Earthing a 3KW Inverter or not

[Keithwill]

Having read recently about a funster deliberating over a Aire offering an earthed or unearthed EHU. My Renault based Rimor has an earthed EHU connected to the RCD board. I have added a 3KW inverter which is completely independent from the Habitation electrics apart from adding its output to a microwave and then to a double pole isolation switch and on to the EHU RCD consumer unit/distribution box where earthing is connected. The Inverter is supplied by 2 Lead Acid 130Ah batteries and charged via a couple of 130watt flexible solar panels. The only connection to the van and habitation electrics is the 230v live/neutral/earth output from the inverter plug to the consumer unit.
Should I Earth the Inverter [spike?] separately or is the earth circuit from the inverters 230v output socket 3pin safe to use.
The inverter casing is not earthed and it is not connected to any chassis or habitation "Negative earth" and is isolated using the double pole switch prior to using any EHU be it earthed or not.
It was wired this way so that even 3amp european hookup would do lighting tv etc and 3kw inverter could be used independantly if necessary for microwave and kettle and single hob. Also with a separate cheap solar setup that can be pointed to the sun whichever direction I had to park.

 

[Spriddler]

The advice here from a couple of knowledgeable Funsters may help..........

Inverter grounding – when there is no EHU connection to the sockets

This will be a long post & is only likely to be of much interest to a small group of people. Feel free to scroll on by! It is a variation on a topic often discussed. Most vans start of with 230v sockets powered by an EHU connection & an inverter is added later. Sockets can often be powered by...

www.motorhomefun.co.uk

 

[headlight]

Having read recently about a funster deliberating over a Aire offering an earthed or unearthed EHU. My Renault based Rimor has an earthed EHU connected to the RCD board. I have added a 3KW inverter which is completely independent from the Habitation electrics apart from adding its output to a microwave and then to a double pole isolation switch and on to the EHU RCD consumer unit/distribution box where earthing is connected. The Inverter is supplied by 2 Lead Acid 130Ah batteries and charged via a couple of 130watt flexible solar panels. The only connection to the van and habitation electrics is the 230v live/neutral/earth output from the inverter plug to the consumer unit.
Should I Earth the Inverter [spike?] separately or is the earth circuit from the inverters 230v output socket 3pin safe to use.
The inverter casing is not earthed and it is not connected to any chassis or habitation "Negative earth" and is isolated using the double pole switch prior to using any EHU be it earthed or not.
It was wired this way so that even 3amp european hookup would do lighting tv etc and 3kw inverter could be used independantly if necessary for microwave and kettle and single hob. Also with a separate cheap solar setup that can be pointed to the sun whichever direction I had to park.

Just for your information 260AH of lead acid batteries are rated to deliver about 52 A/H.
A microwave of say 1,000 watts will draw about 100 A/H when running, maybe 50% more on start up so you would be drawing roughly twice your batteries rating which will reduce their life.
Also a 3,000 watt inverter will draw about 300 A/H if delivering its full power, again well over your batteries ratings.
If you want to stick to your batteries ratings then you shouldn't use anything that draws more than about 50 A/H or about 600 watts.
Drawing more than this will result in reduced battery life and probably inverter shut downs due to low voltage.
The more often you do this the quicker your batteries will die.
Personally I wouldn't run bigger than a 600 watt inverter with your batteries.

 

[Lenny HB]

Agree crazy to try and run a 3k inverter off 260ah of lead if you are going to stick with lead you will need at least 1250ah of Lead batteries.
So best to fit Lithium.

 

[headlight]

Agree crazy to try and run a 3k inverter off 260ah of lead if you are going to stick with lead you will need at least 1250ah of Lead batteries.
So best to fit Lithium.

Agreed or don't run a microwave or anything that draws more than about 600 watts which makes it pretty pointless to have fitted/fit a 3,000 watt inverter.

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[tinkertaylor]

Have you got any installation instructions from the inverter, my victron inverter asks for earthing?

 

[Lenny HB]

Have you got any installation instructions from the inverter, my victron inverter asks for earthing?

Some inverters can be earthed some can't so important to read instructions. If they can be best to fit an earth then you can fit an RCD.

 

[Keithwill]

Thanks to all for advice. Before fitting the additional batteries and inverter I read through the thread suggested by Spriddler before installing the modifications. Some additions to the conversation have been added but as with a lot of threads the conversation usually results in no definitive answers, only conflicting views by some "experts" who lose us with tech terms and debate between themselves on who's right and wrong on a technical issue. The last post actually nearly explained an answer:

It has to be done by a relay, to allow you to operate in both modes: ehu-relay open, and stand alone relay closed/ bonded. Unless you remove the bond manually, each time you connect to ehu; but, that’s until you forget once.
If you have ehu and the bond, that becomes very dangerous, as you will link the ehu neutral to your chassis, very bad. To the chassis is only bonded the PE.
Hence, if folk don’t understand AC earthing it’s hard to explain, and best for them to seek professional help.

Perfect, thanks. Yes, this is what I was eluding to. Having a relay which operates when on ehu with a n/c contact which ties the DC - to AC N. When on ehu this relay operates to open the connection (and also power the fridge and charger).

Now if only the experts could explain "which operates when on ehu with a n/c contact which ties the DC - to AC N" means in laymans terms and identify the relay needed and the connection and wiring details that would answer my question.

Why has the capacity of Lead acid batteries suddenly been downgraded! When deciding on battery capacity it was extensively quoted as "the safe working capacity of a lead acid leisure battery should be calculated as no more than 50%. Quite a few threads on here work on that assumption, which I assumed would give me roughly 130AH to use. Why are these batteries rated at 130AH each when there is no way that even half of that is actually usable capacity.

 

[Raul]

Just to clarify, the floating earth does not tie to DC- , don't do that. It ties to the N AC output only in one place: inside the inverter. This floating earth is a return path for fault current back to source: inverter, not on DC -.
But, as Lenny mentioned in his last post, make sure your inverter is capable of being earth bonded.

 

[Otter Spotter]

Thanks to all for advice. Before fitting the additional batteries and inverter I read through the thread suggested by Spriddler before installing the modifications. Some additions to the conversation have been added but as with a lot of threads the conversation usually results in no definitive answers, only conflicting views by some "experts" who lose us with tech terms and debate between themselves on who's right and wrong on a technical issue. The last post actually nearly explained an answer:

Perfect, thanks. Yes, this is what I was eluding to. Having a relay which operates when on ehu with a n/c contact which ties the DC - to AC N. When on ehu this relay operates to open the connection (and also power the fridge and charger).

Now if only the experts could explain "which operates when on ehu with a n/c contact which ties the DC - to AC N" means in laymans terms and identify the relay needed and the connection and wiring details that would answer my question.

Why has the capacity of Lead acid batteries suddenly been downgraded! When deciding on battery capacity it was extensively quoted as "the safe working capacity of a lead acid leisure battery should be calculated as no more than 50%. Quite a few threads on here work on that assumption, which I assumed would give me roughly 130AH to use. Why are these batteries rated at 130AH each when there is no way that even half of that is actually usable capacity.

Lead batteries will degrade quickly if you drain them below 50% whereas Lithium will let you use nearly the full 100% without degrading the battery. An expert will give you a better answer .

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[VXman]

Agreed or don't run a microwave or anything that draws more than about 600 watts which makes it pretty pointless to have fitted/fit a 3,000 watt inverter.

Can you elaborate on this? Is it just about not taking your batteries below 50% or are you saying if ran a 900 watt kettle for say 3 minutes are you saying this will damage 260AH of lead acid battery even thought the batteries have plenty of charge. In other words is it also the amount of power you are drawing, not just to do with the level of charge in the battery?

 

[Lenny HB]

Why has the capacity of Lead acid batteries suddenly been downgraded! When deciding on battery capacity it was extensively quoted as "the safe working capacity of a lead acid leisure battery should be calculated as no more than 50%.

It is the maximum discharge rate you are exceeding you shouldn't discharge a LA at more than the C5 rate which for a 100 ah battery is 20 amps. 1000 watts is is 83 amps at 12v so support that you need
83/20*100+10%=456.5ah of battery, the 10% is for inverter inefficiency.

 

[tinkertaylor]

are you saying if ran a 900 watt kettle for say 3 minutes are you saying this will damage 260AH of lead acid battery even thought the batteries have plenty of charge.

Yes he is

 

[autorouter]

Now if only the experts could explain "which operates when on ehu with a n/c contact which ties the DC - to AC N" means in laymans terms and identify the relay needed and the connection and wiring details that would answer my question.

You want something that disconnects the neutral wire from the earth when an EHU supply is available, and reconnects it when the EHU is disconnected.

A relay is an electrically operated switch. It has a magnetic coil which pulls two power contacts together when a small current is passed through the coil.

