Rechargeable batteries

Audioguru

Joined Dec 20, 2007
11,249
NiCd/NiMH - I can trickle charged at c/10
No.
Energizer, panasonic and other manufacturers say that a Ni-MH cell should be trickle charged at only C/40 so that they last a long time.

I have 4 AAA NiMH 1100mAh, so I should find a charger with ~110A?
No.
110A will melt the wires and the battery will disappear in a loud BANG!

1100 x 10% = 12 hours
Only if the battery is completely dead. C/10 will over-charge a fully charged Ni-MH battery (but is OK for an old Ni-Cad battery).
You should have a circuit that shuts off when it senses that the battery is fully charged.

For an 1100mah 2/3 A it says I can do a 500mA max peak charge rate? Is this safe if I know the batteries are fully discharged (or < 10%) and only charge for 1 hour?
Sooner or later you will try to over-charge a battery that is already charged and your extremely simple high current circuit will blow it up.

You should use a battery charger IC that has been designed by experts. It senses that a battery has some charge then reduces the charging time to avoid a problem. It properly shuts off when the battery is fully charged.
 

Thread Starter

agroom

Joined Oct 15, 2010
60
No.
No. 110A will melt the wires and the battery will disappear in a loud BANG!
Sorry, meant 110mA.

Only if the battery is completely dead. C/10 will over-charge a fully charged Ni-MH battery (but is OK for an old Ni-Cad battery). You should have a circuit that shuts off when it senses that the battery is fully charged.

Sooner or later you will try to over-charge a battery that is already charged and your extremely simple high current circuit will blow it up.

You should use a battery charger IC that has been designed by experts. It senses that a battery has some charge then reduces the charging time to avoid a problem. It properly shuts off when the battery is fully charged.
I won't argue with this, in fact, it's my major concern. I'm absolutely wanting to use a pre-designed charger. I guess it all comes down to not knowing what's available. I'm not capable, nor ever wanted to, make my own charger IC, and in hindsight, had I known what questions to ask, it might have forgone much debate. For my application, are there ones already made or do they have to be custom designed? Would you (anyone) be willing to suggest a charger that already works for this application?

This is the battery I have and need to make a 4-battery 4.8v battery pack. Is something like this all I would need?

My apologies for the late reply, personal things came up and this got put on the back of the list.
 

Audioguru

Joined Dec 20, 2007
11,249
You have a Ni-MH battery. Instead of re-inventing one why don't you use a Ni-MH battery charger IC that is made by the experts at a semiconductor manufacturer like Maxim-IC.

The cheap "charger" you showed will DESTROY most Ni-MH batteries because it doesn't do all the things I talked about that a REAL battery charger does.
 
Last edited:

bountyhunter

Joined Sep 7, 2009
2,512
Working 35 years as an engineer taught me to never overlook the obvious and always seek the easiest path:

Why don't you just use NI-CD batteries? They are very tolerant of overcharge, even sustained overcharge of rates as high as C/10. You can use a basic dumb charger circuit. The loss in capacity compared to MI-MH is not terrible, the newer NI-CDs have a lot more capacity than the ones made five years back.

I bought a bunch of cheap Chines NI-Cds from harbor freight tools and stuff them in many things, from a super high current LED flashlight to the old cordless phone in my lab. I have some of them for many years.
 

Thread Starter

agroom

Joined Oct 15, 2010
60
As I said, I'm really not interested in making a charger, I'd really just like to purchase one. Ideally I want a rapid/quick charger, but would do with a slow charge if that was my only option.

It would seem to me like there should be thousands of these on the market...no?
 

Audioguru

Joined Dec 20, 2007
11,249
I bought some Energizer Ni-MH AA cells that came with a charger that is simply a regulated current and a timer that shuts off in 6 hours. It is stupid because it extremely over-charges a battery cell that already has some charge remaining. If a fullly charged cell is accidently loaded then it gets very hot after over-charging for 6 hours.
 

Thread Starter

agroom

Joined Oct 15, 2010
60
I picked up one of these and works great. Still way out of my price range for effectively using it, but it works for now.

My question is, I have a 4 AAA 1000mAh NiMH battery pack I'm charging with it. Can I charge multiple battery packs in parallel as long as I don't exceed the mAh rating (which I think is around 3000). Also, would it properly charge packs that are discharged at different levels? i.e. 2 battery pakcs, one mostly dead the second half dead.
 

