Can someone explain electrical stuff to me

DJFuji

Diamond Member
Oct 18, 1999
3,643
1
76
I've noticed that different chargers charge my cell phone battery at different rates. What am I looking for here? Amps?

As in the more amps = the more juice = the faster the charge?

Will too many amps damage equipment?

I also have a 4-port USB charger for my car. (this one: http://cgi.ebay.com/4-Ports-Ca...WQQrdZ1QQcmdZViewItem)

It works fine except that it takes FOREVER to charge. It delivers so little juice that I can be in the car for an hour and a half and my battery will only charge maybe 15%.

Is this because of the device or is my retractable usb cable not capable of handling that kind of current? Or is it because there are 4 ports on the charger? Or is it because it's just poor quality?

The chargers i've bought in the past from the sprint store would charge a phone to full battery in about an hour or less. Why?
 

edro

Lifer
Apr 5, 2002
24,326
68
91
The charge rate is Amps per Hour, usually listed as mAh.
The higher the mAh, the faster they charge.
The faster they charge, the more heat is released.
The more heat that is released, the shorter your battery life will be.

Usually, a longer charge is more healthy for the battery.
It usually ensures a longer discharge length as well.
 

Gibson486

Lifer
Aug 9, 2000
18,378
2
0
4 port USB charger? You are charging it from USB? From a car?

Is so, you are only charging from 5V with a 500mA max output. It should charge, just not as fast. How many volts is the batt? what is mah rated at? Are you using a usb charger for your phone or did you make a charger your self?

edit:

Oh...I see... it's a 4port usb thingy WITH a fm transmitter. The problem here is that you will NOT get 500mA from this crappy thing, even though the spec calls for it.

is this it?

http://www.cross-mark.com/port...mitter-ipod-p-470.html


It is a cheap thing that is made in china. All the power is probably going towards the fm transmitter and whatever power is left is going to usb. Yeah, it's 5V, but it won't give you 500mA.
 

0roo0roo

No Lifer
Sep 21, 2002
64,795
84
91
well my lg wall charger is 5v output at 1amp.
usb is 500mA then that might explain the pathetic charge rate
use a normal ciggy charger.
 

mugs

Lifer
Apr 29, 2003
48,920
46
91
Originally posted by: edro
The charge rate is Amps per Hour, usually listed as mAh.
The higher the mAh, the faster they charge.
The faster they charge, the more heat is released.
The more heat that is released, the shorter your battery life will be.

Usually, a longer charge is more healthy for the battery.
It usually ensures a longer discharge length as well.

It's not "per" hour. The charge rate is usually in milliamps, and the capacity of the battery is in milliamp-hours (mAh), which is mA * h, not mA / h as (milli)amps per hour would be.

So charging a 2900 mAh battery @ 200 mA would take 14.5 hours, because 2900 mAh / 200 mA = 14.5 h (think back to unit conversions that you learned in some high school science class, cancel out the matching units)
 

Paperdoc

Platinum Member
Aug 17, 2006
2,438
344
126
As Mugs said, mAh is the product of mA times hours. For a first simple thought, it is how many hours the battery will output a certain current in mA before it is dead. But in fact, a battery's output VOLTAGE drops off slowly as it is used, and hence the current output in mA also drops off, so there is never a constant output current. The mAh rating is the integrated mA versus hours output curve. It does tell you (with the voltage) the total energy that can be stored in and used from the battery.

Anyway, for charging a similar situation arises. First of all we must recognize that a charger hooked up to a battery must provide a VOLTAGE that is slightly higher than the battery's voltage; otherwise it cannot push amps into the battery and charge it up. The charging current depends on how much excess voltage is supplied. But too large a charging current can damage the battery in several ways. So a good charger limits its charging current by controlling its output voltage; however, this is dynamic because, as the battery is charged, its own output voltage rises slowly and the charger must supply marginally more voltage to keep the current flowing. At just the right voltage, the charger must stop doing this because each battery type has its correct maximum voltage. That is why it is so important to use the right charger for the battery you are trying to charge. A good charger will limit its charging current during charging, then stop charging at the right voltage, and probably keep checking to see whether a tiny top-up charge is necessary if the battery is still sitting there discharging slowly in the charger.