The coil takes a very small amount of power, and you buy the relay with the coil of the correct voltage for the job. In a vehicle, most relays have a 12V coil. But they are available with 5V, 12V, 24V and 240V coils. If you want to switch the relay with a mains supply, as in this case, you want one with a 240V coil.

The power contacts in the simplest case are two contacts that pull together when the coil is energised and becomes magnetic. When not energised, the contacts are off (open), and when energised they are on (closed). This arrangement is described as 'Normally Open', ie when not energised, the contacts are open. Abbreviated to 'NO'. This simple relay is not quite what you want for this job.

Another variant of the relay has three power contacts. The contact flips from one to the other when the coil is energised, like a 2-way switch does. In detail, the common contact is connected to one power contact when the coil is not energised. The common contact disconnects from that contact, and flips to the other contact when the coil is energised.

When not energised, the common (COM) contact is connected to the 'normally closed' (NC) contact. When energised, the COM contact disconnects from the NC contact and connects to the 'normally open' (NO) contact.

A relay like this will have five terminals: two for the coil, and three power contacts: COM, NO and NC.

So for your case you want a 5-terminal relay with a 230V coil, and you can use the COM and NC power contacts. The NO contact can just be ignored.

 

[PeterCarole29]

Not wanting to digress from the op question but 3kw multiplus has an earth point
Then I assume this connection goes to the earth consumer unit on 240v side ? It is positioned lower middle of the unit and is a bolt stud with nut fixing

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[VXman]

Yes he is

Sorry for not being specific enough. Can someone elaborate on that and explain the technical stuff in reasonable plain English?

 

[Lenny HB]

Not wanting to digress from the op question but 3kw multiplus has an earth point
Then I assume this connection goes to the earth consumer unit on 240v side ? It is positioned lower middle of the unit and is a bolt stud with nut fixing

The Multiplus has a relay that changes the earth over as required, the neutral of the inverter output is earthed as default but the link can be removed if required.

 

[Lenny HB]

Can you elaborate on this? Is it just about not taking your batteries below 50% or are you saying if ran a 900 watt kettle for say 3 minutes are you saying this will damage 260AH of lead acid battery even thought the batteries have plenty of charge. In other words is it also the amount of power you are drawing, not just to do with the level of charge in the battery?

Sorry for not being specific enough. Can someone elaborate on that and explain the technical stuff in reasonable plain English?

A 900 watt kettle will draw approx 83 allowing for inverter efficiency, if you value your batteries and want them to have a long life the max load you should draw from 260ah batteries is 52 amps (C5 rate).
Drawing 83 amps on a regular basis will shorten their life. If you were to do it occasionally say once or twice a week that would be OK but a kettle ½ doz times a day is not a good idea.

 

[Otter Spotter]

Can I ask if one has a 3000w invertor and you use it for boiling a kettle, is the invertor working at max capacity and thus draining battery or would it be working at lower rate than its maximum.
I ask as I have a 3000w invertor and currently only use it for kettle and have shied away from using our microwave via the invertor to date, the microwave is a 800w Boch microwave/grill, I will want to use it via invertor but what issues can I expect? Battery is currently 110ah lithium.

 

[Lenny HB]

Can I ask if one has a 3000w invertor and you use it for boiling a kettle, is the invertor working at max capacity and thus draining battery or would it be working at lower rate than its maximum.
I ask as I have a 3000w invertor and currently only use it for kettle and have shied away from using our microwave via the invertor to date, the microwave is a 800w Boch microwave/grill, I will want to use it via invertor but what issues can I expect? Battery is currently 110ah lithium.

It will use the same power as the device you are using plus about 10%.

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[headlight]

Keithwill the problem isn't the amount of amps you're taking out of the batteries it is how fast you are taking them out as you are taking them out much faster than your battery is rated to do so.
You are correct that a lead acid has 50 per cent usable amps.
It's just that it is not rated to deliver those amps as fast as you are intending to draw them
Do it regularly and you will shorten the batteries life or even damage a cell which means the battery is kaput.
I only posted to try and save you future problems with your batteries.

 

[autorouter]

Why has the capacity of Lead acid batteries suddenly been downgraded! When deciding on battery capacity it was extensively quoted as "the safe working capacity of a lead acid leisure battery should be calculated as no more than 50%. Quite a few threads on here work on that assumption, which I assumed would give me roughly 130AH to use. Why are these batteries rated at 130AH each when there is no way that even half of that is actually usable capacity.

I think there is some confusion over amps (A) and amp-hours (Ah). The units are not user-friendly, you have to get your head round them.

Amps (A) is a rate of flow of electric charge. It is easy to measure with a multimeter or clamp meter.

