<span class="highlight">Battery</span> charging queries...

Hi all,

I was told that number two battery in the duel battery set up is never fully charged during normal vehicle operation - I have a redarc isolator system - and that to fully charge the second battery it needs the occasional charge with a battery charger. My second battery is a 115Ah lead acid deep cycle. Any thoughts on this?

I do not own a dedicated battery charger but I have a Projecta 1500A jump start battery (33Ah). This jump start battery has a 2700mA battery charger (that fits only in to this specific model with a certain plug). The Projecta battery pack automatically cuts out when the charge is complete. Could I link this battery pack up by the jump leads to the second battery that needs a charge and charge them together - would this work? Any problems with doing this? If this is OK could this be done whilst the second battery is still under the bonnet or should the battery be isolated. Thanks for any advice

Qldrrr
Back Expand Un-Read 0 Moderator

Reply By:- Sunday, Jan 03, 2010 at 01:11

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

Reply By: RV Powerstream P/L - Sunday, Jan 03, 2010 at 11:20

Sunday, Jan 03, 2010 at 11:20
To overcome the bulk of the problems there is equipment available that can separate and smart charge your batteries the same as 240V smart charging so the reality to achieve efficiency is there but it is at a cost but then how much does it cost to keep killing batteries and equipment with under charging, overcharging and under capacity.
No battery seller will tell you how as they just want to keep selling you batteries.
Ian
AnswerID: 397417

Reply By: poppywhite - Sunday, Jan 03, 2010 at 11:29

Sunday, Jan 03, 2010 at 11:29
I dont believe that big long reply is entirely accurate. There is gigabytes if info on this subject on this forum. Use the search function and you will be entertained and educated for hours.I think member 'drivesafe' has what you are looking for.
AnswerID: 397421

Follow Up By: Marty-VIC - Sunday, Jan 03, 2010 at 12:35

Sunday, Jan 03, 2010 at 12:35
the big long reply is far from accurate and in fact as inaccurate as the information Drivesafe dribbles.
This time I am with Powerstream. All up cost for reasonable system $200 and if you dont have a decent mechanical Redarc style battery isolator $300. Really depends how much power you use daily. With low price of solar panels today may be the better route to go or a combination of both if looking for long term reliable solution.
0
FollowupID: 666264

Reply By: ABR - SIDEWINDER - Sunday, Jan 03, 2010 at 12:06

Sunday, Jan 03, 2010 at 12:06
Hi QLDrrr

Here is my own setup and it works well.

I have always used MRV70 105ah batteries and get around 3 years from them.

My fridge is switched on 24/7 and I work only 5km from home so the aux battery never charges up on work trips.

I have a 50A plug mounted at the grill and this is wired and fused directly to the aux battery.

When I get home I simply plug into to wall mounted ABR 20A charger, I do this weekdays only as I tend to drive enough on the weekend to keep the battery full.

The other good reason the have a mains charger is that most new cars, my new Prado 150 included drop the alternator voltage to around 13.4V once the engine is hot, most batteries would like to be charged at 13.8V so this is quite important.

Your plug pack type charger is only designed for your jump start unit and should not be used on the car battery.

Here are some pictures of my setup.






Regards

Derek from ABR

AnswerID: 397428

Follow Up By: Qldrrr - Sunday, Jan 03, 2010 at 14:45

Sunday, Jan 03, 2010 at 14:45
Derek, great stuff, thanks for taking the time to show me this, it looks the goods

Qldrrr
0
FollowupID: 666279

Reply By: Member - Mike DID - Monday, Jan 04, 2010 at 10:20

Monday, Jan 04, 2010 at 10:20
The main problem with charging DeepCycle batteries (if they're not AGM) is that it takes a LONG time to charge them.

If you drive for long enough after a heavy discharge; and if the Alternator output is compatible with the battery you have, it will charge to 100%.
AnswerID: 397546

Follow Up By: Member - Kiwi Kia - Monday, Jan 04, 2010 at 12:21

Monday, Jan 04, 2010 at 12:21
Yeah, fair enough Mike but we are only talking about the last 5% or so of charge.

KK
0
FollowupID: 666444

Sponsored Links