Sunday, Jan 03, 2010 at 01:11
Qldrrr,
your second
battery will almost certainly be under- or over charged, or a combination of these as time passes.
Reason being is that there are a number of variables defining a 100% charged
battery.
First of:
battery type and associated charging voltages.
Then, duration of charging and amount of voltage reaching your
battery (governed by your alternator/regulator combo and sometimes ECU/temperature sensor).
Temperature of your
battery, load currents.
Without a dedicated and matched
battery charge management system, the whole thing becomes a hit and miss affair.
Occasional topups with a matched
battery charger can certainly charge your
battery up to almost 100% of residual capacity, but can neither heal the wounds left by overcharging, nor reverse the normal ageing process (and the associated loss of capacity).
As to the suitability of your jump start
battery charger:
It could work, but
check a few things first:
batteries to be wired/charged in parallel need to be of the same type (e.g. flooded/flooded, AGM/AGM).
As you want to rely on the charger to detect the point in time when the batteries are full, all batteries in parallel need to be in reasonable good nick.
If a
battery has been damaged by overcharging or is of old age, the charge acceptance drops to a point which could interfere with the charger's decision making.
What could be affected is the change over from boost to float and to charger off, or from boost to charger off.
If only one of the two batteries prevents the charger from either switching to float or off, both batteries could get overcharged and you end up with not one but two damaged batteries (especially in case of VRLA AGM or GEL).
The batteries also should read within half a Volt before wiring in parallel or else be prepared for some sparking.
One more important consideration:
Because the second
battery together with the smaller one results in a much larger capacity than the one the charger was designed for, the charger most likely will get confused as to the switch over thresholds for boost/float/off.
It could work
well at lower temperatures, but it might miss the switch overs at higher
battery temps.
If there's some load current during charging, it almost certainly won't switch at the right times.
At the least, watch the charging process for a few times with a voltmeter connected, and you'll get a much clearer picture what goes on.
You want to see the voltage rise to around 14.4V before the charger reverts to 13.6V float and then off (three stage charging), or after sitting a few hours on 14.4V then switches off (two stage charging).
The whole thing becomes a rather time consuming experiment, but then, some people don't mind..
Best regards, batterymeister
AnswerID:
397384