[Elecraft] KX3 Smarter Charger

Wed Jan 30 16:30:25 EST 2013

Good statement, Chip.  Right on the mark.

For quite a while now (since inception?), Elecraft's design philosophy has been to make their products "bulletproof".  That's not the same as being perfect, but there is also heavy emphasis on best value per dollar spent.  This is a close approximation to perfection for "value markets".  At the same time, even in higher end markets, Elecraft products are feature-wise highly competitive.

The 200 mA charge rate is a good example of bulletproofness.  At this rate, there is very little that can go wrong, even if one or more cells is defective or even just beyond its service lifetime, or if the op overcharges the cells.  Since Elecraft can't control the characteristics or histories of the cells an op puts in his/her KX3, this approach is probably the best compromise in pure design terms.  Sure, there will be some users that see a 12 or 16 hour full charge cycle as being unacceptable.  But at the same time, their charging solution just works, keeps support and warranty (and customer dissatisfaction) issues at bay, and meets the requirements (charging the batteries).

As Chip said, the electronics is packed pretty tightly in a KX3.  You wouldn't want an inadvertent defective cell [at $5 to $10] to damage $1500 worth of radio, especially by heating or fire.

In consumer electronics (where I work), our products have charging requirements that are remarkably similar to Elecraft's with the KX3.  Certainly we have mishaps, and some of them can be pretty spectacular in fact, but these are all due to manufacturing defects, not a defective design.

Just my $0.02 worth.

Matt Zilmer

-----Original Message-----
From: elecraft-bounces at mailman.qth.net [mailto:elecraft-bounces at mailman.qth.net] On Behalf Of Chip Stratton
Sent: Wednesday, January 30, 2013 11:55 AM
Cc: Elecraft List
Subject: Re: [Elecraft] KX3 Smarter Charger

Smart chargers for Nimh rely on the cell to show a certain percentage of voltage drop when full charge is attained - around 10 mV per cell. This occurs most reliably at fairly high charge currents. With 8 cells in series, that voltage drop can easily be masked by what is happening in other cells, such that while some cells are still charging, others may be getting seriously overcharged to their detriment.

This type of charging also requires a constant current charge to allow detection of voltage depression. Constant current supplies use switching regulators - so more noise in the shack.

Additionally, as Nimh cells age, that voltage depression becomes less pronounced. I've had even good quality smart chargers miss end of charge even when only a single cell is involved.

Then you have to keep in mind that these cells are very close to some expensive high density electronics. I think rupture or outgassing of Nimh cells is rare, but I wouldn't want to chance it. It seems Elecraft's more conservative approach is wiser.

Chip
AE5KA

On Wed, Jan 30, 2013 at 1:30 PM, Walter Underwood <wunder at wunderwood.org>wrote:

