Welcome guest. Before posting on our computer help forum, you must register. Click here it's easy and free.

Author Topic: 12V -> 5V 1A using L7805CV  (Read 2926 times)

0 Members and 1 Guest are viewing this topic.

yamadanao

    Topic Starter


    Newbie

    • Experience: Beginner
    • OS: Unknown
    12V -> 5V 1A using L7805CV
    « on: June 21, 2017, 04:01:18 AM »


    I need to convert 12V (may vary from 11 to 14V - motorbike battery) to 5V 1A (microusb phone charger). I have the L7805CV positive voltage regulator.

    here is the date sheet of l7805cv


    Which capacitors I need to connect at input and output? Any other stuff is needed?

    (I need the whole thing to be smallest possible)

    DaveLembke



      Sage
    • Inventor of the Magna-Broom 3000 =)
    • Thanked: 590
    • Certifications: List
    • Computer: Specs
    • Experience: Expert
    • OS: Windows 7
    Re: 12V -> 5V 1A using L7805CV
    « Reply #1 on: June 21, 2017, 07:11:36 AM »
    I'd use this circuit attached to protect from reverse polarity by use of that diode. The Voltage regulator I would mount to a passive heatsink. Thats why it has that metal backing with the hole through it is to be mounted to a heatsink to draw heat away. A small drop of thermal compound the same used for CPU and GPU heatsinks on computers and this mounted to the flat of a flat unpainted bare metal surface for best results. Not quite sure why making as small as possible is a concern as for there is not much to this circuit anyways with just a diode, voltage regulator, and 2 capacitors. Biggest concern is you said its for a motorbike battery, so I am assuming this is for a motorcycle that is exposed to moisture from rain, puddles and all that. You would then want this PCB to be protected from the weather. One option is to places it into a box of some sort and then pour silicone epoxy all around it to encase the circuit board in a barrier from water. BUT that voltage regulator is going to produce heat and so you need to have the metal that its mounted to exposed and not encased in silicone gel. The silicone gel is the same as used for caulking etc, where it takes about 24 hours or so to set.

    On some other projects I had that I wanted water proof I used a 2-part epoxy that mixes evenly with a syringe. I made use of a empty clear TIC-TAC container which had the opening where TIC-TACs normally exit for a USB cable to pass through. I popped this piece out threaded my USB cable through TIC-TAC hole and then soldered the 4 USB wires to my small PCB, and then placed the board into the clear TIC-TAC container and injected this 2 part epoxy into the TIC-TAC container, and then slid the white plastic TIC-TAC container top down the USB cord and  snapped it back into the TIC-TAC container body and then the epoxy gave off heat as it was solidifying, then cooled. Now my device i made was protected from water from the length of wire all the way to device encapsulated inside the epoxy.

    You can get creative and reuse containers.

    One such container that comes to mind for your application is an altoids container. Its a metal container that is sold with the mints. You could mount the voltage regulator to the bottom of the altoids case and use the entire metal surface of it as a passive cooler. The surface area of the altoid case should be plenty to keep that voltage regulator cool especially with the top lid on it as well to draw heat away. Use of a long screw to mount the voltage regulator to the bottom flat of the tin with thermal compound, and a nut tight on the outside bottom of your tin. The extra length of screw used to mount it to your motorbike with 2 washers and a nut at the final end of it were ever it mounts. 1 long screw should be plenty since its light and nothing should bump it to snap that screw off. The screw also will act as a passive heatsink to whatever metal surface that is mounted and tightened to.

    The heat produced will be determined by the draw through it, the closer you get to maximum current draw, the hotter its going to get.

    If you go with altoid case, I would pour silicone gel caulk into it once your sure your circuit was successful. You will want to use like an old credit card or something on the bottom of your PCB to avoid the solder connections from shorting out on the altoid case. I have used expired credit cards for stuff like that insulators. As long as its the older cards that dont have any metal on them to short to that is. The newer credit cards with embedded chips have a few electrical connections on them that could short a circuit if used, but older plastic credit cards or store cards etc they make good insulators.

    I love to recycle and repurpose empty containers from stuff to save myself from having to buy cases for projects. Seems as though candy containers work awesome for small container needs.  ;D

    Lastly, make sure your not going to pull greater than 1.5 amps through this. Some phones are fine on 1.5 amps, but such as if you have a tablet that charges off of a microUSB it could pull around 2.5 amps. If you have a wall charger for this phone and it says 1.5 amps or less on it for the 5V then you should be fine, but if its a greater draw then you will need a drop down voltage regulation circuit that can handle the current demands of the battery charge.

