iPod charging; how to go from 2 amps to 1 amp?

[mikefromsac]

I have an iPod Classic and it has a sensor to not allow charging unless the power is 1 amp or less (at 5 volts). When I travel, I take an EC 22400mAh External Battery which provides 2 amps at 5 volts for iPhones, iPad, etc. I need a way to charge the iPod so I was thinking of modifying a USB charging cord to drop the amps to 1. How would I do this?

- Resistor?
- If so, what size?
- How to install into the USB cable, which wire would I spice it into?
- Any other ideas?

Thanks in advance, - Mike

[Simon]

I'm very confused. I device will take as much current as it wishes until the device supply the current cuts the supply under the control of some sort of current limit. There is no way to actually limit the current if anything I would have thought your device would stop charging if the current is being drawn drop too low. I think you need to check the specifications again.

[mikefromsac]

That's what I thought. The iPod classic seems different. From the Apple discussion board: "... the iPod has a self presevation circuit that limits the current to 1 Amp, using D- and D+ voltage, if the current goes above 1 Amp, the charging circiut in the iPod shuts down ..."

[Simon]

Well if you buy a wank product like an iPad what you expect. All the product has to do is limit it charging current it does not need to shut down if it itself decides to take more current it's a conflicting statement. Most lithium ion batteries have a built in charge controller which limits the current so the device does not need to shut down it just does its job.

[mikefromsac]

Wow, I don't know how to reply to this. I didn't design it and Apple products are pretty popular here in the states. The iPod has been sold for over 10 years and it requires the iPhone 1 amp charger and won't charge from a 2 amp iPad charger. I just thought people on this board might have an idea on how to modify a USB cord to bring a 2 amp charger to 1 amp. I thought it might be an easy and fun project for a beginner like me. I didn't mean to offend anyone because I bought an Apple product ...

[Simon]

No offence taken it's just the Apple are notorious for making things difficult for people who want to tinker. For starters you can't take the batteries out without voiding the warranty and you can't replace your own battery. So the idea that you can create modifications is most certainly not something Apple would be happy with.

I don't know how they are doing this it must be some sort of communication protocol between the device and the charger if they really are doing this. It sounds like it amounts to making you buy 2 chargers when you only need one. Usually obviously not in Apple world it is the load that controls the amount occurrence it is charging not the charger this is a pretty universal concept but obviously not for Apple. I don't know if anybody else knows what they have done and how they do it but my suspicion is they would have done their best to make it tamperproof. Maybe you're lucky and it's just something silly like a resistor but tells the device which charger it is but I suspect Apple have been cleverer than that.

[mikefromsac]

Gotcha, I just thought there would a way to limit the amps coming out of the charger to 1 amp instead of 2 amps using some kind of resistor in a custom charging cord I could assemble.

[Simon]

Well you could have a current limited output but that would just confuse the device being charged, it is the device being charged that is usually resposible for liiting it's current intake, although all smart phones seem to charge on a 500mA USB port but will charge faster on a 1A charger but to detect that more current IS available and shut down is just pure evil, if you only need one amp you only take one amp, why shut down because the charger could provide 2A if you wanted to use it ?

[biffster]

You might actually find that it's nothing to do with the charger's ability to provide a certain current. Apple devices normally require a certain voltage on the D+ and D- pins to allow charging to start. That's how they make people buy Apple chargers rather than cheaper generic versions. You can Google what voltage the iPod needs on D+ and D- (it's not the same for every device) and check what your iPad charger actually gives you to see if it will work. I've made up cables before that generate the correct voltage on those pins using resistors between V+, D+, D- and V- 

[mikefromsac]

That makes more sense to me from my limited knowledge. Here's the specs from Apple for their chargers:

iPhone Charger (which will charge the iPod fine)
5 volts
1.0 amps
5 Watts

iPad Charger (won't charge an iPod Classic)
5.1 volts
2.1 amps
12 watts

Can the 0.1 volt make the difference?  If so, what size resistor do you recommend?

