istruggle2gate11 Posted November 17, 2006 Share Posted November 17, 2006 Hi all, Anybody advise me how to take power from the car and reduce it down to a constant 5v? Im guessing an inline resistor pack or the like (IIRC the resistor pack on a flapper system takes it down to 3v?) Not bothered about size of the solution as "heavy is reliable" Cheers Quote Link to comment Share on other sites More sharing options...
pugwash Posted November 17, 2006 Share Posted November 17, 2006 don't know if this will help rog but i "think" that carputer converters will supply a 5v rail for a PC. It might be switchable too! no idea how many amps on the rail it will provide so it depends on what you need really! Quote Link to comment Share on other sites More sharing options...
istruggle2gate11 Posted November 17, 2006 Author Share Posted November 17, 2006 don't know if this will help rog but i "think" that carputer converters will supply a 5v rail for a PC. It might be switchable too! no idea how many amps on the rail it will provide so it depends on what you need really! Good Call, Hardly need any amps. its only to power a MP4 recorder device. Quote Link to comment Share on other sites More sharing options...
LandyManLuke Posted November 17, 2006 Share Posted November 17, 2006 What current draw will you need at 5v? for small currents, a 3 pin regulator is imho the simplest, best way of doing it. Edit: Maplin link here Quote Link to comment Share on other sites More sharing options...
istruggle2gate11 Posted November 17, 2006 Author Share Posted November 17, 2006 What current draw will you need at 5v?for small currents, a 3 pin regulator is imho the simplest, best way of doing it. Edit: Maplin link here Seems perfect lmate, so how are they installed / wired up? Do they need assembly on a PCB? Quote Link to comment Share on other sites More sharing options...
rtbarton Posted November 17, 2006 Share Posted November 17, 2006 Don't use a resistor unless you are drawing a constant current, and even then it won't be regulated against changes in input voltage. The 3-pin regs (7805 &c) mentioned above are by far the beat bet. Quote Link to comment Share on other sites More sharing options...
LandyManLuke Posted November 17, 2006 Share Posted November 17, 2006 Pretty simple, three pins - ground, voltage in, 5v out. no other components required. A fuse on the input, just like any other circuit. The package should be fixed to a heat sink to help it dissipate heat, they can get rather warm. Don't really need a PCB, could solder it on a bit of veroboard, or just solder straight to the legs. would be a good move to put some heatshrink on the legs, or 'pot' them in hot glue, though i don't know if either of those ideas would stand up to the warmth it produces. every time i've used them they've been on a bigger circuits, in a box, so protecting/insulating the pins hasn't been a problem. Quote Link to comment Share on other sites More sharing options...
LS26 Posted November 17, 2006 Share Posted November 17, 2006 What current draw will you need at 5v?for small currents, a 3 pin regulator is imho the simplest, best way of doing it. Edit: Maplin link here Brilliant! Every time I visit this site I learn SO MUCH! Just one question though - it appeared that these things expect an input of 35v - or is this the max perhaps? Rog (another one) Quote Link to comment Share on other sites More sharing options...
LandyManLuke Posted November 17, 2006 Share Posted November 17, 2006 yup that's max, typically they'll run off an input about 2v above the required output. though different specifications are available. Luke Quote Link to comment Share on other sites More sharing options...
FridgeFreezer Posted November 18, 2006 Share Posted November 18, 2006 What Luke said - 78_05__ will do what you want (the "_" bit can vary between manufacturers / specs). Easiest is bolt it to a bit of metal that allows you to bolt it to the body somewhere, that should sink more than enough heat. Solder wires to the legs, a bit of heat shrink over the top for robustness and bob's your uncle. Alternative is to butcher an old relay and solder it into the case of one, giving you a regulator "relay" that plugs into a stock socket with spade terminals. A metal cased one would be ideal. Quote Link to comment Share on other sites More sharing options...
LandyManLuke Posted November 18, 2006 Share Posted November 18, 2006 Alternative is to butcher an old relay and solder it into the case of one, giving you a regulator "relay" that plugs into a stock socket with spade terminals. A metal cased one would be ideal. Nice, I'll remember that one, good idea. Quote Link to comment Share on other sites More sharing options...
istruggle2gate11 Posted November 18, 2006 Author Share Posted November 18, 2006 Pretty simple, three pins - ground, voltage in, 5v out. no other components required. A fuse on the input, just like any other circuit.The package should be fixed to a heat sink to help it dissipate heat, they can get rather warm. Don't really need a PCB, could solder it on a bit of veroboard, or just solder straight to the legs. would be a good move to put some heatshrink on the legs, or 'pot' them in hot glue, though i don't know if either of those ideas would stand up to the warmth it produces. every time i've used them they've been on a bigger circuits, in a box, so protecting/insulating the pins hasn't been a problem. Thank you Luke, part is ordered. Regarding the relay cases, good idea fridge, Kind of got a lot of old Rangie Relays from the "donours" Quote Link to comment Share on other sites More sharing options...
