daredevil

Cygolite Dual Extra. The battery was given a complete charge 5 days ago and used for 1/2 hour. It has now sat since then. Do I bother giving it any charge at all at this time for my 1/2 commute in the morning? No charge, partial charge, full charge? My guess is it still has plenty of charge left, does it really matter as far as the maintanence of the battery is concerned. Thanks

cyccommute 

Probably not. However, I always start with a full charge on my batteries to insure that there isn't any darkness on the way home. That's bad.

For more info then you'll ever need...but it's good stuff anyway...go to https://www.buchmann.ca/. There's lots and lots of good information to keep you from killing your battery prematurely (you're gonna kill it anyway but why hurry the process )

banerjek

No charge. NiMH batteries last a long time. I charge mine depending on how much juice they have and how much I need. This means that when there is just a bit of darkness, I might charge them once a week, while now I must charge after every ride. The batteries are still good years later.

Allen

It's best to fully discharge and then recharge a NiMh battery, it helps to prevent "memory effect". That said, don't store a battery partially charged, it's better to fully charge a battery that is not going to see regular use.

Zero_Enigma

This is my experience with NIMH's. I charge my cells full all the time then store them when I need them. My cells hold for quite some time. If you use very little of the battery each time and your lights say the battery will last you like 5 hours and you only travel say 30mins round trip a day with the light then I'd give it a charge once a week or two. I always give my cells a top up charge when in storage every 2-3 weeks but my cells seem to hold well even at 4 weeks without any recharging. Still the batteries will self discharge thus why I do a every two week top up.

By doing a top up every two weeks you keep the battery as full as possible and if it's not full it takes less time to charge up then a drained battery. It is good to fully discharge your battery (not all the way till the battery is dead with no voltage but say if the light states 5 hours then leave the light on for 5 hours then charge it up afterwards) then charge it back up every 50 or so charges just to condition the battery.

How are you liking the light? I'm considering going with a Cygolite Dual Cross 300 but no fundage. I like the 5-6 hour full power run time and about 9hr on low and that's about a 20W equivlence (tho I'd skeptical and thinking it may be more 15W true but hey if it's a true 20W par then bang on sweet).

Zero_Enigma

Phantoj

The NiMH battery is affected by memory also, but to a lesser degree. No scientific research is available that compares NiMH with NiCd in terms of memory degradation. Neither is information on hand that suggests the optimal amount of maintenance required to obtain maximum battery life. Applying a full discharge once every three months appears right. Because of the NiMH battery’s shorter cycle life, over-exercising is not recommended.

A hand towel must be cleaned periodically. However, if it were washed after each use, its fabric would wear out very quickly. In the same way, it is neither necessary nor advisable to discharge a rechargeable battery before each charge — excessive cycling puts extra strain on the battery.

https://www.buchmann.ca/Chap10-page2.asp

moxfyre

NO! You do NOT want to make a habit of fully discharging a NiMH battery! A NiMH battery will lose its ability to hold a full charge more rapidly the more it is deeply cycled (discharged to nearly empty, then recharged). Older NiCd batteries WERE prone to the "memory effect", but this is much less important for NiMH batteries... for optimal lifetime a NiMH battery should only be deeply discharged every few months (see the site I've linked below).

An excellent online authority on rechargeable batteries is Battery University, here's a page on nickel-based batteries with useful facts about NiMH and NiCd batteries: https://batteryuniversity.com/partone-4.htm

I refer often to Battery University since I often have to restore expensive and unusual battery packs for laboratory equipment. The site explains charging algorithms for different types of battery chemistries in great detail.

daredevil

It's worked very well so far. I felt it was the most ecomomical thing out there until I come up with the cash for something better. I guess until a guy gets an HID, there's always a desire for more light. The latest to catch my eye is the Night Rover Classic Plus Dual Beam. 32W halogen for 199.

Allen

Thanks Mox,
I've been confusing the NiCd with NiMH batteries. Good link.
Thanks again,

--A

moxfyre

No worries, just wanted to set the record straight!

The properties of rechargeable batteries are totally non-intuitive. But fortunately there are only 4 common types: NiCD, NiMH, Lead-acid, and Li-ion. Having an online reference is really helpful. I recommend that everyone who uses expensive battery packs refers to it, so as to get the longest life out of them.

superslomo

Whether you need to charge it or not has mainly to do with the length of time you are planning on using it. If you need the extra half hour of burn time, then run the charge. Depending on the Cygolite you have, it may have a smart charger. I know the Cygolite Dualcross 300 that I have has the smart charger, but other lights that they make don't have the same device. If that is the case, be very attentive to the battery status as you do not want to overcharge it.

ItsJustMe

If you have a good smart charger, you shouldn't have to worry about memory effect at all, just your charge level.
Memory effect is something you almost certainly don't need to worry about anyway. Unless you are charging your battery with a constant current charger exactly the same amount every time and discharging it exactly the same amount every time, you probably will never notice a memory effect.

