Can I safely connect my Inverter to my EHU input socket? (1 Viewer)

[Divertrev]

Although I have a twin Gaslow system I’m looking to utilise my Solar/Lithium system to greater effect e.g. Induction Hob and/or the inbuilt Truma Water Heater, Fridge etc.
My Rig & Kit
Burstner Delfin
2kw Renogy Inverter with mains switchover facility. Earthed to chassis.
The Inverter outlets connect to 240v sockets via RCDs and are independent circuits from the original mains sockets that run from the EHU input.
240v weatherproof external outlet socket from the inverter fitted.
300ah FOGSTAR Drift Lithium battery.
Solar panels totalling 380w
30amp B2B.

Seemingly I am now able to run a standard EHU cable from the external outlet that’s powered from the Inverter to the 3-pin original Burstner EHU Input which in turn has an RCD Consumer Box panel. All the EHU electrics remain unchanged from the original Burstner Delfin installation as my additional electrics from Solar Panels and Inverter go direct to the Fogstar Leisure Battery and do not go via any Burstner circuits.

Because I’m using the original mains EHU input I’m “fooling” the system to think it’s on a mains site hook up and therefore powers up the Truma water heater and the fridge too!

On the face of it I have enough wattage/Amp-hours to run up to a 2kw induction hob and alternately run the Truma HW heater. I have the Fogstar Battery Management App which tells me what is occurring and herein is my question. The Truma HW Heater should be drawing 3.9 A on the 900 W or 7.8 A on the 1800 W settings. According to my Fogstar App it’s drawing between 70-80 Amps!! Not for very long as I shut it down very promptly.

Am I doing something dangerously wrong and potentially frying my circuits and killing my battery or is the App giving me a false reading? None of the other meter readouts are indicating anything other than a normal draw.

Some helpful guidance from electrically minded Funsters please.

 

[meanders]

I suspect the App is showing amps going out of the battery at 12v nominal and the 3.9/7.8A are at 230V nominal. I.E very roughly 900W and 1800W.

Multiply the 3.9 and 7.8 x 20 to get those figures at 12V giving just shy of 80A and 160A at 12 V. The lower one matches the figure you report.

Watts = Volts X Amps. For the sake of simplicity in calculating, 230V is 20 times bigger than 12V.

 

[chaser]

Presumably if you connect it to your ehu it's going to try charging your battery as well.

 

[Divertrev]

I suspect the App is showing amps going out of the battery at 12v nominal and the 3.9/7.8A are at 230V nominal. I.E very roughly 900W and 1800W.

Multiply the 3.9 and 7.8 x 20 to get those figures at 12V giving just shy of 80A and 160A at 12 V. The lower one matches the figure you report.

Watts = Volts X Amps. For the sake of simplicity in calculating, 230V is 20 times bigger than 12V.

Thank you Meanders, I think your reasoning is bang on. I understood the formulae but had overlooked that the App is measuring a 12v battery. So to be sure, I'm not in reality frying my cables and battery then and more importantly I'm not likely to fry myself!?

 

[Divertrev]

Presumably if you connect it to your ehu it's going to try charging your battery as well.

Yes I suppose it would be. Not sure what the consequences to that are. I'll be interested to receive some feedback on that one.

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[meanders]

Nothing is free so relying totally on the battery charger, you would eventually empty the batteries. I would be inclined to turn the charger off whenever you connect it.

 

[Divertrev]

Nothing is free so relying totally on the battery charger, you would eventually empty the batteries. I would be inclined to turn the charger off whenever you connect it.

Not clear on your response. I think you are referring to the 'circle' of the battery sort of charging itself. As you say nothing is free and if it was it would be the answer to the planet's conundrum of clean limitless energy for free! My query with the 'circlular' discharge/charge is, is it causing damage?

 

[TheBig1]

there is at least a 10% loss in power inverting 12v DC to 240v AC. So you would rapidly flatten the battery if running the charger and even more if you tried heating or hot water

 

[Tombola]

Yes you can, I used to do it the odd time, and get plenty of questions when on Aires asking why a cable comes out my van window into my EHU.

I have renogy 2000-4000
2x 200 lithium
600w solar

turn off the battery charger that doesnt make sense

And the fridge if you want more longevity
using the truma off it will soon flatten your fogstar but you can see that in the app

 

[stevewagner]

Why don’t you just connect the inverter straight to your consumer unit, which is what it is designed to do? That’s what I did with mine, turning off the battery charger and running the fridge on gas.

