Use Auto battery charger?

[jwag956]

Are there reasons NOT to use a standard Auto battery charger - say a Black and Decker 12V 15A charger to charge various marine batteries (flood)

Background:

I have 2 independent batteries - the dinghy starter, and a solar charged windless battery. I'd like a backup if either of those aren't charged enough.

Second - my Xantrax charger is giving me fits - and I want to make sure my batteries are topped off (currently at 12.5V) - while I slowly effect repairs. I can run the engines of course - but was wondering if the lowly Auto charger would be an option.

 

[tiltrider1]

Auto chargers are designed to deal with a single 12 volt battery. If you are charging a single generator battery or engine start battery then no issues. However if you try to charge a pair of paralleled batteries or 2 6v batteries in series the charger will become confused and turn itself off.

 

[Bacchus]

Auto chargers are designed to deal with a single 12 volt battery. If you are charging a single generator battery or engine start battery then no issues. However if you try to charge a pair of paralleled batteries or 2 6v batteries in series the charger will become confused and turn itself off.

I have heard of issues if trying to charge a large bank but never an issue with a pair of 6V GCs? I don't believe folks with a GCs disconnect and buy a 6V charger.
Some chargers will not charge a very low SOC batty and it is std procedure / necessary to connect a good batty in parallel to get the charge started.

If it's a smart multi stage charger I think it's OK and worth trying. If not a modern smart charger I would be reluctant to use it conne Ted for any length of time to get to 100% SOC as it may overcharge.

I have a bank of 8 - 6V AGM GCs in my motorhome that I use a BatteryMinder.com maintainer. For the large bank I use their selectable 2-4-8A model and it works just fine.
That may be an option for the OP to to keep them topped off w/o risk of overcharging as they are a multi stage smart unit with a maintenance mode that is supposed to prevent / remove plate sulphation. I have had excellent results with these and have kept unused old AGM battys for 10 yrs +/- until needed to be put in service.

 

[CharlieJ]

There are several reasons not to use an automotive type battery charger aboard a boat.
1. Many automobile battery chargers have a N>G bond which is unsafe and will trip a pedestal residual current device (RCD) or an onboard ELCI.
2. Many are cheaply made and have poor voltage regulation.
3. Many do not have a "float" stage and simply maintain the batteries at the absorption voltage which leads to excessive gassing.

Although expensive at about $160, Victron's small and portable 12V/15A Blue Smart IP65 Charger (p/n BPC121531104R) is a feature rich charger with BlueTooth for setting parameters and monitoring by smartphone/tablet.

 

[DavidM]

Auto chargers are designed to deal with a single 12 volt battery. If you are charging a single generator battery or engine start battery then no issues. However if you try to charge a pair of paralleled batteries or 2 6v batteries in series the charger will become confused and turn itself off.

That is a new one on me!!!

Automotive battery chargers can be a simple single step, fixed voltage charger (usually high- 15 V or so) that can be used to boost up a battery or batteries (6V in series or 12V in parallel) but don't leave them on for long and monitor the voltage. Once the voltage gets up in the mid 14s, disconnect the charger.

Or they can be full three step chargers that act no differently than marine chargers.

David

 

[Bmarler]

i tried an automotive maintenance charger once and it ate my zincs in short order.
i wouldn't add a non-marine rated charger without doublechecking with a silver half cell to be sure it's good to go.

 

[tiltrider1]

Automotive battery chargers have changed greatly over the last 10 years. There are commercial grade units that shops use and they have controls that allow a technician to do just about everything. Then there are the portable units sold at auto parts stores or Amazon that are designed for use by idiots. These units won’t charge unless they see 12v coming from the battery first. Meaning, if the batter is down to 10v the charger won’t even turn on. They are so specifically designed to charge a single car battery that they get con fused on bigger banks and multiple battery set ups. What confuses most people is that the charger will actually work for 24 hours and then it will shut off and not come back on until the power button is cycled. So if you want to charge up a bank for 24 hours no problem but if you want the charger to act like a marine charger and go in and out of float mode you will likely find a dead battery bank after a few months.

 

[C lectric]

Auto chargers are designed to deal with a single 12 volt battery. If you are charging a single generator battery or engine start battery then no issues. However if you try to charge a pair of paralleled batteries or 2 6v batteries in series the charger will become confused and turn itself off.

Charging a too large battery system can cause the charger to have a short life as I found out. I can't say it was my to large battery setup for the charger but I was suspicious.

Untill I learned better I use to do exactly that , paralleling and series charging of two 6 V . THe charger never shut off or showed any other type of odd behaviour. It wasn't used for long but after the boat purchase we were tight financially. Once things freed up I replaced it due to the following concern.

The thing that made me change was the concern about the type of transformer they used, called an autotransformer. As mentioned that means part of the primary coil and the secondary coil are joined so in effect it is ONE large coil., not two isolated coils.
THat can produce currents where you don't want them, through the electrical system and in case of a partial failure in the charger could shoot a far higher and AC voltage through the boat system. Damaging equipment and causing
corrosion.