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Inverter - RCBO - Switch Mode
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06-01-2014 1:28am#1
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An existing spur from the inverter will give me the same problem further downstream. Unless you are suggesting the current spike will be lost as heat dissipation I'm not sure how this would help. This is for a mobile application.
The Earth potential difference is provided by an earth spike. Not always a DB.
The inverter otherwise is an unearthed "generator".
What I'm trying to figure out is what's the best way to protect against earth leakage in a circuit similar to this (ignore the galvanic isolator);
I'm thinking of exchanging an existing RCD for an RCBO.
It is required to run SMPS (this is slightly academic as I actually use a DC boost regulator but I'm still curious as to the best approach).
If an RCBO is unsuitable what would you recommend?0 -
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I'm highly dubious there's much in the way of earth fault protection in my super-cheapo chineese mod. square wave inverter.
There is over-current, over-temp and fuses.
There's no DC fuse which I had to install. A 600W inverter @12volt & 80% efficient = 70A fuse...that's a bittov an oversight if you ask me.
Certainly boats and campers are wired differently as there's no building regs and a lot of self builds.
That's not my diagram I pulled it from elsewhere as it's fairly similar to how I would do it.
The relay allows you to double functionality on sockets and wiring which keeps things fairly clean, it also isolates the heavy loads as mains only appliances.
What occurs to me is that a steel hulled boat or a camper is effectively a single insulated appliance resting on an insulator.
The laptop is not an issue it's the transients induced from the laptop power I am wondering about. What got me wondering was why a laptop power brick being double insulated has a wired earth until I learned the filtering is built in.
Although having thought about it, the transients from the charging system are likely to be much more substantial. Given that the AC Earth is bonded to the same metalwork as the DC Ground.
When thinking in terms that an inverter runs a 1000w ring main with no path to ground I am inclined to think it would be prudent to have a provision for this.
A DC power supply will run a car battery down about ~20% slower than an inverter, days would be quite ambitious. Killing a battery kills batteries
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Is there another way I could be missing?0 -
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Do you need an inverter at all?
Nope! Hate the buggers.
Rather looking at it than for it though. Can't seem to find a DC angle grinder
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I did mention earlier this was an academic question.
What is the supply voltage?
What voltage does the laptop operate at?
12V
Please forget about the laptop it was just an example of a switch mode power supply load.
I would like to run any SMPS I want.
The laptop is 19v and is happily running on a DC power regulator as I type this.
I do not understand your question.
Where would the potential difference be, between what 2 points?
What type of failure?
EG.
Say the movement from driving saws through the insulation of a conductor. Later the inverter is fired up, the vehicle is now live sitting on rubber tyres so nothing trips everyone inside is fine, nobody notices.
An earthed outside passer-by touches the van and gets a bang.What is the vehicle, is it a camper, a boat a car?
Are you grounding the frame of the vehicle?
Is the laptop the only load you have?
Where are you getting the DC power supply from, batteries?
Camper.
Grounding (earthing) for isolated inverter use via an earth rod is what I'm currently seeking advice on. [Edit: this is to extend earthing from the frame of the vehicle]
Laptop, lights, sound, tools, dry cell devices, .....all mod cons. bar electric heat, and cooking.
Solar PV, alternator, batteries, mains and expanding :pac:.Many loads in domestic and industrial installations are not protected by RCDs or RCBOs such as cookers, lights, motors and veritable speed drives (which are a type of inverter)
It's not the loads that concern me it's the people.
However I do not want loads operating under normal conditions interfering with the people protection.Generators are frequently used to supply loads that are not protected by an RCD.
I would install an RCD downstream of a generator on circuits that are supplying socket outlets...
Indeed
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Moderators, Home & Garden Moderators, Technology & Internet Moderators, Regional East Moderators Posts: 12,641 Mod ✭✭✭✭
Join Date:Posts: 12338
Sir Liamalot wrote: »Can't seem to find a DC angle grinder.
Really?
I have one of these:
http://www.lowes.com/pd_30691-70-DC411B_0__?productId=3191267 0 -
Moderators, Home & Garden Moderators, Technology & Internet Moderators, Regional East Moderators Posts: 12,641 Mod ✭✭✭✭ Join Date:Posts: 12338
Sir Liamalot wrote: »It might help to mention the inverter is already hard-wired to several socket outlets. Sorry if that was vague it's indicated in the wiring diagram.
Oh, ok.
I assumed that these should be ignored as you said it was not your diagram.
If you wired it as shown in this block cable diagram it will work and the socket outlets will be protected by an RCD:
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Cwaor! Nice.
My batteries will last longer though
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A passer-by would have to touch the live and the neutral on the the output of the inverter to get a shock. Unless the circuit is completed it will not be possible to get a shock.
The passer-by may be "earthed" but the output of the inverter is not.
So a passer-by touching a bare metal panel of a vehicle conducting 240V AC from an inverter short and 0V planet earth is not completing a circuit?Think of this as a stand alone system like a car or a boat, you will not require an earth rod.
Does the rod not provide the needed path to ground to enable the RCD imbalance detection?When it is in circuit the RCDs will be down stream of the inverter so any leakage current from the inverter should not be an issue. It's hard to put an RCD upstream of an inverter. 0 -
Moderators, Home & Garden Moderators, Technology & Internet Moderators, Regional East Moderators Posts: 12,641 Mod ✭✭✭✭ Join Date:Posts: 12338
Sir Liamalot wrote: »So a passer-by touching a bare metal panel of a vehicle conducting 240V AC from an inverter short and 0V planet earth is not completing a circuit?
OK, so the panel is at 240V right?
That is 240V with respect to the neutral on the output of the inverter.
So the passer-by by touching the metal is not completing the circuit, see the "not shocked person" in these diagrams:
Does the rod not provide the needed path to ground to enable the RCD imbalance detection?
An RCD measures the current that flows down the phase conductor (live) and compares it to the current returning on the neutral conductor. When the circuit is functioning correctly these currents are equal. If there is a difference of > 30mA then the RCD will trip. It's hard to put an RCD upstream of an inverter.
No, it is easy to install an RCD upstream of an inverter.0 -
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tehehe you busted my post deletion I was doubting myself...not a bad thing though had a root in the electrical closet and found I had an MCB on the main AC in where I thought I bought an RCD.
Single insulated DC inverters have an earthing point on the casing for external earthing.
Yeah ideally you wouldn't bond the DC ground and the AC earth to the same point. It causes all sorts of problems (including mental ones
), galvanic corrosion can be a big resultant issue.
Realistically you sacrifice the potential risk to batteries and electronics for the safety of people and do what you can with diodes, anodes, trips and fuses.
Earthing can be achieved easily through the mains connection but that's not always available.
So far this is the best info I've found on the subject. Actually re-reading over it verifies what you said earlier, so thanks.0 -
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