Does anyone know if there is any way to use the Surface RT with an external battery pack?
I know there are surface RT compatible powerbanks on sale right now but those are really expensive!
Afaik, the surface charges with 12V whereas USB ports output at 5V.
The only difference that I can tell is that the power output is different. This should just result increased charging times but should not have any safety issues at all.
If you aren't aware what a difference between 12v and 5v means in electronics, you probably shouldn't be giving advice like "should not have any safety issues at all". I mean, you're probably right in this case (though only "probably") but if you think that voltage = power output, it's only by sheer luck.
To answer your actual question, I am not. However, I strongly advise against simply... experimenting with this sort of thing on your own. You could easily start an electrical fire, damage your tablet, or do one of many other unpleasant things.
The surface uses a 7.4V battery pack. Attempting to connect a 5v supply to charge without a stepup converter will not charge the surface at all and instead lead to damaging your 5v supply as the surface attempts to supply 7.4v to it, which may also damage the surface too.
In electronics nothing is more important than the correct voltage. Take a raspberry pi, many people (including myself) use them for electronics projects. Both me and a friend added ultrasonic rangefinders to our pi's except I observed the fact that the module in question uses 5v signalling and my friend did not. We both connected the +5v and ground lines to the corresponding points on our pi's. I connected 1 GPIO pin of the pi to the trigger pin of the HC-SR04 (module in question) as did friend. The pi uses 3.3V on its GPIO pins, the HC-SR04 is safe with a 2.7v-5v trigger voltage, thats fine. The echo pin however is +5v. I ran my echo pin through a voltage divider to give myself a 3.0v output instead, this is safe for the pi (it is fine with 2.7-3.3). My friend did not, he connected the echo pin direct to the pi, tried to use the sensor for the first time ever and found he didnt get any results, do a few test lighting an LED and he found he could no longer use that pin, he damaged it.
I would be more concerned about the surface damaging the supply than the other way around in this case.
However you are correct in believing the device charges at 12V (2A or 4A depending on whether its an RT or pro charger). The surface would have the correct voltage regulation to charge the battery and supply 5v to USB internally. There are 4 wires within the charger. Red: +12V, Black: Ground, Blue: charger detection, Yellow: signal for the charger LED. I don't think its known *exactly* how the yellow and blue wires function, the surface does charge without them. Blue is rumored to be something to do with the RT charger identifying itself as a 2A device and telling the pro to not draw more than 2A (it draws 4) hence damaging the charger but exactly how it does that is unknown. If the 12V supply can supply more than 4A your golden. A supply capable of higher currents than the device needs is actually perfectly safe, current is drawn by the device from the supply, the supply does not force the current at the device. If a device requires 2A and the supply is capable of 10, the supply will still only give out 2 as that is all the device is drawing. A device drawing more than the supply can cope with on the other hand IS DANGEROUS. Lets say you were to use a 5v>12v converter from a computer USB port to charge a surface, a computers USB only supplies half an amp under normal conditions (and by shorting D+ and D- it can do 1.2), the pro trying to draw 4 combined with the inefficiency of 5v-12v stepup converters will cause a current draw so large on the USB port that I would be surprised if damaging the USB port is the only thing to happen, you could fry the entire USB controller easily, damaged USB controllers can then cause their own issues, primarily with this amount of current the possibility of fire.
If you want to charge your surface. Find a voltage source *above* 12V (but not too high above) and use a voltage regulator to make a clean 12V. Then make sure both the regulator and battery can cope with the current. The regulator will determine how far above 12V you are safe to go, some might safely regulate 100V to 12 (most likely a switch mode regulator which although highly efficient won't output a clean 12V, it will have alot of voltage drops and spikes) whereas some might only do 20 to 12 (linear, much less efficient but a very clean 12v, stick a heatsink on it as they get warm). A car battery btw is not 12V, its 12.6 nominal and when fresh off the charger as much as 14.
Yeah, I know the basics of electrical physics. Not a complete speculating noob.
