True sine wave inverter wanted."reviews"

[zoaman]

Hi as we have joined up with some rallies for this year we are looking to poss go off grid on some of them.We have a been looking at some pure(true) sine wave inverter.Our van is fitted with 2 x 100 watt solar panel.
I also have a sine wave genny but not fused on taking it,weight and smells of fumes puts me off a little.
So i would be looking for something in the regeon of 2000w /4000 max rating.
If cold the heating would be run on gas and fridge.but thing like tv non 12v(flat screen 24") and lighting,water pump .incl showers.so could be on a little while pumping water.
Also how are you running yours.back thru to the ehu lead(i would have to turn the charger off) so all the plugs work inside the van.or just a extention lead from the main inverter unit? although this would not look professional.
Thoughts please! and recommendations on make models.as didnt want a cheap eastern one.Although most probably do come from there.

 

[ProfJohnL]

Pseudo, quasi or modified Sine wave inverters can have some pretty high conversion efficiency typically better than 90%, becasue the output is switched between discrete power rails which minimises losses. However the down side of this type of multiple square wave output is it can upset some electrical and electronic devices and cause them to be noisy or run hotter than usual or even damage them.

The alternative is the pure sine wave output devices which very faithfully mimic the normal mains supply, but the compromise is the conversion efficiency suffers and can be as low as 60%.

I suggest that work out you most common load demand and choose an inverter to meet that demand, and then selectivity turn low priority devices off when you want to use power elsewhere to keep the demand within the capacity of the inverter.

Ideally you should choose an inverter that is only slightly bigger than the load you want to use and always try to run it close to that load, as the inverters will lose efficient if you operate well below their capacity.

I am not aware of any inverters that are specifically manufactured with caravans in mind, but there are several marine versions, and some include quite sophisticated mains chargers to look after the storage batteries when mains is available. As these tend to be for the marine market their weight has not been minimised for caravan usage.

 

[zoaman]

Pseudo, quasi or modified Sine wave inverters can have some pretty high conversion efficiency typically better than 90%, becasue the output is switched between discrete power rails which minimises losses. However the down side of this type of multiple square wave output is it can upset some electrical and electronic devices and cause them to be noisy or run hotter than usual or even damage them.

The alternative is the pure sine wave output devices which very faithfully mimic the normal mains supply, but the compromise is the conversion efficiency suffers and can be as low as 60%.

I suggest that work out you most common load demand and choose an inverter to meet that demand, and then selectivity turn low priority devices off when you want to use power elsewhere to keep the demand within the capacity of the inverter.

Ideally you should choose an inverter that is only slightly bigger than the load you want to use and always try to run it close to that load, as the inverters will lose efficient if you operate well below their capacity.

I am not aware of any inverters that are specifically manufactured with caravans in mind, but there are several marine versions, and some include quite sophisticated mains chargers to look after the storage batteries when mains is available. As these tend to be for the marine market their weight has not been minimised for caravan usage.

Hi Prof.very good information and that was the reason for looking for a true/pure sine wave.However i wasnt aware of the usage amount being 60% effecient.Also that the overkill over a higher than needed rating will lose effifency too.1 thing that i ws aware of was there weights.,and with some there size.
As our van is equiped with 90% of low electrical usage items.the only big thing is our tv.This for minimal usage is not a must.we do have a 13yr daughter which does like he tablet.but this can be charged in other ways.So as mentioned with the higher rate of some equipment not liking modified wave.i think that i will have to look a bit more into it and way up the pros and cons as to weather or not its worth using 1 or not.

 

[Woodentop]

2KW generator?? What are you running - floodlights for the whole site?

For most purposes a 400W Honda running on gas will do all that is needed and they make very little smell and run very quietly. If the fridge and heating run on gas then your only load is lighting which should be LED about 2W each, the pump which only draws maybe 20-30W but for a short period and both of these at 12V off your battery. The TV is the only mains draw which would typically be 35-40W tops.

 

[zoaman]

2KW generator?? What are you running - floodlights for the whole site?

For most purposes a 400W Honda running on gas will do all that is needed and they make very little smell and run very quietly. If the fridge and heating run on gas then your only load is lighting which should be LED about 2W each, the pump which only draws maybe 20-30W but for a short period and both of these at 12V off your battery. The TV is the only mains draw which would typically be 35-40W tops.

