IM looking to buy48v 6kw lfi ,how do you justify big idle consumption in this case 150w for 6kw model i see it as disadvantage over hfi. It is 3.6kw per day just for the idle consumption .I will have 16 lifepo4 280ah batteries ,so what would you buy LFI or HFI ?
low frequency inverter
- Thread starter mmdb
- Start date
Ths toms ... Only freezer/ fridge and small water pump... As i understnd LFI have a power saving mode in which if there is load less than 25w will use only 6-7w on idle which is great because i will rarely be in off grid cabin ,but that raise another question about batteries (presuming fridge will use no power or less than 25w when compressor is not runing),that batteries will almost always stay at full charge or near full charge ,and i read its not good for lifepo4 longevity
Steve_S
Offgrid Cabineer, N.E. Ontario, Canada
Shop around, the better quality inverter the more efficient.
My Samlex EVO in idle (not power-saver mode) only uses 18W and the unit is also 94% efficient. Victron's have similar specs. Power saver modes for most Inverter systems are a disappointment for many, as a common issue is the "demand sense pulses" which cause LEDS to blink (including microwave, coffee maker tec) unless the minimum Watt threshold is sensed and the Inverter wakes up.
I'm 100% offgrid 7/24/365 and so power-saver is fairly moot. The only real benefit would be if it was a part time home when you could put the Inverter on Power-Save so it can run the fridge etc when no one is there.
NOTE: If an inverter wanders off 59-61Hz frequency threshold your clocks will slow or speed up. Some powersave modes affect the frequency, Generator charging is done at the generators frequency, so if it is off, that will affect everything too. Lower Cost systems can be seriously affected by such and often do have wandering frequency rates.
My Samlex EVO in idle (not power-saver mode) only uses 18W and the unit is also 94% efficient. Victron's have similar specs. Power saver modes for most Inverter systems are a disappointment for many, as a common issue is the "demand sense pulses" which cause LEDS to blink (including microwave, coffee maker tec) unless the minimum Watt threshold is sensed and the Inverter wakes up.
I'm 100% offgrid 7/24/365 and so power-saver is fairly moot. The only real benefit would be if it was a part time home when you could put the Inverter on Power-Save so it can run the fridge etc when no one is there.
NOTE: If an inverter wanders off 59-61Hz frequency threshold your clocks will slow or speed up. Some powersave modes affect the frequency, Generator charging is done at the generators frequency, so if it is off, that will affect everything too. Lower Cost systems can be seriously affected by such and often do have wandering frequency rates.
MurphyGuy
It just needs a bigger hammer
- Joined
- May 20, 2020
- Messages
- 4,129
You should run the math on that.. its a huge issue. 150 watts over 24hrs = 3.6kw of wasted energy. That's over half of the battery's capacity being wasted just to keep the inverter at idle.
We have a couple of Sunny Islands which idle at 25w each and they use up 1.2kWh of juice out of our 25kWh pack every 24 hours.... and I even complain about that.
Hedges
I See Electromagnetic Fields!
- Joined
- Mar 28, 2020
- Messages
- 20,600
Presumably two for split-phase?
At least in single phase, the Sunny Island master can take the load and wake up the slave when more is required:
"12.2 Sleep Mode
Using the parameter "250.10 SleepEna" set to "Enable" allows the sleep mode to be activated in
single-phase utility grids which the master uses to switch off the slaves when the power value allows
this."
With two, 1s2p, instead of 25+25 = 50W, should be 25 + 6 = 31W. With four, instead of 100W would be 43W.
I'm wondering for my 2s2p if it might sleep two, for 62W.
You could obviously use a transformer to get 120/240 out of a 1s2p configuration, but that would likely not save anything. I read transformer idle losses are around 1%, so a 6 kW transformer could burn 60W.
I plan to add a 9000VA balancing transformer on the load panel (would be load-shed at 70% DoD). Possibly connected by relay only when off grid.
Also idle mode (or night time sleep, if that works for two of them in series configuration) so when loads disconnected for low battery it saves power at night, then turns on for AC coupled GT inverters.
