12V socket keeps killing USB car chargers - Stromtrooper Forum : Suzuki V-Strom Motorcycle Forums
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post #1 of 5 Old 11-06-2016, 02:42 PM Thread Starter
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12V socket keeps killing USB car chargers

All this is on my 2007 DL1000, if it matters.

I have a 12V socket on the handlebars, wired in what seems to me an odd fashion: instead of connecting to the nice aftermarket fuse block (seen below):


...the socket's wires terminate in an SAE plug, just like the plug people usually wire directly to the battery for a battery tender. So I have a pair of these SAE plugs back near the battery, like this:

To clarify: one SAE plug goes to the battery and came with a 7.5A fuse in-line on the positive side. The other SAE plug goes directly to the 12V socket, and has no fuse in-line. But, it is protected by the 7.5A fuse when powered, since it goes through the battery tender connection.

If I connect the 12V socket to the battery tender plug, I have power at the 12V socket when the bike is on (either key in "on" or engine running). I can run a 12V tire inflator off the 12V socket, no problem. Specifically, I have this Sears Craftsman inflator, which I originally bought to use with my car:
Sears.com

That's great, but I also want to be able to charge my phone when I'm out.

So far, I can't. Every time I plug a USB car charger into the 12V socket, it not only won't charge, it no longer works at all! I've now been through 2 of them. WTF is going on here?

One of the chargers says it can take a maximum input of 4.2A at either 24V or 12V. The other doesn't give an input current, only a voltage (again, 24V or 12V). Both chargers are dead as can be, after I tried to use them with the 12V socket on my bike.

Is the 12V socket somehow frying the USB chargers with too much current? How is that possible? I don't see why the chargers would draw more current than they can handle, otherwise they'd fry immediately - or else pop a fuse - when I used them in the car. I don't have to worry about the maximum current rating when I'm using the USB chargers in my car, so why would it be any different on the bike?

FWIW, the circuit supplying the 12V socket in the car has a 20A fuse. So if the USB chargers are somehow "dumb" and will draw more current than they can handle, you'd think they'd fry themselves in the car, too.

Is there such a thing as a special motorcycle-only, 12V USB charger? I thought the motorcycle's power system wasn't that different from the car's, but maybe I'm missing something.

Last edited by DesertBike; 11-06-2016 at 02:51 PM.
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post #2 of 5 Old 11-06-2016, 03:11 PM
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I suspect the polarity is reversed on the 12v socket.

The compressor probably doesn't care as it would run either way.
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Ron B. VK2OTC
2007 Yamaha XJR1300

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post #3 of 5 Old 11-06-2016, 03:18 PM Thread Starter
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Thank you. You are spot on. I stumbled across this thread:

https://www.stromtrooper.com/general-...e-phone-2.html

where someone had exactly the same problem, a few years ago. And just as you said, he found that the 12V socket had been wired backwards.

I just checked my socket with the multimeter. Same deal as thread above - center goes to ground (negative), shell to positive - the exact opposite of how it should be.

I had no idea reversed polarity would kill a USB charger, but it does seem to be the case.

Fortunately, that's an easy fix! I was going to re-wire the 12V socket to go through the fuse block, anyway, so I can swap the polarity while I'm at it.
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Last edited by DesertBike; 11-06-2016 at 03:27 PM. Reason: gratitude
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post #4 of 5 Old 11-06-2016, 09:32 PM
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Good stuff! Glad to see it's sorted.
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Ron B. VK2OTC
2007 Yamaha XJR1300

RIP Bucko
1979-2008 - Riding on forever
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post #5 of 5 Old 11-09-2016, 08:12 PM Thread Starter
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Happy ending: I got my new USB chargers today, and indeed the one I bought for the bike does charge from the 12V socket.

I'm going on a couple of long-ish rides in the next few days, so it's good to have a way to charge my phone while I'm out.
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