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| Wiring Wonderland [message #104130] |
Mon, 25 October 2010 11:47  |
Luvn737s
Messages: 1106
Registered: June 2007
Karma: 2
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Senior Member |
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I have had an ongoing problem with my coach 12V house system. It seems like EVERYTHING (almost) is on one 20A circuit. By everything, I mean:
A/C blower in High
Hallway light
Bedroom lights
Dinette lights
Cockpit fans (mounted by the the rear view mirror)
Forward Fantastic Fan roof vent
Bathroom FF roof vent
Entry lights
Outside Porch light
Water pump
Probably a few more I'm leaving out. Needless to say that little 20A fuse blows fairly often.
Shouldn't the 12V house system be split up among some of the heavier load items with separate fuses? Also, how can I make sure that when the genset starts, it only draws from the battery and not through the whole 12V system (the generator should have diodes to prevent this, right?)?
Randy
1973 26' Painted Desert
Ahwatukee (Phoenix) AZ
[Updated on: Mon, 25 October 2010 11:49] Report message to a moderator |
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| Re: [GMCnet] Wiring Wonderland [message #104136 is a reply to message #104130] |
Mon, 25 October 2010 12:28  |
Ken Henderson
Messages: 8726
Registered: March 2004
Location: Americus, GA
Karma: 9
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Senior Member |
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Randy,
You're correct in that the loads should be distributed to multiple fuses and
the '73 house wiring diagram shows 8 such fuses. I haven't compared those
to the list you gave of common items, but it's pretty obvious someone's
cobbled up your wiring. No one's going to be able to say much to help you
without eyes and hands on the coach.
But I CAN tell you that you don't want to put diodes (isolators) in as
you've suggested. If you feed the output of the converter to the batteries
through diodes, those batteries will NEVER reach full charge. The PD
converter monitors its own output; when you insert the 0.6-0.7 VDC forward
voltage drop of a diode between that output and a battery, the battery can
never reach its correct charged voltage. The alternator overcomes that
problem by taking its sense voltage from "downstream" of the isolator so
that its output is enough higher to overcome the diode drop.
As for the Onan blowing that fuse, No, that should not happen, ESPECIALLY
with your supposedly dedicated starting battery -- the Onan's 12 VDC
circuits, including the starter, should draw NO current from the rest of the
house circuits.
You've got a lot of wire tracing to do. Preferably with the wiring diagrams
at hand to guide you back toward a sensible arrangement.
Ken H.
Americus, GA
'76 X-Birchaven w/Cad500/Howell EFI+ & EBL
www.gmcwipersetc.com
On Mon, Oct 25, 2010 at 12:47 PM, Randy <Acrosport2@hotmail.com> wrote:
>
>
> I have had an ongoing problem with my coach 12V house system. It seems like
> EVERYTHING (almost) is on one 20A circuit. By everything, I mean:
>
> A/C blower in High
> Hallway light
> Bedroom lights
> Dinette lights
> Cockpit fans (mounted by the the rear view mirror)
> Forward Fantastic Fan roof vent
> Bathroom FF roof vent
> Entry lights
> Outside Porch light
> Water pump
>
> Probably a few more I'm leaving out. Needless to say that little 20A fuse
> blows fairly often, especially when the genset is started which I think
> tries to draw starting current from the house battery through that little
> fuse.
>
> I installed a battery isolator by the PD converter so this wouldn't happen.
> My goal was to have the genset (on the road) or external extension cord
> power (at home or at hookups) the PD unit to recharge both the house and
> genset starting batteries (remember I've got a old setup with the dedicated
> genset battery in the back).
>
> Shouldn't the 12V house system be split up among some of the heavier load
> items with separate fuses? Also, how can I make sure that when the genset
> starts, it only draws from the battery and not through the whole 12V system
> (the generator should have diodes to prevent this, right?)?
