Charging Ni-MH 2200 Ah battery

[KenC]

Have just received my multi cable adaptor for the Toolkit RC M7 AC charger , so can try charging all sorts of things .... however as a newcomer to this after a 20 year gap sometimes this new tech throws me.    On my old SB Battery Services charger for flight packs, you jus entered the V and number of cells plus Ah rating and left it to cycle, knowing it was designed to select the correct parameters.     When I connect the M7 AC  it reports the battery and I select Nm HI  to be sure.  It then selects a 2A  charge to 7.4 v    The battery is rated externally as 6v and  states charge 220mAh  for 14 hours !    

 

So who is right, do we need to only use the old "futaba" chargers and leave it till the light goes out after hours , or will this quicker charge of this very modern charger cause a problem with the battery ?

[Denis Watkins]

It is normal to charge nihms at 1 tenth C Ken, or on the morning of flight, in a rush, I will go to 1A

In your case, 1 tenth C is 220mah for 10 hours

In a rush, mine take 2.2 hours, but is rare I do it.

Walwart chargers, you may have seen, like an oversize plug, charged 14 hours, for 6v, at just over 7v going in.

Like most packs, nimhs don't take overcharge well, and will " vent " on getting very hot, making the pack useless.

Stick to 1 tenth C, 220mah or there abouts for 10 hours. 

150 mah would work for 14 hours

 

Edited August 1, 2023 by Denis Watkins

[KenC]

Thanks Denis, how silly that the charger does not have a set program for these sort of batteries. It does have a  user battery program, so I shall start my own selection of parameters.  Just to set the store out for future behaviours. May I press upon your assistance to  table these  settings for my most likely uses. 

 

2200 Ah NmHI  6v  charge at 22mah as needed to achieve a terminal voltage of  ------------------   ( 7v) ?

5000 6S Lipo   50c   set to Lipo 6s  and if charging  for flight that day , charge to a maximum voltage of  ??????  at 5A 

When flying never allow the voltage to fall below ??????    Am I correct in thinking that 3.8v per cell is the safe upper limit  and therefore a total voltage of 22.8v ?.

[Frank Skilbeck]

Ken, youi want 220 ma for.a 1/10 C charge on 22ma, but for Nimh batteries when they are fully charged there is then a small voltage dip and this.what the.smart chargers look for, but 220 ma is basically a trickle charge anyway.

 

As for.the.lipos then.yes, but the minimum voltage will depend what load you put on them, 3.8v per cell off load is fine, but under load the voltage will drop below this well before the battery has run down any appreciable amount. On charge your smart charger will automatically restrict the voltage to 4.2v per.cell. It will charge at 5A and once the cells reach 4.2v start reducing the current the lipo being fully charged when the current gets to.0.1A. It's a good idea to balance charge the Lipo to keep the cells balanced.

Edited August 1, 2023 by Frank Skilbeck

[Denis Watkins]

Be aware of Volts Ken, but they are not the full story. A very healthy pack can still put out a lively volts reading while the remaining capacity can be grim.

Yes, check volts, but together with capacity.

 

Nimh and lipo are wildly different.

Nimh is 1.2v per cell, not 1.5v like a good dry cell, so where is your 6v coming from, unless you have 5 cell nimh?

Lipo, are near critical and approaching damage at 3v per cell and should aim to finish any load at 3.5v

MAX charge on a lipo is 4.2v per cell, and all reputable chargers stop charging at 4.2V.

You see where volts alone are not everything, you 6S must not exceed 25.2V and will never do so when using approved charger.

Importantly your lipo should hold 5000mah and that can be measured.

My 4.8V nimh holds 2200mah, and uses about 300mah after about 6 flights, no retracts or flaps by the way.

Measure how much you put back into your lipo for some idea of condition.

Repeat

Volts are not the whole story

 

 

Edited August 1, 2023 by Denis Watkins

[KenC]

Thanks Frank and Denis ,  I still am looking for a voltage per cell to maintain as my healthy maximum  for charging the Lipo , I understand that 4.2v per cell is the max and above that would cause damage, but I understood that to get maximum longevity one should never head for the safe maximum , rather aiming slightly below that . What voltage3 per cell would you suggest as a regular ceiling for this 6s  5000 battery ?

 

Oh and in answer to the question on the number of cells in the NmHI , both are 5 cell 2200 Ah .

 

Edited August 1, 2023 by KenC

[Frank Skilbeck]

Ken, no 4.2v per cell is fine, just don't store them at that voltage, fine the day before you go flying, but not for weeks. If you're not going to use them for a while set your charger to storage charge and it'll charge/discharge them suitable for long term storage.

[KenC]

Thanks Frank.