| Alternator Belt Squeal [message #335040] |
Fri, 13 July 2018 09:56  |
 |
Matt Colie
Messages: 8547
Registered: March 2007
Location: S.E. Michigan
Karma:
|
Senior Member |
|
|
It is about time that this got broken out into its own topic.
What I am going to post here is largely the result of things I learned before Chaumière came into the family.
Before and during the depression (I am out of the business now), I made a decent income doing "boat work". A good portion of this work was upgrading the house electrics for owners that now wanted the boat to be a "Performance Cruiser". A performance cruiser is a retired racing boat that now is comfortable below and has some amenities. One of the amenities lacking from all racing boats is anything you would expect in a motorhome. House electrics is a big one. Most boats have two smaller "Marine/Deep Cycle" batteries and an A/B switch. If the race is longer than one over-night, they are often in trouble. That is where I wrote quotes. As the emotional connection to a sailboat is every bit of that we have with our coaches, you can understand why this is done.
The typical engine is supplied with a tiny alternator capable of 30~40 amps. It is usually turned by a small metric belt and now the owner wants to be able to recover the bank in less than an hour. (Sailors don't like to run the engine at all.) This just can't happen.
Problem: If you go to any of the alternator suppliers (like Balmar.net) you will see that alternators over 100 amp are all supplied with either a dual sheave or K6/8~Poly-V/Serpentine sheaves and there is a reason. It just works out that at ~1.75Hp (1.3kW) ~ 100Amps in a 12V nominal ~14V) all that any single belt can do. The companies that supply for this market also supply independent regulators that both do not supply field current for ~30 seconds so then engine can get running (the new cars do the same thing) but can also be equipped to limit output current. Yes, these things are trick, but you do pay for the privilege.
This is where my adventure with our GMC comes in.
I did everything I could with the existing alternator to stop the squeal. But we have always drycamped a lot with the electric refrigeration. To mitigate the morning startup squeal (at some venues, we might have been dry, but we were not alone) I even bought a $pecial belt that promised to survive at higher tension and set it in at maximum with a belt jack and a tension gauge. I would still squeal on occasion.
This is where being an engineer with tools and instruments becomes a dangerous thing.....
The coach is supposed to have an 80Amp alternator. That should never squeal a belt. So, I started a serious investigation not solely because I was worried about tearing up my new 30+$ belt. On these cold starts, the terminal at the house bank could go to 14.6. A little higher than I might like, so, I put a current probe on the alternator output lead. If the 87 it was attached to did not have a peak trap, I might have missed. I was, after all, somewhat distracted by the noise and such coming off the alternator belt. With the engine at a fast idle, the output had dropped to the high 70's and squeal had stopped. OK, what is the problem here?
Then I hit the Peak button....
It recorded a peak current of 98 Amps!! Whoa Momma!!!
This should not be possible with an 80 amp Delco 27SI machine. But that rating counts on it being all OE parts (fat chance at 35yo), some expected line loss and normal batteries at the end of that line. None of those assumptions were good in my case. The house bank was a 4D when I got it and was replaced shortly after with a pair of GC2s. The line loss was also messed with. Apparently the PO (No Complaint) had replaced some of the involved conductors with upsized marine (which is AWG not SAE), and the machine had been messed with too. When I got the rear casting replaced, the very knowledgeable guy in the shop mumbled something about it being changed to a 100. (Quite honestly I do not hear well and just stored what I thought I heard.) In a discussion years and miles later, this was a common mod even done without an owners request because the 100 parts were now more common (<$).
Now comes another little gotcha. It got me two ways. Chaumière is a 73-23 with the house bank in the right front. The cable from the isolator to the house bank is about 2' and maybe 2.5 to the main engine battery. That with the lower resistance of the large conductors, made this current possible.
Now why doesn't every coach have this issue?
There are two very good reasons even with the 100 amp 27si:
- The conductor size to the house bank is probably a little smaller (can change with model year).
- The wire length to the house bank in a 26 is WAY longer than it is for a 23.
This is another place that hit home.
I replaced the buzzbox with a 9140 (added a wizard later), and also later installed a Bogart Trimetric. I had always had trouble recovering the house bank on the APU. The battery monitor told my why. The best it ever did was 27 amps. This was now real surprise when I measure the terminal at the PD9145 as 14.4 and at the house bank was 13.4. This would be almost impossible to correct with copper. (My place for the converter is across from the head and the house bank is in the far corner.) So, I got a PD9260. I ran an 120V line to the right front and put it at the passengers right ankle along with capable conductors. Now I can change the house at 57amps. (I have to thank RobM here. He pointed out that the 9260 is lower height than the 9x45, and that is why I did not just move what I had.)
I am about a day way from test running and cam breakin, then all I need to do is shove the frame back in and do the 937 things required.
Matt
Matt & Mary Colie - Chaumière -'73 Glacier 23 - Members GMCMI, GMCGL, GMCES
Electronically Controlled Quiet Engine Cooling Fan with OE Rear Drum Brakes with Applied Control Arms
SE Michigan - Near DTW - Twixt A2 and Detroit
|
|
|
|
GMCforum
Search
Help
Register
Login
Home
