Alternator noise suppression

[bharvey2]

I went back to read the original post hoping for details on both wiring and antenna location but couldn't find the answer to either. Is the antenna mounted on the hood or is it above or behind the cab? Are the radio's +/- leads running close to the alternator or could they be moved further away? The original report stated that the sound was a whine with a bit of static. There may be multiple sources of noise here. Fuel injectors and PCM/ECM come to mind. If you can steer wiring away from those that might help some.

 

[buddrousa]

Watch the video and apply the fix for the alternator

 

[Chris155]

That's easy enough that it's certainly worth a try. Could the alternator be the source of the noise even though the radio is not connected to the vehicle's electrical system? It's still present when I power the radio from a separate battery with the engine running.

I'm not sure, but it's a free thing to try. Mine were clean on ac voltage and charged good but I knew they were causing the problem because it started immediately after replacing the original.

 

[WA0CBW]

I understood it to be the "whine" was on his transmitted signal.

 

[OkieBoyKJ5JFG]

So, it sounds like radiated RF noise from the ignition or alternator. Maybe.

I thought that might be the case, but I wasn't sure if that was something that actually happens. I defer to your greater knowledge and experience on that.

It doing it on some bands and not othes is curious. If it's not doing it when you are cross banding, then there may be some filtering in the radio that's catching that noise.

I'm not 100% sure on that. I'll have to recruit someone to check it in an organized way. I'm reasonably sure I was on a VHF repeater when it happened a few months ago and I was on a UHF repeater when it was reported last night. As I said, I'm not sure if it was happening on crossband, but it does make sense that my home radio may have filtered something out. I know I haven't done enough investigating yet, but I hoped you guys could give me some ideas about what to investigate.

Like i said, some vehicles are noisy and some of this may just need to be something you live with.

I was afraid of that.

A magnetic mount antenna moved around to varioius places on the vehicle might be something to try. Usually with RFI, the solution is to move the radio/antenna away from the source.

I'll try it, but the antenna is mounted at the very rear of the driver side bed rail, so I doubt the coax runs near anything which generates RF interference. Perhaps it runs near the fuel pump, but it's surprisingly difficult to find out where that is. My Google searches just keep coming up with "it's inside the fuel tank". Yeah, but driver side? Passenger side? In the middle? Near the top? Near the bottom?

 

[OkieBoyKJ5JFG]

I went back to read the original post hoping for details on both wiring and antenna location but couldn't find the answer to either. Is the antenna mounted on the hood or is it above or behind the cab? Are the radio's +/- leads running close to the alternator or could they be moved further away? The original report stated that the sound was a whine with a bit of static. There may be multiple sources of noise here. Fuel injectors and PCM/ECM come to mind. If you can steer wiring away from those that might help some.

The antenna is mounted in the driver side rear stake pocket and the coax runs under the bed rail, down the front of the bed, and up through the drain hole in the driver side floor. The radio is under the driver's seat.

I moved the (-) lead from under the hood to a grounding point inside the cab, but I don't think the power leads are the problem because last night I ran the radio on a battery with no connection to the vehicle's power supply and I still got the whine. The battery was in the bed of the truck behind the driver's seat, so neither the power lines nor the coax ran anywhere near the engine compartment.

 

[OkieBoyKJ5JFG]

I understood it to be the "whine" was on his transmitted signal.

Yes, that's correct. That's why I've been assuming it's something generating an RF signal.

 

[OkieBoyKJ5JFG]

The antenna I'm using is a Diamond SG7900 Super Gainer. I may try a different antenna on the principle that perhaps the vehicle is generating some RF that a less sensitive antenna wouldn't pick up. I could live with less "punch" from my truck radio. It's kinda nice to have, but not 100% necessary. Mainly, I use it because it works well without any real ground plane.

 

[bharvey2]

The antenna is mounted in the driver side rear stake pocket and the coax runs under the bed rail, down the front of the bed, and up through the drain hole in the driver side floor. The radio is under the driver's seat.

I moved the (-) lead from under the hood to a grounding point inside the cab, but I don't think the power leads are the problem because last night I ran the radio on a battery with no connection to the vehicle's power supply and I still got the whine. The battery was in the bed of the truck behind the driver's seat, so neither the power lines nor the coax ran anywhere near the engine compartment.