Any charger might do these functions and still be slow if it cannot actually deliver the maximum charging current a weak battery can stand. For example, you might have a battery that can be charged at a maximum rate of 1.0 amps (1000 mA), but if your charger can only supply 300 mA the charge rate will be slower than with a better charger. Worse, many of the cheap chargers may be rated for, say, 500 mA max but actually will only deliver that to a dead battery, delivering much less charging rate to a partially-charged battery.

You cannot predict exactly the time it takes to charge a battery. Suppose the battery is labelled 1800 mAh, and your charger says it can delivery 1000 mA. Quick math says it will take 1.8 hours. But in fact, even with a good charger, it will proably take 2 to 4 times that much time, because over the entire charging cycle the charger's output into the battery will not stay at the max (1000 mA), but will decrease as the battery voltage rises.

Bottom line on your questions is, you are right, some chargers will do the job much faster. As a very rough guide, the amps rating of the charger will tell you something. But that still is not the whole story, because the real detail is in the way it ramps up voltage and maintains a charging rate (amps) as the battery's own voltage increases due to the charging action. And what they really can't tell you on the label is how well it does this without damaging the battery either by charging too fast, or by going up too high on the final voltage. For those things it's more reputation of the charger manufacturer or, if you can find it, actual performance tests that look closely at these questions.
 

DJFuji

Diamond Member
Oct 18, 1999
3,643
1
76
Wow thanks so much for that writeup, paperdoc. I knew there were some electricity geniuses here at ATOT.

So a few questions:

a) An AC wall charger for my cell phone says the following:

Input: 100-240v ~ 0.2A 50-60Hz
Output: 5V = 1A LPS

I assume that means the plug can handle between 100 and 240V but what is 50-60Hz and what does 0.2A mean? Why do my other chargers say 0.3A or 0.5A?

What is LPS?

Does the 1A on output mean that that's the theoretical max juice being supplied to the device?

b) Is USB charging (even through a USB wall AC charger) limited to 500mA because of the USB cable or something?

c) Is it "better" for a device like a phone to be charged from a computer/usb port rather than a AC wall unit, since the USB port will charge slower ("healthier for the battery")?

d) If i'm buying a cell phone car charger (mini USB), is it safe to buy an "OEM" part from ebay? Sprint sells the adapters but at $30 that's extortion. I really wanted a USB car adapter with 4 ports so that i could simultaneously charge all my usb devices, but if none of the ports provide much power, i guess there's no point to it.

 

0roo0roo

No Lifer
Sep 21, 2002
64,795
84
91
input range just tells you that it works in the us and overseas. 110v 60hz us... in uk its 220~ 50hz for instance.
just tells you u can travel with it without frying it.

and no, usb cable doesn't limit it, spec for pc usb probably would. usb generic charger would probably follow the same limit.

http://docs.info.apple.com/article.html?artnum=60939
manufacturer specific apples ac charger uses a usb plug, but its 12v 1amp.
probably just takes longer to charge from a real usb port.
 

Paperdoc

Platinum Member
Aug 17, 2006
2,438
344
126
DJFuji, to your questions:

a. The input specs just tell you what the charger can accept from the wall. In USA, Canada, here we have 110 to 120 v AC at 60 Hz. In many European countries it's 220 to 240 v AC, at 50 Hz or 60 Hz. The "Hz" stands for hertz, aka cycles per second, the frequency of the alternating current. Your charger can automatically adjust for either voltage standard, and handles both common frequencies, so it can be plugged in in many places. Now, the actual plug prong configuration often is different to prevent people from making a mistake and plugging something into the wrong outlet. You can buy very simple adapters for just this purpose to allow you to plug yours into a European outlet, since it can handle the electrical characteristics properly. That is much cheaper and simpler than buying a power transformer. The "0.2 A" part just tells you the adapter will pull current at about 0.2 Amps from the wall. Other chargers that consume more probably also output a higher maximum charging current when needed. The output into the battery will be about 5 v, but you have not shown any note whether it is AC or DC. I presume there is no note about that. Some devices, like my electric shaver, have the AC-to-DC conversion system built into their own cases and are designed for a particular AC input from their chargers. Others, like battery chargers and, I suspect, your cell phone, depend on having the completly proper DC voltage supplied from the charger. The "1A" means that is the maximum current it will supply to the device. I don't recognize the "LPS" abbreviation.