P=IV
Power of a 5V 2.1A is 10.5w
The original power adapter supplies 12V at 2A = 24w
My physics may be rusty but, I was under the impression that it would still charge at lower power output albeit half as fast. I've read that the RT when using the 48W charger would still charge at the same rate as the 24w. This means that the current that is drawn by the surface rt is capped at 2A. Hence, I believe that there would be any significant issues with drawing 2A from a charger that is designed to output 2A anyway though at a lower voltage.
If I'm still wrong here, would love some clarification.
lambstone said:
Yeah, I know the basics of electrical physics. Not a complete speculating noob.
P=IV
Power of a 5V 2.1A is 10.5w
The original power adapter supplies 12V at 2A = 24w
My physics may be rusty but, I was under the impression that it would still charge at lower power output albeit half as fast. I've read that the RT when using the 48W charger would still charge at the same rate as the 24w. This means that the current that is drawn by the surface rt is capped at 2A. Hence, I believe that there would be any significant issues with drawing 2A from a charger that is designed to output 2A anyway though at a lower voltage.
If I'm still wrong here, would love some clarification.
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The wattage is not of concern. The voltage and current must be treated independently. Also, consider that you are trying to charge a 7.4v battery from a 5v supply, the current will not flow from the 5v to the 7.4v (assume old electrical flow not real electron flow), it will end up doing the opposite, 7.4v flowing towards the 5v.
So lets say you step up the 5v to 12v, there is inefficiency in doing that. To get 12V @2A you would not be drawing 5v @2A, you would more likely be drawing 5V @4 or 5A.
As 6677 says, the Voltage and current (and not the power) are what matters. Power (Wattage) is a derived value (and you correctly gave the derivation); it's handy for making comparisons when certain core assumptions are valid but meaningless on its own. In this case, the core assumptions are *not* valid: not all chargers are producing the same Voltage.
To take another example of where assuming all Watts are created equal would get you in trouble, consider an incandescent light bulb. Light bulbs are rated in Watts because incandescent bulbs operate by turning electrical power (Watts) into heat (also measurable in Watts) via resistive filaments that can only dissipate a limited amount of heat. Thus, a 60W bulb has a filament designed to dissipate 60W of heat. However, since power is a derived value, let's look at what it actually means: In the USA (mains run at about 120V) we can use Ohm's Law: P=I*V; V=I*R, so I=V/R, so P=V*V/R=V^2/R, so R=V^2/P. Therefore, the resistance of a 60W bulb in the USA is (120^2)/60=2*120=240 Ohms. Cool. Now, let's take that 60W bulb from the USA and connect it to European mains. It should still consume 60W of energy and produce the same amount of light, right? After all, it says "60W" right on the box! Hmm... but European mains run at 240V. The resistance doesn't change; it's a physical property of the filament. So, using P=V^2/R, we get P=240*240/240=240W That's four times as much as the bulb is meant to handle; it will flash very brightly (much brighter than normal) and burn out instantly! The bulb isn't defective, it just wasn't made to handle 240V. The "60W" on the box is based on an assumption of 120V; the bulb itself does nothing to ensure that it only consumes 60W.
While the basics of Ohm's Law will equip you to understand things like I describe above, it is *not* enough (by itself) to make assumptions about complex electronics. Even a 101-level electrical engineering course will make that abundantly clear; there are many more forces at play in the world of electronics than the familiar and relatively-easily-understood Voltage, current, resistance, and power.
Thanks guys for clearing the air. Man, I thought it would have been possible to jerry rig a Surface Charging USB cable to be used with battery packs.
So from what I understand, to avoid unnecessary complications, it would be best to find a way to supply 2A @ 12V. Obviously finding a power supply that natively does so is most ideal. But there is an alternative of stepping up the voltage from 5V to 12V with will lead to losses due to conversion inefficiency which basically rules this out.
12V Power Bank
I found a 12V 2.5A external battery pack listed above. This seems to work doesn't it? It has a 12V output with a max draw of 2.5A. The Surface RT draws a maximum of 2A from your power source. I can simply splice the provided cables with the Surface Charging Cable and it sounds to me it'll work.
Since the Surface RT is reported to have a 31.5Wh battery, this battery pack seems to have a 78Wh battery making it rather ideal.
