Home » Public Forums » GMCnet » [GMCnet] rectifier diode?
| [GMCnet] rectifier diode? [message #155793] |
Fri, 06 January 2012 22:59  |
Brian Waddell
Messages: 409
Registered: March 2010
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My engine batt goes dead over time when connected up....when disconnected ......no problem.......I think I have traced the problem to the rectifier? diode ? isolater?....that finned device on the firewall with three electrical connections on it. My service manuals call it a diode. I can't find any working explanations in the manuals On this list I read where, with engine running ,there are voltages that can be measured. I measured these with different meters and the numbers are ..top 14.3v....middle erratic from 2 to 13 ,,,bottom nothing......Are these devices available at any auto parts or rv parts place?....are there different ratings for them.....hope someone will tell me what they can....thanks....brian 77 ele 455
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| Re: [GMCnet] rectifier diode? [message #155796 is a reply to message #155793] |
Fri, 06 January 2012 23:13  |
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ljdavick
Messages: 3548
Registered: March 2007
Location: Fremont, CA
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Brian,
I think you are referring to the battery isolator. It allows the alternator to charge the chassis and house battery banks, like the combiner that Gene has documented. Jim K has it <http://appliedgmc.com/prod.itml/icOid/986>
Gene's write up is here <http://www.gmcmhphotos.com/photos/showphoto.php?photo=24994&size=medium>
Larry Davick
Sent from my iPad
On Jan 6, 2012, at 8:59 PM, Brian Waddell <sperline1@hotmail.com> wrote:
>
> My engine batt goes dead over time when connected up....when disconnected ......no problem.......I think I have traced the problem to the rectifier? diode ? isolater?....that finned device on the firewall with three electrical connections on it. My service manuals call it a diode. I can't find any working explanations in the manuals On this list I read where, with engine running ,there are voltages that can be measured. I measured these with different meters and the numbers are ..top 14.3v....middle erratic from 2 to 13 ,,,bottom nothing......Are these devices available at any auto parts or rv parts place?....are there different ratings for them.....hope someone will tell me what they can....thanks....brian 77 ele 455
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Larry Davick
A Mystery Machine
1976(ish) Palm Beach
Fremont, Ca
Howell EFI + EBL + Electronic Dizzy
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| Re: [GMCnet] rectifier diode? [message #155797 is a reply to message #155793] |
Fri, 06 January 2012 23:15 |
Mr ERFisher
Messages: 7117
Registered: August 2005
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try this
http://gmcmotorhome.info/chassis.html#Isolator
gene
On Fri, Jan 6, 2012 at 8:59 PM, Brian Waddell <sperline1@hotmail.com> wrote:
>
> My engine batt goes dead over time when connected up....when disconnected
> ......no problem.......I think I have traced the problem to the rectifier?
> diode ? isolater?....that finned device on the firewall with three
> electrical connections on it. My service manuals call it a diode. I can't
> find any working explanations in the manuals On this list I read where,
> with engine running ,there are voltages that can be measured. I measured
> these with different meters and the numbers are ..top 14.3v....middle
> erratic from 2 to 13 ,,,bottom nothing......Are these devices available at
> any auto parts or rv parts place?....are there different ratings for
> them.....hope someone will tell me what they can....thanks....brian 77 ele
> 455
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
>
--
Gene Fisher -- 74-23,77PB/ore/ca
“Give a man a fish; you have fed him for today --- give him a URL and
-------
http://gmcmotorhome.info/
Alternator Protection Cable
http://gmcmotorhome.info/APC.html
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| Re: [GMCnet] rectifier diode? [message #155803 is a reply to message #155793] |
Fri, 06 January 2012 23:48 |
Ken Burton
Messages: 10030
Registered: January 2004
Location: Hebron, Indiana
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Yes, they are available from most RV stores. They are a common item used in many RVs with multiple battery banks. I have a new spare one my basement somewhere that I got surplus for $15 or $20.
Jim K. sells them.
http://www.appliedgmc.com/prod.itml/icOid/986
That said, I doubt that your discharge problem is the isolator.
With the engine off, the top and bottom terminals of the isolator should read the battery voltage of the two battery banks which should be in the neighborhood of 12.6 to 12.8 volts. The center terminal should read ZERO.
The center terminal is the output of the alternator. With the engine running, the center terminal should read 14.7 volts plus or minus a few 1/10s of a volt.
With the engine running the top and bottom terminals should read .7 volts or so less than the center terminal or about 14.0 volts.
Once you determine that your isolator is indeed doing what it should then we can discuss what is running your battery(s) down when the engine is not running. I do not see how it could be the isolator unless we have a multiple failure inside of the isolator.
