Voltage spike question

[confused]

I have been told that my inverter/charger has a problem with the AC input which has been caused by a voltage spike exceeding 280V. My issue with this is that my 230v 6kva generator is equipped with an AVR, which I understand will, typically, only allow a voltage of plus or minus 3% of the units voltage. I am being asked to believe that a 22% voltage spike is possible. Does this sound reasonable to anyone?
Secondly, and I'll admit to grasping at straws here, the inverter/charger is protected from the generator by a 230v 40amp Siemens 5SM3 314-0 RCCB, shouldn't this have tripped if 280 plus volts shot down the cable?
Regards
Confused

PS the generator has a Sassin 20Amp 3SB28 Phase and neutral circuit breaker as well.

[Mike90250]

many pieces of gear (motors, big transformers) can cause spikes, that travel along the power line, till they upset something.

Generators are also a possible source, even with an AVR, if a large load drops off, you can still get a spike.

Midnight Solar makes some great suppressors, that may help solve your issue

http://www.midnitesolar.com/pages/pages.php?article_ID=49

What kind of inverter and system do you have ?

[confused]

Hi Mike, thanks for coming back to me.
I have a Rich Electric 3000W 24V inverter/charger and a Yanmar clone generator.
The problem occurred when I had the generator feeding power into the charger and I plugged in my air compressor (2HP).
Nothing else was plugged into the generator and the compressor was plugged into a house socket, so was being powered from the inverter. The inverter boasts power assist, so in theory the generator and the inverter should be helping each other out.
The reason for the question, is that I am trying to get it fixed under warranty but they have come back and told me definitively that a spike of more than 280V hit the box and I don't see how that could have happened given the circumstances.
Regards
Confused

many pieces of gear (motors, big transformers) can cause spikes, that travel along the power line, till they upset something.

Generators are also a possible source, even with an AVR, if a large load drops off, you can still get a spike.

Midnight Solar makes some great suppressors, that may help solve your issue

http://www.midnitesolar.com/pages/pages.php?article_ID=49

What kind of inverter and system do you have ?

[inetdog]

Hi Mike, thanks for coming back to me.
I have a Rich Electric 3000W 24V inverter/charger and a Yanmar clone generator.
The problem occurred when I had the generator feeding power into the charger and I plugged in my air compressor (2HP).
Nothing else was plugged into the generator and the compressor was plugged into a house socket, so was being powered from the inverter. The inverter boasts power assist, so in theory the generator and the inverter should be helping each other out.
The reason for the question, is that I am trying to get it fixed under warranty but they have come back and told me definitively that a spike of more than 280V hit the box and I don't see how that could have happened given the circumstances.
Regards
Confused

'
I think you may have revealed the source of the problem with the additional information about the compressor.

A compressor is a large motor load which will draw very high current when trying to start, especially if working against static pressure in the tank.
That means that it will try to draw very high current (up to 10x the full load current) when you switch it on.
Now if that current surge is high enough to trip the generator and/or inverter output breaker, you suddenly have a high current (inductive in nature) flowing in the motor windings.
If a protective device suddenly opens while that current is flowing, the resulting inductive kick (of opposite polarity) can easily exceed the voltage threshold of the inverter's output circuitry.
A surge suppressor might have saved you in this case.
Do not take motor starting for granted, even with "power assist" on your side.

If you need to run this compressor off the inverter in the future, you will probably need to get some sort of soft start unit or VFD (variable frequency drive) and you may also need to provide an unloader valve system and check valve to allow the compressor to start against zero pressure and the pick up the tank pressure once it is up to speed.

[confused]

Thank you very much inetdog for coming back to me on this one.
I will take you recommendations on board.
I rather suspect that in future, I will simply run the compressor directly off the generator, to avoid in the future all of the grief that this issue has caused me.
once again, thanks for the information.
regards
Confused
(a little more so every day)

'
I think you may have revealed the source of the problem with the additional information about the compressor.

A compressor is a large motor load which will draw very high current when trying to start, especially if working against static pressure in the tank.
That means that it will try to draw very high current (up to 10x the full load current) when you switch it on.
Now if that current surge is high enough to trip the generator and/or inverter output breaker, you suddenly have a high current (inductive in nature) flowing in the motor windings.
If a protective device suddenly opens while that current is flowing, the resulting inductive kick (of opposite polarity) can easily exceed the voltage threshold of the inverter's output circuitry.
A surge suppressor might have saved you in this case.
Do not take motor starting for granted, even with "power assist" on your side.

If you need to run this compressor off the inverter in the future, you will probably need to get some sort of soft start unit or VFD (variable frequency drive) and you may also need to provide an unloader valve system and check valve to allow the compressor to start against zero pressure and the pick up the tank pressure once it is up to speed.

[confused]

Hi Inetdog

I have re-read your reply and had a think about it.
You say
"Now if that current surge is high enough to trip the generator and/or inverter output breaker, you suddenly have a high current (inductive in nature) flowing in the motor windings.
If a protective device suddenly opens while that current is flowing, the resulting inductive kick (of opposite polarity) can easily exceed the voltage threshold of the inverter's output circuitry. "

I have 2 queries:
What if the generator carried on quite happily, which it did.
and does this "high current" actually mean a voltage spike.
Sorry if this sounds like a stupid question but I'm not clear on what an "inductive kick" is.
The only thing of a protective nature in the inverter, let go in such a way as to fry the AC input circuitry.
The inverter has an AC input circuit breaker but in the manual it claims that this is "designed to protect the internal wiring inside the unit only".
It seems a bit odd, given the nature of people who have to purchase off grid inverters. We tend to have to run a water pump, or a compressor or a welder etc
so it seems a little strange that the inverter manufactures can get away without offering protection for this sort of scenario.
It feels a bit like selling a new car without seat-belts. Years ago one would have got away with it, but not now.
Ok that's the rant over.
regards
Confused

'
I think you may have revealed the source of the problem with the additional information about the compressor.

