# Why does battery chargers say not to plug into extension cords or power strips?



## Frijid (Feb 26, 2013)

I need to charge a set of batteries right now, but the manual says to plug the charger straight into the wall outlet. I'm afraid to do so, cause it's storming right now and i'm worried if i plug it straight into the wall, if their is a power surge, it may fry the charger. why can't i plug it into a surge protector?


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## Mr Happy (Feb 26, 2013)

Frijid said:


> why can't i plug it into a surge protector?



You can. There is no reason at all why not.


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## rc51mike (Feb 27, 2013)

I'll hazard a guess it's because the manufacturer does not want to be held responsible when someone's house burns down because it was actually a faulty extension cord that caused it. It is obviously a bigger concern plugging high draw things into low draw extensions but in this day and age...


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## Frijid (Mar 7, 2013)

I was more concerned about surge protectors, (perhaps i should have made the question more clearer) I'd like to plug my chargers into my APC UPS so that way it would be protected from brown noise, power spikes, surges, etc. when the power gets to high or to low, it will kick off of the main AC and run on the battery until the level comes back down to normal, then it goes back to the main AC lines. i don't want to cause a fire, yet i also don't want to damage my equipment. last night the power surged in my area and the transformer overloaded and shut down, and i had the charger plugged into the main line, and i was worried it would fry the batteries or the charger. i'd like to plug it into the UPS (it has 6 plug in's, 3 are to the battery and surge protector, and 3 are NOT to the battery, just the protector) 

Being hooked up to a surge protector, would the batteries still be able to fully charge, or would it cut down on the charging current the charger is putting out, meaning longer charge time and/or not being able to fully charge the batteries?


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## TEEJ (Mar 7, 2013)

I plug chargers into surge strips and never had a problem, if that helps.


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## StorminMatt (Mar 7, 2013)

I wouldn't worry about this. A heater would be a different matter. But a battery charger draws less current than the average table lamp.


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## moldyoldy (Mar 7, 2013)

Frijid said:


> I was more concerned about surge protectors, (perhaps i should have made the question more clearer) I'd like to plug my chargers into my APC UPS so that way it would be protected from brown noise, power spikes, surges, etc. when the power gets to high or to low, it will kick off of the main AC and run on the battery until the level comes back down to normal, then it goes back to the main AC lines. i don't want to cause a fire, yet i also don't want to damage my equipment. last night the power surged in my area and the transformer overloaded and shut down, and i had the charger plugged into the main line, and i was worried it would fry the batteries or the charger. i'd like to plug it into the UPS (it has 6 plug in's, 3 are to the battery and surge protector, and 3 are NOT to the battery, just the protector)
> 
> Being hooked up to a surge protector, would the batteries still be able to fully charge, or would it cut down on the charging current the charger is putting out, meaning longer charge time and/or not being able to fully charge the batteries?



The consumer grade APC UPS units operate as a pass-thru for the AC line on the battery supported side. If the power fails, the circuitry starts the inverter in a few milliseconds and continues supporting the load. During an AC power failure, the UPS outlets that are only "surge protected", and not with battery support, drop out and shut off. IOW, plugging in the battery charger to either side of the UPS is OK. It just depends if you want charging of your batteries to continue during a power failure.


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## Power Me Up (Mar 7, 2013)

Frijid said:


> I'd like to plug my chargers into my APC UPS so that way it would be protected from brown noise, power spikes, surges, etc.



I run all of my office off of an APC Smart UPS, including several chargers - no problems here!

With a UPS that puts out a normal sine wave, the device has no way of knowing that it's running off a UPS and will work exactly as normal. If you've got a lower end UPS that puts out a modified sine wave (i.e. basically a stepped square wave) then some devices don't work so well, but most power bricks these days are switch mode types and will still run fine.


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## moldyoldy (Mar 7, 2013)

additional comment: UPS units generally have only surge protection via a variety of devices which include "Full time multi-pole noise filtering", but no dB specification is commonly given. However the APC SurgeArrest units add an important feature - EMI/RFI Noise rejection (100 kHz to 10 MHz). This can vary from 20dB to 70dB. FWIW, a Topaz true isolation transformer has a rejection of 120dB. IOW, 70dB for an 3 stage RLC filtering system is impressive. This keeps a lot of line noise out of the systems. Most battery chargers will not be affected by noise reduction, only AC voltage spike reduction. However radios and such will care about incoming noise reduction. For an example, look at the APC *Network *SurgeArrest device with 70 dB of noise reduction.


