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| A good reason to keep your Isolator [message #347463] |
Sat, 07 September 2019 08:26  |
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RF_Burns
Messages: 2277
Registered: June 2008
Location: S. Ontario, Canada
Karma: 3
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Seems a lot of people want to remove the Isolator when they install a combiner. Here is a good reason why you should keep the Isolator and install the combiner across it.
A couple of days ago when I started the Murray, the GEN light stayed ON. Checked the DigiPanel and it showed only 12V. So I got out the voltmeter and checked the alternator voltage at the Isolator and it was near zero volts. My alternator was 11 years old, so I guess it had a good run.
I pulled the alternator and opened it up. The problem was clear, the jumper strap at the output stud was burnt off inside. The plastic insulating washer was burnt off inside and badly melted on the outside. I cleaned up the stud, replaced the insulating washers and replaced the jumper strap. Checked the bearings and brushes, everything else looked ok. Re-installed and we were back in business with a working alternator.
It was clear that the alternator output stud was likely (or would have) shorted to the case of the alternator. If I didn't have the Isolator, the battery current would have flowed back through the #10 alternator wire causing lots of current, smoke and maybe flames. Its what us electronic types call I Norton.
So you may want to keep your Isolator for just another layer of protection. The 0.7 volt drop across the Isolator that some say limit the battery charging is a red herring. The alternator uses a remote voltage sensing wire which is connected to the battery. The alternator's internal regulator uses feed-back from this wire and automatically raises its output voltage to compensate for any voltage loss.
Just my 2 cents!
Bruce Hislop
ON Canada
77PB, 455 Dick P. rebuilt, DynamicEFI EBL EFI & ESC.
1 ton front end
http://www.gmcmhphotos.com/photos/showphoto.php?photo=29001
My Staff says I never listen to them, or something like that
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| Re: A good reason to keep your Isolator [message #347481 is a reply to message #347476] |
Sat, 07 September 2019 13:46  |
6cuda6
Messages: 975
Registered: June 2019
Karma: -6
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Senior Member |
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Matt Colie wrote on Sat, 07 September 2019 12:51JBO wrote on Sat, 07 September 2019 12:21Cool...
I've been contemplating upgrading to a 100 amp with the dual pulley myself and keeping the current as a road back up.
Jim,
Hang on before you go that expense.
Borrow an ammeter and get the house bank way down and watch the charging current right after start up. Your 27SI is at least an 80 amp number, but bet it never gets close. A 100 amp won't do any better. The problem is the almost 30' (10m) of #10SAE (not AWG) wire to the house bank. The alternator will limit its output voltage by what it sees in the cab, so 14.4 is all you will have up front. The resistance to the rear is the charge killer.
Our coach had a similar problem the other way. The PD9140 in the back could never get near 40. I ended up adding a PD9260 at the passenger's right ankle to get by the lead length issue. It worked.
From both technical advise and personal experience, 100 amp is over the limit of a single belt. This can be a long story at an table at Mansfield.
I had the opposite problem.
My coach has the house bank in the left front. My 27SI was supposed to limit at 80amp. Well, GM never counted on a pair of GC2 (T105) just a few feet away. I could not keep a belt when we dry camped. I finally went to double. Then I put in a Bogart Trimetic and watched as it climbed to 92 on a cold start at after a multi-day dry camp. That was just the house bank!! In a later test with a Bell current probe an a Fluke 87 (we are talking about the good stuff here) I saw 98+ for a short time in the power lead out of the alternator.
Matt
So Matt, if you were to rewire for your encountered problem what gauge would you have guestimated? I think im going to run into something similar here as my converter is on the left side of the coach, between the kitchen and the closet (so about 20 feet down the left side) and the house battery is in the right front of the engine compartment.
Im going to replace the converter in a couple weeks and if pulling wire is needed, nows the time.