A compressor is a large motor load which will draw very high current when trying to start, especially if working against static pressure in the tank.
That means that it will try to draw very high current (up to 10x the full load current) when you switch it on.
Now if that current surge is high enough to trip the generator and/or inverter output breaker, you suddenly have a high current (inductive in nature) flowing in the motor windings.
If a protective device suddenly opens while that current is flowing, the resulting inductive kick (of opposite polarity) can easily exceed the voltage threshold of the inverter's output circuitry.
A surge suppressor might have saved you in this case.
Do not take motor starting for granted, even with "power assist" on your side.

If you need to run this compressor off the inverter in the future, you will probably need to get some sort of soft start unit or VFD (variable frequency drive) and you may also need to provide an unloader valve system and check valve to allow the compressor to start against zero pressure and the pick up the tank pressure once it is up to speed.

[russ]

It seems a bit odd, given the nature of people who have to purchase off grid inverters. We tend to have to run a water pump, or a compressor or a welder etc
so it seems a little strange that the inverter manufactures can get away without offering protection for this sort of scenario.
It feels a bit like selling a new car without seat-belts. Years ago one would have got away with it, but not now.

Sorry but one has to be aware of what they are buying.

[mapmaker]

Sorry if this sounds like a stupid question but I'm not clear on what an "inductive kick" is.

When current starts flowing in a wire, it sets up a magnetic field around the wire. When the current stops flowing, the field collapses and induces a reverse current in the wire. If the wire is coiled up (like in a motor or relay coil) the inductive kick can be quite high in voltage.

Some inverters have better built-in protection against this sort of thing (you get what you pay for)... I like Mike's suggestion of trying a Midnite SPD to see if you can add extra protection to the inverter.

--mapmaker

[inetdog]

When current starts flowing in a wire, it sets up a magnetic field around the wire. When the current stops flowing, the field collapses and induces a reverse current in the wire. If the wire is coiled up (like in a motor or relay coil) the inductive kick can be quite high in voltage.

Close but no cigar. The collapsing field creates a voltage which tries to keep the current flowing in the same direction through the coil. The field collapse may induce enough voltage across the coil to arc across the contacts that were used to open the circuit.

You may be thinking of the ringing current reversals which occur in a circuit where there is a capacitor across the open contacts. One classic case of that is the old distributor and coil car ignition.

[mapmaker]

Close but no cigar.

You're quite right... It's amazing how much clearer it seems at 5:30 PM than 5:30 AM when I wrote that post

--mapmaker

[confused]

Thank you everyone for taking the trouble to reply, as usual it is educational.
Although I have to say Russ, given that proposition, we would all have to be an expert in everything.
We learn as we go, seems to be the nature of my life and that's sometimes a painful experience.

Regards
Confused
( A little less so this morning than before)

[confused]

I apologise if I appear to be "banging on" on this issue but for future reference, I need to resolve this, as I don't want it to happen again.
I have looked at Mike's suggestion of the Midnight SPD and the one that fits the purpose would be the MNSPD300, as I run at 220/230v. The problem with that is that it's clamping voltage is 700v and in my case the inverter's manual says it will not cope with anything above 250v.
Subsequently I have scoured the internet looking for a product that would help and either I am looking in the wrong places or I'm looking for the wrong thing, as it doesn't seem to exist.
What do other people use to avoid this sort of issue, are we all just living with our fingers crossed. I'd love to think that was a simple breaker or fuse that I could mount on a Din rail.

Back to the blown circuitry in the inverter, just so that I can get my head around what happened.
The generator is plugged into the inverters charger port and running charging the batteries. I plug the compressor into a house socket and when I start the compressor, the inverter's charger AC input breaker does not just pop but the circuitry of the charger circuit gets fried. So let's suppose that an "inductive kick" thumped out of the compressor's motor. The resultant voltage spike must have echoed around the entire house wiring before coming back through the inverter and then either passed through the charger input to hit the generator and bounce back to destroy the circuitry or destroyed the charger circuitry before getting to the generator.
The point that I am attempting to make here, badly perhaps, is that everything else turned on in the house must have been hit as well, as was the inverter but only the charger circuit was affected. What heck was the AC input breaker there to protect? Just wondering!
I'd be grateful if someone is patient enough to explain it to me and perhaps answer the first question. What do others use to avoid the same issue.
Regards
Confused

[Mike90250]

Even Grid power has lots of spikes, when your power neighbor switches off his microwave, or arc welder, or big table saw. Daily, I would expect to see lots of 300-400V spikes on the system. So the 300V SPD is about the lowest voltage, robust piece of gear you can use. Maybe add a highly rated computer surge strip on the generator, but you seem to have a unlucky combo of events & gear.

[mapmaker]

What heck was the AC input breaker there to protect? Just wondering!

That type of circuit breaker is not tripped by voltage. It is tripped by excessive current, not voltage.

I'm not sure what is the best solution for your problem

--mapmaker

[ncube]

Hi Mike, thanks for coming back to me.
I have a Rich Electric 3000W 24V inverter/charger ....
Confused

Hi Confused,

I'm sorry for your unfortunate experience. I would like to ask you though, what is your opinion on your Rich Electric inverter/charger? Their inverter designs/specs look really good and they seem to be well-made. I've been looking for reviews or real-life experiences with regard to their inverters but unable to find any. I would appreciate if you can share your thoughts and experience. Sorry this question is a bit OT but I'm unable to PM you to ask the question.

Regards,
ncube