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Discharging a battery

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Froskoy

New Member
Hi,

I want to discharge a 24V battery at a current of 800mA using some resistors.

If I was using one resistor, I make the value to be 30Ω using Ohm's Law.

The thing is, the power would be around 20W and I only have 2W resistors, at best.

What can I do to make this work?

Thanks very much,

Froskoy.
 

qdn

New Member
You could put 10 of 300Ω resistors in parallel to make your 30Ω, each resistor would dissipate 1.92W.
 

audioguru

Well-Known Member
Most Helpful Member
Do you know what you are doing?
A few types of batteries are destroyed (lead-acid)or catch on fire (Lithium) if they are dischargerd too low.
 

Froskoy

New Member
@audioguru: Yes, thanks for the concerns. It's a NiMH battery. It is OK to discharge it until the voltage for each cell drops to around 1V per cell which equates to 20V for the whole battery.
 

Sceadwian

Banned
audioguru, better watch what you say =)
Lithium's do NOT catch fire if they're discharged too low, they simply go into a coma and are never useable again. They catch on fire if they're overcharged well past being full (that's where the real fireworks come from) And if a dead cell is forcefully charged by a stupid charger they'll also catch fire, though not as spectacularly as overcharging a full cell.
 
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audioguru

Well-Known Member
Most Helpful Member
Of course an idiot will try to charge a dead lithium battery and cause it to catch on fire.
 

RCinFLA

Well-Known Member
If the Li-Ion cell have dwelled at 1.5V/cell and lower for a few days, a recharge should be avoided. Copper shunts may have formed inside the cells, leading a partial or total electrical short. The cell becomes unstable. Charging such a battery would cause excessive heat and becomes a safety issue.

If a Li-Ion battery is inadvertently overcharged it become unstables if charged to higher voltages. When charging above 4.30V, the cell causes plating of metallic lithium on the anode; the cathode material becomes an oxidizing agent, loses stability and releases oxygen. Overcharging causes the cell to heat up. If left unattended, the cell could vent with flame.
 
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Sceadwian

Banned
1.5? The lower limit for a lithium cell is 2.7 volts per cell, in a series pack it's 3 volts or the pack can develop an inverted cell.
 
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