Battery Charger Timer

[chrisrosenb]

Over the years, in my shop,

 

[WarnerConstCo.]

Very Nice Chris.

I just take mine off the charger when they are full but, I only have one cordless tool. [embarassed]

 

[Rick Christopherson]

That's a nice timer, Chris. I could use one like that for the remote valve on my compressor. I have a solenoid valve in the basement with a remote switch in the garage, but I have a tendency to forget to turn the switch back off and the compressor constantly cycles all night long due to a bad regulator.

I too worry about forgetting a battery on the charger when I am not using the shop regularly. I try to charge them only when I know I will still be down there when it is finished, but even that's not a guarantee that I won't forget. Just don't leave it in an unplugged charger for too long either.

It's unfortunate that so many woodworkers don't realize that the reason why their batteries aren't lasting very long is because they leave them in the charger. Even the intelligent chargers, like Festool chargers, are not intended to keep the battery on them for extended periods. With an intelligent charger, overnight is fine, but going beyond that will begin to degrade the battery. The worst thing I have heard about is where people put their chargers on cycling timers that keep topping off the battery every day or every week.

 

[Alan m]

i have been playing with this idea myself for a while but cannot find a timer that i like. what i would like is similar to an electronic microwave. in that i could tell it to come on for an infinitly variable  amount of time . this would allow the timer to be used for other more accurate jobs
if you have multiple batteries and chargers such as i have , all with different charge times it is very handy not to have to sit over them .

 

[AlexThePalex]

It sounds like a smart idea to put a timer in the chain. If I needed it I think I would go for one of these:

[attachthumb=1]

[attachthumb=2]

They come as cheap as 3 for 10 euros now.

 

[tDot]

At the risk of sounding a little uneducated, why is it bad to leave the batteries on the charger?  Why is it bad to leave the battery on a charger that is unplugged?

This may explain the sudden demise of my batteries now that I finally have a shop and all my chargers have batteries sitting on them.

 

[Ken Nagrod]

Supposedly it's bad for the battery cells to remain under a constant state of charge instead of charge-use or charge-drain cycling.  Also leaving the charger (transformer) plugged in and powered under no-load can be bad for it.  Different battery chemistries and their electronics respond differently.  I'm of the mindset that I haven't seen enough proof, but I'll follow the recommendations anyway.

 

[PaulMarcel]

I have timers like Alex posted, but those would just do the "top it off each day" trick.  I have a set of plugs installed above a small table and all of them are on the timer.  I have three chargers plugged in so when I need to charge a battery, I twist the timer knob to an hour and typically it does it.  I usually don't keep batteries in the charger even when it is unplugged because I found that at least my DeWalt batteries seem to drain when stored in the unplugged charger.

I know Lithion batteries can have their internal electronics get confused so it thinks the battery is full when it is in fact mostly drained. I think that's the case with my laptop's battery... been that way since the second week I had it.  I think there are ways to reset that logic, but I'm not certain.  Anybody?  Might be useful info for the lithion tool battery owners.

And good idea, Rick, about the compressor.  If I forget to turn mine off and drain it, it will happily sit there for a very long time before leaking enough to kick on the compressor.  So far, it seems to only do that (with a banshee's howl) at 4am.

 

[AlexThePalex]

I have timers like Alex posted, but those would just do the "top it off each day" trick.

The idea is that you set it at a certain interval and then disconnect the battery/charger later yourself when you get back. I don't suppose anybody would drop his batteries in a charger and then walk off for a couple of days or forget they were there.

 

[ajones]

It sounds like a smart idea to put a timer in the chain. If I needed it I think I would go for one of these:

[attachthumb=1]

[attachthumb=2]

They come as cheap as 3 for 10 euros now.

On the down side left unattended they can burn you house/workshop down

 

[WarnerConstCo.]

Very Nice Chris.

I just take mine off the charger when they are full but, I only have one cordless tool. [embarassed]

That is what I do when I am on a job site & when I work in the shop all day. My problem is when I work onsite all day & then work in the shop in the evening.
I am always going off & forgetting the batteries are in the charger.
How do you get by with only one cordless tool?

Rick,
I have also thought of other things that I could use this timer for.

I don't know, just always have.  It is a C-12 though.  I could use another drill but, I am holding out for the C-15

 

[Rick Christopherson]

I have timers like Alex posted, but those would just do the "top it off each day" trick. 

Paul, I am not sure if you said you use these timers to top them off daily, or just said that is what they could potentially do. However, there are many woodworkers that have used timers such as these for that purpose.

The problem with "topping off" the battery every day or even every week, is that the battery is already charged, and this "Topping Off" over-charges them every day or week.

Unlike a lead-acid battery, whose charge percentage is proportional to the battery voltage, NiCad and NiMH batteries have a constant voltage even when only partially charged. Therefore, the charger has to look for a different "sign" in the charge cycle to identify full-charge. Years ago when I was in charge of maintaining some technical sampling equipment, I connected a chart-strip recorder to the batteries to examine their voltage during charge/discharge cycles. There is a "knee" in the voltage graph when the batteries reach full charge (a sudden rise and fall of the voltage). It is this knee that the chargers detect to know the battery is fully charged.

When you top-off a battery that is already charged, this knee-voltage doesn't exist. Other methods for detecting that the battery is at full charge take time to become apparent, so the whole time the charger is looking for these signs, it is charging an already charged battery. The net result is that every time you top off the charge on a fully charged battery, you drive it farther into an over-charged state. It also counts as a charge-cycle, and these battery types have a limit to the number of charge-cycles they can sustain.

LiIon batteries are different, in that they don't have a limited number of charge-cycles, but instead, their life is more time dependent on how much time they spend with a charge on them. Keeping your laptop plugged in all the time shortens its battery life. When your laptop is not in use, unplug it. Plug it in only when it is running.

