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Cummins Onan 6.5 NHDFB 1M Commercial 6500 home backup power project: Advice Welcome

Warwagon

Subscriber
Last Subscription Date
05/12/2020
Got bit by the green disease bad. This will be my 3rd Onan and 2nd 1800 RPM genset. More exactly the 1800 RPM is hard to get over now that I have held a conversation next to one running.

An 1800 RPM Onan Commercial 6500W genset "project" showed up on the ads. Single Phase 240V with the PMG for battery charging. Missing the fuel pump and hour meter reads around 2582 hours (stopped at those hours as it turns out). Looks like it was fed off a remote fuel pump.

Ruin the rear floormat getting it home with wiping the oil off the bottom. Change oil. I order a slip ring cleaning tool. Brush ohm readings are high, open, and high as I turn and stop the engine by hand. When the tool arrives I use the starter to clean the slip rings with everything else disconnected. Remove and clean brushes as well. Advice on here saved the regulator from possible instant death. Ohms were in spec when done.

It fires up using a boat primer to put fuel in the carb. It immediately shuts down after start switch is released. UH-HO! :eek:

Well, lets see how it runs with the switch pressed in. It is slowly speeding up by ear. The throttle shaft is pinned on the idle screw when running: it can't slow the engine down. So I turn the idle screw down. Fire it up again and the AC light comes on and it stays running. :D Relief it's not a popped regulator. Run it awhile using the boat primer and voltages look ok. Will take a 3000W heater load just fine.

Hour meter is not working. :shrug:

Order a Box-O-Parts. Have a weatherproof enclosure built by a welder. Pics for your enjoyment.

Now I have a 120V 5HP air compressor that a 3800W Homelite (and the other 4KW Onan) will start. I found that one winding of the 120v on the Onan 6500W will not start it, but the other 120v winding will. The 240V plug was burned badly when I got the set. Replaced the plug. Checked connections in the control box. Swapped the black and black with yellow stripe on the breakers to rule out a bad connection in the breaker. It follows the winding.

Compressor will spin over a few times slowly and then slow back down and stop. Starts fine on other winding.

(I did turn the engine RPM up to see if it would make a difference and may need to set it back to spec. Turned up governor sensitivity as well.)

Voltages (I get ~240 across the black and black yellow.)

Black to neutral:
124V No load
123V 1500W heater
120V Compressor running and 1500W heater (83V noted while compressor starting with heater on.)

Black-yellow to neutral
124V No load
116V 1500W heater
64V Compressor not starting and stalled (Heater off. Won't start with heater load on either.)

Am I missing a bad connection somewhere or is only one leg of the 240 regulated by the voltage regulator?

The off the shelf 240 to 120v plug uses the black-yellow hot to neutral for 120v. I built a plug that uses the other.
 

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Billy J Shafer

Subscriber
Age
69
Last Subscription Date
09/03/2019
Sounds like it may have a damaged winding. Did they only use one side of the generator.
 

Kevin K

Subscriber
Last Subscription Date
07/12/2019
As Eric said, only one leg is regulated, but check for bad connections. Pull the control board. Behind it is a connection point labeled TB1 on the diagram. Check all the push on spade connectors as they can become loose. You can also check for voltage drop across the breakers while pulling at least a 1500 watt load.
 

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Eric.S

Registered
Now I have a 120V 5HP air compressor that a 3800W Homelite (and the other 4KW Onan) will start. I found that one winding of the 120v on the Onan 6500W will not start it, but the other 120v winding will.
Sorry to say, this is MY opinion
That 120V 5HP air compressor is perfect to ruin small generators, 5HP is about 3,7kW, starting current is 5-7 x running current.
6.5NH in 120/240 configuration can produce 3250W/leg at PF 1 !!

Eric
 

DMeed

Subscriber
Last Subscription Date
07/12/2019
As Eric said, only one leg is regulated,
Just a thought -
-if this is a regulated generator
-and all the load is on the unregulated leg
-could there not be enough power being fed to the field for full load when the other leg is unloaded and calling for no field curent?