Please check your voltages again.
What are you using for a ground reference when you checked the above voltages? I suggest using the aluminum plate that the isolator is mounted on. That plate should be wired direct to the negative terminal of the engine battery.
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
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| Re: [GMCnet] rectifier diode? [message #155831 is a reply to message #155793] |
Sat, 07 January 2012 12:26 |
Bob de Kruyff
Messages: 4260
Registered: January 2004
Location: Chandler, AZ
Karma: 1
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| Brian Waddell wrote on Fri, 06 January 2012 21:59 |
My engine batt goes dead over time when connected up....when disconnected ......no problem.......I think I have traced the problem to the rectifier? diode ? isolater?....that finned device on the firewall with three electrical connections on it. My service manuals call it a diode. I can't find any working explanations in the manuals On this list I read where, with engine running ,there are voltages that can be measured. I measured these with different meters and the numbers are ..top 14.3v....middle erratic from 2 to 13 ,,,bottom nothing......Are these devices available at any auto parts or rv parts place?....are there different ratings for them.....hope someone will tell me what they can....thanks....brian 77 ele 455
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Most likely you have a parasitic load on the chassis battery side of the system such as your radio. One way to see if it's the isolator is to disconnect the chassis side connector on the isolator. It could be the top or bottom connector if you can trace the wiring back a bit--or disconnect both the top and bottom and see if your battery still runs down. If it does, it's a drain on the chassis side circuit. If it still drains--then it could be the isolator which is readily available almost anywhere.
Bob de Kruyff
78 Eleganza
Chandler, AZ
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| Re: [GMCnet] rectifier diode? [message #155840 is a reply to message #155793] |
Sat, 07 January 2012 16:19 |
JohnL455
Messages: 4447
Registered: October 2006
Location: Woodstock, IL
Karma: 12
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Test the isolator the way Ken B listed above with the digital VOM touching each terminal he lists and the other meter probe to a good ground with meter on DC volts scale. The metal panel behind the isolator is the closest assuming it still has a good ground and you get a good connecton through the oxidation all the metal surfaces will have. This is an in circuit engine on test and should provide quick and accurate info on if the unit is working in the real world. You can also test the diodes with the isolator out of circuit using the Ohm meter section, readings from center to outboad should be high in one direction and low by reversing the leads and the same from center to either outboard. There should be no continuity from any of the terminals to the case. Before disconnecting any hots, always disconnect the NEG at each battery so you don't have a short/fire/batt explosion etc. The original eratic numbers you list point more towards a poor meter reading due to bad (dirty) connections to the meter leads. If the batteries are reasonably charged, then the readings should be more stable. We think the drain is elswhere or a defective battery. Todays batteries seem to fail in a "good today/ bad tomorrow" mode than a slow weakening and raised warning flag like the older ones did.
John Lebetski
Woodstock, IL
77 Eleganza II
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| Re: [GMCnet] rectifier diode? [message #216337 is a reply to message #155803] |
Tue, 30 July 2013 21:57 |
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JBO
Messages: 65
Registered: August 2012
Location: South Western Ontario
Karma: 0
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Sorry for resurrecting an old thread but I was doing a search on possible isolator issues and found this thread of interest. I was hoping it might trigger a response from some of the more knowledgeable on this site.
My situation: I have a 78 Royale with the three 3 battery set up. I purchased the unit last fall and I inadvertently ran down the batteries a couple times this summer. One time I had left the boost switch in the boost position for a week or so and another time I forgot to turn the water heater switch off and I believe the red warning light drained all the batteries after that (the switch is inside a cupboard. This two actions totally drained all three batteries both times.
After running the batteries down via the water heater switch I charged all the batteries and did a test with a test light to determine if there was another power drain somewhere. After testing all three batteries by removing the negative cable and using the light between cable and battery. I determined that there was no other power drains.
Everything is fine and dandy until we went on a small jaunt this past weekend. We were driving through dark and stormy weather on Saturday afternoon when I turned on the parking/running lights. Well once we reached our destination the weather had cleared and I forgot about the lights.
I remembered about 30 min later and looked out the window to see if the lights were on. They weren’t, cause the batteries had already been drained down at this point. So I figured I did turn them off.
I had to move the coach about 30 minutes after this and discovered that she was dead. Sliding the booster switch on would not help, she was deader than a door nail. The generator battery did not drain down yet so I fired on the generator and waited for ten minutes or so and the Onan supplied enough juice up to the front batteries and the coach fired up.
This was Saturday afternoon. I plugged into shore power after that and everything is fine. We came home Sunday without incident. Sunday evening I remembered to turn everything off so I would not have another drain down.
