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Author Topic: Where to center tap for generator start power  (Read 1909 times)
Tenor
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« on: July 26, 2012, 10:18:16 AM »

Where should I pick up 12V for starting my generator?  This is also where I pull 12V for the electric generator fan, so there is a pretty good draw.  This generator only trickle charges and does not have it's own alternator.  I have 4 golf cart batteries.  Currently, I pull 12V from the "second" set in the series.  They usually stay lower than the "first" set which is receiving the charge from the inverter.  Would moving that drain cause the batteries to overcharge?

Thanks!
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Glenn Williams
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« Reply #1 on: July 26, 2012, 10:26:35 AM »

Are you pulling 12 volts from a 24 volt bank?
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Tenor
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« Reply #2 on: July 26, 2012, 10:30:09 AM »

Sorry Lee! Yes, pulling 12V from 24V bank.
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Glenn Williams
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« Reply #3 on: July 26, 2012, 10:43:38 AM »

I would invest in a Vanner to keep the two sides balanced. In fact, I did buy one for my house batteries.
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« Reply #4 on: July 26, 2012, 11:13:37 AM »

I do have a Vanner.  However, the 12V draw is not coming through the Vanner.  I could put another 12 batt between the Vanner and the house batts.

Glenn
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Glenn Williams
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« Reply #5 on: July 26, 2012, 12:26:34 PM »

How do you have the Vanner wired into the bank?
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Tenor
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« Reply #6 on: July 26, 2012, 12:48:56 PM »

Batt 24V + to Vanner's 24V+ terminal.  Batt 24V- to Vanner's 24V- terminal.  12V+output from Vanner to 12V accessories.

Glenn
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Glenn Williams
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« Reply #7 on: July 26, 2012, 12:51:54 PM »

Must be a different Vanner than mine. The Vanner I have has Grd, 12 volt and 24 volt.
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Sean
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« Reply #8 on: July 26, 2012, 03:47:39 PM »

Where should I pick up 12V for starting my generator?  This is also where I pull 12V for the electric generator fan, so there is a pretty good draw.  This generator only trickle charges and does not have it's own alternator.


If you want to run a 12v fan, you don't want to "center-tap" anything, unless you have an equalizer on it.   That's a recipe for destroying your batteries.  I recommend you add a separate 12v system for this purpose -- either add a 12v alternator to the genny's prime mover, or else plug a 12v power supply/charger into the genny's AC output to do it.  Then use a separate 12v battery to start the genny and buffer the fan current.

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I have 4 golf cart batteries.  Currently, I pull 12V from the "second" set in the series.  They usually stay lower than the "first" set which is receiving the charge from the inverter.  Would moving that drain cause the batteries to overcharge?


If you are "pulling 12v" from a 24v bank, the bank should be wired as a series of parallel 12v banks, not the other way around.  Again, doing otherwise will destroy the batteries.

-Sean
http://OurOdyssey.BlogSpot.com
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« Reply #9 on: July 26, 2012, 05:55:16 PM »

Is that generator a onan air cooled unit with the starting built into the head ?
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« Reply #10 on: July 26, 2012, 06:38:11 PM »

Sean,
The batteries are as you describe.  What makes things slightly different is that they are in the buses original trays for the 8D's.  So, the top tray is the negative end or "second set" of 6V batts in series for 12V tied with bus bars down to the bottom tray in series with the "first set" or positive end set of 2 6V batteries in series for the other 12V.  So, I wasn't sure where based on the wiring and bus bars to best tie in.

Would it be better to put in a 12V battery supplied by the12V output of my Vanner (tied to the house batteries) to start the genset and run the 12V fan?  At this time, the option of adding an alternator to the genset is not an option.

Luvrbus, the genset is a Kohler 7.5a27 converted marine unit.  Like the Onan, it has the starter built into the head.
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Glenn Williams
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« Reply #11 on: July 26, 2012, 07:30:09 PM »

Glen, I don't think you will get enough amps from a vanner to start the generator a Onan takes a bunch of amps to start the head to spin the way I have saw those hooked up on 24v systems was with 12v battery and a charger

One person I know has a old style converter with a built in charger he doesn't use the ac side for nothing else works for him and he had the old converter.

Don't you need 12v to run the fuel pump and the board also if you change the pump to 24v it causes another hickup
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« Reply #12 on: July 26, 2012, 07:42:35 PM »

Luvrbus, you are right on several issues here.  I do run the fuel pump and control board from the same source.   My Vanner is a 50A unit at 12.8V. 

I just realized that I am running it as a converter, not an equalizer.  Looking at the wiring diagram, it looks as if I can continue to run the Vanner as converter/charger to an additional 12V battery for the generator start/run systems and my house 12V needs.  Currently, I am feeding the house 12V needs directly from the Vanner. 

Glenn
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Glenn Williams
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« Reply #13 on: July 26, 2012, 09:26:09 PM »

FWIW...

I'd wire that Vanner up to do its job as an equalizer, and then pick up all your 12 volt loads off the same place you attach the 12 volt Vanner lead.

You want both a 24 volt and a 12 volt battery cut off to isolate both kinds of loads from the battery set.

Either seperate or a combined switch, but switch 'em both.

Consider the Vanner a part of the battery bank, it stays "inside" from the cut off switches.

My Vanner has resided "inside" with no noticeable effect for long enough.

Your mileage may vary, batteries must be well maintained, charged with some regularity during storage, I'm no engineer, use my advice at your own peril, hoist a cold one in my absence at Clio.

happy coaching!
buswarrior
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« Reply #14 on: July 27, 2012, 05:51:28 AM »

BW,
I have the Vanner "inside" the system as well.  When not in use, the 24V house bank is disconnected from the chassis the Vanner stays attached, but I disconnect the 12V output to those loads.  After a night of sleep, and re reading your post, I should continue to center tap the house bank for the genset, but wire in the Vanner as an equalizer to balance that load?  Seems better than adding another battery.