>
>
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Ken Henderson
Americus, GA
www.gmcwipersetc.com
Large Wiring Diagrams
76 X-Birchaven
76 X-Palm Beach
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| Re: Wiring Wonderland [message #104139 is a reply to message #104130] |
Mon, 25 October 2010 13:09 |
midlf
Messages: 2212
Registered: July 2007
Location: SE Wisc. (Palmyra)
Karma: 1
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Senior Member |
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| Luvn737s wrote on Mon, 25 October 2010 11:47 |
Also, how can I make sure that when the genset starts, it only draws from the battery and not through the whole 12V system (the generator should have diodes to prevent this, right?)?
|
Your coach has been modified by a PO (who's hasn't). A 73 originally had a separate battery that was only connected to the genset and had no connection to the house system. Later a connection was added to the house system but this was again changed when the house battery was moved to the back next to the gen set. Diodes will not fix this as Ken mentioned, but a combiner will isolate the two systems while still allowing the genset battery to be charged from the house system.
I'm not sure this will help but without having hands (and meters) on the coach definite answers are not possible.
Steve Southworth
1974 Glacier TZE064V100150 (for workin on)
1975 Transmode TZE365V100394 (parts & spares)
Palmyra WI
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| Re: Wiring Wonderland [message #104143 is a reply to message #104139] |
Mon, 25 October 2010 13:34 |
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Hi Randy,
My '73 has a fuse panel in the electrical area where the main breakers are. It shows the following: 1. lighting, 2. lighting,
3. furn-range vent, 4. water pump, 5. refrig-toilet, 6. monitor panel, 7. aisle lighting.
Each has a single wire leading out of the fuse panel to the loads. The fuses vary from 5A to 30A., but I haven't checked that against the schematic.
There is a separate trip-type circuit breaker box. It does the roof AC, the vacuum cleaner, main appliance and portable appliance plus main breakers at 40 A.
I've had to trace a couple of shorts in the coach and one has to get into the ceiling panels sometimes to do that.
I think you have some work ahead there. Wish I could help more.
geo groth '73 260 Sequoia
Carson City Nevada 89703
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| Re: Wiring Wonderland [message #104210 is a reply to message #104130] |
Mon, 25 October 2010 18:43 |
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Hardie Johnson
Messages: 483
Registered: January 2004
Location: Raleigh NC
Karma: 0
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Yup, PO messed you up. I have a two 10 position fuse panels from Radio Shack(?), but would prefer ones made from a thermoset plastic, or Ryton. The ABS can over heat and melt. One is back in the cabinet with the PD power supply, the other is under the dash for auxiliary things.
For the supply side, run a wire from the PD charger/DC supply to the first fuse, hooked to the output side. Put a 40AMP fuse in there. This will provide protection for the bus. Then run 5, 10, and 20 amp circuits out to the coach. I have my radio wired to be on all the time, too.
Summit racing has some awesome, expensive blocks, too.
"listen while you work"
Hardie Johnson "Crashj"
1973 26 foot Glacier, White Thing
Raleigh NC
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| Re: Wiring Wonderland [message #104220 is a reply to message #104216] |
Mon, 25 October 2010 20:10 |
C Boyd
Messages: 2629
Registered: April 2006
Karma: 18
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Senior Member |
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2. Do you by any chance have the boost switch on? The boost solenoid also connects the house and engine systems together.
As stated before this is very difficult to diagnose over the net without actually seeing the coach. I totally expect you problem to be a PO wiring problem.
Good Luck.
[/quote]
Sir: I have heard of an on/off boost switch being installed upside down.. Just something to check..
C. Boyd
76 Crestmont
East Tennessee
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| Re: Wiring Wonderland [message #104230 is a reply to message #104130] |
Mon, 25 October 2010 21:39 |
Luvn737s
Messages: 1106
Registered: June 2007
Karma: 2
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Senior Member |
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No, the boost solenoid isn't on. The reason for the isolator with the PD unit was because the Kohler genset (I was told) has no battery charger and needed some source of power to recharge it. I didn't want to hook the house battery and genset battery together full time to be charged simultaneously by the PD unit, so I installed a spare isolator. I sort of understand how an alternator's output would be different from the PD unit (bot through isolators) but absent a better solution, I think this is the better of two evils.