    One thing I would also consider is why reinvent the wheel. If you can pick up a car charger for your phone then simply mount a fused linked cigarette lighter plug to motorbike somewhere and use that for 12volt accessory power direct tap from battery ( with a 3 amp fuse in series with it in case you ever have a short circuit. )  https://www.delcity.net/store/Auxiliary-12-Volt-Power-Socket/p_801417.h_801418.r_IF1003?mkwid=sbFzvw7JK&crid=38094426869&mp_kw=&mp_mt=&gclid=EAIaIQobChMIk-7R34TP1AIVxIuzCh3ruwBnEAQYASABEgLpZvD_BwE

    You then can power all sorts of stuff through this 12VDC aux outlet and greater than just 1.5 amps. Also if moisture is ever a problem the worst case scenario is having to replace the aux outlet. I am assuming your going to only be charging when good weather. The phone charger is also removed from bike when not needed to be plugged into it which will protect from draining your battery dead!  One thing to consider is you will want to have a switch or even safer a relay to only have that 5 volt power working when the bike is running as for even with nothing plugged into the 5 volt side of that circuit, it has a continuous draw of a small amount of power that will drain a battery dead. Relay would tap into use of sensing a run state of the motorbike to energize the coil of relay which then energizes the 5 volt power circuit you need. If you go with the 12Volt aux outlet, you wouldnt need this switch or relay and as long as you remove whatever is plugged into it then your battery wont drain from it.


    patio

    • Moderator


    • Sage
    • Maud' Dib
    • Thanked: 1674
      • Yes
    • Experience: Beginner
    • OS: Windows 7
    Re: 12V -> 5V 1A using L7805CV
    « Reply #2 on: June 21, 2017, 07:18:32 AM »
    Plenty of gas stations and Grocery stores have membership rewards cards...they contain no metal...
       
     
    " Anyone who goes to a psychiatrist should have his head examined. "

    Geek-9pm


      Mastermind
    • Geek After Dark
    • Thanked: 961
      • Gekk9pm bnlog
    • Certifications: List
    • Computer: Specs
    • Experience: Expert
    • OS: Windows XP
    Re: 12V -> 5V 1A using L7805CV
    « Reply #3 on: July 22, 2017, 01:02:53 AM »
    Is this a DIY project?
    The 780X type regulators are for use as replacement on very old equipment.
    They are not suited for new designs, unless extreme simplicity is the objective.
    No capacitors are needed.
    No fuse is needed.
    No diode needed.

    Simple heat sink recommended.

    DaveLembke



      Sage
    • Inventor of the Magna-Broom 3000 =)
    • Thanked: 590
    • Certifications: List
    • Computer: Specs
    • Experience: Expert
    • OS: Windows 7
    Re: 12V -> 5V 1A using L7805CV
    « Reply #4 on: July 22, 2017, 07:13:10 AM »
    Quote
    No fuse is needed.

    I have to make a statement about this. I greatly disagree.  :o

    I'd say that's dangerous to suggest someone making a circuit without a fused link. All projects no matter what they are should have a fuse that will pop to avoid an electrical fire if something went wrong. Fused link should be rated properly to carry the load down stream, and pop before wires glow and as close to the power source as possible so that if the Positive wire with 12VDC gets pinched or chaffed shorting to the frame it doesnt turn the motorcycle into a toaster oven with a 18GA heating element between your legs.  ::)  :P

    I still like the use of a diode to protect from accidental reverse polarity, as well as a capacitor that will smooth out the power in case of noise from the power source. Capacitors if placed at the source as well as the output also will cushion the output side and assist if there was any spikes in current draw so that the voltage regulator functions more smoothly without quick dips or spikes or ripple.

    These parts are small and cheap and no need for greater simplicity and rely solely on the voltage regulator alone. Could it work on just the voltage regular alone.. yes... but its not a design that I would go with. Id rather spend the extra $3 and have some protection with fused link, diode, and caps with the fused link with fuse costing about $2.50 USD of that $3.

