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Author Topic: Volts to start generator  (Read 491 times)

GaryA

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Volts to start generator
« on: October 28, 2017, 07:34:18 PM »
I have a Onan 4000 and was wondering what the minimum volts needed to crank it?  Do some dry camping and check battery voltage often but was wondering how low can I go and still crank?
Gary Alexander
2014 Thor 28z
Waxhaw, NC

WILDEBILL308

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Re: Volts to start generator
« Reply #1 on: October 28, 2017, 08:12:37 PM »
What does your owners manual say?
Bill
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Home base Fort Worth, Texas
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Roy M

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Re: Volts to start generator
« Reply #2 on: October 28, 2017, 08:13:30 PM »
It should crank fast enough to start in good tune on a warm day with 11 vdc.

Utclmjmpr

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Re: Volts to start generator
« Reply #3 on: October 28, 2017, 09:22:27 PM »
 You would NOT want to go that low before starting the gen,, never lower than 12 volts which is 50%.>>>Dan  (Unless you like buying batteries often) (does your Thor have a combiner switch??)
« Last Edit: October 28, 2017, 10:18:45 PM by utahclaimjumper »
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cgmartin

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Re: Volts to start generator
« Reply #4 on: October 28, 2017, 11:31:12 PM »
I would agree with Utahclaimjumper in not going below 12 volts. You don't want something like happened to me to occur. I also allowed my batteries to go down and when I cranked the generator, the batteries were not strong enough to allow the starter Bendix gear to turn the flywheel and became stuck and the Bendix would not retract. I was unable to free the flywheel by hand and had to remove the generator, unbolt the starter and free it.  It is probably a once in a thousand occurrence, but it can happen.

GaryA

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Re: Volts to start generator
« Reply #5 on: October 29, 2017, 07:02:39 AM »
Thanks for the info.  However, if you're dry camping and go one night with the heater (blower) on, your Voltage will drop to 11.3 or 11.4.  You shouldn't have to crank the Genny everyday?? 
Gary Alexander
2014 Thor 28z
Waxhaw, NC

Ernie n Tara

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Re: Volts to start generator
« Reply #6 on: October 29, 2017, 08:22:03 AM »
If you only have one battery, you can certainly expect to run the generator every day and are fortunate if the furnace runs all night.

Ernie
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GaryA

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Re: Volts to start generator
« Reply #7 on: October 29, 2017, 08:39:02 AM »
I have 2 size 27 deep cycle batteries run in parallel. After 1 night they are at 11.3
Gary Alexander
2014 Thor 28z
Waxhaw, NC

Ernie n Tara

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Re: Volts to start generator
« Reply #8 on: October 29, 2017, 09:40:31 AM »
Eleven point three is very dead. Are you using a panel meter or a real multimeter. I suspect the former or you are measuring with a heavy load. If that is an accuate messurement then you need new batteries

Ernie
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Gary RV_Wizard

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Re: Volts to start generator
« Reply #9 on: October 29, 2017, 09:41:42 AM »
Voltage varies with battery condition as well as state of charge, plus it measures different when there is an active load than when at rest. The "don't go below 12v" advice is based on a battery at rest (zero amp load). Even a tiny power draw can make that "at rest" 12v read as 11.5v.

Quote
After 1 night they are at 11.3

Doesn't tell us much without knowing what sort of load were operating. If the furnace ran most of the night, plus some lights in the early evening, you could well run a pair of Group 27's down to 11.3. Use of an inverter can also dain them quickly. On the other hand, those batteries could simply be weak and not taking much charge. How old are they, and what type? The typical marine/RV battery is probably good for maybe 3 years if treated kindly. Maybe only one year if not.
Gary
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Gary Brinck
Summers: Black Mountain, NC
Home: Ocala National Forest, FL

GaryA

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Re: Volts to start generator
« Reply #10 on: October 29, 2017, 10:02:25 AM »
Using a multimeter and batteries are 18 months old and well maintained. I am checking the voltage when nothing is working and maybe a light on.
Gary Alexander
2014 Thor 28z
Waxhaw, NC

Gary RV_Wizard

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Re: Volts to start generator
« Reply #11 on: October 29, 2017, 10:18:57 AM »
A pair of brand new Group 27's is good for about 210 AH and 11.3v says you have used about 90% of their capacity.  However, at 18 months old, with frequent discharges to the 11.3v level, I would guess those batteries are toast.  You probably have half [or less] of the original capacity.  Take them into a shop for a load test (auto parts stores do it free) and I'll bet they test very low.

