Author Topic: USB charger circuit for car  (Read 5226 times)

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Offline CharybdisTopic starter

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Re: USB charger circuit for car
« Reply #25 on: April 16, 2019, 12:56:50 am »
Hi there I was wondering about F1 specs.
Is it ok to put a 3A fuse?
does it have to be fast, or slow?
Thank you so much :)
 

Offline soldar

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Re: USB charger circuit for car
« Reply #26 on: April 16, 2019, 11:49:37 am »
For a while I had a car which would kill any 12V to USB adapter which was plugged in when cranking the engine. I had to remember to unplug before cranking and I killed quite a few when I forgot. Especially if I killed the engine in traffic and wanted to start in a hurry.

I guess I could have put some protection but I always thought I would remember to unplug it.
All my posts are made with 100% recycled electrons and bare traces of grey matter.
 

Offline madires

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Re: USB charger circuit for car
« Reply #27 on: April 16, 2019, 01:09:23 pm »
Hi there I was wondering about F1 specs.
Is it ok to put a 3A fuse?
does it have to be fast, or slow?

The things to consider are the inrush current (mostly by filter caps), the maximum load current and over-voltage situations (suppressed by TVS). I'd suggest to go for a medium blow fuse rated slightly higher than the maximum load current to be able to deal with short overloads by inrush current or over-voltage. BTW, you could add a power resistor in series with the fuse to help with the power dissipation (less for the LM339) and to limit current. In this case a fast blow fuse could be used.
 

Online jfiresto

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Re: USB charger circuit for car
« Reply #28 on: April 16, 2019, 03:19:51 pm »
For a while I had a car which would kill any 12V to USB adapter which was plugged in when cranking the engine. I had to remember to unplug before cranking and I killed quite a few when I forgot....

I have an old car, that lacks a central suppressor, which may see up to 80V load dumps if you respect the original equipment requirements.

I used an off the shelf, 12V USB car charger, and designed and placed a circuit upstream that disconnects the charger around 24V, well below its 36V absolute limit. I can dig up and post the design if there is interest.

I decided that was less work than designing and making an extra robust charger.
-John
 

Offline CharybdisTopic starter

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Re: USB charger circuit for car
« Reply #29 on: April 17, 2019, 11:21:45 pm »
Thank you for all your replies.
Hi there I was wondering about F1 specs.
Is it ok to put a 3A fuse?
does it have to be fast, or slow?

The things to consider are the inrush current (mostly by filter caps), the maximum load current and over-voltage situations (suppressed by TVS). I'd suggest to go for a medium blow fuse rated slightly higher than the maximum load current to be able to deal with short overloads by inrush current or over-voltage. BTW, you could add a power resistor in series with the fuse to help with the power dissipation (less for the LM339) and to limit current. In this case a fast blow fuse could be used.

I'll go for a medium fuse then. I would take the fuse 3 times greater than the amount delivered to the usb. Am I right ?
Also, is it safe to put the fuse AFTER the diode 1.5KE diode ?
Thank you  :)
 

Offline madires

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Re: USB charger circuit for car
« Reply #30 on: April 18, 2019, 01:17:59 pm »
The fuse should be the first component in a circuit to protect the circuit and the power source. For a maximum load of 1A please try a fuse rated for 1.4 or 1.6A, but not 3.15.
 
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Offline CharybdisTopic starter

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Re: USB charger circuit for car
« Reply #31 on: April 18, 2019, 11:18:12 pm »
Thank you Madires
 

Offline CharybdisTopic starter

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Re: USB charger circuit for car
« Reply #32 on: November 20, 2019, 03:23:04 pm »
Ciao guys :)
Finally I made the order with all the components and beyond (50 different items  ;D )
I was wondering if I can replace the HER203 diode that has "Maximum average forward rectified current 2A"
with some diodes from the 1N400x family that I already have at home, even though they have "Maximum average forward rectified current 1A" and my regulator will provide up to 1,5A to devices.
Thank you very much for your help once again :)

875850-0
« Last Edit: November 20, 2019, 03:26:39 pm by Charybdis »
 

Offline madires

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Re: USB charger circuit for car
« Reply #33 on: November 20, 2019, 05:45:28 pm »
I think 1N400x should be fine as protection diode.
 
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Offline rvalente

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Re: USB charger circuit for car
« Reply #34 on: November 20, 2019, 07:54:48 pm »
Im using the lm2596 boards for 3 years on my 307 as phone charger set at 5.1v, never tested in load dump and im not woried. Short the d+ ans d- for fast charging
 

Offline tooki

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Re: USB charger circuit for car
« Reply #35 on: November 20, 2019, 10:58:09 pm »
That's a fair point that I hadn't considered!
... and this is why every single summer, dogs and small children die inside locked cars. People do not understand that it can take as little as 10-15 minutes to reach lethal temperatures inside the car.

As for this charger, at an ambient temperature of 24C, it only takes an hour in the sun to reach 50C. So you can imagine how after a whole day, it could reach a lot more.

https://www.t-online.de/leben/familie/kleinkind/id_69606574/so-schnell-wird-hitze-im-geparkten-auto-lebensgefaehrlich.html

https://www.dogingtonpost.com/how-hot-does-it-really-get-inside-a-parked-car/

 

Offline mc172

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Re: USB charger circuit for car
« Reply #36 on: November 20, 2019, 11:36:40 pm »
I'm aware of the issues of pets and children left in cars and I think that people that subject their pets to such torture should be subjected to it themselves, swiftly followed by castration - I just hadn't thought about the usage case where the car either wasn't running or had nobody in it, i.e. without A/C running or windows down, car moving, direct sunlight etc. as is the usual nature of a hobby device where the OP doesn't specify anything other than it's a Fiat Panda.  ;)
« Last Edit: November 20, 2019, 11:42:55 pm by mc172 »
 

Offline CharybdisTopic starter

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Re: USB charger circuit for car
« Reply #37 on: November 21, 2019, 06:13:08 am »
That's a fair point that I hadn't considered!
... and this is why every single summer, dogs and small children die inside locked cars. People do not understand that it can take as little as 10-15 minutes to reach lethal temperatures inside the car.

As for this charger, at an ambient temperature of 24C, it only takes an hour in the sun to reach 50C. So you can imagine how after a whole day, it could reach a lot more.

https://www.t-online.de/leben/familie/kleinkind/id_69606574/so-schnell-wird-hitze-im-geparkten-auto-lebensgefaehrlich.html

https://www.dogingtonpost.com/how-hot-does-it-really-get-inside-a-parked-car/



I don't think you should worry that much as this charger will be used for a maximum of 3 hours straight, twice a week in the worst scenario.
I consider myself as a very pessimistic person but I think you are worrying a bit too much ;) as I will use this charger only when I'm driving, I don't want to left my phone in the car charging for a limitless amount of hours.
Oh and I don't have any dogs and kids  :-DD
 


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