Bull Bar Cowboy Posted November 18, 2006 Share Posted November 18, 2006 Just a word of caution, From a design engineers point of view there is one simple calculation that is often missed. Going from 14.4 to 5 volts means losing 9.6 volts ………. This will be lost as heat within the device and it is all too easy to stray beyond the device dissipation limits and yet stay safely within the current handling capability of the chosen device. Ian Quote Link to comment Share on other sites More sharing options...
istruggle2gate11 Posted November 18, 2006 Author Share Posted November 18, 2006 Ian, Need to ask you to expand on that one please, Im not electronics minded at all, how do I stay within the said parameters? I just assumed that if was designed for 40v downwards, then 12v would be just ticking over - The device I am powering is 100ma. I was going to do as fridge suggested and house it in an old relay case which would be attached to the body. Too late now as Ive got the parts on order, but one further question on these devices was if it fails does it just stop and lose power or will it revert back to 12v? Quote Link to comment Share on other sites More sharing options...
TheRecklessEngineer Posted November 18, 2006 Share Posted November 18, 2006 If it fails, it will just die. 12v wont be applied to the device. 100ma at a 9.6v drop, will generate 0.96W. A relay case probably might just be able to cope with this (it would get uncomfortably hot - think about a 1W resistor), but I would fit it to something larger. If you have good thermal contact between the case and the body then it would be ok...try and fit the device on the same side as the body Make sure you fit a mica washer, and use a nylon nut and bolt, between the device and the heatsink or you will make the heatsink live! Quote Link to comment Share on other sites More sharing options...
minivin Posted November 18, 2006 Share Posted November 18, 2006 Just looked on a datasheet for a generic 7805 and the input voltage maybe upto 35VDC, however it must be stressed that this device is only capable of delivering 1.0A. If you take it to max output on current then you will be requiring that it be strapped down on a decent heatsink or something aluminium preferably, with heatshink compound between it and it's sinking material. Quote Link to comment Share on other sites More sharing options...
istruggle2gate11 Posted November 18, 2006 Author Share Posted November 18, 2006 Thank you guys, just going to rip out the heatsink from one of the old pc's. Quote Link to comment Share on other sites More sharing options...
Bull Bar Cowboy Posted November 18, 2006 Share Posted November 18, 2006 Minivin, you have fallen into the trap ………… a 7805 with 35V on the input and delivering 1amp would need to dissipate 30watts …….. even with atomic heatsinks, that is way beyond its capabilities. The devices normally do not just die…………. they tend to go into self oscillation before thermal shutdown. Themal shutdown is device controlled, but they also make good 3 pin fuses. Rog……….. your application is just fine……… a 7805 will handle that with ease...... as long as you use some form of heatsink as Fridge suggests Ian Quote Link to comment Share on other sites More sharing options...
landmannnn Posted November 18, 2006 Share Posted November 18, 2006 The simplest way must be to buy a £20 inverterr from maplins/argos etc and use the players mains adapter. Have you thought of using a mobile phone in car charger? Mine has a 5V outpput. Quote Link to comment Share on other sites More sharing options...
LandyManLuke Posted November 18, 2006 Share Posted November 18, 2006 The package should be fixed to a heat sink to help it dissipate heat, they can get rather warm. I have been using a regulator, similar to the one refered to above, to supply my onboard logic/parallel port interface, which draws perhaps a few hundred mA. It is bolted to a finned heatsink, total surface area perhaps 10 square centimetres, in a enclosure perhaps 0.8 L volume. It has been fine for the last 3 years. The TS78 series is rated to a maximum operating temperature of ~150 deg C, with operating specification given over the range 0 to ~125 deg C. A TO-220 package will dissipate 2 W without heatsink A ITO-220 package will dissipate 10 W without heatsink The heatsink is connected to ground (pin 2), metal to metal contact (perhaps with some heatsink jointing paste) is what's needed for heat dissapation. Luke Quote Link to comment Share on other sites More sharing options...
LandyManLuke Posted November 18, 2006 Share Posted November 18, 2006 The simplest way must be to buy a £20 inverterr from maplins/argos etc and use the players mains adapter.Have you thought of using a mobile phone in car charger? Mine has a 5V outpput. £20 to go from ~12v dc, up to ~230 AC(ish), back down to 5v dc, using something big,cumbersome and inefficient? or pence for a IC, smaller than a matchbox? Quote Link to comment Share on other sites More sharing options...
landmannnn Posted November 18, 2006 Share Posted November 18, 2006 £20 to go from ~12v dc, up to ~230 AC(ish), back down to 5v dc, using something big,cumbersome and inefficient?or pence for a IC, smaller than a matchbox? Fair point. Although........... Big, cumbersome, inefficient...... could this possibly describe a Land Rover? Quote Link to comment Share on other sites More sharing options...
TheRecklessEngineer Posted November 18, 2006 Share Posted November 18, 2006 Fair point. Although...........Big, cumbersome, inefficient...... could this possibly describe a Land Rover? Never! Mine disposes of unwanted fossil fuel extremely efficiently.... Quote Link to comment Share on other sites More sharing options...
istruggle2gate11 Posted November 20, 2006 Author Share Posted November 20, 2006 for small currents, a 3 pin regulator is imho the simplest, best way of doing it.Edit: Maplin link here WTF, are you guys having a laugh, have you seen the size of these things It caused massive confusion in the workshop, Dirtydiesel was scared, he couldnt work out how to weld himself a solution for fitting and it took me about three miliseconds to break a leg off one (not good with fiddley things!). Good job I bought two eh. But seriously, thanks guys, although I have only done a temp rig up at the moment, it works A1 Quote Link to comment Share on other sites More sharing options...
LandyManLuke Posted November 20, 2006 Share Posted November 20, 2006 glad to help. Quote Link to comment Share on other sites More sharing options...
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