If it is indeed 12V @2A or more then yes, it should charge an RT
Use a power gorilla I use one for my macbook pro and other usb items
Just saw flyer for Surface pro/RT powerbank
Got an email with flyer for Surface + laptop Powerbank. I haven't put an order yet but you can check it out at -> qi-infinity website
It seems they already include Surface adapter and its on sale. I have Lenovo X1 carbon laptop and they have proprietary connector for that one included as well. So I might go with them
Related
Question is related to voltage and amper: original touch cruise's adaptor is marked as "output: 5V 1A LPS"
I have another one that I bought for my ex HTC Kaiser; this adaptor is marked as "output: 5.5V 500mA"
Can I use the second one for touch cruise? Is there a general rule when it comes to such electracal small differences?
Thank you.
the amps never matter they are pulled not pushed
the volts can cause issues as usb is 5volts and
not 5.5volts so by following the std a device could still
be toast if provides with 5.5volt but i doubt it though
No reason to doubt that.
In fact I saw some cellphones with USB-Charging capabilities, which didn't work after charging with a little more than 5 Volts.
Seems to be different from phone to phone if >5V does damage or not.
I would refrain from feeding 5V device with a 5.5V power source, especially considering this 5.5V is probably going straight into to the VBus line of the USB client hardware, not just into charging circuits.
Also, saying that "the amps never matter they are pulled not pushed" is WRONG. Indeed, the device "pulls" the current from the power supply, but if it attempts to pull more than the power supply can provide, you may end up frying the power supply, and i mean, frying it literally, like in "overheating and melting it up".
BTW, sorry about such a nasty first post, but i really don't like the though of someone possibly frying a device because of a forum post.
I just measured the output of my OEM charger, it was 5.24V so a bit more than the standard 5V. Would this be a problem?
I always thought that the current from USB chargers was seldom exactly 5V anyway.
satfly said:
I just measured the output of my OEM charger, it was 5.24V so a bit more than the standard 5V. Would this be a problem?
I always thought that the current from USB chargers was seldom exactly 5V anyway.
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Click to collapse
Don't panic, you are in the good range:
"The specification provides for no more than 5.25 V and no less than 4.75 V (5 V±5%) between the positive and negative bus power lines"
(http://en.wikipedia.org/wiki/USB)
And i presume that you 've made the measurement without any device connected to the power supply ?
I have older chargers for that output 5.0v / 550mA and have noticed that the Captivate outputs 5.0v / 700mA.
1. Can I safely use the older, 550mA chargers with the Captivate and what will the effect be?
2. Can I safely use the Captivate's 700mA charger with the older phones and what will the effect be?
Thanks.
1. Yes, you can use it. But it will charge slower.
2. Yes, you can use it. I believe that just because the charger output is higher amperage doesn't mean that it will affect the phone adversely. Think of it this way: A lamp is plugged into the wall outlet at your house. That outlet is rated at 120v 15A. The bulb isn't using all 15 amps, so no problem. But if you were to turn the voltage up or down, the lamp will get brighter or dimmer respectively.
The Captivate can take up to a 1A (1000 mA) charger.
Truceda said:
1. Yes, you can use it. But it will charge slower.
2. Yes, you can use it. I believe that just because the charger output is higher amperage doesn't mean that it will affect the phone adversely. Think of it this way: A lamp is plugged into the wall outlet at your house. That outlet is rated at 120v 15A. The bulb isn't using all 15 amps, so no problem. But if you were to turn the voltage up or down, the lamp will get brighter or dimmer respectively.
The Captivate can take up to a 1A (1000 mA) charger.
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Another question. You sound smart on this so how about using the nexus one car charger on this? Fits perfect and I don't see why not, but still Leary. .. what do you think?
As long as it puts out 5v, (which is USB standard), you are fine. The amperage is only relevant if the device REQUIRES it. For instance if the device draws 1A and your charger could only handle 550mA your device will charge very slowly.
On the other hand if your charger can handle 1.2A and your device only draws 700mA, then your charger will only output 700mA.
