The Victron Argodiode battery isolators let one alternator charge two or three batteries at once without connecting the batteries together. Drain your house battery flat and your starter battery stays full. It’s the old-school way to split charge, with no software and no settings. Here’s what Victron’s datasheet says about the range, and where a modern DC-DC charger is the better choice.
Victron Argodiode Isolators: Models
| Model | Max current | Batteries | Energize input | Studs |
|---|---|---|---|---|
| 80-2SC | 80A | 2 | No | M6 |
| 80-2AC | 80A | 2 | Yes | M6 |
| 100-3AC | 100A | 3 | Yes | M6 |
| 120-2AC | 120A | 2 | Yes | M8 |
| 140-3AC | 140A | 3 | Yes | M8 |
| 160-2AC | 160A | 2 | Yes | M8 |
| 180-3AC | 180A | 3 | Yes | M8 |
Source: Victron Argodiode Battery Isolators datasheet.
All models work on 12V and 24V systems. The rated current is both the maximum charge current and the maximum alternator current, so match the isolator to your alternator’s output.
Voltage Drop and the Compensation Diode
Diodes always drop some voltage. Victron uses Schottky diodes to keep it low, at about 0.3V at low current and about 0.45V at rated output. The datasheet warns that this drop can stop batteries reaching a full 100% charge and make them age early.
To fix that, every model has a compensation diode that slightly raises the alternator’s output voltage to offset the loss.
Energize Input
Victron explains that some alternators need DC voltage on their B+ output before they start charging. A diode isolator blocks that return voltage, so the alternator won’t wake up. The “AC” models have a current-limited energize input that powers B+ when the engine run/stop switch is closed.
Who It’s For
- Boats and older vehicles with conventional alternators and lead-acid batteries.
- Simple multi-battery setups where you want no settings and nothing to fail in software.
Who Should Use a DC-DC Charger Instead
- Lithium house banks. An isolator passes alternator voltage straight through, with no charge profile. A Victron Orion XS or Orion-Tr Smart controls the charge.
- Smart (Euro 6) alternators that vary their voltage.
- Long cable runs, where the isolator’s drop adds to cable losses.
Victron’s Argo FET isolators are another option with a much lower voltage drop.
Good to Know Before You Buy
- 0.3-0.45V voltage drop.
- No charge control.
- Fixed size. Pick the model to match your alternator’s maximum current.
For the complete spec sheet and current manual, see the Victron Argodiode battery isolators page.
Worked Example: Sizing for a Boat Alternator
A boat with a 90A alternator charging a starter battery and one house bank needs a two-output isolator rated at least 90A. The 120-2AC fits, and its energize input wakes alternators that need voltage on B+. If you add a second house bank or a bow-thruster battery later, the 140-3AC handles three batteries from the same alternator.
| Alternator output | Two batteries | Three batteries |
|---|---|---|
| Up to 80A | 80-2SC / 80-2AC | 100-3AC |
| Up to 120A | 120-2AC | 140-3AC |
| Up to 160A | 160-2AC | 180-3AC |
Based on the datasheet ratings; always match the isolator to the alternator’s maximum output.
Worked Example: What the Voltage Drop Means
Suppose the alternator regulates at 14.4V. Without compensation, the battery side of the isolator would see about 14.4 − 0.45 ≈ 13.95V at full current. That’s enough to recharge a lead-acid battery partway but not to complete absorption. With the compensation diode connected to the alternator’s sense input, the alternator raises its output by about the diode drop, so the batteries see close to the intended 14.4V. Estimates using Victron’s published drop figures.
Wiring Overview
- Alternator B+ connects to the isolator’s input stud.
- Each output stud goes to one battery positive, through a fuse sized for the cable.
- The compensation diode connects to the alternator’s voltage sense wire, where the alternator has one.
- On AC models, the energize input connects to the engine run/stop circuit so it powers B+ only while the engine runs.
- All battery negatives share a common ground with the engine block.
Mounting and Cooling
Diode isolators turn their voltage drop into heat, so at 100A and 0.45V that’s roughly 45W (estimate). Victron fits the isolators with heat sinks for this reason. Mount them vertically with the fins running up and down, in a ventilated spot away from the engine’s hottest surfaces, so air can rise through the fins.
Argodiode vs Argo FET vs Cyrix vs Orion
| Device | How it works | Voltage drop | Best fit |
|---|---|---|---|
| Argodiode | Diodes | ≈ 0.3–0.45V | Simple lead-acid systems |
| Argo FET | MOSFETs | Much lower | Same uses, less loss |
| Cyrix combiner | Voltage-sensing relay | Negligible when closed | Lead-acid with a standard alternator |
| Orion XS / Orion-Tr Smart | DC-DC charger | Regulated output | Lithium and smart alternators |
If you’re starting fresh with a lithium house bank, the DC-DC route gives a proper charge profile. For an older boat with lead-acid batteries and a conventional alternator, the Argodiode remains a simple, settings-free choice.
Charging From Shore Power Through an Isolator
An isolator isn’t only for alternators. A single-output battery charger can connect to the isolator’s input stud so it charges every connected battery, the same way the alternator does. Victron’s datasheet lists this use alongside alternator charging. Keep in mind that the same voltage drop applies, so a charger with a voltage-sense wire, or a slightly raised absorption setting, helps the batteries reach full charge.
Quick Checklist Before You Buy
- Your alternator’s maximum output in amps.
- How many batteries you want to charge: two or three.
- Whether your alternator needs voltage on B+ to start charging, which means choosing an AC model.
- Your battery chemistry. For lead-acid, an Argodiode is a straightforward fit; for lithium, look at the Orion range.
- Stud size for your cable lugs: M6 on the smaller models, M8 on the larger ones.
FAQ
What does a Victron Argodiode isolator do?
It lets one alternator charge two or three batteries while keeping them separated, so draining one doesn’t drain the others.
How much voltage does it lose?
About 0.3V at low current and 0.45V at rated output, according to Victron.
Can I use it with lithium batteries?
It will pass current, but it doesn’t control charging. For lithium, a DC-DC charger is the safer choice.
Do I need the energize input?
Only if your alternator needs voltage on B+ to start charging. If you’re not sure, the AC models cover both cases.
Will an isolator drain my batteries when the engine is off?
No. The diodes only let current flow from the alternator to the batteries, not between the batteries, so each one stays separate when the engine stops.
Sources: Victron Argodiode Battery Isolators product page and datasheet, victronenergy.com, accessed Oct 2026.
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