Nimh charger question ?

[curry87]

I have a Nimh/Nicd battery charger that charges the following batteries at the following rates is there any danger the batteries will be damaged though overcharging if left in the charger for too long ?

AAA / R03 / Micro (Ni-Cd) 250mAh 6h15
AAA / R03 / Micro (Ni-MH) 700mAh 19h
AA / R6 / Mignon (Ni-Cd) 800mAh 7h
AA / R6 / Mignon (Ni-MH) 1300mAh 11h15
AA / R6 / Mignon (Ni-MH) 2100mAh 19h
9V Block/R22/PP3 (Ni-Cd) 120mAh 8h
9V Block/R22/PP3 (Ni-MH) 160mAh 11h


• Output current: 145-160mA for R6/AA, 50-55mA for R03/AAA, 18-22mA for
R22/9V

 

[tvtech]

Hi curry87

Speaking strictly from my NiMH 9V PP3 charging experience, the charging time seems about right with the 18-22mA available current. What you need to do is to continue to monitor the charge voltage after the battery has charged fully after the said 11 Hours. Carefully monitor this voltage for say an additional 48 hours or more to ensure it never rises above 10.15V.

I use a circuit that I have designed that is part of a bigger project. I cut charge Voltage off at between 10v and 10.1V depending on ambient temperature. It never goes beyond 10.1V even if left on charge for Months.

Initial charge current is 100mA with a totally flat battery. Charge time is 3.5 Hours with a 250mA PP3 flat battery.

Hundreds of charges per battery. They love it. No matter who the battery manufacturer is.

What I am trying to say is, if the manufacturer of your charger has got fragile PP3 sorted, the rest of the batteries you put in your charger will be OK.

Anyways, here is Ansmanns guide. My favourite for NiMH PP3 rechargeables.

Cheers

 

[audioguru]

I have a similar very cheap Ni-MH battery charger.
It is made by the Energizer battery company and it came with four AA cells.

Its problem is that it is STUPID and it cooks cells that are already charged. It is simply a timer and it does not detect when the cells are charged so it does not shut off and it severely over-charges and over-heats them.
Another problem is that if the power fails while it is charging then when the power returns the timer starts over again from the beginning which cooks the cells.

 

[curry87]

At what rate can these cells be charged at 0.01c,0.005c ? so that it does not overcharge them but keeps them alive and kicking and stops them losing charge though self discharge over time like the electric razor always plugged in the charger example?

 

[audioguru]

Energizer has battery applications Manuals on their website. They recomment a 0.1C max trickle charge current for their old Ni-Cads and 0.025C for their Ni-MH cells.

The max trickle charge current is the same for a Ni-Cad AA (600mAh) cell and for a Ni-MH AA cell (2400mAh) maybe due to heating.

 

[curry87]

So charging a battery at a trickle charge rate indefinitely shouldn't over charge a nimh cell ?

 

[audioguru]

So charging a battery at a trickle charge rate indefinitely shouldn't over charge a nimh cell ?

Energizer recommends a trickle-charge current no higher than 1/40 C for their Ni-MH cells.
Panasonic recommends 1/20C to 1/30C. They say it is the heating that is the problem.

I charged Ni-Cads at the same time as I charged Ni-MH cells. The Ni-Cads became cooler as they charged but the Ni-MH cells became warm. When fully charge both types began heating about the same.

 

[tvtech]

The funny thing is...if you follow the ANSMANN guide/PDF I posted...you are good to go.

The important thing to do is to ensure that the battery never overcharges. That can ONLY be accomplished by Voltage Cut - Off. Nothing to do with current ever.

Voltage people. Voltage.

The battery is fully charged @ said voltage.

Keep it there. Voltage right = charge right = trickle charge for ever.

Kind of hard for me to explain it here...all I know is it works.

FWIW: I will post my NiMH PP3 findings here for interested parties. The temperamental PP3 is a an absolute beaut once you understand it. Remember...it has 7 (seven) cells to deal with. In one tiny package.

Gotta keep it cool when charging. That's part of the secret.

Cheers

 

[tvtech]

Forget what makers say....or provide with their useless "chargers". They want profits. Bottom line.

That they can actually market crap that destroys their product line ...beyond me. Surely, they would have the resources to design something that actually charges NiMH batteries properly..instead of destroying them as in audioguru's post above.

