JerryRice
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How do I power this in the car?

Sat Jul 14, 2012 10:23 pm

Hello Everyone, I hope you are doing well!

I recently (finally) got the Raspberry PI working with my Alfa Wifi Adapter. If anyone needs help there pleas ask.

Now the main reason for my RPi was to use it in my car. Now that I got it all working.. I went to the car, and realized - my powered hub (which is mandatory) is for a 120v wall plug. And I am not getting a converter for the car.

The dilemma is - how do I power this in the car? I currently use a Belkin 2 port USB in my lighter socket to power the RPi - but how to power the Alfa wifi adapter without the hub?

note: I have seen special 12v USB hubs for US$90+ and that I am not interested in purchasing. There must be a way.

I can do soldering and have experience (basic) many I can cut up the Alfa USB plug and split it up to be powered by the 12v Belkin while the other side goes to the PI.

Any ideas?
Jerry Rice - alias

Eben has BALLS-OF-STEEL!

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jbeale
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Re: How do I power this in the car?

Sat Jul 14, 2012 10:29 pm

Any 12V -> 5V 1.5A USB car adaptor should work, I think, to power the hub, the R-Pi and the WiFi. Or maybe get a 2 A device, just to be on the safe side. They are pretty cheap on ebay, amazon, etc. Below is one example. I can't believe anyone would sell a $50 USB hub, that's way too much.
http://www.amazon.com/PowerGen-Dual-Hea ... SB+charger

JerryRice
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Re: How do I power this in the car?

Mon Jul 16, 2012 9:03 pm

Hello and thanks. This wont work. What I need is a hub that will be interconnected. For example I need to connect one USB male of the hub into the RPi and then have two or more avail ports.
Jerry Rice - alias

Eben has BALLS-OF-STEEL!

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penguintutor
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Re: How do I power this in the car?

Tue Jul 17, 2012 7:28 am

To power a USB hub in the car you need a DC-DC converter.

If you look on your plug for the hub (wallwart) it should tell you what supply you need.

In my case DC 5v 3A

The link below is to a suitable one in the UK, but you should be able to find something similar elsewhere:

http://www.maplin.co.uk/universal-3a-dc ... ply-228639

JerryRice
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Re: How do I power this in the car?

Tue Jul 17, 2012 6:15 pm

Thanks for that but I was hoping for a low power device. Those things will kill the battery when the car is parked.
Jerry Rice - alias

Eben has BALLS-OF-STEEL!

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jbeale
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Re: How do I power this in the car?

Tue Jul 17, 2012 7:14 pm

You can get switching supplies that are > 90% efficient, and they're not even very expensive. They deliver the current used by the load, which is not necessarily the maximum current rating on the label (eg. 2A or 3A). If you're worried about killing the car battery, you need to work on the current drawn by the load. At 5V and 350 to 500 mA, the R-Pi just by itself is using about 2 watts of power. That is small for a PC, but hardly a "micropower" load you can leave connected to your car battery 24/7 without thinking about it.

A typical car battery might be rated for 70 amp hours, at 12 V that is 840 watt-hours. Let's say you'll allow the battery to drain to 50% charge (lead-acid batteries should never be left discharged, due to sulfation). That means you can run a R-Pi from the car battery about 420/2 = 210 hours or 8 days. So that might actually work, until you go on vacation. This is a rough order-of-magnitude estimate and I haven't accounted for the 12V -> 5V converter efficiency or any extra peripherals like display, audio system etc.

Ocean20
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Re: How do I power this in the car?

Wed Jul 18, 2012 3:32 am

I have a Belkin USB adaptor that plugs into my cigarette lighter in the car. I use that to power my iphone and I guess it provides 5 vdc @ 1 amp. I found that if I use a powered USB hub at home and connect one of the USB ports from the hub to one of the USB ports on the rpi the rpi seems to boot up and go to the prompt. Not sure whether powering the rpi with a powered USB hub is the right thing to do but it might work using Belkin cigarette adpator I mentioned.

BenWiley4000
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Joined: Sun Jun 24, 2012 1:36 am

Re: How do I power this in the car?

Wed Jul 18, 2012 3:54 am

Have you tried your supply that you say won't work? My hub totally shouldn't be doing its job according to the numbers but it's doing finee.