What should be the connections to each side of the boost solenoid. The house battery power seems to come through a large circuit breaker then back to the coach.
I plan to trace the wire that attaches to the 20A Fuse For Everything and split it up into number of separate fused circuits. I have a few open slots in my fuse panel. I like the inline fuse idea from the PD to the bus but I thought the PD's internal fuse covered that.
Randy
1973 26' Painted Desert
Ahwatukee (Phoenix) AZ
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| Re: Wiring Wonderland [message #104231 is a reply to message #104130] |
Mon, 25 October 2010 21:48 |
Luvn737s
Messages: 1106
Registered: June 2007
Karma: 2
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Senior Member |
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I have been able to keep the 20 A fuse from blowing by not having the genset supply power while the fuse is connected. Knowing that so many loads are on that fuse, I have made a conscious effort to not run all of them simultaneously, but separately they seem to do okay. I charge the house batteries from a generator or extension cord with the fuse removed.
When the fuse blows, it's not a little pop for the fuse. It is melted and annihilated! The only thing I can think of is that the recharge wire back to the genset battery is drawing major amps everytime the genset starts bit only the 20A fuse blows. All the rest down to 5A (I think) seem to do fine.
Randy
1973 26' Painted Desert
Ahwatukee (Phoenix) AZ
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| Re: [GMCnet] Wiring Wonderland [message #104236 is a reply to message #104216] |
Mon, 25 October 2010 22:12 |
James Hupy
Messages: 6806
Registered: May 2010
Karma: -62
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It kinda sounds like the high amperage circuit in the boost solenoid is
fried and therefore acting like a shunt circuit all the time. Easy to check
and they do fail from time to time.
Jim Hupy
Salem, Or
78 Royale 403
On Mon, Oct 25, 2010 at 5:45 PM, Ken Burton <n9cv@comcast.net> wrote:
>
>
> tphipps wrote on Mon, 25 October 2010 18:58
> > Excellent fuse blocks are also available at West Marine. Marine stuff is
> more expensive, but generally a better choice for the coach environment.
> Get an enlarged copy of the original wiring diagram and start to isolate
> the house circuits. It sounds like your house and chassis batteries are
> combined or crossed somewhere along the way, especially since you stated
> that the high speed on the A/C blower blows the same 20Amp fuse that the
> house batteries are also blowing. The original diode isolater is in the 12v
> circuit to isolate the 2 storage batteries from each other. This also
> serves to isolate the 12v Engine circuit from the 12v House circuit.
> > Good Luck, electrical problems are always fun, not. :)
> >
> > Tom Phipps, 75 GMC Ex-Avion
>
> The one thing the Tom did not explicitly state in his excellent post is
> that the AC blower is on the Engine battery.
>
> You have to think of the GMC as two separate electrical systems. The
> engine side and the house side. There are only two OEM designed and
> installed cross connections between the two systems. They are the isolator
> and the boost solenoid.
>
> As Tom stated above The AC/heater fan should not have any connection with
> or be drawing current through a fuse on the house electrical system.
>
> Before chasing PO wiring for the cross connection I would check out the two
> OEM designed cross connections.
>
> 1. I have never seen it happen but you could have a double short in the
> isolator. You might disconnect either the top or bottom lead(s) of the
> isolator temporarily just to if the Ac blower still works on high and still
> blows the fuse. I doubt this is your problem but it only take a moment.
>
> 2. Do you by any chance have the boost switch on? The boost solenoid also
> connects the house and engine systems together.
>
> As stated before this is very difficult to diagnose over the net without
> actually seeing the coach. I totally expect you problem to be a PO wiring
> problem.