b. I had to think about the term "USB Charging" for a minute, and OrooOroo provided the clue. Apparently your device is built so that it can be connected to something else via a USB cable for data exchange, etc. A normal USB connection includes two lines for DC power supplied by the "host" (e.g., a computer or a dock) to the client device. By design, these lines are limited to drawing no more than 500 mA from the host. Now many such client devices, like your cell phone, can also be hooked up to a dedicated power supply "brick" or charger instead of depending on having a computer handy to act as host. Since this charger does not have to be limited to the 500 mA that a usual host is, it would be possible to design it to provide more. However, that would be wasted if the device (your phone) were not designed to accept more power if it were available. My guess is the manufacturer would not design this way, and just stick to the 500 mA max limit. But maybe not - the dedicated charger you have is labelled "1A".

c. Charging more slowly (e.g. from a USB port limited to 500 mA max) may be better for the battery, depending on how the unit was designed. Certainly it is possible to design for much larger charging currents with the right battery and charging circuit. IF the battery is designed for faster charging at higher currents, there is little advantage to deliberately going slow at 500 mA max. However, my suspicion is that your cell phone, apparently designed for charging mainly through the USB connector power leads, may be designed for only the 500 mA max input, anyway. If that is so, and it has decent self-protection circuitry, it may never draw more than 500 mA no matter what the charger can do.

d. Is an OEM charger as good as one from the cell phone maker? Impossible to say. In each case it depends on how the overall system controls the voltage and current to the battery. IF the cell phone has all that control system built into the phone itself so that all it needs is a reliable 5v DC source that can supply up to 500 mA, either charger could be just as good because the design of the charger is not too critical. My speculation is that this is how the phone was designed, since it "normally" would function with that kind of DC supply from any old USB connector, no matter what source. BUT if the cell phone really depends on the charger to do all the regulation of charging voltage and current, an OEM device might not do quite the same job. IF you beleive them, manufacturers sometimes alert you to this by saying very prominently that you MUST use only their charger. If they don't say that, you're probably OK with OEM.

You started out by saying the 4-port USB adapter system seems to charge your cell phone battery slowly. That may be because you are using all 4 ports for something at the same time, and here's why. The car cigarette outlet supplies 12 to 14v DC, and the adapter has to cut that down to 5v DC. The cheap simple way to do that is to put inside a resistor so that, at the expected output current, about 8 volts "drops" across the resistor and thus 5v are available as output. Using 500 mA max as the output current can give you the resistor value for the design. Or it could be a slightly more complex voltage regulator circuit. But if you actually plug in several USB devices, each using, say 100 to 300 mA, the actual current flowing through the resistor is more than 500 mA and the voltage drop is greater, leaving a slightly low output voltage to the USB devices. (Even cheap voltage regulators can show an effect like this, although less pronounced than a simple resistor.) For many such devices, a supply of 4.7v instead of 5.0 would be no problem - they can tolerate some deviation from ideal. The one device that DOES have a problem with this, though, is a battery charger! If it is going to charge up a battery, it needs to give the battery a voltage only a little bit - say, 0.05 to 0.15 v - higher than the battery already is. But if the voltage available to the charging regulation circuit is less than what is needed, the charging will proceed at a VERY low amperage and be very slow. So try charging the cell phone with nothing else attached to the 4-port unit, and the cell phone turned off. See if it is much faster. IF that makes a difference, try changing your system in the car a little. You will need to "manufacture" a second cigarette lighter outlet. Maybe your car already has an extra "power outlet"; otherwise you can buy an adapter to give you two from one. Plug your 4-port adapter into one of them. Then plug the special car charger for your cell phone into the other outlet. In this way your cell phone charger will have independent access to the full cigarette lighter supply with no inteference from the 4-port adapter's innards.

