I need help understanding inverters and their effect on batteries

[Goneoff]

I need help understanding inverters and their effect on batteries. I have 2 x 140ah wet batteries situated under the rear passengers seats, I have two solar panels on the roof and understand their limitations replacing charge.

 

When off EHU I want to have the facility to run a small pod coffee coffee machine rated at 1200w and a microwave rated at 750w these by nature although perhaps power hungry would not be working very long during each session of use 5 - 10 min max.

 

I would prefer a pure sine wave inverter just to make sure the appliances work and that I don't screw them or future appliances up. So I don't need to get into the benefits or otherwise of modified sine inverters.

 

My questions are:-

 

1. What size of inverter would I need.

2. Should the inverter be hard wired to my batteries into a dedicated power socket?

3. If it has to be hard wired would the inverter have a continuous drain on my batteries when not in use?

4. Will the power surge on the batteries when running either the coffee machine or microwave ultimately reduce the life of my batteries?

 

Any help would be appreciated.

 

Thanks

 

[John52]

My questions are:-

 

1. What size of inverter would I need. - about 1500w or above

2. Should the inverter be hard wired to my batteries into a dedicated power socket? - you need thick cables (probably supplied with the inverter) as short as possible between the batteries and inverter. The mains cable can be pretty much as long as you like. You need a hefty switch or relay to disconnect the thick cables to the inverter because there will be a battery drain when not in use - the inverter may have its own switch for this purpose.

3. If it has to be hard wired would the inverter have a continuous drain on my batteries when not in use? Yes - see above

4. Will the power surge on the batteries when running either the coffee machine or microwave ultimately reduce the life of my batteries? Yes.

 

Using batteries for any kind of heating, other than low wattage things like an electric blanket which I have, is problematic because of the high power consumption which is increased even further by the inefficiency of the inverter.

Have you considered a pressure cooker?

 

[KeithM]

1. 2000 watt should do it and have some leeway

 

2. inverter needs to be wired direct from batteries with isolation and fusing in circuit. then to any number of 240v sockets you require, again with isolation and fusing, you will still only have 2000 watts available though..

 

3. Yes but that is what the isolation switch is for. (turn it off when not required)

 

4. any use of any battery reduces its life

 

aside:

 

The coffee machine and microwave will both load the battery bank about 120 amps each.

You will not be able to use them at the same time. ;-)

 

 

Edit: better proof reading required

 

[StuartO]

Drawing 1200 watts from batteries, even if the inverter was 100% efficient, would mean drawing 100 amps and if you did this for 10 minutes it would have a big impact on the batteries, even if two big ones shared the current evenly.  Ten minutes is a long time.

 

I would guess this would have a disproportionate adverse impact, as the cost of a cup of coffee, much though I love nice coffee!  (We carry a Tassimo machine but we use it only when hooked up to an EHU.  At other times we boil water and use Azira, which makes quite a  decent cup.)

 

Before commiting yourself to an inverter installation in the MH, why not buy the inverter and rig up a test installation and run the coffee machine via the inverter from a battery on the bench?

 

[KeithM]

1200 watts (allowing for inefficiency) is 120 amp load on a 12v system.

 

120 amps for 10 minutes is 20 amp.hrs.

 

Battery bank nominally 280 amp.hrs

 

Percentage of capacity used just over 7%

 

The percentage used will be higher if the batteries are not new and capable of full capacity.

[KeithM]

StuartO - 2016-10-26 11:27 AMDrawing 1200 watts from batteries, even if the inverter was 100% efficient, would mean drawing 100 amps and if you did this for 10 minutes it would have a big impact on the batteries, even if two big ones shared the current evenly.  Ten minutes is a long time.

 

I would guess this would have a disproportionate adverse impact, as the cost of a cup of coffee, much though I love nice coffee!  (We carry a Tassimo machine but we use it only when hooked up to an EHU.  At other times we boil water and use Azira, which makes quite a  decent cup.)

 

Before commiting yourself to an inverter installation in the MH, why not buy the inverter and rig up a test installation and run the coffee machine via the inverter from a battery on the bench?

What would your last paragraph prove, other than it will work.

[John52]

Some inverters have a peak power rating of double the continuous power rating. I got mine from eurocar parts before the price went up after the fall in the pound through Brexit - but they frequently have discount code sales of 20 - 30%. - currently 30% HALLOOWEEN30 Unfortunately the biggest one they do is 1100w (too small for your coffe maker) http://www.eurocarparts.com/ecp/p/car-accessories/car-accessories-products/in-car-power/voltage-converter/?549777111&0&cc5_827

[Goneoff]

John52 - 2016-10-26 9:30 AM

 

My questions are:-

 

1. What size of inverter would I need. - about 1500w or above

2. Should the inverter be hard wired to my batteries into a dedicated power socket? - you need thick cables (probably supplied with the inverter) as short as possible between the batteries and inverter. The mains cable can be pretty much as long as you like. You need a hefty switch or relay to disconnect the thick cables to the inverter because there will be a battery drain when not in use - the inverter may have its own switch for this purpose.

