Galvanic isolator test

[fudd]

Until I get the time to get an isolation transformer installed I have fitted a galvanic isolator. I've read Gibbo's site and it says to periodically test for faults. Is it some kind of non continuity test or what.

Thanks Steve P

[Keeping Up]

Do you have a multimeter, or can you borrow one? Ideally one with a "diode test" position? If so, you should disconnect the shore line and then check the GI for continuity in BOTH directions and it should show a voltage drop of between 1v and 3v depending on the model of GI (and should be identical in both directions).

 

If not, as a minimum you can just test for continuity (eg by using a battery and a small bulb).

[fudd]

Do you have a multimeter, or can you borrow one? Ideally one with a "diode test" position? If so, you should disconnect the shore line and then check the GI for continuity in BOTH directions and it should show a voltage drop of between 1v and 3v depending on the model of GI (and should be identical in both directions).

 

If not, as a minimum you can just test for continuity (eg by using a battery and a small bulb).

I have one and I will test it tomorrow.

Thank you. StevevP

[Gibbo]

If not, as a minimum you can just test for continuity (eg by using a battery and a small bulb).

 

Or combine the two methods to get a better reading...

 

Power a bulb through it, then measure the voltage drop across it whilst it's powering the bulb. A 10 watt bulb is about best. Then use a digital multimeter on the ohms range. It should read extremely high (above several tens of kOhms). Some cheap digital meters give duff readings on this last test.

[Keeping Up]

Or combine the two methods to get a better reading...

 

Power a bulb through it, then measure the voltage drop across it whilst it's powering the bulb. A 10 watt bulb is about best. Then use a digital multimeter on the ohms range. It should read extremely high (above several tens of kOhms). Some cheap digital meters give duff readings on this last test.

 

Yes that one can be somewhat unpredictable (which is why I suggest using one with a "diode test" position if possible)

[Gibbo]

Yes that one can be somewhat unpredictable (which is why I suggest using one with a "diode test" position if possible)

 

Indeed. Proper digitals use a test voltage below 0.25 volts for the resistance range to avoid forward biasing any semi junctions. Cheap ones use whatever the battery voltage happens to be less a bit.

[fudd]

Or combine the two methods to get a better reading...

 

Power a bulb through it, then measure the voltage drop across it whilst it's powering the bulb. A 10 watt bulb is about best. Then use a digital multimeter on the ohms range. It should read extremely high (above several tens of kOhms). Some cheap digital meters give duff readings on this last test.

It's a DI-LOG DL114. It

Should be ok.

[Keeping Up]

It's a DI-LOG DL114. It

Should be ok.

 

Should be OK, although the diode test range says it has an open-circuit voltage of just 1.5v so if the GI is the type with LED indicators, which generally don't conduct until around 2v, it may just show up as open-circuit. However Gibbo's suggestion of combining the test with that of measuring the voltage across a small bulb will confirm everything if that is the case.

[fudd]

Should be OK, although the diode test range says it has an open-circuit voltage of just 1.5v so if the GI is the type with LED indicators, which generally don't conduct until around 2v, it may just show up as open-circuit. However Gibbo's suggestion of combining the test with that of measuring the voltage across a small bulb will confirm everything if that is the case.

It's a basic Victron with no leds. I'll see what happens. Thanks again.

[fudd]

I've disconnected the shoreline and tested it with my multimeter. One way read 745 and the other 852. Now I am confused.

[Keeping Up]

I'm assuming that, on its diode test range, the meter reads the voltage drop across the diodes, so these readings correspond to 745 mV and 852 mV.

 

Normally a diode is stated as requiring about 600mV to conduct, so for two diodes in series (which the non-LED type of GI usually has) a reading of 1200 mV would be expected. However I see that your meter tests at a very low current (approx 0.1 mA) so I would guess that your diodes are just starting to conduct at this lower indicated voltage. The widely quoted theoretical 0.6 - 0.7 volts forward drop is true only at a particular current level for any diode; all diodes start to conduct slightly at a lower voltage than this, just as they also drop a much higher voltage at high currents.

 

It is unlikely that the diodes would be perfectly identical at this point on their chracteristics, which is well outside their normal operating range, so a mismatch corresponding to 372 mV per diode in one direction and 426 mV per diode in the other, is probably not significant.

 

I would take it from these readings that your GI is working properly. Now make a note of the readings, to see if they suddenly change over time (which would indicate a problem). Then reconnect your shoreline and forget about it for 2 or 3 months unless anything odd happens (for example always repeat the test if a fuse or circuit-breaker has operated)

[Boat&Bikes]

I've disconnected the shoreline and tested it with my multimeter. One way read 745 and the other 852. Now I am confused.

