GaryA
Well-known member
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?
Volts to start generator
- Thread starter GaryA
- Start date
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WILDEBILL308
Well-known member
What does your owners manual say?
Bill
Bill
Roy M
Well-known member
It should crank fast enough to start in good tune on a warm day with 11 vdc.
Utclmjmpr
Well-known member
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??)
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
Well-known member
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??
Ernie n Tara
Well-known member
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
Ernie
GaryA
Well-known member
I have 2 size 27 deep cycle batteries run in parallel. After 1 night they are at 11.3
Ernie n Tara
Well-known member
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
Ernie
Gary RV_Wizard
Site Team
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.
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.
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.
GaryA
Well-known member
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 RV_Wizard
Site Team
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.
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.
GaryA
Well-known member
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.
hedhunter9
Well-known member
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
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
Gary RV_Wizard
Site Team
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.
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.
GaryA
Well-known member
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.
Back2PA
Well-known member
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GaryA
Well-known member
Thanks, eye opening. When I show 11.4 on voltmeter I can still bring in the slide or start the genny.
WILDEBILL308
Well-known member
Discharging to 50% is a good way to shorten a batteries life.
Bill
Bill
youracman
Well-known member
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...............................
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...............................