>
> Good Luck.
>
> --
> Ken Burton - N9KB
> 76 Palm Beach
> Hebron, Indiana
> _______________________________________________
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> List Information and Subscription Options:
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| Re: [GMCnet] Wiring Wonderland [message #104241 is a reply to message #104237] |
Mon, 25 October 2010 23:04 |
James Hupy
Messages: 6806
Registered: May 2010
Karma: -62
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Senior Member |
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Is your magnetic switching solenoid still located in the generator
compartment, or has it been moved to another location? That could shed some
light on the problem, but it is really hard to diagnoise electrical problems
without being there to lay hands on the components. When a solenoid is
"fried" (I will use that non scientific term to describe a condition where
the internal high amperage contacts have welded themselves together and do
not open the circuit when the magnetic coil releases or that circuit is
opened) it can be checked by isolating the solenoid from any current flow
from any source, and then checking for continuity across the large terminals
where the battery cables normally are located. When that boost solenoid is
actuated, you essentially have one very complex interconnected network and
it was never intended to be operated for anything but a very short time.
Other than that, I would not think that the AC fan motor should run on high
speed at any time except when the engine is running as the high speed
circuit is powered from the engine's alternator. If this is not the case,
then I would suspect that someone has modified the electricals. I am sorry
to say if this is the case, it complicates troubleshooting a great deal. Try
to be systematic in your approach. Do one component at a time until you
discover something you don't understand, and then ask more questions. We
will all try to help.
Jim Hupy
Salem, Or
78 Royale 403
On Mon, Oct 25, 2010 at 8:22 PM, Randy <Acrosport2@hotmail.com> wrote:
>
>
> How would I check that? Go slow and NO MATH! :o
> --
> Randy
> 1973 26' Painted Desert
> Ahwatukee (Phoenix) AZ
> _______________________________________________
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| Re: Wiring Wonderland [message #104243 is a reply to message #104231] |
Mon, 25 October 2010 23:22 |
Ken Burton
Messages: 10030
Registered: January 2004
Location: Hebron, Indiana
Karma: 10
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Senior Member |
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| Luvn737s wrote on Mon, 25 October 2010 21:48 |
I have been able to keep the 20 A fuse from blowing by not having the genset supply power while the fuse is connected. Knowing that so many loads are on that fuse, I have made a conscious effort to not run all of them simultaneously, but separately they seem to do okay. I charge the house batteries from a generator or extension cord with the fuse removed.
When the fuse blows, it's not a little pop for the fuse. It is melted and annihilated! The only thing I can think of is that the recharge wire back to the genset battery is drawing major amps every time the genset starts bit only the 20A fuse blows. All the rest down to 5A (I think) seem to do fine.
|
You are going to have to draw some of this out so we can understand what is wired to where. I'm getting really confused. First you listed a bunch of stuff that was all getting power through the same fuse. Now you state that you have multiple fuses for these items. You also state that you have two isolators. One for the engine alternator and one for the gen set battery? That is not going to work. The engine driven one has a circuit that ups the alternator voltage to make up for the loss in the isolator. Your genset system does not have such a circuit. Either you need a combiner for the gen set battery instead of the isolator, or better yet if you have rear mounted batteries, start the Kohler from the start the house battery(s).
The converter makes 12 volt DC for the house system from 110 generated by the Kohler. So there is no back circuit between the 12 volt DC house system and the Kohler unless you are talking about a circuit through a combiner to charge the Kohler starting battery.
If you are recharging the Kohler battery through a 20 amp fuse I can understand that fuse blowing. It is very common for a battery to take much higher than that initially in charging current and then taper off after a few minutes. I could take 50 amps or possibly more right after starting and then taper down after a few minutes.
Where exactly is this 20 amp fuse that is blowing? Is is a 1.25 inch long glass fuse in the 12 volt house system. Why do you think that all of these other items that you listed before are running through it?