Yes i thought of a 2000w to be well within its limits.but as prof has suggested its not effecient to do this,so a lower watt would be suffice.Its not really about the watts it more about the model and has any one used /tested a particular model and had good spec performance from it.As non pure sine waves and modified are not best for delicate electrics.So im looking for a tried and tested model. as didnt want to run it back thru the vans system and poss destroy the van components.Ive even looked a another battery but then theres the dreaded weight.As i can split the charge in % with our solar unit.The battery is a 110ah so is it good but enough for a week or more???

 

[Woodentop]

Try CPC, they don't sell rubbish!

 

[ProfJohnL]

We had a query a few month ago from someone who wanted to run a mobile salon in the awning of a caravan for caravan rallies etc. when grid mains may not be available.

They needed a 230V supply of 3kw capacity - but not all the time, so looking at the average loads we could establish the total power required for a weekend.

We did a few calculations and established that the power demands could be met with 4 x 110Ah batteries and a set of solar panels, with a marine type inverter/charger. Even allowing for autumn gloom the panels should provide enough of a top up to the batteries to provide the estimated power demands of the business.

As the salon was only used at weekends, it left the rest of the week to fully recharge the batteries from a combination of solar or or mains through the charger section of the inverter.

The key to the solution was the fact they had a transit van, and that had both the space and weight capacity to carry the batteries and the inverter and the awning salon was powered by an 230V EHU cable from the inverter.

Another benefit of looking at multiple batteries, was that some marine inverters need 24 or even 48Vdc inputs. This means the components of the inverter are less stressed as the step up can be as little 5 or 10 x rather than the 20x from 12Vdc.

I have only related this as perhaps can you consider fitting the batteries and inverter in your car rather than the caravan.

 

[zoaman]

We had a query a few month ago from someone who wanted to run a mobile salon in the awning of a caravan for caravan rallies etc. when grid mains may not be available.

They needed a 230V supply of 3kw capacity - but not all the time, so looking at the average loads we could establish the total power required for a weekend.

We did a few calculations and established that the power demands could be met with 4 x 110Ah batteries and a set of solar panels, with a marine type inverter/charger. Even allowing for autumn gloom the panels should provide enough of a top up to the batteries to provide the estimated power demands of the business.

As the salon was only used at weekends, it left the rest of the week to fully recharge the batteries from a combination of solar or or mains through the charger section of the inverter.

The key to the solution was the fact they had a transit van, and that had both the space and weight capacity to carry the batteries and the inverter and the awning salon was powered by an 230V EHU cable from the inverter.

Another benefit of looking at multiple batteries, was that some marine inverters need 24 or even 48Vdc inputs. This means the components of the inverter are less stressed as the step up can be as little 5 or 10 x rather than the 20x from 12Vdc.

I have only related this as perhaps can you consider fitting the batteries and inverter in your car rather than the caravan.

Thanks for the information.I do have quite a bit of payload left in the caravan.and as said the solar power unit can be adjusted to % for the connection of 2 batteries.it just that there is not the ideal place to have a second battery fitted.Basically it would need to be either under the bed or cooker in a suitable container.The later would be the ideal as it over the twin axles but there the gas.the first is also ideal but behind the axles.and at 25kg is not the best.So as stated i can put a ssecond battery in the car and and rig up a permanant lead from the truma unit.and just connect it when needed.but will also have to get a inverter for a 240v supply.Im thinking for all the extra work ect.is it worth it just for a tv really?

 

[ProfJohnL]

Thanks for the information.I do have quite a bit of payload left in the caravan.and as said the solar power unit can be adjusted to % for the connection of 2 batteries.it just that there is not the ideal place to have a second battery fitted.Basically it would need to be either under the bed or cooker in a suitable container.The later would be the ideal as it over the twin axles but there the gas.the first is also ideal but behind the axles.and at 25kg is not the best.So as stated i can put a ssecond battery in the car and and rig up a permanant lead from the truma unit.and just connect it when needed.but will also have to get a inverter for a 240v supply.Im thinking for all the extra work ect.is it worth it just for a tv really?

I'm really sorry but I do find your posts difficult to read with your use of abbreviations and symbols, lack of proper spaces and capitol letters. The danger is I may miss the point you are trying to make or get it entirely wrong.

