Question 1: Some Shunt manufacturers rate their shunts from -50 to 50A and others from 0-50A. What in a shunt if any can prevent it from sensing reverse current?

Question 2: Have anyone measured PF before and after an inverter. On the older 5kva/4 kw inverters I would expect the PF to be the same before and after the inverter, but what happens with the new 5kva/5kw units supplied as a 1 PF unit? It would be interesting to see if an inverter has any effect on PF at all. 

Question 2: I did it with a PF1. When is grid conected inverter can improve power factor. For example, i conected a 300 w charger  and the results, off grid, were 250W 540 VA. Ongrid, results were 250 W 450 VA. It seems the inverter tries to pass reactive power to the grid.

Question 1: I don´t know. 

1 hour ago, Jaco de Jongh said:

Question 1: Some Shunt manufacturers rate their shunts from -50 to 50A and others from 0-50A. What in a shunt if any can prevent it from sensing reverse current?

A shunt is a resistor. It is not going to care which way the current is going. So if it can do +50A, I'm pretty sure it can also do -50A. So essentially it's the same thing. Reverse current will show a reverse voltage drop.

1 hour ago, Jaco de Jongh said:

Question 2: Have anyone measured PF before and after an inverter. On the older 5kva/4 kw inverters I would expect the PF to be the same before and after the inverter, but what happens with the new 5kva/5kw units supplied as a 1 PF unit? It would be interesting to see if an inverter has any effect on PF at all. 

Don't be confused by the PF1 marketing. All it means is that the boost stage is the same size as the final stage. Modern inverters all use a DC/DC boost stage to take the 48V input to around 400VDC, and then use a final "switching" phase that makes 230VAC from that. Old inverters had a 4kw boost stage and a 5kva final stage, so it meant you could power 5kva loads as long as the power factor was no more than 0.8, in other words as long as the real power is never more than 4kw.

The uprated boost stage in the new inverter has no effect on the power factor of the inverter (or rather the charger part) or the loads. That will remain exactly the same.

If the unit is not charging, then the power factor should be the same on both sides. If it is charging, the power factor on the input might be different. Some units go to some trouble to keep their power factor at 1, some might even correct power factor so that the input has a better power factor than the output. In the case of the Axpert, the power factor will be the same or worse, that is what I would expect.

22 minutes ago, plonkster said:

A shunt is a resistor. It is not going to care which way the current is going. So if it can do +50A, I'm pretty sure it can also do -50A. So essentially it's the same thing. Reverse current will show a reverse voltage drop.

Thanks, I thought the same. 

 

24 minutes ago, plonkster said:

the power factor will be the same or worse, that is what I would expect.

Also part of a crazy suspicion I have, i wondered if anybody ever bothered to measure and record this.  

30 minutes ago, plonkster said:

so it meant you could power 5kva loads

So effectively I could power 5 kw resistive loads from my inverter constantly ?

17 minutes ago, Jaco de Jongh said:

So effectively I could power 5 kw resistive loads from my inverter constantly ?

Correct, with the old one you could only power 4kw.

I completely understand why you need both numbers. It's essentially limited to either number, whichever one is exceeded for your system/loads.

So if you have a big electric motor with a power factor of 0.7, then you are limited to 3500W of real power (even though the boost stage is 4kw), because the final stage can only handle 5kva and you're maxed out.

Similarly, if you have a 4500VA load at 0.9 power factor, you are also maxed out because the real power component is already 4000W.

Edited October 25, 20186 yr by plonkster

I have a 100 Volt -100 Amp  Shunt connected to PZEM powermeter between the Inverter and battery bank . The meter displays volts ,amp, power and energy . The meter only displays power flowing in 1 direction . If I understand correct this is what the meter is capable of doing .If the wires is reversed it displays power to the opposite direction .If I get another meter will I be able two to connect both to the same shunt and display power in both directions . Thanks

54 minutes ago, Chris Louw said:

The meter only displays power flowing in 1 direction

Hi Chris, i guess the coding was done only to calculate flow in one direction. 

 

55 minutes ago, Chris Louw said:

If the wires is reversed it displays power to the opposite direction .If I get another meter will I be able two to connect both to the same shunt and display power in both directions

Effectively yes. Its sorry that you have to buy one more to see the reverse flow. I assume you feed back to grid then if you want to measure it?

Thanks Jaco for your replie . I run off grid so no feedback. Also have a power meter in the DB . Currently there is no battery management on the battery bank only balancers .

The meter is used 1. To calculate the los of power from the battery bank to the BD .

2. By switching the connection from the shunt to the meter I can see the amount of power removed from the battery bank at night and the amount of power put back when charging the next day .The ratio no is +- 1.26 .Try to keep the batteries going until I can buy lithuimbank with all the equipment I need .

3 hours ago, Chris Louw said:

I have a 100 Volt -100 Amp

I seem to have missed this part somehow. 100 volt <> to Grid voltage.