AA Ni-MH battery charger output current mA - Page 1
Forum section: electronics / beginners

author: jayboydog
author_rank: Newbie
timestamp: April 23, 2018, 01:37:07 am
content: Thinking about different cheap AA Ni-MH 1.2v battery chargers. two look identical. both have 120v AC input. different brands yet both have label reads "200mA x 4". I measure current mA by opening the circuit with a piece of paper between charger and battery then close the circuit with meter probes adjacent to each side of the paper, but each outputs different mA to each battery depending on 1,2,3,4 batteries charging at same time.#A120mA 90mA 72mA 60mA,#B60mA 60mA 60mA 60mA.what is "200mA x 4" supposed to mean?A third charger is called "smarter". will charge 1,2,3 or 4 batteries at same time. I do not get a mA output as whichever individual channel I am in series to measure mA causes "error" on the charger display for that channel. the other batteries continue charging. why is the meter measuring mA in series with a battery causing "error"?

author: dacman
author_rank: Frequent Contributor
timestamp: April 23, 2018, 02:08:37 am
content: "Smart" chargers can usually charge both NiCad and NiMH. They take measurements on the batteries, they do not just source current. Placing the leads in series would not be something the charger would understand.

author: Audioguru
author_rank: Super Contributor
timestamp: April 23, 2018, 03:26:33 am
content: Your meter measures current by connecting a resistor in series and measuring the voltage across the resistor. A smart charger sees the battery with too much resistance in it and shows an error.

author: IanB
author_rank: Super Contributor
timestamp: April 23, 2018, 03:46:26 am
content: Quote from: jayboydog on April 23, 2018, 01:37:07 amWhatever the marketing people want it to meanA more useful number to look at is how many hours it should take to charge a typical battery. If the charger is really charging at 60 mA then a typical 2000 mAh battery would take about 36 hours to charge, which is silly. Nobody would wait that long.Make and model number of the chargers would be helpful.

author: Circlotron
author_rank: Super Contributor
timestamp: April 23, 2018, 04:14:55 am
content: Quote from: IanB on April 23, 2018, 03:46:26 am

author: paulca
author_rank: Super Contributor
timestamp: April 23, 2018, 06:45:48 am
content: The 200mA will be peak current. It is only likely to deliver anything like this when the batteries are virtually flat. As they charge their resistance changes and the current falls away.NiMhs are notoriously hard to charge correctly. So most cheap chargers just back off the current quickly and effectively trickle charge them from 75% or so, meaning they can be just left on overnight or for a whole day without overcharging them. By the time the batteries are full the charging is only putting in the power which is being dissipated as heat.The smart charger will push current into the battery for a period of time, then it will pause and watch the voltage which will relax back a bit. They keep repeating this looking for a specific drop in voltage. I can't remember if the delta-v happens when current is flowing or when it's removed. However the delta-V is very small and hard to spot, I've never had a NiMh charger which gets it right, so I typically rapid charge them on a timer then switch to trickle charge.

author: jayboydog
author_rank: Newbie
timestamp: April 23, 2018, 08:07:26 am
content: thank you for the responses. My AA Ni-MH 2500mAh 1.2v batteries could not power my radio scanner using 4 x AA when each battery's no load voltage dropped to 1.24 - 1.3v.I inserted two batteries into a charger which outputs 90mA to each and two batteries into a charger which outputs 60mA to each. at 4 hours of charging, the batteries no load voltage measured 1.35 - 1.37v. at 8 hours of charging, no load voltage measured 1.38 - 1.39mA. at 10 hours of charging the no load voltages were 1.4 1.4 1.37 1.37v.what charging is needed to increase the no load voltage measure from 1.24 to 1.4v ?I read statements such as "a 2400mAh battery being charged with 100mA will require 28.8 hours to recharge." (1.2 x mAh/mA). but how does such a calculation take into account the battery's voltage when starting the recharge? is a different mA x time charging required to raise the battery's voltage from 1.25 to 1.3v from raising the voltage from 1.3 to 1.35v?

author: paulca
author_rank: Super Contributor
timestamp: April 23, 2018, 08:55:45 am
content: If you want peace of mind, just plug them into the charger and leave them for a full day to charge.If that is too long then you'll need to invest in a much more expense (or cheap and dangerous) fast charger.