Question about Onan Generator

[Son_of_Norway]

Something I have never understood about generators (I have an Onan 6.5 Emerald III.) A 12-volt DC battery is used to start the generator, which then produces 120V AC. The battery supplies the energy needed to run the generator, right? So, while the generator is running, does it send a 12-volt DC current back to the battery to keep it charged, or does the generator just continue to drain the battery until the battery no longer has enough voltage to keep it running?

So if the generator drains the battery, then there must be a converter in the circuit to keep the battery charged, just like the alternator on a car engine. OK, I'm no electrical engineer, I just want to be sure that I understand this correctly.

Thanks for your tolerance on this post.

[time2roll]

Son of Norway wrote:
Something I have never understood about generators (I have an Onan 6.5 Emerald III.) A 12-volt DC battery is used to start the generator, which then produces 120V AC. The battery supplies the energy needed to run the generator, right? So, while the generator is running, does it send a 12-volt DC current back to the battery to keep it charged, or does the generator just continue to drain the battery until the battery no longer has enough voltage to keep it running?

So if the generator drains the battery, then there must be a converter in the circuit to keep the battery charged, just like the alternator on a car engine. OK, I'm no electrical engineer, I just want to be sure that I understand this correctly.

Thanks for your tolerance on this post.

Put your meter on the battery terminals. 13.6+ volts and you are charging. 12.5 volts or less and you are not charging. Post your measurement and you will be an honorary electrical engineer.

[deltabravo]

Son of Norway wrote:
The battery supplies the energy needed to run the generator, right?

No, it only supplies power to "start" the generator.

[Kpackpackkelley]

I think it’s better for the converter to charge your batteries because if the generator has away to charge they will usually over charge your battery if you run them a long time.

[RLS7201]

joebedford wrote:
If I'm on shore power, I also have my city water connection hooked up so it doesn't make sense for the generator to power the hose.

And that folks is why we need more mental health care facilities.

Richard

[joebedford]

wa8yxm wrote:
What they do is power the hose SAME exactly as if you were on shore power so the converter recharges the battery

If I'm on shore power, I also have my city water connection hooked up so it doesn't make sense for the generator to power the hose.

[wa8yxm]

Onan makes many generators SOME do in face recharge the battery but the ones marked RV do not. What they do is power the hose SAME exactly as if you were on shore power so the converter recharges the battery..... I might add it also provides power to the Onan's fuel pump. The rest of the Onan is self powered.

[bounder39zman]

the Emerald III had a small (1 amp) charging system, using a stator winding labeled the "B" winding. this winding operated the electric choke heater on older models, and provided enough 12v, using a resistor and diode on control board for fuel pump and ignition system, and controls. Newer (last 20 years or so) generators relied on RV converter to keep batteries from discharging. Commercial versions all have 12v charging systems. BTW...NEVER a good idea to disconnect battery from generator when running. Like a car alternator, you risk shocking and damaging control board components.

[DrewE]

drsteve wrote:

Son of Norway wrote:
The battery supplies the energy needed to run the generator, right? So, while the generator is running, does it send a 12-volt DC current back to the battery to keep it charged, or does the generator just continue to drain the battery until the battery no longer has enough voltage to keep it running?

No. The battery supplies the energy needed to start the generator, not to run it. Once the generator is running, there is no drain on the battery.

Built-in RV generators do typically need 12V power when running, not just when starting. If the generator is getting that power from a battery that is not being otherwise recharged, it will be a drain on that battery. Generally things are set up to the converter, powered by the generator, is powering the 12V system including the generator's control electronics and also charging the battery, but without that the generator very definitely will be draining a battery in most RVs. (The 12V power is needed for the generator's fuel pump, control electronics, etc.)

There are of course different designs of generators, and I'm sure there probably are some RV installations that do not require external 12V power once running, as well as some that have a 12V charge circuit built into the generator. To my knowledge, they're distinctly in the minority; most are set up as described above.

[Chum_lee]

mchero wrote:
My 93 Pace Arrow Diesel had a 3 cylinder Kubota generator that had a small alternator.

In addition to being used in RV's, some generators are designed to work as "stand alone" power supplies. IF/when that is the case, the manufacturer generally provides some way of recharging the starting battery if an electric start is provided. It's not necessary if your stand alone genny uses a pull start as its sole means of starting. Many motorcycles use an alternator, which also functions as a starter to save weight

Chum lee

[drsteve]

Son of Norway wrote:
The battery supplies the energy needed to run the generator, right? So, while the generator is running, does it send a 12-volt DC current back to the battery to keep it charged, or does the generator just continue to drain the battery until the battery no longer has enough voltage to keep it running?

No. The battery supplies the energy needed to start the generator, not to run it. Once the generator is running, there is no drain on the battery.

[mchero]

My 93 Pace Arrow Diesel had a 3 cylinder Kubota generator that had a small alternator.

[maillemaker]

As others have said, the generator will automatically charge the house batteries through the battery charger built into the converter when running, but generally, it will not charge the chassis battery unless the "AUX BAT" switch is pressed. (not recommended for long term charging)

My MOM switch is powered by the house batteries, but AUX BAT is powered by the engine battery so the key must be in RUN for the batteries to be ganged.

This is so you cannot permanently gang the house batteries to the engine batteries while the engine is off - otherwise you could accidentally drain both your house and engine batteries and be stuck.

My Onan 4BGE will also shut down if the engine battery is disconnected (mine starts from the engine battery). But while running the inverter charges the house batteries.

Strange that it would actually run off of the engine battery but not charge it. I did not know that.

Steve

[wopachop]

DrewE wrote:


In general, there's little reason to ever have the disconnect switch disconnected that I can work out; the main one is perhaps when doing maintenance on the wiring or batteries.

For me it's when on shore power and dont like my wfco doing the charging/maintaining.

I had thought the battery was just to start the genny. That was fun to learn.

Just did a quick test on my 5500.
Prime button pulled 1.2amps
Starting was over 100a.
Running it pulled 2.5a and steadily dropped to 1.54a where it seemed to hold.

[Dusty_R]

If it was just the fuel pump that lost power, the generator engine would continue to run until the carb bowl ran empty.

Dusty