Timer cut charge controle - a bad thing?

[Roelant]

I've been reading up on several of the battery- and charging related discussions that took place here, like the one here and the battle for the best charger seems to be mainly between between the BC900 and the MH-C9000. Both quite sophisticated devices using measurement and formulas to determine whether the battery is optimally charged and/or to quit charging (or switch to tickle charge). I'm a happy C9000 user for over some time now (even imported mine from the USA as it wasn't distributed in Europe jet), but as some of you gadget-savvy guys her might recognise, neither of these devices are very "girlfriend-friendly".

So I went looking for a 'safe' and 'easy' to use charger to have beside the C9000, one she could use without me having to explain it to her. Put short... Primary objective: no buttons. Secondary objective: be good to my batteries. Those to put together, usually ends up with the advice 'value charger' or 'overnight charger'. Which is ok: I'm using Eneloops mostly, so a speed-charger isn't required if you have batteries ready when you need them. However, I've noticed that the lot of these chargers are using 'timer cut' charger-controle. They charge the battery at a low current (which, in my book, is good) for a predefined period of time, usually somewhere 14-16 hours.

Now I've been able to get my hands on a very sweet priced MQN04 - the 'overnight' charger from the Eneloop-series from Sanyo. But guess what: it's the only timer-cut charger. It charges for 16h, with 2,4V/250mA for AA and 2,4V/120mA for AAA wich seems both good slowcharge-settings for a 2000mAh AAA and 800mAh AAA. But still: timer cut. (reference)

And since using 'smart' chargers' (deltaV based cutoff) is the hot thing to go with right now, I was wondering... has this 'old fashion' way of charging become a bad way of charging? Or is there actually nothing wrong with it, as long as you "take it slow" with a low charging-current?

 

[mdocod]

Hi Roelant!

Welcome to CPF!

Slow charging with a timer isn't too bad, especially if the charging rate has been properly selected (0.1C). When the cells are mostly depleted it is a perfectly acceptable method of charging in my opinion.

The only reasons to not like this charging method are:
1. It's slow
2. If the cell isn't mostly discharged, it will sit there for awhile and be over-charged,, but at this slow of a rate, there isn't going to be much heat buildup so the issue is minimal..

-----------

There are smart terminating chargers that are simple "insert cell and walk away" type deals. They sometimes have 1 button, but it doesn't have to be pushed, it's just for initiating a discharge, and then it automatically switches to a charge when the discharge is complete.

Here's an example of a charger, that from the looks of it online here, is a simple "drop-in cell and walk away".... I don't see any buttons on it at all. Charge rate of 2A is perfect for most AA cells IMO.
http://www.batteryjunction.com/tpec-tp1hr.html

Eric

 

[Mr Happy]

Timer cutoff is still a bad way of charging. The fixed current will be too high for some batteries and too low for others. Partially discharged batteries will get overcharged. And the batteries will not be maintained in the best condition.

But I am confused about what the problem is with the C9000 as a simple charger. Here is how to use the C9000 to charge batteries:

1. Put the batteries to be charged in the charger
2. Plug in the charger
3. Walk away
4. Come back later when each slot says "Done"
5. Take out the batteries and use them

No other charger you can buy will be simpler than that.

 

[Roelant]

Thanks.

hey sometimes have 1 button, but it doesn't have to be pushed, it's just for initiating a discharge, and then it automatically switches to a charge when the discharge is complete.

Well, the 'no button' demand was a metaphor for 'easy to use', didn't mean to exclude any device that actually did have a button up front.

Charge rate of 2A is perfect for most AA cells IMO.

2A seems a bit on the high end for me. The reason I've bought the Maha is that I wanted to treat my batteries properly to extend their lifetime. And from what I've read, charging them somewhere within 0.1C and 0.4C seems to be the gentle charging-rate to go with? For Eneloops, 2A would be 1C. Hence why I've been avoiding quick-chargers and the sorts.

Timer cutoff is still a bad way of charging. The fixed current will be too high for some batteries and too low for others. Partially discharged batteries will get overcharged. And the batteries will not be maintained in the best condition.

Which I can agree on - to a certain amount. In this case, the amount seems just fit for the batteries (which makes sense, as they came together).

But I am confused about what the problem is with the C9000 as a simple charger. Here is how to use the C9000 to charge batteries:

[...]

True, but default charge-rate is 1A - which I consider to high. I actually avoid charging them with anything above 0.4C and my personal default is charging them 600mAh. Thus, to have them charged likewise, you'd have to adjust charge-rate. And that would add the steps of confirming charge-mode and selecting the charge-rate for every battery.

