Battery charging

[Robdog65]

Hi guys I was hoping someone might steer me in the right direction for charging a secondary battery in my boat . I have been using a vsr switch which has just died and was wondering am I better off using a dc dc charger like a redarc instead ? My second battery is a 120 amp agm for running my minnkota electric or a fridge and my motor is a 75hp Honda which has a 35amp alternator. My concerns are is the vsr giving the agm the charge it needs or is it actually hurting the battery and is a 20 amp dc dc type charger going to get enough from the motor to work properly ?  I know there's a lot of 12volt experts on this site so hopefully someone can give some advice ! Cheers in advance Robdog 😁

[vern]

Just replace the vsr and may be look at a faster charging battery like a spiral cell or two. My understanding is the dcdc would take longer to charge a low battery

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[HKB Electronics]

It would seem it has been working ok to date as you haven't indicated you were having
problems charging the battery so why change it?

Keep in mind a DCDC charger draws more than it supplies due to loses within the charger, with
a 35A alternator and say the charger drawing 25A you only have 10A left to run the motor
and other accessories, without the charger if your battery is low it will pull down the voltage
and will self limit its draw so in this instance it might be better than using a DCDC to limit the current.

[RebsWA]

I have been using a BEP marinised (totally sealed, flashproof) VSR since 2008 when I replaced the starter battery and used the old one to run the electronics as a single battery couldn't handle the increasing load and I kept getting low voltage warnings.
At that time I had a Johnson outboard with a 20amp alternator I think, that output a constant 14.4 volts.
In 2013 I upgraded to a new Suzuki outboard and replaced the second battery with an AGM.
The Suzuki has a 40amp alternator and also regulates a constant 14.4 volts.
My setup has the marine starting battery only to start the outboard.
The AGM runs everything else.
Never has a hint of a problem with battery management and that's good when 20 miles or more out to sea.
Cannot see the need for a DC to DC as you will probably find your Honda has a regulated 14.4 volt output and I wonder how a DC to DC would last in a marine environment.

[Troopy_03]

With such a limited supply as an outboard motor alternator, you are better off sticking with the VSR, and putting a 240V charger on it once a week or so, to fully charge the battery. This would also depend on how often you use the boat. And another point, it is worth considering completely isolating the battery if the boat is being left idle for any length of time.

[Robdog65]

Thanks guys , it looks like my vsr has died and I thought being an agm that you'd get a better charge for it out of a dc dc charger. I do use a cteck 15 amp marine smart charger to keep it charged at home when not in use. I think I might up the cabling that runs from the motor to the agm as it's quite thin to get a better charge and maybe get another vsr and stick with that as that will also be a cheaper option. Sounds like a BEP marinised one might be the go. Thanks fellas

[RebsWA]

Thanks guys , it looks like my vsr has died and I thought being an agm that you'd get a better charge for it out of a dc dc charger. I do use a cteck 15 amp marine smart charger to keep it charged at home when not in use. I think I might up the cabling that runs from the motor to the agm as it's quite thin to get a better charge and maybe get another vsr and stick with that as that will also be a cheaper option. Sounds like a BEP marinised one might be the go. Thanks fellas

Can you explain upgrading the cable from the motor to the AGM? I would have thought the motor cable to the start battery would be sufficient as it has to handle the current draw for the starter motor. Do you mean upgrade the cable from the start battery to the AGM? Not trying to be clever, just trying to understand.

[Robdog65]

Good pick up Rebs I meant the cable from the vsr that runs forward to my second battery.