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There seem to be two main classes of domestic battery chargers - "intelligent" chargers which charge batteries individually, until some measurement(s) of the batteries determine that charging should cease, and dumb chargers which charge all batteries at the same rate.

These terms are marketing-speak and have no real formal definition. However, is it possible to approximate the functionality of an intelligent charger, simply by charging one battery at a time?

I am mostly interested in domestic batteries with NiMH chemistry.

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closed as unclear what you're asking by Leon Heller, PeterJ, Voltage Spike, Dmitry Grigoryev, Dave Tweed Sep 30 '17 at 12:01

Please clarify your specific problem or add additional details to highlight exactly what you need. As it's currently written, it’s hard to tell exactly what you're asking. See the How to Ask page for help clarifying this question. If this question can be reworded to fit the rules in the help center, please edit the question.

  • \$\begingroup\$ Do you mean battery chemistry, use case, or what? I can fill that in... but I am unaware of whether these are of import. \$\endgroup\$ – Dan Gravell Sep 25 '17 at 12:13
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    \$\begingroup\$ Fill in any specifics you can. There is no official or technical definition of "dumb" and "intelligent" when it comes to chargers. It's mostly marketing speak. One man's "intelligent" can be another man's "dumb". In a technical context the terms are nearly meaningless, especially when they stand without any context whatsoever. \$\endgroup\$ – Dampmaskin Sep 25 '17 at 12:54
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    \$\begingroup\$ If by your definition "intelligent" vs "dumb" is charging batteries directly connected in parallel or not, then yes you can make a dumb charger "intelligent" by charging one at a time. If the definition is different, then well, no. It is either unclear or self-contained what you are asking since what Dampmaskin said holds true: there is no intrinsic meaning to "dumb" or "intelligent" in this context. \$\endgroup\$ – Wesley Lee Sep 25 '17 at 13:13
  • \$\begingroup\$ NiMH requires a charger which supports it, which includes a bit of intelligence to look for the charge termination condition: maximintegrated.com/en/app-notes/index.mvp/id/4496 \$\endgroup\$ – pjc50 Sep 25 '17 at 13:13
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    \$\begingroup\$ Ok, I just did. Hope the extension of the answer is useful as well. \$\endgroup\$ – Dampmaskin Sep 25 '17 at 14:52
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It depends on the charger(s). There is no official or technical definition of "dumb" and "intelligent" when it comes to chargers. It's mostly marketing speak. One man's "intelligent" can be another man's "dumb".

In a technical context those terms are nearly meaningless, especially when they stand without any context whatsoever.

In order to have a meaningful technical discussion about chargers, we first need to know what battery chemistry we're discussing, and then, we need to discuss specific features and categories of features, related to charging that particular type of battery.

Some more or less random examples of terms that would be more conductive to a meaningful discussion:

  • constant current mode, or current limiting
  • constant voltage mode
  • float charge, or trickle charge
  • cut-off voltage, or temperature cut-off, or (in the case of NiMH and the like) voltage drop cut-off, etc.
  • different forms of battery diagnostics, detection etc.
  • cell balancing (in the case of multiple cells being charged in series)
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  • \$\begingroup\$ Thanks - these are beyond my knowledge to discuss, so I hope someone with more knowledge who nevertheless has a question in this area can pick this up and write a better question. \$\endgroup\$ – Dan Gravell Sep 25 '17 at 15:39
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is it possible to approximate the functionality of an intelligent charger, simply by charging one battery at a time?

I am mostly interested in domestic batteries with NiMH chemistry.

No. A 'dumb' charger can do several cells several in series (with all cells getting the same charge) because it charges continuously at a low enough rate that Nicad and NiMH cells can be overcharged without damage. Applying the same technique to individual cells has no advantage other than being able to charge a single cell.

To charge at a faster rate the charger must have some 'intelligence', ie. a method of monitoring the battery's state of charge and cutting off when it is full. The reason such chargers do each cell individually is that each cell could have a different state of charge when inserted, so they must be monitored and charged separately.

There are two methods of detecting full charge in Nicad and NiMH batteries:- temperature rise, and 'delta-peak' voltage measurement. The charger may also have a timeout, which is not very 'intelligent' but serves as a backup in case the main method fails.

The graph below (taken from ST application note An Intelligent One Hour Multicharger for Li-ion, NiMH and Nicad Batteries) shows typical curves and how the charger responds to them.

enter image description here

Delta-peak is usually easier to implement than temperature change because it is purely electronic. However it does have some issues that increase the 'intelligence' required for reliable end of charge detection.:-

  1. When charge current is first applied there is often an initial 'hump' in the voltage which might be incorrectly detected as end of charge. This 'false peak' can be avoided by delaying the start of delta-peak detection by a few minutes.

  2. The voltage drop (-DV on the graph) at full charge is only a few millivolts and happens slowly, so a high resolution low drift voltage measuring circuit is required. 'Smarter' chargers don't just look for a voltage drop, but take the derivative of the curve to determine the inflection point.

  3. The small signal can be swamped by voltage variations due to poor battery contact. To combat this the charger can stop charging while measuring, to reduce the effect of current passing through the varying contact resistance.

This adds up to quite a lot of 'intelligence' being required to get reliable and safe fast charging.

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Single cell gang chargers work best with CC and CV declining current till cutoff work best for each cell due to mismatch.

But simple chargers work well if used properly for full charge with thermal cutouts.

Essentially the formula is: battery capacity divided by charge rate and then multiplied by 1.2 (the 1.2 result gives us a bit of wiggle room to accommodate variables like battery resistance, charge rate reduction when the battery gets close to "full charge", etc.)

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