Amp-hours is an amount of electric charge. So if charge flows at the rate of 10 amps for 13 hours, then a total amount of charge that has flowed through the wire is 10 x 13 = 130Ah. It is very difficult to measure electric charge directly, it's easier to measure amps, and time, and do the calculation.

It is the exact opposite of water flow in a pipe, where the amount of water is in litres, and the flow rate is in litres per second, or litres per hour.

There is in fact a proper official unit of electric charge, called the Coulomb. If there's a current of 10A in a wire, that means 10 coulombs per second are passing through the wire.

One amp-hour (Ah) is the amount of charge through a wire when 1 amp is flowing for one hour. Since 1 amp is 1 coulomb per second, and an hour is 3600 seconds, that means 1Ah is just 3600 coulombs. It is an amount of electric charge. However, nobody uses coulombs, they always use Ah, so I won't mention them again.

Batteries store electrical charge. A 130Ah battery can store 130Ah of charge. Some batteries are degraded rapidly by taking too much of that charge out in total. Some lead-acid batteries don't like going below 50%. Some lithium batteries can be taken down to 10% or even 5% without degradation.

The other question is how fast can the charge be taken out. A starter battery will happily provide several hundred amps for a few seconds, but likes to be charged up asap afterwards. Other batteries like gel types are best kept below an amp rate of C5, ie a fifth of the Ah capacity. So a 130Ah gel battery should not be discharged faster than 130/5 = 26A.

Other battery types have other discharge rate (amps) limits, but C5 is a reasonable average for leisure batteries. Lithium batteries generally have higher permitted discharge rates than lead-acid batteries.

It's a common mistake to think that a 130Ah battery can be discharged at 130A. That's a C1 discharge rate, and only the best lithiums will do anything like that.

 

[Lenny HB]

One amp-hour (Ah) is the amount of charge through a wire when 1 amp is flowing for one hour. Since 1 amp is 1 coulomb per second, and an hour is 3600 seconds, that means 1Ah is just 3600 coulombs. It is an amount of electric charge. However, nobody uses coulombs, they always use Ah, so I won't mention them again.

Thank goodness for that.

 

[Keithwill]

You want something that disconnects the neutral wire from the earth when an EHU supply is available, and reconnects it when the EHU is disconnected.

Reading other posts it is stated that "the only connection between earth and neutral should ONLY be inside the inverter. So now I am confused as to how an external relay would be wired to accomodate this.
Many thanks to contributers to this thread so far, I think the lead acid battery explanations especially have surprised many.
I think as of today the definitive answer to earthing is still elusive. I nearly bought a Renogy 2kw inverter with a earthing system inbuilt but decided the extra £159 could be saved by a simple 3way switch!
My inverter is a pure sine wave chinese "budget" model. I doubt it has any swtchable earth and there are no real instructions. I will remove the UK outlet socket and check wiring regarding earth but no earthing inside will be the most likely outcome.
The EHU unit has a small enclosure that it is wired into which houses 2 outlet plugins labelled in Italian [ 1 to control unit for sockets and charger and 1 for fridge. ] The two earth wires are connected direct to the EHU incoming earth, live and neutral are connected to a mcb switch. There is no connection anywhere I can see that connects earth wiring to neutral as would be in a domestic consumer unit. I imagine this is a very common 230v setup as most Motorhomes are built in the EU.
Previous owners have added various lighting and switching to the 12v system but the 230v circuit and ehu circuit are manufacturer standard, ie very basic european regs of 2014/15. To get to a stage where full automatic earth coupling / un-coupling would be to change to a "consumer unit with RCD and mcb tripping" and installing a relay as previously detailed. I am assuming all these modifications would only be workable if my cheapo inverter has internal earthing capabilities. Or the inverter isolated from the original 230v system entirely and rely on a "don't touch anything metal" safety system ;-(
Thanks again to all you electricians who have explained the shortcomings of our battery systems and safety.

 

[GrahamPye]

Since this seems to be a quite active thread (and indeed as others have said very informative - I have an Electronic Engineering degree so I should know all this stuff!!) I'd like to add a couple more questions:

What are the pros and cons of wiring all the van's mains sockets to the inverter as opposed to just providing one (or a small number) to be powered by the inverter. Which I s how I have it wired (experimentally) at the moment. I know that I have to avoid the inverter powering the mains charger and stopping the fridge switching to mains, but anything else?

