Electromagnet

[science923]

I am doing a project involving building an electromagnet in order to observe the effects of the EMF on the fermentation of Saccharomyces cerevisiae (Baker's yeast). However, I am having some difficulties calculating the strength of the EMF and constructing it. I want to coil a wire around plastic bottles with the fermenting medium inside and connect the ends to a power pack (one used to jumpstart a car; it's 300 Amps starting power) with crocodile clips. I'm not sure if this is too much power for a wire. I also want to coil the wire around more/less times each bottle to create different strengths and therefore different independent levels. I am not sure how this will work and I am concerning about getting electrocuted. What type of wire should I use? I think I need some sort of insulation on it, but does it still work then? Also, would the plastic melt? I want to do this experiment for at least 12 hours.
The other thing I want to do is calculate the strength of the EMF. I have found a few equations online, but I'm not sure what to do about the core. I don't want to have an iron one, just the bottle, but how do I put that in? Do I have to do that? There is something about permeability, but I don't know how to calculate that. Any help would be greatly appreciated and please feel free to criticize any flaws in the experiments. I haven't taken physics yet so I am missing some fundamentals.

[rmarz]

science923 - I'm not sure what the effect on fermentation will be in the presence of a strong magnetic field, but you may want to do some research on the difference between EMF (electromotive force) and MMF (magnetomotive force). You mention EMF in your note, but may be confusing the two. Your idea of putting up to 300 amps through a coil around a bottle containing your fermenting medium has some obvious dangers. First, 300 amps of DC current is capable of melting, overheating or violently destroying a length of copper wire. When you research MMF you will see that 300 amps of wire through a single turn of wire will produce the same magnetic field as 1 amp through a coil of 300 turns. Each represents 300 ampere-turns of field strength. I'm still not sure how this applies to your hypothesis or whether an EMF field is more appropriate. Perhaps a little more investigation is appropriate before starting in earnest.

Rick Marz

[science923]

I really did not mean electromotive force or magnetomotive force. I mean electromagnetic field.
I have been concerned about the safety issues of course, but this was suggested to me by a peer and my only other idea was to use an alkaline battery. I tried that and the batteries ran out of power very quickly and started to open up which was worrying. What kind of power source would be the safest? I also think the 300 amps is way too much. Also, it is not possible to turn the wire 300 times. I've tried that and I can at best get 50.

[rmarz]

science923 - One way to start is to pick a copper wire gauge and determine it's safe current carrying capacity in amperes from a copper wire table. If you are able to wind 50 turns of this wire around your container, calculate the length of the wire you will use. Going back to the copper wire table and determine the resistance of that length of wire in ohms. Now you will have to calculate the power needed to drive your coil. Say you want to drive the 50 turns with 5 amperes, yielding 250 ampere-turns. You find that the DC resistance of the wire is 2.4 ohms. The equation E=I*R becomes E=5*2.4 or 12 volts DC. Or said another way, 12 VDC across a 2.4 ohm load will drive 5 amperes through the load. What power source might be readily available to provide that kind of power? If you have access to an automobile battery charger, that might work well. The power-pack you originally mentioned could be used as well, but most of these handy units are powered by batteries that have between 10-15 ampere-hour capacity. In that we are going to draw 5 amperes, they will discharge in 2-3 hours. Clearly the small alkaline cell will not be of much use. Good luck, write back if you need further assistance. Do you have any reference material as to the strength of the field you are trying to develop? That will certainly influence many factors in your design.

Rick Marz

[rmarz]

science923 - Here is a typical copper wire table you can use. There are many others on the web.

Rick Marz

[science923]

I found a 1.5 amp power pack and tested it out and it worked great. Thanks for your help.