Rare earth magnet and a 9 volt battery

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cheapNdisgusting
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Rare earth magnet and a 9 volt battery

Post by cheapNdisgusting » Fri Oct 10, 2014 3:01 pm

I'm working on a project with LEDs, 555 timers, resistors, and a couple caps. It will be powered by a 9 volt battery. Does anyone know if a rare earth magnet can be used to hold the battery in place? I know it will hold it - but will the magnet affect the battery life? It will require a battery change every 3 months or so and the magnet would make the change very easy.

Thanks for any and all comments on this.
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Re: Rare earth magnet and a 9 volt battery

Post by haklesup » Fri Oct 10, 2014 5:56 pm

I can's say for 100% sure but I expect that it should not have a significant negative impact on life or leakage. The metal case of the battery will direct most field lines into itself and not enter the core of the battery. the terminal end of the battery may not be completely shielded but the bottom should be making no place for most of the field to loop through in the core. Even if they did, I'm not so sure a static magnetic field would cause much of a problem on a chemical system. An alternating field might be a problem though. Batteries are often used adjacent to magnetic components like relays without any problems.

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Re: Rare earth magnet and a 9 volt battery

Post by cheapNdisgusting » Fri Oct 10, 2014 6:17 pm

Thanks for your input hacklesup - I think I will try it.
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Re: Rare earth magnet and a 9 volt battery

Post by Janitor Tzap » Fri Oct 10, 2014 6:42 pm

Here's a PDF on a paper done on the effects of magnetic fields on batteries.
http://www.ul.ie/cpi/sites/default/file ... ystems.pdf

From what I quickly skimmed over.
They found some interaction with the electrons, increasing the current flow.


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Re: Rare earth magnet and a 9 volt battery

Post by cheapNdisgusting » Sat Oct 11, 2014 6:45 am

Tzap - thanks for the reply. I read the PDF and understood about half of it. LOL

I will do some "pondering" on it because I'm not sure what I just read. :???:
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Re: Rare earth magnet and a 9 volt battery

Post by haklesup » Sun Oct 12, 2014 12:26 am

it says it increases current density which I suppose translates into higher discharge and charge currents but not necessarily more capacity and the max current still may be limited by the chemical system and its temperature. Its significance may be in making smaller battery terminals in high energy systems. The link was just an abstract and we did not learn the magnitude of the field to compare to that of your magnet.

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Re: Rare earth magnet and a 9 volt battery

Post by cheapNdisgusting » Sun Oct 12, 2014 8:22 am

Thanks for the replies.

I am going to go out on a limb here and draw a conclusion that has a 50/50 chance of being correct.

Current problem: Whether to use Velcro or a rare earth magnet to secure a 9 volt battery in a hobby project built with parts that are + or - 5% to 10% within the specifications, some new and some recovered from previous projects, and will be forgotten about in a year or so, = probably doesn't make a whole lot of difference how the battery is secured.

No small animals were harmed (or even sighted) while drawing this conclusion.

Seriously - thanks for the comments on something I had no idea about. This is how we learn. :shock:
cNd

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Re: Rare earth magnet and a 9 volt battery

Post by cheapNdisgusting » Thu Oct 16, 2014 9:23 am

OK, I just performed an extremely unscientific experiment. I just took two identical circuits with a 555 [astable mode] driving a 4017 decade counter/divider which in turn flashed [one at a time] 10 superbright LEDs. The flash rate was about 2 per second. Two new 9 volt batteries out of the same package were the power sources. I put two rare earth magnets (approx 3/8") on one battery (both on the same side) and nothing on the other battery.

I turned them both on at the same time - and they both ran continuously until the batteries went dead. Four days/nights later they both died within an hour of each other. So without repeating it over and over - the magnets had little to no effect on the batteries.

The battery without the magnets lasted just slightly longer but it was too close to call.

No furry animals were harmed but a couple were traumatized.
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Re: Rare earth magnet and a 9 volt battery

Post by Janitor Tzap » Sat Oct 18, 2014 9:12 am

Yeah,
Not very scientific. :lol:

But it does make one wonder. :?

There is currently EMP {ElectroMagnetic pulse} testing going on to see what the effects are on electronics and batteries.
So far......
Batteries are not effected when they are not drawing a current.
And even if the battery is operating a circuit during the EMP event.
The most batteries will survive the event.

Here's a link to a EMP Car Test.
http://www.discovery.com/tv-shows/other ... p-bomb.htm


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Re: Rare earth magnet and a 9 volt battery

Post by zotdoc » Tue Oct 28, 2014 1:53 pm

interesting film of an emp attack, anyone know how to protect a car from this scenario?

