MEP-803a panel lights flickering

[m32825]

I've been burning last year's fuel to get ready for hurricane season. Last night I turned on the panel lights and noticed that they were flickering. It's not an "on/off" flickering, more of an intensity change. Sometimes a little brighter, sometimes a little dimmer. The change lasts a fraction of a second.

I got out the voltmeter. At the NATO connector I see 28.06VDC and 0.018VAC. At the S2 input I see 26.6VDC and from 0.720 to 0.760VAC wandering around. I see the same thing at the lights, they are incandescents if that makes a difference.

I'm looking at the schematic trying to figure out what to check next. Suggestions? Thanks!

-- Carl

 

[Scoobyshep]

Complete speculation here. But when the dash board lights of a car do a consistent intensity change it usually means the alternator is failing.

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[Guyfang]

How long are you running the set before taking the volt measurements? If the set has been running more then a few minutes, the DC voltage should come down from a high of 28 volts. Could be the alternator, but how about taking a reading after a half hour?

 

[m32825]

It had been running for 26 hours when I took the measurements. The batteries were on the Noco Genius right up until I started, so they were in good shape at the beginning. Five hours later the measurements are all the same.

-- Carl

 

[m32825]

The mystery continues, checked the lights this evening and they were steady as a rock! System has been running continuously since I observed the problem. I hate intermittent problems.

I checked the voltages again, virtually identical to before. Shut it down and let things settle for half an hour or so then checked the battery voltage. It's got two Optima red tops and they were at 27.6V.

 

[Chainbreaker]

I'm not hands on familiar with the 803 but just wondering if there might be a rusty/corroded high resistance ground somewhere common to the panel's meter grounding.

 

[Scoobyshep]

I'm not hands on familiar with the 803 but just wondering if there might be a rusty/corroded high resistance ground somewhere common to the panel's meter grounding.

That would be easy to test. Volt test Negative side of the light to the negative battery terminal can do positive to positive also. Anything other than 0 would show a bad connection

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[Guyfang]

So who out there has a like set, and will go out and take the same measurements? We have seen a few times, problems where the alternator lets AC into the DC system. For all I know, the small AC voltages you found my be normal? Dont think so, but someone should at least check. But when we had the problems, the AC voltages were way higher. Like 50 volts. Thats what the battery charging alternator puts out. About 50 VAC. Then its rectified to VDC. Then its a clear case of the blocking diode, or the alternator being hooked up wrong, or the + output cabe being hooked up without the non conducting washer in place.

 

[m32825]

Thanks for the input guys, I will be running it again this weekend and try your ideas. I plan to look at the panel light voltage with a scope and see what it looks like. That's assuming I can get it to happen...

 

[Farmitall]

Can you video the fluctuation?

I'd start by checking all the wiring connections associated with the panel lights for corrosion or loose connections. I don't have my schematics with me at the moment but from memory it's a pretty simple circuit and should be easy to check them all in a few minutes......pay particular attention to any ground connections, they will be common to all the lights.

 

[Ray70]

To charge a 24V system you need about 27-28V ( typically you need 13.6V per battery ) so I think you are in the ballpark. The only issue could be the speed of the fluctuation. Your alternator output could be swinging drastically rapidly ( often exaggerated when hot ) yet a digital volt meter may be smoothing out the voltage output, giving you false readings.
My previous experience is that the alternator output should be a pretty steady voltage, you should not see large voltage spikes or droops.
As the battery comes up to full charge the amperage output will come down, but output voltage should remain constant and remain above approximately 27V -28V
As Scoobyshep said, voltage fluctuations at the alternator are often the early signs of voltage regulator / Alternator failure, but I would expect you would need a swing of at least 5 volts or more to cause your lights to flicker.

 

[m32825]

That would be easy to test. Volt test Negative side of the light to the negative battery terminal can do positive to positive also. Anything other than 0 would show a bad connection

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I measured 2 ohms from negative battery terminal to ground on one of the lights, and 4 ohms from the positive side the the light. That doesn't seem bad, but then again I'm not sure what the good range should be.

Pro tip: if you ever find yourself in a tight spot and need an arc welder, a 1/2" Craftsman wrench between the positive terminal and the starter case makes a surprisingly good electrode.

 

[m32825]

Okay, back to this problem with more data, I caught it on video! Watch from 1:20 to 1:50 keeping an eye on the temperature gauge. It drifts down slowly, then pops back to normal when the lights do, fuel gauge does the same thing. So it's something that affects both lights and gauges. Suggestions?

 

[kloppk]

Interesting..
The first thing I'd suspect is diode CR1. I've diagnosed a few sets where CR1 is failing causing 24 v problems. Inspect it and see if it looks cooked or cracked. Pull on it and see if it breaks in half. If that's the problem I'd suggest replacing it with two of the CR1's in parallel. Its under sized for the circuit. CR1 is a 1N5406 diode.

Next I'd inspect shunt MT4 to see if the plates appear solid or corroded.

Next I'd suggest cleaning the contacts in the J6/P6 connector. The 24 v for the control cube flows thru it.

 

[Ray70]

Woa! that flickering at 1:15 is no alternator voltage fluctuation! it's more like a total loss of voltage, the lights go virtually OFF completely.
There's no reason that should be happening with the batteries and alternator in tact.

Does everything else DC related sound ok when that happened? Did you hear the fuel solenoid clunking back and forth at the same time?

You are either loosing power, loosing ground, or you have something pulling away virtually all the voltage in the lighting circuit ( if nothing else acts up at the same time.

I 2nd Kurt's idea about CR-1. I suppose a quick dirty test would be to clip a jumper across it while the machine is running. If the problem disappears completely you have a failing diode ( don't forget and leave the jumper on after shutting down the machine )

 

[kloppk]

Woa! that flickering at 1:15 is no alternator voltage fluctuation! it's more like a total loss of voltage, the lights go virtually OFF completely.
There's no reason that should be happening with the batteries and alternator in tact.

Does everything else DC related sound ok when that happened? Did you hear the fuel solenoid clunking back and forth at the same time?

You are either loosing power, loosing ground, or you have something pulling away virtually all the voltage in the lighting circuit ( if nothing else acts up at the same

From the audio it sounded like he was toggling the panel lights on and off then.

 

[m32825]

Sorry, should have mentioned that prior to 1:20 I was toggling the panel lights. Figured I would exercise the switch a bunch to see if it would make something happen.

 

[Guyfang]

Let me remind you here. The MT4. Even with everything turned off, its hot. I know it sounds stupid, but lots of folks forget that. So when inspecting it, remove the neg battery terminal, or, be REAL careful. I still own several tools that have large places that have been melted out of them due to the MT4.

 

[Ray70]

Ah, I see! I watched the video during a meeting, without sound... ( I was trying to 1/2 pay attention to the meeting! ) So I didn't realize you were switching the lights off!
The flickering towards the end of the video seems more indictive of a failing voltage regulator. You will need to watch the voltage with a scope to verify, a DMM won't capture the voltage dips.

 

[kloppk]

If the alternators regulator is failing the Charge meter should dance about during the flickering.
Likely in the Negative range when the lamps are dim and in the Positive range when they brighten up.
Too bad the charge meter wasn't in the video.