Need help figuring out Onan generator output.

[modelaratrod]

I recently picked up and Onan commercial EFI generator with a PTO that was on the outside of a piece of equipment. Therefore, the labels are all gone or unreadable.
I have called Cummins and given them every number I could find on it and they cannot tell me what it is.
It does have a Subaru 22 horsepower engine on it, a 30 amp breaker, and it puts out two legs of 120 vac.
The only date I can find on it is on the muffler and it shows 2012.
I'm looking at wiring it up with some 10 AWG that will be rated for the 30 amps but I'm not sure how many watts it can actually output.

 

[modelaratrod]

Pic

 

[modelaratrod]

 

[modelaratrod]

 

[BillK]

No numbers stamped anywhere on the actual generator part ?

 

[modelaratrod]

No numbers stamped anywhere on the actual generator part ?

Not that I can find.

 

[LopezBart]

Typical output of a 3600 rpm generator in KW is 1/2 the hp rating of the (gas) engine; diesels a bit more sometimes. At 120v that would be 91 amps total so something is off a bit. Today's Onan commercial units (7000 EFI series) appear to run at reduced RPM (2880) for reduced noise; that would derate the engine, of course. Those generators are rated at 2 x 30A (58.3 amps total) 120V for RV use which seems to match what you're seeing. https://www.cummins.com/generators/onan-qg-7000-efi

 

[modelaratrod]

It looks like this but I've seen the 5k that also looks the same and has the same single 30 amp breaker.

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[modelaratrod]

It has two 120 hot legs a neutral and a ground with one 30 amp breaker that seems to be a double breaker on the under side but with a single poll on the front?
I'm putting this in an rv conversion and don't wanna try to pull 7k watts if it's only a 5 k.

 

[LopezBart]

If you look at the spec sheets, you'll see that the different models run at different RPM:
5500 runs at 2400 rpm, the 7000 at 2880 rpm. If it runs, I'd use that to tell 'em apart.

 

[modelaratrod]

If you look at the spec sheets, you'll see that the different models run at different RPM:
5500 runs at 2400 rpm, the 7000 at 2880 rpm. If it runs, I'd use that to tell 'em apart.

How would you know what the rpm it's running at ?

 

[modelaratrod]

With the 30 amp 120/240 breaker would it be safe to wire it with a 25' or less 10/4 sjoow cord whether it's a 5500 or 7k generator?

 

[micromind]

If the breaker is 2 pole (two breakers with their handles tied together) then it is very likely 5KW (5,000 Watts) 120/240. Each breaker will have 120 volts to neutral/ground and 240 between both of them. Very common for a generator this size.

22HP is way more than enough for this unit, usually 10HP is enough.

If the generator is connected directly to the breaker ( no electronic stuff in between) and is 60HZ, then the only possible RPMs are 3600, 1800, 1200, 900 and lower. The RPM it runs at is dependent on the number of pole pairs it is wound with. This cannot be changed.

RPM and HZ are directly related, if the RPM is slightly high, the HZ will also be slightly higher, same for lower.

If it's one of those newer inverter generators then RPM doesn't have any effect on HZ as it is set electronically.

 

[micromind]

With the 30 amp 120/240 breaker would it be safe to wire it with a 25' or less 10/4 sjoow cord whether it's a 5500 or 7k generator?

Yes, #10 is good for up to 30 amps and the breaker is 30 amps. The size of the generator doesn't matter, current is limited to 30 amps by the breaker.

With #10 at 120/240 you could run more than 100'.

 

[LopezBart]

How would you know what the rpm it's running at ?

I use one of those cheap inductive tachs from Amazon - less than $20.

 

[LopezBart]

Looking at service instructions, it appears these units have a drive belt; the engine and generator run at different rpms.

 

[American Locomotive]

It's likely either an Onan 7.0 HGJAA or 5.5 HGJAA. They use a belt-drive generator end, which allows the engine to run at different speeds. As mentioned, the 5.5 runs at 2400 RPM, the 7.0 runs at 2880 RPM. Easiest way would be to start it, and get a little cheap small engine tach that connects to a spark plug wire.

Strangely enough, none of the Cummins/Onan literature mentions that they're belt drive.