If I don't do anything, 4 x 25 = 100W no-load draw, maybe 16 hours of winter night is 1600 Wh to power the inverter until sun comes up. With a 20 kWh battery, that's almost 10% of capacity, the difference between 70% DoD load-shed and 80% DoD battery protect shutdown.
What I really need to do is make a 20% DoD signal to disconnect excessive loads (laundry, A/C, yard lights, refrigerators), so they only run when PV has battery full and don't drain it in the evening.
There will be no microwave we don't do that here ..even if it's small 1 room cabin inside there is brick BBQ with chimney for cooking and heating and outside is gazebo with big brick pizza oven and another brick BBQ with chimneys ..we always cook and bake on wood ..coffeemaker will not be there only vine beer whiskey )) and non alcoholic drinks for children's
MurphyGuy
It just needs a bigger hammer
- Joined
- May 20, 2020
- Messages
- 4,129
We don't live in a backwoods hut or small cabin or anything like that.. our home is a normal brick house and it draws a consistent 600 to 1000 watts continuously. 3 Freezers, 3 PC's, television, well water, sump pump, etc.. Something is always running and its usually more than one thing.
My 25kWh pack is a bit undersized as it will only run the house for a day without some kind of charging input. Been waiting for another good deal on some EV cells to pop up so I can add another 25kWh's to it.
And yes, the two SI's are for a 120/240 split phase system. I'm building another system for a neighbor and will be using a transformer on his single SI unit so he can run his well pump when needed. Probably going to put a switch on the transformer so he can turn it off when the 240 isn't needed.
In our house there has never been a period in the last 8 years where we have had no power useage- the inverter wouldn’t know what idle was..
If you aren’t there, and everything is turned off, idle current from inverter won’t fully discharge your batteries.
You can’t say the inverter is using 3.6kwh/day unless you are using zero power.
Of course everyone has a different situation, but for a typical off-grid setup it’s a non issue.
Noneyabussiness
New Member
- Joined
- Aug 28, 2020
- Messages
- 54
If it is a cheap transformer based inverter, the above modifications may help reduce idle current... particularly this bit,
" This solved the problem.... now idle currents were down in the sub 1 amp range.... in fact now it could be alive all the time, and waste less than 20 watts..... less than their sleep mode...... so 3 and a half turns around a 65mm e core made the thing very very acceptable as a front line unit "
There is a picture of the very easy modification.
MurphyGuy
It just needs a bigger hammer
- Joined
- May 20, 2020
- Messages
- 4,129
Idle current is expended regardless of how much power you're drawing from the inverter. Idle current is the power to run the electronics, waste from the transformer, leakage, etc.
If your inverter has a 150w idle current and you hook up a 1000 watt load, your bats will be delivering 1150 watts.
Only time an inverter doesn't draw an idle current is if its off, or has a standby setting. Sunny Island inverters draw 4w in standby and 25w at no-load idle.
And yes, the idle power will draw your batteries down to the point at which the inverter's own disconnect shuts it down.. and on a Chinese inverter, probably even past that point.
Right, I learned in a webinar from Solarwatt= BMW, that their battery management is learning the consumption curves and organizes the charging so, that the battery is only near fully charged late on daytime, to keep the full charged time low. Toyota runs their hybrid car bateries at 30 to 70% SOC
Hedges
I See Electromagnetic Fields!
- Joined
- Mar 28, 2020
- Messages
- 20,600
To be a bit more precise, at 1000 watt load the Sunny Island 6048 is about 95% efficient, so add 50 watts.
It appears the 25W idle current is included in the graph below, so 1050 watts.
At 6000W load around 92% efficient. 6000 / 0.92 = 6522 watts from battery.
I'm able to curve-fit the efficiency fairly well with the following:
PowerLost = 25W + (0.4% x PowerDelivered)^2
The "squared" would come from IR^2 losses, dissipation in MOSFET and transformer goes as square of current.