 

[mouppe]

My Apple laptop- which is my main computer and which I use daily- is almost three years old now, and because I have been ridiculously anal about fully charging and exhausting the battery completely since day one, I still get almost four hours use from a charged battery.

If you take care of rechargeable batteries, they can really last a long time.

 

[PaulMarcel]

I have timers like Alex posted, but those would just do the "top it off each day" trick. 

Paul, I am not sure if you said you use these timers to top them off daily, or just said that is what they could potentially do. However, there are many woodworkers that have used timers such as these for that purpose.

The problem with "topping off" the battery every day or even every week, is that the battery is already charged, and this "Topping Off" over-charges them every day or week.

Unlike a lead-acid battery, whose charge percentage is proportional to the battery voltage, NiCad and NiMH batteries have a constant voltage even when only partially charged. Therefore, the charger has to look for a different "sign" in the charge cycle to identify full-charge. Years ago when I was in charge of maintaining some technical sampling equipment, I connected a chart-strip recorder to the batteries to examine their voltage during charge/discharge cycles. There is a "knee" in the voltage graph when the batteries reach full charge (a sudden rise and fall of the voltage). It is this knee that the chargers detect to know the battery is fully charged.

When you top-off a battery that is already charged, this knee-voltage doesn't exist. Other methods for detecting that the battery is at full charge take time to become apparent, so the whole time the charger is looking for these signs, it is charging an already charged battery. The net result is that every time you top off the charge on a fully charged battery, you drive it farther into an over-charged state. It also counts as a charge-cycle, and these battery types have a limit to the number of charge-cycles they can sustain.

LiIon batteries are different, in that they don't have a limited number of charge-cycles, but instead, their life is more time dependent on how much time they spend with a charge on them. Keeping your laptop plugged in all the time shortens its battery life. When your laptop is not in use, unplug it. Plug it in only when it is running.

Wow, thanks for the good detail.  I didn't know how they knew when they were full for the Nicads.  My quote was that those daily timers are only useful for topping off, which I know isn't effective.  That's why I have a bathroom fan timer on mine.  A quick twist sets it to 60 minutes of charge.  I only have to remember to take the batteries out since they do seem to drain when sitting in the charger cradle.  I need another bathroom timer for the compressor; your previous comment gave me that idea and I know I have a spare around here somewhere.

 

[Kristian]

Sorry for being slightly off-topic but I'm also using an interval-timer on my wireless router at home. I shuts the router off at 1 AM and turns it back on at 4 PM just before I come home. It saves a bit on the electrical bill and the router is totally crack-proof in the period were it's shut off. 

- Kristian

 

[Rick Christopherson]

Chris,
Doing what you describe could be done. However, how it would be done would depend on further information about the timer. If the timer uses a contact-closure for its outputs, then it is a piece of cake. If the timer outputs a 120 volt signal, then it would be slightly more complicated. Tell me more about the timer.

 

[festoolsnob]

Sorry to be somewhat sidetracked here. Can we return to why it is bad to leave the batteries on charger.

I know Li Ion batteries prefer not to be 100% charged all the time, but what about Festool NiCd batteries on the LC45 charger.

I thought the Festool charger switches to a maintain level once the pack is charged. So it will basically switch off, but it monitors, and then now and again pump in a few milliamps, to top it off, and so on.

Never mind your Ryobi or Dewalt batteries that got fried, one would expect their chargers to be less than perfect, I trust the Festool charger is top of the line and will not kill the battery, am I correct?
I am under the impression that leaving my Festool NiCd batteries on the Festool charger while not in use is perfectly fine.

 

[kfitzsimons]

I have a question about rechargeable batteries and charging while we're on the subject. I purchased a Fein drill several years ago and it came with 4  9.6volt Nicd batteries. I've only used two and have never charged the two extras.  When the two I'm using start to go bad, will the other two I've saved charge and work as new? I would also think the same question would apply to Festool.

 

[Rick Christopherson]

Festoolsnob,
Even though the Festool chargers have a maintenance mode, it is not intended for long term storage. Maintenance mode is intended to protect the battery during the short term after a full charge. The self-discharge rate on the batteries is not very high. Because I have so many interchangeable batteries, it is not uncommon for me to have a battery sit for 6 months without use. Yet when I do go to use it, there is plenty battery power left in it. At a minimum, there is more than enough battery left after 6 months of sitting, to operate the drill while I put a fresh charge on another battery.

The bottom line is, if you are using your drill frequently, the battery will still be fresh after sitting on the shelf. If you are not using your drill frequently, then the amount of time sitting on the charger will be excessive. There is nothing gained, and much to lose, by leaving your batteries on any type of charger.

 

[Rick Christopherson]

When the two I'm using start to go bad, will the other two I've saved charge and work as new? I would also think the same question would apply to Festool.

I am not sure about long term storage, and have read that they can be stored in either a charged or discharged state. However, I would be concerned about year-long storage completely draining each cell to the point of deactivating the chemical contents. (I read one recommendation that supported this concept.)

For this reason, I would store them charged in a cool (not cold) dry location, and recharge them only when they have fully self-discharged. For a good battery, this is probably about once per year. Until you know how long they will last before complete self-discharge, simply put them in the tool and confirm that they still have some power left, beginning at probably 8 months, and once per month after that. If the tool runs at all, leave them in storage for another month. Once you know how long they take to self-discharge, then use that as your long-term baseline.

By the way, the batteries should not be stored for long term like this while connected to a tool, as this may discharge the battery prematurely. This is the same reason why they should be stored in a dry location, as humid air can discharge them a little faster.