Inverter size

[Alan]

Since our motorhome we have managed with a 300watt inverter but I am finding it more and more difficult to walk anywhere when away in the camper,I’ve now bought a power chair to travel with so bring a numpty I hav’nt got a clue which sized inverter I need and as I’l probably go to the Lincoln show if any one can help with the size I need it would be greatly appreciated.The chair is a 24volt 12 amp lithium battery and below is a picture of the charger.

 

[Alan]

It should have said first motorhome we’ve had a 300watt inverter

 

[Pausim]

1.2A at 230V is 276Watts so you would be getting close to your 300Watts. Is your inverter a pure sine wave one? If not it might worth getting one that is and has a little more capacity.

 

[Alan]

Thanks the one I’ve got is’nt a pure sine wave,I’l see what’s available at the show.the one I’ve got is about 18years old and over the years it’s been hardwired to batteries clipped and it’s now just on a cigarette lighter plug for charging phones

 

[AdrianChen]

It may have a bearing on the inverter, but what leisure batteries do you have?

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[Alan]

It may have a bearing on the inverter, but what leisure batteries do you have?

I have 2 X100 amp lithium

 

[AdrianChen]

I have 2 X100 amp lithium

That's good, should handle a few charges, and a good size inverter. 600w would be plenty and give a bit of headroom but I would go for pure sine wave if using it for the charger.

 

[fred_jb]

You need to be aware that a more powerful inverter connected to 12V via a standard cigarette lighter type socket may blow the fuse supplying it if used to its full capacity for multiple chargers, and ideally should be permanently wired to the leisure batteries via heavier cables and a suitable fuse.

If you decided to do this it might be worth going for a 1000W inverter as you could also use that for an electric travel kettle. We find that much quicker and more convenient than boiling a kettle on the gas ring.

.

 

[Alan]

You need to be aware that a more powerful inverter connected to 12V via a standard cigarette lighter type socket may blow the fuse supplying it if used to its full capacity for multiple chargers, and ideally should be permanently wired to the leisure batteries via heavier cables and a suitable fuse.

If you decided to do this it might be worth going for a 1000W inverter as you could also use that for an electric travel kettle. We find that much quicker and more convenient than boiling a kettle on the gas ring.

.

We’re on our way back to Lincolnshire today so will have a look at Lincoln motorhome show and see if anyone’s fitting inverters the 1000 watt one does seem the better option,We have to be a bit frugal with power usage as our fridge is Compressor and the van is only fitted with the equipment it came with,100 amp solar 2o amp bat to bat and 10 amp mppt controller

 

[AdrianChen]

We’re on our way back to Lincolnshire today so will have a look at Lincoln motorhome show and see if anyone’s fitting inverters the 1000 watt one does seem the better option,We have to be a bit frugal with power usage as our fridge is Compressor and the van is only fitted with the equipment it came with,100 amp solar 2o amp bat to bat and 10 amp mppt controller

Inverters can be very useful, and it is nice to be able to use normal stuff from home.
The problem with them is whatever you use, has to be replenished, so the system would ideally be balanced.
100w Solar and 20amp b2b isn't a great deal, so I wouldn't go too mad on inverter size!
Of course you can fit a big inverter, intending not to use the full capacity, but at some stage you will! Also the bigger the inverter the more it will use on standby if you leave it on.
If you look at Victron, bare in mind they use VA rather than watts to rate their output - Whilst its the most accurate method you should consider that 500VA will be roughly about 400w - I wont go into why there's a difference but it's due to the "power factor" of the device being used.

We have Victron kit, the inverter is good in that it is quite efficient, and can be set to have a very low standby power consumption, and the Pure Sine wave is apparently pretty accurate.

Good at the show!

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[Alan]

Inverters can be very useful, and it is nice to be able to use normal stuff from home.
The problem with them is whatever you use, has to be replenished, so the system would ideally be balanced.
100w Solar and 20amp b2b isn't a great deal, so I wouldn't go too mad on inverter size!
Of course you can fit a big inverter, intending not to use the full capacity, but at some stage you will! Also the bigger the inverter the more it will use on standby if you leave it on.
If you look at Victron, bare in mind they use VA rather than watts to rate their output - Whilst its the most accurate method you should consider that 500VA will be roughly about 400w - I wont go into why there's a difference but it's due to the "power factor" of the device being used.

We have Victron kit, the inverter is good in that it is quite efficient, and can be set to have a very low standby power consumption, and the Pure Sine wave is apparently pretty accurate.

Good at the show!

We very rarely go on hookup so I’l probably have more solar and a bigger b to b fitted in the near future.

 

[cyberyacht]

That being the case, it may be worth while going for a bigger inverter that will run a kettle/toaster. Stick to a sensible size like 1000-1500W and that will cover most stuff.

 

[fred_jb]

That being the case, it may be worth while going for a bigger inverter that will run a kettle/toaster. Stick to a sensible size like 1000-1500W and that will cover most stuff.

