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Old 03-04-2015, 10:56 AM   #1
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12v to USB adapters that will work at float voltage

While boondocking, I use 12v to USB adapters to charge phones and other electronics.

I'm finding that most of these are extremely voltage sensitive. They work great in a car with the engine running, passably in the trailer when shore power is connected, and poorly if at all while boondocking when the battery voltage drops to near 12.0 volts.

Has anyone found a USB charger that works well at these voltages?
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Old 03-04-2015, 11:10 AM   #2
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Jammer,

I have two kinds, Belkin and Griffin. Never had any trouble with ours, so far.
We boondock often, with laptops, Ipad, Ipods, phones, etc. However we have 4-6v lifeline batts, 200w solar and 2-EU2000 generators. I do not let the batteries get that low.


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Old 03-04-2015, 11:18 AM   #3
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Just remember two things....

1) There there two different USB standards with regards amps, and not all devices are equal - some will charge on the 500mA standard some need the higher (2.1A) version.

2) Many devices now have intelligent charging whereby it recognizes the electronics of the device and anyone with a recent Apple product has experienced the 'charging not supported on this device' warning message displayed on their iPhone/iPad etc.
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Old 03-04-2015, 06:31 PM   #4
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Ours work fine at float or charge voltage. I've seen what you describe when our voltage was low (in our case the converter was putting out ~11 volts), but not with a reasonably charged battery.
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Old 03-05-2015, 01:15 PM   #5
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At 12.0 volts, your batteries are about 60% discharged. To ensure long life, you shouldn't discharge lead-acid batteries more than 50%, which equates to a resting voltage of 12.2VDC. If you must discharge to that level, and don't mind replacing your batteries more often, so be it. In that case, you might try a small inverter that will plug into a 12V receptacle, then plug an outlet strip into the inverter, and plug your 120VAC chargers into the strip. Many inverters will stay online down to about 10.5VDC.

Something like this:



Your thread title mentions "float voltage" - for wet-call lead-acid batteries, that should be about 13.2V. You're working with almost-dead batteries at 12.0V.
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Old 03-05-2015, 01:38 PM   #6
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It is hard to say how the USB chargers are built but the electronic circuitry to have a regulated 5 volt power supply that the USB system uses is now super common and probably on a microchip. The input voltage should have little to no effect on what comes out. I would think they would work from 10 to 15 volt input with no different output.

I don't know why you are having problems with changing input voltage. I have used a lot of different 12 volt to USB chargers with no issues.
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Old 03-05-2015, 03:17 PM   #7
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Quote:
Originally Posted by Gnorts View Post
At 12.0 volts, your batteries are about 60% discharged. To ensure long life, you shouldn't discharge lead-acid batteries more than 50%, which equates to a resting voltage of 12.2VDC. If you must discharge to that level, and don't mind replacing your batteries more often, so be it. In that case, you might try a small inverter that will plug into a 12V receptacle, then plug an outlet strip into the inverter, and plug your 120VAC chargers into the strip. Many inverters will stay online down to about 10.5VDC.
<snip>

Your thread title mentions "float voltage" - for wet-call lead-acid batteries, that should be about 13.2V. You're working with almost-dead batteries at 12.0V.
Not necessarily.

Battery voltage varies with temperature; sometimes we camp in the cold. Several tenths of a volt in weather approaching freezing.

There are inevitably some losses between the battery and the 12v outlet, even with a well-designed and well-maintained electrical system. Several tenths of a volt.

The published float voltages are at no load. With a light to moderate load, say, several amps for lighting, there is a drop, not usually significant by itself but, once again, several tenths of a volt.

I don't believe that in my situation battery life will be limited by cycle count. We may have cycles down to 80% DoD from time to time but as long as the batteries are recharged promptly and it's not a daily / weekly thing the effect is negligible. Maybe we get an expected life of 500 cycles instead of 1000 cycles, doesn't matter, the batteries will age out or fail for some other reason before we get there.
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Old 03-12-2015, 01:38 PM   #8
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I use the Scosche USBC202M Dual 10 Watt adapter. Although pricier than most others, I have never had one fail and this particular unit provides 2 high Amp USB sockets that will charge iPads and will turbo charge the iPhones.

Click on the link above to get it on amazon.
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Old 03-14-2015, 11:07 AM   #9
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USB 3.1 or USB-C

Since we are on the subject of USB connections. Has anyone got there hands on the new Apple Mac Book? Only one port, USB-C. The latest and greatest Universal Serial Bus (USB). Perhaps we should all get our adapters ready.

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Old 03-14-2015, 12:16 PM   #10
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What Jammer said...plus, depending which chart you believe, 50% is 12.06V and 60% is 12.2V.

I personally try to charge when my Trimetric hits 12.0, since it only shows one decimal point, I assume it rounds down to 12.0V displayed at 12.04V actual. Good enough for me. As Jammer states, that is rare, and I am usually no lower than 12.2 - 12.3V anyway.

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