The important thing is the voltage, it needs to be 5v +/- 3% ...
I actually use a generic car charger I bought at walmart with 2 USB ports on it, and it works well for every USB powered device I own ... ZUNE, iPOD, phones etc.
OK. Thanks for the reply. I had read that a phone requiring 700mA that uses a 550mA charger could damage the charger and possibly the phone. That's what made me wonder. And that's what led to the question.
Let's make this a bit more interesting. There's a local, highly-reputable cell phone repair store that has stopped selling car chargers because, they say, the rapid charge is not good for the phone's battery. Their recommendation is to use an inverter (no, they don't sell them) so that you can then plug a standard wall charger into it or a USB cable if the inverter is so equipped. The AC current that results from utilizing the inverter is more consistent than the current flowing from a car charger. So...I purchased an inverter for less than $20 and use it to charge the Captivate in my car.
OK ... not sure we need to get this far down in the weeds on this but here goes ....
The USB2 standard for power distribution is 5v and the thresholds are 4.4-5.25V.
Power is supplied in units of 5v power ... 1 unit is 5v at 100mA, no device can draw more than 5 units from any one port. If you have ever seen a portable hard drive with 2 USB connectors it is because it requires more than 500mA to operate and by using 2 ports the device can draw up to 1A. For dedicated chargers the 4.4-5.25v still applies but shorting the D+/- and disabling the data connection allows the device to detect that it is connected to a dedicated charging port and draw a maximum of 1.8A.
In keeping with the above guidelines, when connected to your computer the Captivate can draw no more than 1 unit of power which is [email protected], when connected to a dedicated charger the phone can draw [email protected] and stay within the standard. (yes, it caps itself at 1A, I know).
OK ... the next bit is going to be hard to digest because there are plenty of examples to the contrary ... there is a standard for mobile USB chargers, and it requires wiring them as dedicated charging ports. What this means to us is that, in theory anyway, a mobile USB charger should allow a device to draw up to 1.8A from it (highly unlikely ... but that's the standard as written).
Here is the problem, if the device is plugged into a dedicated charging port and tries to draw it's maximum rated current, that amount of current may not always be available or it may fluctuate. This fluctuation is what causes problems. Have you ever turned you car stereo up real loud and seen your headlights dim in beat with the music? Same thing, the power system is being drawn down. There are a couple of ways to stabalize your power system ... install a large capacitor (mine is 2 Farad) to provide "conditioning", or go the transformer route.A tansformer provides conditioning, but only on its own outputs... while a large cap will condition the entire power system if installed correctly.
So yes, using a quick charger on your phone can cause issues if your car has a ****ty power system or a large stereo system which is not set up properly (again, ****ty power system). Make sure your charging device is within the standard, and you should be fine wether it is USB via a cigarette lighter port or a 110V transformer.
I appreciate your detailed, helpful reply.
Other than the important 5v parameter, what I've taken away from your information is that a car charger can be used in a vehicle with a power supply that is known to be stable, and that either a whole-car conditioning system or an inverter should be used on one with a, shall we say, "less than stable" power supply (PG version ).
Jack45 said:
I appreciate your detailed, helpful reply.
Other than the important 5v parameter, what I've taken away from your information is that a car charger can be used in a vehicle with a power supply that is known to be stable, and that either a whole-car conditioning system or an inverter should be used on one with a, shall we say, "less than stable" power supply (PG version ).
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Pretty much ...
There's more than one way to skin a cat, and that Transformer will cost you a whole lot less than a 2 Farad capacitor. I hate cats, but they serve a purpose.
@Battlehymn - one more question for you
I have converted from iPhone to the captivate (no haters please) - finally found a physical form factor with specs i like and the captivate rocks.
Anyway, I have some extra external batteries I used with my iphone that i want to use with my Captivate. I just bought a Female iPod connector and I am planning to connect it to a micro USB connector - the pinout is straight forward, but here is my question:
Should I connect the D+/- (short them together)? That is my plan. My batteries are 1900 or 1000 mAH - I assume that even if the phone tries to the draw 1.8A, the batteries have a circuit to only discharge so fast.