Repeatedly discharging below around 12.0v is hard on the typical battery. True deep cycles like GC2 (golf cart) or a Trojan 12v like the 27TMX will hold up longer/better than the usual marine/RV hybrid type.

One winter of storage can also pretty much kill a battery. To maintain capacity, the charge must be kept up near 100% even though the RV is not in use. Failure to do that will severely reduce capacity for the next season.
« Last Edit: October 29, 2017, 10:23:42 AM by Gary RV_Wizard »
Gary
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Gary Brinck
Summers: Black Mountain, NC
Home: Ocala National Forest, FL

GaryA

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Re: Volts to start generator
« Reply #12 on: October 29, 2017, 10:23:55 AM »
I keep the motorhome plugged in while at home and about an hour after unplugging they read 12.3. Havi g a hard time thinking they're toast.
Gary Alexander
2014 Thor 28z
Waxhaw, NC

hedhunter9

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Re: Volts to start generator
« Reply #13 on: October 29, 2017, 10:36:42 AM »
Gary,
  Are they Marine/RV Deep Cycle or a "true" Deep Cycle.

12.3 volts with no load after an hours is low..  The batteries may not be toast,
But they are not in the best of condition.

Bob
Bob n Sharon
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Northern Indiana

Gary RV_Wizard

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Re: Volts to start generator
« Reply #14 on: October 29, 2017, 10:38:21 AM »
12.3v is no more than 70% charge, so you are starting out at 70% and going down from there.

To me, that says they have been used fairly hard, perhaps repeatedly deep discharged, or overcharged during recovery, or both.  Your situation is not unusual.
« Last Edit: October 29, 2017, 10:40:53 AM by Gary RV_Wizard »
Gary
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Gary Brinck
Summers: Black Mountain, NC
Home: Ocala National Forest, FL

GaryA

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Re: Volts to start generator
« Reply #15 on: November 02, 2017, 06:58:10 PM »
But....thanks for the replies but 12V batteries are not going to stay at the full 12 volts after some use.  How low is average after a day or 2 being used.  I know it depends on whats being used but I'm under the impression, based on comments, thAt you guys think a battery that shows 11.4V is a bad battery.  Please help.
Gary Alexander
2014 Thor 28z
Waxhaw, NC

Sun2Retire

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Re: Volts to start generator
« Reply #16 on: November 02, 2017, 07:13:41 PM »
Attached is a battery state of charge chart (I did not create this chart). 11.4V represents a completely dead battery. It may not have been "bad", but discharge to this level is likely to cause damage.
Scott
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GaryA

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Re: Volts to start generator
« Reply #17 on: November 02, 2017, 07:38:03 PM »
Thanks, eye opening. When I show 11.4 on voltmeter I can still bring in the slide or start the genny.
Gary Alexander
2014 Thor 28z
Waxhaw, NC

WILDEBILL308

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Re: Volts to start generator
« Reply #18 on: November 02, 2017, 07:48:19 PM »
Discharging to 50% is a good way to shorten a batteries life.
Bill
2003 Bounder 38N
300 HP 5.9 Cummins
Allison 3000MH Trans.
Towing 2014 Honda CRV
Home base Fort Worth, Texas
A man who carries a cat by the tail learns something he can learn in no other way.
-Mark Twain-

youracman

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Re: Volts to start generator
« Reply #19 on: November 02, 2017, 10:27:15 PM »
To your original post, Gary-

In my Onan service manual it states: "Measure battery voltage at genset while attempting to start or prime from local or remote switch: recharge or replace battery if voltage drops below 9 VDC ......................."

I measured a 1v drop at the battery connection to the Onan solenoid when I crank my MicroQuiet 4000 (Spec K) ...... from 12.5v to 11.5v.  (Maybe another data-point of interest: The steady-state starter current I measured was 57.5 amps and the momentary inrush current could be 4X that from what I read.)  The 9v mentioned in the manual would indicate that the open ckt battery voltage would have to be at least 10 v.   But...........at 10v, the battery state of charge would likely be zero ......... hmmmm.  So much for the arithmetic.   :)

Another interesting line in the manual: "Cranking voltage dips below 6 VDC: microprocessor aborts start attempt."

