A question of voltage drop - Page 3 - Fiberglass RV


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Old 12-10-2012, 11:48 PM   #29
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Originally Posted by David Tilston View Post
Fluke meters are just a bit expensive. I might also add that they are named very ironically.
Yup, John Fluke ironic.
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Old 12-10-2012, 11:52 PM   #30
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Originally Posted by SilverGhost View Post
Oh boy....

No load voltage of a fully charged 12V battery is 12.65V. Charging voltage is specified as 13.8V to 14.2V, with a tolerance to 13.4V on the low end and 14.5V on the high end. Too high voltage and some systems shut down and accessories get damaged. Extended use below 13.4V the battery will not charge correctly and fails early (1-2 years instead of 5-7 years).

Measuring at the power outlet will be after a couple fuse panels and, on some cars, through a control module. So after a half dozen or more connections there can be a significant voltage drop.

[soap box]
How are you checking voltage at the cigarette lighter? It's just a heater coil with a handle that gets hot after being plugged into a power outlet for a few moments.
[/soap box]

And why do you have to drive the car to test the charging system? Attach a good DVOM or volt meter to the battery (I just threw mine out this morning as it was reading .5V low), start the engine and rev it up for about 5-10 seconds before letting it idle. Read the voltage with everything turned off (door shut? dome light?) at idle then at about 2000 to 2500 RPM. Turn on your lights (high beams), a/c fan high (and the a/c), rear window defroster, radio about 50% volume on a strong signal, bum heaters and such if you have them. Read voltage at idle and at 2000 to 2500 RPM. Let the voltage stabilize at both speeds before making your reading.

Now a well designed system in good condition will be able to keep above 13.5V with all those loads on with the RPMs up. A great system can do it at idle. If you get below 13V at idle or 13.3 at higher RPM you will have issues. If you don't think those loads are realistic - So Florida in slow traffic on a cold night will have lights, a/c to keep the humid air from fogging the windows, rear defroster to keep that window clear, heated seats to keep warm while a/c is keeping windows clear, wipers to clear the condensation on the outside (or in a cruel twist when it stars raining). Worst was Missouri though - defroster got the inside of the windshield clear just in time for the condensation build up on the outside.

Back to your regularly scheduled program,

Jason
Note Bold in Quote. If you use a high impedance voltmeter there voltage drop will be in milivolt range.
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Old 12-11-2012, 10:52 AM   #31
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Originally Posted by Byron Kinnaman View Post

Note Bold in Quote. If you use a high impedance voltmeter there voltage drop will be in milivolt range.
Assuming the control module is not regulating the voltage to a preset value.

And I doubt the type that you plug into the power outlet is very accurate or high impedance (also likely drawing power from the power outlet to operate). But handy for a quick look on overall system voltage.

Jason
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Old 12-11-2012, 07:55 PM   #32
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Big first question - What is the tow vehicle? Make, model, year, options.

It it is a new or nearly new vehicle the source of the problem could be vastly different than if it is an older vehicle.

Did the problem just show up or has it been continuing?

Test, don't guess. Go to an auto parts store and have them run charging system diagnostics with their test set. It's quite impressive what the new test sets can do and most of them give a printout of test results. Remember, you don't have to buy anything. They all advertise that it is a free test. In most towns there are a few different auto parts store chains so drop by a few and get a second or third opinion.

The complexity of the current generation of cars/trucks is such that simple DC voltage tests can only show that there is a possible problem, not isolate it to a specific component or connection. If I was troubleshooting I would do a systematic test of the charging system and I would have a set of schematics to work from. And that would be after a trip to the local Advance Auto Parts store for that FREE in situ system test.

Trying to troubleshoot a problem (and I agree there is a problem) via remote consultation is doomed to failure. And it could be an expensive failure.

If I was a betting man I would bet that you have already spent money replacing a perfectly good battery by not thoroughly analyzing the problem.
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Old 12-12-2012, 04:43 AM   #33
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Perhaps the problem has something to do with this?


Inexpensive voltmeter

I notice the O.P. bought one. Raz
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Old 12-12-2012, 06:06 PM   #34
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A number of people have suggested that I should go to an automotive mechanic for a full diagnosis. Sadly, my experiences with mechanics has been less than positive.

A couple years ago, my truck failed its emmission test. They quoted $5000 to repace either the injectors or the fuel pump. I took the truck elsewhere. He did an oil change and air filters, and got a very good test pass score.

A few years earlier, I had a car break down at the beginning of a northbound road trip. I had the car towed to a mechanic. When I arrived at the shop, the mechanic said in his russian accent "Car is piece of sheet. Should have towed it to wrecker.". It was Friday, and I went home by bus. That evening I went online and did my research. On Saturday, I went in and fixed it myself. It was running as smooth as silk. The shop was closed on the weekend and the entrance was blocked. On monday I came back and told the mechanic I'd fixed the car and wanted to drive it home. He was totally shocked. That day I earned his respect, and continued to go to him until he moved on to another industry.