Oh, you'll note I said "cell phone turned off". If the phone is turned on, whether you are calling or not, it is using power from the battery. During calls it uses more power. Even when you're not calling, if you are in a low-signal area it uses power just to keep in contact with the towers. All that power use consumes some of the charging current you are doing at the same time, so it can really lengthen the charging time. Now, I know you normally will keep the phone turned on. This is just to explain why the charging time can get longer - I'm not suggesting you stop using the phone in the car just so it will charge up quickly.
 

polarmystery

Diamond Member
Aug 21, 2005
3,888
8
81
I salute Paperdoc for spending so much time on his posts explaining things to the OP. Honest help is rare nowadays.

:thumbsup:
 

DJFuji

Diamond Member
Oct 18, 1999
3,643
1
76
Yeah totally, eaj0010.

Paperdoc, you are the man. That was a HUGE help. Thanks so much.

I'll give it a shot with the 4 port USB adapter plugged directly into the power socket. I was only using one usb port, but the usb adapter was plugged into one of those 3-way power splitters which gives you 3 cigarette lighter adapter outlets. Plus, the actual usb cable i was using for power was one of those retractable thin-style usb cables. Not sure if that makes a huge difference, but I know that when i used a regular cigarette lighter charger, it charged much faster than even using a single USB port.

For reference, I have the sprint mogul Pocket PC. I have a piece of software which monitors the mA the battery is pulling (about "150mA" when idle and medium brightness, about "+180" when plugged into the aforementioend wall charger). While this is interesting, I have a feeling that this data is not nearly accurate enough to use for anything. Is this suspicion correct?

I guess i'll probably just buy a regular car charger off ebay. I'm tempted to buy liek a brand name 2-port USB splitter but i suspect it wont charge as fast and i'd rather give up the USB option.

I dont know if i trust the 3-port splitter either because it's of poor build quality and every time i plug in my phone, it emits a high pitched whine.
 

Howard

Lifer
Oct 14, 1999
47,982
10
81
Originally posted by: edro
The charge rate is Amps per Hour, usually listed as mAh.
The higher the mAh, the faster they charge.
The faster they charge, the more heat is released.
The more heat that is released, the shorter your battery life will be.

Usually, a longer charge is more healthy for the battery.
It usually ensures a longer discharge length as well.
WTF
 

darthsidious

Senior member
Jul 13, 2005
481
0
71
Originally posted by: Paperdoc
DJFuji, to your questions:

a. The input specs just tell you what the charger can accept from the wall. In USA, Canada, here we have 110 to 120 v AC at 60 Hz. In many European countries it's 220 to 240 v AC, at 50 Hz or 60 Hz. The "Hz" stands for hertz, aka cycles per second, the frequency of the alternating current. Your charger can automatically adjust for either voltage standard, and handles both common frequencies, so it can be plugged in in many places. Now, the actual plug prong configuration often is different to prevent people from making a mistake and plugging something into the wrong outlet. You can buy very simple adapters for just this purpose to allow you to plug yours into a European outlet, since it can handle the electrical characteristics properly. That is much cheaper and simpler than buying a power transformer. The "0.2 A" part just tells you the adapter will pull current at about 0.2 Amps from the wall. Other chargers that consume more probably also output a higher maximum charging current when needed. The output into the battery will be about 5 v, but you have not shown any note whether it is AC or DC. I presume there is no note about that. Some devices, like my electric shaver, have the AC-to-DC conversion system built into their own cases and are designed for a particular AC input from their chargers. Others, like battery chargers and, I suspect, your cell phone, depend on having the completly proper DC voltage supplied from the charger. The "1A" means that is the maximum current it will supply to the device. I don't recognize the "LPS" abbreviation.

