Saturday, December 5, 2009

how to tell a smart from a dumb charger

How to tell if it is a dumb or smart nimh battery charger. But keep in mind, assume all chargers are dumb unless proven otherwise!

1. RTFM!!!! Yes believe it or not, reading the frigging manual or even the frigging box can tell you. If you havent bought it yet, just go to the manufacturer's website and see the specs or even download the PDF manual. There may be certain code words like

1.a. negative delta V, sometimes abbreviated as

- [triangle]V

  The triangle means delta or change in. Delta is used by scientists as a shorthand for "change in". The dash is a negative sign. V = voltage. So that means when a nimh battery is full the voltage it emits slightly drops (hence the negative delta). This is the signal for the charger to either stop charging or go to trickle charge mode.

update: sometimes instead of - delta V, the phrase used is "charging control method: Peak detection" or similar. Conversely, if under the charging control method, the value is something like "timer" or "nil" then its dumb.

1.b. timer. If the word "timer" or "timer shut off" is written and there are no other indicators, most likely it is dumb. A smart charger turns of or goes into trickle charge mode when the battery is full, thats the definition of a smart charger. A timer dumb charger automatically turns off after XX hours have passed, usually 12 hours, no matter what. This is just a safety measure to avoid wasting electricity and super overcharging (thats bad) the batteries if you left the charger plugged in and went on vacation or something. If on the other hand, it has "timer" and other indicators like # 1.a. then its smart.

1.c. look for charging tables. If there is a table that so and so MAH battery takes so and so hours to charge, be very careful because real men dont compute, they just plug in the charger and the smart charger takes care of stopping the charging.

1.d. the dont ask, dont tell policy. If the packaging or the manual says NOTHING about it being either smart or dumb, then assume its ghey ... este ... assume its dumb. So for every charger, assume its dumb unless the instructions say so

2. test it yourself. a smart charger will detect if the battery is full and stop. This is easier if the charger has individual charging channels. Get one half full and one drained  battery and see if the half full batt stops charging sooner than the almost empty batt. This is the main disadvantage of the powerbase 4AA smart charger versus unomat chart charger. The unomat has 1 channel per battery, the powerbase 4aa has 1 channel per 2 batteries but the powerbase 2AA has one channel per battery

2.a. charge 1 almost full battery and one empty battery and measure the time needed to full charge or for the charger to stop charging. Obviously the empty  battery will take longer to charge

2.b. charge an empty battery, measure the time it takes. unplug charger and remove battery. Wait several min for it to go to room temp. Charge it again and measure the time. This should take only a few minutes.

3. Price of the charger minus the price of the included batteries. If its cheap, most probably its dumb. the going price for 1 eneloop AA is 150+ pesos so minus the cost of the batteries from the total cost to get the price of the charger. A powerbase 2AA smart charger is probably 600 pesos, 900+ for powerbase 4AA and unomat 4AA costs 1000 pesos but it has individual charging channels so there is no reason to buy the 4AA powerbase. The powerbase and unomat chargers i mentioned come with AA/AAA nimh batteries. Since they are not LSD-nimh batteries, they are low cost so minusing their value from the total price of the charger still gives you a decent price. I've seen dumb chargers go for 100-300 pesos without batteries.

UPDATE: this is what the symbol for delta V looks like. Although usually the triangle is not smaller than the V

UPDATE: #2b or
2.b. charge an empty battery, measure the time it takes. unplug charger and remove battery. Wait several min for it to go to room temp. Charge it again and measure the time. This should take only a few minutes.
Seems to not always work. I've had reports of powerbase chargers failing just this one test. Must be a design flaw or something


Saree said...

Where could I possibly buy the Unomat charger that comes with niMH batteries that you mentioned? Thanks for this post!! I am also curious if a SANYO charger would be enough.

Vince said...

the unomat seems to be out of stock in the Electronics botique branches I checked. It might not be available anymore. A sanyo charger will be OK if its really one of the smart models offered by sanyo

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