Trickle Charging While on Vacation?

Each time I leave my 1995 854T in a cold garage (~ 6C) while on a
winter vacation, I return to find the battery dead. My Volvo dealer
says it's normal due to the drain from the security system. This year,
I'm thinking about setting up a charger to come on daily for an hour or
so, charging it at the low setting of 2 amps.

Is this better for the battery than allowing it to discharge fully? Is
1 hour per day at 2 amps likely to be too much or too little over a 3
week period?

Java

 

Use a battery Tender Jr. It will switch on and off automatically and
keep the battery up to charge with no hassle.

 

Keeping the battery charged is definitely better thatn letting it
discharge. A full discharge is very hard on a standard (not deep
cycle) battery and should be avoided like the plague. It is also very
hard on the battery to sit in a discharged state for any period of
time. There are a number of trickle chargers that will keep it in
good chape while stored. Alternatively, simply ensure it is fully
charged before storing the car and disconnect the battery. It will
loose a little charge over a 2 month period, but not enought o be a
problem.

 

Even deep cycle batteries suffer from a full discharge unless they
are NiCads. The Battery Tender Jr. seems like a great battery
maintainer, and will also charge batteries if given enough time. You can
find them for $30 on Ebay.

 

Thanks to all who have responded. It sounds as though the Jr. is the
ticket.

Java

 

You're welcome. The Tender also comes with two sets of plug-in
leads: alligator clips and a separate set of ring terminal leads that
you can install on the car, so you can just plug it into the Tender when
you leave it sitting.

 

Aside from purpose chargers, is it a Relly Bad Thing(tm) to just hook up
a regulated power supply to the battery or will that also do the trick?
I have the same problem with my oldtimer convertible which does not see
the light of winter.

Maarten

 

I'm thinking of a laboratory power supply, set so 12 or 13 V. It will
not give more than that voltage and the current will drop to almost 0
when the battery is full.
I'm wondering if that is bad for the battery or not.

Oh, and I'm Dutch

Maarten

 

That depends on what you mean by "regulated." If it switches off
when the battery voltage hits 13.6 or so, and doesn't try to charge at
10 amps, it may be ok. But seriously, why not spend $35 for a real
battery maintainer?

 

Is the power supply happy connected to a 13V unlimited current supply if
the mains fails?? Many are not.

Steve H

 

There are standing recommendations to use only chargers and not power
supplies for charging batteries, however, the failure mode that Steve
mentions above, which is probably the reason for such recommendations,
is easy to protect against. Just fit a blocking diode of a large enough
amperage rating on the +ve lead, and crank up the output voltage by .2V
to take account of the voltage drop across the diode. This prevents the
battery supplying voltage to the output terminals of the power supply if
the mains fails, or, if someone 'helpfully' turns the PSU output down.

Ken P.

 

A battery charger is just a regulated power supply with the voltage
preset and a high current capability. A trickle charger is just a
regulated power supply with the voltage preset and a low current
capability.

The problem with using a normal regulated power supply is if you make an
error in setting the voltage. If it is too low you won't get a full
charge and if it is too high you will burn off the electrolyte and ruin
the battery. I think the power supply should be set at 13.6 volts or
slightly less, not 12 or 13 volts. That makes a big difference.

Battery manufacturers should have a spec sheet which lists the optimum
trickle charge voltage.

Also, never set a battery on a concrete floor. That shortens the life.
I am not sure exactly why except the floor is a huge thermal sink and
causes condensation in humid weather. It also causes a thermal gradient
in the battery.