problems with an Inverter

[aircond_gypsy_63]

I have an inverter rated at 2500 w/5000w surge. it has multiple safeties for hi / low voltages ect.. being a modified sine wave type it does not like to "start" different motor or heating element loads. So heres the problem...I'm powering a fridg., Air cond., heater or a convection micro combo. (not all at once) and the Inverter unit bogs down at startup on the fridge. which does need to be online 100%. the fridge in "ultramodern" i.e. energy saver and runs at 20% to 35% duty cycle over a given timeline (on/off on/off....) this process over loads a safety and the inverter goes on stand by 'till it is cycled on/off to reset. I was told by a friend that a capacitor might solve this problem. So off to Google I go to find out about capacitors...
I'm not smart enough to get this one figured out on my own before reaching my 50th b-day so I'm here asking for help to solve my problem
thanks... Ac gypsy

 

[aircond_gypsy_63]

this one cant be so tuff can it?...
assume a load at 120 volts -3500 watts.
what type of capacitor would I need to cover the surge and where do I mount the thing?

 

[Sceadwian]

It's not as simple as that. You can't just tack the cap on and the inverter will suddenly magically be happy. The inverter itself has to from start to finish be designed for that kind of starting load. What you need is an inverter designed to run AC motor loads directly (true sine wave) As far as a modified sine wave inverter goes, a typical AC motor is a dead short to ground on start. A capacitor can buffer that power surge briefly, but a large enough capacitor to do that is going to also cause a significantly higher initial load than even the motor itself.

 

[aircond_gypsy_63]

It's not as simple as that. You can't just tack the cap on and the inverter will suddenly magically be happy. The inverter itself has to from start to finish be designed for that kind of starting load. What you need is an inverter designed to run AC motor loads directly (true sine wave) As far as a modified sine wave inverter goes, a typical AC motor is a dead short to ground on start. A capacitor can buffer that power surge briefly, but a large enough capacitor to do that is going to also cause a significantly higher initial load than even the motor itself.

Thank you for the info here.
Lets see if I've got this right... So the "battery effect" of the cap is offset by it's rapid charge up cycle... would this occur just once when powering up the circuit or every time the fridge cycles on/off? I dont understand why for instance when I pwr up an electric drill the inverter surges briefly but catches up very quickly, but takes much longer to get the fridge past its start phase.
the fridge rating in watts is only in the 800-900 range...well within the limits of the inverter even before taking into account the 30 sec. surge window that the inverter is supposed to handle before tripping the safety inside it.
If I had the $$$ to get the true sine wave model I would but alas this is not the case, so I'm stuck with what I have and still need to find a way to help the inverter... any Ideas?
Robert

 

[audioguru]

Can't you or the utility fix the problem of the mains dropping out which requires having the inverter?
Can the battery and its wiring handle the very high current when the fridge starts?

 

[aircond_gypsy_63]

the unit is mounted in a Big truck cargo box, coupled to two deep cycle batteries, which are recharged when the vehicle is running. the high current is handled by 4 2/0 cables..