want to find or design a battery charger / battery saver

[Electronic Dork]

As being my first post, thanks in advance that this forum is here!

My issue: it appears that batteries (laptops, integrated NiCd, etc.) are damaged if they are left charging continuously. Many rechargeable appliances keep the trickle charge on indefinitely. (how many dead DustBusters are out there...?)

I know there are some chargers available that shut off when the battery is fully charged.

What I want is one that will turn back on when the voltage drops to a certain level; that way I can leave my battery-powered appliance on the charger so it is ready to use once a month, but is not sucking electricity and slowly being killed at the same time.

Ideally there would be the option to fully discharge once the low-voltage threshold is reached, which I think would further extend the battery life of occasionally-used items. (Of course, for laptops you would not want it to discharge on you.)

I'm not a seasoned electronicker, so details will be lost on me. However, if you know of any commercially available, I'd like to hear about it. And if you have ideas on how to build one, I'd love to hear them.

thanks!

 

[MikeMl]

Devices with lead-acid batteries can be left on float charge forever, if the float voltage is correct, and corrected for ambient temperature. Read this about charging lead-acid (SLA, AGM) type batteries.

Devices with NiCd batteries (like your dustbuster) can be trickle charged with a very low level constant-current. The problem with the commercial devices is that they overdo it, and hit them too hard. I get much longer life out of NiCad/NiMH powered rechargable devices by plugging them into a standard 24hr plug in timer, the kind that can be set to 1 hour on every 24 hours. Say I run down my rechargable power drill. I plug the charger into the timer and rotate the dial just past the normal 1 hour on point, and turn the timer on manually. This means that the charger is powered normally for ~23 hours, at which point the timer clicks off. It stays off for 23 hours, and then comes on for 1 hour and this cycle keeps repeating; 1 on/23 Off for days to weeks.

The initial 23 hour period is long enough to recharge the first cycle. The subsequent 1 hour per day mini cycles are enough to put back the charge lost to self-discharge, but lets the battery just sit for 23 hours a day... The tool is ready to go the next time I need it. I have done this with the batteries on Walkie Talkies and got much longer life out of them compared to letting them cook in the charging stand.

 

[4pyros]

The cost of all those "smart chargers" may outweigh the cost of replacment batterys. Look up smart chargers. Andy

 

[Electronic Dork]

thanks, Mike
good idea for a simple battery saver, I'm going to give it a go

 

[Electronic Dork]

Andy-
that's true for replaceable batteries, but for integrated you have to toss the whole item, which can add up and add to the landfill

and for laptop batteries, they are bloody expensive, so $50 or $100 so save a few batteries is worth it in the long run

plus, I just think its a good idea

pete

 

[blueroomelectronics]

Laptop batteries already have smart power management, not much you can do to improve on it. Dustbusters not so much.

 

[4pyros]

that's true for replaceable batteries, but for integrated you have to toss the whole item, which can add up and add to the landfill

Yes I tend to stay away from the stuff with built in batterys. Shavers drive me nuts. Seems like the manufacters make them to kill the rechargable battery in short order so you have to get a new one every year of so. Sometimes I will take the battery out and run off the charge cord because the blades and motor are still fine. Andy

 

[Electronic Dork]

So far it appears that there is no existing "really smart charger" unit like I am looking for. Anyone have ideas for how to make one?

 

[blueroomelectronics]

MAHA makes a great AA-AAA NiMH / NiCAD charger the MH-C9000.

 

[Electronic Dork]

MAHA makes a great AA-AAA NiMH / NiCAD charger the MH-C9000.

apparently you did not read the original post; it has nothing to do with AA or AAA batteries or unfounded opinions. I'm hoping to find someone (like Mike, above) with useful solutions.

I already dug up a digital timer I had so I can run one item for as little as 1 min per day, which based on his experience should help the lifetime of that unit. But there is more somewhere out there...

 

[4pyros]

Thare are lots of charge control chips out thare or you can use a pic controller. The pic mite be the best whay to go so you can tailer the charging for differant batterys. Can you program a PIC? did you look up smart charge controlers? Andy

 

[crutschow]

Yes I tend to stay away from the stuff with built in batterys. Shavers drive me nuts. Seems like the manufacters make them to kill the rechargable battery in short order so you have to get a new one every year of so. Sometimes I will take the battery out and run off the charge cord because the blades and motor are still fine.

I also am irate over devices with built-in batteries that can't be easily replaced (iPhone anyone?). It should be illegal unless they warrant it for a least 10 years.

I had a Norelco beard trimmer that was perfectly fine until the battery went dead. Fortunately, by removing a single screw I was able to open it, and found a single AA NiCd battery with welded leads inside. I replaced it with a Radio Shack single AA battery holder (there was just enough room) and a new NiMH AA. The new battery has a higher mAh rating so it takes about a day to fully recharge rather then the 15 hours the original required. But if I hadn't been able to replace the battery, the trimmer would have been junk, and I would have had to buy a new one.

 

[blueroomelectronics]

I have a top of the line Braun cordless toothbrush, it also has a none user replaceable battery that I'm looking forward to replacing.

 

[4pyros]

Yes we need wireless power now!

 

[Electronic Dork]

Thanks Andy, now we're getting somewhere (I hope).
I'm a blank slate right now. I nothing about board design or PIC programming, but if pointed in the right direction I could certainly learn about them. Once I have a general idea, perhaps I can find someone to actually design something;.