Rich Mondor,
Brockville, ON
77 Hughes 2600
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| Re: A good reason to keep your Isolator [message #347484 is a reply to message #347463] |
Sat, 07 September 2019 15:24 |
Rick Staples
Messages: 126
Registered: May 2014
Location: Johnstown, Colorado, USA
Karma: -1
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Senior Member |
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Bruce,
I agree completely with you. A "combiner" isn't going to charge your batteries any faster unless there's a problem in the system. Besides, I like the other thing my "dual voltage" system allows: higher voltage to the A/C fan in high position, 16+ volts to my refrigerator "12V" heating element which runs only when the engine runs, and an easy way to trigger my electric fuel pump "safety" cutoff relay which shuts off the pump when the engine (alternator) stops.
BTW, I don't know about others, but the schematic for my coach shows a "0" gauge wire from the front (auxiliary battery switch) to the living area junction block (in the utility cabinet with the buzz box), and then a "1" gauge wire to the rear auxiliary battery switch where the house battery cable connects. Only a short (~ 1 or 2 foot) length of 10 gauge from the isolator to the front aux. bat. switch.
My .02,
Rick Staples
Rick Staples, '75 Eleganza, Johnstown, CO
"Advice is a dangerous gift, even from the Wise to the Wise, and all paths may run ill." -Tolkien
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| Re: A good reason to keep your Isolator [message #347485 is a reply to message #347484] |
Sat, 07 September 2019 15:59 |
6cuda6
Messages: 975
Registered: June 2019
Karma: -6
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Senior Member |
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Rick Staples wrote on Sat, 07 September 2019 16:24
BTW, I don't know about others, but the schematic for my coach shows a "0" gauge wire from the front (auxiliary battery switch) to the living area junction block (in the utility cabinet with the buzz box), and then a "1" gauge wire to the rear auxiliary battery switch where the house battery cable connects. Only a short (~ 1 or 2 foot) length of 10 gauge from the isolator to the front aux. bat. switch.
My .02,
Rick Staples
I wish i had yhe original schematics for our Hughes then i'd see the gauge size....at it stands i can only visual compare and read what other have.
Rich Mondor,
Brockville, ON
77 Hughes 2600
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| Re: A good reason to keep your Isolator [message #347490 is a reply to message #347481] |
Sat, 07 September 2019 18:52 |
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Matt Colie
Messages: 8547
Registered: March 2007
Location: S.E. Michigan
Karma: 7
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Senior Member |
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6cuda6 wrote on Sat, 07 September 2019 14:46Matt Colie wrote on Sat, 07 September 2019 12:51JBO wrote on Sat, 07 September 2019 12:21Cool...
I've been contemplating upgrading to a 100 amp with the dual pulley myself and keeping the current as a road back up.
Jim,
Hang on before you go that expense.
Borrow an ammeter and get the house bank way down and watch the charging current right after start up. Your 27SI is at least an 80 amp number, but bet it never gets close. A 100 amp won't do any better. The problem is the almost 30' (10m) of #10SAE (not AWG) wire to the house bank. The alternator will limit its output voltage by what it sees in the cab, so 14.4 is all you will have up front. The resistance to the rear is the charge killer.
Our coach had a similar problem the other way. The PD9140 in the back could never get near 40. I ended up adding a PD9260 at the passenger's right ankle to get by the lead length issue. It worked.
From both technical advise and personal experience, 100 amp is over the limit of a single belt. This can be a long story at an table at Mansfield.
I had the opposite problem.
My coach has the house bank in the left front. My 27SI was supposed to limit at 80amp. Well, GM never counted on a pair of GC2 (T105) just a few feet away. I could not keep a belt when we dry camped. I finally went to double. Then I put in a Bogart Trimetic and watched as it climbed to 92 on a cold start at after a multi-day dry camp. That was just the house bank!! In a later test with a Bell current probe an a Fluke 87 (we are talking about the good stuff here) I saw 98+ for a short time in the power lead out of the alternator.
