Sizing shore power and galvanic isolation
How to match Pro Charge Ultra and isolation transformers to your berth supply and onboard battery bank.
Marina shore power is rarely “plug in and forget”. Voltage, available amperage, earth topology and galvanic corrosion paths all affect how you size the AC-DC charger, whether you need galvanic isolation, and how aggressively you can charge the house bank without tripping the pedestal.
Sterling’s Pro Charge Ultra range remains the go-to for multi-stage charging on board — but the shore side of the install deserves the same attention as battery capacity and inverter loads.
Step 1 — Know your berth supply
Record before you specify:
- Shore voltage (230V / 110V) and maximum pedestal current
- Onboard AC distribution — dedicated charger circuit vs shared with inverter/combi
- Existing isolation transformer or zinc saver already fitted
- Battery bank voltage (12V / 24V / 48V) and chemistry (lead-acid vs lithium)
Step 2 — Size the charger output
- Charger family
- Pro Charge Ultra — multi-stage AC-DC
- Rule of thumb
- Charge current ≈ 10–20% of bank Ah (lead-acid); follow BMS limits for lithium
- Shore limit
- Ensure charger + inverter loads stay under pedestal breaker
- Isolation
- Galvanic isolator or isolation transformer where marina earth creates corrosion path
Galvanic isolation — why it matters
When the vessel is earthed to shore via the shore cord, stray DC currents can accelerate hull zinc loss and affect neighbouring boats. Isolation breaks the direct metallic path while keeping AC safety earth arrangements compliant with your classification and marina rules.
Sterling supplies galvanic protection products alongside charging hardware — specify them as part of the shore-power chain, not as an afterthought.
“Most warranty calls we see on marine charging trace back to undersized shore circuits or missing isolation — not the charger itself.”
Sterling Power marine support
Under way vs on berth
Remember alternator and DC-DC charging while under way — Saturn B2B can supplement shore charging when you leave the marina. Size shore and under-way paths together so you are not fast on passage and slow on berth, or vice versa.
Need a check?
Email berth details, bank size and existing AC layout — our marine desk can suggest Pro Charge Ultra model, isolation product and fuse/discount points before you pull cable.