A/C voltage regulator?

[MatBirch]

Got a problem that is confusing me. I have an inverter that sees more than 12v when the vehicle is running, so it’s output voltage is higher than it should be. This is causing the GFCI receptacles to shut down.
Is there an AC regulator that can be used to settle the voltage, WITHOUT causing it to go too low when the DC input voltage is lower ( vehicle not running).

Thanks!

 

[rlitman]

The output voltage of an inverter is controlled by the inverter circuitry, and does NOT follow the input voltage.

 

[wyliesdiesels]

Got a problem that is confusing me. I have an inverter that sees more than 12v when the vehicle is running, so it’s output voltage is higher than it should be. This is causing the GFCI receptacles to shut down.
Is there an AC regulator that can be used to settle the voltage, WITHOUT causing it to go too low when the DC input voltage is lower ( vehicle not running).

Thanks!

That is a strange problem and i dont think its related to the voltage. The normal running voltage of a car would need to be more than 12v to charge the batteries so this is not an anomaly.

And a GFCI has no way of knowing what the voltage is because all it measures is current going out on the hot leg and current returning on the neutral leg. Incoming voltage is inconsequential to the function of a GFCI.

 

[Captain Spaulding]

You are chasing the wrong issue. As the others said, the output voltage of an inverter doesn’t increase with input voltage, and even if it did, the GFCI doesn’t care. Likely your problem is the lack of ground/neutral bonding which will trip a modern GFCI.

 

[MattT]

The output voltage of an inverter should be controlled by the inverter circuitry, and should NOT follow the input voltage.

Fixed it for you. Inverter output voltage will fluctuate with DC bus voltage if it isn't set up to control it properly. If the OPs inverter is a cheap one it's certainly possible it's not regulating properly.

 

[slow]

what kind of inverter? Most higher end units, such as those with a gfci should be fine. Some inverters don't have 0 volts on the neutral, but -60 volts and +60 on the hot, resulting in gfci tripping instantly.

 

[Innovate1]

Got a problem that is confusing me. I have an inverter that sees more than 12v when the vehicle is running, so it’s output voltage is higher than it should be. This is causing the GFCI receptacles to shut down.
Is there an AC regulator that can be used to settle the voltage, WITHOUT causing it to go too low when the DC input voltage is lower ( vehicle not running).

Thanks!

Yes. It's called a decent inverter. It must be REALLY cheap or broken if it doesn't regulate the output voltage.

 

[rlitman]

Yes. It's called a decent inverter. It must be REALLY cheap or broken if it doesn't regulate the output voltage.

No, just broken. Inverters BY DEFINITION regulate the output voltage.

It is possible for a low input voltage to an inverter cause a low output voltage, but it is not possible for a high input voltage to translate to a high output voltage.

As for the GFCI, while it is SUPPOSED to only measure current, it can be tripped by other causes as well. A sufficiently high harmonic voltage can trigger it for example, and a cheap inverter may produce just those sort of harmonics.

 

[MattT]

Inverters BY DEFINITION regulate the output voltage.

Inverters convert DC voltage input into some kind of AC voltage output. There is nothing in their definition regarding how tightly they'll control the voltage of the AC output.

It is possible for a low input voltage to an inverter cause a low output voltage, but it is not possible for a high input voltage to translate to a high output voltage.

If low bus voltage can cause low output voltage how is it impossible for high bus voltage to cause high output voltage

 

[rlitman]

...If low bus voltage can cause low output voltage how is it impossible for high bus voltage to cause high output voltage

A low input voltage can lead to an overload condition where the output is clipped.

Look up how switching mode power supplies work.

 

[MBfreak]

In the "school book" explanation of the working of the current transformer in a GFCI the incoming and outgoing currents balance each other out, so no flux in the magnetic core and no seconday voltage to the tripcoil in the GFCI.
As long as the amount of harmonics ( ie currents with other frequencies then the 60 Hz , read up on fourier analysis) are reasonably low this is correct.
If there is a large amount of harmonics, also known as THD ( total harmonic distorsion) there may be a substantial leakage field around the ferrite core, and this field may well be asymmetrical.
Which will cause a magnetic flux, induced voltage in the CT secondary and a trip.
There are GFCI´s ( at least in europe) designed to handle large thd in the load current.

A cheap inverter may have quite some thd. Anything above 5 % should be considered substandard .

Ola

 

[theoldwizard1]

Likely your problem is the lack of ground/neutral bonding which will trip a modern GFCI.

