Delayed Charging

[Jim Eh.]

I have noticed that my alternator does not start to charge until air pressure has built up to 70 (or so). From what I can see, it appears that the alternator is direct drive. Why would it need air pressure to "engage" the alternator. BTW, I have not had the bus on the road yet, just in the build process, so the only movements for the bus is shunting it around at the shop into an open/available bay to work on it.
I plan on installing a one lunger compressor (110v) off a 10 gallon tank unit and connecting it to the wet tank solely for the purpose of have air available to move the bus right away to a more friendly/less sensitive spot for warm up when in a campground.

[chessie4905]

   I have a small Sears 10 gal oilless compressor back in a rear bay for building up air before starting engine or in campgrounds. Just don't forget to bleed water from tank once in a while. When I bought my coach, tank was half full of water.

[bevans6]

The air pressure delay is built in for a number of reasons, I think the primary one is to delay the use of the AC/Heat blowers until the engine has warmed up a bit and the AC belts are tightened by their air cylinder.  On my MC-5C the delay also allowed the original belt driven alternator belts to be tightened by their air cylinder.  MCI built everything the same, it wouldn't surprise me to find that delay for the alternator is a hold over from earlier vehicles.

Brian

[gumpy]

If you put a voltmeter on your batteries, I think you'll see that the direct drive alternator is actually charging from startup, even thought the light on the dash says it isn't.  This light is a holdover from the belt tensioned alternators of yore.

[TomC]

This is what I have bought for my truck for starting in the morning and portable air. A bit more expensive then other air compressors, but really quiet. http://www.californiaairtools.com/ultra-quiet-oil-free-air-compressors/2-0-hp-air-compressors/cat-4620a/ Good Luck, TomC

[Jim Eh.]

Thanks for the info. I have not checked if it is actually charging or not (at the batteries) but thought that the light is wired in series between ignition and the regulator so I can't figure out how it could be delayed.
That's a wicked/awesome compressor Tom. Amazing how quite it is in the video comparison.

[Jim Eh.]

Waitaminute! There was an issue with the charging when I was bringing the unit home. It was the dead of winter and I am pretty sure the air system was a little funky but my attention was on the charging system which died right at customs - both sides - at the border while trying to complete importing the bus into Canada.
I had to meet my BIL at the border (he did the transport for me) because he was having charging issues and the bus was shutting down. Well the customs guys on the US side were getting a little antsy as it was getting close to shift change and they mentioned it would be nice to be able to go home on time. Long story short, we got through customs - both sides - and proceeded north until we stopped in a small town for dinner. Alternator failing again. Eventually I put my portable generator and a 24v battery charger into a luggage compartment and ran a set of booster cables out the door to the battery bay direct to the batteries. Lots of power to get home. I figured it was going to toast the alternator but it would be a lot cheaper doing that than a sizeable tow bill and better than a long wait in the middle of winter.

Just as I got up to the city limits the air compressor quit and I had just enough air to make it to the shop door when the generator ran out of gas. From there I simply ran an air hose and plugged in the battery charger to an extension cord to drive the 100' left to get into the warmth.

Anyway I was wondering why after the bus warmed up and the air system worked again (non maintained dryer froze up) the charging system suddenly started working again. I think I had better look further into this air/charge thing.   

[gumpy]

The Not Charging telltale is connected to the Blower Relay. That relay is actually controlled by
R terminal of the alternator. The regulator is activated through the field relay which is switched when the master
switch is turned on. So, the alternator should be charging when first started up, regardless of the air pressure
and what the tell tale light indicates.

I can't figure out what you are trying to say regarding the not charging and air system problems while trying to import the bus.

[Jim Eh.]

I was just wondering if the two incidences were related as I did nothing to fix the charging system. I had total electrical (charging) failure while bringing the bus home and I simply checked the wiring, alternator mount security, things like that on the charging system and after the bus warmed up and the air system was fixed to realize it was then working fine. I still have not changed any components in the charging circuit.

What de-activates the "not charging" light?

[gumpy]

What de-activates the "not charging" light?

The blower relay is controlled by an air pressure switch. It should go off at around 100 PSI.

[Jim Eh.]

The Not Charging telltale is connected to the Blower Relay. That relay is actually controlled by
R terminal of the alternator.

"The blower relay is controlled by an air pressure switch. It should go off at around 100 PSI."

Sorry ... but I'm confused (which isn't really all that unusual).

[gumpy]

Do you have a manual?  Look at Section 7 for the Electrical charging schematic.

[Jim Eh.]

Yes I have a "9" manual. it is back at the shop. I tried to have a look today but things go the way they do ...
Don't get me wrong, the charging system is working as is the air system. It just doesn't sit well with me when things "fix" themselves and I don't understand/know why.
Thanks for the patience.

[gumpy]

Well, I should clarify that the information I'm talking about is related to an MC9. I noticed your tag indicates you have an MC12. I "believe" that the electrical is the same, but honestly, I don't know that for a fact so as they say, your mileage may vary.