Unless they purposely build them to destroy their rechargeables.......pointless effort. May as well use throw away cheap batteries.

The logic is way beyond stupidity....................

Thanks and cheers

 

[3v0]

They make more money by selling more batteries. Money talks.

 

[tvtech]

They make more money by selling more batteries. Money talks.

Rechargeables dude. Do you get it????

Sit back and think.

Thank you.

Oh yes, cheers as well

 

[audioguru]

Forget what makers say....or provide with their useless "chargers". They want profits. Bottom line.

That they can actually market crap that destroys their product line ...beyond me. Surely, they would have the resources to design something that actually charges NiMH batteries properly..instead of destroying them as in audioguru's post above.

Unless they purposely build them to destroy their rechargeables.......pointless effort. May as well use throw away cheap batteries.

The logic is way beyond stupidity....................

Thanks and cheers

I have had my Energizer cheap charger and many Energizer Ni-MH AA cells for many years and they keep on going strong. I have about 24 of them and not one has ever failed. I charge them when they don't power the load properly anymore and rarely try to "overcharge" cells that are already charged. The cells are very warm but not too hot when the charger times out.

 

[kiriakos-gr]

I have a Nimh/Nicd battery charger that charges the following batteries at the following rates is there any danger the batteries will be damaged though overcharging if left in the charger for too long ?

This charger is a very slow and old boat, there is no fear about damaging batteries.

The true modern ANSMANN AA chargers, needs mostly true batteries so to work with them.
There is so many no-name batteries with fake specs, and one powerful charger will make them toast.

I own many batteries and chargers by ANSMANN ,
Two "Energy for speed" chargers .
One " Energy 8 " battery station
And the " Digital LCD Tester "
AA 2850mah Digital
AAA 1100mah ( another mini animal )
Plus many Sanyo AA 2700 & Sanyo Eneloop.

Lots of quality, but at a price, as always.
The fast chargers haves even small cooling fans.

The bottom line is that for AA any charger who gives less than 600mA per Cell,
is an outdated toy.
All those ANSMANN uses pulses and not constant current,
they are designed to keep the batteries in top shape, by living them on those battery stations all the time.

 

[3v0]

Rechargeables dude. Do you get it????

Sit back and think.

Sit back and think ????

Bad chargers allow the battery companies to reduce the cell life span and thus make more money.
This allows them to look like they are in favor of technology.

 

[curry87]

So in theory i could leave a pp3 nimh 220mah 8.4v battery in this charger without any fear of it being damaged though overcharging just want some conformation.

 

[tvtech]

So in theory i could leave a pp3 nimh 220mah 8.4v battery in this charger without any fear of it being damaged though overcharging just want some conformation.

No. Please read my post No 2 in this thread.

PP3 NiMH battery should never go above 10.15V ever if charging/charged. Even if left in the charger for Months.

Take a multimeter and check your PP3 after being on charge for 48 Hours or more with the charger still connected. If the meter reads more than 10.15V ....your charger is busy destroying your battery the longer you leave it charging.

Please see the data sheet I posted in my post No 2.
And please read my post No 8.

Hope this helps

Cheers

 

[tvtech]

Was going to say something. I forgot what it was though. I think it was about the destructive policy of building first class rechargeables and then destroying them with dumb chargers. Doe's not make sense. Which ever way you look at it.

The logic defies me. I don't get it. And hope I never do. If I ever think along these self defeating lines...someone shoot me please.
Because then I have clearly lost my sanity

Cheers

 

[curry87]

thx again.

Once last thing about the nimh cell is it better for the cell to fully discharge them right down to around 1v or so and then fully recharge them back up to 1.45v or to do partial discharges and then partial recharges do i have worry about the memory effect is it just now an ancient myth ?

 

[tvtech]

Here is what Duracell have to say about this. Check out page 10 of this Duracell guide:

Good policy to follow?? I think so.

Cheers

 

[kiriakos-gr]

No there is no worry about memory effect on the NiMH.
And so recharge them freely, no matter how half-full they are.
But an modern charger it is a must have.
And if it can do fast charge too, it must have a fan.

And another tip will be to own a charger with controllable charging speed,
In slow speed you can charge any no-name old ones.
And at fast speed the latest models of 2009 and after.
Like the Ansmann AA 2850mA digital and AAA 1100mA ( Both fast rechargeable models , that do not take damage from fast charging)