I just got my hands on a Griffin AC Wall Charger (USB) for the iPad and iPhones/iPods. It outputs 2.1 amps. Would it be harmful to use the charging block on my HTC Sensation, since the charger that came with it is at 1 amp?
And the survey says....YES
Sent From My Pocket
Why do you say that? Why would it damage anything?
From what i've learned, more ampere is okay, less is harmful.
If the charger produces more ampere than needed, the device
will still just consume the 1A it's supposed to get from the charger.
If the charger produces less ampere than needed, the charger
tries constantly to supply the device with 1A which it can not reach,
resulting in overheating and maybe destroying the charger
(and thus maybe damaging the device).
Are both 5V? I guess more than this could be harmful.
It's been a few days since i had this in school, so i can not guarantee for correctness,
maybe some of the smarter guys/girls here could acknowledge/deny my statements just to be sure.
brndklng said:
From what i've learned, more ampere is okay, less is harmful.
If the charger produces more ampere than needed, the device
will still just consume the 1A it's supposed to get from the charger.
If the charger produces less ampere than needed, the charger
tries constantly to supply the device with 1A which it can not reach,
resulting in overheating and maybe destroying the charger
(and thus maybe damaging the device).
Are both 5V? I guess more than this could be harmful.
It's been a few days since i had this in school, so i can not guarantee for correctness,
maybe some of the smarter guys/girls here could acknowledge/deny my statements just to be sure.
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Click to collapse
You are correct.
The phone (which actually contains the charger) will pull as much current as it needs from the power supply (the thing we plug into the wall and incorrectly call a charger).
Part of the charging circuit should stop the phone drawing more current than the PSU can supply and causing damage.
Voltage is the important one that must be 5v DC.
Idealy you need a PSU that can provide more current than the device can possibly drain, that way it will relieve the load on the battery and the excess current can then go towards charging the battery.
I would figure it would draw too much and damage it. I had one of those iGo chargers and it was only 0.75 amps and it made noise so I stopped using it altogether. The charger's I'm getting are rated at 2.1amps and have a DC current of 5V so from what I read above it should be alright since the phone limits the charger to 1amp.
The mA (or A) rating on the PSU is the maximum it can provide, not the amount it will actually pull.
The amount it pulls is down to the resistance of the device.
Think of your car's alternator, mine provides 95A.
My headlight bulbs are 55W, so at 14V they each draw only about 4A of that 95A.
Using the formula V=IR, rearranged to R=V/I we get 14/4=3.5 Ohms, so the resistance of each bulb is 3.5 Ohms.
xaccers said:
The mA (or A) rating on the PSU is the maximum it can provide, not the amount it will actually pull.
The amount it pulls is down to the resistance of the device.
Think of your car's alternator, mine provides 95A.
My headlight bulbs are 55W, so at 14V they each draw only about 4A of that 95A.
Using the formula V=IR, rearranged to R=V/I we get 14/4=3.5 Ohms, so the resistance of each bulb is 3.5 Ohms.
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+1
Good to see there are a few people here who know, and can apply, Ohm's Law.
Also, I have the Griffin charger that looks like a small cube. It works fine.
The noise you hear is from the PSU circuit in the supply (SMPS = switch mode power supply). It takes your house voltage/frequency and converts it to a high frequency/low voltage DC for your phone's charging circuit to use. Thats the noise, and it is normal, although bothersome!
Matt
mrg02d said:
+1
Good to see there are a few people here who know, and can apply, Ohm's Law.
Matt
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I fear we may be a dying breed Matt
Hi guys.
I have a bit of a tech question in regards to the charging dock for my sony xperia z.
I know how these smartphones can chew a lot of power and can go flat pretty quickly. so i charge the phone from a 240v power supply which has a 5v usb output rated at 2.1 amps. I know it charges faster than using the official charger which is rated at 1.5 amp as i have done my tests at work where i have the equipment to do so on my desk. I understand that it might reduce the life of the battery and probably not recommended as the battery is a lipo (kaboom).
