High Alternator Voltage

Topic: High Alternator Voltage (Read 1247 times) previous topic - next topic

High Alternator Voltage

October 04, 2011, 09:48:08 pm

So my alternator voltage has been running pretty high. It's somewhere around 15.6V on the MM. I need to get back there and check which one I have (hoping the adjustable), but I read on the Leece-Neville pages that it could also be a symptom of a bad battery. Has anyone had high voltage like this and if so, was it just a simple matter of adjusting the voltage or was it being caused by other symptoms?

Re: High Alternator Voltage

Reply #1 – October 04, 2011, 09:57:46 pm

Verify with a digital voltmeter at battery and then battery isolator and then at alternator output with engine running.

Re: High Alternator Voltage

Reply #2 – October 04, 2011, 11:20:44 pm

And if it's high, pull it off and take it to an auto electric shop. A lot of components may not like 15.6V for very long especially if voltage is occasionally spiking so why take a chance? EZ to pull after disconnecting batteries. Would have a local shop fix it before opting for a remanufactured unit in worst case. Throw a couple of new belts on at the same time.

Re: High Alternator Voltage

Reply #3 – October 05, 2011, 12:13:35 am

Also check the remote sense wire (assume there is one) that goes from the alternator to the battery side (usually engine battery) of the isolator. I think a bad/open connection would cause the alternator to increase voltage.

Re: High Alternator Voltage

Reply #4 – October 05, 2011, 09:23:04 am

If the voltmeter confirms the high voltage, that is very high. Check the batteries with either a hydrometer, available at most auto parts stores for under $10, or a battery load tester, available from Harbor Freight & Tools for under $20.

If you are going to take off the alternator, take a photo of the wiring before you start and mark each wire just to be sure you put it back on the right way.

It really isn't hard to do and will save a lot of money if you do it yourself.

Re: High Alternator Voltage

Reply #5 – October 05, 2011, 11:47:50 am

One of the leading causes of aircraft radio failures are voltage spikes. The cause may range from loose wires to internal regulator/alternator problems. As I remember, you recently had a failure with your Audit display. If we jump from aircraft radios to Foretravels and look for microprocessors that might be damaged by improper voltage, the big ticket items that come to mind are the engine and transmission computers. Yesterday's photo post of the burned section in the computer was not pleasant.

In reading some of the mfg. spec sheets for some of the newer batteries, I noticed that improper charging voltage can cause damage to these very expensive batteries in as little as one day.

Just as air pressure is the heart of our suspension/braking system, battery voltage is the same for all of our on board electronics. This is the big reason I installed digital voltmeters in front of me where I can monitor the health of the system whether driving or parked. It may not catch the transients but will act as a blood pressure cuff to indicate possible problems in several components early on.

Brett and Kent both have important points. Photos do make it so much easier to put things back together and nothing like digital readings at the batteries, isolator and alternator.

With our U300, a simple mistake when installing a new battery isolator by the last owner caused me a lot of head scratching until I finally traced all the dozen or so symptoms back to that one little miscue. Guess I'm saying that a very small component failure in the charging system can possibly show up in other places as a big problem.

Re: High Alternator Voltage

Reply #6 – October 06, 2011, 02:15:59 am

I just had a new alternator installed. At the back of te unit I am putting out 15.1 volts I lose a volt at the isolator and the run of cable takes a bit more so am 13.3 to 13.8 at the batteries. Also if you have a weak or discharged battery you will get a higher output. After all us charged 13.6 to 13.8 where the silverleaf tells me it is sitting running down the road.

Re: High Alternator Voltage

Reply #7 – October 08, 2011, 09:28:11 pm

Well, tried fixing this issue today, but seems I messed things up more than I helped! With the engine running, I checked with the volt meter on each battery and I'm seeing about 16V. I couldn't find the isolator. I did check at the alternator and it was about 17V. I think shut down the engine and turned on the generator. Sitting in the mid-13Vs off the converter at the battery. I then checked each battery with a hydrometer and each cell read good on both batteries. After that, I figured I'd go mess around with the voltage regulator on the alternator to see if I could lower the voltage via the little High, Med, Low selector plate. It was on medium so I switched it to low. However, I foolishly removed the brush and springs and I THINK upon putting them back, I probably did not line up the brushes as they were originally. Now, I'm not getting any voltage out of alternator. Engine running with everything hooked back up it's reading 0V. Does anyone know if you can purchase new brushes or new voltage regulators for these things? Otherwise, I may just have to buy a new alternator given that I think it's been the high voltage issue anyway.

