Engine Alternator/Voltage regulator charging problem

As q quick update, replacingthe alternator replacement definitely seems to have fixed the issue.

Left Texas and made it to Orlando and looks like everything was charging properly, with the same behavior as it had before (in relation to the charging system).

Generally the voltage meter reads about 13 - 13.5 volts, though seems to range between 12.5 and 14.

On a side note, my odometer was displaying ERR1 since bought this RV, and with the prior owner. Made my day when I was able to fix it yesterday, and only did this by mashing the buttons randomly while going down the road. Tried doing this before and not sure what made it work this time. Am guessing somehow I triggered a reset of something. Odometer looks like it's incrementing fine, not sure how accurate, but it's incrementing, and trip counter works too

Thanks everyone!

As a final followup, have detailed this whole process in the hopes that it will help the next person who experiences the same issue.

Link to Post

As a cautionary note, it's on my blog, and it's a fairly comprehensive log of everything I did, including suggestions from this thread (gave credit too).

Will start on road Monday to my next destination and will report back here status after that trip.

Thanks a bunch everyone!

Richard,

That will work on those few coaches out there with B.I.R.D. relays.

Most don't have them.

Here's a little food for thought.
When you need to run your generator to charge the chassis battery while driving. Why monkey around with jumper cables or change wire locations on the isolator relay. When you start your coach engine, the isolator relay is energized. Or in some cases the the chassis battery will start charging when the coach batteries get to 13.3 volts. So the converter should charge the chassis battery while running down the road. KISS

Richard

Yes, the generator can power the on-board converter or charger to charge the house battery and a jumper can be used to charge the chassis battery from the house battery.

But, let's be clear, I would NOT use jumper cables-- too easy for one end to jump off when you hit a bump. And, with the other end connected to a charged battery, it could easily arc weld/start a fire. Hard wire is fine.

Another safe option is to located the battery isolator and, after labeling, move the wires from the house battery lug over to join the chassis battery lug. Be sure to return the wires to their original position or all batteries will be discharged with generator/shore power off.

kutch2001 wrote:
He also mentioned, as an idea to anyone "in a bind", that there are alternatives if the alternator stops working and need to get from point A to point B. Can run the generator with jumper cables from the house batteries to the engine batteries. The generator would keep the house batteries charged, while the jumper cables would keep the engine batteries charged from the house batteries. Might work also if use solar panels.

I've done that on a 500 mile trip. It was working great till the generator cut out because I was low on fuel. Oops. Panic trying to find a fuel station. Easiest way to test the alternator is turn the headlights on and confirm it maintains voltage. I fired up the RV to get ready for Easter. In the context of this thread, I hit my headlights and anything else I could turn on. The voltage blipped 1/10th of a volt and came back up to 14.2 volts. The battery was a little low from sitting for 3.5 months, as it normally sits at 14.3 volts.

As a very quick update, will post more in depth soon, had the spare alternator tested at local auto parts store and it passed the test, though they only tested as if it was 100 amp instead of 160 amp (long story).

Took me a little less than two hours to remove, install, cleanup, test, find tools, etc. It seems to work fine. Neighbors were here in the RV park and didn't want to smoke them out with diesel exhaust, so only ran it for a minute. The battery gauge showed about 14 volts, revved a little and needle went up a tiny amount but then seemed to compensate.

Will be giving more of a test tomorrow.

Was talking with a board member here and he mentioned that the rebuilt alternators that have been "sitting around awhile" might work for a week, a month, a year, who knows. There was a tag on the spare that has date of 8-10-97. Unsure what that means, whether it's a reused tag or original to alternator, no idea.

He also mentioned, as an idea to anyone "in a bind", that there are alternatives if the alternator stops working and need to get from point A to point B. Can run the generator with jumper cables from the house batteries to the engine batteries. The generator would keep the house batteries charged, while the jumper cables would keep the engine batteries charged from the house batteries. Might work also if use solar panels.

The problem occurs when you end up with a pulsed DC output. The regulator has a relatively slow response time ie high frequency noise filtering. This means that it will react to an average voltage of the pulsed DC, rather than the peak voltage. The average voltage is going to be .707 of the peak, which means the peak voltage will be 1.4 X higher than 14.3 volts. That is around 20 volts peak comming out of the alternator. Depending on the output diode ratings, the output diodes may be OK with that, or that might make them a little unhappy.

When rectifying AC to DC, one uses some sort of storage device (capacitor) to store the voltage and supply current inbetween the pulsed output. That capacitor will charge up to the peak voltage, and assuming it is large enough to handle the load, will only discharge slightly. In the case of an alternator, the battery is the storage device and charges to the peak voltage. This means that the regulator is seeing the full peak voltage out of the alternator, so it regulates to 14.3 volts.

RLS7201 wrote:

wolfe10 wrote:
Running the engine (and alternator) with the battery disconnected will likely blow the diodes in the alternator.

I'd like to see further discussion, as to why this is true or not.

My thoughts are, the diodes do no more that rectify AC to DC and pass the electrons along to the system. The batteries do smooth the ripple but the system should tolerate that. The regulator will still control the rotor field strength. So voltage should be stable. So why would the diodes be compromised with no battery in the system?

Richard

Running the engine with battery disconnected will cause the alternator to output maximum voltage; I don't know if it will damage the alternator over the long run, but it can certainly do overvoltage damage to other electronics, such as radios, lights, computers, etc. These things aren't meant to run on 18 or so volts.

RLS7201 wrote:

I'd like to see further discussion, as to why this is true or not.

Richard

Richard,

Good question. Will probably have to wait for an electrical engineer to give the answer.

But, I can tell you from marine wiring experience that the better battery switches have a field disconnect for the alternator to prevent damage were someone to turn the battery switch to OFF while the engine/alternator are running: http://www.westmarine.com/perko--battery-switches--P009_272_004_007