On 7/2/2023 12:46 PM, Ralph Mowery wrote:> > 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.Read CAREFULLY the intent of each of these ports lest you toast something that wasn't expecting a particular "power flavor".> 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.The port is *power* limited.> How does the USB port know what voltage to put out and more important > how does it regulate that ?It can only "safely" deliver 5V@100mA to a load. At that point, the load must be functional enough to negotiate a higher voltage or current. The thinking being that a device that can't *handle* the higher voltage will never *request* it. A compliant host will, thus, never deliver it. PoE uses a similar scheme -- using hardware signaling to negotiate a "power class" and then in-band signaling to negotiate other characteristics ONCE THE PD IS OPERATIONAL. PoE, as originally envisioned, only handled the hardware negotiation at device insertion. So, you couldn't power down the device and have *it* request the reapplication of power -- unless it electrically disconnects and reconnects from the PSE. [This is shortsighted. E.g., I let my devices "sleep" drawing a tiny amount of power from the PSE -- just enough to run the power request protocol -- so they can pretend to disconnect/reconnect without actually breaking that contact *or* having to incur the cost of running an ethernet interface to communicate their wishes to the PSE]> The second pack also charges off a 5 volt usb port. It must havve a > boost inverter built in ?
car emergency start battery
Started by ●July 2, 2023
Reply by ●July 3, 20232023-07-03
Reply by ●July 3, 20232023-07-03
On 7/2/2023 4:37 PM, Ralph Mowery wrote:> 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.This to allow for more rapid charging of devices, among other things. I have some "USB power sources" that are used to power small laptops, etc.> 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.OTOH, it's a market that is ripe for chinese knockoffs... some of which may not be very benevolent towards "other" applications.
Reply by ●July 3, 20232023-07-03
On Mon, 3 Jul 2023 08:37:29 -0700, Don Y <blockedofcourse@foo.invalid> wrote:>On 7/2/2023 12:46 PM, Ralph Mowery wrote: >> >> 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. > >Read CAREFULLY the intent of each of these ports lest you toast >something that wasn't expecting a particular "power flavor". > >> 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. > >The port is *power* limited. > >> How does the USB port know what voltage to put out and more important >> how does it regulate that ? > >It can only "safely" deliver 5V@100mA to a load. At that point, >the load must be functional enough to negotiate a higher voltage >or current. > >The thinking being that a device that can't *handle* the higher >voltage will never *request* it. A compliant host will, thus, >never deliver it. > >PoE uses a similar scheme -- using hardware signaling to negotiate >a "power class" and then in-band signaling to negotiate other >characteristics ONCE THE PD IS OPERATIONAL. > >PoE, as originally envisioned, only handled the hardware >negotiation at device insertion. So, you couldn't power >down the device and have *it* request the reapplication >of power -- unless it electrically disconnects and reconnects >from the PSE. > >[This is shortsighted. E.g., I let my devices "sleep" drawing >a tiny amount of power from the PSE -- just enough to run the >power request protocol -- so they can pretend to disconnect/reconnect >without actually breaking that contact *or* having to incur the >cost of running an ethernet interface to communicate their wishes >to the PSE] > >> The second pack also charges off a 5 volt usb port. It must havve a >> boost inverter built in ? >Have you tried anything like these? https://www.mouser.com/ProductDetail/Silvertel/Ag9724-FL?qs=OlC7AqGiEDk%2F39a1EjJkjw%3D%3D 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 by ●July 3, 20232023-07-03
On 7/2/23 12:46 PM, Ralph Mowery wrote:> > 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. >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.> 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 ? >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.> The second pack also charges off a 5 volt usb port. It must havve a > boost inverter built in ? >If it's a decent enough car jump starter, yes. However, I have seen some very sorry "designs" in that field. -- Regards, Joerg http://www.analogconsultants.com/
