NiMH batteries

Reply

  #1  
Old 12-12-08, 01:27 PM
Gunguy45's Avatar
Super Moderator
Thread Starter
Join Date: Dec 2007
Location: USA
Posts: 21,119
Received 2 Votes on 2 Posts
NiMH batteries

Ok, figured here was as good as anywhere else. Seem to remember there were a couple of folks around who have really studied batteries (I hope).

I have NiMH AA batteries for cameras and such. Better to recharge as soon as they don't operate the electronic device anymore, or drain them more using another item, like an LED flashlight or similar?

I know they say, use the cordless tool NiCads until they don't function, then let them cool, then recharge. But those are more motors than electronics. I know I can take the ones that won't run a saw or drill and use them in a flashlight for hours more.


BTW..I'm using the Bunny brand and one of their better chargers.

If a Mod knows a better forum, please move it over there for me?
 
Sponsored Links
  #2  
Old 12-12-08, 02:16 PM
Member
Join Date: Sep 2008
Location: northest U.S.
Posts: 158
Received 0 Votes on 0 Posts
according to theory nicad batteries have memory and need to be used up and then recharged,if you use one for a short period and then recharge it,it will think that it only need to be used that period of time and adjust power usage to that time,on the NiMH batteries they dont have a memory and it is best to recharge them fully after you use them and you can keep them in the charger....but chargers produce heat and heat shortens battery life reguardless of composition.
I hope this helped
 
  #3  
Old 12-12-08, 04:24 PM
Member
Join Date: Nov 2006
Location: Erie, PA
Posts: 305
Received 0 Votes on 0 Posts
Originally Posted by Gunguy45 View Post
I know they say, use the cordless tool NiCads until they don't function, then let them cool, then recharge. But those are more motors than electronics. I know I can take the ones that won't run a saw or drill and use them in a flashlight for hours more.
Actually, I've been told that with tools you are supposed to use them until the performance degrades. Supposedly if you use it until it stops working, you can revers charges or something goofy.
 
  #4  
Old 12-12-08, 04:39 PM
Gunguy45's Avatar
Super Moderator
Thread Starter
Join Date: Dec 2007
Location: USA
Posts: 21,119
Received 2 Votes on 2 Posts
Well...I mean't until the drill won't drill well or the saw doesn't saw well. I sorta mis-stated it.

Keep the opinions coming...Thanks!!
 
  #5  
Old 12-12-08, 05:09 PM
mango man's Avatar
Member
Join Date: May 2004
Location: Sw FL
Posts: 2,122
Received 0 Votes on 0 Posts
I came accross this intersing site on Battery technology the other day

Do and don't battery table

<table border="1" cellpadding="4" cellspacing="0" width="100%"><tbody><tr align="left" valign="top"><td>
</td><td>Nickel-cadmium
(NiCd)
</td><td>Nickel-metal-hydride (NiMH)</td><td>Lithium-ion
(Li-ion)
</td><td>Lead-acid
(Sealed or flooded)
</td></tr> <tr align="left" valign="top"> <td>Used in</td><td>Two-way radios, power tools, medical.</td><td>Similar application as NiCd; higher density.
</td><td>Cell phones, laptops, video cameras.</td><td>Motorcycles, cars, wheelchairs, UPS.</td></tr> <tr align="left" valign="top"> <td>Charging</td><td>Do run the battery fully down once per month; try to use up all energy before charging.

Do not leave battery in charger for more than 2 days because of memory.

Avoid getting battery too hot during charge.

Charge methods: Constant current, followed by trickle charge when full. Fast-charge preferred over slow charge.
Slow charge = 16h
Rapid charge = 3h
Fast charge = 1h+
</td><td>Do run the battery fully down once every 3 months. Over-cycling is not advised.

Do not leave battery in charger for more than 2 days because of memory.

Avoid getting battery too hot during charge.


Charge methods:
Constant current, followed by trickle charge when full. Slow charge not recommended.
Battery will get warm towards full charge.
Rapid charge = 3h
Fast charge = 1h+
</td><td>Do charge the battery often. The battery lasts longer with partial rather than full discharges.

Do not use if pack gets hot during charge. Check also charger.

Charge methods: Constant voltage to 4.20V/cell (typical). No trickle-charge when full. Li-ion may remain in the charger (no memory). Battery must remain cool. No fast-charge possible.

Rapid charge = 3h
</td><td>Do charge the battery immediately after use. Lead-acid must always be kept in a charged condition. The battery lasts longer with partial rather than full discharges. Over-cycling is not advised.

Charge methods: Constant voltage to 2.40/cell (typical), followed by float held at 2.25V/cell.
Battery must remain cool. Fast charge not possible; can remain on float charge.

Slow charge = 14h
Rapid charge = 10h[/SIZE]
</td></tr> <tr align="left" valign="top"> <td>Discharging</td><td>Full cycle does not harm NiCd.
NiCd is one of the most hardy and durable chemistries.
</td><td>Avoid too many full cycles because of wear. Use 80% depth-of-discharge.
NiMH has higher energy density than NiCd at the expense of shorter cycle life.
</td><td>Avoid full cycle because of wear. 80% depth-of-discharge recommended. Re- charge more often. Avoid full discharge. Low voltage may cut off safety circuit</td><td>Avoid full cycle because of wear. Use 80% depth-of-discharge. Recharge more often or use larger battery.
Low energy density limits lead-acid to wheeled applications
</td></tr></tbody></table>
 
  #6  
Old 12-13-08, 06:56 AM
Gunguy45's Avatar
Super Moderator
Thread Starter
Join Date: Dec 2007
Location: USA
Posts: 21,119
Received 2 Votes on 2 Posts
Excellent Mango....
I think I've been to that site before, but that chart is perfect.

Thanks a Bunch
Vic
 
  #7  
Old 12-13-08, 08:18 AM
Member
Join Date: Nov 2006
Location: Erie, PA
Posts: 305
Received 0 Votes on 0 Posts
I found the reason you shouldn't completely discharge tool battery packs:

Beware of completely discharging A SET OF BATTERIES, because you may encounter reverse voltage in the weakest batteries, which will do real harm to that battery cell.

Most NiCad and NiMh manufactures warn about mixing old and new batteries for that reason. That is especially true in many of the higher voltage power tools where a set of batteries may contain up to 15 individual batteries or cells.

Tool manufactures like DeWalt suggest people recharge batteries just after you notice they are starting to get weak to avoid this problem. They also say that even though they and most other tool manufactures make quick chargers, the best battery life can be achieved by topping off battery sets with at least a 4 hour slow charge, so that all the cells are as closely charged as possible.

As a note, most NiCad and NiMh battery curves are pretty sharp. Once you notice power is running out, you have little to gain by attempting to squeeze the last 5% out of you battery set and a lot to loose if it hurts a cell in the set.
 
Reply

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Thread Tools
Search this Thread
Display Modes
 
Ask a Question
Question Title:
Description:
Your question will be posted in: