mattonthesea
Well-known member
Very useful info. Thanks
Does that mean that modern invertors will/should have transformer isolation between AC input and AC output?
Electrocution risk in marinas
- Thread starter Beneteau381
- Start date
Does that mean that modern invertors will/should have transformer isolation between AC input and AC output?
mjcoon
Well-known member
Years ago I sent YM a snotty letter pointing out that they had meant to recommend the use of isolating transformers but had called them "autotransformers". (Which very definitely don't!)
rogerthebodger
Well-known member
Are you talking about combined inverter chargers or just an inverter as an inverter have DC input and a AC output.
An combined inverter charger has AC input with DC output on the charger side or a DC input with a AC output inverter side.
My view is that all chargers should have an isolating transformer on thee AC input side to isolate the AC and DC side of the boat power setup
mattonthesea
Well-known member
I was looking at this one. It appears to have an AC in and out with a automatic switch between AC in and 12V in when on/off shore power.
2000W 12V Pure Sine Wave Inverter with UPS Function
Correct me if I'm wrong
oldmanofthehills
Well-known member
Nothing in the online spec to suggest ac to ac isolation. The old inverters used to have a tranformer thus effectively separating dc and ac, but isolation not always in modern switched mode supplies ie probably is but checkI was looking at this one. It appears to have an AC in and out with a automatic switch between AC in and 12V in when on/off shore power.
2000W 12V Pure Sine Wave Inverter with UPS Function
Correct me if I'm wrong
westernman
Well-known member
What do you connect the earth to?I was looking at this one. It appears to have an AC in and out with a automatic switch between AC in and 12V in when on/off shore power.
2000W 12V Pure Sine Wave Inverter with UPS Function
Correct me if I'm wrong
Presumably it does not have an earth relay as a marine inverter/charger would.
mjcoon
Well-known member
I've only seen the insides of low-power switched mode power supplies, but they had optical coupling from output to input side to maintain the isolation, and the PCB marked accordingly.
oldmanofthehills
Well-known member
I can see how optical diodes could just give big enough input for photo sensitive receivers at low power, but a 2000W internal laser and giant internal ‘solar’ panel seems an unlikely solution for a 2000W inverter.
If there is isolation it will be via transformers
rogerthebodger
Well-known member
This device being a UPS to indicates a battery charger powered by mains supply incorporating an inverter which is a power supply device. which have different earthing requirements.
I have separate mains battery charger and inverter and what I have done in the following.
The battery charger as a power using appliance with a metal case has that metal case connected to the incoming earth line and the live and neutral si supplied via an RCD so f there is a live to case fault th RCD will trip cutting off the mains supply.
My inverter being a mains power supply device that supplies mains power via an RCD to any power appliances needs the neutral connected to the earth line to provide an path for any leakage current where a powered appliance has a live to case fault.
Having a combined device without knowing the detailed internal construction ans operation its difficult / imposable to specify a safe earthing connections and we don't have the detailed knowledge to make a determination.
Personally I would not use a combined charger / inverter on my boat. I do have a UPS at home on my computer due to our load sheading
mjcoon
Well-known member
Ha ha! (But I could not see a smiley.) Yes, of course, the power isolation is via a transformer. Though I do wonder how they manage it in the tiny transformers that are used in low-power wall warts. The optical coupling is in addition, providing a feedback loop. I would be extra impressed if such were used in a DC->AC inverter, especially how power, as for a AC->DC wall wart.
Stemar
Well-known member
I don't know if it's changed now, but around 40 years ago, that wasn't necessarily the case in France.
rogerthebodger
Well-known member
There are various stiles of mains distribution setup like TI, TT, TN and each have their pros and cons.
The Where I live is TNCS or some time called PME
BS 7671 lists five types of earthing system: TN-S, TN-C-S, TT, TN-C, and IT. T = Earth (from the French word Terre) N = Neutral S = Separate C = Combined I = Isolated (The source of an IT system is either connected to earth through a deliberately introduced earthing impedance or is isolated from Earth.
Is TNCS the same as PME ( Protective Multiple Earthing )
TN-C-S is considered PME (protective multiple earthing) when the supply PEN (protective earth neutral) or CNE (combined neutral earth) conductor is earthed at multiple points of the supply, as well as the source itself, therefore providing a low- impedance path to Earth for all parts of the PEN conductor.
The UK has 3 earthing types
Mains electricity systems are categorized in the UK according to how the earthing is implemented. The common ones are TN-S, TN-C-S and TT.
In France the TT system
oldmanofthehills
Well-known member
At the substation the earth and neutral will be the same voltage in TNCS. Any distance away, they wont be as the earth or earth path wire has resistance. Any earth wire is also capacitatively coupled to the live wire so can have voltages induced in it if long enough.
Enough on a 5kn separation to blow 60v surge protection fuses in electronics, and still sometimes detectable on shorter domestic runs if using high impedance testing equipment.