 

 

When i test my GI i get a reading of around 850 which i read somewhere(GI instruction manual i think) is as it should be,between 800/900.

 

Ian.

[fudd]

Thanks again. I think I have now discovered that our system is one of the 'earth not bonded to hull' types. I lifted up a bit of the floor and found a stud with a 6" piece of earth cable attached to it. The other end was floating in the air. It has obviously been cut. Maybe it was cut when the genny was installed. I have looked for another earth bonding point but I can't find it. I see no reason why it should be in an inconspicuous position if only for reasons of connecting it up in the first place. I'm going to go see if I can find my system in Gibbos site and ask questions after.

[Gibbo]

Thanks again. I think I have now discovered that our system is one of the 'earth not bonded to hull' types.

 

So it's a floating electrocution machine. Probably illegal as well as dangerous.

[fudd]

So it's a floating electrocution machine. Probably illegal as well as dangerous.

It won't be in about an hour. I'm running a 6 mm earth to where it was cut off.

As an aside, is there a way of finding out if it is earthed and I can't find the connection? Maybe hidden behind the genny or under the floor?

Edited December 19, 2012 by fudd

[nicknorman]

It won't be in about an hour. I'm running a 6 mm earth to where it was cut off.

As an aside, is there a way of finding out if it is earthed and I can't find the connection? Maybe hidden behind the genny or under the floor?

You can use an ohm-meter to check for continuity between the boat side of the GI and the hull. However, that will only tell you that they are connected, it will not tell you the current-carrying capabilities of that conductor. Your idea of running a dedicated new wire is the best one. ps be sure to use a multi-strand earth wire, not a solid single strand wire such as might be found in domestic wiring.

Edited December 19, 2012 by nicknorman

[STUBAG]

So it's a floating electrocution machine. Probably illegal as well as dangerous.

Ifully agree with the first sentence, but when you say "illegal", exactly er...how? Would it result in a visit from a lawman:"You are under arrst on suspicion of having an un-bonded vessel on this waterway". Did you REALLY mean illegal?

[Gibbo]

Ifully agree with the first sentence, but when you say "illegal", exactly er...how? Would it result in a visit from a lawman:"You are under arrst on suspicion of having an un-bonded vessel on this waterway". Did you REALLY mean illegal?

 

Yes, but I qualified it with "probably".

 

The ABYC says the hull should be bonded.

 

The RCD says the hull should be bonded.

 

The BMEA says the hull should be bonded.

 

The relevant ISOs say it should be bonded.

 

If you don't bond it, it could kill someone. It's highly likely that the owner could be prosecuted for man slaughter. There's no defence of "But I didn't know" because all the regs/guidelines/standards say it should be bonded. Exactly how that relates to "illegal" I don't know because I'm just an engineer not a lawyer. Hence the "probably".

[STUBAG]

Yes, but I qualified it with "probably".

 

The ABYC says the hull should be bonded.

 

The RCD says the hull should be bonded.

 

The BMEA says the hull should be bonded.

 

The relevant ISOs say it should be bonded.

 

If you don't bond it, it could kill someone. It's highly likely that the owner could be prosecuted for man slaughter. There's no defence of "But I didn't know" because all the regs/guidelines/standards say it should be bonded. Exactly how that relates to "illegal" I don't know because I'm just an engineer not a lawyer. Hence the "probably".

Sorry, I missed the "probably"!Wouldn't we all be a lot safer if "should" became "must"? (Some people call me a literalist, others say I'm a stirring little s**t!

[blackrose]

Thanks again. I think I have now discovered that our system is one of the 'earth not bonded to hull' types. I lifted up a bit of the floor and found a stud with a 6" piece of earth cable attached to it. The other end was floating in the air. It has obviously been cut. Maybe it was cut when the genny was installed. I have looked for another earth bonding point but I can't find it. I see no reason why it should be in an inconspicuous position if only for reasons of connecting it up in the first place. I'm going to go see if I can find my system in Gibbos site and ask questions after.

 

Someone had disconnected the earth bond and installed a galvanic isolator? Or perhaps another person who had installed the GI hadn't checked the earth bond.

 

Anyway, there's not much point having a GI or isolation transformer if there's no hull/earth bond, but more importantly it's dangerous.

Edited December 20, 2012 by blackrose

[fudd]

Someone had disconnected the earth bond and installed a galvanic isolator? Or perhaps another person who had installed the GI hadn't checked the earth bond.

 

Anyway, there's not much point having a GI or isolation transformer if there's no hull/earth bond, but more importantly it's dangerous.

I installed the GI. I only found out it wasn't earthed when I followed Gibbos installation drawing. Then I found the earth cable had been cut off.