PDA

View Full Version : terrible interference when fridge comes on.


CardinalFJ60
10-22-2012, 08:57 AM
Anyone who's been on a run with me since I got the fridge will attest that it puts off some wicked RF interference when the fridge compressor kicks on. To the point where I have to squelch it out to about 75-85% of the travel on the squelch knob. :eek: With my HT, I can walk toward the rear of my 60 when the fridge's compressor is on and hear the intereference, I walk away...no more sound. so it's got to be from the fridge.

No one else seems to have that issue (??)

What could be the culprit? Should I just throw on a Choke? any ideas on how to track this down would be great.

I have the fridge wired straight to the aux battery with 10g. it is however still on the cig lighter plug.

Jacket
10-22-2012, 09:00 AM
Where is the wiring for the radio? Do they share any part of the circuit, or run right next to each other to the aux battery?

Romer
10-22-2012, 09:06 AM
My guess is the ground. The outlet you have the fridge, might try taking the ground directly to a chassis bolt rather than running it back. Same for the Radio.

If they are on the same positive (fuse), might try finding separate sources

CardinalFJ60
10-22-2012, 12:29 PM
Where is the wiring for the radio? Do they share any part of the circuit, or run right next to each other to the aux battery?

Both are run straight to the Aux. battery (separately of course, each on 10g) and IIRC they run right next to eachother under the hood...'cept that the Ham Power stops at the console, and the fridge runs straight back along the PS interior

CardinalFJ60
10-22-2012, 12:31 PM
My guess is the ground. The outlet you have the fridge, might try taking the ground directly to a chassis bolt rather than running it back. Same for the Radio.

If they are on the same positive (fuse), might try finding separate sources

They used to be on the same positive, then I ran a separate power/ground to the fridge to try to fix that interference - no improvement with that...hmmm...ground is the next I'll check.

Romer
10-22-2012, 12:36 PM
They used to be on the same positive, then I ran a separate power/ground to the fridge to try to fix that interference - no improvement with that...hmmm...ground is the next I'll check.

Could be a loose or improper ground. Might also check to make sure the ground from your battery/alt has a good connection. I remember having to take teh bolt off and grind a bit in the engine block on my 40 to get a good contact

measure from battery to a point on the chassis, should be very few miliohms. measure from the fridge ground to chasssis and should be the same

Make sure all your connections are tight with good metal to metal contact

Air Randy
10-22-2012, 03:00 PM
Or, the motor in your fridge that runs the compressor could just be bad i.e. a brush has a slightly too large gap to the armature and is sparking. Or there is an inadequate or loose ground inside the fridge chassis.

If you know someone that has the same fridge as you do, try plugging their's into your rig in the same configuration as yours. If the noise goes away, its the fridge. If it stays, it is somewhere in the eletrical system of your truck.

CardinalFJ60
10-22-2012, 03:55 PM
Or, the motor in your fridge that runs the compressor could just be bad i.e. a brush has a slightly too large gap to the armature and is sparking. Or there is an inadequate or loose ground inside the fridge chassis.

If you know someone that has the same fridge as you do, try plugging their's into your rig in the same configuration as yours. If the noise goes away, its the fridge. If it stays, it is somewhere in the eletrical system of your truck.

Doh. why didn't I think of that!?? Oh Perrrrry..where are you?

nakman
10-22-2012, 04:08 PM
Doh. why didn't I think of that!?? Oh Perrrrry..where are you?

Jacket's in Lafayette, dude.. :o


You could also just stick a battery back there, then wire the fridge up directly to it- bypass everything. Sometimes it's easier to diagnose if you can see the whole circuit in front of you.. :confused:

I think you're on the right track with the ground though, just pull the cig plug out, pop off that ground wire, then run something completely separate to what you know is a solid ground. If that fixes it, then do it again but more prettier. :D

CardinalFJ60
10-22-2012, 04:47 PM
how about just leaving it plugged into AC and disconnect the DC?

Corbet
10-31-2012, 09:17 PM
That would probably work too.

What brand fridge? My Engel definitely does not cause any issues. Both my fridge and HAM are wired to the same fuse block (under passenger seat) then direct from there to the battery.

DaveInDenver
11-01-2012, 06:25 AM
Yeah, what brand? Engel provides a chassis ground screw just for this reason. At a high level Engel's swing motor works on AC and there's a DC-fed inverter that drives it. There are then two supplies that provide DC to this motor driver, one a fairly simple AC/DC supply when on shore power and another DC/DC supply for 12V. They do this because the motor runs at 27V IIRC, so they have to boost the 12V.

It might seem odd, but they are usually quite a bit more noisy when used on battery than on the mains. So Engel built the case so the inverter and supplies live inside a shielded enclosure. If the fridge case itself is left floating or has a poor ground connection, the thing will be a huge RFI source. It's pretty important to do this if you run HF, there are three switching supplies in your fridge that will swamp your RX.

If you don't have an Engel it might not be exactly the same situation, but for Engel and ARB fridges a good test is to run the fridge on AC and see if the noise abates or changes, then you know it's just a matter of grounding the case. If this does not help, then you have to get more aggressive with chokes and bypassing. The majority of the noise should be fixed just grounding the case, though.

CardinalFJ60
11-01-2012, 07:12 AM
Yeah, what brand? Engel provides a chassis ground screw just for this reason. At a high level Engel's swing motor works on AC and there's a DC-fed inverter that drives it. There are then two supplies that provide DC to this motor driver, one a fairly simple AC/DC supply when on shore power and another DC/DC supply for 12V. They do this because the motor runs at 27V IIRC, so they have to boost the 12V.

It might seem odd, but they are usually quite a bit more noisy when used on battery than on the mains. So Engel built the case so the inverter and supplies live inside a shielded enclosure. If the fridge case itself is left floating or has a poor ground connection, the thing will be a huge RFI source. It's pretty important to do this if you run HF, there are three switching supplies in your fridge that will swamp your RX.

If you don't have an Engel it might not be exactly the same situation, but for Engel and ARB fridges a good test is to run the fridge on AC and see if the noise abates or changes, then you know it's just a matter of grounding the case. If this does not help, then you have to get more aggressive with chokes and bypassing. The majority of the noise should be fixed just grounding the case, though.

what a great response. thanks. With that description, it's sounding like a grounding issue more and more. It's definitely a "Huge RFI source".. I'll be messing with it this weekend and will report back. It's an ARB 47l model (50qt).

another question...any ill-effects for my radio by getting swamped with RF? I usually squelch it out.

DaveInDenver
11-01-2012, 07:28 AM
Attached photo of the connections on an Engel MT45, the chassis ground is in the lower right. I suspect most fridges will have this. If not, screwing a ground strap to the case, maybe under a bolt or something, would achieve the same thing. Although it's not necessarily going to be the case that all manufacturers take the time to design their cases for RFI. I wouldn't be surprised to hear Engel actually tests their fridges for EMI/EMC.

The noise is unlikely to be strong enough to cause any damage unless /maybe/ you touched the antenna to the noise source. It just takes inches in air to attenuate the noise from damaging to irritating. Or at least the signal strength goes down enough that your radio AGC can deal with it to protect itself. I should clarify, this is the case with noise generated from a fridge or computer or whatever, which is relatively low power. You would not want to hold your HT inches from a 50W mobile antenna while it's transmitting, that would likely ruin your HT.

The problem really with RFI like this is that a strong local noise source will desensitize your radio's RX. When you squelch out the noise or gain is reduced it will take a very strong signal from other radio operators before you hear anything. So a fridge 10 feet away might generate the same local signal strength as a regular station 25 miles away, for example.