b. I had to think about the term "USB Charging" for a minute, and OrooOroo provided the clue. Apparently your device is built so that it can be connected to something else via a USB cable for data exchange, etc. A normal USB connection includes two lines for DC power supplied by the "host" (e.g., a computer or a dock) to the client device. By design, these lines are limited to drawing no more than 500 mA from the host. Now many such client devices, like your cell phone, can also be hooked up to a dedicated power supply "brick" or charger instead of depending on having a computer handy to act as host. Since this charger does not have to be limited to the 500 mA that a usual host is, it would be possible to design it to provide more. However, that would be wasted if the device (your phone) were not designed to accept more power if it were available. My guess is the manufacturer would not design this way, and just stick to the 500 mA max limit. But maybe not - the dedicated charger you have is labelled "1A".

c. Charging more slowly (e.g. from a USB port limited to 500 mA max) may be better for the battery, depending on how the unit was designed. Certainly it is possible to design for much larger charging currents with the right battery and charging circuit. IF the battery is designed for faster charging at higher currents, there is little advantage to deliberately going slow at 500 mA max. However, my suspicion is that your cell phone, apparently designed for charging mainly through the USB connector power leads, may be designed for only the 500 mA max input, anyway. If that is so, and it has decent self-protection circuitry, it may never draw more than 500 mA no matter what the charger can do.

d. Is an OEM charger as good as one from the cell phone maker? Impossible to say. In each case it depends on how the overall system controls the voltage and current to the battery. IF the cell phone has all that control system built into the phone itself so that all it needs is a reliable 5v DC source that can supply up to 500 mA, either charger could be just as good because the design of the charger is not too critical. My speculation is that this is how the phone was designed, since it "normally" would function with that kind of DC supply from any old USB connector, no matter what source. BUT if the cell phone really depends on the charger to do all the regulation of charging voltage and current, an OEM device might not do quite the same job. IF you beleive them, manufacturers sometimes alert you to this by saying very prominently that you MUST use only their charger. If they don't say that, you're probably OK with OEM.

You started out by saying the 4-port USB adapter system seems to charge your cell phone battery slowly. That may be because you are using all 4 ports for something at the same time, and here's why. The car cigarette outlet supplies 12 to 14v DC, and the adapter has to cut that down to 5v DC. The cheap simple way to do that is to put inside a resistor so that, at the expected output current, about 8 volts "drops" across the resistor and thus 5v are available as output. Using 500 mA max as the output current can give you the resistor value for the design. Or it could be a slightly more complex voltage regulator circuit. But if you actually plug in several USB devices, each using, say 100 to 300 mA, the actual current flowing through the resistor is more than 500 mA and the voltage drop is greater, leaving a slightly low output voltage to the USB devices. (Even cheap voltage regulators can show an effect like this, although less pronounced than a simple resistor.) For many such devices, a supply of 4.7v instead of 5.0 would be no problem - they can tolerate some deviation from ideal. The one device that DOES have a problem with this, though, is a battery charger! If it is going to charge up a battery, it needs to give the battery a voltage only a little bit - say, 0.05 to 0.15 v - higher than the battery already is. But if the voltage available to the charging regulation circuit is less than what is needed, the charging will proceed at a VERY low amperage and be very slow. So try charging the cell phone with nothing else attached to the 4-port unit, and the cell phone turned off. See if it is much faster. IF that makes a difference, try changing your system in the car a little. You will need to "manufacture" a second cigarette lighter outlet. Maybe your car already has an extra "power outlet"; otherwise you can buy an adapter to give you two from one. Plug your 4-port adapter into one of them. Then plug the special car charger for your cell phone into the other outlet. In this way your cell phone charger will have independent access to the full cigarette lighter supply with no inteference from the 4-port adapter's innards.

Oh, you'll note I said "cell phone turned off". If the phone is turned on, whether you are calling or not, it is using power from the battery. During calls it uses more power. Even when you're not calling, if you are in a low-signal area it uses power just to keep in contact with the towers. All that power use consumes some of the charging current you are doing at the same time, so it can really lengthen the charging time. Now, I know you normally will keep the phone turned on. This is just to explain why the charging time can get longer - I'm not suggesting you stop using the phone in the car just so it will charge up quickly.

As I'm working in a related area, I wanted to add a few comment to your post. First of all, I think it's a pretty good crack at explaining this stuff to someone who doesn't know much about it. This might be a little technical, so this is probably more for your benefit than DJ Fuji's. Apologie in advance if I misinterpreted something you wrote.