Audioguru

Joined Dec 20, 2007
11,249
I'm working on a project that I want to permanently install 4 NiMH AAA rechargeable batteries (in series). The plan is to hook the batteries up to a charging plug and charge it with an external DC wall plug. I don't really know what the technical names are called, but here's a picture of what I have in mind.
You cannot charge the battery with a DC Wall plug. You also need a charger circuit.

1. I basically don't know anything about recharging batteries, so I'm afraid of "over charging" them. I've read the battery charger wiki page and it specifically said intelligent chargers work well for NiHM batteries:

For Ni-Cd and NiMH batteries, the voltage across the battery increases slowly during the charging process, until the battery is fully charged. After that, the voltage decreases, which indicates to an intelligent charger that the battery is fully charged. Such chargers are often labeled as a ΔV, "delta-V," or sometimes "delta peak", charger, indicating that they monitor the voltage change.
Yes, an intelligent charger will work well.

These are the batteries I have.
I would NEVER buy those expensive but cheap Chinese battery cells.

2. Where do I find an intelligent charger & plug like the one in the picture? 4 AAA batteries would require a 5v charger because they're in series right? Or do I use 1.2V?
Duracell and Energizer battery companies sell the battery cells with an inexpensive charger.
One Ni-MH cell is fully charged when it measures 1.4V to 1.5V. Then four in series need a charger with an output that is 5.6V to 6.0V. The charger limits the current. When the charger detects that the battery is fully charged then it shuts off.

If this is successful, there's other projects I'd like do the same for only with different sized batteries like 3v CR2/123 and 3.7v Trustfire 18650/14500s. Which I assume would use the same techniques, just scaled to the voltages of these and not the AAA I'm using for this project.
They are Lithium batteries and their charger is completely different to avoid a nasty fire. Lithium batteries also need a circuit that disconnects the load when the voltage runs down a little.
 

Audioguru

Joined Dec 20, 2007
11,249
I picked up one of these and works great. Still way out of my price range for effectively using it, but it works for now.

My question is, I have a 4 AAA 1000mAh NiMH battery pack I'm charging with it. Can I charge multiple battery packs in parallel as long as I don't exceed the mAh rating (which I think is around 3000). Also, would it properly charge packs that are discharged at different levels? i.e. 2 battery pakcs, one mostly dead the second half dead.
It charges high current cells in a PACK used in model cars.
It says not to use it to charge your cheap Chinese cells. It also says not to use it to charge cells that are discharged too low.

You must NEVER charge batteries in parallel.
 

Thread Starter

agroom

Joined Oct 15, 2010
60
It says not to use it to charge your cheap Chinese cells. It also says not to use it to charge cells that are discharged too low.
What says that? There wasn't much for documentation with it, just a sheet that repeated the product page in broken English.

You must NEVER charge batteries in parallel.
Noted, thanks. But um, how do you charge the battery packs that are made in parallel then? I hope the answer isn't "you don't!" because you can't tell me there not a single battery pack in the world that doesn't utilize parallel power sources for extended use :)
 

Thread Starter

agroom

Joined Oct 15, 2010
60
I would NEVER buy those expensive but cheap Chinese battery cells.
Well unfortunately I'm trying to learn all this on a very very limited budget. They got good reviews, but I actually ended up finding a deal on some Tenergy premium 1000mAh, so I got them instead. They came out like $.08 more each.


They are Lithium batteries and their charger is completely different to avoid a nasty fire. Lithium batteries also need a circuit that disconnects the load when the voltage runs down a little.
I've done a lot more reading on this since my original post and think I've got this down. Before I ever try anything though I'll hopefully post up here to double check. But at the most I'll be using 3-4 batteries which 1. all need to be balanced and so I need a balancing circuit, and 2. like you said, a charger designed for Li-Ions.
 

Audioguru

Joined Dec 20, 2007
11,249
I have one Tenurgy Li-Po battery cell. My friend bought 10 of them from China and they costed almost nothing (including shipping to Canada) so he gave one to me. Their performance is very poor.
Thunder Power Li-Po battery cells (assembled in USA) are much better.
 

Thread Starter

agroom

Joined Oct 15, 2010
60
Most of what i do is testing & for fun, nothing that needs or requires any serious performance. I read the reviews on DX and usually only buy those that people have tested and rate high. I've had a few bad cases with them, but overall I've actually been very satisfied.
 
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