Introduction
Galvanic corrosion is one of the most damaging threats to underwater boat metalwork, but it’s preventable with proper galvanic isolation. In this guide, you’ll learn why galvanic isolators matter, how to identify when your isolator needs testing, an – most importantly – how to test your isolator using simple tools and the proven professional method. By the end, you’ll have the confidence to perform reliable testing that tells you the true condition of your galvanic isolator without expensive professional service calls.
Every boat that’s connected to an electric hookup needs galvanic isolation to prevent corrosion to its underwater metalwork, which can, of course include the hull, drive shafts, propellers, outboard, Sail Drives etc. Without galvanic isolation, anodes are soon dissolved, and then, once the anodes are spent, galvanic corrosion starts to eat away whatever else is under water, as galvanic currents leach away the metal, at a molecular level, leaving hulls pitted, propellers soft & brittle, and outboards with ruined casings.
Galvanic isolators have become the go-to solution to resolve the problem of galvanic corrosion. In terms of blocking galvanic currents, they are every bit as good as an isolation transformer, and can have other additional benefits, such as built in surge protectors, and earth leakage warning devices, which are essential if your boat has “tech” on board, such as battery chargers, solar, (and even a TV or microwave).
The very latest galvanic isolator models have advanced self-test circuits built into them, but for models that don’t have such a facility, periodic testing is strongly advised.
When testing a galvanic isolator, only the earth connection is tested. The Live & Neutral don’t form any part of the test. In fact, if you’re testing a wired in isolator, the Live & Neutral won’t even be connected to the device – only the earth passes through it.
Plug-in galvanic isolators, the most popular type, typically have Live & Neutral conductors entering & leaving the device, but they play no part in the operation of the isolation function. The Earth conductor is normally connected to the LARGEST of the terminals in the connectors. In the UK, the earth conductor is coloured yellow/green. Other countries may use different colours.
There are two main ways of testing a galvanic isolator. The first method, which we do NOT recommend, uses a simple multimeter set on its “Diode Test” range. The idea is that the multimeter passes a small current through the isolator, and simultaneously measures the Voltage across it. However, not all multimeters are “powerful” enough to supply sufficient current to give a reliable result, and often result in “Fail” readings when, in fact, the isolator is fine.
We would strongly advise against using this method to test your galvanic isolator. It’s unreliable, and you could end up buying a replacement isolator when it’s not needed. Needless to say, we won’t be going into that test method here.
An altogether better testing method is to use a few electrical components, and to make up a simple testing circuit. You don’t need to know anything about electronics to do this, and you don’t even have to be able to solder. Here’s a list of what you’ll need:
- Multimeter (a cheap one is fine)
- 470 Ohm, 1 Watt resistor. A lower Wattage is fine, but smaller ones are fiddly to handle.
- 10Amp connector strip
- 1/2 metre of hookup cable (Red)
1/2 metre of hookup cable (Black) - 9V battery (PP3)
- Battery connector for the PP3
Click to Magnify
Wire the components up, as shown in the diagram below.
I’ll show you the test procedure for a hard-wired galvanic isolator, first, but a plug in one is exactly the same, except that you’ll be testing between both ends of the isolator cable, using the Earth conductor only, which, as I mentioned earlier, is usually the largest connector at each end, (but please check if in doubt). The pictures should help make things clear/
SAFETY: Turn off all power to the boat’s electrical system before removing the isolator.
First, ensure that you make the electrical system safe to work on, then completely remove the galvanic isolator from the circuit.
Set your multimeter to read DC Volts, on the range closest to 10 Volts. If your multimeter is an autoranging model, just set it to DC Volts, and the meter will select the appropriate range automatically.
Click to Enlarge
Refer to the diagram above, and connect the RED conductor to one of the isolators terminals, and the BLACK conductor to the other. If your isolator has lights one should illuminate.
Wait 5 seconds for the reading to stabilize, then write down the reading you see on the meter. Expect reading to be between 0.75V and 3.0V for a good isolator. These voltages indicate that the isolator is safely blocking galvanic currents while still allowing isolation transformer functionality. If it is 0V, the isolator may be short circuit. If the reading is higher than 3.0V, the isolator may be open circuit.
Swap the red and black conductors around. Expect a similar reading on the meter, and, if the isolator has lights, the other light should come on. If there is a variation between the readings of more than 20% your isolator may be faulty, (but repeat the test to be sure).
Click to Enlarge
And that’s it! You’ve just tested your galvanic isolator the way the professionals do it, (well, almost). The reading you have should be reliable, and tell you the true condition of your galvanic isolator.
You can now reconnect your isolator, and switch the electrics back on. Keep records of your test readings for future comparison and maintenance tracking.
Summary
To quickly summarize the testing procedure:
- What you tested: Only the Earth connection passes through the isolator; Live & Neutral do not
- Expected readings: Readings should be between 0.75V and 3.0V for a good isolator
- When to replace: If readings are 0V (short circuit) or above 3.0V (open circuit), the isolator may be faulty and may need replacement
- Test reliability: This method provides reliable results, unlike the unreliable multimeter “Diode Test” method
About The Author
Author: Ed Watt
Ed is the Technical director of the Galvanic Isolator Co., the UK’s leading specialist mfr of marine galvanic isolators. His background in electronics spans more years than he’d like to remember. His many hobbies include narrowboating and amateur radio.
