Hi guys,
just wondering how to run a 6v 3w water pump from 2xAA batteries. I don't think a boost converter is enough as it doesn't provide enough amps?
Thanks in advance.
Your biggest problem is not the voltage, it's the number of batteries that you drain within a week.
Within a few hours?
2000 mAhr * 2 * 1.5V= 6 Whr
6 Whr / 3 W = 2 hr
Use a 6v lead acid battery ( eg motorbike battery)
You can get a boost converter that will boost the 3V from the batteries to 6V, and still supply the 500mA of current needed by the pump. That isn't a problem.
The problem is that you simply can't get that much power out of a pair of AA batteries. There's no such thing as a free lunch. Getting the 3W at six volts means you need to pull 3W out of the batteries. Since the batteries are providing only 3V, that means you need to pull an amp of current out of those AA batteries. That's not going to happen. Due to the internal resistance of the batteries, the battery voltage will drop when you try to get that much current, which means the boost converter needs to draw even more current, which means the battery voltage drops further...
Just to make things even worse, the boost converter isn't going to be 100% efficient. I would assume an efficiency of 80% or so, which means you need to pull 20% more power from the batteries than the pump requires.
Two possible solutions:
The easy one is to switch to using 4xAA batteries to provide the 6V. No boost converter needed, and the battery current is now the same as the pump current. AA batteries can handle half amp, but barely. You will be changing batteries very frequently. You might want to consider using C or D batteries instead.
The other option would be to switch to a 3V lithium rechargeable battery. Lithium batteries can generally supply huge amounts of current when needed. You will need not only the boost converter, but also have some means of recharging the battery.
ok thanks. ill try 4xaa!
You did say AA batteries, but as people have responded, you're using a lot of power for that size battery. You might consider lithium-polymer batteries instead, the kind they use in electric-powered model airplanes. They work much better for high discharge rates.
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