Before the advent of a multi-stage marine battery charger, boaters experienced damaged batteries from over or under charging while using shore power. The reason for this was boaters had no choice but to use automotive type chargers. This type charger used voltage that was too high that results in off gassing that killed many batteries.
Today, buyers have quality marine chargers available to them. These chargers use special multi-stage charging, that monitor the voltage in the batteries. With some models being able to operate all the time if you do the installation correct.
To help you understand what to look for in a quality marine battery charger, I answer some popular questions that marine charger buyers ask.
What Is A 3-Bank Onboard Marine Charger?
A 3-bank onboard marine charger allows you to leave the batteries in the boat. First you mount and leave the charger installed in the boat all the time. Second, you don’t have to hook anything more to it to charge, just a plug in the AC cord attached to the charger. Inside an onboard charger are micro-computer controllers and the charge rate adjusts as the battery gets charged.
How Do I Size An Onboard Marine Charger?
Deciding what size charger to use is up to the user, dependent on some important factors.
- First, sizing will depend on the battery size (Group size & Amp hour capacity) and type (Wet, Gel, AGM etc.).
The general consensus, is to size a hard wired onboard charger for at least of 10% of the banks rating in Amp Hours (Ah). The formula is as follows:
(Amp Hours) multiplied by (10%) = The amount of amps needed for correct recharge.
For example: A 300Ah battery bank, sized at 10%, would get a 30A charger.
- Second, is what kind of recovery charge time is appropriate for your use.
All chargers have an amperage rating. This rating states how fast they can re-charge depleted batteries. The higher the rating, the quicker the recovery time. To help you choose a proper recovery time, check out the formulas below:
(amp hour rating of battery) divided by (charger rating in amps)= measurement
Next, (measurement) + 10% for top ups = required amps
A word of advice, using a higher rated charger for the intention of fast charging, isn’t a great idea. While chargers with lower amp hour output do have slower recharge. They are better for helping to reduce overcharging your batteries.
- Third, is whether your boat has a continuous or intermittent source of AC power to run the charger.
Continuous Power (Shore)
If you spend a lot of time parked at the dock, you can pick a smaller charger. While you should consider voltage drops, many high quality chargers are “power factored.”
One factor you have to consider, is are there any DC loads your boat will use while at the dock. At dockside, DC devices can consume power and rob it from what your charger feeds the bank. Such as DC lighting, refrigeration, computers, TV’s, stereo. Ensure you have the capacity to power the DC loads and float-charge your batteries.
For example: Say you have a 10A dock-side load, with a 20A charger. This means that 10A is feeding your DC loads and the remaining 10A is going into the bank for charging. Your charger may be too small for your needs. In this example it’s in your best interest to pick a 30A charger to maintain a charge rate of 10% of Ah capacity.
In this instance you spend your time cruising or anchored out, and aren’t plugged in except every so often. Make sure to have stored “juice” to recharge DC loads and batteries in the time available. Take the total amp hour rating explained before and divide them by the hours available.
If you power your charger off a generator, get the largest charger as your batteries will accept. This is important to keep generator run times as short as possible.
Which Features Are Important For A Marine Charger?
Pick A Charger That Is UL 1236 Stamped
Quality boat chargers design should meet the ABYC / UL 1236 standards. These standards deem the proper safety and isolation of the AC and DC wiring in a battery charger. UL stamped chargers undergo a 1500 volt test! This test to makes sure there is adequate AC/DC isolation inside the charger. Electrical tests like this are paramount for safety out on the water.
Small Boats Need Sealed Chargers
If you have a small vessel (sport/fishing boat, kayak, etc) that’s gets wet, you need to buy a sealed charger. This allows for use in harsh environments and can operate if submerged for a short period of time.