[C320-list] Batteries & Fridge

[Allan S. Field]

Jeff - What you say makes perfect sense and is somewhat what I expected.
When the dealer told me to leave the fridge on with the charger connected,
it was with lead cell batteries and the Promariner battery cooker.  I have
since replaced the batteries with gel (about 6 years ago and still doing
great) and the Xantrex 3-stage charger.  Thanks Jeff - as always, you get
shed light on my dim knowledge of anything electric! - Allan

-----Original Message-----
From: c320-list-bounces at lists.catalina320.com
[mailto:c320-list-bounces at lists.catalina320.com] On Behalf Of Jeff Hare
Sent: Friday, October 30, 2009 9:16 PM
To: C320-List at Catalina320.com
Subject: [C320-list] Batteries & Fridge

Hi fellow 320 folks. 

The argument in favor of leaving the refer on to protect the batteries,
while leaving the charger on for extended periods doesn't make sense from an
electrical engineering point of view.  Particularly with multistage chargers
that serve up *constant-voltage* float mode.

No charger with a high a float voltage should be left on indefinitely.
Period.
   
Measure your charger's float voltage at the battery terminals with a good
volt meter and decide based on YOUR OWN charger whether long term float
charging is safe for your batteries. 

13.3v max (13.8v Gel batts) or under is fine. 
 
If your float voltage is any higher than the above limits, or your batts
require a lower float, Don't leave the charger on for extended periods. Just
don't. 

Having a fridge or even a simple light bulb on WON'T affect the float
voltage, since the charger's JOB is to hold that voltage constant in float
mode regardless of the loads attached (within reason). 

So if the charger wants the voltage at 13.8v, the fridge's measley 4amp draw
ain't going to affect that.  Turn on your fridge and prove to yourself that
the voltage at your battery terminals remains the same.  

Some people claim *annecdotal* evidence that their batteries died once when
left on shore power while the fridge was off at the time, and conclude that
the fridge would have prevented this overcharging. 

That isn't proof that the batteries wouldn't have fried even if the fridge
was on. 

Some people (myself included) have had their ProMariner die and either
provide either too high or too low a voltage to the batteries.

In either case the batteries won't survive an extended spell like this. The
fridge being on won't help with over-voltage and will ensure fast battery
discharge in the low-voltage case.

So, leave the fridge on if you want cold beer and take comfort knowing that
it doesn't detract or contribute anything to the charging equation...  At
least in our physical universe.   :)

If you don't  believe me,  believe Georg Ohm.  ;)

Cheers!
-Jeff