powering usb hub at 12V from car battery - Page 1
Forum section: electronics / general

author: esrevinU
author_rank: Newbie
timestamp: May 15, 2016, 09:58:38 am
content: Hi,I'm not an electronics engineer and as I follow the EEVblog videos for fun and I thought this is the best place to ask this question.I'm into astronomy and on the field I'm powering my scope using a car battery. I want to use a single cable connection between my scope and my computer and for this I want to use a powered USB hubhttps://www.anker.com/products/A7515111. The problem is that this hub is powered at 12V (5A max for the charging ports which I will not use).My question is: How can I (which gadget can I use to) get a regulated/stabilized 12V for powering this hub from my car battery considering that the charged battery voltage can vary depending on how charged/discharged the battery is?I found this:https://www.amazon.co.uk/Amperor-LCD-Volt-Stabiliser-Regulator/dp/B000ZLRXG8. What is your opinion on this gadget? Do you have other ideas?Thanks in advance

author: jitter
author_rank: Frequent Contributor
timestamp: May 15, 2016, 01:15:29 pm
content: The hub will have its own voltage regulator on board if it's running off 12 V, so the actual supply may not need to be perfectly 12 V. A little more won't likely present a problem, espcially since you're not going to draw a lot of current from the hub (no charging, as you said).I'd probably power it straight off the cigarette lighter, but without running the engine.

author: meeder
author_rank: Regular Contributor
timestamp: May 15, 2016, 01:23:49 pm
content: But a lot of cars switch of the lighter socket when the car is switched off.

author: esrevinU
author_rank: Newbie
timestamp: May 15, 2016, 06:39:48 pm
content: Quote from: jitter on May 15, 2016, 01:15:29 pmQuote from: meeder on May 15, 2016, 01:23:49 pmIt's not my case, I will not use the car battery, but an extra one for the job.Quote from: jitter on May 15, 2016, 01:15:29 pmThank you jitter!But, I would prefer to have an extra gadget which gives me a "clean" 12V. Do you have an advice for this?

author: Monkeh
author_rank: Super Contributor
timestamp: May 15, 2016, 06:50:25 pm
content: The varying voltage is irrelevant, the hub will have an internal power supply to regulate it.If you're running it off a loose battery, not a car's electrical system, just get on with it and run it. It'll be fine.

author: jitter
author_rank: Frequent Contributor
timestamp: May 15, 2016, 08:25:29 pm
content: I agree with Monkeh, especially now that I know that no charging system (like the alternator of the car) is attached.The voltage of a battery is more than clean enough, even if it's not a perfect 12 V. As Monkeh says, that's irrelevant as all voltages the hub needs are going to be derived from the 12 V and they will all be lower (e.g. 5 V) and regulated by on board voltage regulators. It doesn't really matter if the battery voltage is 12 V or 13.8 V, or perhaps if it has drained to 11 V, it's going to be more than enough for the hub to step down.And adding the unit you linked to in your first post will only drain the battery quicker without any real benefit (other than maybe some protection, but I assume you're going to fuse the lead anyway).

author: esrevinU
author_rank: Newbie
timestamp: May 19, 2016, 09:37:26 pm
content: Thank you all for comments!... but ... (You give me some ideas) now I want more!Do you think my USB hub (2 min tear down :goo.gl/SaEjZc) will burn (or my laptop) in flamesif powered by the charger attached (first photo in the link).I must keep the power supply at 13.5V as the 12V is too low for my main gear (my telescope mount-EQ6).Thank you!

author: XOIIO
author_rank: Super Contributor
timestamp: May 19, 2016, 09:56:11 pm
content: From what I understand, powered usb hubs only connect the data lines and ground, so the supply voltage shouldn't be able to go back through at all, unless something went wrong. (it would be regulated to 5v for the usb ports anyhow)

author: Monkeh
author_rank: Super Contributor
timestamp: May 19, 2016, 10:18:00 pm
content: Quote from: esrevinU on May 19, 2016, 09:37:26 pmYou'll be fine.

author: Red Squirrel
author_rank: Super Contributor
timestamp: May 19, 2016, 11:41:26 pm
content: Can always check to see if there is a discrete regulator in it, then check the datasheet to see the voltage range.

author: Delta
author_rank: Super Contributor
timestamp: May 19, 2016, 11:48:37 pm
content: You will struggle to find a cleaner power supply than a battery!Just crack on and stop worrying!EDIT-- I wouldn't even worry about 12V vs 12.6V vs 13.8V vs 14V - you'd be AMAZED at how much the voltage wanders around from most AC/DC power supplies...

author: jitter
author_rank: Frequent Contributor
timestamp: May 20, 2016, 05:41:04 am
content: Indeed, especially the types that say "for office equipment use only" or "for I.T.E. use only", or similar. I found that they may not actually be filtered or stabilized as well as "normal" AC/DC adapters.Another think to keep in mind is the wire resistance of the adapter. Usually they're barely thick enough, thin enough to cause quite a drop in that wire when higher currents are drawn.@esrevinUYour hub has voltage regulators strewn across the pcb. All those inductors on that board betray the presence of switch mode power supplies on it. And sure enough, in one of your photos I can clearly see severalFR9888s. These are adjustable step down DC/DC converters.This really make sthe actual voltage of the 12 V input quite irrelevant, as long as the minimum input for a required output is present. Chances are your hub might work flawlessly with voltages far lower than 12 V, e.g. 9 V. A little higher is also OK as it's well within the input range of the regulators.