Is this charger able to charge these?

[dgc]

Hello everybody!
I just bought a bundle with a Varta Pocket Charger and some Ready2Use rechargeable. (11€ for the charger and 4 2100 mAh AA)

Now, reading the specs written on the cell and the charger, I'm starting to doubt this charger will ever fully charge my cells.

On the charger I read:
AA: 2x (3V 160-185mA)
AAA: 2x (3V 70-80mA)

and on the website I read that it has a 15 hours safety timer.

On the cells I read:
AA: Charge: 15h 210mA
AAA: Charge: 15h 80mA

It seems to me that it will be able only to fully charge the AAA but not the AA, am I wrong?

Thanks,
dan

 

[dgc]

No one is able to answer? I don't belive this!

 

[abvidledUK]

Put them in twice !

Seriously, test for rt after one charge.

Same after two charges.

Different ?

PS: It does state "re-energize" rather than charge...

I would take this to mean top-up.

Perhaps an e-mail to Varta would clarify the situation.

 

[Norm]

Looks like the charger should be OK, the standard nimh batteries shown on the Varta sight are higher capacity 2700mAh versus your batteries 2100 mAh so I would say the charger should be fine
Norm

 

[dgc]

Following abvidledUK suggestion I mailed the question to VARTA. Here is the answer translated from Italian.

Sorry for the late answer - I forwarded the problem to technical office in Germany.

In the past times the recharge time was based on a charge factor of 1.5.
That means that with 100mAh {I think she means mA} charging current you'll need 15hours to charge a 1000mAh (1000/100x1.5)

Nowadays charge factor of 1.2 seems to more realistic, but many competitors use a charge factor even of 0. {Again... I think she means 1}

The 11 declared hours {where? I never spoke about 11 hours!} for the AAs are a little "aggressive" because they're measured in ideal laboratory conditions and they don't consider pressure, temperature and use conditions.
In every case, even the worst case, you'll have the fully charged cells after 14 hours, long before the safety timers ends.

We understand that the information may generate doubts, so it'll be our mission to simplify and explain clearly in the packages in the near future.

I don't know why they apologize about "late answer"... It took only two days to reply! That was fast enough to me.:goodjob:

Coming to what she said.
Using the formula she gives I obtain a slightly-less-than 14 hours charge time for the AA in the best case: 2100/185*1.2 = 13.6 hours. (Using the lowest current declared on the charger leads to 2100/160*1.2 = 15.75 hours... The safety timer would end in this case) So if I use a charge factor of 1.2 it seems that this is able to charge my cells.

 

[65535]

What's a charge factor charging time is just mAh's of the pack or cell divided buy current of the charger.

So charging a 2100mAh @ 160 mA will take 2100mAh/160mA 13.25 hours

and their high capacity cells will take over 16 hours so I don't know what the deal is.

 

[SilverFox]

Hello Dgc,

It appears that your charger charges at a set amount for a set period of time.

A "standard" charge is 0.1 C for 16 hours. In your case, 0.1 C would be 210 mA (2100 mAh cells). Since the charger seems to be rated at 180 mA, your cells would be slightly undercharged, compared to a "standard" charge.

The amount you put into a cell is dependent on the charge rate. Less is put in at higher rates. At 1.0 C, you end up with around 105 - 110%.

The problem with this charger is that it does not have any way to limit the charge when you charge cells that are only half empty. You will end up over charging if you leave them on for the full 15 hours. However, the charge rate is small, so the over charging damage will also be small. In this case, you may want to manually limit the charge to around half the 15 hours.

Tom

 

[dgc]

Thanks 65535! Trying to answer your question I discovered an error in my previous post and spot the bug! Post above corrected. Now everything is clear

"Charge factor" is a translated term so maybe in English you use a different word to refer to the same thing. It measures how much of the current you're supplying to a cell effectively charges it. I thinks it basically depends on battery construction. A charge factor equal to 1 (which is what your equation uses) would the perfect thing but is impossible to build in the real world.

The basic equation is:

Charge time{hours} = Charge factor * Battery capacity {mAh} / Charging current {mA}

Take a look at the following picture for example (this is the AA cell object of discussion):


Why would it report a 15h charge time with a 210mA current when it's only a 2100mAh? Isn't 10hours enough? No! Because some of the current goes wasted (I don't know where... Probably in heat)

The data displayed on that cell are calculated using a "charge factor" of 1.5 or a "cell efficency" of 1/1.5 = 0.66. That means that only 2/3 (or 66%) of the current you're giving to the cell really charges it. In fact if you calculate 2100 mAh / (210mA * 0.66) (or, as int the equation at the beginning: 1.5 * 2100mAh / 210mA) you'll find 15hours of charging time.

The lady at Varta is explaining that 1.5 "charge factor" is an old value and that with newer cells you can use a "charge factor" of 1.2, that means a (1/1.2 = 0.83) 83% "cell efficency". It means that 83% of the current you're giving to it really charges it, the other 17% is wasted.

This way, feeding the battery with 185mA means that it's in fact charging with a 154mA current (83% of 185mA) which leads to a 13.6hours charging time (1.2* 2100mAh / 185mA).

Concluding: the answer of my original question is "Yes, the charger is able to charge these cells, but it's at it's limits".
Specifications tells that it uses a charge current between 160mA and 185mA (I don't know what it depends on). Well, if the current stays above 168mA (= 1.2*2100mAh/15hours) it will fully charge the cell within 15hours, otherwise it won't. Because 168mA is pretty close to 160mA and away from 185mA I think that it's reasonable to suppose that it will fully charge the cell.

HTH

 

[dgc]

Thanks for the hints SilverFox. Reading what you wrote I believe that charging current value (between 160mA and 185mA by specs) depends on the charge left in the cells.