Does 1 Volt REALLY matter?

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sorcerer

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I've been given a fully-functional, if old, HP6735B laptop but there's no charger with it. Searching Ebay for a charger lists suitable ones with an output of 18.5V, 3.5A.

In my 'junk and/or surplus box' I have maybe a dozen laptop chargers, two of which have the correct connector but are listed on their labels as outputting 19.5V rather than the 18.5V that an HP6735B charger should. Safe to use? Or will that extra pesky little volt fry things?

For the sake of about £10 to £15 some of you will be wondering why I just don't buy a new one but I wouldn't be a true northerner if I didn't think of this option first ;)
 
Northerner.. Thought only the pesky Yorkies tried that :-D.

to answer your question, I would say that it does need to be the correct voltage. But I can't say that with 100% certainty. So wait around till you get some more answers from more knowledgable peeps than I on this one.

Sorry.
 
I would not hesitate to use the 19.5v charger. Many consumer electronics are capable of handling a 20% margin of error. So you should be good plus or minus about 3.7 volts. At 1 volt you are just barely over 5% off.
 
The 18.5/19.5 is regulated down to the various voltages needed by the individual laptop circuits and the regulators can handle quite a range of input voltages. One volt is likely well withing that range. I wouldn't hesitate to use either adapter but I would be wary of lots of cheap Chinese junk adapters.
 
My 120v at home is really 123v

My 24v low-voltage thermostat is running at 26v

1.5v batteries are more like 1.65v batteries when new.

11.1 v LiPoly batteries are about 12.6 charged...

I think 1 volt on almost 20v is well within spec. It's just barely over 5%
 
Should be fine as others have said.

You would actually be more likely to have an issue if the voltage was lower rather than higher.
Several model laptops won't run unless they detect the power supply puts out the minimum power it expects.
 
You're good to go.. Most of the laptop DC to DC buck converters are rated for 30V, one volt isn't going to hurt.
 
As everyone has said, Voltage should not be a big issue. Its the Amps that matter. If your feeding a 18.5v@3.5Amp circuit 24v@1Amp, it wont function, but shouldn't damage anything except the power supply. Now, if your feeding a 18.5v@3.5Amp circuit 19.5v@5amp, your probably going to fry something. I believe most laptop power supplies are 19.5v@3.5Amps, so you should be golden. Might recommend staying with a 65 watt psu, just for safeties sake, but there is enough discussion on here about whether a 90w will hurt to say that your probably ok.
 
jbartlett323 said:
if your feeding a 18.5v@3.5Amp circuit 19.5v@5amp, your probably going to fry something.
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The power rating of the supply simply means it can deliver the rated voltage at up to the rated current level with good regulation, not that it's going to over-power/fry the device simply because it's capable of delivering more power (current) than the device draws.
 
jbartlett323 said:
As everyone has said, Voltage should not be a big issue. Its the Amps that matter. If your feeding a 18.5v@3.5Amp circuit 24v@1Amp, it wont function, but shouldn't damage anything except the power supply. Now, if your feeding a 18.5v@3.5Amp circuit 19.5v@5amp, your probably going to fry something. I believe most laptop power supplies are 19.5v@3.5Amps, so you should be golden. Might recommend staying with a 65 watt psu, just for safeties sake, but there is enough discussion on here about whether a 90w will hurt to say that your probably ok.
Click to expand...

This isn't exactly correct - You can use a power supply with a higher current capacity, the laptop will only draw as much current as is required - the charger will put out only what is required. It's the old ohms law thing. I=E/R
 
Here's my take.

Polarity/Connector - This is a must. The center pin is usually hot and the outer shell is ground. Reverse that and sparks fly. Obviously, the connector length and diameter must match.

Voltage - The 1 Volt difference is negligible but I wouldn't do it. I have done it in a pinch just to see if a laptop would power or to see if the battery starts to charge but I haven't done it long term. I'd never sell a customer an adapter that didn't match V exactly. 1 V doesn't mean much in AC circuits but I'm not sure about the charging/running circuits in laptops. I've never read anything definitive from the manufacturers on this so I err on the side of caution.

Amps/Watts - If your current adapter, pun intended, is rated at 65 Watts/3.35 Amps that is the absolute minimum amount of potential power needed. You can safely go larger. Lets say a 90 Watt/5.0 Amp model. Unlike voltage, your laptop will only take the amount Amps/Watts it needs at the current, pun intended, time.
 
mr m said:
Here's my take.

Polarity/Connector - This is a must. The center pin is usually hot and the outer shell is ground. Reverse that and sparks fly. Obviously, the connector length and diameter must match.

Voltage - The 1 Volt difference is negligible but I wouldn't do it. I have done it in a pinch just to see if a laptop would power or to see if the battery starts to charge but I haven't done it long term. I'd never sell a customer an adapter that didn't match V exactly. 1 V doesn't mean much in AC circuits but I'm not sure about the charging/running circuits in laptops. I've never read anything definitive from the manufacturers on this so I err on the side of caution.

Amps/Watts - If your current adapter, pun intended, is rated at 65 Watts/3.35 Amps that is the absolute minimum amount of potential power needed. You can safely go larger. Lets say a 90 Watt/5.0 Amp model. Unlike voltage, your laptop will only take the amount Amps/Watts it needs at the current, pun intended, time.
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Couldn't agree more.

Almost exactly what I would've said myself, if I could've been bothered to write it :D

(IT is my secondary vocation; electronics is my forte. I'm a qualified electronics design engineer with nearly 30 years experience.)

The 1 volt difference *shouldn't* be a problem and there's a good chance the voltage regulation circuity will handle it, possibly even indefinitely but there's also a chance it could cause premature failure of some components. Impossible to say without studying the laptop's power regulation circuit diagram. So, personally, I would stick to the correct voltage.
 
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I've used Dell on HP and vice versa (19.5 vs 18.5 (usually)) for laptops in the shop if the customer doesn't bring in their adapter no issues. Some of them complain about the adapter not being genuine but still powers it.
 
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