 

[Mr Happy]

True, but default charge-rate is 1A - which I consider to high. I actually avoid charging them with anything above 0.4C and my personal default is charging them 600mAh. Thus, to have them charged likewise, you'd have to adjust charge-rate. And that would add the steps of confirming charge-mode and selecting the charge-rate for every battery.

I personally believe that for AA Eneloops 1 A is a really perfect charging rate. All my Eneloops work really well when I charge them at 1 A on the C9000. It corresponds to 0.5C and Sanyo say in the Eneloop Q&A that a charge rate of 2 hours is what they recommend.

So my opinion is don't worry about trying to use lower charging rates. There is really no need.

 

[Marduke]

True, but default charge-rate is 1A - which I consider to high. I actually avoid charging them with anything above 0.4C and my personal default is charging them 600mAh. Thus, to have them charged likewise, you'd have to adjust charge-rate. And that would add the steps of confirming charge-mode and selecting the charge-rate for every battery.

A charge rate of 1A is approximately .4-.5C for most AA cells.

But if you want slower while still having function, the LaCrosse BC-900 has a default charge rate of 200mA if you just throw some cells on and walk away.

 

[TakeTheActive]

Slow Charging Produces Large Crystals...

...True, but default charge-rate is 1A - which I consider to high. I actually avoid charging them with anything above 0.4C and my personal default is charging them 600mAh...

...Slow charging produces large crystals, and large crystals produce voltage depression....

Reference: A Look at Slow Charging

 

[crazyk4952]

I would not trust the timer charger that you are using for NiMH batteries. Using this type of charger can significantly reduce the lifetime of your batteries.

If you want a 'simple' charger that works really well and will not over/undercharge your batteries, I would look at the MAHA HM-801D charger. It will charge 8 AA/AAA batteries independently. When the first battery is inserted, it defaults to charge at 2000 mA (which should charge most AA batteries in around 1 hour). If you wish to select the 1000 mA option, just press the 'soft charge' button within 5 seconds of the first battery being inserted.

It also has a 'condition' button for keeping the cells in good working order.

I have been using this charger for about 1 year now and I have no complaints!

http://thomasdistributing.com/shop/...html?SP_id=&osCsid=km6dft2etlg2dlpvfd8dcn43m0

 

[snakyjake]

But I am confused about what the problem is with the C9000 as a simple charger. Here is how to use the C9000 to charge batteries:

1. Put the batteries to be charged in the charger
2. Plug in the charger
3. Walk away
4. Come back later when each slot says "Done"
5. Take out the batteries and use them

No other charger you can buy will be simpler than that.

I'm still slightly confused about the C9000 charger, because apparently the charger isn't really done when it says it's "Done". I read that it still does a top-off charge 2 hours after saying "Done". So if you want maximum charge, wait 2 hours after "Done".

I still don't understand why a NiMH battery is more difficult than charging a lead acid on a 3-stage charger+pulse. I don't know if it is because of battery chemistry, or if its because there's not a huge demand for more technology in a NiMH chargers.

 

[Mr Happy]

You don't have to wait after it says "Done". The top off charge is there because it is better than not having a top off charge. You make it sound as if it is something bad.

The problem with charging nickel chemistry is that you cannot use voltage to do a good job of detecting the end of charge. Different cells have different voltages, and the same cell can have different voltages at different charge rates. Therefore you need to look at rate of change of voltage, or rate of change of temperature. And those things are harder to do well.

 

[snakyjake]

You don't have to wait after it says "Done". The top off charge is there because it is better than not having a top off charge. You make it sound as if it is something bad.

I don't think the top-off is bad, what I think is wrong is something (or someone) saying "done" when not 100% complete.

99% complete does NOT equal done. Only 100% complete can equal done.

If the charger still needs to do something to charge to maximum capacity, then it isn't 100% complete, therefore it is not done.

Jake

 

[Mr Happy]

I don't think the top-off is bad, what I think is wrong is something (or someone) saying "done" when not 100% complete.

99% complete does NOT equal done. Only 100% complete can equal done.

What you are missing is that with nickel chemistry charging is not a linear process. It may take for example 1 hour to reach 95% of charge, 5 hours to reach 99% of charge, and 15 hours to reach 99.9% of charge. When are you going to say charging is done?

You have to be practical about these things. Most rational users will be happy to take the battery after 1 hour and start using it. There is more value in using the battery than watching it sit on a charger.

