switching bench power supplies overloads my epever inverter

[Scph9002]

If i use switching electronics connected to my inverter like dc labs or normal led acid battery chargers they trigger overload with way lower current than what the inverter can handle.

The inverter and or the connected switching supply is giving of buzzing and ticking noises.

Anyone know why? I have made sure (i think) everything is grounded properly so im not getting ac ripple in dc inputs or between dc inputs of inverter and dc outputs of the chargers.

 

[Bud Martin]

What is the model of the Inverter?
What is the exact system setup? Can you show the wiring diagram?

 

[Scph9002]

What is the model of the Inverter?
What is the exact system setup? Can you show the wiring diagram?

ip1500

its just batteries to inverter to dc lab

chassi/ac ground of inverter is grounded to to earth ground and dc negative is grounded to same earth ground

 

[Bud Martin]

Is this the one?

https://www.amazon.com/EPEVER-1500W-Pure-Sine-Inverter/dp/B07JPZBKSD

12V?
What kind of battery?
What is DCV on the DC input of the inverter when you start putting load on AC output of the inverter?
Can you use lamp as the load to see if it will stay on?

 

[Scph9002]

yes.

Lifepo4 battery. Its 12v 560ah near full. 13.1v More than enough. I can easily push over 130 amps making coffe with it without excessive voltage drop or issues. But with light load while using dc labs pulling over 25 amps from labs/chargers etc my inverter just craps out lol. No excessive voltage drop just ticking noises

 

[Bud Martin]

I did not look at the user manual yet.
Does it have ECO mode to reduce standby current?
Most inverter with ECO mode requires to have 40W or to keep the inverter stay on otherwise it will go to sleep mode when it detect load <40W.

 

[Scph9002]

check this out. Maybe easier to understand my issue.

Pulling to much amps from switching dc labs and battery chargers craps my inverter out but pulling 3x more amps with non switching supplies is no problem

 

[Bud Martin]

Only 16V @ 22A, yeah, not much power at all.
So if the charger is connected directly to wall outlet, it works fine, right?
I wonder how much AC current it is drawing from the inverter, may be it has high enough spike to trip the inverter protection circuit.

 

[Scph9002]

Its around 75% efficiency on the dc lab. less than 500 watt where coming from the inverter

It works fine on main ac. Works better on another epever inverter but it is larger 2000 watts. It craps out also early but can handle more "dirty" amps

Making coffee peaks 1500 watts from inverter no problem at all ;P

 

[efficientPV]

It doesn't surprise me. It only draws amps at the peaks. I had a 150W inverter and tried to power a small switching wall wart power pack. Even with nothing connected to the wall wart the little inverter crapped out as it couldn't take the caps charging. You are drawing significant peaks of current with that power supply and the inverter is seeing it as a problem.

 

[Scph9002]

epevers inverters are pure sinewave

 

[mikefitz]

Your issue is due to a poor quality inverter that cannot tolerate the high current 'pulses' that the switching power supply takes.

Mike

 

[sunshine]

chassi/ac ground of inverter is grounded to to earth ground and dc negative is grounded to same earth ground

Grounding the dc negative is probably not a good idea for reasons other than a possible cause of your problem.

 

[mikefitz]

Grounding the dc negative is probably not a good idea for reasons other than a possible cause of your problem.

Since all inverter manufactures recommend this for safety, why is it not a good idea?

Mike

 

[stienman]

You've run into the difference between watts and volt-amps.

Inverters are often rated in VA, while loads are often rated in watts. In a DC circuit they are the same, but not in AC.

The power factor describes the relationship for a given load. In your case, that Velleman LABPS3020SM power supply has an abysmal power factor rating of 0.61.

The equation for power factor is PF = W/VA. So if you have the power factor and watts, then VA = W/PF. You power supply is, therefore, drawing 1.6x the power it uses. Note that this doesn't mean you're losing that power - as a reactive load, it draws on one portion of the cycle, and then feeds back on the other portion, so the total consumed energy is still the same as watts, however the inverter sees a 1.6x load during portions of its cycle, even though the power supply isn't actually consuming that much energy.

So at 22.2v and 16.7A output, your power supply is providing 370w. With a conversion efficiency of perhaps 85% it's consuming 436w, so generating about 66w in heat, and 370w in output energy. Given the conversion efficiency and the power factor, the maximum VA that power supply can use is right about 1,200VA, which is a common power design limit for electronics.

If it's actually consuming 436w, and has a power factor of 0.61, then its apparent power is 436/0.61 --> 715VA

Given that you're running a least your lights, and possibly other loads, off that 1,500VA, and most of them are likely similar in terms of power factor. Cheap LED lights are often just barely above 0.5 power factor - so they consume nearly twice the apparent power (ie, VA) than their rated wattage.

There are some things you can do to match the loads to your inverter, but honestly it's best to simply buy the inverter that is rated for the continuous VA that your loads need, or buy loads that have a 0.95+ power factor so the watts equals the volt-amps.

This is why a lot of people ignore VA vs W and simply handwave the issue by suggesting you always buy an inverter 2x larger than your loads. It's not a bad way of doing things, but it's also not the most efficient or effective way to design a system.

 

[stienman]

You can get meters that will measure the power factor for you, such as this one:

https://www.amazon.com/Current-Amperage-Voltmeter-Multimeter-Transformer/dp/B07JB9B2QL

This might be helpful on the output of the inverter in diagnosing why the inverter is complaining.

 

[sunshine]

Since all inverter manufactures recommend this for safety, why is it not a good idea?

Negative on the DC battery side.
I unearthed my negative too long ago to remember the actual reason why and have never encountered a problem since to justify re-earthing.

Sorry for the lame explanation.
One other benefit is not getting sparks when using a mains soldering iron on the 12v live DC cables.

 

[RCinFLA]

Assuming you don't have too small gauge battery cable, the problem is likely the simple rectifier-capacitor for the AC to DC conversion in the switching power supply. With the simple rectifier-capacitor, the power the switching power supply is takiing from AC input is all delivered in short high current pulses near the peaks of AC voltage input.

Newer, more expensive supplies, have power factor correction between rectifier and filter capacitor. This is usually a sinewave profiled boost pre-switcher that draws current as a sinewave profile earlier in the AC input sinewave cycle to charge the filter cap in the power supply thereby spreading the current demand over the whole sinewave AC input. These will do no good for a modified sinewave inverter though. MSW inverters can actually damage the PF correction circuitry.

Most new computer switching power supplies have power factor correction due to EU regulations for power factor on devices drawing more than 75 watts.

Inverters, transformers, and generators are actually rated for VA not watts. As power factor gets worse the amount of actual power they can deliver is reduced. Their internal losses is proportional to the square of their output current.

 

[stienman]

...using a mains soldering iron on the 12v live DC cables.

?

One of these day's you're going to have a bad day...

 

[Hedges]

I also have trouble running a VFD, which has diode-capacitor front end.
When off-grid, battery inverter is OK, but GT inverters which look for in-spec sine wave give errors.

Linear supplies also have diode-capacitor, but with small transformer isolating it from line, doesn't load line as heavily.

Maybe a transformer before your switching supply. Maybe just a series resistor or inductor.
You don't want a switching supply fed too low a voltage. But if it is rated for something like 90 to 250V as many universal supplies are then a transformer stepping up from 120V to 240V could sag under load without going out of spec. Leakage inductance and winding resistance would limit peak curent.