search results.

  19. Kay Reply

    Hi there!

    I have an HP dv6 laptop that I’ve had for a little more than 2 years. The original power adapter started giving me a problem in that it wouldn’t always supply power to the laptop (the light next to the port wouldn’t always come on, when I plugged it in). I would try it unplugging and plugging it back it in a couple of times and sometimes it worked, others it didn’t.

    I found a replacement HP adapter online for $30 and bought it but it’s not exactly the same as the original one.

    Original (65 Watts)
    Input: 100-240V ~ 1.7A(1,7A) 50-60Hz
    Output: 18.5V(18,5V) — 3.5A(3,5A)

    Replacement (90 Watts)
    Input: 100-240V ~ 1.5A(1,5A) 50-60Hz
    Output: 19V(19V) — 4.74A(4,74A)

    I read this article and it mentioned that the voltage should be as close as possible. Since the voltage differs by half a volt, am I okay to use it or should I look for one that is exactly the same? Also, would the higher wattage harm my laptop or battery in any way?

    Thank you very much.

  20. Mark Jacobs Reply

    @Kay
    Using a slightly higher voltage might have a negative effect on the life of your battery. As Leo says in the article “The device may work with voltages that are close, but often at the cost of shortening the lifespan of the batteries being recharged.” It’s a controversial subject and there are opinions on both sides, but I tend to the better safe than sorry approach.

  21. Rob Reply

    My tomtom worked fine until I used wrong in car charger.Now it won’t start even after mains charge and resets.The charger is input DC=12v. Output DC=10.5v fuse 5A PositiveCentre pin. Tomtom label 5v DC 2A positive pin.Have I “cooked” the battery or worse?

    I don’t know about the battery, but putting 10.5 volts into a device that expects 5 volts is a Bad Thing and could have damaged the electronics inside.

    Leo
    03-Apr-2013
  22. Mildred Reply

    I am looking for an external battery pack for my laptop. I have seen they all say 19 volts but my laptop charger says 19.5volts=2A. Can i use the battery pack?

    Thanks.

    Best I can say is “maybe”. It’ll probably work, but it may shorten the life of your computer’s battery by being off by half a volt.

    Leo
    13-Apr-2013
  23. ELMon Reply

    Hi Leo … I need help I have laptop
    19 V …2.15 A…is required power supply
    now my new adapter is 19 V …1.58 A

    it is ok to use that adapter to my laptop?..

    • Leo Reply

      It’s OK to use, but it may not charge as quickly, or if you’re using the laptop, it may not charge at all.

      • Maxim Reply

        And also his new adapter could potentially overheat or even burn out the power supply, if I understood correctly from the article?

  24. Hermes Reply

    Hi Leo,

    Can you please help me with this question. I am about to buy a jumper battery from cobra.com called jumperpack. It soppoused to have a usb port with 2.1 amps. My question is can I charge my laptop that takes 19.5 volts at 4.6 amps ? providing that I have the right connection or adapter to go from a usb to my laptop charge connector. I am a truck and bus technician and use my laptop in order to do diagnostics so sometimes I am in a road test and all of a sudden it is a longer road test and my battery runs low and sometimes the bus or truck does not a 12 v power supply for my inverter TRIPP 400 watts. so It would be great that I can provide power to my laptop just to finish my job may be 30 minutes to an hour sometimes. would the 5 volts provide enough power to my laptop ?

    Thanks a lot

    • Leo Reply

      No. USB puts out 5 volts only and that’s definitely not appropriate for laptop re-charging.

      • Lee Reply

        You stated that USB provides 5Vout. You also stated that the power supply output voltage must equal the voltage of the device that you’ll be charging (or at least that’s how I interpreted what your article stated). So, does that mean that the batteries in our USB powered device has a voltage of 5V (i.e. USB voltage input to device = 5V and device battery that needs to be charged =5V)?

        • Leo Reply

          No. There is very often circuitry in the devices that convert as appropriate.

  25. cezar Reply

    can i ask question leo i if the voltage is not same and the current is higher what is the effect?

    • Leo Reply

      Depends on how different the voltage is, but in the worst case it can damage the components.

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