Yes agreed. We find our air fryer a bit of a game changer but that takes 1500W so we can only use it on EHU at the moment. I would need to upgrade our 1000W Renogy invertor to the 2000W version to use the air fryer off grid.

 

[Bessy765]

You will use approx 26 amps @ 12 volt d.c. to produce 1 amp @ 240 volt a.c. Allowing for voltage drop and inverter efficiency.

 

[Pausim]

You will use approx 26 amps @ 12 volt d.c. to produce 1 amp @ 240 volt a.c. Allowing for voltage drop and inverter efficiency.

Useful calculation though I would be a tad more optimistic than that using the figures for my Victron Phoenix 12/500 and lithium batteries.
1A x 230V = 230W
230W / 12.8V (Lithium voltage) = 18A (approx.)
18 / 9 x 10 (90% efficiency) = 20 A
The higher nominal voltage of lithium batteries (12.8V compared to lead acid’s 12V) improves the equations. In practice both battery types should operate above their nominal voltage levels through most of their useable range.

Having done this calculation it leaves me wondering whether battery Ah are as useful a comparison of battery capacity as I had thought they were. 100Ah at a lithium nominal voltage of 12.8V = 1,280 Wh whereas 100Ah at a nominal voltage of 12V = 1200Wh. This means the lithium battery has a 6% larger capacity than its lead acid equivalent. Am I missing something?

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[funflair]

Useful calculation though I would be a tad more optimistic than that using the figures for my Victron Phoenix 12/500 and lithium batteries.
1A x 230V = 230W
230W / 12.8V (Lithium voltage) = 18A (approx.)
18 / 9 x 10 (90% efficiency) = 20 A
The higher nominal voltage of lithium batteries (12.8V compared to lead acid’s 12V) improves the equations. In practice both battery types should operate above their nominal voltage levels through most of their useable range.

Having done this calculation it leaves me wondering whether battery Ah are as useful a comparison of battery capacity as I had thought they were. 100Ah at a lithium nominal voltage of 12.8V = 1,280 Wh whereas 100Ah at a nominal voltage of 12V = 1200Wh. This means the lithium battery has a 6% larger capacity than its lead acid equivalent. Am I missing something?

Watts and watt/hr are a far more reliable indicator of capacity but we have all got hung up on amps and amp/hr, when it's a 24v battery the amps makes even less sense

 

[Bessy765]

Useful calculation though I would be a tad more optimistic than that using the figures for my Victron Phoenix 12/500 and lithium batteries.
1A x 230V = 230W
230W / 12.8V (Lithium voltage) = 18A (approx.)
18 / 9 x 10 (90% efficiency) = 20 A
The higher nominal voltage of lithium batteries (12.8V compared to lead acid’s 12V) improves the equations. In practice both battery types should operate above their nominal voltage levels through most of their useable range.

Having done this calculation it leaves me wondering whether battery Ah are as useful a comparison of battery capacity as I had thought they were. 100Ah at a lithium nominal voltage of 12.8V = 1,280 Wh whereas 100Ah at a nominal voltage of 12V = 1200Wh. This means the lithium battery has a 6% larger capacity than its lead acid equivalent. Am I missing something?

Optimism is great reality is often disappointing. If you expect less and get more great

 

[MisterB]

Yes agreed. We find our air fryer a bit of a game changer but that takes 1500W so we can only use it on EHU at the moment. I would need to upgrade our 1000W Renogy invertor to the 2000W version to use the air fryer off grid.

i would bite the bullet and go for the 3000w version and 'tempt' Alan to buy your 1000w inverter ....

 

[fred_jb]

!

i would bite the bullet and go for the 3000w version and 'tempt' Alan to buy your 1000w inverter ....

That's a thought I suppose! My 1000W won't be available until we get back from the current trip in about 2 weeks, but let me know if you would be interested Alan.

I might have to go for the 2000W model as that would be a straight swap spacewise. I think the 3000W model is bigger and may not fit In the space available.

 

[MisterB]

!

That's a thought I suppose! My 1000W won't be available until we get back from the current trip in about 2 weeks, but let me know if you would be interested Alan.

I might have to go for the 2000W model as that would be a straight swap spacewise. I think the 3000W model is bigger and may not fit In the space available.

and of course cable sizes might need to be increased, but you might have to do that anyway?

just checked and the 3000w is 40mm longer, same height and width ....

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[Bessy765]

We have the Victron 12/2000/80-30 inverter charger, we run a Tassimo, 1000w induction hob and at times our Dometic Freshjet 2200 A/C we are limited in practicalities to carry more the 2 x 100 ampTransporter Lithium

 

[fred_jb]

and of course cable sizes might need to be increased, but you might have to do that anyway?

just checked and the 3000w is 40mm longer, same height and width ....

