Amperage vs Voltage - Which is more dangerous?

By Rick
Oct 27, 2003
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  1. Rick

    Rick TechSpot Staff Topic Starter Posts: 6,304   +52 Staff Member

    Yes, it should be fine.

    I'm using a 16v / 4.5a power supply with my IBM thinkpad, which is designed for 16v / 3.2a

    What I've gathered from this thread is voltage kills electronics, not amperage. I imagine that if you get a severely underrated power supply you might burn out the power supply, but the laptop should remained unharmed regardless.
  2. Nic

    Nic TechSpot Paladin Posts: 1,928

    Its safe so long as it's a voltage regulated power supply. Almost all units are these days, except for some very cheap and nasty imports from the far east.
  3. alphnumeric

    alphnumeric Newcomer, in training Posts: 209

    Think about it this way. The voltage (V) is water presser. The current (I) is the water flowing through hose. And the resistance (R) to current flow is the hose. In this case the laptop is the hose. If you raise the pressure (voltage) then more water (current) goes through the hose (laptop). Too much pressure and your hose will blow. If you match the voltage as close as possible the current will take car of itself and you won't have to worry about it. If the supply is under rated for the current (not enough) it just won't work. Hope that helps.
  4. StormBringer

    StormBringer Newcomer, in training Posts: 2,871

    As long as the battery doesn't develop a flaw that causes it to draw more current. Normally that wouldn't be as crucial because the charger isn't going to allow it to happen, but batteries are subject to flaws(as are all electronic devices) If your charger is capable of delivering more current, it can possibly cause a problem if the battery develops a flaw. As I said, this is not really a big problem, and unless you are trying to use a battery that is ready for the junk heap anyway, then you probably have nothing to worry about.

    As Alphanumeric already said, the load(battery in this case) will only use the amount of available current that it needs. As long as it is operating properly, having more than that available isn't a problem. Only real caution in this would be if the battery gets unusually hot, or shows any signs of defect at all(refusing to hold a charge, losing its charge quickly, etc) then don't keep using it, this would be a battery problem which might allow the extra current to be drawn by the battery and cause some damage.
  5. Percydood

    Percydood Newcomer, in training

    Amperage vs Voltage

    I would like to get in on this one. Sorry it's a bit late.
    If you are retrofitting a piece of equipment with a new power supply it is quite simple. The voltage must be the same as the original within a certain percentage. Too high and the components will frazz. Too low and the circuit will not get enough power. And that's the thing. Power. All circuits consume power and you must try to get it to match. If the power supply you have has more current capacity, then that is OK. If the circuit tries to use more, the power supply won't struggle. If the supply struggles, the voltage will sag and you may get unpredictable operation. Higher current capacity is OK because the circuit should be fused to protect it in the event of a fault condition.
    So, in summary, always match the voltage and the current should be at least the same or more.

    Incidentally, while the folks here are correct, current kills, it still comes back to power. A car battery can produce hundreds of amps for a short time but it is only 12 volts. Voltage has to overcome resistance for current to flow (in simple terms. I know current always flows in a circuit that has a voltage supply.). My bodily resistance is in the order of 10 millions ohms and that is why I can stick my fingers across my car battery with no effect. While there is current flowing, it is only about a millionth of an amp. Not enough to hurt. But remember, it only takes about 5 thousandths of an amp (5 milliamps) for 5 seconds to arrest your heart. At 240 volts (yeah, I'm from the UK) and with about 10 million ohms, I will draw about 24 microamps (which should be OK but I ain't giving it a go!) but if my resistance was less and it depends on your biology, it could rise enough to cause damage. Power = Volts times Amps.
  6. tbrunt3

    tbrunt3 Newcomer, in training Posts: 495

    To add my two cents to this and my almost 20 years as a Licensed Electrican here in Michigan it is the amps that will kill you . We work on a lot of live circuits and I tell all the Apprentices I work with as well so teh remember it. The amps are what hurts. But that was a very good explanation buy you both. This is a great place with a lot of professional people form all over the world.
  7. PFJ

    PFJ TechSpot Enthusiast Posts: 132

    Good thread...nice to see that the subject has been revitalised. When I am dealing with newbies in the area of electricity I always quote my old teacher "mills kills - volts jolts" - re-enforcing what Percydood has remarked upon.

    Two other points I would like to add - the importance of considering inrush current and polarity when looking at replacement power supply units.

    Mr X appears to be within all our criteria for a nice replacement but he encountered problems. I wonder did he consider polarity?

    Mr.X
    Just a thought.
  8. Percydood

    Percydood Newcomer, in training

    Volts Can Be Dangerous!

    Just a thought actually. If you have an electric shock, you should get yourself down the hospital and get an ECG. It is well known that if you have enough volts to give you a bloody good belt but with insufficient current to cause a heart failure, it is still possible for your heart to be beating incorrectly. I don't know what the proper medical name is for this. People have died up to 24 hours after a seemingly harmless electric shock. In fact, here in the UK, someone died following taking part in an hypnosis show where they were told they had a million volt shock! They died the next day. They never actually touched anything electrical but the shock was enough for their heart to fail. AND a considerable number of people die each year after sticking a 9 volt battery across their tongue!!!

    I'm not trying to scaremonger, but I do believe that electricity should be shown some considerable respect.

    And good point about inrush current.
  9. PFJ

    PFJ TechSpot Enthusiast Posts: 132

    Interesting stats on voltage that everyone should be aware on in Techspot. The message is - "respect".

    In my occupation I deal with high voltages on a daily basis (~30kVDC) on cathode ray tubes. I've had my fair share of jolts but this normally ends up in expletives and I'm more vexed with myself than to worry about the biological results.

    I wonder could this all tie in with my arrhythmia :eek: ?
  10. SNGX1275

    SNGX1275 TS Forces Special Posts: 12,250   +213

    Got any way to back that up? I find that very hard to believe.
  11. Percydood

    Percydood Newcomer, in training

    Danger! High, well low voltage....

    I don't understand why it happens but apparently people do die from 9 volt batteries. When I say a considerable number of people die you have to consider that it is a 9 volt battery. Apparently 3 people die from this each year. I'm still here and I've done it so I don't suppose it's much of a risk and I don't have the official stats to follow it up in answer to your question. But I can believe that it is probably true. Stranger things happen. You'd have to be unlucky to be struck by lightening or attacked by a shark, so they say.

    Here's a poser for all of you though. Let's say you are sat in a plastic bath (tub) full of soapy water. You are sat at one end away from any earths and some evil person drops an electric fire or other electrical appliance in the other end. Electricity takes the shortest route which, assuming the appliance is not earthed would be from the live terminal to the neutral terminal. If this is true, why are you at risk of death from electric shock? I have an explanation but no-one has ever categorically explained this and I would like your opinions. DON'T TRY THIS THOUGH AS IT IS LIKELY YOU WILL DIE!!!!!! :dead:
  12. PFJ

    PFJ TechSpot Enthusiast Posts: 132

    I think we have deviated from the original thread which dealt with compatability of a power supply and a laptop. However, I like this deviation and perhaps Percydood could post it as a new thread?
    It appears that many of us Techspotters are from a technical background and enjoy a good techncial debate (site:StormBringer & Alphnumeric's interesting discertations)

    Good question re: bath tub and electric shock!

    I'll ponder that one and come back.
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