Even if you do, the memory effect on NiMH is only 0.05 volts per cell, hardly noticeable. But if you have a good smart pulse charger, you just won't ever see a memory effect problem.

daredevil

I don't have a smart charger. How long is too long to charge it? It's a battery the size of a small water bottle. 12 hours or less?

cyccommute 

I'll agree that you don't want to make a habit of deep discharge of an NiMH which, by the way, is what daredevil is flirting with by not recharging very often after use. But that's not the whole story. From the page cited at the batteryuniversity (Buchmann is the same author I cited):


# High self-discharge - typically 50% higher than nickel-cadmium.
# High maintenance - nickel-metal hydride requires regular full discharge to prevent crystalline formation. nickel-cadmium should be exercised once a month, nickel-metal-hydride once in every 3 months.

The more important note above is the second one. Nickel chemistries tend to recrystallize in the cell by growing larger crystals. A larger crystal has less ability to make electricity because all to the interesting stuff happens - electrochemicalwise - at the edges of the crystal. Larger crystals have fewer edges and the battery eventually becomes a useless brick. NiCd does this is spades which is where the memory effect comes from but NiMH does it too just not to the same extent. I have a charger - a Maha C777 - that will discharge the cells to their lowest voltage and then pulse charge back to full charge. I do this once a month or so on my NiMH packs and nearly every time on my NiCd packs.

However, if you don't have this capability, it's best not to mess with it. It's very easy to go below the proper voltage and damage the cells. Figure out what the capacity of your battery is, daredevil, and then run the lights for long enough to reach within 10 or 15% of that capacity, then recharge. In your case, I'd suspect that four 30 minute commutes is going to be pretty close to your capacity. If the battery sits for several days (a week or longer), you should proably recharge it before use.

ItsJustMe

The right answer is, "Get a smart charger"

You want to charge it until it's full. So how long to charge depends on how full it is to start with, how much current your charger delivers and at what voltage, the uptake capacity of your battery (which is not constant, it decreases as the battery reaches full charge and varies depending on ambient temperature).

In fact, I think in most cases it IS actually impossible for a dumb charger to charge a battery as completely as a smart charger can, even if you get the charge time perfect. Modern smart chargers do an analysis of the battery when they first connect, and they will do pulse conditioning of the battery while it's charging, which can significantly extend both the capacity and the lifetime of the battery. Also at end of charge they'll kick into modes that "fill in the corners" of the battery's capacity.

Basically I assume that if I don't have a smart charger, I'm going to either overcharge or undercharge; getting it perfect is almost impossible. Smart chargers are cheaper than a new battery, so I figure it's worth buying them because otherwise I'll probably forget and leave the thing charging overnight sometime and fry the battery.

I wouldn't even bother buying a rechargeable battery without a smart charger.

ItsJustMe

Keep in mind that the quickest way to grow crystals around the electrodes is to discharge a cell below 0.95 volts per cell. If you run a NiMH battery down below there, you will incur irreversible crystallization around the electrodes and the cell will be permanently damaged. The more you do it the worse it will be.

So while running them down is probably OK, running them dead is worse than not doing anything.

daredevil

So until then, and it will be a while, how long is too long? I know there isn't an exact answer but what would be wise?
I know it doesn't hurt to do partial charges. Maybe I should just do that until I get a smart charger?

daredevil

That's the info I was looking for. Thanks.

banerjek

The battery should not get hot. Once it starts getting warm, disconnect the charger. Don't go by time.

BTW, you can get smart chargers for batteries that you already have. Smart chargers are the way to go -- faster, better, less hassle.

superslomo

I have a smart charger for my L&M Arc, and the battery is definitely pretty warm/hot by the time it finishes. Same thing with the Li-Ion batteries for my camera. Not sure how hot it is permitted to get, but I thought that was pretty much par for the course.

daredevil

oops, mine has been warm after every charge I've given it. I don't have the literature with me right now but I believe instructions were to charge for 12-14 hours. Would that only be if it was nearly completely discharged?

Another thing I was unaware of is that you are supposed to let the battery sit for 1/2 hour before hooking it up after charging.

moxfyre

That's right, you don't want your NiMH battery to get much above body temperature when charging... a NiMH cell should be about 35-40 C (95-105 F) when fully charged. If charged far beyond that, the pressure and temperature will rise rapidly, and all kinds of bad things can happen.

ItsJustMe

Heat is OK in moderation. Good smart chargers actually have a heat sensor to regulate this. My AA charger in fast mode will send NiMH AAs up to about 130*F; pretty warm but not really hot.

rajman

Is this what happened to my Energizer NiMH AA's? I was in the habit of running them down to zero light, thinking that full discharge was the way to go.

I've used them for about 40 cycles, and now with a full charge they give a weak light on my halogen light (PB 5000x). It seems to me they aren't giving out the right voltage, but I have the same problem on the 'bright' setting (which should double the voltage).

Should I get a new set and just recharge them every time I use the light? When I was using the light/batteries last year, I could get 4-5 h from the lights before recharging (1 week of commuting), which may have caused the problem.

Phantoj

My NiMH battery pack has some kind of thermocell or something inline with the batteries. I think the packs at battteryspace.com have it too.

I use a smart charger from batteryspace.com after I fried my old one.