Power Bus Spikes from Inverters

[wanttaja]

I'm looking at installing a 120VAC inverter on my Fly Baby's power bus to run a small motor-driven appliance (12V motors not available). I am a bit worried at whether it'll induce glitches in the power bus that might hammer what little avionics I have.

Anybody have any insight into power problems induced by inverters? I won't be using the device often, and only on the ground, so I can kill the avionics master before using it.

Ron Wanttaja

 

[gismo]

I'm looking at installing a 120VAC inverter on my Fly Baby's power bus to run a small motor-driven appliance (12V motors not available). I am a bit worried at whether it'll induce glitches in the power bus that might hammer what little avionics I have.

Anybody have any insight into power problems induced by inverters? I won't be using the device often, and only on the ground, so I can kill the avionics master before using it.

Ron Wanttaja

Cheap and/or poorly designed inverters can and do generate a fair amount of noise on their inputs in the form of repeated rapid changes in current but as long as your aircraft battery is in reasonable shape and connected to the bus there's virtually no chance that what you propose would harm anything.

 

[denverpilot]

Motors pull a lot of current at startup or if they stall. Plan accordingly on the size of the inverter.

Don't use the steady-state power draw of the motor as the controlling figure in how many amps are required.

Also most cheap inverters don't output true sine-wave AC. Make sure that doesn't bother your motor. Or buy an expensive one.

 

[wanttaja]

Motors pull a lot of current at startup or if they stall. Plan accordingly on the size of the inverter.

Don't use the steady-state power draw of the motor as the controlling figure in how many amps are required.

Also most cheap inverters don't output true sine-wave AC. Make sure that doesn't bother your motor. Or buy an expensive one.

Got one with a "Modified sine wave" output, rated at 200W, and the device it's powering is listed as 120V 0.6 Amp. I've tested it using an old Odyssey battery for power (got a new one in the plane). Seems to work OK, but I need to slap an ammeter on the power and see how much it draws. Fortunately, I'll only run it for very short times each flight. I'm installing a warning buzzer so I don't leave the inverter on.

Thanks, Denverpilot and gizmo....

Ron Wanttaja

 

[PW_Plack]

...I am a bit worried at whether it'll induce glitches in the power bus that might hammer what little avionics I have.

Anybody have any insight into power problems induced by inverters? I won't be using the device often, and only on the ground, so I can kill the avionics master before using it.

Ron, if you want some insurance, get one of the inline filters sold by auto parts and stereo stores for use on the power feeds to powerful car stereos. They fairly light, relatively cheap, effective, and pretty stout. Make sure to get the kind which have three terminals: + in, + out, and ground.

Or save even more cost and weight, and print a one-item checklist on a label next to the inverter which says, "AVIONICS MASTER OFF!"

Note: Some inverters and DC-to-DC voltage converters can also generate RFI which makes it hard to use the radio. (Probably not an issue on the ground.)

 

[denverpilot]

Yeah I've hit that RFI problem. Especially in VHF and above weak-signal contesting. The cheap tower antenna rotators are all AC driven.

We'd flip the inverter on, swing the antenna stack, and flip it off. Everything on 6m and often on up into 2m (just above AM Aircraft) would be trashed while the cheap inverter was on.

Very good point Paul. Make sure it doesn't trash your radio. Tune in a weak far away ATIS with the inverter off and then switch it on and see if the noise floor jumps significantly.