    Geek-9pm


      Mastermind
    • Geek After Dark
    • Thanked: 961
      • Gekk9pm bnlog
    • Certifications: List
    • Computer: Specs
    • Experience: Expert
    • OS: Windows XP
    Re: 12V -> 5V 1A using L7805CV
    « Reply #5 on: September 29, 2017, 02:51:47 PM »
    The data sheet shows the 780x is safe up to about 40 volts DC.
    https://www.sparkfun.com/datasheets/Components/LM7805.pdf

    That is  way above the 14 vile limit in a motorbike.
    My own experience with the 780x is the blow  to open circuit when distressed.
    An a vehicle should already have fuses for accessorizes.


    patio

    • Moderator


    • Sage
    • Maud' Dib
    • Thanked: 1674
      • Yes
    • Experience: Beginner
    • OS: Windows 7
    Re: 12V -> 5V 1A using L7805CV
    « Reply #6 on: September 29, 2017, 03:02:09 PM »
    Quote
    An a vehicle should already have fuses for accessorizes.

    A phone doesn't...re=read the Post.
       
     
    " Anyone who goes to a psychiatrist should have his head examined. "

    Geek-9pm


      Mastermind
    • Geek After Dark
    • Thanked: 961
      • Gekk9pm bnlog
    • Certifications: List
    • Computer: Specs
    • Experience: Expert
    • OS: Windows XP
    Re: 12V -> 5V 1A using L7805CV
    « Reply #7 on: September 29, 2017, 07:20:44 PM »
    A phone doesn't...re=read the Post.
    You are right, here wants to use a motorcycle battery.
    Now then, What would the fuse do? The  7805  has a higher level of integrity.
    But f he wants a fuse, that is OK.



    patio

    • Moderator


    • Sage
    • Maud' Dib
    • Thanked: 1674
      • Yes
    • Experience: Beginner
    • OS: Windows 7
    Re: 12V -> 5V 1A using L7805CV
    « Reply #8 on: September 29, 2017, 10:10:26 PM »
    Wow.
       
     
    " Anyone who goes to a psychiatrist should have his head examined. "

    Geek-9pm


      Mastermind
    • Geek After Dark
    • Thanked: 961
      • Gekk9pm bnlog
    • Certifications: List
    • Computer: Specs
    • Experience: Expert
    • OS: Windows XP
    Re: 12V -> 5V 1A using L7805CV
    « Reply #9 on: September 30, 2017, 12:12:26 AM »
    Might be the OP has gone.
    For what it is worth, the main reason for using fuses is to reduce fire and property damage. An to help prevent harm to prole.

    A common fable is that a fuse will protect delicate equipment. 
    It only prevents the equipment for catching fire. The fuse commonly used is a 3AG and is often used in electronic equipment in addition to use in automobiles.

    Fuses that can act fast enough to prevent electrical damage to a smartphone, tablet, computer, radio or similar device and hard to find. Most fusee only react to thermal overload and can take several milliseconds to respond to excessive current flow.

    Here is a spec sheet:
    http://www.mouser.com/ds/2/643/3AG-1136042.pdf
    I have copied part if the PDF and placed it below.
    Another point often overlooked is the resistance of the fuse itself. The resistance can have some impact on the functionality of the circuit. A fuse that is rated at 50MA might have a voltage drop of 3 volts, depending on the specific type of fuse you want. A fuse with a high resistance may have r fast blow times. But the voltage drop may interfere with reliable power delivery.
    So the current practice is to put protection built into the device you are using. The smartphone, radio, camera or whatever device you have should protect itself. The fuse is sometimes required to satisfy the insurance companies. Put do not pretend that a fuse will protect you better than  the device does by itself.

    BTW: Obviously some laptop computer should have had fuse protection. However, once a lithium-ion battery starts to burn, you can not stop it with a fuse.

    The point  being made: Fuses are required due to meet legacy rules by agencies. But they have little ability to prevent damage from a moderate over voltage condition.

    See attachment. Olen type of 3AG fuse for 400 ma with hold at 400 MA for 5 hours. At 800 MA it might take 5 seconds  to blow. Not good enough to prevent permanent damage to an electronic circuit.