Firstly, as you mention, the USB spec limits a host device to 500mA of current. A dedicated charger can support more (1.5A is a common limit on external chargers). However, recently, there has been an addition to the USB spec called the USB charging spec, which allows these special devices to support upto 1.5A of supply current.

Unlike how you mention, LiIon battery charging (I'm assuming his phone is new enough to use a LiIon battery) is very C-V sensitive. When the battery is low (say below 2.5V or so), you have to charge the battery very slowly (around C/10 mA, where C is the battery capacity in mAH). Once the voltage crosses a threshold, you can charge with a much higher current (around C), and finally, when you get high enough voltage on the battery, the chargin current has to drop drastically again. Therefore, you can't just hook up the output of a regulator to a LiIon battery, That would be dangerous in the extreme, as pumping high currents to a LiIon battery when it's at a low voltage can cause it to explode! Therefore, if you ever get the urge to play around with a LiIon battery's charging curve, be extremely careful. Also, the supply voltage of a USB device is guaranteed (atleast according to spec) to be between 4.75 and 5.25, while the LiIon battery tops off closer to 4V. So if you wanted to charge a battery using a USB device, you need to regulate the current going into the battery on the phone. Even if you use a custom connecter/external charger, in theory it's possible to regulate the output current and voltage of the regulator in the charger instead of the phone, but I'd be extremely surprised if anyone did that. It's much more efficient (and safer) to simply have the charging control circuit built into the phone. The charger's job is simply to provide a high enough voltage with a reasonably controlled range and reasonably high maximum current capacity.

I'f be very surprised if someone used the "cheap way" of converting 12V dc to 5V dc you suggested. However you size the resistor in that case, you're going to run into massive problems in some cases. If you size it for 1 500mA load, then when you connect 4 500mA loads, the voltage collapses to 1.25V. If you size it for 4 500mA loads, then you run into issues when you plug in only 1 500mA load, the output jumps to about 12V. That's massive variation that would violate most specifications. I'd bet they probably use either a linear regulator (which is cheaper/less noisy/less efficient) or a DC/DC converter (pricier/more noisy/more efficient).

If you're interested in learning more about the interface issues between car chargers and cellphones, you can read the USB specification (which is more general and describes conne ctions between generic hosts and slave devices), or the CEA-936A standard (which deals with carkits and cellphones).
 

Dessert Tears

Golden Member
Feb 27, 2005
1,100
0
76
Originally posted by: jamesave
Is this La Crosse battery charger really good?

http://www.amazon.com/Crosse-T...&qid=1213924650&sr=8-4
There are apparently problems with earlier firmwares, but I have no idea what the current firmware is. I have a v32 or v33, and certain batteries seem to have significantly lower capacity than the others. I don't know the root cause, but the batteries with good performance were charged on a Maha charger that I had previously. In terms of price versus feature set, it's a good deal. There have been several charger threads that you should be able to find with a search.
 

Paperdoc

Platinum Member
Aug 17, 2006
2,438
344
126
Darthsidious, thanks for the excellent technical additions. From what you say about Li Ion batteries, that is one area where the user is best to use only the charger supplied with the device, expecting that the designers took all that into account in their work.

And to you and others, thanks for kind words.
 

0roo0roo

No Lifer
Sep 21, 2002
64,795
84
91
Even if you use a custom connecter/external charger, in theory it's possible to regulate the output current and voltage of the regulator in the charger instead of the phone, but I'd be extremely surprised if anyone did that. It's much more efficient (and safer) to simply have the charging control circuit built into the phone. The charger's job is simply to provide a high enough voltage with a reasonably controlled range and reasonably high maximum current capacity.

yup, chargers for lithium ion devices are "dumb", its why you have 10 dollar car adaptors and such. they only regulate voltage or chance ac to dc. and their job is to simply provide enough of it. the charge circuitry is always built into the device. i doubt his battery is so delicate that it can only handle 500mA of generic usb. he should get a dedicated adaptor and stop using generic hubs for charging.