> I can think of one reason to avoid charging every time external power 
> is applied -- external batteries. If you are running from 14V LiFePo 
> batteries on the trail, you don't want to charge the internal NiMH 
> batteries at the same time.
>
> wunder, K6WRU
>
> On Jan 30, 2013, at 11:22 AM, Rich Heineck wrote:
>
> > During charge at 200mA, the NiMH batteries can typically reach 1.5V
> each, for 12V total.  Add in the extra voltage for path resistance, 
> isolation diode, and charging regulator overhead, you get up over 
> 13.5V, which is why the recommended voltage is 13.8V.  Charging at 
> lower supply voltages would have required a switching boost regulator 
> which then gets into problems of space, RFI, and cost.  It is possible 
> to put some charge into a depleted set of batteries from a lower 
> supply voltage but they just won't be able to get fully charged.
> >
> > Because the battery holders will hold any kind of AA cell, we opted 
> > for
> safety and charge reliability when it came to selection of how the 
> charger operates.  With 8 NiMH cells in series, the influence of 
> things like temperature, cell condition, and other factors make 
> automatic detection of full charge at moderate charging currents 
> unreliable.  A timed charge may not be elegant, but it's the approach 
> recommended by the major battery manufacturers when not doing a fast, 
> smart charge.  And the latter requires much higher current and was 
> just not feasible in the KX3 due to safety, power requirements, heat, RFI, and a few other things.
> >
> > Hopefully this helps explain a bit why the charger operates as it does.
> >
> > 73,
> > Rich  AC7MA
> >
> >
> >
> >
> > On 01/30/2013 10:33 AM, Alan Davenport wrote:
> >> Your questions are valid. I asked the same ones myself. I'm also
> disappointed in the charger. I also found that it is very fussy about 
> input voltage. I run my 12v rigs in my shack off deep cycle marine 
> batteries which I keep topped off with a high end marine smart charger 
> (ironic!) When the smart charger shuts down because the batteries are 
> topped off the charger in the KX3 refuses to charge its batteries 
> while stating "input voltage too low". There is nothing wrong with my 
> shack batteries. This issue (input voltage too low) occurred even when 
> the shack batteries were brand new. (I had replaced them all just 
> prior to hurricane Sandy.)
> >>  I'm sorry Elecraft. All your other gear it a grand slam home run. 
> >> This
> charger is just a bloop single.
> >>  73 de Al, W2GZN
> >>
> >> ________________________________
> >>  From: "kissov at me.com" <kissov at me.com>
> >> To: elecraft at mailman.qth.net
> >> Sent: Tuesday, January 29, 2013 5:53 PM
> >> Subject: [Elecraft] KX3 Smarter Charger
> >>   I don't claim to know about battery charging but why can't the
> charger stop when the batteries get to "X" volts and start charging 
> when the total battery voltage drops below "Y" volts, would this 
> feedback system add to the cost of the charger.  I bought a "smart 
> charger" at Harbor Freight for $5.99 the red light goes green when the 
> batteries ( 4 NiMH) are fully charged and when you put depleted 
> batteries in it it blinks red. Why can't the charger in the KX3 be 
> totally transparent? load and forget.  I found the whole charging 
> instructions confusing after an initial 16 hour charge do I 
> occasionally give it a 4 hour charge or what ? do I want a lot of hot batteries in there?
> >>
> >> K6CG
> >> ______________________________________________________________
> >> Elecraft mailing list
> >> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> >> Help: http://mailman.qth.net/mmfaq.htm
> >> Post: mailto:Elecraft at mailman.qth.net
> >>
> >> This list hosted by: http://www.qsl.net Please help support this 
> >> email list: http://www.qsl.net/donate.html 
> >> ______________________________________________________________
> >> Elecraft mailing list
> >> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> >> Help: http://mailman.qth.net/mmfaq.htm
> >> Post: mailto:Elecraft at mailman.qth.net
> >>
> >> This list hosted by: http://www.qsl.net Please help support this 
> >> email list: http://www.qsl.net/donate.html
> >>
> >
> > ______________________________________________________________
> > Elecraft mailing list
> > Home: http://mailman.qth.net/mailman/listinfo/elecraft
> > Help: http://mailman.qth.net/mmfaq.htm
> > Post: mailto:Elecraft at mailman.qth.net
> >
> > This list hosted by: http://www.qsl.net Please help support this 
> > email list: http://www.qsl.net/donate.html
>
> --
> Walter Underwood
> wunder at wunderwood.org
>
>
>
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:Elecraft at mailman.qth.net
>
> This list hosted by: http://www.qsl.net Please help support this email 
> list: http://www.qsl.net/donate.html
>
______________________________________________________________
Elecraft mailing list
Home: http://mailman.qth.net/mailman/listinfo/elecraft
Help: http://mailman.qth.net/mmfaq.htm
Post: mailto:Elecraft at mailman.qth.net

This list hosted by: http://www.qsl.net
Please help support this email list: http://www.qsl.net/donate.html