I would like to discharge a 12V battery but I don't have any 12V appliance. Can I use a 220V hair dryer to discharge it? Don't know if they are a completely resistive load

 

Go to an auto parts store and get a 12V taillight bulb.

 

I would like to discharge a 12V battery but I don't have any 12V appliance. Can I use a 220V hair dryer to discharge it? Don't know if they are a completely resistive load

Should work, depends largely on the internals of the HD.
Most have a heating element and a small Universal motor.

 

What is the battery capacity, and how fast do you want to discharge it (and why)?

 

Assuming a 2kW hair-dryer, it will take a while. The element would be about 26Ω, which would take 5.5W at 12V. (Same as a tail-light lamp)

 

If the motor is in circuit, it's just a few ohms for AC variety.

 

What is the battery capacity, and how fast do you want to discharge it (and why)?

The battery is 100Ah and I want to discharge it as a final test to know if it's OK. If it takes the corresponding hours to discharge assuming is full, I would be OK.

As Ian0 stated, a hair dryer would take too much time.. my hair dryer is 1200W so it has a resistance of aprox 40 ohms. Correct me if I'm wrong but that means

hours = 100 * 40 / 12 = 333 hours

I'll look for a power resistance then, thanks for the responses

 

Is it a lead-acid battery? Is it new? If so, avoid the temptation to discharge it and believe the manufacturer. A full discharge really doesn't do a lead-acid battery any good.

 

As Ian0 stated, a hair dryer would take too much time.. my hair dryer is 1200W

So what about the motor?

 

Many hair dryers use a low-voltage motor, and connect it in series with the heating element.

 

You must monitor the voltage and not discharge it to below about 11.5V. At that point it will have about 20% charge left. I think 20% is a good stopping point.

https://cleversolarpower.com/lead-acid-battery-voltage-chart-12v/
Do NOT EVER discharge the battery to over empty. You will damage it.
So, however you do this test, you must monitor it and then fully recharge the battery after the test is done.

 

Is it a lead-acid battery? Is it new?

Is a LifePo4 lithium batthery.. for what I know, it that be safely discharged to 100%. It has a very strange behaviour.. I asked about on another thread. It's quite new.. it only has few cycles of use

 

The same thing applies.

https://footprinthero.com/lifepo4-battery-voltage-charts
There is a pretty good reason the last entries are in red.
So, why not stick to 20% as an end point? That will let you work out the full capacity and not damage the battery.

 

Many hair dryers use a low-voltage motor, and connect it in series with the heating element.

Mine reads 12.5Ω across the 120v input on high !

 

https://footprinthero.com/lifepo4-battery-voltage-charts

Thanks for the link didn't know that I had to wait some minutes to measure its open circuit voltage

So, why not stick to 20% as an end point?

The thing is that the batteries (I have two) show more than the 100% voltage according to the manufacturer (13.46V) after charging them with a charger.. so I certainly don't know if I can trust the voltages. I have 13.89V on one, and 13.56V on the other :/
To be sure, I can discharge it to 100% and immediately charge it again to a safer state

 

Many hair dryers use a low-voltage motor, and connect it in series with the heating element.

The last time I checked, the motor was in parallel with a tapping off the heating element, with the element acting as a potential divider.