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Cigarette lighter using rechargeable AA batteries

Discussion in 'Power Electronics' started by Burn, Jan 31, 2010.

  1. Burn

    Burn

    7
    0
    Jan 31, 2010
    Hi,

    I want to build a joule thief which can boost the output power of an AA rechargeable battery from 1.2v to something like 8~12v.

    These AA batteries tipically have 2000~2500mA


    The idea is to build a battery powered cigarette lighter. Thanks !
     
  2. Resqueline

    Resqueline

    2,848
    1
    Jul 31, 2009
    A typical cigarette lighter draws around 4 Amps (=48W). Boosting the voltage 10 times translates to a 10 times higher current draw on the AA cell; = 40 Amps. And that is disregarding the inverter efficiency.
    The load resistance the cell will see is thus less than 1.2V / 40A = 0.03 Ohms
    Some of the better Ni-Mh AA cells have an internal resistance of around 0.05 Ohms.
    I've seen claims about some 1.6V Ni-Zn technology AA's having less than 0.02 Ohms resistance, (though I calculated it to be 0.03 Ohms) but even that won't cut it:
    The max power [W] that you can draw from a cell is when external resistance equals internal resistance.
    So for a Ni-Mh AA that is 0.6V/0.05*0.6V=7.2W (which means you'd need 8-10 cells in series to do the job)
    And for a good Ni-Zn it's 0.8V/0.02*0.8V=32W (which means you could get away with 2 cells in series)
    But remember that the batteries then would generate as much heat as the cigarette lighter itself.
     
  3. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,131
    2,662
    Jan 21, 2010
    NiCads have a lower internal resistance than NiMH. SLA even lower.

    Having said that, I'd approach this as an academic exercise rather than as a practical project opportunity :)

    This page http://www.buchmann.ca/article4-page1.asp (and I think they mean milliohms rather than milliwatts in the table) gives you some indication of internal resistances for cell types. (remember to divide these figures by the number of cells to get the per-cell internal resistance)

    I think you'd have a better chance with D cells (certainly SLA cells are available in that size)

    A major issue would be the connection to the cells. You would have to use cells that are terminated with solder tags rather than bare cells -- the connection resistance would be far too high.

    You would need to look at the datasheets on individual cells to determine if the discharge rates are possible for the cell.

    Another issue would be that you would almost certainly need to generate another higher voltage source to power your regulator. It is difficult to imagine any of the more efficient designs starting up on their own from 1.5V. You might need a more specialised "joule thief" type of inverter to generate an initial 12V rail to power the main inverter before using the generated 12V rail for continuous operation (or not -- you could use 2 regulators, it's not like a bit of inefficiency here would be a real issue).

    More practically, you may be better off creating your own specialised "cigarette lighter" from a coil of nichrome wire of sufficient length to glow red hot from just a 1.2V supply. Since this device would be small enough to turn on when brought to the cigarette, it need not require the relatively large thermal mass of a conventional car cigarette lighter.

    I would estimate that you could probably create a device that used perhaps only 10W (i.e. 8A) and would only need to be operated for a couple of seconds. The major issue here would be the contact resistance and the switch. It may be sensible to use a small inverter to provide gate voltage for a high current mosfet that has a very low RDSon.

    At a minimum, I think you'd still be looking at a sub-C sized cell.

    OK, here's the specs I found on a sub-C cell. It is rated for up to 30A discharge. http://www.gpbatteries.com/pic/330SCH-ZRS1161rev2.pdf Note the voltage at 30A, also note that the effective capacity is much lower, still it looks like you'd get 6 minutes use at 30A which is pretty good.

    This page has more battery types listed: http://www.rechargeable-battery-review.com/data-sheets/battery-specs/gp-battery-data-sheets.html

    From a quick look, it appears that the AA sized cells top out at a recommended max of 6.6A. (D cells go to 50A)
     
    Last edited: Feb 1, 2010
  4. Burn

    Burn

    7
    0
    Jan 31, 2010
    Thanks for all the answers :)

    It looks like this will be a complicated thing to do. But I have seen some videos on youtube where they light up cigarettes with a piece of stell wire and two AA alkaline batteries.

