Is it possible to make toast without fire or wall electricity? How would I go about doing this?(The reasons I need to do this are difficult to explain, and not particularly interesting)
I think using thin pieces of wire, attached to the right resistor, will give it enough heat to glow hot enough (like a toaster). So lots of batteries and resistors. Wire too. Now you’ve got to find the right resistor for the right battery to achieve this. Plus a type of housing, so you don’t burn yourself.
Of course you can do it. You’re going to need a helluvalot of D cells, unless you’re planning on 12 volt batteries. Nichrome would be my first choice for wire.Here is a datasheet giving temperature/amperage references for common sizes.
My toaster uses 850 Watts. It is a two slice affair so a toaster for 1 slice able to make the toast in the same time that mine does would be 425 Watts.
Using a 12 volt storage batter this would require 35 amps and a 100 amp-hour battery would last about 3 hours.
Use Nichrome or other resistance wire that has a total resistance of about 1/3 Ohm at the operating wire temperature.
You will probably need some sort of housing to keep breezes from taking away too much heat.
Nichrome doesn’t solder worth a damn so you will have to spot weld leads on it you want leads.
If you are willing to take a little longer to make the toast you can use less power and make the batter last longer but there is a minimum temperature required. I have no idea what that temperature is.
Go to a trailer-and-RV store. There are toasters and even ovens that run on 12 volts.
“Help! I’m stuck in the wilderness with a battery and some bread and I MUST HAVE TOAST!”. 
[total hijack] Speaking of being out in the wilderness … A guy was preparing for a trip into the Amazon rain forest and asked his buddy to check his equipment list. The buddy looked the list over and said, “You seem well prepared, but you forgot the gin and vermouth.”
“Why would I pack that into the jungle.”
“Well, when the time comes that you are totally lost and without help, pull out the gin and vermouth and mix a drink. Someone is sure to pop out of the jungle and say, ‘That’s not how you make a Martini!’ and you are saved.” [/total hijack]
OK, factual answer has been given, cheap humor has been played, so now I must add my own.
With regard to the thread title, “How can I turn bread into toast with batteries?”
- Take piece of bread, toast it.
- Serve with AA or other appropriately sized cells.
- Voila! Toast with batteries!
I’ve heard the “gin and vermouth” joke but I heard it as a deck of cards. When you’re lost in the forest, start playing solitaire, and someone will pop out and say “you can put the black 3 on the red 4.”
How many D-cells would I need? What about if I were to use 12 volt batteries? Also, how long would the batteries last if I am using them to heat nichrome wire to 400-500 degrees F? How would I go about constructing a toaster? Can I use one long peice of wire, or will heat decrease apprecieably with length?
Quick back-of-the-envelope type of estimate using the data sheet provided by danceswithcats. 18 inches of #10 Nichrome wire looped back and forth to cover the slice of bread. I’m not sure 18" would cover the bread very well but it’s not bad. You need a reflecter behind the wire to reflect that heat onto the bread. And this is a one side at a time toaster. Sorry.
Current is about 16 Amp. You need about 125 carbon-zinc D cells in parallel each one delivering .13 Amp. Unfortuately this is a minimum estimate because the different cells’ voltages will be slightly different under discharge so the current from a battery having a high voltage won’t necessarily go into the wire. Some of it will go into batteries with lower terminal voltage at whatever current they are putting out. This is wasteful and calls for a few more batteries than calculated.
A carbon-zinc cell will put out about 1.3 Amp-hours at .13 Amp discharge current which is what the above is based on. Other batteries will have more capacity but some of them, such as Alkaline, have much less capacity than their quoted nominal if the discharge current is too high. You would have to look up the specs on various batteries to find the best ones and I don’t feel up to it.
Incidently, I don’t think 400-500 F is hot enough. I think that would produce a pretty dull red toaster element and I think toaster elements are pretty orange. Probably up around 800-1000 F. Nichrome will stand up to 1100 C (over 2000 F).
Most RVs do not have a lot of 12-volt distributed wiring; they’ll use 12 volts to run something like a water pump or some lights, but most RV appliances are 110-volt domestic appliances that run off an inverter. While I don’t dispute that 12-volt appliances may be available, they are certainly not common. Most yachts, RVs and the like will use propane stovetops/ovens rather than electrically-powered. We even use a propane-powered refrigerator - 12-volt “coolers” are available, but don’t have the capacity of a propane refrigerator.
Which begs the question, why is a propane stove out of the question? You can make toast fairly easily and quickly on a propane element, as opposed to the rigamarole of trying to do it from batteries. Unless you’re designing a toaster for the Space Station, electrical toasters without a wall outlet would seem to be an inappropriate and inefficient way of doing the task.
Futzing around with wires and resistors only ends up giving you a do-it yourself inneficient toaster. You may as well either take a battery powered toaster with you or spear the bread on a suitable stick and toast it over a campfire.
There’s all this talk of D cells. What is it in this question that rules out a big fat car battery?
Ahem. See my first post. But the customer wants D cells and the customer is always right. Right?
It’s a completely impractical idea but “paper and pencil” is cheap and I’m retired and my time is even cheaper so why not fiddle around with it for a few minutes.
The limting factor will be current flow. You’ll need enough batteries in series toget 12 volts, nine with nominal 1.5v Alkalines, and enough of those sets in parallel to get sufficient current flow. You didn’t say what kind of D cells as I’m pretty sure that nickel metal hydride will give more peak current flow. Yes, they make NiMH true D cells but they cost alot. Nominal voltage is 1.2V but the cells actually have lower internal resistance so they provide more voltage to low resistance loads which allows more current to flow.