Everything is fine until Monday after work, when I went to start her up and found the cock pit completely dead again. No power what-so-ever. Booster switch not helping. The Onan did fire up though. I grabbed my battery charger and started charging the starting battery. I noticed the underhood light was not coming on. I had the charger on for less than ten minutes when I noticed the under hood light very bright. I went to go remove the charger and noticed the light was off again and the vehicle was dead again. After fumbling around for a bit I noticed the light very bright again. I’m thinking that’s strange and doesn’t make a lot of sense.
This had me thinking that perhaps something else was wrong. So I went back and did the battery tests with test light and determined that nothing is drawing any power.
I then did a search on this site. I found this thread on the isolator and decided to test mine to see what the readings would be. So about 24 hours after driving and starting these are the multi meter numbers:
Battery 1) Starting battery 12.7 v
Battery 2) Firsthouse battery 12.68v
Battery 3) Second house/generator battery 12.55
After starting vehicle
Battery 1) Starting battery 14.7 v slowly dropping down after checking after 5 minutes so to 14.4
Battery 2) Firsthouse battery 14.68v seemed to stay the same
Battery 3) Second house/generator battery 14.62
I decided to look at the isolator with the volt meter and found this as the vehicle was running:
Top post starting battery 14.55
Center post alternator 15.28
Bottom post house battery 14.51
I then turned off the vehicle and had these readings at the isolator
Top post starting battery 13.0
Center post alternator 12.02
Bottom post house battery 12.8
Once I noticed the reading from the center isolator post I tested with my test light to see if it would light the test light at 12v, it would not. So I disconnected the alternator wire from the isolator, reading stays the same. I disconnected all the wires from the isolator and I was still having readings on all three posts.
Isn’t that kinda strange? The other thing I find weird is that I retested again tonight all my batteries with a test light to see if there is a draw. There is not. I even determined that if I had a draw on my staring battery (underhood light) it would not cause my two house batteries to light the test light. So that had me wondering how I managed to drain all three batteries earlier in the summer by leaving the boost switch on and the water heater.
Does anyone out there in GMCLand have any thoughts on this particular situation that looks like it has slowly turned into a novel?
Cheers, Jim
Jim Owens,
78 Royale,
Out skirts of Kitchener, Ontario
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| Re: [GMCnet] rectifier diode? [message #216360 is a reply to message #216337] |
Wed, 31 July 2013 04:33 |
Ken Burton
Messages: 10030
Registered: January 2004
Location: Hebron, Indiana
Karma: 10
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Either I am misunderstanding the conditions under which you took your readings or then is something wrong with them. I'm wondering what you are using for a ground reference as you are probing the various terminals.
I can not see how you can have a reading on an isolator if all of the were disconnected. 49 or 4 5years ago I wired up sono-alerts on my vehicles that would beep if the lights were on and the ignition was not. Today you can get various polarity sensitive beepers at Radio Shack and do the same thing. I still lie the Sono-Alerts.
I told Arch this about 10 years ago, he did it and wrote something up on this. If you can not find it written up and still want to do it. Post here and I'll explain more. It is a simple add on.
and
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
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| Re: [GMCnet] rectifier diode? [message #216372 is a reply to message #216362] |
Wed, 31 July 2013 08:03 |
jhbridges
Messages: 8412
Registered: May 2011
Location: Braselton ga
Karma: -74
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Ever wonder why some digital meters sell for less than $10, and some for a couple hundred or more?
And you're correct, the screaming hi-z input atuff will give accurate but useless readings on sollid state stuff if there's a leakage current around.
--johnny
--------------------------------------------
On Wed, 7/31/13, Bruce Hislop <bruce@perthcomm.com> wrote:
Subject: Re: [GMCnet] rectifier diode?
To: gmclist@temp.gmcnet.org
Date: Wednesday, July 31, 2013, 11:26 AM
Jim,
Your center bolt readings on the isolator can be caused by a
combination of high impedance digital meters and parasitic
leakage in the high current isolator diodes. The
isolator diodes can leak a bit of current and without a load
to drain this current away, today's sensitive DVMs will read
this voltage. Good old analog meters presented a load
which drained this current away.
Use your test light as a load by connecting it to the center
bolt, then measure the voltage there using your meter.
I also find that many inexpensive DVMs can be fooled into
reading higher DC voltages when there is some AC component
present. Alternators generate 3 phase AC which is then
rectified into pulsing DC. The battery normally
filters this pulsing DC into pure DC. However the isolator
prevents this filtering at the center terminal. The
DVM then see's pulsing DC at the center terminal and reads
the peak voltage rather than the RMS value. Analog and
better quality meters will read the RMS value which
represents the DC value.
