Previous in Forum: What Is Effect On Generator In Case Loss Of Excitation?   Next in Forum: Selection Criteria and Sizing of Diesel Generator
Close
Close
Close
12 comments
Rate Comments: Nested
Commentator

Join Date: Aug 2011
Posts: 93

Inverter Current

08/22/2013 12:35 PM

Hello,

I have a doubt in Inverters.

I have observed that the input current drawn by the inverter from the battery is smaller compared to output three phase current connected to the motor.What is the Relation between input DC and output 3 phase current of inverters?

Register to Reply
Interested in this topic? By joining CR4 you can "subscribe" to
this discussion and receive notification when new comments are added.

"Almost" Good Answers:

Check out these comments that don't yet have enough votes to be "official" good answers and, if you agree with them, vote them!
Guru

Join Date: Feb 2011
Location: Atlanta, GA
Posts: 1053
Good Answers: 110
#1

Re: Inverter current

08/22/2013 12:44 PM

It depends upon the inverter, but most are better than 90% efficient. So the input wattage generally (roughly) equals the output wattage. Current will depend on the relative voltages, so if battery voltage is less than RMS AC voltage, then the battery amperage will be greater than AC amperage. If battery voltage is higher than AC voltage, then battery current will be lower than the AC current.

__________________
Think big. Drive small.
Register to Reply Score 1 for Good Answer
Guru
Safety - Hazmat - New Member Engineering Fields - Retired Engineers / Mentors - New Member Engineering Fields - Piping Design Engineering - New Member Hobbies - DIY Welding - New Member Fans of Old Computers - PDP 11 - New Member

Join Date: Feb 2007
Location: Stronger Than The Storm
Posts: 2394
Good Answers: 203
#2

Re: Inverter Current

08/22/2013 9:44 PM

The power you can get out cannot be less than the power you put in. If you lower the input voltage you will also increase the input current, likewise for the power out. An inverter generally doesn't care what the input voltage or current is, just that it more than is taken out of it (power= voltage * current).

For example: the input could be 100 amps at 1 volt or 1 amp at 100 volts (100 watts either way) just so long as it is greater than the power out, 90 volts at 1 amp or 90 amps at 1 volt (90 watts) assuming 90% efficiency of the inverter. You have to put in more than you take out and the design of the inverter is what determines what is put in and what is taken out and likewise the output power (p=I*E) must be less than the input power. This is true no matter whether it is a single or three phase input and/or single or three phase output. Power in >Power out.

Good Luck, Old Salt

__________________
Any day on the green side of the grass is a GREAT DAY!, --- me +++++++++. I believe creativity is an inherent part of everyone. --- Kermit T. Frog
Register to Reply
Guru

Join Date: Feb 2011
Location: Atlanta, GA
Posts: 1053
Good Answers: 110
#4
In reply to #2

Re: Inverter Current

08/23/2013 12:21 AM

The power you can get out cannot be less than the power you put in.
I think you meant "The power you can get out cannot be more than the power you put in."

__________________
Think big. Drive small.
Register to Reply Score 1 for Good Answer
Guru
Safety - Hazmat - New Member Engineering Fields - Retired Engineers / Mentors - New Member Engineering Fields - Piping Design Engineering - New Member Hobbies - DIY Welding - New Member Fans of Old Computers - PDP 11 - New Member

Join Date: Feb 2007
Location: Stronger Than The Storm
Posts: 2394
Good Answers: 203
#6
In reply to #4

Re: Inverter Current

08/23/2013 9:09 AM

K Fry-

Yes. Thank you for your alertness.

Good Luck, Old Salt

__________________
Any day on the green side of the grass is a GREAT DAY!, --- me +++++++++. I believe creativity is an inherent part of everyone. --- Kermit T. Frog
Register to Reply
Guru

Join Date: Feb 2011
Location: Atlanta, GA
Posts: 1053
Good Answers: 110
#7
In reply to #6

Re: Inverter Current

08/23/2013 11:52 AM

Strange that your answer, which was very good (but for the typo) was marked off topic. I've marked it back on topic.

__________________
Think big. Drive small.
Register to Reply
Guru
Safety - Hazmat - New Member Engineering Fields - Retired Engineers / Mentors - New Member Engineering Fields - Piping Design Engineering - New Member Hobbies - DIY Welding - New Member Fans of Old Computers - PDP 11 - New Member

Join Date: Feb 2007
Location: Stronger Than The Storm
Posts: 2394
Good Answers: 203
#9
In reply to #7

Re: Inverter Current

08/23/2013 12:33 PM

K Fry-

Thank you for the complement, even with my typo. Fingers become spastic at later hours. They have a mind of their own. I appreciate the removal of the OT. Usually I can see why I get an OT, Experimental Experiments especially, but not on this one.