    Can't I use the same mechanism ?
     
  5. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,131
    2,662
    Jan 21, 2010
    Kinda what I was suggesting -- use nichrome wire and a single cell. Your original question seemed to suggest that you wanted to use a car cigarette lighter.

    This is something to experiment with. I'd still go for NiCad batteries, simply because they are very tolerant of abuse, and this is really abusing the cell :)

    Get yourself some nichrome wire and determine what length is required to *just* start to glow a little. Start with a long piece of wire and make it shorter and shorter until you find the right length.

    You can get more than you'll need very cheaply on ebay: http://shop.ebay.com/?_from=R40&_trksid=p3907.m38.l1313&_nkw=nichrome+wire&_sacat=See-All-Categories (and probably from other places too)

    I have no idea what gauge you would need, or a ballpark length. Once you've found the right wire size and length you should measure the resistance and the voltage across it when operating. Then use ohms law to determine the current.

    I'd start with the smallest gauge of wire as that will give you the lowest power consumption, and consequently the ability to use the smallest battery. Be aware that the "correct" length will change depending on the type of battery you use, the size of the battery you use, and how easily the heat can radiate away (so winding the wire into a tight spiral will make it hotter because heat can't escape so fast).

    A quick glance at some specs indicates that 32 SWG (0.27mm diameter) has a resistance of about 20 ohms per metre. If we assume that 6A at 1V is the highest power we can take from an AA Nicad, then the minimum length of this gauge of wire would be about 8 cm would be the minimum length. That seems too long to coil up without risk of shorting, so maybe a smaller gauge would be better. You do have to be careful that the wire heats up and doesn't act as a fuse. Winding a longer length around a ceramic sheet of some type, or making your own stiff coil may be an option.
     
  6. Burn

    Burn

    7
    0
    Jan 31, 2010
    Probably my bad since I'm Portuguese and my English is not the best one you can read. :D
    Thanks ! That was all I needed to ear. :)
    I guess I will just have to find NiCd batteries since I just have NiMH laying around.

    I've tried to use a piece of wire that I took from a broken space heater with a 5v 1000mA power adapter. Used a 10cm (+- four inches) wire with 0.3mm thickness and a resistance of 8ohm and IT WORKED ! :D
     
  7. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,131
    2,662
    Jan 21, 2010
    Try using a quarter of that (2.5 cm) with a single AA NiMH cell. That load should be OK for a NiMH cell.
     
  8. Burn

    Burn

    7
    0
    Jan 31, 2010
    Thanks for all the answers.:D

    I've managed to create a simple lighter using 0.16mm nichrome wire and it does work well (even though the batteries die pretty soon).

    I've created a wooden based prototype and a friend of mine liked the idea and asked me if I could create a herb vaporizer based on the same principle. I told him that using AA batteries wouldn't be the best idea, but he insisted in making something portable even if I had to use more AA batteries. Given this I've designed a box capable of holding 6 AA batteries.

    The biggest difference is that instead of touching my cigarette directly with the heating element I would wrap a borosilicate tube with the heating element to vaporize the herbs.

    Now, in order to protect them from burning I was thinking about some sort of small circuit (it really needs to be small) that would read the temperature and cut the power when it reaches a certain level.

    Now I'm not an electronics engineer, but I've tried to draw a simple circuit based on other transistor based circuits. Could someone tell me if it would work?

    [​IMG]

    VR1 would be used to control the temperature limit and TR1 is a PTC thermistor. T1 would be a transistor acting like a switch and D1 would be a diode to protect the transistor. I'm just explaining this in case it doesn't make any sense to you :p

    If this circuit does work can someone tell me how can I calculate all values for the components in order to be able to maintain a temperature ranging from 150º to 300º Celsius?

    What do you say ? Could this work ?