 

[nadogail]

It's likely either an Onan 7.0 HGJAA or 5.5 HGJAA. They use a belt-drive generator end, which allows the engine to run at different speeds. As mentioned, the 5.5 runs at 2400 RPM, the 7.0 runs at 2880 RPM. Easiest way would be to start it, and get a little cheap small engine tach that connects to a spark plug wire.

Strangely enough, none of the Cummins/Onan literature mentions that they're belt drive.

Why not connect a frequency meter and adjust your throttle to get the frequency you want?

 

[modelaratrod]

Why not connect a frequency meter and adjust your throttle to get the frequency you want?

We're trying to determine if it's a 5.5 or 7kw.

 

[nadogail]

We're trying to determine if it's a 5.5 or 7kw.

Apply the 2 Horse Power per KW guesstimates

 

[Mr onetwo]

Go over to SmoKstak and they will help you out...much, much more knowledge over there. https://www.smokstak.com/forum/forums/onan-generators.1/

 

[American Locomotive]

Apply the 2 Horse Power per KW guesstimates

They use the same engine for both models.

 

[modelaratrod]

They use the same engine for both models.

This is the issue.

 

[dcg9381]

They use the same engine for both models.

This is the issue. (It does have a Subaru 22 horsepower engine on it, a 30 amp breaker, and it puts out two legs of 120 vac.)

22hp is a lot. A single 30A double pole breaker or single pole? You said it has 2 legs of 120V. Assuming each leg has a 30A breaker, you're at about 5760 watts - which is consistent with 10ga wire.

 

[modelaratrod]

It has a single pole breaker that both legs of 120 are ran thru, so it's a double pole on the back of the breaker single on the front.

 

[The Cobbler]

I've watched several James Condon videos on You Tube , he does a lot of generator repairs & diagnosing. he recently aquired a load tester that he can adjust the load , for testing . prior to that he used electric space heaters . while watching the frequency, voltage etc he pushes them to the limit to see how they are performing. maybe you could run something similar?

 

[micromind]

If you can measure the pulley diameters, it's pretty easy to calculate.

The generator end will be either 1800 or 3600 RPM. If the engine pulley is smaller than the generator, it'll be 1800. If it's larger, it's 3600.

 

[TheEquineFencer]

Here's my take on it. 30A x 240V = 7200 Watts , it's probably a 7000W 120/240V generator. "Assuming you have a double pole breaker," both poles are tied/locked together. Check the voltage between the two hot legs L-L, (Line to Line), then check Line to Neutral, (L-N) on both wires to verify.

If you want to know what it'll actually do, put a load, resistive, like incandescent light bulbs or hot water elements or a combination submerged in water, (not the bulbs obviously) at close to the ratings needed and use a clamp on Amp meter and test it. 120-130V 100W bulbs are fairly accurate. When it starts to droop below 60Hz, do the math, Volts times Amps equals Watts. If it only pulls 25A @ 240V, you have a 7000W generator that'll only pull 6000 watts, it happens, check the valve adjustment and such then. If it drops below rated, the generator will cut off for under Hz (frequency) most likely.

The breakers are designed to protect the wiring, not the equipment. Personally, I'd use a wire at least one gauge size above the breaker rating on the generator. That'll "probably" compensate for voltage drop to whatever you're powering as long as long as you stay with in specs for the run of the wire. Google "voltage drop calculators."

 

[Metal-Marc]

120-130V 100W bulbs are fairly accurate.

Accurate and rare. Good luck finding these.

 

[modelaratrod]

I picked up a spark plug wire tach and it's showing a steady 2400 rpm so that would be consistent with the 5.5k model.

 

[u3b3rg33k]

It has a single pole breaker that both legs of 120 are ran thru, so it's a double pole on the back of the breaker single on the front.

one handle does not a single pole breaker make. "internal tie" double pole is probably the name you're looking for.

 

[rd65]

You will find that Onan parts are STUPID expensive, at least the ones I have looked up are. We just sent a P6000E to surplus/auction because it needed a carb. It was left with water in the aluminum float bowl, corrosion led to a hole in the bowl. Our welder made a sad attempt to weld it, failed big time. New carb from Cummins $730.00. A carb for the same size Honda engine is under $100.