bad battery or not (arguing with Sears)

phatman

Observer
Odyssey tech manual has the recommended charging profile (Page 15):

http://www.odysseybattery.com/documents/US-ODY-TM-001_0411_000.pdf


Bulk to 14.7v,
Absorb at 14.7v until current flow drops below 0.001 of C10 amps (for example: 100ah (battery capacity or C) x 10 (C)10)) = 1000a x .001 = 1a)
Or, absorb at 14.7v for 6-8 hours
then drop to
Float at 13.6v


In other words, basically the same charge profile as any other lead-acid battery except it likes to get up to 14.7v on the bulk and keep it there during the absorb, instead of bulking up to 14.4v and dropping to 14.2v for absorb the way most chargers do (and most manufacturers recommend).

A 3-stage 14.4v/14.2v/13.6v charger will still get the job done - but it'll take longer (prolly an extra day or two of sitting at float voltage) to creep up those last couple of percentage points to reach 100% full.

that's helps. i thought that i might be over charging the batteries for some reason. i remember reading Optima suggesting the lead/ acid setting and was not sure why. I also noticed that Batteryminder made a specific charger for Odyssey. after reading your post i check the Odyssey owner manual and it reads "Low power 2.0 amp chargers for storage charge will keep a fully charged battery fully charged but cannot recharge if the ODYSSEY battery becomes discharged." why would that be? it also talks about returning 105-108% of charge and that most chargers only get 80%-90%. I'm guessing they make the assumption a 2amp charger will not have the brains to do that.
 

dwh

Tail-End Charlie
after reading your post i check the Odyssey owner manual and it reads "Low power 2.0 amp chargers for storage charge will keep a fully charged battery fully charged but cannot recharge if the ODYSSEY battery becomes discharged." why would that be?

Resistance.

A battery has an internal resistance to current flowing through it. That resistance is highest when the battery is dead, and also becomes higher as the battery approaches fully charged.

There is also the voltage differential to be considered. Most low power "trickle" chargers are not multi-stage. They are preset to a certain voltage (usually 12.6v or 12.8v) and limited to a max of 2a of current flow.

Say the battery is at 10v (dead) and the charger puts out 12.6v. That differential may not be enough "punch" to overcome the resistance of the dead battery and allow current to flow.



it also talks about returning 105-108% of charge and that most chargers only get 80%-90%. I'm guessing they make the assumption a 2amp charger will not have the brains to do that.

It's not about the brains of the charger. Chargers (even smart ones) really have no idea how full the battery is, they are just set to pump juice until a certain point is reached.

But if you draw out 100 amp*hours from a battery, you'll have to put back more than that to get it full again, since some watts will be consumed doing things like making heat and converting electricity into the chemical reaction that a battery uses to store energy.


EDIT: And the reason most chargers don't get the battery full, is they are set to too low of a voltage to fully activate the chemistry.
 

dwh

Tail-End Charlie
OK, so if I have a 3 stage charger and set it to 2 amp then it should work.

As long as the battery isn't dead, that will probably get some current to flow through the battery.

But, if you've got a 3-stage, then I would crank it to the max.

Odysseys are rated to handle a max of C*4 charge current. That would be 400a of charge current for a 100ah battery (yea, total recharge from dead in 15 minutes IF you have a nuclear sub handy to supply that much charge current).

Most batteries are rated to handle C/4 max, which would be 25a charge for a 100ah battery.
 

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