I only took a few numbers from the above graph. This equation provided a reasonable fit but not TOO good, as in the following link:
Help needed - 48VDC system (Skoolie)
The “conversion penalty” at 48v will be quite a bit lower than 15%. For a Victron unit, I can tell you it will be 8% or less. Victrons are top shelf and have demonstrated ~90% efficiency. Anyone want to test their mpp 48 volt all in one unit?
diysolarforum.com
Sunny Island shuts down to protect battery from over-discharge, default 80% DoD (at least for lead-acid). Each inverter has two relays which can be programmed with various status, including two states of charge. 70% DoD is default for load-shed, disconnecting non-critical loads so inverter can keep running until sun comes up.
Some charge controllers (e.g. Midnight Classic) have programmable relays. I think state of charge is one option, so could control load-shed or inverter shutdown.
MurphyGuy
It just needs a bigger hammer
- Joined
- May 20, 2020
- Messages
- 4,129
That's what we do. One of my aux relays drive a large 160amp ABB load shedding contactor with a dual-stage coil. But the way I have my system set up, it shuts down all the loads, not just some of them. When the battery drops below 40%, we start conserving energy by turning stuff off.. at 15%, the system shuts off the entire house.. at which point I start up the generator and send energy into the AC2 contacts.To be a bit more precise, at 1000 watt load the Sunny Island 6048 is about 95% efficient, so add 50 watts.
It appears the 25W idle current is included in the graph below, so 1050 watts.
At 6000W load around 92% efficient. 6000 / 0.92 = 6522 watts from battery.
View attachment 29277
I'm able to curve-fit the efficiency fairly well with the following:
PowerLost = 25W + (0.4% x PowerDelivered)^2
The "squared" would come from IR^2 losses, dissipation in MOSFET and transformer goes as square of current.
I only took a few numbers from the above graph. This equation provided a reasonable fit but not TOO good, as in the following link:
Help needed - 48VDC system (Skoolie)
The “conversion penalty” at 48v will be quite a bit lower than 15%. For a Victron unit, I can tell you it will be 8% or less. Victrons are top shelf and have demonstrated ~90% efficiency. Anyone want to test their mpp 48 volt all in one unit?
Sunny Island shuts down to protect battery from over-discharge, default 80% DoD (at least for lead-acid). Each inverter has two relays which can be programmed with various status, including two states of charge. 70% DoD is default for load-shed, disconnecting non-critical loads so inverter can keep running until sun comes up.
Some charge controllers (e.g. Midnight Classic) have programmable relays. I think state of charge is one option, so could control load-shed or inverter shutdown.
We put our computers on a UPS system with a marine battery to prevent power issues when the grid goes down or a load shed event happens.
The SI's seem to run most efficiently at around 2000 watts output. My home usually burns between 800 and 1200, with short spikes to 2500 when we turn on big appliances or take showers. When we start conserving, that 800 to 1200 can be reduced to a steady 500 watt draw, which works out to a couple fridges, a couple freezers, and some lights.
RCinFLA
Solar Wizard
- Joined
- Jun 21, 2020
- Messages
- 3,563
Idle current is more a function of a particular inverter design then whether it is high freq or low freq type.
Driving MOSFET's high speed switching input capacitance is major overhead. Poorly designed PWM output filter can add significant idle power.
There are tricks done to partially shut down MOSFET sections based on load demand to save idle power. If not done well this can negatively impact inverter reliability when subjected to surge loads. It takes a finite amount of time to recognize heavier load and bring shutdown sections back on line. This can overstress the sections that were on before surge that are subjected to a short period of overload stess.
Driving MOSFET's high speed switching input capacitance is major overhead. Poorly designed PWM output filter can add significant idle power.
There are tricks done to partially shut down MOSFET sections based on load demand to save idle power. If not done well this can negatively impact inverter reliability when subjected to surge loads. It takes a finite amount of time to recognize heavier load and bring shutdown sections back on line. This can overstress the sections that were on before surge that are subjected to a short period of overload stess.