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[autorouter]

Water heating requires a very large amount of heat energy. To heat one litre of water by one degree C requires about 1.2Ah from a 12V battery.

So a Truma water heater which heats 10 litres from 10°C to 40°C will need 1.2 x 10 x 30 = 360Ah. That's in theory, so add 10% to 20% for inefficiencies. So yes, it would easily empty a full 300Ah lithium battery. That's why people use gas, or hookup.

 

[meanders]

Why don’t you just connect the inverter straight to your consumer unit, which is what it is designed to do?

Surely then you runa significant risk of connecting EHU unless you have a phase matching device or auto disconnect when you connect EHU (that would need to be break before make)? Without it, something would have to give but I suspect the inverter would fail.

 

[LithiumConvert]

Could be useful to run the fridge on a ferry. (if you have enough SoC for the voyage.)
But as said above turn off the charger and Truma.

My query with the 'circlular' discharge/charge is, is it causing damage?

Not directly. But no point in running things at full power just for the sake of it. (and wasting 10% or more)

 

[stevewagner]

Surely then you runa significant risk of connecting EHU unless you have a phase matching device or auto disconnect when you connect EHU (that would need to be break before make)? Without it, something would have to give but I suspect the inverter would fail.

If you did connect EHU it automatically switches over

 

[meanders]

So do you have something like a contactor in circuit or hat detects as soon as mains power is detected,?, or is it a fancy inverter with the live mains controller built in? Not seen any with that, but it doesn't mean they don't exist. It basically the same as.UPS.

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[RedFrame]

Water heating requires a very large amount of heat energy. To heat one litre of water by one degree C requires about 1.2Ah from a 12V battery.

So a Truma water heater which heats 10 litres from 10°C to 40°C will need 1.2 x 10 x 30 = 360Ah. That's in theory, so add 10% to 20% for inefficiencies. So yes, it would easily empty a full 300Ah lithium battery. That's why people use gas, or hookup.

I'm sure your figures are correct, however.... I have just, this morning, heated 15ltrs of water for a shower and only 85Ah have been removed from my Lithium store...

Cheers
Red.

 

[Bessy765]

We have 700 watts of solar 2 x 100 amp Transporter Lithium and a Victron 12/2000/80 inverter charger. This will power share when on hook up if the current needed is more than the sites supply (Belgium site 6 amp)
Had the system designed to allow the fridge (3 way) to run from the inverter if required no B2B as not required so no need for extra sockets etc. works fine noe into its fourth year and 26000 miles no problem. Unless the site includes power not used or paid for electric. Find it will run the Freshjet 2200 for several hours if the sun is about as long as you don’t try to turn the van into a fridge.

 

[Tombola]

I have just, this morning, heated 15ltrs of water for a shower and only 85Ah have been removed from my Lithium store...

I had similar readings when tested a year or so ago, I suspected solar was adding at the time too

 

[Lee Fryer]

The Renogy inverter has a pass through when on ehu, I just conected the charger to ehu point, and separate conetion to inverter, and all sockets to inverter, so when conected to shore power every thing works as should, when not only sockets are conected to inverter.

 

[Keithwill]

A reasonably safe way to do it is to run the output from the inverter to a dedicated socket for appliances needing over 3 amps. EHU are sometimes limited to 3 amps so will not want to have this socket available when on hookup. Continue this cabling on to another socket for another appliance, kettle, toaster etc. Continue this to a double pole isolator switch and then to the output side of the MCB connected to the incoming EHU cable. I would never have the inverter and the ehu supply connected at the same time, use the double pole isolator to disconnect from the ehu circuit and always switch the onboard charger off as it does control the 230v supply and switching on some motorhomes. Check your motorhome electrical control documentation to find out about charger and control box isolation.
I have interconnected all sockets and plugs and switches with twin and earth cabling but a reliable earthing system should be researched. There is an ongoing thread about earthing which gives good advice on how to get a safe system. Inverters do not supply live neutral and earth, they supply positive and negative alternating current and very rarely are they earth capable without extensive electronic supplements.

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[MisterB]

I've had a my set up running for a while now, though it is wired differently.
My incoming supply goes through a surge protection device before the main consumer unit. The 3000w Renogy inverter is wired into the consumer unit and 304Ah lithium and I have two radial circuits from the inverter, via the two 3 pin socket outlets, one that feeds the microwave and the other feeds a single socket for the kettle and also the Truma. There are other radial circuits to other sockets from the consumer unit, but they only work when connected to EHU.
I am conscious only to use the Truma for hot water for short periods, when on battery power, but it seems to be ok so far. My next 'test', will be to see if I can heat the water when driving without taking too much out of the battery (recently fitted a B2B but haven't really used it, but I don't see why it shouldn't work?) so I can arrive at the park up with hot water already in 'the tank'.