I have other stories too, if you would like to hear them.

Sadly, showing up at a mechanic blind is foolish. You need your bullshit detector turned on so you can call them on their BS. I haven't serviced this car yet as we have only had it a few months. I have a referral from a good source, but sometimes referrals aren't guaranteed either.

Derek
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Old 12-12-2012, 06:16 PM   #35
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A number of people have suggested that I should go to an automotive mechanic for a full diagnosis. Sadly, my experiences with mechanics has been less than positive..........
Derek
I agree with much of what you said. I think a least one person's advice was to go to an auto parts store like Auto Zone where they do free electrical tests. They can test your battery or alternator for free. Of course, they are hoping you will buy parts there, but you can take the free test results with a grain of salt and decide for yourself what to do .
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Old 12-12-2012, 07:12 PM   #36
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Originally Posted by Thomas G. View Post
I agree with much of what you said. I think a least one person's advice was to go to an auto parts store like Auto Zone where they do free electrical tests. They can test your battery or alternator for free. Of course, they are hoping you will buy parts there, but you can take the free test results with a grain of salt and decide for yourself what to do .
Yes, this was suggested. Around here, I think Canadian tire will do these tests for you. The question is - am I willing to trust my alterator to someone who's primary job skill is looking up part numbers on the in house computer system. *sigh* it sounds mean to even say it. At least a mechanic, with the training and experience he accumulated to get his ticket, should know what he is doing. The challenge is finding a mechanic who applys his skills honestly.

Derek
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Old 12-12-2012, 07:24 PM   #37
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Originally Posted by glamourpets View Post
Yes, this was suggested. Around here, I think Canadian tire will do these tests for you. The question is - am I willing to trust my alterator to someone who's primary job skill is looking up part numbers on the in house computer system. *sigh* it sounds mean to even say it. At least a mechanic, with the training and experience he accumulated to get his ticket, should know what he is doing. The challenge is finding a mechanic who applys his skills honestly.

Derek
Well...you have to start somewhere! And the tests suggested don't fall into the "rocket science" category...if you don't trust the results from the first Canadian Tire guy you take it to, go to the one across town and see if they get the same results there.

There's only so much we internet advocates can do/suggest- sooner or later you'll have to take the plunge and go to a real live person. Getting a simple test done first might better equip you to decide whether the possible mechanic in your future is whistling Dixie or giving you the straight scoop.

Knowledge is power!

Francesca
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Old 12-12-2012, 07:47 PM   #38
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It does not take a rocket scientist to hook a volt meter to you alternator and tell you if it's producing 14Vs.
If it's producing less than 14 volts you need a new alternator.
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Old 12-12-2012, 08:26 PM   #39
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Originally Posted by Francesca Knowles View Post
Well...you have to start somewhere! And the tests suggested don't fall into the "rocket science" category...if you don't trust the results from the first Canadian Tire guy you take it to, go to the one across town and see if they get the same results there.

Francesca
One of the things I was realizing today, as I pondered this problem- my trailer wiring may provide the answer I seek. The brake controller requires a direct connection to the battery. As I result, I have a connector inside the car cabin that gives direct access to the battery without even opening the hood. A battery needs at least 13 volts to charge. Ideally it should be getting 13.5 to 14 volts under driving conditions. If its not, either the alternator is dieing or the alternator is receiving incorrect output data. Either way there is a problem that needs to be corrected.

I will not get to this task for a few days as we are amidst the chaos of the christmas season. Only 10 days to go!

Thankyou to everyone for their wisdom on the subject. My posting style can be a little bit sarcastic. Sadly, in a world where a mechanic can earn commission by selling you extra parts you don't really need, it is worthwhile to do your research first. The whole "filtered cigarette lighter" idea floated earlier was something I had not even considered.
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Old 12-12-2012, 11:03 PM   #40
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It does not take a rocket scientist to hook a volt meter to you alternator and tell you if it's producing 14Vs.
If it's producing less than 14 volts you need a new alternator.
If only the world were so simple...
The alternator only produces anything if the regulator directs it to, and if any control logic that triggers the regulator is working, and if the wiring connecting those bits is intact.

As I said earlier, when my Focus stopped charging at the high rate, it was not the alternator:
Quote:
Originally Posted by Brian B-P View Post
My 2004 Ford Focus wasn't charging the battery properly, and I found that it never reached 14V. The problem turned out to be a bad connection in the wiring harness to the alternator: the Focus charging system is designed to work in two steps, dependent on various conditions, and the failed connection was keeping it from being switched into the higher-voltage stage. A replacement wiring harness fixed that. It runs as high as 14.2 V (measured at the lighter socket).
The required replacement wiring harness cost me about $50, which is a small fraction of the price of the alternator... and if I had replaced the alternator, it would not have fixed the problem.
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