If I do want to put all the mains powered devices (with the above restrictions) on the inverter, does the team favour a manual switch or an automatic change with an appropriately wired relay? And is it necessary to switch both live and neutral - I presume yes in case the EHU has live and neutral swapped.

And as discussed above and in the other helpful thread) earthing is challenge too...

Finally, if I do go for a manual switch (which I'd prefer not to) is there anything more attractive (i.e. less industrial looking) than the commonly recommended Heschen rotary switch?

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[tinkertaylor]

240v in a van isn't for the faint hearted especially with fixed sockets. Tbh self installers with no electrical background need to be very wary of what they are installing, especially when ehu is added into the equation.

I have an victron inverter fitted as per their instructions. If I was to do it again I would try an avoid 240v (inverter fed) and stick to gas, diesel and 12 volt appliances. I'm a fully qualified electrician with inspection and test certification.

List what you need 240v for and I'm pretty sure 90% of applications can be replaced with a 12 volt one or isn't vital to your motorhome use/fun.

 

[Lenny HB]

If I do want to put all the mains powered devices (with the above restrictions) on the inverter, does the team favour a manual switch or an automatic change with an appropriately wired relay? And is it necessary to switch both live and neutral - I presume yes in case the EHU has live and neutral swapped.

I used a 240v 30amp double pole relay for my auto switching, coil wirthed to incoming mains (via a fuse). Relay N.C. all sockets in the van are connected to the inverter, relay N.O. all sockets connected to incoming mains. Fridge & charger only connected to incoming mains.
Mainland Europe often don't worry about which way live and neutral are connected so best to switch both poles.

Basic circuit of what I did.

 

[Insider]

Sorry for not being specific enough. Can someone elaborate on that and explain the technical stuff in reasonable plain English?

Consider it like walking versus running. You could walk 10miles but if I asked you to sprint 10miles at your fastest pace how far would you get? Same with batterys, esp Lead Acid. They hold an amount of energy(represented in AmpHr typically) which is akin to the distance(miles). How quickly they deliver this is akin to walking versus running(represented in Amps ypically). If you "run" too fast then likely you'll have heart damage and if you discharge the lead acid batteries too fast then they'll have the equivalent of heart damage - they'll work but not at the same pace/capacity. Microwave, hairdrier, heating water=running. Led lights, charging phone=walking.

 

[GrahamPye]

List what you need 240v for and I'm pretty sure 90% of applications can be replaced with a 12 volt one or isn't vital to your motorhome use/fun.

Ah, but the definition of vital means different things to different people In my case vital means my wife's hairdryer (very vital!) and my coffee machine and toaster. I realise that the last two could be replaced by an AeroPress and a gas grill but since I have to have the inverter for the hairdryer I might as well use the other two appliances as well.

I used a 240v 30amp double pole relay for my auto switching, coil wired to incoming mains (via a fuse). Relay N.C. all sockets in the van are connected to the inverter, relay N.O. all sockets connected to incoming mains. Fridge & charger only connected to incoming mains.
Mainland Europe often don't worry about which way live and neutral are connected so best to switch both poles.

Yes, that's what I thought. Where are you on the earth connected to neutral debate? And where in your wiring do you have RCD(s)?

All these relays and RCDs will probably take up a lot of space and I've pretty well filled the "power" area under one of the seats already, I'd also like more than two MCBs to split the mains wiring up a bit :-(

Finally, I see you've retained the mains connection to the Electroblock. I'm superseding the mains charger in the Bloc with a separate one (partly because the built-in one is about to die!) so I'm wondering if I actually need to give the Bloc a mains input at all. The wiring diagram doesn't show the mains going to anywhere other than the charger, but it still puts a little picture of an EHU connection on the control panel when the mains is connected, but I can't think of any other reason why it might need to know that mains was present.

Thanks, Graham

 

[Lenny HB]

Yes, that's what I thought. Where are you on the earth connected to neutral debate? And where in your wiring do you have RCD(s)?

I did fit an RCD but it is redundant as I couldn't earth the neutral on my inverter.

Finally, I see you've retained the mains connection to the Electroblock. I'm superseding the mains charger in the Bloc with a separate one (partly because the built-in one is about to die!) so I'm wondering if I actually need to give the Bloc a mains input at all. The wiring diagram doesn't show the mains going to anywhere other than the charger, but it still puts a little picture of an EHU connection on the control panel when the mains is connected, but I can't think of any other reason why it might need to know that mains was present.

Mains to the ELB only supplies the charger for Hab & Cab batteries and a light for mains connected on the control panel.
I still use the EBL charger as I have Gel batteries.

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