20vdc to usbc adapter - Page 1
Forum section: electronics / general

author: waoj
author_rank: Contributor
timestamp: March 15, 2023, 02:57:51 pm
content: I have several lithium battery packs that output 5-22v on a DC barrel jack.I spliced together a cable that fed my last laptop 20vdc from this and if you didn't mind looking at heat shrink, it worked fine/Well, I just upgraded my laptop. The new one has a smaller plug (the hp blue tip) and I don't have a single damn tip that fits this beast. Why on earth they need to make so many random tips is beyond me.You'd think all possible geometries of barrel connectors had already been discovered by man, but I guess not.I could source barrel tips, and remake my splice job with the new style.But this thing can also charge via usbc. I used a usbc meter to verify it takes 19.8v in. so, 20v nominal probably. so I got to thinking.It would be of greater utility to me, to have a usbc style connector than this new barrel connector.so I googled for dc-in to usbc adapter. And nothing.I found plenty of usbc-in to dc barrel output. But I need the reverse.Yes. I know that it wouldn't work to charge phones that need 5/9v. That's fine. It'd probably need to buck down to 5v to perform negotiation. My 20v power banks also have a usba 5v port on them that's concurrently live with the variable output port, so that might help here too.Is there a better forum for usb-c hacking than here?

author: tom66
author_rank: Super Contributor
timestamp: March 15, 2023, 03:32:17 pm
content: The problem with USBC is you can't just present 20V on the output. The devices start at 5V and then negotiate up to 20V within their capability over a serial interface, distinct from the USB signalling, it's done over the CC pin on most chargers/devices (though in the USB standard's absolute defiance of consistency, they support communication modulated onto VBUS too.) 20V is unlikely to work directly because the charger has to advertise its capability and the device needs to know how much current it can pull. If it does work, it will draw current at the lowest permitted level, probably 45W, which might charge your laptop but is unlikely to do so if it is in active use unless it uses a low power CPU.A cheaper option might be to buy a USB-C car charger that accepts 12-24VDC in, you can likely supply the unregulated power to that module and it deals with the power negotiation.

author: David Hess
author_rank: Super Contributor
timestamp: March 16, 2023, 01:11:55 am
content: Lenovo sells a 12 to 24 volt USB-C PD adapter which does exactly what you want:https://www.lenovo.com/us/en/p/accessories-and-software/chargers-and-batteries/chargers/40ak0065ww

author: NiHaoMike
author_rank: Super Contributor
timestamp: March 16, 2023, 04:18:29 am
content: I wonder if it could be done with a linear regulator for the initial 5V which is bypassed when 20V is requested. How much current does it take at 5V while it's requesting 20V?

author: waoj
author_rank: Contributor
timestamp: March 19, 2023, 05:20:00 pm
content: I read 12/24 as meaning either 12v or 24v. But you used the word "to" which implies compatability with an infinite number of voltages between 12 and 24.I know 12 doesn't mean 12. There's always some wiggle room. cars nominal voltage is around 14 "while the engine is runninh" right? never mind mine is a plug in hybrid...But I've definitely seen 120/240vac electronics that did NOT work at 208v. I remember some smoke being released... So I don't assume a range unless I read a range.Do you have one of these Lenovo adapters David, to test if it supports 19, 20, or 21v? (careful, it could break it) It looks like the car connector on it is easily removed and replaced with a barrel jack which would be nice as the automotive connector is rather fickle, and large to carry around.Do most car accessories secretly accept 12 TO 24v? (I know there are some 24v vehicles, maybe semi trucks?) If so that opens so many options for car-intended adapters. I actually have the remnants of a LifePowr brand usbc car charger whos tip melted due presumably to poor contact on the horrid automotive accessory power port that I could try with. Just looked at it and its labeled 12-18v input! I did not expect that. But perhaps it makes sense if it has a boost converter but not a buck, and they designed it knowing 20v was the usbc voltage for laptops.BTW for those wondering, yes my laptop is extremely low power.I used a usb c meter to measure a 7 watt floor, peaking to 14 watts coming in via usbc with a battery fully charged. It was hard to believe. But it's an hp er1152-nr 2-in-1 tablet in case that helps.It comes with a 19.5v 45w charger brick with HP's latest small barrel connector with a blue tip. 3-wire, 4.5 mm barrel says the manualIt also supports usbc charging.

author: tom66
author_rank: Super Contributor
timestamp: March 19, 2023, 06:04:54 pm
content: In order to support USB-C, the device is almost certainly a buck-boost converter. This is because it needs to accept 12V in and output 5, 9V, 15V or 20V. That's two buck modes and two boost modes. So in the 24V mode it just operates in buck all the time. It's very likely to therefore work over a continuous range.These types of devices are pretty common nowadays, they use 4 transistors to transition between being a buck converter and a boost converter. Some older designs use a discrete buck followed by a discrete boost, but those are pretty uncommon nowadays.

author: waoj
author_rank: Contributor
timestamp: March 19, 2023, 06:14:05 pm
content: I was actually doing some reading on USB C PD. And there is something new called PPS (programmable power supply). I think it's the latest version of PD. And if supported/negotiated, the receiving device can ask for voltages in steps of 20mv. Imagine it making up for loss in the cable with that!I wish there was a usb tinker-er forum akin to eevblog but specific to usb.

author: David Hess
author_rank: Super Contributor
timestamp: March 23, 2023, 05:05:54 pm
content: Quote from: waoj on March 19, 2023, 05:20:00 pmI have one but my variable bench supply is only 1 amp so not suitable for a full power test. It would take 5+ amps to test its full input range.

author: ve7xen
author_rank: Super Contributor
timestamp: March 23, 2023, 05:29:53 pm
content: Quote from: NiHaoMike on March 16, 2023, 04:18:29 amProbably very little. But the hard part is implementing USB-PD, not the power supply.Modules do exist that take DC in and provide USB-PD out. Search AliExpress for SW3516, SW3518, SW3526 modules. I think this family is buck-only, so you need to supply >20V for 20V USB-PD. For more capability look for IP2368 modules, they generally have charging capability and it's buck-boost. There are probably more options than these.

author: NiHaoMike
author_rank: Super Contributor
timestamp: March 24, 2023, 02:37:44 am
content: Quote from: ve7xen on March 23, 2023, 05:29:53 pmWould it be possible to bit bang USB-PD with a microcontroller?