    DaveLembke



      Sage
    • Inventor of the Magna-Broom 3000 =)
    • Thanked: 590
    • Certifications: List
    • Computer: Specs
    • Experience: Expert
    • OS: Windows 7
    Re: 12V -> 5V 1A using L7805CV
    « Reply #10 on: September 30, 2017, 01:39:34 PM »
    My point in fuse was so that if the 12V + wire ever made its way to chassis ground it would pop a fuse close to + battery post. The regulator would smoke long before a fuse would blow but damage self contained within the enclosure of the 5 volt regulator box. On modern cars they moved the fuse box for main heavy duty fuses into engine compartment close to the battery. In cars years ago you just had the fuse panel under the dash. These days you will find both as well as relays in a moisture resistant box nearest to the battery. Thats why I suggest an insulated enclosure fuse such as the weather resistant 2 piece push and turn with has an o-ring to keep water out of the fuse compartment or another water resistant fuse holder nearest to the + battery post so that if the wire going to this regulator box gets chaffed or pinched or through heat or vibration somehow the conductor makes its way to the frame or another metal object connected to the frame which is used as a return leg, that this fuse nearest to the battery will pop and they dont have a red hot wire burning the inside of their groin etc.  ;D  Its a much safer design to have the fuse nearest to the + battery post vs trusting a length of wire leading to a box never to short to common return ( aka Negative post ).  :)

    Geek-9pm


      Mastermind
    • Geek After Dark
    • Thanked: 961
      • Gekk9pm bnlog
    • Certifications: List
    • Computer: Specs
    • Experience: Expert
    • OS: Windows XP
    Re: 12V -> 5V 1A using L7805CV
    « Reply #11 on: September 30, 2017, 09:20:42 PM »
    Point made.
    The fuse is t o prevent fire and burns.
    BTW, the OP did not say much about his smartphone.
    The 7805 is a good regulator, but it is not a battery changing circulate. So it is not clear if it will change the smartphone. They make cheap 12 volt to smartphone adapters that claim to properly change the battery.  I don't have at hand any specs on how they work. But when the battery goes above 4.7 bolts, the charge circuit should turn off. The 7805 regulator will keep  giving out 5 volts. He might want to do some testing with voltmeter and Milli amp meter to see how well it works.
    Here is a reference that indicates you should not charge a small cell for more that 2 or 3 hours unless you have a smart charger.
    http://batteryuniversity.com/learn/article/charging_lithium_ion_batteries
    Quote
    The Li ion charger is a voltage-limiting device that has similarities to the lead acid system. The differences with Li-ion lie in a higher voltage per cell, tighter voltage tolerances and the absence of trickle or float charge at full charge. While lead acid offers some flexibility in terms of voltage cut off, manufacturers of Li-ion cells are very strict on the correct setting because Li-ion cannot accept overcharge. The so-called miracle charger that promises to prolong battery life and gain extra capacity with pulses and other gimmicks does not exist. Li-ion is a “clean” system and only takes what it can absorb.
    I read that to mean do not go above the 4.3 volt point of the battery used in most smartphones.  The above links warns about trying to "top off" a lithium battery. They don't work that way.

    DaveLembke



      Sage
    • Inventor of the Magna-Broom 3000 =)
    • Thanked: 590
    • Certifications: List
    • Computer: Specs
    • Experience: Expert
    • OS: Windows 7
    Re: 12V -> 5V 1A using L7805CV
    « Reply #12 on: October 01, 2017, 10:59:11 AM »
    Myself... I'd add a 12V accessory/aka cigarette lighter plug. And use a car charger for phone. Just would then need a pouch for phone to tuck into and not fall out of. Just add a 3 amp fuse in series with the 12 V accessory outlet. They would want to pay more for the ones that have weatherproof cap to seal when not in use and not want to be using it in rain etc as for it would eat itself if wet operation and 12v phone charger likely also not weather resistant.

    Also... velcro wire tie strap to take extra slack in charge cord and secure it to bike so the front wheel doesnt eat your phone if cord gets snagged by front wheel and it yanks it all to eat it into the front wheel etc. Wire from battery tap to 12V accessory plug could be zip tied to frame in locations that dont exceed 120F, in areas that are hot the insulation can melt and short the wire to chassis and blow that 3amp fuse closest to the + battery post.

    patio

    • Moderator


    • Sage
    • Maud' Dib
    • Thanked: 1674
      • Yes
    • Experience: Beginner
    • OS: Windows 7
    Re: 12V -> 5V 1A using L7805CV
    « Reply #13 on: October 01, 2017, 05:29:33 PM »
    The whole project is imho ridiculous...plus it appears he's been abducted...
       
     
    " Anyone who goes to a psychiatrist should have his head examined. "

    DaveLembke



      Sage
    • Inventor of the Magna-Broom 3000 =)
    • Thanked: 590
    • Certifications: List
    • Computer: Specs
    • Experience: Expert
    • OS: Windows 7
    Re: 12V -> 5V 1A using L7805CV
    « Reply #14 on: October 02, 2017, 05:45:38 AM »
    Can only hope abducted and not gone due to an electrical fire due to lack of fuse.  :P