heated bobbers

[KC0MRZ]

Hi I'm a student for electronics and a friend asked me if I could make a heated bobber for ice fishing out side so his slip bobber will still slip. I've look all over the place to find somehow to heat this bobber without getting it too hot so it don't burn the string or himself. Does anyone have any ideas to help me out on this, it will have to fit in a bobber so it can't be too big. I was thinking of somehow heating a coil of somekind but how do I do this without getting it too hot or wearing the battery down. any help would be great.

[Rodney]

Regardless of what type element you use to heat things, you might think about using a 555 timer set up to give an adjustable pulse width where the heating element receives full power for a few microseconds, is off for several more, then on again. This will be less wasteful of power and should be easily adjustable for conditions by varying the pulse width ratio. If you really wanted to get fancy, you could have the ambient temperature adjust the pulse width ratio by using a thermistor or equivalent in the timing circuit.

[Bernius1]

How long does he expect it to stay warm?

[haklesup]

That may be a tough nut to crack. A fair amount of engineering is needed to match the heater, the battery and the operating conditions (cold and wet)and put in a package that meets the need. Problem is power density. Heating elements tend to draw large amounts of power while batteries are limited in their capacity. You will want to heat as small a volume as possible, probably only where the line passes through the sleeve, to conserve power and thermally insulate the volume outside that which you wish to keep thawed.<p>Use a rechargable battery like NiMh for good power density, lithium may be too expensive for your liking but tend to come in more shapes. Try replacing the fishing line with a small 2 conductor cable if that's practical. You can eliminate the battery and run it indefinately. Do not use AC power, that will almost certainly make it a fish repeller if any current leaks into the water. (the adjustable duty cycle idea is good but you should have a duty cycle in the seconds not ms). One more thought, Batteries work poorly when they are cold. You generally can't get the full capacity out of them if they are frozen. Each technology has different characteristics (more engineering research for you). If you end up using a dropping resistor in series with the heater core (for limiting the power) you can tape it to the battery to keep it warm as well or keep the battery in the insulated warm zone with the heater.<p>Find some resistance wire as small as you can get it and spiral wrap it around an aluminum spacer (cylinder) and pass the line through there (adjust the # of turns to adjust power usage). Make sure the battery is not so heavy that it sinks the bobber and seal the whole thing well. Make sure any electrical insulating material you use between the wire and spacer is not also a good heat insulator (laquer may be a good choice)<p>You may find that a better solution is not electrical but chemical. Try taking some of that chemical jel from inside one of those first aide kit heating pads and filling part of the bobber or possibly lubricating the bobber with silicone, lithium greese or similar inert stuff (some bike chain lubes) before use (if that dosen't scare the fish that is) There are a number of chemical compounds that generate an exothermic reaction when mixed with water. A small hole in the bobber to let the water in slowly can be engineered to your needs (perhaps consume dry contents in 1 hour). Not sure what that would be but it must be non-toxic<p>Perhaps someone out there can help estimate how many watts it would take to keep a 5cm long, 2.5mm diameter (estimated size of the Al Spacer)unfrozen when half submerged with a typical air temp of say -10C (ug - thermodynamics). Anything more than the minimum power required (plus about 10% for engineering margin) will just cause premature battery rundown. Probably easiest to just make a guess and do some experiments in the home freezer to fine tune the result. Use a simple resistor submerged in a cup of water wired to a variable PS. Let the whole thing freeze then turn up the power incrementally until it just starts to melt. Find a resistance-voltage-current operating point you are happy with (as compared with the selected battery's capacity)and use that as a model to design the heater core.<p>If all that is not clear, email me (see profile) and I will make a sketch for you. Good Luck

[Dean Huster]

I know what it's like trying to keep a dog's 5-gallon watering bucket ice-free. It's no heat tape job. It takes bunches of watts to achieve that feat, especially when you consider that ice fishing temps are nowhere close to the freezing point. Water quickly sucks massive numbers of BTUs from anything it touches. Add to that the cooling added by evaporation and such and you have a mess on your hands. How about a small shack, generator and salamander heater instead. Then you'll stay warm, too!<p>Dean

[KC0MRZ]

Ok, since I'm only going to school for electronic Technition and NOT engineering. I think this is way over my head. Thanks a bunch for all the replies. I really appreaciate it.

[chessman]

Never been ice fishing before, so I don't know how far you have to walk to your spot from where you park. What about carting out a 12V gel cell to where you are fishing? You could put it on a sled and push or pull it there if you have to walk far. That might solve a few of your power problems, if it's at all possible.<p> To actually heat the bobber, I think you'd be able to use a comparator, sawtooth generator, opto-isolator, and a TRIAC to control the duty cycle of a 120V AC signal (from an inverter off the car battery). The final signal could run through a coil around the center of the bobber.<p>More specifically, run a 60Hz sawtooth from 0-whatever voltage you choose (i say 5-10V) into one side of the comparator, and a constant DC voltage from a pot into the other side. A PWM signal will be output with a 60Hz frequency, so run that through an opto-isolator so you don't kill yourself. The signal then goes to the gate of a TRIAC, and the TRIAC output controls the amount of 120V AC run through the heating coil.<p>Of course, this is all assuming your buddy will be able to cart a 12V car battery out to where he's fishing.<p>If you have any questions about this, I've built a theater lighting controller that uses this same technique of controlling AC so feel free to email me!<p>Update: just read the other posts again, making me think, I don't think it would be that hard to seal the bobber so it is water-tight.
But then I had another though: would the 60Hz signal cause a large enough vibration to repell the fish? I don't know....<p>~Kyle<p>[ January 15, 2003: Message edited by: chessman ]</p>

[billdar]

What if you did it chemically instead of electricly? Using that handwarmer liquid or some other, slow exothermic material?