Community Forums

TQ60 · 09-30-2013, 05:52 PM

Get a pin and stick it in the wire.

Have has many connectors fail!

YC1 · 09-30-2013, 05:57 PM

Quote:

Originally Posted by TQ60

Get a pin and stick it in the wire.

Have had many connectors fail!

What he says. Digital voltmeters will fool you and read full voltage on a bad connection until a tiny load is applied.

You need to work your way back on that cable. Put a poster board thumb tack into the wire and measure it.

DawnAndChris · 10-01-2013, 07:49 PM

Here are the latest developments:

If I make the connection at the green arrow on the circuit board, I get a huge voltage drop.

If I load the converter, I get a huge voltage drop. (they are independant, each happens on its own.)

The drop never travels beyond the junction, at the orage arrow. Batteries and Isolator never drop.

At the converter, with a load, the voltage can drop to 01 or ZERO! I thought it was the converter, until I found another significant drop at the circuit board too (without converter in circuit).

I thought it might be two problems (bad board & converter), but am not sure how likely that is. I am not really sure what to think now. I would appreciate any ideas!!!

I loaded the batteries outside of this circuit, and they never dropped like the circuit did.

YC1 · 10-01-2013, 08:22 PM

So lets fix one problem and chase the other away or you may indeed have two problems.

Grab that needle/pin as suggested and measure an inch or two away from that junction on the B wire. If the voltage holds there move closer to the junction. It would be very easy to have bad connections piled on each other. Do NOT disconnect any wires at the junction until diagnosed. If the voltage holds up at the junction then move the pin along the D wire watching for any drop. Once you get that line working you can work your way towards the converter. Great diagram. Be patient. This should be a very simple issue (to an ET of course).

DawnAndChris · 10-01-2013, 09:02 PM

YC1, Thank you for the advise! I will do as you suggested tomorrow, weather permitting.

It is a good question about how far up B does the drop effect. C, D, and E are completly effected - but only when loaded at one (or both) of the green arrows.

I have looked at the connection points in the diag. They appear to be tight, clean, un-damaged, and the ends seem solid. I havent seen any damaged wire. I checked continuety and for signs of a short, but maybe I should look again. My head is spinning a little bit after all the checking and testing lol.

When running off the batteries, the low voltage wont run anything in the coach for long. When running off the Converter, there doesnt seem to be any voltage drop at all. Everything is 13.7 ish. That might indeed point to the B wire. I have checked the isolator and batteries while on converter power. It usually hits 13 ish, but not the full 13.7. I thought my bats were not 100% and they might rise once charged. But now you got me thinking... maybe that is the drop happening both directions. I will double check that too!

Thank you for all the great ideas, and for sticking with me! I deeply appreciate your efforts!

YC1 · 10-02-2013, 06:28 AM

If you see the voltage go low anywhere on the A wire stack the wires together that are on the isolator and your problem will probably go away. Just as a test of course.

Since you indicate things work on the converter that removes the junction, C and D wires from the issue. If power from the converter is able to run things through those wires the battery should be able too. However your issue is between the battery and the junction and the most likely suspect is the isolator, a common failure item.

You just about have it now.

DawnAndChris · 10-02-2013, 12:03 PM

I forgot to mention one key fact.... When running off the alternator, the 12v system was fine too. It connects at the isolator along with the battery feed (line A).

You were right!!!! The issue was corrosion on the line A feed at the isolator. The alternator feed was connecting fine; which is why it worked when running.

This has been very enlightening! I never saw a sign of the problem that high up in the circuit, and I never saw all the symptoms until a load was applied.

2 lessons learned!!!

I cant thank you all enough!!!! Your help is greatly appreciated!!!!

YC1 · 10-03-2013, 05:02 AM

Congrats! Well done. It is always fun playing "20 questions" because folks will not think some clue is important or they just forget and sometimes asking what seems to be the same question but in a slightly different way will elicit the clue that solves these mysteries.

The other lesson you learned is to not just take a shotgun approach and hope it gets fixed. Finding the actual problem and then fixing it gives you satisfaction and confidence that it is really fixed. The diagram you provided along with your descriptions made it easy for an experienced tech. Getting the load on the lines was key to sorting it out. Often using a digital voltmeter a person will get fooled. I still use a test light often to make sure I'm not getting tricked.

DawnAndChris · 10-03-2013, 07:57 AM

And you were right all along; it was a bad connection!

I have definetly learned a lot on this one!

Thank you again!

TQ60 · 10-03-2013, 01:54 PM

This approach is to divide and concor, pick some spot in the middle, carefully make a valid measurement under failing conditions then follow the direction the measurement takes you.

Sometimes it is easy and fast, in your case not so much.

After checking the ends using the middle approach removes 1/2 of what is left with each step.

Test lights are good as they indicate dips in voltage well.

Digital are worthless for pulse type things unless you use AC measurements, but test light is a good cheap and easy trick for things like this.

A headlight would work better...but in concert with voltmeter to confirm voltage unloaded.

DawnAndChris · 10-03-2013, 09:18 PM

I went the wrong direction at the middle point. I had this "drawing down the voltage" thing on the brain, but that is the symptom I saw. The problem happened all of a sudden; I never thought corrosion would be such an instant type problem. I thought it was the relay because it was clicking softly and not opening or closing, and it showed the voltage drop. (History - I just found a 30amp DC breaker on the load side of the relay. I had tripped it earlier in the year by arching a wrench at the batteries. Oops! I thought that when this breaker tripped, I had fried the relay - since the breaker was on the wrong side to protect it.) I replaced the relay and everything seemed fine; the switch started working, voltage was normal, life was good. But the voltage only showed a problem when loaded. I thought I tested everything, lights worked etc.... Then went to shore power shortly after. I didnt realize I still had a problem until I went boondocking. Shore power works; alternator works, batteries are good (this i know). Came back and started thinking about the relay switch mechanism and the controlling mother board. As soon as they connected to the circuit, the voltage dropped significantly. Then I found that loading anything off the converter, voltage dropped to zip. Then I was thinking the AC to DC side worked but questioned the direct DC side of it. But that never explained the Alternator.... scratching my head when you fine folks suggested that I test the B wire. Then I found the corrosion. Funny thing, the alternator and batteries share the same output post on the isolator. Only one of the leads wasnt connecting due to corrosion. It seems very logical now, but wow... it was a long road to get that far. I should have looked at the big picture instead of focusing on one of the lower level symptoms. I should have tested the circuit under a load!

I am very greatful to have all the advice and support! You guys are great!

Dunner · 10-03-2013, 10:51 PM

Poor ground and corrosion will do strange things to a circuit. Dirty connectors will also lead you astray. One of the first things I do is reseat all the connectors I can find.

YC1 · 10-04-2013, 03:51 AM

Owning a telecommunications service company that works on vehicle electrical systems every day it never ceases to amaze me at the strange problems that occur and how illogical their symptoms seem to add up. After repairing the issue the forensics are fun and helpful. In any case with multiple symptoms I always recommend fixing the "obvious or first" thing you find and often other symptoms clear. The worst are the intermittent problems. Heat, cool, bumps, etc. can drive a tech and customer crazy.

In one of my suggestions I highly recommended to NOT just start cleaning and tightening things. Problems can come back if you don't find the true source. Teaching technicians to NOT pull and tug on wires until you get some voltage readings is difficult. Keep a note pad as well because after a few measurements you may or will forget or lose confidence in what you measured.

Making the block diagram made it easy for an experienced tech to diagnose.