    Thanks again ! :)
     
  9. Resqueline

    Resqueline

    2,848
    1
    Jul 31, 2009
    Yes, it might just work, but there's no positive feedback to give hysteresis so the relay would pull & release slowly giving the contacts a hard time. It might still live long enough though.
    But how about just using a PTC fuse as the heating element itself, and nothing else? It should be self regulating and would surely reach 150-180ºC.
     
  10. Burn

    Burn

    7
    0
    Jan 31, 2010
    Well, I guess you're right about the hysteresis control. Isn't it possible to use some kind of capacitor connected to the transistor's base to avoid powering on/off in short amounts of time ?

    Anyway, using a PTC fuse seems to be a lot easier. Do you have any specific reference I should search for ? :D
     
  11. Resqueline

    Resqueline

    2,848
    1
    Jul 31, 2009
    You'd have to use two transistors & two extra resistors to get proper hysteresis. The relay in itself adds hysteresis though but it's a little late and of unknown magnitude.

    Just Google for PTC fuse and you'll find lots of info about them. Their tripped temperature seems to be a little elusive but it's there. A low thermal derating factor would indicate a high trip temperature.
    Axial lead strap types (as used in battery packs) which are flat and would be easy to get good thermal contact with seems to have a 125ºC surface trip temp. but Littelfuse's A line would reach a higher temp than their B line for example.
    I'm sure there are different compositions from different manufacturers though, you'll just have to do some research..
    I have an old low-voltage soldering pencil using PTC tecnology so I know it can reach around 300ºC.
    Here are some measurements I just did on some PTC's I had lying around:
    Old unknown brand: 150ºC
    "X" brand, U & X series: 140ºC
    Bourns, R series: 130ºC
    Bourns, metal smd: 105ºC
    "Delta" brand, C series: 100ºC
    The temp's were measured with an IR-camera so they might not be very accurate.
     
    Last edited: Feb 9, 2010
  12. Burn

    Burn

    7
    0
    Jan 31, 2010
    I've tried to vaporize tobacco at 130~150ºC, but I think there wasn't enough heat. I think I need something between (at least) 180ºC and 250ºC. Higher may be good, but lower doesn't seem useful.

    Either way I've searched here on local electronics stores and couldn't find any "low power" PTC fuses. Is it possible to use them with such low voltages as 1.2v ?
     
  13. Resqueline

    Resqueline

    2,848
    1
    Jul 31, 2009
    Ok, you may have to search to see if there's something like PTC heating elements then, they work at higher temp's for sure.
    The nice thing about PTC's is that the applied voltage doesn't matter much, they draw the power they need to keep at the trip temp. If you use a low-voltage (16-30V) rated PTC then I figure 1.2V is enough to trip them, but it'll draw twice the current it would do at 2.4V though.
    I don't think "low power" is the term to use btw. You'll simply want it as physically big as will fit in your application.
     
  14. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,131
    2,662
    Jan 21, 2010
    Enough heat, or high enough temperature?

    2 different problems, which was it?

    Remember that at temperatures above about 230 C you will start to burn the tobacco.

    When you say vaporise, what do you actually mean? Do you want to drive off the volatile components without burning them?
     
  15. Burn

    Burn

    7
    0
    Jan 31, 2010
    Sorry, when I said "low power" I really wanted to say "low voltage". Every PTC fuse I could find required more than 12V. :p

    I believe I didn'd have a high enough temperature. As a consequence it didn't generated enough heat.

    What I would like to do is to drive off the volatile components without burning them. That's why I wanted to avoid direct contact between the nichrome wire and the tobacco itself.
     
  16. eleseur

    eleseur

    1
    0
    Jun 20, 2010
    What an interesting thread, i made an account just to post a reply. Anyway if you are looking for an excellently designed AA powered vaporizer i suggest you check out the magic flight launch box. I have one to vaporize my herbs and it works great. I'm very interested in reverse engineering one due to the fact that mine won't last forever and i want to try some new designs. Anyway hope this info is helpful and i'll try to attach some pics of my launch box. Btw the electronics on this device are so simple its stupid. Its just a copper wire welded with silver solder to a brass screen. Very effective convection vaporizer.
     

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