VIPOW batteries!

[transistor495]

I just bought 4pieces of VIPOW rechargeable 2700mAh NiMH AA batteries. The battery spec.s says that it allows fast charge of 2.4hrs at 2700mA current. Is it safe?
Other spec.s written are:
5hrs at 810mA
15-16hrs at 270mA(standard charge)

I'm using a Camelion charger that outputs 2.8v at 150mA for two series batteries and the charger spec.s says that it takes approx 21.5hrs for charging 2300mAh battery. So I assume my batteries will take around 25hrs for charging fully. Is this correct or not I just wanted to make sure.

And finally, NiMH's are not affected by overcharging right?

 

[transistor495]

So nobody knows about VIPOW batteries

 

[kssoin]

Hi Transistor495,
Fast charge is generally a one hour charge. For ex 2800mAH Battery can be charged at 2800mA (2.8Amps) for one hour. Standard slow charge is a ten hour charge ie at 280 mA. No fear at this rate but at fast charge of 1XC no more than i hour. I hope it helps.
BTW I am going to make a charger for my tool baterry packs using Max 713 IC. I bought one in delhi today for Rs 300

Karanbir

 

[audioguru]

You must NEVER over-charge a Ni-MH battery cell. When your battery charger IC detects a full charge then it should turn off or reduce the charging current to a 1/40C trickle charge current that is 70mA for your battery cells.

Your charger might over-charge the cells a little. Maybe its current is 150mA when the cells are half-dead then its current reduces as the cells' voltages rise.

 

[Sceadwian]

If you're really worried about over charging one simple way to help prevent it (as long as it's not a delta T charger) is to put heatsinks around the battery and supply a good air flow. Overcharging a NiMH is bad but what actually does it is the overheating that happens when the battery becomes full. Active cooling of the batteries during charging, especially fast charging will extend their life.

There are commercial chargers available at typical electronics stores which will do 15 minute charges on NIMH batteries, this however will result in much shorter battery life.

 

[transistor495]

Excellent!..Superb!!...Fantabulous!!!

The performance of my batteries is truly unbelievable! I've attested the fact that is written on the battery pack -1 VIPOW battery replaces 1000 alkaline batteries. My previous 700mAh NiCd cells lasted only 4hour on my high current drain application. Now these new batteries charge level still on top after 15+hours. Actually I'm waiting for them to become dead and go for the next charging

Thank you AG, Sceadwian for the replies. My charger doesn't have any full charge indicator and I think it continuously outputs 150mA of current. As the charger spec.s says it takes 21.5hrs for 2300mAh battery, so I've applied 25hrs and seems ok. You know 150mA is even far below the standard charge current specified by the battery(15hrs at 270mA it is!). So I think 25hrs hasn't made any overcharging issues.

Soon I'll go for a automated charger to save my batteries

One more question: If I'm leaving the NiMH batteries idle for a long period, which is the safest condition -discharged/half charged/ or full charged?

 

[audioguru]

New (for about one year) Energizer and Sanyo Ni-MH cells hold a charge for many months. They come "pre-charged".
Old Ni-MH cells lose their charge in about 1 month.

Cheap Chinese solar garden lights still come with old-fashioned and toxic Ni-Cad cells that fail in about 1 year.

 

[Sceadwian]

If you don't want to get an automated charger and you know the charge state of your batteries just buy one of those timer modules. I have one for my sons RC battery pack which is a stupid wall wart charger, I just set it to charge for 8 hours and after the pack is full I set it up to charge for 15 minutes every 6 hours to keep it topped off for when it's needed. those are Nicads though if you have good sells you may only want to set it up to charge for 15 minutes once a day.

 

[transistor495]

New Sony cells advertises that they holds their 85% of charge even after 1year. What the other cells do regarding this, I dunno.

Sceadwian, I'll have a look at those timer modules. This 25hrs is too long, so it'll be good if I can make an overnight charging of 16hrs at 270mA with a timer cut-off set-up. Let me see.

 

[audioguru]

Energizer and Sanyo also have new Ni-MH cells that hold their charge for a long time. They are sold "pre-charged".
Also they can be charged and discharged many more times than older cells.

I have a cheap Energizer charger for Ni-MH AA cells . It charges at 500mA for 6 hours. It has a 6 hours timer.
If it tries to charge cells that are not completely dead then it over-charges and cooks them.
If it tries to charge cells with a lower capacity than 2500mAh then it also over-charges and cooks them.

 

[Sceadwian]

Sound like a very stupid charge audioguru. The night thing about fast charging batteries is the dip when a NIMH reaches full charge is much more obvious, but it would have to be bellow 80% charge if not 70% when you started or as you said... bad things happen. Personally I think all chargers like that should have temperature monitors, Watching for temperature peaks is almost better than voltage for detecting a fully charged pack, and the heat when you're overcharging is what actually does the damage.

 

[transistor495]

I cannot understand how reliable is the temperature detection on the batteries kept in a charger unit. While charging in progress, the charger itself gets hot and transfer the heat to the batteries through connectors

My batteries covered 25+hrs of successful operational time and still continues the show..I should have bought these batteries earlier

 

[Sceadwian]

The charger base would need to be designed for it, it's relatively reliable. Fed a steady current at a known temperature a batteries temperature will jump when it's reached it's full charge state.

 

[audioguru]

Ni-Cad cells get cooler when they are charging and Ni-MH cells get warm. They both get hot when being over-charged.

 

[Sceadwian]

Cooler, really? Didn't know charging a NiCad was an endothermic reaction. I think the main point is to detect over charging. Brief period of over charging are safe for battery chemistry, the higher the sensitivity of the thermal sensing the less damage would be done though. Mind you the batteries woudl have to be rested after discharge to allow them to reach ambient temperature before charging or it doesn't work.

 

[transistor495]

I'm thinking about NiCad application extension upto atmospheric coolers and memory modules

 

[Sceadwian]

Any energy they absorb has to be taken back out of them, at much less than idea efficiency.