Re: High Alternator Voltage

Reply #8 – October 08, 2011, 09:57:48 pm

Quote from: Benjie Zeller – October 08, 2011, 09:28:11 pm

Does anyone know if you can purchase new brushes or new voltage regulators for these things? Otherwise, I may just have to buy a new alternator given that I think it's been the high voltage issue anyway.

Benjie,
Any good alternator shop should be able to repair your alternator.They can check the alternator for proper voltage/amps and proper operation. If you just want to tinker all the parts are available. No need to buy a new one.
Pamela & Mike

Re: High Alternator Voltage

Reply #9 – October 09, 2011, 03:14:48 am

Yes, just go to an automotive electric shop and they can sell or order brushes but they should be able to repair it for around $125 unless something major. Would not buy a new one, no advantage over having a shop fix yours.

Re: High Alternator Voltage

Reply #10 – October 09, 2011, 10:12:14 am

Thanks Pierce! I'm going to swing by Texas Alternator Starter Service on Monday. I really want to avoid taking the alternator off unless I have to. I watched the mobile mechanic messing with the alternator, belts, etc and these rear radiator rigs are not very conducive to working on anything that is belted. I know I can do it, but it'll take much longer than fixing it myself if its just a matter of new brushes or new voltage regulator.

Side note, does anyone know if I should be seeing voltage at the positive terminal on the alternator when not running? It's 0V engine running or not. On a set up without an isolator obviously you would see approximately 12V since the positive terminal would be directly tied to the battery, but I'm wondering if the isolator creates an open circuit when the alternator is not exciting the middle terminal?

Re: High Alternator Voltage

Reply #11 – October 09, 2011, 11:32:49 am

Benjie,

Our coaches are different but on mine with the key off, I have constant +12V at the small terminal that excites the alternator. Large cables/terminals are NOT hot.

A remanufactured alternator ordered up has been done in an assembly line (at least for cars). Minimum wage workers strip alternators, put the parts in bins then bead blast the bodies, put a meter on the components, replace the brushes/bearings as quickly as they can. Not too much individual incentive to really do a careful job.

The local shop on the other hand, stays in business by providing a quality product that does not have to be sent back if it does not work. They establish a reputation, the word spreads and they get satisfied, repeat customers. Bearings are available in quite a few grades. The local shop is much more likely to use better quality bearings, heat sink compound applied carefully, etc, etc, with their name on the product.

Rear radiators are a pain the the behind. Sorry you can't just quickly pull it. With our U300, the bed goes up and in several minutes, the alternator is out if you don't mind working with your head down a little. All belts are super fast to replace. Don't mean to rub it in just wish they all had EZ access.

Re: High Alternator Voltage

Reply #12 – October 09, 2011, 11:37:58 am

Benjie, there is one other point with some of these alternators you may not be aware of. Many of them have what I think is called an exciter.

As I understand it they are sort of like an electrical clutch. When you start the engine the alternator will not start generating current until the engine reaches an rpm of around 1400. This allows the engine to start and idle without the load of the alternator. If you ever noticed that you dash voltmeter did not show voltage over 13V just after starting but the voltage jumped up after revving the engine, your alternator probably is an exciter type. This would not have any bearing on your over voltage situation but it might confuse the issue if you are testing the alternator when the engine is not running or just started and kept at idle.

I'm sure others on the FF will have much greater knowledge than I do and will chime in if I am correct about this issue.

Re: High Alternator Voltage

Reply #13 – October 09, 2011, 01:00:36 pm

Benjie:

My alternator has 4 wires attached to the four terminals.
Many car alternators have only three.

The two heavy welding cables are for alternator output of up to 160 amps, which is a lot. Both of these heavy cables are red, but one (ground) terminates at the engine block and the other (positive) terminates at the diode isolator block. The positive terminal will read zero volts when the engine is not running because of the diode isolator block (unlike a car).

The two small wires are for battery voltage (red wire) and for exciting the field (white wire).

The red and white disappear into the start battery wiring harness. The red wire should read battery voltage at all times, while the white should read battery voltage only when the ignition is turned on. With ignition "off", white wire should read zero.

