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what if i connect a battery to the electromagnet?

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dl09

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lithium ion batteries have a maximum discharge rate. this is a thought experiment. if i connect a 18650 lithium ion battery with a maximum discharge rate of 2.8 amps to an electromagnet, 1 wire is connected to the positive terminal and the other wire is connected to the negative terminal, without a resistor, would the
18650 lithium ion battery discharge at the maximum discharge rate?
 

Depending on the wire, it would either burn out -or- the battery might explode. You were warned!

The rated maximum discharge is the most current you can safely take from it over a sustained period, not the maximum amount it is capable of producing. I will actually produce significantly more current but overheat in doing so.

Brian.
 

No, it will discharge at the current set by the internal battery impedance and coil resistance which might exceed the permitted maximum discharge current. Safety datasheets say: Don't short a lithium ion battery!

You might adjust wire gauge and number of turns to get a safe coil resistance.
 

what if the advertisements say maximum continuous discharge rate is 10 amp?
 

only rely on manufacturer's specification
NOT on advertisements
 

You forgot to tell us the resistance of the electromagnet or the current it draws at the battery fully charged voltage of 4.2V.
Maybe the resistance of your electromagnet is 0.1 ohms and it will draw 4.2V/0.1 ohms= 42A!
Then what do you think will happen when the battery is VERY overloaded?

Maybe your 18650 battery has a built-in protection circuit that disconnects it automatically when it is overloaded?
 

Hi,

Li-ion need a safety circuit (over-current protection) to prevent excessive current output, some are in-built, others not. "maximum continuous discharge rate is 10 amp" means: Do not exceed this value, and only for brief periods, despite the wording. "maximum discharge rate of 2.8 amps" means maximum you must ensure is not exceeded, presumably continuously until the battery runs out of steam. Ambiguous continuous 2.8A then 10A - it can't be both. The cell datasheet or specifications wil say the internal impedance, I assume about 50 milliohms more or less, Ohm's Law will be useful to use to do a more rigourous thought experiment about what to expect before doing a practical experiment.

You could get a disposable 9V alkaline battery (only 250mAh or something like that from what I remember about the discharge curve and capacity), a 1A fast fuse, a 1 Ohm, 10 Watt resistor and some 2.5mm well-insulated wire, and a DC 250V >10A/100W on/off switch between the battery and the fuse and use the ammeter setting on your DMM to see "uncontrolled" current draw from a battery in a safer way before trying with the Li-ion.
 

Measure the resistance of your electromagnet if it is 0.5 ohm say ... at 3.0 volts this is 6A, your 18650 cell will not provide this for very long at all ...
 

Measure the resistance of your electromagnet if it is 0.5 ohm say ... at 3.0 volts this is 6A, your 18650 cell will not provide this for very long at all ...
Why do you say 3V when an 18650 Lithium-Cobalt Ion battery cell is dead when its voltage is only 3V? it is 4.2V when fully charged.
 

Depends on the Lithium chemistry, but most of the energy is delivered at 3V, a quality industrial Li-Fe-PO4 ( prismatic ) delivers from 3.3 to 2.9V

the polymer ones have higher voltages but are not as good energy wise, 3v is good enough for the above calc, no need to be pedantic ...

also there is no reference to Li-Co from the OP - only Li-Ion
 

Looking in Google for "18650 Li-Ion battery" shows many pages of ordinary inexpensive 18650 3V to 4.2V ones.
Looking for "Li-FePO4 battery" shows 3.2V cell batteries of all shapes, sizes and voltages and the few 18650 ones are very expensive.
A 18650 Li-Ion battery rated at only 2.8A maximum discharge rate is probably very cheap or it has a low current protection circuit inside it. Maybe it is rated ay a capacity of 2.8Ah, not a maximum discharge current of 2.8A.

D109, please post the sales sheet or datasheet of the battery cell.
 

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