Introduction
Galvanic corrosion is one of the most damaging threats to underwater boat metalwork, but it’s preventable with proper galvanic isolation. In this guide, you’ll learn why galvanic isolators matter, how to identify when your isolator needs testing, an – most importantly – how to test your isolator using simple tools and the proven professional method. By the end, you’ll have the confidence to perform reliable testing that tells you the true condition of your galvanic isolator without expensive professional service calls.
Every boat that’s connected to an electric hookup needs galvanic isolation to prevent corrosion to its underwater metalwork, which can, of course include the hull, drive shafts, propellers, outboard, Sail Drives etc. Without galvanic isolation, anodes are soon dissolved, and then, once the anodes are spent, galvanic corrosion starts to eat away whatever else is under water, as galvanic currents leach away the metal, at a molecular level, leaving hulls pitted, propellers soft & brittle, and outboards with ruined casings.
Galvanic isolators have become the go-to solution to resolve the problem of galvanic corrosion. In terms of blocking galvanic currents, they are every bit as good as an isolation transformer, and can have other additional benefits, such as built in surge protectors, and earth leakage warning devices, which are essential if your boat has “tech” on board, such as battery chargers, solar, (and even a TV or microwave).
The very latest galvanic isolator models have advanced self-test circuits built into them, but for models that don’t have such a facility, periodic testing is strongly advised.
When testing a galvanic isolator, only the earth connection is tested. The Live & Neutral don’t form any part of the test. In fact, if you’re testing a wired in isolator, the Live & Neutral won’t even be connected to the device – only the earth passes through it.
Plug-in galvanic isolators, the most popular type, typically have Live & Neutral conductors entering & leaving the device, but they play no part in the operation of the isolation function. The Earth conductor is normally connected to the LARGEST of the terminals in the connectors. In the UK, the earth conductor is coloured yellow/green. Other countries may use different colours.
There are two main ways of testing a galvanic isolator. The first method, which we do NOT recommend, uses a simple multimeter set on its “Diode Test” range. The idea is that the multimeter passes a small current through the isolator, and simultaneously measures the Voltage across it. However, not all multimeters are “powerful” enough to supply sufficient current to give a reliable result, and often result in “Fail” readings when, in fact, the isolator is fine.
We would strongly advise against using this method to test your galvanic isolator. It’s unreliable, and you could end up buying a replacement isolator when it’s not needed. Needless to say, we won’t be going into that test method here.
An altogether better testing method is to use a few electrical components, and to make up a simple testing circuit. You don’t need to know anything about electronics to do this, and you don’t even have to be able to solder. Here’s a list of what you’ll need:
- Multimeter (a cheap one is fine)
- 470 Ohm, 1 Watt resistor. A lower Wattage is fine, but smaller ones are fiddly to handle.
- 10Amp connector strip
- 1/2 metre of hookup cable (Red)
1/2 metre of hookup cable (Black) - 9V battery (PP3)
- Battery connector for the PP3
Click to Magnify
Wire the components up, as shown in the diagram.
I’ll show you the test procedure for a hard-wired galvanic isolator, first, but a plug in one is exactly the same, except that you’ll be testing between both ends of the isolator cable, using the Earth conductor only, which, as I mentioned earlier, is usually the largest connector at each end, (but please check if in doubt). The pictures should help make things clear/
SAFETY: Turn off all power to the boat’s electrical system before removing the isolator.
First, ensure that you make the electrical system safe to work on, then completely remove the galvanic isolator from the circuit.
Set your multimeter to read DC Volts, on the range closest to 10 Volts. If your multimeter is an autoranging model, just set it to DC Volts, and the meter will select the appropriate range automatically.
Click to Enlarge
Refer to the diagram above, and connect the RED conductor to one of the isolators terminals, and the BLACK conductor to the other. If your isolator has lights one should illuminate.
Wait 5 seconds for the reading to stabilize, then write down the reading you see on the meter. Expect reading to be between 0.75V and 3.0V for a good isolator. These voltages indicate that the isolator is safely blocking galvanic currents while still allowing isolation transformer functionality. If it is 0V, the isolator may be short circuit. If the reading is higher than 3.0V, the isolator may be open circuit.
Swap the red and black conductors around. Expect a similar reading on the meter, and, if the isolator has lights, the other light should come on. If there is a variation between the readings of more than 20% your isolator may be faulty, (but repeat the test to be sure).
And that’s it! You’ve just tested your galvanic isolator the way the professionals do it, (well, almost). The reading you have should be reliable, and tell you the true condition of your galvanic isolator.
You can now reconnect your isolator, and switch the electrics back on. Keep records of your test readings for future comparison and maintenance tracking.
Summary
To quickly summarize the testing procedure:
What you tested: Only the Earth connection passes through the isolator; Live & Neutral do not
Expected readings: Readings should be between 0.75V and 3.0V for a good isolator
When to replace: If readings are 0V (short circuit) or above 3.0V (open circuit), the isolator may be faulty and may need replacement
Test reliability: This method provides reliable results, unlike the unreliable multimeter “Diode Test” method
About The Author
Author: Ed Watt
Ed is the Technical director of the Galvanic Isolator Co., the UK’s leading specialist mfr of marine galvanic isolators. His background in electronics spans more years than he’d like to remember. His many hobbies include narrowboating and amateur radio.