Yes, I checked that too, and it might just fit. I went overboard on cable sizes with future upgrades in mind so that's all OK. Need to save up for some Lithium batteries though to make best use of a more powerful inverter!

Our current 2 x 100 Ah AGMs are not really up to the job. These are under the driver's seat and the simplest option would be to do a straight replacement if the lithium sizes are compatible. However we have a lot of awkward to get at storage under the transverse bed, forward of the gas cupboard, and I'm wondering whether to relocate a lot of the electrics into that space.

Main problem is that my other half is not convinced that any further upgrades are justified!

 

[MisterB]

Yes, I checked that too, and it might just fit. I went overboard on cable sizes with future upgrades in mind so that's all OK. Need to save up for some Lithium batteries though to make best use of a more powerful inverter!

Our current 2 x 100 Ah AGMs are not really up to the job. These are under the driver's seat and the simplest option would be to do a straight replacement if the lithium sizes are compatible. However we have a lot of awkward to get at storage under the transverse bed, forward of the gas cupboard, and I'm wondering whether to relocate a lot of the electrics into that space.

Main problem is that my other half is not convinced that any further upgrades are justified!

does she know that the Renogy 3000w and lithium upgrade youre planning comes with a free new handbag/shoes/dress ....

 

[Lenny HB]

Make her suffer and fit Victron, 3 times the price but you won't regret it.

 

[Bessy765]

Tell the Victron is cheaper to run and will power a hairdryer??

We have the Victron 12/2000/80-30 inverter charger, we run a Tassimo, 1000w induction hob and at times our Dometic Freshjet 2200 A/C we are limited in practicalities to carry more the 2 x 100 ampTransporter Lithium

Cable size upgrade

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[Alan]

Thanks for your replies but at the show I still had no idea which one to buy but eventually went for the victron500, Offgrid power solutions made up the correct cable and fuse and all I have to do now is fit it,I got 10% discount with being a funster which is always a bonus.thanks again Alan

 

[TheCaller]

I'm pleased to see that RogerIvy & nigelivy got you sorted & that sounds like a good solution.

The chair is a 24volt 12 amp lithium battery and below is a picture of the charger.

The information listed on the charger is typical of most chargers & needs a bit of explanation.
The Input side says 180-240v & 1.2A. The charger will draw the maximum current at the bottom of the voltage range, not the top, so the correct calculation of power draw is 180 x 1.2 = 216W.

The Output side says 24V & 2.0A. At first sight that looks like 24 x 2 = 48W. But that 24V is misleading. It tells us that it is a charger suitable for a battery rated at a nominal 24V. But a Li-Ion battery will actually be something more than 24V - exactly how much more will depend on the type of Li-Ion chemistry in use. It doesn't tell us how much more, but for the sake of discussion, let's assume it's 26V. But you can't charge a 26V battery with 24V, nor even with 26V. In reality, the output voltage is probably in the 28-30V range, or possibly a bit more. So the power usage now becomes 30 x 2 = 60W.

60W is a long way short of the 216W that the input side would have you believe. It's unlikely that the charger is so inefficient that it can only output less than a third of the power it is absorbing - it would get very hot very quickly!

I don't know enough to explain the difference, but the output side seems to give the best guide to power required. We know chargers get warm, so clearly they are going to require more power in than out. But it seems improbable that a charger outputting 60W would need more than say, 100W to be able to do so. 40W lost as heat would still make a charger very warm to the touch - ever tried putting your hand on an old 40W light bulb when lit?

Your batteries are not a limiting factor & would cope with a much larger inverter than you need to power this charger, so it now becomes a question of 'what else would you like to power at the same time?' If the answer is 'not much', then the Victron 500VA inverter gives you the option of charging laptops or similar at the same time, should you later decide to do so. It's small enough not to waste a lot of energy just powering itself & doesn't need massive cables, but does give you a decent spare overhead if needed.

If you did want to run coffee machines, air fryers, kettles etc, then it's a whole different ball game & you would also need to consider how to replace the energy you were taking out of the batteries.

Watts and watt/hr are a far more reliable indicator of capacity but we have all got hung up on amps and amp/hr, when it's a 24v battery the amps makes even less sense

Very true!!

 

[autorouter]

60W is a long way short of the 216W that the input side would have you believe. It's unlikely that the charger is so inefficient that it can only output less than a third of the power it is absorbing - it would get very hot very quickly!

I don't know enough to explain the difference,

When the charger is first plugged in, there is an inrush current which fills up the reservoir capacitors, this lasts only a fraction of a second. After that it settles down and as you say is likely to be at least 80% to 90% efficient, so will take less than 100W. The manufacturers have to state the maximum amps it takes, even if that's only for a fraction of a second.

I would imagine that the 300W inverter would power that charger comfortably, and a nice new 500W Victron Pure Sine Wave inverter most certainly will. Victron inverters are particularly good at coping with inrush currents on startup.