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car emergency start battery

I bought 2 car emergency start battery packs from Amazon. One has about

15.5 volts on the open circuit battery cables. It also has one USB port that is labled for 5 volts and 9 volts. Another port labled 12 Volta 10 amps. That port puts out about 15.5 volts open circuit.

The other pack has 11.7 volts at the battery cable, then a USB port labled 5 v, 9v, 12 V with lower amps for the higher voltage. There ia another 12 volt port at 10 amps that puts out 11.7 volts.

How does the USB port know what voltage to put out and more important how does it regulate that ?

The second pack also charges off a 5 volt usb port. It must havve a boost inverter built in ?

Reply to
Ralph Mowery
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The USB ports have to be connected to corresponding USB ports on chargers or batteries, and they negotiate what voltage to put there and how much current to draw. It is not just dumb electronics.

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Reply to
Carlos E.R.

I knew the data rates and currents were always being upgraded but did not know the voltage was raised in some cases. I had thought they were always just 5 volts.

Did a little more research and found out there is a lot of electronics in those battery packs to do what I thought was a simple job of starting a car or providing voltage to charge a cell phone.

Reply to
Ralph Mowery

Project Farm did a study of these units.

Joe Gwinn

Reply to
Joe Gwinn

Classic USB was 5 volts. Newer versions can negitiate for 20 or 48, up to 240 watts.

Reply to
John Larkin

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Reply to
Carlos E.R.

Some USB-C connectors are rated at 5A!

John

Reply to
John Walliker

The c connector is the first USB connector that makes sense. It uses several pins for power.

I assume that someone sells the negotiation chips to let us design a box that gets lots of power from USB. There are chips and baby boards for PoE, a similar situation.

PoE has the advantage that lots of power is available from even the wimpiest compliant hubs.

Reply to
John Larkin

Have you tried anything like these?

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I'm doing some products that can use PoE or a 24 volt wart, and buying a module like this sure looks easy.

Other people make almost drop-in parts too.

Reply to
John Larkin

A USB port delivering 15.5V without anything requesting that or even without anything connected to it? I would treat that whole unit as suspicious. If it was mine, I'd return it.

By negotiating up, as requested from the connected device. Never down, because if it starts high you might fry older and potentially still expensive USB hardware.

Regulation occurs via switch mode conversion. On a portable car starter with several Li-Ion batteries in series via buck.

If it's a decent enough car jump starter, yes. However, I have seen some very sorry "designs" in that field.

Reply to
Joerg

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