Model Boat Mayhem - Forum

Please login or register.

Login with username, password and session length.
Pages: [1]   Go Down

Author Topic: Ni-MH Charging Problem  (Read 1309 times)

bigbilly

  • Shipmate
  • *
  • Offline Offline
  • Posts: 3
  • Model Boat Mayhem is Great!
  • Location: norfolk
Ni-MH Charging Problem
« on: April 05, 2015, 09:05:20 AM »

I am a complete novice to RC boats and as I suffer with old age in my finger joints decided to buy a RTR launch.
It came with one battery i.e. ProBoat 8.4V 1600mAh battery pack and a 12V car type charger.  After what I considered a reasonable charge time (12 hours on a power pack) I took the boat to my local boating pool where it only lasted a couple of minutes, if that.  I tried several times again but no luck.
On a visit to my local model shop I bought another battery pack and a mains charger but was told by the assistant that these batteries were notorious to get their first charge ???  Anyway after several attempts now I cannot get either battery fully charged.


Where am I going wrong in what should be a very simple operation ?


Many thanks


Bill
Logged

malcolmfrary

  • Full Mayhemer
  • *****
  • Offline Offline
  • Posts: 5,568
  • Location: Blackpool, Lancs, UK
Re: Ni-MH Charging Problem
« Reply #1 on: April 05, 2015, 09:29:26 AM »

A 12 volt car type charger for a 8.4 volt battery just sounds wrong unless the charger had current limiting built in.  If it didn't, after a short time on charge, it would probably have killed the battery.  This is guesswork, the only way to remove guesswork is by using a meter to get the actual voltages and currents involved, these days they are cheap enough.
Logged
"With the right tool, you can break anything" - Garfield

bigbilly

  • Shipmate
  • *
  • Offline Offline
  • Posts: 3
  • Model Boat Mayhem is Great!
  • Location: norfolk
Re: Ni-MH Charging Problem
« Reply #2 on: April 05, 2015, 10:14:33 AM »

Only one battery was ever charged with the 12V car charger that came with the set.  The other battery has only ever been charged with the mains charger that was recommended by the model shop.


Bill
Logged

Time Bandit

  • Full Mayhemer
  • *****
  • Offline Offline
  • Posts: 175
  • Model Boat Mayhem is Great!
  • Location: Deizisau, Germany
Re: Ni-MH Charging Problem
« Reply #3 on: April 05, 2015, 10:54:13 AM »

Ever thought about that the batteries were fully loaded and the motor consumes the 1600 mA in a few minutes  {-)

YouŽll need more capacity then whithout overloading the hull.
Logged
regards

Tobias

inertia

  • Guest
Re: Ni-MH Charging Problem
« Reply #4 on: April 05, 2015, 11:41:35 AM »

Bill

I suspect that by a '12v car-type charger' you mean one that has a plug which fits into the 12v lighter socket of your car and NOT one designed to charge a (full-size) car battery. It's not a good idea to use this type of fast charger for the first few charges of a new battery.

The "mains" (slow) charger is a better bet but you've not said what its output current(s) is e.g. 100mA. It should be marked clearly on the charger. You need to calculate how long a full charge should take with this beastie by dividing the battery capacity (1600maH) by the charger's output (e.g. 100mA) and then multiplying the answer by a factor of about 1.4. So if your charger does put out 100mA then the equation is (1600/100) x 1.4 = 22.4 hours. This will fully charge a pack from a value of 1.0v per cell, which can be considered as the minimum voltage to which the pack should be allowed to discharge. Any lower voltage runs the risk of damaging one or more of the cells in the pack.

NiMH packs will take three or four full charges before they reach maximum capacity. That said, Time Bandit may well be correct in that the motor is taking so much current from the battery that it's flat in just a few minutes. 1600maH is a very small-capacity battery by these days' standards; 5000maH is quite commonplace. You would need a special power-monitoring meter to measure just what sort of current the motor is drawing under load e.g. http://www.4-max.co.uk/wattmeter-budget.htm

The other thing to consider is that the battery packs may have been sitting around so long in stock that they have become fully discharged (by virtue of their own internal resistance) and are now beyond rescue. For that reason alone it's advisable to buy batteries from a supplier who sells a lot of them and so is constantly replacing his stock. These guys are recognised as one of the best suppliers in the UK http://www.componentshop.co.uk/

DM
Logged
Pages: [1]   Go Up