I'll be glad to hoist several cold ones in your absence!

Glenn
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Glenn Williams
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« Reply #15 on: July 27, 2012, 06:23:11 AM »

These guys may know the best way but with a control board costing 200+ I would go with the battery all the Vanners I been around do spike from time to time blowing head lights JMO
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« Reply #16 on: July 27, 2012, 07:43:41 AM »

First of all, if the generator has an alternator, why not just "isolate" the system with its own 12V battery.  That way you can start the generator if the house battery bank gets discharged.

Next, I don't know much about Vanners, but if it is rated at 50A, how would it be able to furnish the current for the generator starter?

The suggestion of having the Vanner "charge" a 12V battery that is used for the generator would get you close to isolating the generator and would give you the ability to start it in the event of a a house battery problem.  That said, you don't need to go that route if the generator has an alternator.

Jim
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Jim Shepherd
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« Reply #17 on: July 27, 2012, 07:55:31 AM »

 Jim,
The alternator does not have it's own alternator.  It uses the generator head to supply a low current to charge the battery back up.  It is a converted marine unit, so an electric cooling fan became necessary since it no longer has a lake to keep it cool.

Luvrbus,
If I understood BW right, and my Vanner diagram, you still center tap the 24V batteries for the generator start and control and fuel pump.  The Vanner just balances the load between the batteries, it does not directly supply the cranking amps.  The only load on the Vanner are interior lights, fans refrigerator control and a few other small items.  Never are all used at the same time.

Glenn
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Glenn Williams
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Sean
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« Reply #18 on: July 27, 2012, 09:01:01 AM »

...
If I understood BW right, and my Vanner diagram, you still center tap the 24V batteries for the generator start and control and fuel pump.  The Vanner just balances the load between the batteries, it does not directly supply the cranking amps.
...

This is not entirely correct.  If you put a large load on the 12v center tap, such as attempting to start an engine, the Vanner will do its level best to supply as much current as it can.  If the batteries themselves are not up to the task, this can overstress the Vanner.

Moreover, the amount of lower-bank depletion caused by starting will mean the Vanner has that much more work to do over the long haul to equalize the system.  Lastly, the Vanner can never make up for the stress difference between starting and non-starting loads, so eventually the lower half will become permanently out of balance with the upper half, which will ultimately result in the Vanner working full-time and constantly draining the entire bank.

Perhaps I was not forceful enough in my original post:  I strongly recommend that you install a completely separate 12v battery to start your generator.  Get a small, inexpensive 12v battery charger to recharge this battery from the 120vac generator output.  Together these items should set you back less than a C-note.  I would also suggest you use this system to run your 12v cooling fan, although, frankly, you would be better off all around by changing to a 120vac cooling fan.

-Sean
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« Reply #19 on: July 27, 2012, 11:18:23 AM »

Thanks for th clarification Sean!  I do have a 120v fan on the system, but I had to add the 12v fan in addition to keep the generator at 160.  It occurs tome that I might be able to delete the fan with some improved shrouding. I'll see if there is a way to get a alternator onto this generator.
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Glenn Williams
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« Reply #20 on: July 30, 2012, 05:54:10 PM »

Tenor,

It does have an alternator although a very small one made just to charge the genset batt.

If you connect the genset start circuit into the bus engine elect system it will confuse the bus engine voltage regulator'

I had this problem in a 12v system and just added a small separate batt for the genset only. My bus alt went nuts until I did this.
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« Reply #21 on: July 30, 2012, 07:00:28 PM »

Been working on making all of the changes! 

I had a 100A 12V alternator and Regulator from my 73 Winnebago (the parts are actually much newer) laying around, so I took the day and adapted it to run off of the generator.  JUST got it finished.  Charges like mad.  No more center tap.  It has it's own start battery.  Later I'll run a light to the dash to let me know the genset is running.

Thanks for all the help!

Glenn
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Glenn Williams
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« Reply #22 on: July 31, 2012, 04:26:16 AM »

When I was running my truck cross country with the Onan 6.5 commercial, it too had only a 5amp battery charger built into it.  I had a single 8D deep cycle for the refer mainly, and just used a 20amp smart battery charger to keep the 8D charged.  Also had an ignition operated solenoid that charged the deep cycle going down the road.  Good Luck, TomC
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« Reply #23 on: July 31, 2012, 01:40:53 PM »

A 100A 12V alternator is way overkill for a normal genset batt. I used a lawn mower batt for my 5.5 Onan and the built in genset alt kept it well charged since this batt gets very little use. The alt was built into the genset flywheel.

In case of any start problems I had it connected by a switch to the bus 12v engine batts which was open otherwise. In your case you could connect it to the center tap.

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« Reply #24 on: August 02, 2012, 06:58:17 PM »

An update to this post.  Earlier, I mentioned that my Vanner was wired to the 24VPos, the 24VNeg and the 12.8V output went directly to the loads.  That is how the unit is diagrammed on it's own case.  I had contacted Vanner with the model numbers for an updated schematic.  The one they sent was not exactly for my unit.  Turns out, this unit is ONLY a CONVERTER!  I found that once I sent a second wire from the 12.8V Output to the lower battery, it would drain the upper battery!

So, when acquiring a Vanner, READ the label!  The converters do not work as Equalizers.  I happened to have a second unit that is an actual Equalizer and I have it installed as discussed earlier.  Works like a charm.

Glenn
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Glenn Williams
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« Reply #25 on: August 03, 2012, 04:31:51 PM »

Excellent report.

Terminology is king!

happy coaching!
buswarrior
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