- Mike

[Aodhan145]

If i recall you need to put some voltage on the D+ or D- pins to charge the old ipods. The newer charger might not have that. Measure the voltage on D+ and D- pins of the usb from each charger.

Edit: Just found a website https://www.voltaicsystems.com/blog/choosing-usb-pin-voltages-for-iphones-and-ipads/

[Whales]

Can the 0.1 volt make the difference?  If so, what size resistor do you recommend?

No it will not.

If anything is stopping you charging your '1A device' on a '2A charger' then it is entirely artificial (or a fault).  A '5v 2A' charger will supply any amount of current up to 2A.  0.1A is fine.  1.5A is fine. 

[ade]

Today we take USB charging for granted, but the iPod Classic was designed at a time most PCs had dodgy USB ports. 

If I recall, it was common back then to shut down if the current rises beyond a certain threshold (500ma or 1A) to prevent burning out the port on the host side.  This may be caused due to incorrect resistance value (or short) on the USB port.

[The Magic Rabbit]

This idea that the iPod classic wont charge from a 2A supply is just nonsense. I've been doing just that for over 4 years. It won't charge from an official Apple 2A charger, but that's because of the way their chargers are designed. A universal 2A iPod charger works fine, and even charges at a faster rate than the original charger.

I'm not sure of the exact method, but as far as I know there's a particular way the D+ and D- have to be wired to tell the system it's connected to a charger and not a communication device. My Sat Nav also uses this method and D- is grounded while D+ is connected to 5V via a 5k resister. This doesn't work for the iPod though, but I suspect a similar idea.

With standard USB ports, they have two modes of operation - standard and charge. In standard mode the current draw is limited to usually around 500mA (though this isn't always implemented), and in charge mode up to 2.5A

The answer to trouble free charging with Apple devices is usually to avoid Apple chargers and get a "compatible" charger since they tend to be far more universal. Apple like to play silly buggers with their extras so you have to buy more of them and can't share them between devices.

Sent from my XT1039 using Tapatalk

[mikefromsac]

Thank to all for the replies. I try again using the battery power bank.

[mikefromsac]

It works! Apparently, you have to plug in the iPod first, then into the power bank (at least with my iPod). Same with my Apple charger if you're not using the 1 amp version. Problem solved, thanks guys!

[Porch]

My automotive USB charger has two USB ports. One marked A (Apple) and the other marked NA (Not Apple). Seems silly they have to do this. 

[Agent24]

It would be possible to make an incredibly bad product that relies on the charger to limit current rather than the device itself, but Apple are not that useless.
Neither will your 2 Amp iPad charger try to 'ram' 2 amps down the iPod's throat, as it were.

The problem is entirely an artificial incompatibility created for the purpose of either profit, or more likely, safety in the other direction - that is, so you cannot connect a device which needs 2 Amps to a charger which can only supply 1 amps. This would be a problem as the device could overload the charger and damage it or cause fire etc.

From a safety standpoint, it does make sense to have each device only work with the charger designed for it, but for those in the know, it's an unwanted annoyance.

[Richard Crowley]

Apple devised a scheme to allow their gadgets to discover how much charging current is available from a "dumb charger" (i.e. not an actual USB port)
Apple use a pair of resistor voltage dividers on the +D and -D pins to set those pins to specific voltages (some fraction of 5).
The specific voltages tell the gadget how much current is available from the charger.
Here is one description of the scheme. There are almost certainly many others available online.
http://www.epanorama.net/newepa/2010/08/18/apple-charger-secrets/

[tooki]

I hate when people take the tone of "[manufacturer] is evil and did this on purpose to screw people over". They didn't. In the case of Apple, when the first iPod that could charge from USB* was released, there existed no standard for high-current USB charging as there is now; consequently, every manufacturer came up with their own system. Why do this at all? Because computer USB ports are normally 500mA, with overcurrent detection, causing the port to simply shut down if an overcurrent condition occurs. The solution is to have chargers identify themselves so the device knows how much current it can draw. That way you don't have an iPod trying to pull 1A from a 500mA computer USB port, while allowing 1A charging from a wall wart.  These systems fail when the device and charger are not designed for each other, so the charger identification fails and the device won't charge (if it's designed properly).