Where is the PD unit wired to the house 12 volt electrical system?
Why do you think that the AC blower on high is wired through the house electrical system?
Either I'm very confused or you have a whole bunch of strangely wired 12 volt DC circuits in which case we are going to have to attack all of these symptoms one at a time.
Ken B.
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
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| Re: Wiring Wonderland [message #104274 is a reply to message #104130] |
Tue, 26 October 2010 11:25 |
Luvn737s
Messages: 1106
Registered: June 2007
Karma: 2
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Senior Member |
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I'll try to come up with a diagram, but there's quite a bit I don't know.
There are 3 other fuses, but not for the items I listed. I would remove the 20A fuse (co-located with the PD unit in the electrical compartment below the drawers in the hallway) and saw what items lost power.
There is a wire that goes from the isolator in that same electrical compartment back to the genset battery. When the starter engages, that wire should also sense the same draw, right? When the genset starts there is a high recharge draw, but that should be buffered through the PD unit.
What is the benefit of a combiner, if I don't really want any electrical connection between the genset battery and the house battery? Does the combiner only combine when it has to and isolates otherwise?
Doesn't having the dedicated genset battery eliminate the need for a long run of large diameter run wire from the front of the coach (where the house batteries are) to the genset?
Randy
1973 26' Painted Desert
Ahwatukee (Phoenix) AZ
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| Re: Wiring Wonderland [message #104279 is a reply to message #104274] |
Tue, 26 October 2010 12:22 |
Ken Burton
Messages: 10030
Registered: January 2004
Location: Hebron, Indiana
Karma: 10
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Senior Member |
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| Luvn737s wrote on Tue, 26 October 2010 11:25 |
I'll try to come up with a diagram, but there's quite a bit I don't know.
There are 3 other fuses, but not for the items I listed. I would remove the 20A fuse (co-located with the PD unit in the electrical compartment below the drawers in the hallway) and saw what items lost power.
There is a wire that goes from the isolator in that same electrical compartment back to the genset battery. When the starter engages, that wire should also sense the same draw, right? When the genset starts there is a high recharge draw, but that should be buffered through the PD unit.
What is the benefit of a combiner, if I don't really want any electrical connection between the genset battery and the house battery? Does the combiner only combine when it has to and isolates otherwise?
Doesn't having the dedicated genset battery eliminate the need for a long run of large diameter run wire from the front of the coach (where the house batteries are) to the genset?
|
I'll answer some of the questions that I can.
The PD unit will not necessarily "buffer" current going to the Genset battery. The PD unit puts out 13.8 or 14.0 volts and can supply up to its full current rating while maintaining 14.0 volts. The model I have is 40 or 45 amps) The battery will draw whatever it needs, so a fully charged battery it will only be one or two amps while a recently used battery may try to draw 50 or 75 amps short term.
The benefit of a combiner is that it does not have a .7 volt loss so you get set battery will fully charge over time. If the PD unit is putting out 14.0 volts through a combiner you will see 14.0 volts at both the house and the genset batteries.
In the same senerio if an isolator is used instead of a combiner your gen set battery will only see 13.3 volts during charging due to the .7 volt loss through the isolator. At 13.3 volts charging voltage it would take weeks to fully charge the genset battery.
We have the same loss through the OEM isolator when charging from the engine driven alternator except the alternator voltage is increased (automatically) by .7 volts to 14.7 to make up for the loss through the isolator. If we had a way to make the PD unit put out 14.7 volts then an isolator could be used.
Having a genset battery in the rear does indeed reduce or eliminate the loss through long wire from front to rear when starting the generator. In later years GMCs the house batteries were moved to the rear and used to start the Onan. If you have a front house battery(s) then you should probably keep the rear genset battery.