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Re: Rare earth magnet and a 9 volt battery

Post by cheapNdisgusting » Wed Oct 29, 2014 6:58 am

Duct tape and plastic film?
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Re: Rare earth magnet and a 9 volt battery

Post by haklesup » Wed Oct 29, 2014 5:52 pm

Most EMP not produced by a nuclear bomb would be limited in energy and bandwidth roughly by the size of the apparatus used to produce it. I once saw a video clip from DOD and they showed a van with a cone shaped antenna inside with a spark gap powered by a HV transformer. It just ticked as reporters clicked their cameras (I'm sure it was a dummy). I saw similar apparatus though in a science show in a lab of someone who studied it, he had a much larger cone and his room was shielded. Constructing such a thing with this purpose in mind has questionable legality. I doubt the van sized thing could overstress a circuit but it would definitely mess up wifi or a network for example

Most modern ICs are protected against moderate electrical overstress by their input protection diodes however its hard to say how a high energy spike will be picked up by any assembly without testing. The energy would need to couple to the supplies or IO pins so as to at least double the supply voltage for some milliseconds before I would expect permanent damage. The coupling is a function of the rise time, field voltage in the same way a transformer turn is. I would guess you would need 10s of V/m and Mhz rise times to even enter the band (at this level its not much different than an AM signal on a radio antenna)

To damage a car, whose IC devices undergo the most stringent specifications in the industry (military are tested more but automotive are tested harder) and whose body is a ground plane/ faraday cage would take a very large EMP, it would need to couple to the wire harnesses exposed and not be attenuated by various already existing suppression components as they enter shielded modules. I would guess you would need locally thousands of V/m to annoy a modern car.

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Re: Rare earth magnet and a 9 volt battery

Post by zenobia » Thu Oct 30, 2014 1:58 am

Does it mean that in order for that car and plane (used in video) to explode. It will need high energy of emp?

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Re: Rare earth magnet and a 9 volt battery

Post by MrAl » Thu Oct 30, 2014 9:45 am

Hi,

For comparison, a CRT TV creates a field across the tube oriented from left to right, so that when an electron passes by it changes the direction of the electron so that its path either bends left or right, or up or down (two oriented fields).
You can do the same thing with a magnet by holding it on one side. It will either push or pull the electron so ti will either move away from or closer to the magnet depending on the orientation of the poles of the magnet. The interaction occurs because of the field and because the electron is moving.

For a battery that is not conducting there will be no electron movement so no interaction. When the battery is conducting there will be migration of electrons from one end of the battery to the other but also left and right as they jump about in a somewhat random manner, but with some preference for one direction that is perpendicular to the magnet assuming the magnet is on the side of the battery. This creates a situation similar to but not identical to the TV. The somewhat random motion will now be slightly biased to one side, so basically the current distribution will be concentrated more toward one side.

This would be hard to calculate because the magnet field spreads out naturally and even more due to the steel case, assuming it has a steel case. It might also affect the chemical reaction itself close to the magnet. So the best thing to do is probably a test like the one that was done in this thread using the exact magnet that is intended for the actual application. If the current is low it should not make much difference, but a sensitive test would be nice to see.

A more sensitive test would be to power a resistor with the battery while measuring the current level. The current level could be changed for several tests, but of course the most important is the current level that will be used in the application. For the purpose of investigation though the most important level could be different: it could be higher or lower current. It could be that we can observe a lower current change better than a change with higher current because the meter wont be able to resolve the small change. So a meter with 5 digits is a good idea and probably a light current to start with.

To perform the test measure the current and move the magnet toward the battery. Any change in current distribution or chemical activity is bound to show up as a change in current. We could get unlucky though and have one effect cancel another, but that's not likely, so if we dont see any change then it is very probable that it cant be affecting it very much.
LEDs vs Bulbs, LEDs are winning.

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Re: Rare earth magnet and a 9 volt battery

Post by haklesup » Thu Oct 30, 2014 11:41 am

"Does it mean that in order for that car and plane (used in video) to explode. It will need high energy of emp?"

EMP does not necessarily cause explosions. It induces current in wires and other metal objects that in turn damage microelectronic circuits. I suppose a short circuit in proximity to flammable material could result in a fire but blowing up w car with an EMP ray is probably pure Si Fi. Since EMP energy like any electric field decreases by the cube of the distance from the source, one would have to have a fantastically large EMP source to cause damage to anything at a distance.

The real threat from EMP is not from blowing things up or even frying a circuit. It comes from disruption of telecommunications and internet. As I stated out, probably only an A-Bomb could generate sufficient EMP to do real damage and if that's in play, were in a lot more trouble than a fried circuit.

Back to the battery (so I don't totally hijack the thread). Just as a battery could be damaged by excessive charge current, so too could EMP induce such a large current under ideal hypothetical conditions. From a practical standpoint, that would probably never happen except maybe in an MRI tube

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