How to make a battery charger (Question)

Are there any "rules" when choosing a battery charger? Lets say I have a 5v supply with 500mA current. What should the charger specifications be?

Charging a battery depends

Charging a battery depends on the type of battery, so we can’t help you if you don’t tell us.

Hello Markamas,

NiCad are simple LiPo can be more complicated

I assume…

I would assume that you are trying to charge a large car battery. At that supply level, it is going to take a VERY long time.

I was thinking LiPo or NiMH

I was thinking LiPo or NiMH and no it’s not a large car battery. Just a small battery or battery pack to power an Arduino Mini, 2-3 sensors and a couple of small motors or micro servos.

Ah yes,

Not a car battery… Got it.

Now, is it a Lipo or a NiMH?

Oh and…

5v, 500mA… USB power maybe?

Battery basics

Now, I’m not that familiar with LiPo but for NiMH, charging is very simple: every battery has a specific charge (a specific amount of Ah or mAh (Ampereshour)), this is a value that indicates how much current a battery can devliver for a specific amount of time. It’s as simple as this: a 7 Ah battery is capable of supplying 7A for 1 hour, or 3.5A for 2 hours or 14A for 30 minutes before it runs empty.

The charging depends on this value: if you charge a NiMH at a tenth of it’s rated Ah’s (for instance 700 mA for a 7Ah battery) you’ll never overcharge your battery and it’ll take 10 hours to charge (700 mA10hours= 7000mAh or 7Ah), this is called trickle charging. This is theoretical, because in real life the charging will happen with a specific efficiency and it’ll take about 12-14 hours to completely charge a NiMH battery on trickle current.

If you want the charging to be done more quickly, you can increase the current: a 7Ah battery will be charged in 1 hour if you use 7A of charging current. But beware: the higher the charging current the higher the chance of over-charging (and damaging) your battery. Also, your battery’s life-time will reduce faster if you charge it faster. A possibility is to monitor the cell voltage of your battery during charging. This way you can fast-charge (high current) to 80% or so of the complete charge and after that switch to trickle charging (low current). As mentioned before, you can leave a NiMH battery at a trickle charge indefinitley without damaging it.

Wow this was really the

Wow this was really the answer I was looking for! Thanks!

Reminder

Just to make sure you get this: don’t charge LiPo’s this way, their charging is way more complicated and dangerous and I actually have no idea about the details of that. Want to make your own charger ==> go NiMH

Yup I was thinking NiMH all

Yup I was thinking NiMH all the way!