Where to center tap for generator start power

Tenor · 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!

Lee Bradley · July 26, 2012, 10:26:35 AM

Are you pulling 12 volts from a 24 volt bank?

Tenor · July 26, 2012, 10:30:09 AM

Sorry Lee! Yes, pulling 12V from 24V bank.

Lee Bradley · 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.

Tenor · 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

Lee Bradley · July 26, 2012, 12:26:34 PM

How do you have the Vanner wired into the bank?

Tenor · 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

Lee Bradley · 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.

Sean · July 26, 2012, 03:47:39 PM

Quote from: Tenor 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.

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.

Quote
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

luvrbus · July 26, 2012, 05:55:16 PM

Is that generator a onan air cooled unit with the starting built into the head ?

Tenor · 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.

luvrbus · 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

Tenor · 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

buswarrior · 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

Tenor · 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