When on EHU, the pass through facility of the Renogy inverter allows everything to function on 240v as normal without having to have a change over switch etc.

 

[dawsey]

Short answer - yes you can if sensible safely precautions are taken -
and you understand that the invertor will not power some of those heavy load devices for very long.

If using Invertor direct to the vans sub main (240V distribution board) - you need to remember to isolate either the 240V feed to the main control block (ie electroblok) to isolate the inbuilt 12V battery charger, or isolate the 12V circuit from the control unit connecting the leisure batteries to prevent the circular circuit as described in previous posts. You seriously risk damaging your charger or your main control block if you don’t do this. While these units do usually have some sort of crude charge current limiters, older ones were designed in the era before lithium batteries with very low internal resistance. They thus rely to a large extent on the much higher and ever increasing internal resistance of a lead acid battery as it charges, which limits charge current. The extremely high sustained currents possible with lithium batteries were not considered. It’s why charge current controllers are needed whem lithium batteries are used (aka B2B chargers). They are designed to safely and rapidly charge your lithiums while protecting all parts of the original charging circuits and the alternator by limiting and controlling the otherwise extreme charge currents possible with lithium batteries - and of course using a charge profile suitable for lithium batteries. Incorrect charging/cheap chargers are one of the principle cause of all these lithium battery fires we now hear so much about. The risk with the larger/higher end lithium batteries used in marine/MoHo is however greatly reduced due to the commonly specified inbuilt Battery Management Systems (BMS) - but it’s probably only a matter of time before the real nasties start to creep in
as they have done with all those electric bikes and scooters.

I did it by connecting the outlet of the invertor (exact same one as yours) to the main consumer unit via a 3 way industrial selector switch where there are two inputs - but only one can be selected. So one is the feed from the external EHU input socket and the other is the output from the invertor. I can thus select one or the other, but not both.

Then I put a 50A ideal diode in the 12V link between leisure batteries and the Schaudt Electroblok in my old Hymer - so the inbuilt mains charger can not charge the lithium leisure batteries, but the batteries can discharge to power all the normal 12V circuits as normal via the original 50A fuse. The leisure batteries will still charge from solar, or from the engine via B2B, (an integrated Renogy 50A MPPT/B2B unit) and they even trickle charge via the B2B when the starter battery is fully charged and the van is undercover but on EHU in winter (via voltage rise). It’s a bit belt and braces, but it is safe, robust, foolproof and all bases are covered.

We have used the system for 18months of living in the van. We use (alternatively) air fryer, microwave, hair dryer, TV, roof air con and all manner of other 240V stuff every day. Our 240V circuits are permanently live, only switched off when driving. The 200Ah of lithiums are kept topped up by 600W of roof solar via the MPPT/B2B. It has worked flawlessly for the whole time. We almost never need to plug in, and virtually never do, even when we can. There’s lots of free EHU in france if you know where to look.

Strangely - the only time we have ever needed to plug in EHU is full summer in south of france, where ambient temperatures are so high and the sun is so strong you have to park under a tree, then with mimimal solar (because of the shade) you need EHU for the A/C.

Alternatively you can run the ehu input to the socket at the rear of your invertor - this is neater and deletes the need for a changeover switch. You still need to disconnect/isolate your charger or use an ideal diode to protect your main 12V distribution block.

 

[RedFrame]

My next 'test', will be to see if I can heat the water when driving without taking too much out of the battery (recently fitted a B2B but haven't really used it, but I don't see why it shouldn't work?) so I can arrive at the park up with hot water already in 'the tank'.

This is exactly what we do, it stays hot for an unexpectedly long time.

Cheers
Red

 

[autorouter]

Water heating requires a very large amount of heat energy. To heat one litre of water by one degree C requires about 1.2Ah from a 12V battery.

I'm sure your figures are correct, however.... I have just, this morning, heated 15ltrs of water for a shower and only 85Ah have been removed from my Lithium store...

Yes, wrong again. Actual experimental measurements are always better than theory. Your figure is quite reasonable, and my calculation was way out. I somehow was out by a factor of 12. Here's all the steps, for anyone who wants to check how I worked out the figures, which now agree with your measurement..

Heat energy is measured in Joules. It takes 4184J to heat one kilogram of water from 20°C to 21°C. It varies slightly over the range of 0°C to 100°C, so usually a figure of 4200J is a reasonable average value.