It has been reported on this site by others that the small red wire does not show battery voltage due to resistance in the wiring harness. Some follks have run a seperate wire from the battery to the regulator on the alternator to resolve this "high charge voltage" issue.

Hope this helps

Re: High Alternator Voltage

Reply #14 – October 12, 2011, 11:49:05 pm

Step 1 - Pulled the voltage regulator off to try and adjust the voltage. Pulled the brushes out of their holes only to find out that they must be re-inserted exactly the way they were or they will not make good contact. Mistake #1 as my alternator then went from outputting 17 V to 1.6V.

Step 2 - Purchased new brushes and a new regulator. Mistake #2, discovered there's a fuse on the remote sense wire and it's blown! Not sure if this happened before I started working on the alternator or after, but have the sickening feeling that this might have been the cause of my alternator's high voltage as it was probably seeing 0V at the remote sense input. Now thinking if I had just known about that fuse or the function of the remote sense and checked voltage there before messing with everything else I may have solved all my problems with a quick 10A fuse!

Step 3 - Tomorrow going to try a new voltage regulator, but worried that the new brushes I purchased might not be making very good contact. Was warned that the old brushes may have worn a groove in the slip rings. If this is the case, it's going to require I pull the alternator and take it to Texas Alternator Starter Service which is what I was trying to avoid.

Step 4 - Guess I may get to experience changing and tightening belts after all!

While it looks like a lot of this could have been avoided, it's been a good experience since I'm not sure I would have even known about the remote sense fuse if I hadn't gone looking for the isolator. The next time I have alternator problems I'll have working knowledge of exactly what I'm looking at and where to start trouble shooting!

Re: High Alternator Voltage

Reply #15 – October 13, 2011, 12:24:37 am

Benjie

That's the way we all learn. Good for you. Let us know exactly where the remote sense fuse is located. Don't remember seeing one down by my isolator.

When you install new brushes, it compresses the springs more since the brushes are longer so they push harder against the ring. May work OK and quickly conform to the shape. Hope so.

Perhaps this is the way people learn to be "factory trained" mechanics or is that my "school of hard knocks"?

Re: High Alternator Voltage

Reply #16 – October 13, 2011, 12:38:55 am

I was actually wondering about that. Thought I might let the thing run for awhile to see if it might conform to the grooves or whatever on the slip rings.

My remote sense wire works its way down to the isolator and ties to one of the battery posts. The fuse was maybe 2-3 ft off the isolator connection.

Re: High Alternator Voltage

Reply #17 – October 13, 2011, 01:44:25 am

Right niw, I think you need to pull the whole unit and get it rebuilt. Heat and our high draw cooks these units. It is charging the house batteries that does it after dry camping or being unplugged. I hsve found that I get around 5 to 7 years one one before rebuilding is required.

Re: High Alternator Voltage

Reply #18 – October 13, 2011, 02:27:56 pm

Touchdown! Changed the voltage regulator and we have joy! 15 V at the alternator and 13.8 V at the two batteries!

Re: High Alternator Voltage

Reply #19 – October 13, 2011, 04:57:30 pm

Quote from: Benjie Zeller – October 13, 2011, 02:27:56 pm

Touchdown! Changed the voltage regulator and we have joy! 15 V at the alternator and 13.8 V at the two batteries!

That's good news. You are becoming "da Man."

Re: High Alternator Voltage

Reply #20 – October 13, 2011, 11:32:59 pm

Quote from: J. D. Stevens – October 13, 2011, 04:57:30 pm

That's good news. You are becoming "da Man."

LOL! Let's not get too far ahead of ourselves. Keep in mind, I think all of this could have been avoided had I just looked for that darn remote sense fuse

Not to mention the fact that I think I fried the old VR while messing around with the alternator without removing the battery terminals. I know better, but it comes from years of doing electrical work with my dad who owns an electrical contractor firm in Central IL. We often worked hot on short, small jobs. Can't tell you how many times I fried a screwdriver or my hand!

Re: High Alternator Voltage

Reply #21 – October 13, 2011, 11:45:42 pm

Yep. I did a lot of hot work. Some with the Chief Engineer's ok, some not. That 115v 400 hz would really bite, but the 4160 would blow you across the room.

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