I don't boondock (and there may be good reasons not to run the big engine for a minute or two)  but if your rig is like most it might be prudent to start the big engine to get 14v or so to the Onan solenoid; then shut off the big engine after the Onan starts.  Dunno.  I believe the Onan would love it.........I know mine spins noticeably faster when the Ford is running; and it starts quicker.

Just my $.02

Safe travels...............................
Ed Sievers/Denver, CO
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Lou Schneider

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Re: Volts to start generator
« Reply #20 on: November 03, 2017, 03:52:12 AM »

I measured a 1v drop at the battery connection to the Onan solenoid when I crank my MicroQuiet 4000 (Spec K) ...... from 12.5v to 11.5v.  (Maybe another data-point of interest: The steady-state starter current I measured was 57.5 amps and the momentary inrush current could be 4X that from what I read.)  The 9v mentioned in the manual would indicate that the open ckt battery voltage would have to be at least 10 v.   But...........at 10v, the battery state of charge would likely be zero ......... hmmmm.  So much for the arithmetic.   :)

No, to get 9 volts at the starter motor means the battery voltage has to be >10 volts while delivering 57.5 amps.  That's very different than the battery being at 10 volts open circuit.

GaryA

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Re: Volts to start generator
« Reply #21 on: November 03, 2017, 02:51:37 PM »
To your original post, Gary-

In my Onan service manual it states: "Measure battery voltage at genset while attempting to start or prime from local or remote switch: recharge or replace battery if voltage drops below 9 VDC ......................."

I measured a 1v drop at the battery connection to the Onan solenoid when I crank my MicroQuiet 4000 (Spec K) ...... from 12.5v to 11.5v.  (Maybe another data-point of interest: The steady-state starter current I measured was 57.5 amps and the momentary inrush current could be 4X that from what I read.)  The 9v mentioned in the manual would indicate that the open ckt battery voltage would have to be at least 10 v.   But...........at 10v, the battery state of charge would likely be zero ......... hmmmm.  So much for the arithmetic.   :)

Another interesting line in the manual: "Cranking voltage dips below 6 VDC: microprocessor aborts start attempt."

I don't boondock (and there may be good reasons not to run the big engine for a minute or two)  but if your rig is like most it might be prudent to start the big engine to get 14v or so to the Onan solenoid; then shut off the big engine after the Onan starts.  Dunno.  I believe the Onan would love it.........I know mine spins noticeably faster when the Ford is running; and it starts quicker.

Just my $.02

Safe travels...............................

Thjank you!
Gary Alexander
2014 Thor 28z
Waxhaw, NC

Charlie 5320

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Re: Volts to start generator
« Reply #22 on: November 04, 2017, 11:18:02 AM »
Thanks, eye opening. When I show 11.4 on voltmeter I can still bring in the slide or start the genny.

You may be can, but when the voltage is low the amp draw goes up causing extra heat. Not good. You need to check the output from your converter. I just replaced a Magnetec converter in my coach that would never fully charge my batteries. It only put out 12.59 volts even after using the batteries to move the slide in and out. I replace the converter with a PD9260 and it took 24 hours to get my batteries fully charged.

Those slide motors aren't cheap, and I do every thing I can to make sure they are getting the correct voltage.
« Last Edit: November 04, 2017, 11:20:16 AM by Charlie 5320 »
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Utclmjmpr

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Re: Volts to start generator
« Reply #23 on: November 04, 2017, 11:45:16 AM »
 Like Charlie above states,,when voltage drops, amperage goes up and creates big heat!..This is what burns up expensive motors ,relays, and other electrical parts ,,not a good practice.>>>Dan
38' American Tradition 38TT/330 turbo Cummins
Jeep liberty 4 down
72 VW Baja 4 down
Cedar City, Utah
USAF vet. 59-63
The difference between intelligence & stupidity is: intelligence has it's limits
      Albert Einstein.
President Western GM Coach chapter FMCA

 

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