Re: (ET) Multi-bank 12V chargers

["David Roden" <etpost drmm net>]

On 19 May 2017 at 12:19, Ken Olum wrote:

> In the absorption phase, the charger (on the AGM setting) holds a
> constant voltage of 14.4V and the current slowly drops as the battery
> finishes charging.  Then at some point it decides it is done, goes to
> 13.2V float for 24 hours, and then shuts off.  Presumably it decides
> the absorption phase is done because the current has dropped to some
> level, and this level seems to be somewhat below 1A. 

A typical IU(I) profile for a 50ah battery at 2.4 vpc would go:

1. Charge at constant current as hard as you can until the on-charge 
voltage 
reaches 2.4 volts per cell;

2. Hold that voltage until the current falls to 0.02 * C20 (1 amp);

3. (a) shut off, (b) go to float, or (c) equalize at that same 1a until 
either the voltage stops rising, or reaches 2.6vpc.

It sounds like your charger is acting pretty much as I'd expect, if it 
were 
designed to charge a 50ah battery at around 5 amps.  Is that the 
situation, 
or are the Ox batteries bigger than 50ah? 

What's weird here is that this seems like a thoroughly conventional 
charging 
profile.  I wonder why Minn Kota is so obsessed with keeping it secret.  

> I would not leave this charger connected indefinitely.  

I wouldn't either.

> Even in the off phase it watches the battery voltage and restarts the
> charging processes if it falls below 12.6 (I think).  

That seems a little high to me.  Open circuit voltage is a pretty 
inaccurate 
way to judge SOC, but typically a battery at 12.6v is close to fully 
charged.  You'd think the charger would wait until it falls to maybe 
12.4v.  
With an AGM, that would be a long time -- unless while it's monitoring the 
battery voltage, it's actually drawing current from the battery.  I'd be 
tempted to put a milliammeter between the charger and the battery to 
measure 
idle current.

>  I think it is more likely to repeatedly go through the charging cycle
> unnecessarily.  

I'm not a big fan of leaving even automatic shutoff chargers connected 
forever, no matter what the manufacturers claim.  I learned the hard way.

> But even if it not completely "charge and forget", I think it is at
> least "charge and forget until morning". 

Lots of merit in that ...


David Roden - Akron, Ohio, USA

= = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = 
Note: mail sent to the "etpost" address will not reach me.  To send 
me a private message, please use the address shown at the bottom
of this page : http://www.evdl.org/help/
= = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = =