Which is the best 15 minute charger

ive had raovac 15-minute charger for over 3 years now, no problems here. i used the batteries for a year on my dslr without issues. and now the batteries are in random places (remotes, mouse, razor, etc) without problems. the charger is crazy, there are fans that blow out warm air so it doesnt overheat while charging. it has never overcharged, and i have timed it many times and never exceeded 15 minutes. and i have yet to notice battery life decreasing. and as soon as my canon flash comes in, theyll go back in service in my photography equipment.

i'll be a sad man when these batteries run out some day. i may have to search ebay and stock up .

yeah all my research I done upto now about these 15min batteries, suggest that ray-o-vac were probably the best, due to the reason, these 15min batteries were specially designed for fast charging, and the charger didn't completely charge them, left about 200mAh uncharged...
In case anyone having the ray-o-vac charger, i suggest they stock up now, amazon and ebay are still selling them, it will completely dissapear in some time, too bad

It is a common "trick" to define 100% as less than 100%, to be able to use a high-speed while reducing the probability of overcharging.

Li-Ion batteries will explode or catch fire if over-charged. Because of this, some manufacturers have defined (and calibrated the battery-full indicator) at 90-95%. A Sony camcorder I have quickly reaches 100%, but if left to itself, it will then slowly crawl up to about 107%.

It is a common problem in the industry, to be able to get short recharge times while never ever failing to stop exactly at the finish line.

Headcase650 wrote in post #3557763
No offense to all the safety monitors on the board but to the Op, don't let all the fear tactics keep you from using a 15 minute charger. Your house wont burn down, the batteries wont melt or explode. Some of my batteries are over 2 years old and get charged at least 4 times a month sometimes double that. The batteries do get warm but they do not get "Blistering" or "sizzling" hot like Ive seen mentioned on some other threads. If you like, just leave them in the charger for 25 minutes and the fan would have cooled them down completely.

At 48 charges a year, you don't even charge the battery 100 times in two years. You wouldn't even know if the battery had been degraded. Most likely these are not 'dead' rechargeables either.

The heating is internal - when it gets to the outside case temperature that is the LAST thing to get heated. Heating is a function of the current and the internal resistance and is proportional to the square of the current.

So, your anecdotal data says nothing about the relative safety or battery life of this charging method.

In order to charge a 2500mAH battery to full charge from zero would take roughly 10A charging current to get it there in 15 minutes. 10A is one heck of a lot of current. Looking at it this way - putting 10A into a battery through the contacts on a AA battery and the spring loaded battery charger connections is highly unlikely.

If they are not getting hot inside (or even outside for that matter), then I would very much doubt the 15 minute claim or that they are being charged even close to 100%. In which case it really isn't a 15 minute charger and I think this is very much the likely scenario - so in that case, you didn't get what you thought you got.

J

I would very much doubt that we are talking about just 10A. 10A * 0.25h would be 2500mAh. But the battery will not convert all energy. The old 0.1C rule normally recommended 14 hours charging time, i.e. 40% extra. Let's be nice here and assume just 12A charging current. The second thing is that the batteries has an internal resistance. Hence it is not possible to push 12A through them using 1.2V. It isn't unlikely that the voltage is 2 or 3V.

If we assume 12A current and 1.8V (50mohm inner resistance), then the battery receives 21W, and converts 14W from electrical to chemical energy. The remaining 7W must be cooled off by the fan. Any current sent through the battery after it is full will be fully converted to heat.

Exactly my point. 7W is a lot of heat/energy in that small of a volume and/or the batteries are being significantly stressed.

In looking at this, I very much doubt that these chargers are truly charging the battery to 100% (or even close) or they are really being damaging to the batteries and a safety hazard.

Either way, it isn't what it is advertised to be.

J.

If I remember correctly, Energizer rates the charging current as 7.5Amps and there's no individual circuit....so it would be more like 3.75amps per battery if charged in a pair...

and its about 80% charge in 15mins what most users claim...Also do remember, while using batteries inside a Digital Camera, the batteries never reach a zero charge as stated. Most digital camera's shut off quite early and there's considerable power left inside batteries...

Add me to the happy Energizer 15 minute charger users. I have been using that charger for 2 1/2 years, the 2500 battery set that comes with the charger still work.

That charger has a fan built in. When charging, the batteries got quite warm, but the fan keeps running after the charging circuit shuts off for 5 mins or so. I like to use it with the cig lighter adapter. In 20 mins while driving, I have a fresh set of working batteries.