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## DrVette (Mar 7, 2013)

Moldyoldy & others are correct, a UPS will protect the device.Many UPS & investors are square wave which works fine for most devices except some laser printers.You need a surge protector on the ups.FYI re spikes, surges etc. these take out modems and other light electronic items.Electrical companis pay vastly more due to "brown-outs" or low voltage.These kill induction motors on freezes, refrigerators, washer & dryers, HVAC compressor etc.Your ?They do that for liability purposes.My information was gathered from 30+ decades in electrical generation.Hope this helps.I need to post regarding ways to cut electrical bills, when I get the desktop back online.


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## inetdog (Mar 8, 2013)

StorminMatt said:


> I wouldn't worry about this. A heater would be a different matter. But a battery charger draws less current than the average table lamp.



But, like a CFL or other non-linear loads, a charger without power factor correction can end up pulling some seriously high peak current compared to the RMS current. 
Probably still not enough to cause real problems with a good sized extension cord or power strip, but one more nail in the coffin of legal liability if they do not warn against it. 
With a power strip you could connect 8 chargers to one wall outlet, all drawing a high peak current. 
Remember that when looking at heating in an external series resistance (the cord and house wiring), the power dissipated in that resistance by a non-linear load can increase faster than the total power going to the load, as the duty cycle decreases but the power drain remains the same.

The additional reason that some appliances, including toasters, coffee pots, etc. warn against using an extension cord is that they are worried that if you put it too far from the outlet or let the cord dangle off a counter, it is more likely to be tripped over, potentially causing an unsafe condition. Again, more aimed at heating appliances than chargers, but putting that language in becomes a habit.


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## eusty (Mar 8, 2013)

DrVette said:


> My information was gathered from 30+ decades in electrical generation.



HOW old are you??! 



Sent using Tapatalk 2.


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## uk_caver (Mar 8, 2013)

To be fair, the decades before Faraday weren't very busy.


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## Verndog (Mar 8, 2013)

eusty said:


> HOW old are you??!
> 
> 
> 
> Sent using Tapatalk 2.



It would appear well over 300 yrs. old. Possibly he is confusing power trips with power strips. :devil:


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## fnj (Mar 9, 2013)

The reason Sanyo NiMH chargers say to always plug directly into a wall outlet is based on the fact that they have temperature monitoring to aid in determining state of charge. What they are really driving at is that the operation is predicated on the charger being in the upright position with the sliding door closed. This is hard to achieve at the end of an extension cord, or the horizontal outlets frequently found on a UPS.

OP: so it depends on what charger(s) you are talking about. Can you be more specific?


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## Frijid (Mar 9, 2013)

fnj said:


> OP: so it depends on what charger(s) you are talking about. Can you be more specific?



its a energizer chfc2 universal charger
[h=1][/h]


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## Mr Happy (Mar 9, 2013)

Frijid said:


> its a energizer chfc2 universal charger



The instructions for that charger simply say _"Never plug battery chargers into an extension cord."_

There are many possible reasons for this advice. One possible reason is that this charger uses a "wall wart" power supply. Such supplies have been known to melt and possibly catch fire if they fail. If the wall wart is plugged into the wall, a meltdown is safer than if it is sitting on the end of an extension cable where it might be next to something flammable like drapes or paper.

Another possible reason is that the charger needs to run for a long time unattended, and someone may unplug the extension cord thinking it is not in use.

You have to pick your own reason why you shouldn't plug your charger into an extension cord. Your reason might be different from other people's reasons. If you can't think of any reason to obey that instruction then you may safely ignore it.


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## fnj (Mar 10, 2013)

Frijid said:


> its a energizer chfc2 universal charger



Given the manual for that unit http://www.energizer.com/SiteCollectionDocuments/pdf/rechargeable/CHFC2_Instructions.pdf, without any hesitation whatsoever my evaluation is that the instruction not to plug it into an extension code is utterly baseless BS. Clearly the orientation of the unit is not dependent at all on how or where the wall wart is plugged in.


