USB-C backup power circuit - Page 1
Forum section: electronics / projects

author: Falken
author_rank: Contributor
timestamp: February 22, 2023, 09:31:12 am
content: Hi,I am updating my camera tether case with a built in battery pack. The pack im using is the Sherpa 100AC from GoalZero which Im planning to use one of the USB-C to connect to a laptop. It supports USB-PD (100W out, 60W in) on its two USB-C ports.The current setup is that I have 230V shore power into a transformer that supports USB-PD (100W) on it's USB-C port, this is currently connected to my laptop. So when connecting to a AC outlet the laptop charges.I'm looking for a circuit that take two USB-C inputs (one from the shore power transformer, the other from the Sherpa) and outputs one USB-PD in a USB-C. What I want is that when shore power is connected the circuit will use that to power the output and when the shore power is cut it will fallback to the Sherpa power. As a bonus it could have a second USB-C output for charging the sherpa inside the case (but that is a bonus only).Im looking at thishttps://www.fruugo.se/power-off-automatic-switching-board-ups-emergency-cut-off-power-supply-module/p-80815591-166915560?language=en&ac=croud&gclid=CjwKCAiAl9efBhAkEiwA4TorimDOwPL3jgMTLwPFhXNklxpbPJSwMoQqxprqkqt5uT57vbuHSgRhUhoC-vgQAvD_BwEbut the caveat "adapter, batter, load must be at same voltage" confuses me. The USB-PD is 5A so the current should be no issue, but since there is a battery included the voltage may vary, right? I need to be able to have both shore power AND the battery powered on at the same time, this is not normal procedure but if I forget to turn off the battery when connecting AC this might happen. Also, it is screw connectors, I need USB-C connectors, perhaps an easy build using USB-C connectors?Do you have any other suggestions for components and do you think it should work given the caveat abovethanks a bunch,Johan

author: ledtester
author_rank: Super Contributor
timestamp: February 22, 2023, 10:51:54 am
content: Is this your Sherpa 100AC?https://www.goalzero.com/products/new-sherpa-100ac-wireless-power-bankThat page says the Sherpa supports “Simultaneous Recharge & Discharge” which suggests you could be charging it using shore power while extracting power from it via USB-PD at the same time and when shore power cut out it would continue to provide power from the internal batteries.There are some things to check, though… see the conclusions of this article:https://goughlui.com/2021/09/03/note-potential-issues-of-using-a-usb-powerbank-as-a-ups/

author: Falken
author_rank: Contributor
timestamp: February 22, 2023, 11:39:40 am
content: Thank you for your quick respons, indeed that is the power bank i have. It does simultaneous charge and discharge, I have tested and works fine as long as the power bank is turned on. The only way to turn it on is to press a button on the device, there seems to be no option "always on when charging" . This means that I need to open up a lid where my computer rest and reach in to turn on the device even if connected to shore power. This is absolutely doable but an inconvenience I want to work around.As a note, I will not use the power bank as UPS as on power failure the internal laptop battery will keep the system running, the power bank is used to extend the operation times when not connected to AC. So if in the field or in case of power failure I will reach in and turn on the battery, but if in studio and connected to AC I would prefer not to.

author: thm_w
author_rank: Super Contributor
timestamp: February 23, 2023, 11:43:01 pm
content: You can find some more photos here:https://www.aliexpress.us/item/2255799995872880.htmlSince it doesn't have proper USB C connectors, you'd need to negotiate the voltage with USB-C dummy adapters.I'm not sure I understand your follow up post though "the only way to turn it on is to press a button on the device... I want to work around". How is this selection circuit going to keep the power bank powered on if you need to press a button? Unless it is continuously draining power, which you probably wouldn't want. Unless it only is checking if a device is connected, and doesn't measure the load current.

author: Falken
author_rank: Contributor
timestamp: February 24, 2023, 08:19:05 am
content: I ordered the board yesterday thinking I will give it a shot. I ordered a couple of USB-C PD -> DC dummy boards too , but Im having a harder time finding a DC -> USB-C PD board for the outgoing power, do you have a suggestion for that side?what I mean with "the only way to turn it on is to press a button on the device... I want to work around" is that for the power bank to provide power from it's ports it needs to be powered on. So if I was to always power the case from this I need to have it started even if I was connected to shore power. What I want is that when connected to shore power the power bank is switched off, it is only turned on when no shore power is available. And the power on of the battery pack is only manual , I will reach in and push the power in button if I have no AC available , I don’t expect the circuits to power on the device automaticallyI see what might not be obvious in my previous posts, so a clarification. My computer is connected via USB-C to the electronics inside the case, I have a USB-C cable coming through the internal platform where the laptop sits, this I want to be the only connection between the computer and the case, I dont want to switch this cable depending of power source. That why im looking into that UPS circuit, but as I said before, I don't require any UPS functionallity, im only looking for the power source switching functions.So usecases:1. AC power from wall outlet -> just plug in the AC powercord to the outlet and the case powers up (this is what is working today)2. No shore power available -> power on the power bank and the case gets power from this