dumb things with smart chargers

[dukeleto]

My smart fast (~1.5h) charger says it charges AAs and AAAs at a different current, and indeed it does, going by charging times.
How does it detect between AA and AAA though?
Is it with the internal resistance of the cell?
All these questions leading up to :
how stupid is it to charge high-capacity D cells with a smart AA charger?

Thanks,
Olivier

 

[SilverFox]

Hello Olivier,

I have a Vanson charger and am not sure how yours works.

My charger has different + contacts for the different sized batteries. The + side of the charger has 4 contacts at different elevations. AAA cells hit the first contact followed by AA, C, and D.

My charger charges AA cells at 500 mA/h and D cells at 700 mA/h.

Assuming your AA cells are 1800 mAh, it would appear that your charger is charging at a rate of 1200 mA/h. If you charge a 9000 mAh D cell at that rate, it would take about 7.5 hours. The problems I see are the different size of the D cells and just realize that it will take some time to charge a high capacity cell. Another consideration is that there may be an automatic shut off circuit in your charger. You may have to reset the charger (by unplugging the unit and then plugging it back in again). Depending on the timer interval, you may have to do this several times.

Tom

 

[dukeleto]

Hi Silverfox, and thanks for the answer;
yeah, I figured there might be a timer, and I've already got an adapter that could allow electrical contact; I was more wondering whether the much lower internal resistance of the D cell could do something strange?

Olivier

 

[3rd_shift]

If that charger charges nicads too, then internal resistance shouldn't even be an issue with your batteries.
I too had wondered about using a superfast charger for bigger Full capacity D cells in the 8 - 11 amp hour range.

 

[Hallis]

IVe got a Maha MH-C204F, which charges both NiMH and NiCad. It has a charge rate of 500mAH/Hour. Took a little over 4 hours to charge my 2200mAH AA's which were apparently dead as doornails, and it took about an hour and a half to charge some brand new 800mAH AAA's. Most of the good chargers know when the cell is almost full. Mine charges at the same rate regardless of the cell.

Maha = Good stuff

especially if you're looking for an inexpensive AA/AAA charger. The model i have is only 2 channel so i have to charge in pairs but the MH-C401 is 4 channel /ubbthreads/images/graemlins/smile.gif even better.

 

[Kevin Tan]

The Nicd/Nimh batts all can be charged to full of around 1.45v, then the voltage will drop down abit as the internal resistance increases as the chemical reaction completes and the rest of the charging current is converting the electrolyte to gas. Most so called intelligent charger have a sort of a monitor for the voltage drop, whereby the charging stops. This type of charger is called delta-charger. This is dangerous as a simple momentary power loss reset the monitored data and restart the charging. Most modern delta charger have a timer and voltage cutoff to arrest this problem



This is the simplest way that I could think of to describe the ways that most

 

[SilverFox]

Hello Olivier,

It was brought up in another thread that a charger designed for smaller cells may not be capable of producing a high rate of charge for an extended amount of time without overheating the charger circuit.

Check it out here and follow the links posted.

Tom

 

[dukeleto]

Oooohhh
thanks alot for the info Silverfox...
Looks like my title was appropriate /ubbthreads/images/graemlins/icon23.gif

Olivier