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
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| Re: [GMCnet] Wiring Wonderland [message #104298 is a reply to message #104279] |
Tue, 26 October 2010 15:22 |
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ljdavick
Messages: 3548
Registered: March 2007
Location: Fremont, CA
Karma: -3
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Senior Member |
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I've wondered what effect combiners would have on the Progressive Dynamics smart charge abilities. Would it boil the Onan battery while trying to bring the house batteries up to snuff, or is that not the way voltage works?
How would it get to the maintenance phase if there were a difference in batteries.
As I'm writing this I'm thinking that I've missed the core concept of battery charging!
Larry Davick
The Mystery Machine
On Oct 26, 2010, at 10:22 AM, Ken Burton <n9cv@comcast.net> wrote:
>
>
> Luvn737s wrote on Tue, 26 October 2010 11:25
>> I'll try to come up with a diagram, but there's quite a bit I don't know.
>>
>> There are 3 other fuses, but not for the items I listed. I would remove the 20A fuse (co-located with the PD unit in the electrical compartment below the drawers in the hallway) and saw what items lost power.
>>
>> There is a wire that goes from the isolator in that same electrical compartment back to the genset battery. When the starter engages, that wire should also sense the same draw, right? When the genset starts there is a high recharge draw, but that should be buffered through the PD unit.
>>
>> What is the benefit of a combiner, if I don't really want any electrical connection between the genset battery and the house battery? Does the combiner only combine when it has to and isolates otherwise?
>>
>> Doesn't having the dedicated genset battery eliminate the need for a long run of large diameter run wire from the front of the coach (where the house batteries are) to the genset?
>
>
>
> I'll answer some of the questions that I can.
>
> The PD unit will not necessarily "buffer" current going to the Genset battery. The PD unit puts out 13.8 or 14.0 volts and can supply up to its full current rating while maintaining 14.0 volts. The model I have is 40 or 45 amps) The battery will draw whatever it needs, so a fully charged battery it will only be one or two amps while a recently used battery may try to draw 50 or 75 amps short term.
>
> The benefit of a combiner is that it does not have a .7 volt loss so you get set battery will fully charge over time. If the PD unit is putting out 14.0 volts through a combiner you will see 14.0 volts at both the house and the genset batteries.
>
> In the same senerio if an isolator is used instead of a combiner your gen set battery will only see 13.3 volts during charging due to the .7 volt loss through the isolator. At 13.3 volts charging voltage it would take weeks to fully charge the genset battery.
>
> We have the same loss through the OEM isolator when charging from the engine driven alternator except the alternator voltage is increased (automatically) by .7 volts to 14.7 to make up for the loss through the isolator. If we had a way to make the PD unit put out 14.7 volts then an isolator could be used.
>
> Having a genset battery in the rear does indeed reduce or eliminate the loss through long wire from front to rear when starting the generator. In later years GMCs the house batteries were moved to the rear and used to start the Onan. If you have a front house battery(s) then you should probably keep the rear genset battery.
> --
> Ken Burton - N9KB
> 76 Palm Beach
> Hebron, Indiana
> _______________________________________________
> GMCnet mailing list
> List Information and Subscription Options:
> http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
_______________________________________________
GMCnet mailing list
List Information and Subscription Options:
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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] Wiring Wonderland [message #104311 is a reply to message #104298] |
Tue, 26 October 2010 17:47 |
Ken Burton
Messages: 10030
Registered: January 2004
Location: Hebron, Indiana
Karma: 10
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Senior Member |
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| ljdavick wrote on Tue, 26 October 2010 15:22 |
I've wondered what effect combiners would have on the Progressive Dynamics smart charge abilities. Would it boil the Onan battery while trying to bring the house batteries up to snuff, or is that not the way voltage works?
How would it get to the maintenance phase if there were a difference in batteries.
As I'm writing this I'm thinking that I've missed the core concept of battery charging!
Larry Davick
The Mystery Machine
On Oct 26, 2010, at 10:22 AM, Ken Burton <n9cv@comcast.net> wrote:
|
I have a big long response typed. I hit the wrong key and lost it all. Here is a short version of my response.