INCORRECT ! As a matter of fact, a GFCI can be used in old 2 wires homes with no ground wire. The basic premise of a GFCI is to compare the amount of current going into the load to the amount of current coming out of the load. If they are different, it trips.

 

[American Locomotive]

It is possible for a low input voltage to an inverter cause a low output voltage, but it is not possible for a high input voltage to translate to a high output voltage.

If the control circuitry of an inverter was poorly designed, it is totally possible for output voltage to increase with input voltage. Switch mode power supplies vary duty cycle of the switching transistors to maintain output. As load increases, the duty cycle needs to increase. If input voltage increases, duty cycle should decrease.

It's entire possible for output voltage to drift up with input voltage if the inverter is poorly designed. For example, the output voltage could increase if the inverter's reference voltage is based on the input voltage, if it has a high minimum duty cycle, or it's some sort of weird self-regulating resonant design that relies on a steady input voltage.

 

[rlitman]

...It's entire possible for output voltage to drift up with input voltage if the inverter is poorly designed. For example, the output voltage could increase if the inverter's reference voltage is based on the input voltage, if it has a high minimum duty cycle, or it's some sort of weird self-regulating resonant design that relies on a steady input voltage.

Not for an inverter. You're thinking of a simple DC-DC switching-mode supply, and in such a supply, those issues might be possible. But in an inverter, the output voltage is AC, which as we all know is ALWAYS changing, so it requires a gate driver that is immune to such issues in order to work at all.

 

[American Locomotive]

The output being AC doesn't mean anything. All switching power supplies function on AC internally, and rely on the output being rectified in some manner to become DC.

Simple inverters have a 12v > 120v transformer with a center tapped primary, and two transistors in a push-pull configuration being run by a dumb oscillator. They just alternate which transistors is on 60 times a second to generate 60hz AC. They don't even have any voltage feedback at all. Their circuit is setup such that it will generate a somewhat high voltage with no load, and then at full load it will be at the bare minimum of acceptable. Many, many cheap inverters are built in the above manner. Any change at all of input voltage will result in big changes in output voltage. They have no regulation, no feedback and no control. Look up "CD4047 Inverter".

Better inverters sample the output voltage and modify the pulse width to regulate voltage. Even better ones apply pwm modulation on top of that to create "true-sine" output. But all circuits with regulation and feedback require a reference voltage that they base their voltage measurements on. This reference voltage is usually provided by a precision voltage source chip, or a precision zener diode. If the designers of the inverter did something silly, like use the input voltage as the inverter reference, than any change in input voltage will result in the output voltage changing.

 

[Captain Spaulding]

INCORRECT ! As a matter of fact, a GFCI can be used in old 2 wires homes with no ground wire. The basic premise of a GFCI is to compare the amount of current going into the load to the amount of current coming out of the load. If they are different, it trips.

Yes it can, but there is more to modern GFCIs. When a non-standard setup is used to source power, like a generator or inverter, you commonly see ground neutral bonding downstream of the power source, and a GFCI will detect what it sees as a neutral to ground short and it will trip.

 

[MatBirch]

Thanks guys!
Ok- so it is a cheap(er) inverter. Samlex SAM3000 12v. Modified sine wave.
It’s not broken, happens on each and every unit. Changing isn’t practical due to a specific mounting requirement, but worse is the entire “governing by committee” aspect which would take MONTHS!
Does not trip the GFCI. It merely turns the little indicator light red, and quits working. Either shut the engine off, or switch to shore power, and it works fine, NO reset needed.
The output voltage of the inverter definitely increases when the engine is running. I can only assume it’s due to the increase in voltage from around 12, to 14.4v. This will also cause further issues if the problem is not identified, as the alternator output will vary depending on loads like the a/c. Possibly causing that GFCI to come on and off?.


I know part of the problem is that the inverter is already GFCI protected, yet the customer insists on feeding another GFCI.
At this point my proposed solution is to add another GFCI. lol.
If I swap out the existing outlet for a standard, the inverter causes no trouble, and is already fault protected. If I then add a GFCI outlet between the shore power plug and the transfer switch, then the shore power input would be protected as well. This change would likely not need to go to committee as the cost would just be absorbed in the hopes of a savings on the warranty/service dept side of the equation.

 

[American Locomotive]

Well here we go, specs for the unit:
Output Voltage Regulation: +13% / - 0%. That's up to 130v, which is pretty extreme.