Some folks with pickups install the antennas on a mount adjacent to the hood, placing the antenna closer to sources of noise. Clearly, not an issue for you, though. Unyielding noise even with a dedicated battery suggests that power wiring routing isn't the primary source of the problem either. Do you have a small AM portable radio? I use one like a divining rod for RF noise sources. This might help you narrow down the primary RF noise source. Were I you, I'd double check the existing ground connections as I mentioned in an earlier post (assuming you haven't done that already) and look in to buddrousa's suggestion on reducing alternator noise. Neither may solve the entire problem but each could help in reducing it.

 

[mmckenna]

I'll try it, but the antenna is mounted at the very rear of the driver side bed rail, so I doubt the coax runs near anything which generates RF interference. Perhaps it runs near the fuel pump, but it's surprisingly difficult to find out where that is. My Google searches just keep coming up with "it's inside the fuel tank". Yeah, but driver side? Passenger side? In the middle? Near the top? Near the bottom?

If the RF interference is being radiated, behind the cab may not be far enough away.

Fuel pump in the tank should run at a constant speed, resulting in a constant pitch on the noise. GM had issues with that in years past, but it was almost always a constant pitch whine.

I think the AM radio idea above would be a good test. Or a 2 meter hand held with the antenna removed to sniff around for the source.

 

[bharvey2]

If the RF interference is being radiated, behind the cab may not be far enough away.

Fuel pump in the tank should run at a constant speed, resulting in a constant pitch on the noise. GM had issues with that in years past, but it was almost always a constant pitch whine.

I think the AM radio idea above would be a good test. Or a 2 meter hand held with the antenna removed to sniff around for the source.

I'd forgot about the possibility of fuel pump noise. It could be a likely candidate considering the antenna location. A good test may be to turn the radio on and then turn the ignition key until the accessories and lights get power but before engaging the starter. The fuel pump will likely run for a few second to prime the fuel system. That may be enough to discern any noise on the radio.

 

[Rred]

Ling time no see.

At this late date I wouldn't comment but the issue still seems unresolved?
1-A magetic mount antenna still is connected to the body/chassis ground. Not directly but capacitatively coupled and that's not usually going to filter out noise.
2-The alternator still MUST be checked. If you can't get a scope to see a dead flat pure DC output, you can have a "leaky" diode. Everything looks normal, but it is pulsing the battery with reverse polarity hits and it will hurt battery life. A DMM may pick this up, if you put it on the AC scale and connect to the alternator. Reverse the leads and try both ways, because DMMs are apparently not all built the same and some are blind to AC depending on the lead orientation. Delco taught me that, back when engineers were allowed to take phone calls.
3-Don't even think about disconnecting the "other" alernator wires unless you know you are not disconnecting the battery voltage sense lead. If you disconnect that, the alternator says "I need full power to charge this!" and it may go over 17 volts and burn out in 30 seconds. (Famous crooked repair shop scam.)
4-The logic of wiring direct to the battery is that if something else fails, it may try to go through the radio to seek ground. And burn out the radio. Rare, but the documented reason.
5-Almost all cars use a "columb counter" next to the battery negative lead/fuse link. That can be problematic, because there is sometimes an explosive fuse link ["pyrotechnic charge"] at that sensor. If the air bags trigger, the car assumes that it should blow that link to cut power to the electric fuel pump, so you don't burn to death. They also kill the starter to discourage you from restarting the damaged vehicle. (And force you to call a repair tow.)
If you bypass this potential explody bit, the coulumb counter gets all confused and the battery management system may get upset. Or may not, no one will say. But for at least 15 years now, some cars use all this to actually SHUT the alternator, letting if freewheel to raise their highway mpg rating, when the battery is at 14.2 or some other high charge.
Car electrics can be nihhtmares today. Assume NOTHING about them.

But until you use a scope or AC sensjng to confirm the alternator is good? One leaky diode can make all that noise. Start there, and build from a solid foundation.

 

[JDKelley]

Move the negative power wire off the battery and to a body ground location closer to the radio. I had an old Chevy that did the same thing when the - lead was connected at the battery. Moved it off to body ground and it resolved the issue.

Don't spend money on the noise suppression device yet. Those just hide the issue. That can be a good thing if every other attempt fails, but try fixing the issue first.

There's some other stuff we can try, but start there.

The fix for this is usually quite inexpensive.

Get an RF suppression condenser that will go between the B+ (output) stud and the alternator case. This will help smooth out the last of the ripple that makes it out of the diode trio, and get rid of that RFI whine. The actual condenser is quite small, about the last joint of your thumb, a small silver cannister with a wire coming out one end.

