power requirements

[royw]

We have two 90AH lead acid leisure batteries, we have a 2kw inverter, just wondering if anyone has gone the route of dual lithium and say a 3kw inverter we have a salon aircon unit and wondering if we could then run it off grid?

 

[Bessy765]

You will use app 28 amps d.c. @ 12 volt to produce 1 amp a.c. @ 240 volts.
I am having fitted two 100 amp lithium, two 170 watt solar panels and an inverter/charger. Even then it will only give around 45 mins air-con Fresh jet 2200.not sure where you are but Tom Donavan
tom.donovan@mullacottcaravans.co.uk 01271 863066 North Devon is the guy who is fitting mine. Has done other work for me to a very professional standard.

 

[royw]

Hi we are in south west france so the commute will be a killer, looking at your figure you saying it will consume 336watts at source to make 240watts at 240 volts, that looks very inefficient dometic themselves claim 90% efficiency which is a lot more optimistic, I was looking at the super b batteries maybe getting two 160 amp ones I have a single solar panel and need to check its power but perhaps adding a second what is the consumption on your aircon ?

 

[funflair]

Hi we are in south west france so the commute will be a killer, looking at your figure you saying it will consume 336watts at source to make 240watts at 240 volts, that looks very inefficient dometic themselves claim 90% efficiency which is a lot more optimistic, I was looking at the super b batteries maybe getting two 160 amp ones I have a single solar panel and need to check its power but perhaps adding a second what is the consumption on your aircon ?

We have 2x160ah Super-B lithium 520watts of solar and 1700 freshjet, the freshjet pulls about 60 or 70amps On the compressor cycle but doesn’t run continuously, I ran it for about 3 hours today and took the batteries down by 70amps, depending on Solar panel Input I think 5 or 6 hours would be possible, I have no doubt that we will be fully charged by lunchtime tomorrow.

Martin

 

[royw]

What solar charger is fitted ?

^{_{Subscribers  do not see these advertisements}}

 

[funflair]

What solar charger is fitted ?

We had 2 off Buttner PP which are not MPPT so I have just swapped one for a Votronic 430 MPP And it gives 15% to 20% more power so the other one will be swapped as well.

 

[autorouter]

looking at your figure you saying it will consume 336watts at source to make 240watts at 240 volts, that looks very inefficient dometic themselves claim 90% efficiency which is a lot more optimistic,

If they quote 90% that will be the best figure, when it is outputting its full power of 3kW. Therefore it wastes 10% of 3kW which is 300 watts. You might expect the wasted power to reduce as you use less power, so that at 1kW it only wastes 100 watts. However often the wasted power of a high power inverter is still high, even when outputting nothing at all. Using 336W to produce 240W output is not surprising.

 

[Bessy765]

You have to take into account using standard wet batteries, their performance suffers with age and cycles, to prevent damage and really shortening their life a 100 amp battery is only good at best for 50 amps. It’s not just the inverters efficency, voltage drop through cables should also be taken into account depending on how close you can site the inverter to your batteries. Totally different situation with Lithium but remember what you take out has to be put back, so time of year location and a clear view of the sky. Most solar panels output rating assumes an ideal placement and high summer temperature reduce the efficiency of solar panels.

 

[autorouter]

For most setups, low power devices are OK, and high-power devices too provided they are used in short bursts. A coffee maker or hair dryer for example.

The problem is a pair of batteries doesn't store much energy - two 100Ah lead-acids only give 100Ah of usable energy. At 12V that is 100 x 12 = 1200 watt-hours. That won't power a sustained load like an aircon for very long.

You'd need a very large solar array to run it, and keep the batteries topped up as well. Mind you, there's more chance with an aircon than a heater, because you normally need aircon when the sun is shining, which is the opposite to a heater.