Re: (ET) Multi-bank 12V chargers

["David Roden" <etpost drmm net>]

On 19 May 2017 at 14:10, Ken Olum wrote:

> It may be that Minn-Kota has some more complex algorithm, such as
> waiting for the rate of decrease of the current to fall below some
> level.  

If I'm not mistaken, Lester Electrical patented their DV/DT algorithm.  I 
don't know about its twin brother, DI/DT (what you're describing).  And 
the 
patent may have expired by now.

For an ET with golf car batteries, you could do a lot worse than a used 
Lestronic or Lestronic II golf car charger.  They're just about 
bulletproof. 
They do tend to overcharge a bit, however.

One nice thing about DV/DT and DI/DT is that they automatically deal with 
the lower peak on-charge voltage as batteries age.  

Setting the voltage threshold for an IU algorithm is a balancing act.  Too 
low, and it undercharges new batteries.  Too high, and it overcharges old 
ones and may never get out of bulk phase.  (Maybe GE had the right idea 
with 
their age-calibrated timer after all, eh?)

Some more sophisticated IU chargers have watchdog timers that end the bulk 
phase (or the charge) if it runs too long, or delivers too many amp-hours. 
 
Using a charger that's too small or too large for the battery can muzzle 
the 
watchdog, though. 

Another method of preventing overcharging is to monitor battery 
temperature 
rise.  That requires at least one temperature sensor in the battery pack. 

Ideally, any watchdog should set an error flag and warn the user.

Charging batteries isn't as easy as it looks, and the more sophisticated 
the 
battery, the harder it is.  That's why commodity rechargeable consumer 
appliances have such crummy battery life.  Chargers are one of the first 
places the bean-counters look to cut costs, since the effects on battery 
cycle life don't show up right away (ideally, about a month past warranty 
expiration).

Also, exaggerating a bit, proprietary replacement batteries are to 
rechargeable appliances as ink carts are to inkjet printers.

(Canon MG2522 scanner/printer with "starter" ink carts: $29.98)
(Canon 245 & 246 ink cart set for MG2522 scanner/printer: $39.99)


David Roden - Akron, Ohio, USA

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