Your, and several other's, postings are the ones I admire and trust the most just as I am sure others do likewise.

Again, Thanks.

Good Luck, Old Salt

__________________
Any day on the green side of the grass is a GREAT DAY!, --- me +++++++++. I believe creativity is an inherent part of everyone. --- Kermit T. Frog
Register to Reply
Guru
Engineering Fields - Mechanical Engineering - New Member

Join Date: May 2008
Location: CHENNAI, TAMIL NADU, INDIA.
Posts: 1851
Good Answers: 65
#3

Re: Inverter Current

08/22/2013 10:08 PM

Dear Mr. sujinvipin,

The DC input Voltage and Current cannot be directly compared with output AC Voltage and Current and it is the POWER that can be compared where efficiency of the INVERTER comes in to picture.

For a given power if the Voltage is low, the Current will be high and viseversa. For AC, the Power Factor comes in to picture.

Thanks,

DHAYANANDHAN.S

Register to Reply
Associate

Join Date: Jan 2008
Location: Bangalore , India
Posts: 52
#5

Re: Inverter Current

08/23/2013 3:25 AM

Hi Sujin

Like Mr Dhan... stated, DC cant be related with AC....

In a single phase inverter you use Opamps to output frequencies from 2 pins and drive mosfet drivers to create AC wave.

The load to the motor will decide the amount of current the battery can discharge.

__________________
Frank - Catch my statement if you can.
Register to Reply Score 1 for Off Topic
Guru

Join Date: Feb 2011
Location: Atlanta, GA
Posts: 1053
Good Answers: 110
#8
In reply to #5

Re: Inverter Current

08/23/2013 12:31 PM

Like Mr Dhan... stated, DC cant be related with AC....


In fact, there is a relationship between DC and AC. The power is the same (if we exclude losses in the inverter). That means that if you know the power at the motor, you can calculate the power at the battery, and therefore its current, given its voltage.

The load to the motor will decide the amount of current the battery can discharge.

This leaves a lot of room for misinterpretation by the OP, and is possibly a source of the OP's confusion. Motor "load" is generally measured in amps, i.e. current. That is only one part of the story, because the motor is also fed at a particular voltage, so power can be relatively high or low, depending on the product of voltage and current. So a motor loaded to 50 amps will draw something other than 50 amps (higher or lower) from the battery, depending upon the relative voltages (at battery and motor). The only case in which the two currents are the same is if the voltages are the same (ignoring losses) or if they vary by a factor equal to the inverter efficiency (accounting for losses).

__________________
Think big. Drive small.
Register to Reply
Guru

Join Date: Feb 2012
Posts: 595
#10

Re: Inverter Current

08/25/2013 12:48 PM

time the 2nd like Mr. dhayanandhan . . . said there is no 1:1/static/ non RMS correlation - trying to go faster my shadow - i'm studing this topic - seen various materials - but i don't fully comprehend the GO! yet . . . so anyway it goes like::

say you pull 3x60Hz from batteries = 180Hz(!) there should be a pre-charge of the primary coils withch is likely PWM-d sines (◄ that's the fuzzy part) - anyway the good inverter adjust to your load at the 2-ndary side (making it even more fuzzier) so only the T>60Hz-1 will start likely to correspond your E conservation more correctly

besides there are the effective values for Ammeters ??? but if their digital then i donno what they show A.RMS or 1/√2·A or A.Max(/peak)

__________________
ci139
Register to Reply
Guru

Join Date: Feb 2012
Posts: 595
#11
In reply to #10

Re: Inverter Current

08/25/2013 1:28 PM

T>(60Hz)-1>16ms (replaces the error above)

__________________
ci139
Register to Reply
Guru

Join Date: Feb 2012
Posts: 595
#12
In reply to #10

Re: Inverter Current

08/27/2013 4:38 AM

some practical results (R1 is DC (A) , R2 is AC (V) -- so it's the integral 1/¶ · 2 for full half-cycle)

__________________
ci139
Register to Reply
Register to Reply 12 comments

"Almost" Good Answers:

Check out these comments that don't yet have enough votes to be "official" good answers and, if you agree with them, vote them!
Copy to Clipboard

Users who posted comments:

ci139 (3); dhayanandhan (1); frankcorners (1); K_Fry (4); old salt (3)

Previous in Forum: What Is Effect On Generator In Case Loss Of Excitation?   Next in Forum: Selection Criteria and Sizing of Diesel Generator

Advertisement