Just my experience with DVM's
Noise also can cause a DVM to give erroneous readings.
When in doubt what I am measuring I get out my scope.
More learned members please correct me here.
--
Bruce Hislop
ON Canada
77PB, 455 Dick P. rebuilt, DynamicEFI EBL EFI & ESC.
Hubler 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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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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| Re: [GMCnet] rectifier diode? [message #216374 is a reply to message #216362] |
Wed, 31 July 2013 08:33 |
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Matt Colie
Messages: 8547
Registered: March 2007
Location: S.E. Michigan
Karma: 7
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Read what Bruce aka rf_burns wrote on Wed, 31 July 2013 07:26
Bruce hit this right on the head......
Here is this guy (me)that has:
An original Simpson 260 (retired), 2 each Fluke 77, a Fluke 87
And
Several versions of light bulbs with wires/clips attached.....
Which does he go to first to diagnose 12V issues??
If you guessed the light bulbs, you have a good start.
I could explain this all, but no better than Bruce did. The real difference is that guys like us know what that the fancy stuff will not always give you the answers that you really need.
To most inexperienced people, one of our high buck meters kind of gets you to the guy in the balloon problem. You get good information that doesn't help you at all....
If you don't have a test light, make up one or more and keep them handy.
Should this be a tech session at Branson?
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: [GMCnet] rectifier diode? [message #216402 is a reply to message #155793] |
Wed, 31 July 2013 12:39 |
JohnL455
Messages: 4447
Registered: October 2006
Location: Woodstock, IL
Karma: 12
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If your engine batt won't run the running lights for 30 min it may need replacement. At this point I would remove all batts and slow charge each a couple days and have professionally bench load tested. The water heater is 120v so that is not it. Be careful with disconnecting wires at isolator as shorting is possible.
John Lebetski
Woodstock, IL
77 Eleganza II
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| Re: [GMCnet] rectifier diode? [message #216406 is a reply to message #216374] |
Wed, 31 July 2013 13:09 |
jhbridges
Messages: 8412
Registered: May 2011
Location: Braselton ga
Karma: -74
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Actually, testing and maasurement would make several - AC, DC, Air, Fuel, Brake Fluid, Regrigerant. I can do an easy hour on simple meters, their characteristics, what does and doesn't work in a paerticular circumstance, and why a $6 analog VOM is the weapon of choice as a forst instrument, H-F notwithstanding.
The concept of trends vs absolutes in measurment is obvious to most hams, and oblivious to most of the Teeming Millions.
A digital meter is useful >only< in cghecking the charging voltage on the GMC, and isn't necessary even then. As long as I can see an uptick in the needle when the alternator comes on line, I have an ides it's working. Since setting the float voltage is beyond the means of most garages, alls you relly need to know is, the violtage goes up indicating the alternator is taking load instead of the battery.
I won't get into RMS metering except to say that a) the H-F cheeep digital is incapable of measuring it with any degree of accuracy which means it's not gonna read properly when the Onan is loaded; and b) When you load the Onan, or even turn on the 3.6 Junkerac, or diddle with the Hiondoo you aren't gonna get an accurate reading because the waveform garbages up with load on these luittle generators. It does on inverter sets as awell, but the distortion is somewhat different. Since there's nothing you can do about it anyhow, a simple trend instrument is sufficient.
--johnny
--------------------------------------------
On Wed, 7/31/13, Matt Colie <matt7323tze@gmail.com> wrote:
Subject: Re: [GMCnet] rectifier diode?
To: gmclist@temp.gmcnet.org
Date: Wednesday, July 31, 2013, 1:33 PM
Read what Bruce aka rf_burns wrote on Wed, 31 July 2013
07:26
Bruce hit this right on the head......
Here is this guy (me)that has:
An original Simpson 260 (retired), 2 each Fluke 77, a Fluke
87
And
Several versions of light bulbs with wires/clips
attached.....
Which does he go to first to diagnose 12V issues??
If you guessed the light bulbs, you have a good start.
I could explain this all, but no better than Bruce
did. The real difference is that guys like us know
what that the fancy stuff will not always give you the
answers that you really need.
To most inexperienced people, one of our high buck meters
kind of gets you to the guy in the balloon problem.
You get good information that doesn't help you at all....
If you don't have a test light, make up one or more and keep
them handy.
Should this be a tech session at Branson?
Matt
--
Matt & Mary Colie
'73 Glacier 23 Chaumière (say show-me-air)
Now with 4 working Rear Brakes
SE Michigan - Twixt A2 and Detroit
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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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