*Early iPods used FireWire, which provides 7W per port of unregulated power. The 3rd gen iPod added USB syncing, but still required FireWire for charging, using this funky dual-headed cable. 4th gen and later all charge from USB.

[Simon]

so why make the device shut down if the supply can supply more than enough power ?

[suicidaleggroll]

so why make the device shut down if the supply can supply more than enough power ?

Because it doesn't know that, it was developed before Apple standardized their charging specs (what different voltage combinations on D+/D- mean, etc.).  The iPod has no idea what the source can supply, so rather than going all in and hoping for the best, it shuts down to prevent damaging the source.

Every company has rules for this kind of thing, and many of those rules are mutually exclusive.  It has nothing to do with Apple forcing people to buy Apple chargers.

[Simon]

So does the iPod have a way of recognising the type of charger? If it does then the standard should have been backward compatible so that the iPod would charge from anything that could provide enough power. If they have multiple standards going then they have simply been reckless and inconsiderate towards their customers who they expect to buy "i" everything's

[tooki]

So does the iPod have a way of recognising the type of charger?

Yes, and the mechanism for it has been explained several times in this thread alone.

If it does then the standard should have been backward compatible so that the iPod would charge from anything that could provide enough power.

And how exactly would that backward compatibility work? It's not like MagSafe (which uses 1wire to tell the computer what kind of charger it is), it's just voltages on the data lines, created by a simple resistor voltage divider in the charger. The iPod can detect the adapters that existed when that iPod model was released. There were no 2A chargers (i.e. 2A on one port) until the iPad, which was introduced years after the final iPod classic was released. So whatever ID voltages Apple chose for 2A, the iPod would not recognize because it came later.

Properly designed USB devices don't just start drawing 500mA without asking (it's not allowed by the standard). It either needs to negotiate with the USB controller, which will tell it how much power it may draw, or use some kind of ID system for dumb chargers. What you don't want is the "charge from anything that could provide enough power" because that could result in the device drawing power from a USB port on a computer that has not approved that much current. Doing so could work fine, or it could result in either a fried hub, excessive voltage drop, the whole USB bus shutting down, etc. (And indeed, some cheeky "fast charging" cables do just this: disable the data lines so that the device cannot negotiate, and use resistors to create the ID voltages to tell the device to draw lots of power, without the USB controller's consent.)

Just because a $2 Chinese USB "hole warmer" pulls 500mA straight off the 5V line with no current negotiation doesn't mean it's good practice.

If they have multiple standards going then they have simply been reckless and inconsiderate towards their customers who they expect to buy "i" everything's

They've got one standard, but it's been extended necessarily over time. Older devices simply have no way of knowing about chargers introduced later.

Now there is a USB charging standard (USB Power Delivery). But a) old devices like the iPod don't know about it since they came before, and b) if Apple changed its chargers to the USB Power Delivery, then people with old iPods and the like would complain that new chargers don't work with existing devices. Typical "damned if you do, damned if you don't" kind of situation.

(There is also a slightly older USB "battery charging port" standard which does allow up to 1.5A charging without any negotiation, but this standard, too, was introduced after the last iPod classic was released.)

[ade]

Newer iPods / iPads + chargers are more "backwards & forwards compatible".

The iPod "Classic" however was based on a very old design (from 15 years ago!) built around FireWire at 12 volts.  When 5V USB support was grafted on, it had a lot of protections to prevent burning out dodgy PC USB ports from that era.  Back then, most computers only had USB 1.1.  Widespread adoption of USB 2.0 came a couple of years after the iPod's introduction.