any help or ideas for a newbie

[Vigo]

What i don't understand is when under load the batteries % runs down really quick, but having a meter on each battery still shows the volts stay the same, no v drop. Its like the batterie's are buggered but the voltage stays constant.

That suggests your battery-to-inverter wiring is dropping voltage due to excessive resistance somewhere in that circuit.

If each battery is at 13.0 that would be 26v and your inverter is showing 24 there, suggesting a ~2v drop in the wiring.

It could be a refresh rate issue, though. As in, something is happening very briefly that is overloading the inverter but the simple voltage and load% readouts dont reflect it. The fact that your ac output voltage is varying so much makes me wonder if you have a power factor issue with your heat pump. Some power meters such as the one linked to earlier in the thread will measure PF. If your inverter has a display mode that shows VA of output and it is much different from the Watt number, that would also suggest a power factor issue. Its also possible that the ac output voltage simply becomes that unstable when voltage at the battery input terminals is low, and that it has nothing to do with PF. All needs further testing..

If you have a mutimeter with min/max you could do several things to figure out how much of the problem lies with the batteries vs the wiring. Do you have a meter with a min/max function?

 

[andyriches]

That suggests your battery-to-inverter wiring is dropping voltage due to excessive resistance somewhere in that circuit.

If each battery is at 13.0 that would be 26v and your inverter is showing 24 there, suggesting a ~2v drop in the wiring.

It could be a refresh rate issue, though. As in, something is happening very briefly that is overloading the inverter but the simple voltage and load% readouts dont reflect it. The fact that your ac output voltage is varying so much makes me wonder if you have a power factor issue with your heat pump. Some power meters such as the one linked to earlier in the thread will measure PF. If your inverter has a display mode that shows VA of output and it is much different from the Watt number, that would also suggest a power factor issue. Its also possible that the ac output voltage simply becomes that unstable when voltage at the battery input terminals is low, and that it has nothing to do with PF. All needs further testing..

If you have a mutimeter with min/max you could do several things to figure out how much of the problem lies with the batteries vs the wiring. Do you have a meter with a min/max function?

hi yes i can get my fluke from work for this to test it for min and max

 

[andyriches]

hi yes i can get my fluke from work for this to test it for min and max

The main cables feeding in the inverter are changed to 35mm,i haven't done the connections between each battery, should i take this to 35mm as well as its currently at 16mm ?

 

[Vigo]

If the batteries were still wired as shown in post #6 you could probably keep the ‘interconnections’ at the smaller size, but if you changed the wiring to the setup shown in #10 as was recommended, they would all need to be the same size. So, if you havent already i would wire them as shown in post #10 and make all those wires the same size. ?

 

[andyriches]

If the batteries were still wired as shown in post #6 you could probably keep the ‘interconnections’ at the smaller size, but if you changed the wiring to the setup shown in #10 as was recommended, they would all need to be the same size. So, if you havent already i would wire them as shown in post #10 and make all those wires the same size. ?

Thanks
I will get this changed tomorrow and see if we have anything more to report

 

[andyriches]

Quick question on working out the time a battery will last on load.
Is the calculation done using 230v or 24v

ie 2kw load at 24v(190 aph battery) DC voltage the current draw will be over 80amps
or because its going through the inverter is it 2kw load AC voltage and just over 8 amps ?

 

[Vigo]

So, this sort of comes down to amp-hours vs watt-hours.

Some batteries are rated in one, or the other, or maybe even both in some cases.

Volts X Amps = Watts

Watt-hours already includes the voltage number, because somebody did V x A to get that number. But, when amp-hours are used to rate a battery, its just assumed that you will use the voltage of that battery to calculate with. So for a ‘12 volt’ battery that was rated at 190ah, you would do 12x190=2,280wh. In reality the voltage is not exactly 12.0000 but calculating it that way is still fine because it builds a little wiggle room into the number.. your actual wh based on actual voltage would be a bit higher.

So for a 2kw load, a 2.28kwh battery would power that for just over an hour, ideally.

If you have any batteries in parallel you would multiply your wh by however many strings you have in parallel. If you had 3 paralleled strings of 2.28kwh batteries, the pack would have 6.8kwh and power the 2kw load for over 3 hours.

 

[andyriches]

So in the case below the batteries are 12v 190aph
Would It be 24v x190 = 4560 per string so a total of 9.12kw ?

 

[SamDeleted]

So in the case below the batteries are 12v 190aph
Would It be 24v x190 = 4560 per string so a total of 9.12kw ?

Spot on

Total 24v 380ah , 9120w

Batteries are in 2s2p

 

[andyriches]

Spot on

Total 24v 380ah , 9120w

Batteries are in 2s2p

So to work out how long that would last time wise what did you do ?
9120/2000 = 4.56 hrs ? And would that be fully depleted

 

[SamDeleted]

So to work out how long that would last time wise what did you do ?
9120/2000 = 4.56 hrs ? And would that be fully depleted

Yep correct minus efficiency,

inverter will be about 80% to 95% efficient,

Add on top 5%~ for losses over cables and fuses


I'd bank on around 4hrs depending on your equipment

 

[andyriches]

Yep correct minus efficiency,

inverter will be about 80% to 95% efficient,

Add on top 5%~ for losses over cables and fuses


I'd bank on around 4hrs depending on your equipment

Thanks for you're help Sam that has definitely cleared up some questions in my head