Interference - VHF and tach

[CaptTom]

Looking for ideas on how to limit electrical interference in two specific areas:

1) There is a VHF radio located about 4 feet from the 2000W inverter. When I key the mike, a loud 60Hz hum can be heard on the receiving end.

2) One of my tachs is fine at the dock, but underway will suddenly jump up to twice the actual RPMs whenever I get above about 1500 RPM. Tachs are fed off the alternators.

The first one is obviously interference, it goes away when I power off the inverter. Not sure where it's getting "in" to the radio though. Do I address the power supply wires, or try to shield elsewhere? And how?

The second one is not so obvious. I've ordered enough primary wire to replace the entire run from the alternators to the gauges. I'm wondering if I should have gone with coax instead.

 

[Billylll]

Are you sure the batteries on the inverter are in decent shape? I have seen this happen when batteries are severly discharged or one cell is going bad. 60 cycle AC hum is induced into the DC buss from the charger on the inverter.
As far as the tachs signals check all the connections. Sounds like by replacing the wiring you will replace all the connections, good move +.
They sound like unrelated problems to me.
Bill

 

[CaptTom]

Batteries are good. They are two separate problems.

I wonder if using coax instead of primary wire for the tachs would help. Anybody ever done that?

 

[Billylll]

CaptTom I'm not sure if shielded wire might benefit the tachs signals? I wouldn't think it would hurt though. If your new primary wire doesn't work perhaps I would try shielded cable next. There is a difference between shielded wire and coaxial cable.

As far as the hum in the VHF I have another idea if the 12VDC link is undersized this can cause ripple or hum in the TX audio. You might want to try your radio on low power if so does the hum go away? If not then the gauge wire to the VHF isn't the problem. If it goes away I'd suspect that a 25 watt transmitter is just too much current draw or voltage drop for the radio to perform within specs. Then again hum in the audio can mean a damaged microphone cable or the shielding in it is compromised.
What happens when you turn the inverter/ charger off does the hum go away or stay?
Bill

 

[CaptTom]

Turning off the inverter makes the VHF problem go away. Didn't try low power, but I did re-wire the power directly to a 12 ga wire from the breaker panel. No improvement. What about those ferrites? Should it have one?

I'll re-wire the tachs, I just got the wire. If that fails I'll look for shielded wire.

 

[Billylll]

Try the square Ferrite chokes Radio Shack carries put it right where the power leads go into the VHF radio and do 8 to 10 turns if possible. I use them to mainly keep my HF SSB out of devices it used to bother. It may not correct the problem. Is the inverters chassis properly bonded?
Bill