JerryRice
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Joined: Tue Jun 19, 2012 3:39 pm

Re: How do I power this in the car?

Tue Jul 24, 2012 3:58 pm

The thing is I cant try it because I wouldent be able to plug it into the wall outlet for it to get its power. Unless I can hack the hub to get its power from another USB power source (12v can lighter adapter)
Jerry Rice - alias

Eben has BALLS-OF-STEEL!

twocvbloke
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Re: How do I power this in the car?

Wed Jul 25, 2012 7:47 pm

It's easy, if you're on;y using the RPi when the car is in use, then all you need is to take a DC-DC adaptor, connect it up to an Acc-On power source (so that when you turn your ignition key to the accessory position, it powers up only then and not drain the battery), connect the adaptor to the existing hub and there you go, power to the WiFi device and the RPi only when you switch on your car's power... :)

This is based on Mini-ITX based projects I've read about that have been installed in cars, which were all usually successful... :mrgreen:

If you want it all hard-wired into the car though, consult an auto-electrician before attempting to wire it in yourself, just to be safe... :)

DaveThornton
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Re: How do I power this in the car?

Fri Jul 27, 2012 4:12 am

I'm faced with the same problem right now. i might have found a work around but I'm not sure if it will harm the pi. i have a belkin car adapter(adapt1) with two usb ports. one will obviously power the pi. for the hub I'm trying to use a non powered hub with an adapter i wired up myself it a A male to A male(adapt2). plugging the hub in to the pi and one end of the adapter(adapt2) in to the belkin(adapt1) and the other end in to one of the ports of the hub. it powers the hub but I'm wondering will it end up damaging the pi?

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tvinzant
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Re: How do I power this in the car?

Fri Jul 27, 2012 4:46 am

I got the following information for a question I posted on the Energizer.com website regarding chargers (Wall and Car). I wanted to know if their chargers dropped their voltage under stress or loads.

Response from Nick Gilham:
Testing of our 10 Watt charger under load gives voltage values as follows:

Image

The USB spec allows for an average voltage of 4.75 to 5.25V when the port is connected under load.

http://www.energizer.com/charging/usb-c ... arger.aspx

I just thought I'd pass on the information for reference. I'm very content with my Kindle Fire Charger at the moment.

Wolfram23
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Re: How do I power this in the car?

Fri Jul 27, 2012 3:58 pm

This isn't that hard, finally found a good schematic. The biggest problem with having it on the Ignition (switched) line is that it will cause hard shut downs, and ideally you want to let the RPi shut down naturally so your SD card doesn't get corrupted.

Anyway, go to this page: http://www.obdsol.com/stn1110/
Down at the bottom, check the STN1110 data sheet. On page 12 figure 6 shows a protection circuit - this is important in a Car PC situation. Secondly you see the "5V" and "3V" boxes.

For the 5V, check this out: http://ww1.microchip.com/downloads/en/D ... 22284A.pdf
It's a 5V, 3A output buck regulator with over 90% efficiency. The PDF includes a recommended schematic/layout.

My plan is to use these, at any rate. Connect the power to the 12V batt line and have the protection circuit in front of everything. 12V from there to a touch screen, 12V into the 5V buck regulator, and probably have another 3.3V regulator as well. Have the switched line acting as a shut down trigger by having it connected to a timer that will then cut power - when the EN input on the buck regulator goes low, it turns it off - cutting power to everything after it. Just need to get a timer that can handle 12V. Might need a second 5V buck regultar with circuit protection, unfortunately. Haven't figured this part out. I guess an alternative would be to run a physical switch to the EN line, so you have to manually power down.

rpidude
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Re: How do I power this in the car?

Thu Aug 02, 2012 1:38 am

I'm *very* paranoid about using one of the cheap USB car chargers as their regulation is very questionable and fried a few cellphone batteries with them. Instead, I ended up building a custom switching power supply that delivers >1Amp. I measured 4.99V unloaded, 4.91V at 1A, and 4.88V at 1.17A. I used a NS LM22672 chip, but there are several other options. If you can DIY, I highly recommend this, else go with a *properly* regulated DC-DC converter.

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