 

[Buckman]

We have a Ring 300w modified inverter and it is more than adequate to cope with the Sky+HD box as that is about the only item that needs to be run on 230v. Laptop, mobile phones, TV etc are all run directly off the 12v supply in the caravan. Water is boiled on gas and fridge on gas. Not sure why a 2000w inverter would be required unless you using electrical heating like curlers or hair drier. Our 100w solar panel copes adequately during the summer.

 

[ProfJohnL]

If I have understood your post correctly, you are considering fitting a second battery in your car, and running 12V the the "Truma" unit ??? What are you referring to?

What we want is enough electrical capacity to power the device. In electrical terms power is the product of Voltage x Current (VxA) For the same power from different voltage sources you need proportionally more current at lower supply voltages.

So for example 12V x 33.3A = 400W = 230V x 1.7A For 12 and 230V systems the current ratio is close to 20:1

But all cables incur power losses which are proportional to the square of the current ( Watts = I x I x R) where "I" is the current and "R" is the resistance of the cable. So if the same cable were used the the 12V losses would be close to 400 x the 230V losses.

It makes more sense to run long cables at higher voltages to minimise transmission losses. It also reduces the cross-sectional area of the cable to more manageable sizes, and reduces infrastructure costs.

This is one reason why the national grid runs its main distribution power lines at 132,000 volts to minimise cable losses.

 

[Woodentop]

If I have understood your post correctly, you are considering fitting a second battery in your car, and running 12V the the "Truma" unit ??? What are you referring to?

What we want is enough electrical capacity to power the device. In electrical terms power is the product of Voltage x Current (VxA) For the same power from different voltage sources you need proportionally more current at lower supply voltages.

So for example 12V x 33.3A = 400W = 230V x 1.7A For 12 and 230V systems the current ratio is close to 20:1

But all cables incur power losses which are proportional to the square of the current ( Watts = I x I x R) where "I" is the current and "R" is the resistance of the cable. So if the same cable were used the the 12V losses would be close to 400 x the 230V losses.

It makes more sense to run long cables at higher voltages to minimise transmission losses. It also reduces the cross-sectional area of the cable to more manageable sizes, and reduces infrastructure costs.

This is one reason why the national grid runs its main distribution power lines at 132,000 volts to minimise cable losses.

Touch on the end there Prof.: National Grid these days actually only run the highest levels - 400KV and 275KV. They do operate a few at 132KV but the majority of those plus 33KV, 11KV, 415V and 240V are generally operated by the supply companies. In most cases 33KV is overhead but in large urban areas - cities and industrial areas and the like - even 11KV is often underground these days.

For interest much of the generation is at 11KV. Dinorwic hydro station in north Wales has six units each producing 11000V at 18500A!! (To save you getting the calculator out, that's around 200MW per unit.) The safety breakers on each unit can each break 250000A and are driven by air at 3750psi. (Oh, my memory for numbers.) When one of those breakers goes you would think the whole mountain was collapsing! The cables exiting Dinorwic go underground for about 8 miles to protect the scenery and are water cooled. The whole station can be remotely controlled from the NG centre at Connahs Quay near Flint - an on-site shift is usually just six people. The station cost £484m to build and it was expected to take well over 20 years to recoup the cost. In fact it turned out to be so efficient when they found the best way to use it, the build cost was recovered in 16 months!! If you ever get the chance to visit it is well worth the time.

I wonder what happened to the 66KV, 6.6KV, 3.3KV and 1.5KV overhead lines of my youth?

 

[ProfJohnL]

Thank you Woodentop.
I stand corrected about the maximum potential used by the GRID.

It simply amplifies my point about efficient transmission and minimising losses.

Ever since I heard about Dinorwic, I have wanted to go and visit it as it represents a suberb way of storing energy and meeting peak demands. I had a close friend who worked for the MEB, and he offered to take me, but I couldn't make the dates he had. Sadly he had to retire due to contracting cancer and passed away after about 18 months. I was under the conception that the operator had reduced sight seeing visits.

 

[ChrisUK]

2000w divided by 12v = 166Amps, assuming 100% inverter efficiency. That's a big cable requirement.

 

[Woodentop]

Thank you Woodentop.
I stand corrected about the maximum potential used by the GRID.

It simply amplifies my point about efficient transmission and minimising losses.

Ever since I heard about Dinorwic, I have wanted to go and visit it as it represents a suberb way of storing energy and meeting peak demands. I had a close friend who worked for the MEB, and he offered to take me, but I couldn't make the dates he had. Sadly he had to retire due to contracting cancer and passed away after about 18 months. I was under the conception that the operator had reduced sight seeing visits.