3. If it has to be hard wired would the inverter have a continuous drain on my batteries when not in use? Yes - see above

4. Will the power surge on the batteries when running either the coffee machine or microwave ultimately reduce the life of my batteries? Yes.

 

Using batteries for any kind of heating, other than low wattage things like an electric blanket which I have, is problematic because of the high power consumption which is increased even further by the inefficiency of the inverter.

Have you considered a pressure cooker?

Many thanks John that just about nails it, cheers. After yours and other replies I've decided against the idea.

[Goneoff]

KeithM - 2016-10-26 10:58 AM

 

1. 2000 watt should do it and have some leeway

 

2. inverter needs to be wired direct from batteries with isolation and fusing in circuit. then to any number of 240v sockets you require, again with isolation and fusing, you will still only have 2000 watts available though..

 

3. Yes but that is what the isolation switch is for. (turn it off when not required)

 

4. any use of any battery reduces its life

 

aside:

 

The coffee machine and microwave will both load the battery bank about 120 amps each.

You will not be able to use them at the same time. ;-)

 

 

Edit: better proof reading required

Hi Keith after yours and other responses on here I have decided not to bother............many thanks for your reply.

[Goneoff]

StuartO - 2016-10-26 11:27 AMDrawing 1200 watts from batteries, even if the inverter was 100% efficient, would mean drawing 100 amps and if you did this for 10 minutes it would have a big impact on the batteries, even if two big ones shared the current evenly.  Ten minutes is a long time.

 

I would guess this would have a disproportionate adverse impact, as the cost of a cup of coffee, much though I love nice coffee!  (We carry a Tassimo machine but we use it only when hooked up to an EHU.  At other times we boil water and use Azira, which makes quite a  decent cup.)

 

Before commiting yourself to an inverter installation in the MH, why not buy the inverter and rig up a test installation and run the coffee machine via the inverter from a battery on the bench?

Thanks for your response I have decided not to bother, doesn't appear worth it............many thanks for your reply.

[PJay]

One thing no has mentioned , is weight. We took our Air con and inverter out to give us more weight for other things

[Goneoff]

Good point; we could get even more useful gear into our van if I wasn't in it!

[StuartO]

KeithM - 2016-10-26 11:46 AM

StuartO - 2016-10-26 11:27 AMDrawing 1200 watts from batteries, even if the inverter was 100% efficient, would mean drawing 100 amps and if you did this for 10 minutes it would have a big impact on the batteries, even if two big ones shared the current evenly.  Ten minutes is a long time.

 

I would guess this would have a disproportionate adverse impact, as the cost of a cup of coffee, much though I love nice coffee!  (We carry a Tassimo machine but we use it only when hooked up to an EHU.  At other times we boil water and use Azira, which makes quite a  decent cup.)

 

Before commiting yourself to an inverter installation in the MH, why not buy the inverter and rig up a test installation and run the coffee machine via the inverter from a battery on the bench?

What would your last paragraph prove, other than it will work.

 

Worthwhile in this context, before cutting holes etc?

 

[joe66]

Just to hijack the OP post, I have a 500w inverter wired in to the LB, is has an on/off switch so presume when it is off swithched off there is no drain on the battery?

[Chuns]

Probably too late, but my Nespresso machine is the sole beneficiary of my inverter. The switch for the inverter is by the dedicated, and only, socket from the inverter. I turn it on, make the coffee, and turn it off. Around three minutes?

 

As this is done in the morning, there is a days worth of driving and solar to recharge, though once I did two nights in the same aire, and the solar panels did their job.

 

I'm a bit paranoid about battery capacity, needing to be absolutely certain that I have enough 12v juice to power my CPAP overnight, and even investigated Battery to battery chargers, but it seems my nervousness is misplaced.

 

[Goneoff]

Chuns - 2016-10-26 10:40 PM

 

Probably too late, but my Nespresso machine is the sole beneficiary of my inverter. The switch for the inverter is by the dedicated, and only, socket from the inverter. I turn it on, make the coffee, and turn it off. Around three minutes?

 

As this is done in the morning, there is a days worth of driving and solar to recharge, though once I did two nights in the same aire, and the solar panels did their job.

 

I'm a bit paranoid about battery capacity, needing to be absolutely certain that I have enough 12v juice to power my CPAP overnight, and even investigated Battery to battery chargers, but it seems my nervousness is misplaced.