I have the same concern that you do on charging two batteries through a combiner when the batteries are at a considerably differently levels of charge or different types of batteries (deep cycle and starting). I agree that you stand the chance of over charging and boiling the higher charged battery .
This is one of the reason I do not use a combiner on the engine and house battery to replace the isolator.
You have the same potential problem with a genset and house battery connected with a combiner. I just do not see a better solution other than possibly combining the genset starting battery with the engine battery instead of the house battery. The genset battery and engine battery are similar types and application and they have similar duty cycles.
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
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| Re: [GMCnet] Wiring Wonderland [message #104313 is a reply to message #104298] |
Tue, 26 October 2010 18:10 |
Mr ERFisher
Messages: 7117
Registered: August 2005
Karma: 2
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Senior Member |
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The low battery takes the most charge
Gene
Not sent from my ipad
On Oct 26, 2010, at 1:22 PM, Larry Davick <ljdavick@comcast.net> wrote:
> I've wondered what effect combiners would have on the Progressive Dynamics smart charge abilities. Would it boil the Onan battery while trying to bring the house batteries up to snuff, or is that not the way voltage works?
>
> How would it get to the maintenance phase if there were a difference in batteries.
>
> As I'm writing this I'm thinking that I've missed the core concept of battery charging!
>
> Larry Davick
> The Mystery Machine
>
> On Oct 26, 2010, at 10:22 AM, Ken Burton <n9cv@comcast.net> wrote:
>
>>
>>
>> Luvn737s wrote on Tue, 26 October 2010 11:25
>>> I'll try to come up with a diagram, but there's quite a bit I don't know.
>>>
>>> There are 3 other fuses, but not for the items I listed. I would remove the 20A fuse (co-located with the PD unit in the electrical compartment below the drawers in the hallway) and saw what items lost power.
>>>
>>> There is a wire that goes from the isolator in that same electrical compartment back to the genset battery. When the starter engages, that wire should also sense the same draw, right? When the genset starts there is a high recharge draw, but that should be buffered through the PD unit.
>>>
>>> What is the benefit of a combiner, if I don't really want any electrical connection between the genset battery and the house battery? Does the combiner only combine when it has to and isolates otherwise?
>>>
>>> Doesn't having the dedicated genset battery eliminate the need for a long run of large diameter run wire from the front of the coach (where the house batteries are) to the genset?
>>
>>
>>
>> I'll answer some of the questions that I can.
>>
>> The PD unit will not necessarily "buffer" current going to the Genset battery. The PD unit puts out 13.8 or 14.0 volts and can supply up to its full current rating while maintaining 14.0 volts. The model I have is 40 or 45 amps) The battery will draw whatever it needs, so a fully charged battery it will only be one or two amps while a recently used battery may try to draw 50 or 75 amps short term.
>>
>> The benefit of a combiner is that it does not have a .7 volt loss so you get set battery will fully charge over time. If the PD unit is putting out 14.0 volts through a combiner you will see 14.0 volts at both the house and the genset batteries.
>>
>> In the same senerio if an isolator is used instead of a combiner your gen set battery will only see 13.3 volts during charging due to the .7 volt loss through the isolator. At 13.3 volts charging voltage it would take weeks to fully charge the genset battery.
>>
>> We have the same loss through the OEM isolator when charging from the engine driven alternator except the alternator voltage is increased (automatically) by .7 volts to 14.7 to make up for the loss through the isolator. If we had a way to make the PD unit put out 14.7 volts then an isolator could be used.
>>
>> Having a genset battery in the rear does indeed reduce or eliminate the loss through long wire from front to rear when starting the generator. In later years GMCs the house batteries were moved to the rear and used to start the Onan. If you have a front house battery(s) then you should probably keep the rear genset battery.
>> --
>> Ken Burton - N9KB
>> 76 Palm Beach
>> Hebron, Indiana
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