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From: firstname.lastname@example.org (Robert Richter)
Subject: Re: Difference between AC adapter and charger?
Date: 22 Oct 2002 19:32:24 -0700
References: <0001HW.B9D43FDF0325BBB11662EAD0@news.covad.net> <0001HW.B9D4EE870344BA681662EAD0@news.covad.net> <3DB01FBB.EAF744F9@usa.net> <0001HW.B9D572FB034E39101662EAD0@news.covad.net> <3DB02E27.email@example.com> <3DB40DB6.5234BEFC@usa.net>
NNTP-Posting-Date: 23 Oct 2002 02:32:24 GMT
w_tom wrote in message news:<3DB40DB6.5234BEFC@usa.net>...
> Many rechargeable appliances such as 'snap on the wall'
> flashlights and dust busters apply a constant DC voltage to
> charge and maintain NiCds. Same can be installed in any
> portable radio or other appliance with an adaptor of proper
> voltage. Always ignore those who must insult others and then
> claim manufacturers say something else. Phil Allison must
> insult when he cannot logically prove his point.
> NiCds can be charged by a constant voltage as manufacturer's
> voltage vs time curves demonstrate. As Phil notes, NiCds get
> warm when they are being overcharged. Heat is how some fast
> NiCd chargers determine when to stop applying excessive
> voltage created by a high current mode power supply. But the
> recharge circuit used so universally for generations never
> applies overvoltage to put a NiCd into that 'warm' region on
> the voltage curve. Same to recharge a NiCd inside the
> appliance. Slow NiCd chargers simply use a constant voltage -
> no problem.
> If recharge voltage is excessive, then NiCds simply no
> longer hold a charge. No danger. Just damaged batteries. If
> the recharge voltage is OK, then, like that 20 year old
> rechargeable flashlight, three NiCds still work just fine,
> whenever needed, for about 4+ years now. Previous batteries
> worked just fine, for over ten years, with application of a
> constant voltage to maintain charge.
> This is a VersaPak portable electric drill. It also uses a
> simple constant voltage to recharge the NiCds - circuit so
> standard even in 1960 NiCd battery chargers. This recharger
> is a constant voltage through a .27 ohm resistor that can
> apply up to 150 ma to a discharged Versapak 7.5 volt NiCd.
> Phil also makes wild assumptions that all wall warts are
> unregulated DC power supplies. Appliance typically are
> powered by a regulated supply wall wart which is cheaper than
> installing power supply circuits inside the appliance.
> Regulated supply wall warts are also less expensive since the
> current limiting circuit is easier inside the wall wart. All
> wall warts, contrary to Phil, must have current limiting
> circuits to obtain a UL rating. But then Phil make wild
> assumptions to justify his insults.
> NiCds were always recharged by a constant voltage power
> supply using a wall wart such as this VersaPak NiCd recharger
> model number VP130. Phil Allison's insults contradict what is
> inside so many NiCd chargers.
> Phil Allison wrote:
> > ** Please ignore the above- it was written by a demeted person.
> > All Ni-Cd makers warn against attempting to use constant voltage
> > charging with their cells - it is dangerous and it does not work. Ni-Cds
> > and lead acid cells are very different.
> > If you apply a fixed voltage equal to the final charged voltage to a
> > discharged Ni-Cd pack then a very large current will flow - this will burn
> > out the charger. Current limiting is essential and the average wall wart has
> > no such thing.
> > As Ni-Cds charge with a constant current their voltage rises and
> > eventually goes through a peak and then falls as they get warm - this is
> > how you know they are fully charged.
> > A fixed voltage, with the addition of a safe current limit to protect
> > the charger, of less value than the previously established peak could be
> > applied and the cell/s would be partly charged - but only partly and that is
> > the problem.
> > If the applied fixed voltage ( still with a safe current limit ) were
> > equal to the peak voltage then the cells will be overcharged and likely
> > damaged.
> > Recommending a standard DC wall wart (unregulated?) with added diode
> > as a Ni-Cd charger is Gung Ho at best.
> > . ... . . . . . . . . ............. Phil
I urge you to look closer again. These
flash-light/dustbuster/radio/cordless phone/etc. chargers either have
solid state electronics that you probably would not understand that
controls the charging (no insult intended; simple meaning elaborate
"smart" charging), or they have a RESISTOR! The voltage is enough
higher than the battery pack (before the resistor) that if a cell goes
from 1.2 to 1.1V (which over-charged NiCd's will do), the current
through the resistor will not be affected much and will still be quite
Even in a device that can run indefinitely on wall-wart power and also
charges the battery with a cheap charging circuit, I suspect the
battery is connected to the load through a diode and a resistor
charges the battery; I seriously doubt that anyone would ever sell a
device with NiCd's connected directly across a DC power supply.
Sealed lead acid--yes, you can do this with SLA's, but not NiCd's.
Not all battery chemistries behave the same.
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