One litre of water is approximately one kilogram. It expands as it heats up, so the exact figure varies, but for most purposes 1 litre = 1 kilogram.

From a 12V battery, 1Ah is 12 x 1 = 12Wh. Since 1 hour is 60 x 60 = 3600 seconds, that means 1Ah = 12 x 3600 = 43200 watt-seconds. 1 watt-second = 1 joule. So 1Ah is 43200J

The energy required to heat one kilogram of water by 1 °C is 4200J, which in Ah is equivalent to 4200 / 43200 = 0.0972Ah, ie about 0.1Ah, from a 12V battery.

The energy required to heat 10 litres of water from 10°C to 40°C is 0.1 x 10 x 30 = 30Ah.

In your case, it's probably 15 litres of water from 10°C to 60°C, which is 0.1 x 15 x 50 = 75Ah.

There would of course be heat losses, so a figure of 85Ah is about right. Now that I've got the calculation correct.

 

[MisterB]

Yes, wrong again. Actual experimental measurements are always better than theory. Your figure is quite reasonable, and my calculation was way out. I somehow was out by a factor of 12. Here's all the steps, for anyone who wants to check how I worked out the figures, which now agree with your measurement..

Heat energy is measured in Joules. It takes 4184J to heat one kilogram of water from 20°C to 21°C. It varies slightly over the range of 0°C to 100°C, so usually a figure of 4200J is a reasonable average value.

One litre of water is approximately one kilogram. It expands as it heats up, so the exact figure varies, but for most purposes 1 litre = 1 kilogram.

From a 12V battery, 1Ah is 12 x 1 = 12Wh. Since 1 hour is 60 x 60 = 3600 seconds, that means 1Ah = 12 x 3600 = 43200 watt-seconds. 1 watt-second = 1 joule. So 1Ah is 43200J

The energy required to heat one kilogram of water by 1 °C is 4200J, which in Ah is equivalent to 4200 / 43200 = 0.0972Ah, ie about 0.1Ah, from a 12V battery.

The energy required to heat 10 litres of water from 10°C to 40°C is 0.1 x 10 x 30 = 30Ah.

In your case, it's probably 15 litres of water from 10°C to 60°C, which is 0.1 x 15 x 50 = 75Ah.

There would of course be heat losses, so a figure of 85Ah is about right. Now that I've got the calculation correct.

Every day is a school day, maths AND science today

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[LithiumConvert]

More maths

Water Heating at the lower Truma setting of 1kW is 4 amps at 240v. Which in turn is 80 amps at 12 volts (ignoring losses)

You need a good alternator and B2B to achieve that.

or you will likely arrive with warm water (and a hot alternator) and a flat leisure battery

 

[Bessy765]

We don’t have a B2B but can drive for some hours with the roof hab air on and still main full batteries helped by 700 watts of solar, regularly pull 100 amps from the alternator, but if in heavy traffic or climbing turn it off.

 

[Tombola]

This is exactly what we do, it stays hot for an unexpectedly long time.

Cheers
Red

I do the same driving along, net loss isn't so bad with the b2b and solar if sunny

 

[RedFrame]

More maths

Water Heating at the lower Truma setting of 1kW is 4 amps at 240v. Which in turn is 80 amps at 12 volts (ignoring losses)

You need a good alternator and B2B to achieve that.

or you will likely arrive with warm water (and a hot alternator) and a flat leisure battery

MisterB has 304Ah of Lithium, so his alternator and B2B won't be doing anything more than they normally do... i.e. charging a leisure battery that's accepting charge.

With that setup he could be driving a 1966 Lotus Cortina with a 3 Amp B2B and the alternator and B2B would be fine on arrival, and his water would be at 60ºC or whatever temp was set.

Having read many of your posts, I'm supprised that you don't comprehend the theory of the storage bank acting as a "sump".

Cheers
Red.

 

[Clive Mott]

Dont do this.
You need a sparky to divert the feed to the socket outlets from your mains fuse box to the inverter and then from the inverter to the sockets. This way there is no operative RCD when you run via inverter. BUT do the mains changever with a Cliveway (yes its me) and not that inside some inverters and you still have full RCD protection. Have a look here.
In essence cut one cable, fit a 13A plug to one end and a free 13A socket to the other end. After that its all Plug and Play and as safe as houses.

Cliveway Priority Switch with RCD

<p>When installing an inverter in a motorhome, campervan or caravan, it's essential that it's installed and used safely. 240V appliances ca...

www.roadpro.co.uk

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