The key equations you’ll want to fiddle with are:
Ohm’s Law: E=IR
Ohm’s powerlaw: P=EI
where
P = Power (watts or Joules/sec)
E = Voltage (volts – it’s called E because another name is “electromotive force”)
I = Current (amperes)
R = resistance (ohms)
You will also find it useful to know:
Series resistance: R(t) = R1 + R2 + …
(take home lesson: six inches of nichrome has six times the resistance of one inch)
Parallel resistance 1/R(t) = 1/R1 + 1/R2 + …
(take home lesson: Splitting a current among N equal wires will give 1/N the resistance of one wire
– or if you prefer: Splitting the current N equal ways will draw N times the current of one wire)
1 calorie = 4.2 joules = 4.2 watts for one second
Two shortcuts (derived from he two Ohms Laws above)
E = I[sup]2[/sup]R
I = E[sup]2[/sup]/R
EXAMPLE: (to illustrate typical math. See “problem”, below)
Let’s say we have a 12V battery that can safely provide 10A. I have a suitable high-drain 12V battery in front of me right now. It’s smaller than a toaster, and weighs less, too. The other parts for my design are essentially negligible (nichrome wire, two test tubes, two bathroom tiles with holes drilled in them to act as the frame/stand, and 2 1-Ft heavy gauge copper wires to hook up the battery_
To draw 10A at 12V, a toaster must have 12V/10A = 1.2 ohms net resistance.
(I’m ignoring the battery’s intenal resistance. You can adjust for it once you’ve built a prototype)
The amount of resistance per inch depends on the diameter of the wire. Smaller wire has more resistance, so it heats up faster, and it also radiates faster, due to its high surface/volume ratio. However, it’s also more fragile, more likely to burn out, and can’t handle as much current (which is fine for our current-limited application). To choose the right size, try using this table
CASE 1:
For the sake of argument, let’s aim at a -ahem- toasty 1000F (much hotter than we need, but we want a margin of error) and we’ll choose 40 gauge Nichrome C wire.
40 gauge (about the diameter of a thread) Nichrome C wire reaches 1000 at a measly .43A, so we could have up to 23 parallel wires, and still draw less than 10A total. Let’s say 24 wires. I like round numbers, and I don’t care if I only reach 950-975F instead of 1000F
40 gauge Nichrome C wire has a resistance of 70.24 ohms/foot. Since we want 1.2 ohms total, we can use 24 parallel branches of 1.2*24 = 28.8 ohms each (4.9 inches – nicely toast sized)
We don’t have to weld them: if we wrap the nichrome evenly between two copper tubes [melting point: 1984 F] 5" apart, each “leg” of the wire will conduct independently, almost as effectively as a welded assembly. Actually, copper will conduct away our precious heat. Let’s use glass bars or test tubes, and run a thick copper wire or strip up the back of them.
Reviewing the math:
Each element is 4.9" (.4166 ft) at 70.24 ohms/foot for a resistance of 28.8 ohms each,
A 28.8 ohm resistance draws .417 Amps at 12V (just a hair under our desired .43 A for 1000 F)
24 of these elements in parallel will draw .417 x 24 = 10.008 Amps – close enough to 10 A for jungle work!
10 A at 12V is 120 W – a fair bit less heat than most household toasters, but I assure you, even a 120W bulb will toast bread. we can place our heating elements very close to the bread to speed things up.
Total materials?
two test tubes, 1/2" dia (toast thickness) x 6" (toast width) 5" apart (toast height)
two 6" bathroom tiles with holes drilled 5" apart: stand/spacer for the tubes
one 12-ft length of nichrome wire (5" x 24 =10-ft, plus a bit extra)
one 12V 10A battery (e.g. a high drain 12AH 12V marine cell or better)
2 1-ft heavy gauge copper wires to hook the battery to the nichrome.
CASE II
Let’s design a 800 F heating element, spaced a bit wider, so I can toast slices for “man-sized” sandwiches instead of those wimpy Wonder Bread™ things. I think bread tastes better slow-toasted, not insta-seared, anyway
The tables say we need .36A to reach 800F with 40 Gauge Nichrome C. That would allow us roughly 28 parallel wires.
At 12V, we need a resistance of 12/.36 = 33.33 ohms per wire
At 70.24 ohms/ft, each wire much be 5.7" to achieve 33.33 ohms
This design would need 13.3 ft of wire–call it 15 ft to allow for factors I’ve deliberately neglected, like the width of the test tubes.
ONE PROBLEM:
Nichrome wire actually has a significantly higher resistance when hot vs. room temperature. These resistances are listed in the tables I linked. You will have to make a modification to the design, in order to draw 10A when hot without drawing much more (and possibly draining, harming, or blowing the battery) in the first few seconds of operation.
I have several ideas, but 'll leave that as an execise for the OP. Why steal all his fun?
Oops, I meant to add: for those who doubt that you can toast bread effectively with 120W or even 30W, allow me to remind you of the EZ-Bake oven.
Those things had a 40-60W bulb, and they could not merely toast bread, but bake it from scratch – like a toaseter oven. ‘Real’ toaster ovens draw much more power than ‘real’ kitchen toasters, due to inefficencies of their design for the purpose of toasting. What we’re building here is an “EZ-Bake Toaster”
Possibly the dullest toy ever – but writing this post enabled me to skip lunch, and stick to my diet, so mock away. I’m happy.
The 12 Volt Toaster
Also keep in mind that, once you figure out the battery arrangement you want to use, adjusting the resistance of the heater so it equals the battery’s source resistance will allow maximum power to flow from the battery to the heater.
Go into a diner and offer to trade them your batteries for some toast.