Coincidentally ours is a Nexpresso machine but I'm reluctant to shorten the life of my batteries by using an inverter when off EHU, just have to get by with the cafetière . . . . blo*dy hell look at the time! Thanks for your contribution

Phil

[John52]

joe66 - 2016-10-26 8:45 PM

 

Just to hijack the OP post, I have a 500w inverter wired in to the LB, is has an on/off switch so presume when it is off swithched off there is no drain on the battery?

 

Yes, the switch on the inverter will stop the drain on the battery. If its switched on with nothing plugged in it will drain about half an amp. Then it will consume about 10% more power than what you plug into it. Some are more efficient than others. So the spec sheet should tell you more accurate.

[KeithM]

joe66 - 2016-10-26 8:45 PM

 

Just to hijack the OP post, I have a 500w inverter wired in to the LB, is has an on/off switch so presume when it is off switched off there is no drain on the battery?

 

Answer to presumption: Correct

 

More info ;-)

 

Check the specification of the inverter although it say 500 watts that may be its peak rating and only for a few seconds, what you need to know is its continuous rating.

[joe66]

Thanks John and KeithM for the replys

[paul_richardson]

John52 - 2016-10-27 9:02 AM

 

joe66 - 2016-10-26 8:45 PM

 

Just to hijack the OP post, I have a 500w inverter wired in to the LB, is has an on/off switch so presume when it is off swithched off there is no drain on the battery?

 

Yes, the switch on the inverter will stop the drain on the battery. If its switched on with nothing plugged in it will drain about half an amp. Then it will consume about 10% more power than what you plug into it. Some are more efficient than others. So the spec sheet should tell you more accurate.

 

Hi All,

 

My Inverter still draws current when switched off by it's own switch.

 

The only way I can guarantee no battery drain is to isolated it from the battery ( I have a large switch to do that).

 

I suspect mine is not the only inverter that does this.

 

You can check yours by disconnecting the 12v supply, turning it off and then reconnecting the supply, you will probably here the "crack" as it is re-connected.

 

Hope this helps

 

Regards,

 

Paul

[Charles]

Yes I was dubious of the replies saying the inverter uses no power when it's switched off with its own little switch. I fitted a proper isolator on my 1000w inverter, it also means it won't get caught and switched on accidently.

[aandncaravan]

The big Inverters would require a very heavy duty switch that would need to be capable of passing 300amps if a 'proper' isolating switch was used by the manufacturer. That is clearly going to be an expensive item, that may also introduce an element of unreliability unless really high quality.

 

Not opened any Inverters but I have always assumed they use an electronic switch on the 'start up' power circuitry which is relatively low current.

A bit like a standby mode for a TV, so generally always drawing something.

Depending on the Inverter that might be little to quite a lot.

Turn on the Inverter and current drain will raise further, even without a load. Depending on the size of the Inverter that can be amps, rather than milliamps.

 

 

The efficiency of Invertors we have seen installed varies from awful to about 80%. The budget ones generally more power hungry.

 

While some of the expensive big units can achieve fair efficiency ratings at the higher currents they are designed for, they seem to be below average when asked to deliver just a few hundred watts.

For example a quality 1500watt unit only ran at about 40% efficient when driving a 360watt TV, yet at 1500watts it was nearly 80% efficient. 40% means the TV is using more than twice the 12v power it would on direct 12v.

 

Also remember that even '230volt' TV's are often designed around 12v'ish electronics, so when run on 230v there will be losses as the 230v is converted back down to 12v. So running a Motorhome TV directly on 12v will always use less power than when on mains EHU.

If that 230v power additionally has to come from 12v habitation batteries via an Inverter running at 40% efficiency it is easy to see that even a really efficient 230v TV is going to hammer the batteries.

 

Add on the 'continuous standby' draw of an Inverter, even when the TV is not being used/Inverter 'off' and the difference between a genuine 12v TV and an Inverter powered one is significant.

 

With a TV being one of the higher 12v consumers in some vans that might be the difference between the battery lasting 3 days free camping with a 'proper' 12v TV versus jut one day on an Inverter TV.

 

 

 

 

 

[KeithM]

Reading Paul's and Charles replies,

 

I have just checked mine and it definitely does not pull anything from the batteries when turned OFF at its own switch.

 

(but it's a big expensive one and not in a motor-home ;-) )

 

Maybe smaller, less expensive ones are different.

[Barcobird]

Goneoff - 2016-10-26 12:43

 

]Thanks for your response I have decided not to bother, doesn't appear worth it............many thanks for your reply.

 

So you have "Goneoff" the idea then !