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## uk_caver (Mar 10, 2013)

I've certainly seen it happen that [at least part of] a manual seems to have been written by copying and editing a manual for a different previous piece of equipment.
Lists of 'safety' or 'correct use' type instructions might be the kind of thing where that would be expected to happen most often, since so much will be the same for multiple products ('don't use in the rain', 'don't use in the bath', etc)


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## Mr Happy (Mar 10, 2013)

I can certainly imagine it is advised to plug a "wall wart" directly into a wall socket for reasons of air circulation, cooling, and clearance from other objects. I don't think battery chargers are the only items where I have read this advice.


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## Tubaman (Mar 10, 2013)

In regard to the issue of plugging a high current item into an extension cord, I have an experience that may shed light (no pun intended - honestly!  ) on the reasoning.

I purchased a power washer several years ago. It worked fine for a month and then just died. I returned it to the vendor and bought an upgrade in the process and was also given a lesson in why so many were failing.

The extension cords were at fault. They were too small a gauge to allow for proper current flow vis a vis their higher innate impedance. That was causing many of the motors to burn out because of incorrect power. The cords in question were 50' runs of 14 gauge. The manual on the new unit (a Karcher btw) explicitly stated no cords over 25' and those must be of at least 10/3 gauge.

i hope that may offer some insight 

tubaman


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## fnj (Mar 10, 2013)

True, but has absolutely nothing whatever to do with an extremely low power appliance.


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## gradio (Mar 10, 2013)

Seems some cheap, probably low line china made extensions cords and power strips got a bad rap some time ago.
Worse when one daisy chains em and plugs too many demanding things to them. Not knowing pro/con about the stuff. 
I remember several of the old cheap extension cords that didn't have a ground prong. Might have been some that wasn't polarized too. Some seem to have small gauge wiring. 
I've had one power strip that was discolored and partially melted housing. I got rid of it. some time later saw a recall on it. I only had a lamp, radio and a fan plugged into it. It sure was warm when I discovered it. And it was a cheap one. Been buying higher priced better quality (I hope) since then. Heavier gauge wiring too.


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## n3eg (Mar 10, 2013)

DrVette said:


> Electrical companis pay vastly more due to "brown-outs" or low voltage.These kill induction motors on freezes, refrigerators, washer & dryers, HVAC compressor etc.



Not to mention switching supplies, which INCREASE current drain as voltage drops. A large switching supply (1 kw or so) will trip breakers during a brownout, if you're lucky and it doesn't overheat extension cords or burn up.


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## zakdk (Mar 11, 2013)

...in the event of a elctrical overload the extention cord will just catch on fire as the copper threads inside are thinner than the ones in your house instalations which are thicker and can withstand/have a higher tolerance to a elctrical overload than a normal extention cord could handle ,hop i helped  .:thumbsup:


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## RCM (Mar 13, 2013)

zakdk said:


> ...in the event of a elctrical overload the extention cord will just catch on fire as the copper threads inside are thinner than the ones in your house instalations which are thicker and can withstand/have a higher tolerance to a elctrical overload than a normal extention cord could handle ,hop i helped  .:thumbsup:


Wall wiring is usually solid core copper, while extension cords are usually always stranded...


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## Illum (Mar 13, 2013)

Wasn't there something about not to use extension cords in electronic theory about sensitive electronics that uses amplifiers? Somewhere I thought I read that the inductive property of a [long] extension cord actually introduce excessive noise into a circuit. Should the sine wave curve of live voltage be used to activate controller circuits that, without proper filters, false triggers would occur. Does that sound logical or am I dreaming these things.


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## arek98 (Mar 13, 2013)

Illum said:


> Wasn't there something about not to use extension cords in electronic theory about sensitive electronics that uses amplifiers? Somewhere I thought I read that the inductive property of a [long] extension cord actually introduce excessive noise into a circuit. Should the sine wave curve of live voltage be used to activate controller circuits that, without proper filters, false triggers would occur. Does that sound logical or am I dreaming these things.


Hmm, how would extension cord differ from wire in the wall in that regard?