Matt
So Matt, if you were to rewire for your encountered problem what gauge would you have guestimated? I think im going to run into something similar here as my converter is on the left side of the coach, between the kitchen and the closet (so about 20 feet down the left side) and the house battery is in the right front of the engine compartment.
Im going to replace the converter in a couple weeks and if pulling wire is needed, nows the time.
Rich,
In your case this will only be between the converter and the house bank. That was my case too, and I kept running the numbers up and decided that the equal loss for both sides (I lost just a little less charge voltage on the ground side as I did the hot) that the arrangement as existed was not salvageable. That is why the new converter in the front. (Installation was a serious PITA as a new 120V line also had to be run.) I could simple not do a double run of 1/0 without tearing into the coach. That is what it would have taken.
In your case, I would do what I sometimes do when confronted with such an issue. I go to the suppliers and total the prices for all the options (spreadsheets are handy) and decide how much the gain in copper is worth. I can remember two suppliers, and I am pretty sure that there was a third.
www.genuinedealz.com
www.delcity.net
Yes, everything is a compromise.
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
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| Re: A good reason to keep your Isolator [message #347503 is a reply to message #347463] |
Sun, 08 September 2019 07:48 |
jhbridges
Messages: 8412
Registered: May 2011
Location: Braselton ga
Karma: -74
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Senior Member |
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Along these lines, I have to wonder a bit. While checking the belt alignment, I noticed an interesting 'wobble' on the return side of the alternator belt. Makes me wonder whether we might benefit from a newer alternator with a clutch fitted. While the V-belt handles the wobble without a lot of problems, I suspect it would quickly take the outer ridges off a serpentine belt. I note pretty much all the new cars are fitted with clutch alternators, I suspect this is why. Compared to the 60s rides, the electric load is grossly larger now and if there are three or four ulses a second to the field, the result without the clutch would be very noticeable.
--johnny
Foolish Carriage, 76 26' Eleganza(?) with beaucoup mods and add - ons.
Braselton, Ga.
I forgive them all, save those who hurt the dogs. They must answer to me in hell
[Updated on: Sun, 08 September 2019 07:49] Report message to a moderator |
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| Re: A good reason to keep your Isolator [message #347505 is a reply to message #347503] |
Sun, 08 September 2019 07:56 |
6cuda6
Messages: 975
Registered: June 2019
Karma: -6
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Senior Member |
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Johnny Bridges wrote on Sun, 08 September 2019 08:48Along these lines, I have to wonder a bit. While checking the belt alignment, I noticed an interesting 'wobble' on the return side of the alternator belt. Makes me wonder whether we might benefit from a newer alternator with a clutch fitted. While the V-belt handles the wobble without a lot of problems, I suspect it would quickly take the outer ridges off a serpentine belt. I note pretty much all the new cars are fitted with clutch alternators, I suspect this is why. Compared to the 60s rides, the electric load is grossly larger now and if there are three or four ulses a second to the field, the result without the clutch would be very noticeable.
--johnny
Clutch alternator is because the alternator stops to abruptly when shut off so the serpentine belt squeals....clutch prevents that.
Rich Mondor,
Brockville, ON
77 Hughes 2600
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| Re: A good reason to keep your Isolator [message #347507 is a reply to message #347463] |
Sun, 08 September 2019 08:03 |
jhbridges
Messages: 8412
Registered: May 2011
Location: Braselton ga
Karma: -74
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Senior Member |
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MOre importantly the clutch removes the jerks. I suspect they are the reason in a higher (100 amp +) alternator. Belt tension will keep the alternator spinning, and when you shut the ignition off, the excitation to the alternator goes away. Thus it provides only the friction load which is minuscule by comparison. If you have a belt squeal on shutdown, you've some other problem.
--johnny
Foolish Carriage, 76 26' Eleganza(?) with beaucoup mods and add - ons.
Braselton, Ga.
I forgive them all, save those who hurt the dogs. They must answer to me in hell
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