I have 2 other slow chargers, and I can't tell any diffrernce which set of battery is from which charger.

TheMafioso wrote in post #3560533
If I remember correctly, Energizer rates the charging current as 7.5Amps and there's no individual circuit....so it would be more like 3.75amps per battery if charged in a pair...

and its about 80% charge in 15mins what most users claim...Also do remember, while using batteries inside a Digital Camera, the batteries never reach a zero charge as stated. Most digital camera's shut off quite early and there's considerable power left inside batteries...

Forget 3.75A - NiCd and NiMH are charged with current, not voltage and two batteries in parallel will not be able to split the charge current 50/50.

So then they charge the two batteries in series. The theoretical limit would then be 7500mA/4 = 1875mA. Most probably, they can't fill more than 1600-1700mA during those 15 minutes, since the batteries can't convert 100% of the current.

Anyone who have made a discharge test to see exactly how much juice empty batteries gets after 15min charge?

I have a Duracell 15 minute charger and have had no problems. It saved my butt once.

pwm2 wrote in post #3561406
Forget 3.75A - NiCd and NiMH are charged with current, not voltage and two batteries in parallel will not be able to split the charge current 50/50.

So then they charge the two batteries in series. The theoretical limit would then be 7500mA/4 = 1875mA. Most probably, they can't fill more than 1600-1700mA during those 15 minutes, since the batteries can't convert 100% of the current.

Anyone who have made a discharge test to see exactly how much juice empty batteries gets after 15min charge?

So it is not a 15 minute charger. It is probably a 1 hour charger with an altered fuel gauge and they just hope no one checks. After 15 minutes, looks like the batteries coming off of it are at 80% or less charge would be my guess.

J.

Even If they are only charged to 80% I'm more than happy with them. I can put a dead set into the charger for 15 or 20 minutes put them directly into a vivitar 283 and get about 120 full power shots off before the recycle time starts to slow. How in the world could anyone complain about that. Plus they are so cheap even if fast charging them kills them 20% faster, who cares?

Headcase650 wrote in post #3562534
Even If they are only charged to 80% I'm more than happy with them. I can put a dead set into the charger for 15 or 20 minutes put them directly into a vivitar 283 and get about 120 full power shots off before the recycle time starts to slow. How in the world could anyone complain about that. Plus they are so cheap even if fast charging them kills them 20% faster, who cares?

Not to complain at all but you probably get just as much with a 1 hour charger. I'm betting that there is not much difference except what was on the box. I think from looking at the numbers it is definitely not a "15 minute" charger. I think this is what is called "falsified advertising."

All batteries voltage comes up really fast when you charge them and then tapers off as they come to full charge. You would probably see pretty much the same performance with any of the normal non-trickle only chargers.

J.

pwm2 wrote in post #3561406
Forget 3.75A - NiCd and NiMH are charged with current, not voltage and two batteries in parallel will not be able to split the charge current 50/50

Why not, identical batteries would have a similar resistance, and if they are used in pair, like in a digital camera, they would be similarly discharged...so won't the current be distributed 50/50 or atleast close to that..

pwm2 wrote in post #3561406
So then they charge the two batteries in series. The theoretical limit would then be 7500mA/4 = 1875mA. Most probably, they can't fill more than 1600-1700mA during those 15 minutes, since the batteries can't convert 100% of the current.

Anyone who have made a discharge test to see exactly how much juice empty batteries gets after 15min charge?

Hmm...well if it'll be series then, won't the current be same in all cells i.e. 7500mA, if the charger acts as a constant current source..

TheMafioso wrote in post #3565314
Why not, identical batteries would have a similar resistance, and if they are used in pair, like in a digital camera, they would be similarly discharged...so won't the current be distributed 50/50 or atleast close to that..

Normal variance in electromotoric force and serial resistance - and charge level - will affect how the current is splitted between the two cells. Different amount of current would mean that the cells would not fill up at the same speed. Besides, if they where charged with 3.75A, then they would only receive about 900mAh during 15min of charging.

TheMafioso wrote in post #3565314
Hmm...well if it'll be series then, won't the current be same in all cells i.e. 7500mA, if the charger acts as a constant current source..

Yes, the intention of charging them in series is that the same current is sent through all cells. The variance in the batteries will mean that the voltage will not be identical to the different cells, but that is not a real problem since they are charged with a current, not a voltage.