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## Mr Happy (Mar 14, 2013)

Illum said:


> Wasn't there something about not to use extension cords in electronic theory about sensitive electronics that uses amplifiers? Somewhere I thought I read that the inductive property of a [long] extension cord actually introduce excessive noise into a circuit. Should the sine wave curve of live voltage be used to activate controller circuits that, without proper filters, false triggers would occur. Does that sound logical or am I dreaming these things.



As arek98 mentions, every electrical outlet in your house is on the end of a very long extension cord that snakes all through the walls, ceilings and attic spaces. A 6 ft extension cord plugged into the wall is nothing compared to the 60, 80, 100 ft of wire behind the wall.


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## Illum (Mar 14, 2013)

arek98 said:


> Hmm, how would extension cord differ from wire in the wall in that regard?



as far as I can figure, they had to have to make the assumption that all wires in the wall is conduit cladded... which could make sense, but yea that was my question as well.


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## Mr Happy (Mar 15, 2013)

Illum said:


> as far as I can figure, they had to have to make the assumption that all wires in the wall is conduit cladded... which could make sense, but yea that was my question as well.



The conduit cladding of wires in the wall is not for any electrical purpose, it is for mechanical protection so you don't hammer a nail through a power cable. (It is also to support the electrical trades by increasing the amount they can charge for installation work, but that is another story...)


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## fnj (Mar 15, 2013)

OK, this is all getting a little silly, so I will list some facts to make it clear that the presence or absence of the extension cord is utterly inconsequential.

1) There is nothing "magic" about the wiring in the building. The conductors are just ordinary copper wire of 14, 12, 10, or other gauge. Unless it is very heavy (below 10 gauge), it is usually solid wire, but the reason for that is simply that it does not have to be very flexible, since it never gets flexed after installation. Normal outlets in a house are usually served with 14 gauge wire; sometimes heavier 12 gauge. The wiring may be enclosed in metal or plastic conduit, but in a house in most jurisdictions it does not have to be. Metal-armored BX cable used to be the norm, but nowadays Romex plastic-sheathed is more common and is considered to be entirely adequate.

2) Similarly, there is nothing "magic" about the wiring in extension cords. Again the conductors are just ordinary copper wire. Since they have to be flexible, they are stranded wire. For cheap extension cords, 16 gauge is common, generally rated at 13 amps. Most 6-outlet power strips are 14 gauge and rated at 15 amps.

3) The ordinary NEMA 1-15 2-prong and 5-15 3-prong power plugs are rated at 15 amps.

4) 14 gauge wire, whether in the wall or in an extension cord, wheher solid or stranded, has a resistance of 0.25 ohms per 100 feet. 16 gauge is 0.40 ohms per 100 ft. 12 gauge is 0.16 ohms per 100 ft.

5) Even if your home is wired with 12 gauge and the run is only 50 feet, there is 0.08 ohms of resistance in each conductor. If there is, say, typically a modest 3 amps of load on that particular run, the total resistance of the two conductors forming the circuit being a total of 0.16 ohms; E=IR tells you that is a voltage drop of 0.48 volts.

6) If your extension cord is 6 feet long and uses 16 gauge wire, there is 0.024 ohms of resistance in each conductor. If all of the 3 amp load on that circuit is connected to the end of that extension cord, the total resistance of the two conductors forming the circuit being a total of 0.048 ohms; E=IR tells you that is a voltage drop of 0.14 volts.

So the voltage drop from your distribution box down cellar to your equipment on the tip end of that extension cord is only 0.62 volts, and only 0.14 of those volts are due to the extension cord itself.

Now, there are additional resistive losses from the transformer on the telephone pole to your distribution box, in your circuit breakers, and at every plug point in the chain - in our case, one wall plug and one plug at the end of the extension cord. Of these, the losses inside the house are slight, and the wire from the pole is not under our control to begin with.

Finally, consider that a charger like the one under consideration is not going to have a current drain from the AC supply of over 0.5 amps, and probably not more than 0.1 amps when charging 2 or 4 AA's, for example.

Guys, the effect of putting that charger on the end of an extension is zero, zip, nada. The current drain is no more than 1/20 the capacity of the extension cord, and the AC voltage it sees is reduced by hardly more than 1/10 of 1% by the extension cord.

Finally, consider that the nominal 120 volt supply in the US in fact is only specified to be held between 114 and 126 V. All equipment is designed to handle a generous amount MORE than that range without any ill effect.


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