What is the trick to replacing rechargeable batteries please

[Rich Webb]

On Mon, 22 Feb 2010 16:03:35 +0000 (GMT), "Dave Plowman (News)"
<dave@davenoise.co.uk> wrote:

In article <Xns9D2750FC21D9Ajyaniklocalnetcom@216.168.3.44>,
Jim Yanik <jyanik@abuse.gov> wrote:
Yes,those slow chargers don't have any sort of charge sensing. they're
just transformers,rectifier and current limit resistor,if the XFMR
doesn't limit on it's own. So,you have no idea of charge time,it's just
a guess.

I'd hope not. A proper slow charger works at constant current.

Like this puppy, with selectable constant-current rates:
<http://www.amazon.com/Crosse-Technology-BC-700-Battery-Charger/dp/B000RSOV50/ref=pd_sxp_f_pt>

I also like it because it charges individual cells, not pairs.

--
Rich Webb Norfolk, VA

 

[Dave Plowman (News)]

In article <Xns9D2750FC21D9Ajyaniklocalnetcom@216.168.3.44>,
Jim Yanik <jyanik@abuse.gov> wrote:

Yes,those slow chargers don't have any sort of charge sensing. they're
just transformers,rectifier and current limit resistor,if the XFMR
doesn't limit on it's own. So,you have no idea of charge time,it's just
a guess.

I'd hope not. A proper slow charger works at constant current.

IMO,rechargeables last much longer with a fast charger.

Not my experience at all. I used a slow charger with a timer for most -
and usually got the stated number of cycles before failure. Although this
was mainly with Ni-Cads which were discharged to the point where the
performance dropped off.

--
*Eat well, stay fit, die anyway

Dave Plowman dave@davenoise.co.uk London SW
To e-mail, change noise into sound.

 

[Dave Platt]

This might explain it better:
http://www.powerstream.com/NiMH.htm

I'm not sure all the information at this site is correct. The
statement that voltage drop should not be used is questionable. The
Microsoft charger used both delta V and either T or delta T (I don't
remember) to terminate charge.

My understanding is that NiMH cells do exhibit a voltage drop after
they're fully charged, just as NiCd cells do. However, with NiMH
cells you don't see an appreciable drop in voltage until after the
cells have already gone into over-charge... and NiMH cells really
don't like being overcharged. If you charge until the voltage drops,
you're likely to overstress the cells and seriously shorten their life.

If you're going to use a voltage-based shutoff with NiMH cells, I
understand it's better to use an earlier-cutoff technique - one which
"notices" that the cell voltage has ceased to rise with time (a "zero
delta V" detect, rather than a "negative delta V").

The good NiMH fast-chargers I've seen, seem to use a three-level
strategy for charge shutoff:

- Temperature sensing, T or delta T (primary)
- Zero delta V (secondary)
- Timer (failsafe tertiary)

The first two tend to work better with a relatively fast charge rate,
as the temperature rise and voltage inflections are more easily
detectable.

--
Dave Platt <dplatt@radagast.org> AE6EO
Friends of Jade Warrior home page: http://www.radagast.org/jade-warrior
I do _not_ wish to receive unsolicited commercial email, and I will
boycott any company which has the gall to send me such ads!

 

[GregS]

In article <hlu152$dfh$1@news.eternal-september.org>, "William Sommerwerck" <grizzledgeezer@comcast.net> wrote:

IMO, rechargeables last much longer with a fast charger.

That might be true. One of the non-professional Web reviews of NiMH chargers
revealed that there was significant difference among them in how much they
heated the cell.

It all depends on the charger. NOT all fast chargers work properly.
I see some make too many charge cycles, and some keep
the battery warm even when done. My old Panasonic cell phone
made the lithium battery expand to twice as thick.
My Maha C7800 charger does NiMh is one hour and they
barely get warm.


greg

 

[William Sommerwerck]

My understanding is that NiMH cells do exhibit a voltage drop after
they're fully charged, just as NiCd cells do. However, with NiMH
cells you don't see an appreciable drop in voltage until after the
cells have already gone into over-charge... and NiMH cells really
don't like being overcharged. If you charge until the voltage drops,
you're likely to overstress the cells and seriously shorten their life.

That is not my understanding. Rather, the harder the charge, the greater the
voltage drop.

- Temperature sensing, T or delta T (primary)
- Zero delta V (secondary)
- Timer (failsafe tertiary)

The first two tend to work better with a relatively fast charge rate,
as the temperature rise and voltage inflections are more easily
detectable.

Which is my understanding, as well.

 

[mike]

William Sommerwerck wrote:

A company (Fortune 500 at the time) I used to work for would raise
their parts prices as the product that the parts went into got closer
to the end of support period.
I was told this was to "encourage" customers to buy a newer instrument
by raising the cost of repairs.

It didn't matter that the parts were "in current production".

Hardly surprising. I could tell you some stories about my dealings with
Sony, but I won't. Suffice it to say that I made friends with the parts
honcha, who was occasionally able to help me a bit. Though her job was
eliminated, we still talk occasionally.

In "encouraging" customers to buy new products -- rather than repairing the
old -- businesses contribute to waste and pollution.


That works because waste and pollution leads to greater corporate profits.