 

[snakyjake]

What you are missing is that with nickel chemistry charging is not a linear process. It may take for example 1 hour to reach 95% of charge, 5 hours to reach 99% of charge, and 15 hours to reach 99.9% of charge. When are you going to say charging is done?

You have to be practical about these things. Most rational users will be happy to take the battery after 1 hour and start using it. There is more value in using the battery than watching it sit on a charger.

If the charger knows it is not 100% complete, and knows it will perform a 2 hour top-off charge, I'd rather have the charger display some sort of information. For example: bulk charge complete, top-off charge in process, top-off charge remaining time. When top-off charge is complete, display would say maintenance.

Jake

 

[Mr Happy]

If the charger knows it is not 100% complete, and knows it will perform a 2 hour top-off charge, I'd rather have the charger display some sort of information. For example: bulk charge complete, top-off charge in process, top-off charge remaining time. When top-off charge is complete, display would say maintenance.

I agree in principle, but sometimes there is a balance to be found between providing more information and keeping user interfaces understandable. I can understand reasons why Maha might have made things the way they are, involving design and manufacturing costs, retooling issues, and so on.

 

[snakyjake]

Here's the issue I'm dealing with:

When the charger displays "Done", has it been topping off < 2 hours? Or > 2 hours?

What % of charge has been completed by "done"? 99%? 90%? If the % of capacity is insignificant, maybe a few second or a minute on my light, then no big deal. It could be the charger does 99% of the charge and says "done", and the difference of 1% is on measured in seconds for a LED light. If so, then no big deal.

Or asked another way, how many more amp hours are gained in the top-off phase?

 

[Mr Happy]

Here's the issue I'm dealing with:

When the charger displays "Done", has it been topping off < 2 hours? Or > 2 hours?

What % of charge has been completed by "done"? 99%? 90%? If the % of capacity is insignificant, maybe a few second or a minute on my light, then no big deal. It could be the charger does 99% of the charge and says "done", and the difference of 1% is on measured in seconds for a LED light. If so, then no big deal.

Or asked another way, how many more amp hours are gained in the top-off phase?

In my experience, the top off charge adds maybe 100 mAh to the total. You could be talking 1950 mAh rather than 1850 mAh on an Eneloop.

However, if you remove the cell from the charger, that extra charge will bleed off within a few days. It is what is known as a "surface charge", it doesn't stick very well.

 

[TakeTheActive]

Already ASKED and ANSWERED...

I don't think the top-off is bad, what I think is wrong is something (or someone) saying "done" when not 100% complete...

​

...99% complete does NOT equal done. Only 100% complete can equal done.

If the charger still needs to do something to charge to maximum capacity, then it isn't 100% complete, therefore it is not done...

The chargers don't know when they're 100% done, or 99% done, or WHATEVER done - they guess.

As someone previously stated here ('somewhere' in the CPF Archives), you're filling a glass from a hose with a sprayhead - not all of the water enters the glass. Also, the charger cannot precisely detect overflow; and it cannot detect that the bottom of the glass may have arrived pre-filled with a few rocks (displacing space for new water to be stored). So, based on the research done by it's designers, it watches for -DeltaV, and/or Max Temp and/or Timer expired, etc... and shuts down.

Only by EMPTYING the glass can you tell how full it was.

...sometimes there is a balance to be found between providing more information and keeping user interfaces understandable...

I agree.

 

[snakyjake]

Fair enough for me. Then I just want a charger to have a simple indicator that tells me when it's bulk charge is "Done" (like the C9000), and another indicator that tells me when the top-off charge is done. Then I'd be happy

 

[SilverFox]

Hello Snakyjake,

With the C9000 there are two ways to tell if you are in the top off charge.

The fast way is to note the time you start the charge. When you come back later, you can look at the amount of charging minutes, then note the current time. This should tell you where you are in the top off cycle.

The second way involves observing the cell voltage. You note the cell voltage, then note it again a few minutes later. If the voltage is raising, you are still in the top off portion of the charge. If the voltage is stable or dropping you are really, totally, done.

Tom

Edit to add: If you want a charger that gives some indication of where you are in the charge, take a look at the Schulze chargers. My Schulze charger has a number scale that increments during the charge. You can glance at it and get an idea of where you are in the charge cycle.

 

[snakyjake]

Thanks for the reply Silverfox. I'll have to do some more research on the Schulze chargers. I'm looking for a charger that does everything a charger should do (it's not like manufacturers haven't had enough decades to make one right).

As for the C9000, why doesn't it measure the voltage for me? I believe this is what a lead-acid 3-stage type of charger does for auto batteries.

Thanks,

Jake