Also, searches on "smart chargers" was a dead end, but a search on "smart charge controllers" looks like a promising path to follow

 

[MrAl]

Hi,

I've used a PIC based design for way over five years now. It's basically a charger that has two modes: full charge or daily charge.
For a full charge i press a button and it starts. For a daily charge i set a pot to the minutes per day and just let it sit as it comes on once per day and charges for the number of minutes it's set for.
I added a few features but that's the basic operation. The circuit was built into the charger that came with the drill originally, replacing the crap circuit it had in there.
The use of this device allowed my replacement batteries to last for a full five years instead of just one if it had been plugged in the whole year rather than once per day.
I've also told countless people over the years to use a plug in timer and i think that many have done that with good results. The timer only has to come on for 1/2 to 1 hour per day to restore the charge lost by self discharge.

The hardware for the PIC is quite simple too, just a transistor or two to supply the current to the batteries and a few resistors for measurements. A pot sets the number of minutes per day but this can be done with a push button switch also, just count the pushes. The pass transistor doesnt even have to be a very high current device because most charge currents are around 100ma to 200ma which is nothing for a transistor these days.
The software is quite simple too, just a long delay (about 24 hours) after which it turns on for the number of minutes desired. For a full charge it turns on for 24 hours and then shuts off and starts the daily timing automatically.

 

[4pyros]

"smart charge controllers" looks like a promising path to follow

Glad to here it, happy reading. Andy

 

[Electronic Dork]

thanks MrAl
just confirming Mike's observation about using a timer has been more than worth the post to me.

you obviously know your way around a circuit board. Any thoughts on a circuit that would shut off at full charge, then come back on after a drop to a certain threshold (for a laptop)? Or taking it a step further and a different one that discharges completely upon dropping to the threshold, then fully charging (occasionally used item like a wine bottle opener)?

Why, you may say? Its my understanding that fully discharging NiCD's makes them last even longer, and reduces the memory effect. Or so I am told.

Any enlightenment on any or all of the above would be great.

I guess I need to learn some electronics for hire someone.

 

[KeepItSimpleStupid]

That sounds like a neat project.

 

[MrAl]

thanks MrAl
just confirming Mike's observation about using a timer has been more than worth the post to me.

you obviously know your way around a circuit board. Any thoughts on a circuit that would shut off at full charge, then come back on after a drop to a certain threshold (for a laptop)? Or taking it a step further and a different one that discharges completely upon dropping to the threshold, then fully charging (occasionally used item like a wine bottle opener)?

Why, you may say? Its my understanding that fully discharging NiCD's makes them last even longer, and reduces the memory effect. Or so I am told.

Any enlightenment on any or all of the above would be great.

I guess I need to learn some electronics for hire someone.

Hi again,


Well, i havent had to discharge mine ever so im not sure how much this really matters. Supposedly it helps so you may want to try it.

It's not really recommended to use the battery voltage itself as an indicator of the state of charge except for indicating extremely charged or extremely discharged. Either of those states we seldom if ever really care about, so it's a good idea just to forget about the voltage except about the way it *changes* when we are charging the cells. Even then though it becomes a bit of a problem when we start having to charge a bunch of cells in series rather than one individual cell. There are methods such as "Minus Delta V" which charge a cell until the voltage starts to dip and then it turn off, but that technique is designed for a single cell not really a pack of cells in series which is common in portable tools. This means we cant even rely on that to work for us.

The only thing that seems to be left is to determine what does work for packs of cells in series and try to use that. We know that voltage measurement does not work except in the extreme charge states, so we can not use that, but we know that if we supply a current through the cells they eventually charge after a certain time period and some finite charge period is considered long enough to charge but not do too much damage, and we also know that the cells all have a self discharge that has to be replenished on a regular basis, so we use this information to design a charger.

Based on the above the scheme then is to do a full timed charge after we use the pack, and do a partial short timed charge on a daily basis. This way we dont do too much damage to the pack with regular use plus we keep the self discharge replenished so the pack is ready for use after a longish period of non use.


As i posted previously, we use a timer that clocks out 24 hours to charge fully (pass transistor turned on the whole time) and another to keep the charger turned on for only 30 to 60 minutes each day. We use a push switch to initiate the 'full' charge cycle, and make the daily timer automatic.
If you want to discharge the cells periodically too, then all we need is another switch to initiate a 'discharge' cycle where we can choose to discharge after some time like a month or two or whatever you think would be appropriate. We need a more heavy duty transistor for this and some load resistance, but even 20 amp MOSFETs are pretty cheap these days so that wont be too expensive either.
If you like, using a PIC (or similar) chip we could program in delays such as two months or more to automatically initiate a discharge cycle, but im not sure how this would work out in the real world because what if a cycle starts just before we go to use the drill and we pick it up and it's almost discharged? Not too nice I think i rather initiate it manually when i think it's appropriate.

Anyway, the project really calls for a microcontroller, but it may be possible to do it with a few timer chips. I've never had to create a delay as long as 24 hours with a timer chip though, but it may be possible with a few of them or maybe with an added divider chip. That would give us the 24 hour period we need for both a full charge and for a daily charge. We only need another timer then to time the 30 to 60 minute daily charge period, and perhaps another timer to time the discharge period.

What sounds best for you, or anyone else reading this? Other ideas for the timing?