Energy Matters Forums

[beenak47]

Hi,
We are on a stand alone system and I recently changed over the inverter to a pure sine wave model. I have a shunt and amp meter fitted in the line to measure amperage in and out of the battery bank and am suprised to see that the new inverter draws 4 amps when only a low wattage light is on. If it's switched onto standby then it draws next to nothing from the batteries. Is this normal with all inverters or are there some more energy efficient then others.

[Gordon-Loomberah]

4A does seem a lot, unless it is a really big inverter... Typically ~1A might be used on a reasonably sized inverter for domestic use when it is ON with no load, standby might be more like 100mW. However, some appliances dont always draw enough power to keep an inverter on, and may become confused by the power coming on and off. Latronics tech people tell me this is the case with some new refrigerators, and recommend to leave the inverter set ON.

What sort of inverter is it, and what was the actual load running when 4A was being drawn? Medium-large inverters will have very low efficiencies when there is only a very small load- due to it taking some power to run the electronics, transformer etc. They become a lot more efficient as the load increases, the power required to run the electronics doesn't increase very much.

When you say you have a shunt and ammeter connected, how exactly do you have them connected? Unless the ammeter is designed to be used across that particular shunt, the reading will be in error. Normally with a shunt measuring large currents like that you would measure mV drop across the shunt and calculate the current from that. 25mV across a 200A 50mV shunt would indicate 100A

[beenak47]

Thanks for your rep[ly.
The inverter is chinese made Power Star W7 3000w continuous 6000w surge, the amp meter is matched to the shunt to read amps across the negative cable.
This inverter replaced a Xantrex modified square wave which I have had in place for the last 6 years, the only reason I replaced it with a pure sine wave inverter is that the Xantrex reduced several DVD players and recorders to rubbish. I have since reinstalled the Xantrex just to see what amperage it was drawing in standby and by the meter early yesterday morning with nothing on except for the hot water service and telephone which draw such a small amount nothing was showing on the meter. I have been wondering what has been draining the batteries and it appears it may be this inverter.
The 4a being withdrawn by the Power Star inverter was taken at the same time in the morning that the Xantrex shows zero.
I have faith in what the meter is showing as it compares nearly the same as the regulator when showing amps available from the panels during the day with a small loss over the line.
I have never had an instrument that measures amperage out of the batteries, so the meter and shunt will eventually be replaced by something better, I just need to find something that will give me more detail.
I hope that explains it better for you.

[Gordon-Loomberah]

The inverter is chinese made Power Star W7 3000w continuous 6000w surge,

OK, specs say 80% nominal efficiency... so low and high end power efficiency are probably waaaay below that.

the amp meter is matched to the shunt to read amps across the negative cable.

It should be ok if the shunt and meter quality is reasonable. I know the ammeters on the regulators supplied with the cheap Chinese WTGs (I have a few of them) are rubbish, and read about twice the actual current being generated. Unfortunately, calibrated shunts and high accuracy meters are quite expensive.

The 4a being withdrawn by the Power Star inverter was taken at the same time in the morning that the Xantrex shows zero.

The best way to compare them is to turn all AC loads off at the switchboard before taking measurements, to eliminate intermittent loads such as fridges etc.

[beenak47]

Can you tell me what you use to measure amperage in and out of the battery bank so as to be able to better manage them and what sort of information is available.
Thanks for your help

[Cherokee Solar]

Hey Beenak47,

I'm not sure whether you mentioned it, but what sort of regulator are you running? I'm running a Plasmatronics PL60 and the 200A shunt is connected to that. It's fairly accurate for reading amps used, although I'm beginning to suspect that without spending huge dollars, there is no such thing as total accuracy. It would be nice for you to be able to get a second opinion on the amount of current drawn as sometimes the cables to the shunt can pick up a bit of electrical inteference too.

Still 4Ah will quickly drain your batteries. Do you turn the inverter off at night? I would at that consumption rate. As a comparison for you, a Latronics 24v 3,000w continuous will use about 0.6Ah whilst on. I don't run it on standby as I've got a pump, refrigerator, smoke alarms, and solar hot water pump controller connected which are on all the time and I don't think the electronics in any of those appliances would operate well on standby mode. With all of them on, but drawing minimal load it's about 1.2Ah - still even that adds up.

Some inverters just aren't that efficient.

Regards

Chris

[Gordon-Loomberah]

Can you tell me what you use to measure amperage in and out of the battery bank so as to be able to better manage them and what sort of information is available.
Thanks for your help

I dont specifically measure current in and out of the batteries, but at the moment I measure voltage, 2 inputs from solar and wind, and total DC loads- currently the inverter and a 4W fan. I use a Graphtec GL200 data logger, which has 10 channels, and can sample at 100ms, although I use 1 sec sampling. In the future some of the spare channels will be used for an additional 2kW tracking array, hydro-electric turbine generation and also tracking vs fixed panel comparison, and maybe PV panel temperature, although my weather station is right next to the PV arrays and air temp, solar radiation, wind speed and humidity combined could probably give a good estimate of panel temp if I could be bothered to figure it out

Here is what the display looks like, so I can see what is going on from tthe house any time of the day, or I can log on from work, 250km away, and monitor it too.

click to de-fuzz

[karlajensen]

if its drawing 4A it should be getting quite warm
4x12=48W being wasted, thats pretty hot and will confirm your suspicion.

Was this an expensive piece of kit? I'm guessing not, hence might be time to sus out something better

[brarmstr]

Mine is consuming 108watts idle power for the same unit ppl are reporting up to 230 watts consumed on idle on the 48 v units getting parts for them is not easy

[offgridQLD]

My Selectronics ps1 48w 6000w - 12000w inverter-charger consumes 60w when on and then 15w in standby mode. I haven't confirmed this but thats that the specs sheet list. It dose add up as 60w is 1.4kwh a day !

from my limited experience like others have said some inverters are better than others. The bigger the inverter usually the more power it will consume even at idle. Some of the cheaper units are very bad and perhaps it just comes down to cost or bad design. That said my inverter is a relatively expensive one and I feel it isn't that efficient at idle on mode though it is a big unit.

I don't want to get off track from the original post but I have a question along the same lines

When reading the front LCD panel of my inverter there is listing for average daily kwh . The manual said its a average kwh day number over the part 7 days. I haven't been at the house just refrigerator and a few tiny standby loads and mine is reading 1.99kwh. Based on this number I take it the internal shunt( the inverter has a few inside ) that gives me this reading doesn't take into account the inverters own idle (power on ) consumption of 1.4kwh day. I really need to know whats coming out of the battery's not through the inverter for true total consumption.

Kurt