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USB over-voltage tolerance? 8.38V?

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USB over-voltage tolerance? 8.38V?

Old 08-06-16, 04:54 PM
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CliffordK
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USB over-voltage tolerance? 8.38V?

I'm heading out on a ride tomorrow, and seem to always have cell phone battery issues with GPS trackers, especially if I keep the screen on for any period of time.

My solar charger is a bit awkward, and seems to work better as an external battery pack than an actual solar device.

So, one of my headlamp batteries also has a USB port. I thought I'd check, and it seems to be putting out about 8.38v (no load) at the USB port. The pack would be extremely easy to tie to the handlebars.

However, that is quite a bit more than the typical 5V that USB is rated for.

Safe or not? Currently I have a couple of older Samsung phones, but I'd also rather not fry them, or their batteries.
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Old 08-06-16, 07:45 PM
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unterhausen
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huh, never checked any of my battery packs, but I would probably skip an 8v pack for usb
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Old 08-07-16, 08:32 AM
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there are external batteries same size as the Phone and smaller..
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Old 08-09-16, 11:50 AM
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Well, I decided not to use the 8.4V pack... yet.
I got one of those worthless replies from my query to Samsung.

Thank you for taking the time to contact us at Samsung Technical Support. We always appreciate hearing from our customers.

I understand that you would like to know if external USB battery pack that puts out about 8.38V is compatible with your S4 mini and S4 zoom phones. I will provide you with the information.

I have checked the information for you and would like to inform you that, if you are using a Samsung genuine battery pack, then it is compatible with our Samsung phones.

Please use the below web-link to access the Samsung battery pack.
Perhaps I'll try the phone that flew out of my shirt pocket at 30 MPH (and still works).
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Old 08-09-16, 03:57 PM
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According to Wikipedia, USB power should be 5 volts +/- 5% or so. I'd say your headlight pack is perhaps purposely nonconforming. I sure wouldn't use it on a USB device.
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Old 08-09-16, 04:14 PM
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On many devices, one is fine if the volts are close, and the amps really just need to be higher.

Some devices are designed to do their own voltage regulation, and can take up to 20V or so... But one never knows, which is why I sent the note to Samsung technical support, and was just blown off.

I presume most of the 12V ==> USB adapters actually have voltage reduction, and hopefully voltage regulation circuitry.

I think the 8.4 V light battery packs were just being cheap. Trying to give an extra option, but without adequate circuit protection.

What might be nice would be a super-sized battery pack, capable of say 5x the power of a standard battery pack, but would otherwise seamlessly fit into the back of the phone (custom rear cover).
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Old 08-09-16, 04:39 PM
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Originally Posted by CliffordK View Post
. . . So, one of my headlamp batteries also has a USB port. I thought I'd check, and it seems to be putting out about 8.38v (no load) at the USB port. The pack would be extremely easy to tie to the handlebars.

However, that is quite a bit more than the typical 5V that USB is rated for.

Safe or not? Currently I have a couple of older Samsung phones, but I'd also rather not fry them, or their batteries.
"No load" is the operative term. Unless your headlamp battery has some sort of regulation that keeps it at 8.4v, it is probably unregulated, meaning the voltage drops when hooked up to a load, like a phone. If your headlamp battery has a usb output, that tells me it was intended to charge usb devices.

It's up to you, but I would carefully test my phone, constantly feeling for overheating (and looking for smoke). Since you are charging your phone battery with another battery, I don't think overvoltage for a brief time (again, while constantly feeling for overheating) will do any quick or irreversible damage.

The real question is whether your headlamp battery can handle enough current to meet whatever your phone draws. My guess is a headlamp draws more current than a phone, so you're probably OK. If it can't, you will notice your headlamp battery getting hot.

Ohm's Law.

Last edited by sea coil; 08-09-16 at 04:43 PM.
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Old 08-09-16, 04:49 PM
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Originally Posted by sea coil View Post
"No load" is the operative term. Unless your headlamp battery has some sort of regulation that keeps it at 8.4v, it is probably unregulated, meaning the voltage drops when hooked up to a load, like a phone. If your headlamp battery has a usb output, that tells me it was intended to charge usb devices.

It's up to you, but I would carefully test my phone, constantly feeling for overheating (and looking for smoke). Since you are charging your phone battery with another battery, I don't think overvoltage for a brief time (again, while constantly feeling for overheating) will do any quick or irreversible damage.

The real question is whether your headlamp battery can handle enough current to meet whatever your phone draws. My guess is a headlamp draws more current than a phone, so you're probably OK. If it can't, you will notice your headlamp battery getting hot.

Ohm's Law.
Since the headlamp batteries are about 10x the size of the phone batteries, I would hope they can handle the load. But, yes, there is a possibility of some voltage drop. Also, voltage does naturally decrease as batteries are discharged. Maybe I'll check the voltage with the headlamp on high beam.

Seeing "magic smoke" may be the point when it is too late.

The thing likes to charge with the LCD on, and does sometimes heat up. The LCD is nice for ride tracking, but it sucks down juice.
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