I haven't seen one docking station out there which will charge at 2.1 amps!! So i bought 2 cheap knock-off charging docks off ebay in the hope i could use the charger with the 2.1 amp output. Both docks rated at 1 amp input and output. I was curious as to why they had a 1 amp input. So i opened it up and found a circuit. I redrew that circuit on paper so i could see what was happening. It is a simple circuit with a mosfet and transistor, which no matter what current you put through it, it will only allow up to 1 amp to pass through. Now why would they have that in there? Is it to make it usb compliant? why not just have a straight through connection to allow for higher current charging? Or do the charging pads on the side of the phone only support up to 1.8 amps (like the original sony dock) but they decide 1 amp is safe enough in case they have a faulty unit or whatever...i don't know.
I know it might seem like a stupid question but this raises another. Does the 2 charging pads on the side of the phone link directly in-line with the usb micro port for charging? or does it have its own regulation as well?
Basically what I want to do is modify the dock so it is a straight through connection, bypassing the circuit in the dock so i can plug my 240v mains adaptor to usb which outputs 2.1 amp so I can get that faster charge. My worry is if those charging pads will handle that sort of current or damage its regulator if it has one or even the usb micro regulator if it has its own? I know people say "it will only draw what it needs"......That statement is only true to those devices which have no battery and rely solely on a power adaptor. If the device has a battery, it will take what it is given, unless there is some sort of regulation to prevent over charging. Like I said, I have done my testing.
I was just hoping someone out there might have some more knowledge on this, specially in regards to the charging pads on the side of the phone. I don't particulaly want to ruin my $700 phone
Hi,
have you actually tried to do the modification? I was thinking about the same thing...
I need a lesson on how USB charging works and what Watts, Volts, and Amps are and how they are different.
Also, does the USB cable play a role in the charging process? As in, are all USB cables capable of transferring the same amount of power?
I have a LG G3 and want to buy a portable charger, but want to make sure I will buy one that is fast enough and will be supported.
Any help is appreciated.
Volts, amps, watts? Check out the Wiki, they're doing great.
Of course, the cable plays a role in the process, e-very-thing plays a role!
The original USB specification was not originally developed with high power delivery in mind, thence it all started with a measly 5V, something which can pose a real problem when delivering high currents because, as voltage drop is proportional to conductor resistance, nasty cheapass cables can cripple current flow badly (so little volts we can't allow to drop them much).
Wanna see an example of a “that sh1te rocks” cable? Check this out: No frills USB to MicroUSB Heavy-duty Cat-5e 5ft/1'5m cable (No one trashes Jersey city! Uuuh, but me. :laugh
Brief summary: for a cable gauge/section is your ally, lenght your enemy. Aiming at keeping the same voltage drop between the supply (charger) and the load (device), the wire section will have to be proportional to its lenght (equal conductor resistance).
Tips: a reduction of 3 points in the AWG scale is about equivalent to doubling the section; -6 points means around double diameter. For example, AWG22 wire has about 4 times the section of AWG28 (4 times the current delivery, lenght being equal of course). And that (AWG22) is about the minimum gauge required to guarantee 2'1A of current flow through 2 meters of cable while still having just some chances of meeting the USB2.0 specifications (±5% in voltage).
Regarding the PSU (yes, Power Supply Unit), buy some decent brand name one. These things charge nothing, they're just power supplies (I've only seen one “charger” with active load voltage compensation; an LG unit which I converted to microUSB and have somewhere lying around).
It's the power management circuitry of your device the master who owns your battery, not the c̶h̶a̶r̶g̶e̶r̶ supply. The battery receives the remaining energy available from that circuitry (up to the maximum charging current for which it is programmed to deliver) after feeding the guts of your device (and minus innefficiencies). That's the reason your phone barely charges if you're USB connected (500mA) while operating it, because only around 2'5W of power are being delivered (5V×500mA) and, after substracting SoC + screen consumption figures plus power conversion innefficiencies, you may still be lucky if your battery “gets some”.
Charger reviews: http://lygte-info.dk/
Don't know about your device but, if it supports Qualcomm QC protocols you may as well benefit from a QC2.0 compliant charger.
Hope this helps. :silly:
Cheers