I don't know about that. I was involved with fitting on-site radio comms in the then 'new' Dinorwic maybe 30 years ago. They were so proud of the place that the station custodian told us we could take whoever we wanted there and take then round ourselves for the sake of an advanced phone call to him.
Get this: with gens empty and running on air at 505rpm (500rom when generating) they can go from nothing to 1320MW in a little over 10 seconds: they can go from full gen to zero in about 4 seconds, but if they did the surge pond - the size of the old Wembley Stadium at the top of the drop shaft would fill in less than half a minute and there would be a water spout 30m across and about 60m high. They can also change the brushes at the top of the armature with the unit turning! Get that!

 

[Hutch]

Thank you Woodentop.
I stand corrected about the maximum potential used by the GRID.

It simply amplifies my point about efficient transmission and minimising losses.

Ever since I heard about Dinorwic, I have wanted to go and visit it as it represents a suberb way of storing energy and meeting peak demands. I had a close friend who worked for the MEB, and he offered to take me, but I couldn't make the dates he had. Sadly he had to retire due to contracting cancer and passed away after about 18 months. I was under the conception that the operator had reduced sight seeing visits.

I don't know about that. I was involved with fitting on-site radio comms in the then 'new' Dinorwic maybe 30 years ago. They were so proud of the place that the station custodian told us we could take whoever we wanted there and take then round ourselves for the sake of an advanced phone call to him.
Get this: with gens empty and running on air at 505rpm (500rom when generating) they can go from nothing to 1320MW in a little over 10 seconds: they can go from full gen to zero in about 4 seconds, but if they did the surge pond - the size of the old Wembley Stadium at the top of the drop shaft would fill in less than half a minute and there would be a water spout 30m across and about 60m high. They can also change the brushes at the top of the armature with the unit turning! Get that!

Woodentop, I promise not to talk about Helicopter Aerodynamics for the next week.

 

[Hutch]

Does it mean we ned Big] wires or little wires for 12 volt electrics.

 

[ChrisUK]

Does it mean we ned Big] wires or little wires for 12 volt electrics.

Very big. As I said, 2000W at 12V is about 166 amps. That's almost welding wire. Academic really as the battery would last about 5 min.
watts=voltsXamps

 

[ProfJohnL]

Does it mean we ned Big] wires or little wires for 12 volt electrics.

Very big. As I said, 2000W at 12V is about 166 amps. That's almost welding wire. Academic really as the battery would last about 5 min.
watts=voltsXamps

Perhaps a little over dramatised, but a fully charged 110Ah battery would last a bit longer unless you are drawing the full load continuously.

You will choose an inverter to handle the maximum load you might want to apply to it. However you can still use the inverter to run smaller loads as required, and in practical domestic or recreational usage, most inverters will be used to power loads smaller than their maximum capacity.

The job of an inverter is to step up a low voltage direct current (DC) supply voltage to a higher alternating current (AC) supply This is far more complex than going the other way for which you would use a transfomer and rectifier.

But in essence both the Inverter and transfomer are examples of constant Power devices, meaning the power (watts) being consumed on the out put of the device determines the power being used from the supply. Nothings perfect and both Transformers and Inverter's do need some power to operate, and generally inverters need more power than transfomers of the same conversion capacity.

But all this means that if you have an inverter with a maximum power capacity of 2kW, but its only powering a 40W television, the inverter will only be drawing just over 40W** of power from the battery not the 2000W it is capable of drawing.

So in reality its unlikely to discharge the battery as quickly as ChrisUK suggests.

** There are generally two types of inverter, those that produce a pure sine wave output, and those that produce a stepped square wave comonally known as Pseudo or Quasi, sine wave outputs.

It needs more power to run a pure sine wave converter the losses could be nearly as high 40%. But the output is very unlikely to damage any sensitive appliances.

Stepped Square wave outputs are more efficient only loosing 10 to 15% of the energy, But their output wave form have some nasty sharp edges, and these can excite damaging electrical resonances in some sensitive appliances.

It should also be borne in mind that inverters are generally less efficient when running at less than their continuously rated power conversion. This might off set any idea of choosing a larger inverter than you need with reliability in mind.

 

[ChrisUK]

I really would not expect the member to use 2kw. But he does need to do some sums.