You'll need a little creativity to find one, since they're not in common use anymore. Find an application from the mid- to late-1970s or so, I think I usually did something like a late 70's Dodge application when I had someone who needed one, back when I was holding down a parts counter.
An alternator is a three-phase generator, with the output going through a diode trio to rectify the three-phase AC into DC. However, a slight high-frequency ripple makes it through the diodes - that's that "whine" that you're hearing. A condenser {capacitor] fills in the valleys in the ripple, smoothing it to be pure DC (or veridam close to it,) without intercession on your part beyond installation.

If it fails, you'll know - the "whine" will come back. Then, just replace it with a like part - use the same application to find the one you did the last time.

Most parts houses carry these in their ignition parts, they should be <$10. You should also be able to get them from automotive electrical shops or starter/alternator rebuild houses - explain what you want, and he'll go pull one out of a boxful of them. Again, should be <$10.

They're usually terminated with 1/4" or 6mm fork lugs. If your alternator has a 6mm output stud (10mm wrench,) you're golden - loosen the nut, slip the fork in, tighten the nut. If you have an 8mm stud (13mm wrench,) you're going to need to go with a 3/8" stud, and you may need a flat washer to keep the fork under the nut, since the closest you'll be able to get is 3/8" (there is no 5/16" or 8mm lug readily available, that I know of.) The 6mm post is VERY much more common!

 

[JDKelley]

I thought that might be the case, but I wasn't sure if that was something that actually happens. I defer to your greater knowledge and experience on that.

I'm not 100% sure on that. I'll have to recruit someone to check it in an organized way. I'm reasonably sure I was on a VHF repeater when it happened a few months ago and I was on a UHF repeater when it was reported last night. As I said, I'm not sure if it was happening on crossband, but it does make sense that my home radio may have filtered something out. I know I haven't done enough investigating yet, but I hoped you guys could give me some ideas about what to investigate.

I was afraid of that.

I'll try it, but the antenna is mounted at the very rear of the driver side bed rail, so I doubt the coax runs near anything which generates RF interference. Perhaps it runs near the fuel pump, but it's surprisingly difficult to find out where that is. My Google searches just keep coming up with "it's inside the fuel tank". Yeah, but driver side? Passenger side? In the middle? Near the top? Near the bottom?

Front-to-back wiring typically runs down the driver's side, inside the frame rail. This encompasses rear lighting, any rear sensors, fuel pump wiring, and possible reversing camera leads.

If you've run your CO/AX at or near the top inside the bed rail, you're far enough away from the fuel pump wiring that it's not a problem. That's going to be just about three feet.

 

[Rred]

When "FM" was an upscale radio and surge supressor strips had to be home-built because they weren't sold yet?
IIRC the rule of thumb was to put a cheap 10mfd. 25V disc cspacitor across the radio's power lines to clamp any noise coming from the alternator. Dirt cheap and easy, usually worked. (Although of course it hid the failing alternator.)
Still, a 10mfd disc cap is easily scrounged and installed to try it.

 

[OkieBoyKJ5JFG]

Update: After trying several of the things suggested here without success, I changed to a different radio and the whine went away. I guess for some reason, the TYT TH-9800 was just inordinately sensitive to whatever RV signal the alternator produces.

 

[Rred]

Thank you for letting us know.
You might still want to confirm that this is an RF/EMI problem and that there is no AC leakage from a weak alternator died. It took me several months once, to find out how subtle the AC leakage can be. And how badly it can affect the battery. Definitely worth making sure.

 

[OkieBoyKJ5JFG]

I'll have that checked.

 

[JDKelley]

Useful tools for auto diagnosis/radio work:
- Seeed studios makes 1, 2, and 4-channel digital storage oscilloscopes that are <$100, and good for any radio work you're likely to run across inside the case. Also useful for alternator ripple.

- There are a few outfits that make these (I got mine from Hantek,) but you can get "oscilloscope frontends" that have oscilloscope probe inputs (typically six or eight) that allow you to diagnose the ignition system all at once. They should also be able to check alternator ripple, and the screen is larger.

"Frontend?" Yah - you plug the inputs into whatever you're checking, the output goes to a laptop, and the laptop does the heavy lifting and display work. It's nice to be able to wire up my ignition coils, #1-#6, in proper firing order, and watch the pulses march across the screen in time to engine speed (although I have to get out the stepper exerciser to run the drive-by-wire throttle. . .) Make sure to keep all wiring clear of the fan and the accessory drive belt! (Sadly, that warning must be given these days, although I'm pretty sure none of you guys need it. It's just the society we live in . . .)