# Maximum possible Current input to VCC pin

I am planning on using a regulated 4.8V nimh battery with an arduino mini pro v5. what is the maximum mAh battery rating that is allowed to be inputted into the VCC pin? and if I my circuit components are using 50mAh what battery mAh rating is best?

A regulated battery? Do you mean a battery under trickle charge? Do you mean a battery and then
a regulator?

Components consume current (mA), not capacity (mAh) - you are confusing the two. The capacity is
simply current times time.

If you battery had 500Ah it wouldn't matter, its the voltage that affects the circuit, and the current
is determined by the circuit. The capacity affects the time it can run for.

You 4 cell NiMH battery will be about 5.3V fully charged, not 4.8V, that's NiCd's. Under active
charging a 4-cell NiMH might exceed the rated max operating voltage of 5.5V for the chips on
the board by a bit.

Thanks for your much appreciated response and sorry about the confusion I am in. I was planning to buy the 4.8V battery and then buy a Pololu 5V Step-Up/Step-Down Voltage Regulator S7V8F5 to regulate to a constant 5V. Is that fine or am I still wrong?

And so if my components consume 50mA and I use a 200mAh battery does that mean that the circuit will run for four hours?

And so if my components consume 50mA and I use a 200mAh battery does that mean that the circuit will run for four hours?

Only approximately. If it is important to run for four full hours, use a battery with more than 200 mAh capacity.

There is no need for a step-up regulator. The Arduino will run very well on 4 NiMH batteries, as long as the voltage is less than 5.5 V. In fact, it will run at 1.8 V at lower clock speed. The other components may be pickier.

Varta 4.8V, V500HT NiMH Rechargeable Coin Cell Battery, Wire Lead Terminal, 510mAh

Should roughly run it for 10 hours

That is fine. If the battery is to be charged in place, MAKE SURE that the voltage never exceeds 5.5 V.

To make sure it never exceeds 5.5V shall I use a voltage regulator and also a PCB for the LiPo?

What LiPo?

Again, the Arduino does not require a voltage regulator with a 4 cell NiMH battery. If your external circuitry requires 5 V, you might consider a step up - step down regulator, like one of these (but they do waste power): Pololu - Step-Up/Step-Down Voltage Regulators

You should not attempt to charge the battery while it is in the circuit.

Sorry about the confusion, I meant if I was to use a 240mAh 1S 3.7v 25C LiPo Battery with a 5V Step-Up/Step-Down Voltage Regulator would I need a PCB for the LiPo? and also would the LiPo be better than the NiMH?

A LiPo would need a boost converter to get to near 5V, 4 NiMH cells would not need a converter.

Define "better" since there are many criteria for selecting a battery chemistry

Alright, so here are my components:

1. Arduino Pro mini 5V ( Typical supply voltage: +5.0 V, Typical supply current: 10-25 mA)
2. Transmitter Module ( Typical supply voltage: +5.0 V, Typical supply current: 03-10 mA)
3. Myoware muscle sensor ( Typical supply voltage: +5.0 V, Typical supply current: 09-14 mA)

They are going to be integrated into a 3D-printed wristband. Hence the battery needs to be small and light. There is no minimal operational time requirement. However the longer the better.

I intend to power through the VCC pin bypassing the Arduino on-board linear voltage regulator.
I am thinking of using this Lithium Ion Polymer Battery - 3.7v 500mAh with a 5V Step-Up/Step-Down Voltage Regulator. The battery has its own PCB that will cut-out the battery when completely dead at 3V.
So Ill have the LiPo battery connected to an external switching voltage regulator connected to the VCC pin.

How does that sound? am I missing anything? I will possibly also use the SparkFun LiPo Fuel Gauge to monitor the battery voltage as an extra measure of safety.

I think you're on track now. You will unplug the battery to charge it?

Yes, ill design the Wristband so that the battery is easily pulled out to be changed/charged with on e of these http://www.adafruit.com/products/1904.