I would try loading up BOTH legs and see what it does. (ie - put a 1500 watt heater on the other 120v and then see if the compressor will start.

(People who know generators better than I should weigh in on this...)

David

PS - Like the design of your enclosure!
 

Kevin K

Subscriber
Last Subscription Date
07/12/2019
I missed the part about the 5HP 120 volt compressor. That's pushing it using only one winding of a 6500 watt generator. If you need to run the compressor, I would suggest you re-phase the generator stator windings to produce 120 volts only with both in parallel, or rewire the compressor motor to run on 240 volts.

The enclosure is nice, but I would add 1/4" screen in the openings to rodent proof it. Your generator has electronic ignition and uses a plastic arm with trigger magnets inside the generator housing. If a mouse builds a nest inside the generator, the plastic arm will break when it hits the nest, requiring you to remove the generator end to replace the arm.
 

Zephyr7

Registered
Sounds to me like the low voltage on the one winding is because you have 120v sensing and the voltage regulator is watching the “other” winding. In this way, the voltage regulator doesn’t see the volt drop caused by the air conditioner, so that windings voltage drops a lot. The other winding will have stable voltage if this is the case. To test, try running the air conditioner on the low-voltage leg, but measure the voltage on the “other” leg. If you see only minimal voltage drop on the “other” leg, then this is what’s going on.

I’d also check all electrical connections to make sure they’re all tight and not corroded.

You don’t normally see 5HP motors running on 120v. I’ve actually never seen one setup this way. Are you sure that’s what you have? If you are sure, is it possible to reconnect the motor to run on 240v (make sure the controls can too)? That might be another option for you. Even without the need to get it running on generator, it’s always best to run motors on the highest voltage available.

You were right to replace the damaged plug. Never try to repair a plug or receptacle, just replace an that are damaged. I’d make sure the mating receptacle for the damaged plug has also been replaced. Too much heat on a connector contact can relax the spring terminals making them loose forever. Loose contacts mean more heating.

Bill
 

Vanman

Subscriber
Last Subscription Date
06/10/2020
That "5 hp compressor" is actually going to be around 1-1/2 hp if it has a 15 amp plug on it. That was blatant false advertising. Same with vacuum cleaners. It's finally been enforced.

As others have said, the regulator is only sensing 120 volts. With load on the other, unsensed line, it will increase excitation, but only enough to keep the sensed line at 120 volts.

Three wire generators with AVRs (120/240 volt) should always have 240 volt regulators. If I owned one, I'd use a small 240 to 120 volt transformer to supply the regulator. This works out to be a good compromise. The loaded line will drop, and the unloaded line will rise, but neither one as much as you're seeing now.

Keith
 
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len k

Subscriber
Last Subscription Date
12/12/2018
Because you have ~ 124 VAC on each hot at no-load I suspect both your windings could be good. And your only seeing a voltage drop on the un-regulated winding.

AC voltage reg only monitors ONE hot lead ( 120V). That 5 hp compressor likely presents a LARGE ~3X starting load, ~11kw. In my experiments on my similar gen (7NHM) I've found without reg ( I used ~36VDC to rotor) I can drop the ~120V to ~95V with 3 kw load if I don't increase rotor voltage.( But my gen has windings in parelle.)
post 13 of ---> https://www.smokstak.com/forum/showthread.php?t=132892&highlight=emergency&page=2

Your compressor may closer to 5hp since on 120/240 configured gen steady state full load (3250W) on unregulated winding only drops the voltage from 121V to 110
Post 52-55 of ---> https://www.smokstak.com/forum/showthread.php?t=113775&page=6


As a test of unregulated hot theory can try finding winding that will not start 5hp load, swap hot that pin 2 of AC voltage reg (VR1) monitors as see if gen will start the load. Pin 2 of reg is connected to hot at TB1. Leave pin 3 of reg connected to neutral ( LO)

Just being conservative I'ld let windings cool for a minute before applying another sever starting load.
Overall it would be better for the gen if you reconnect it to supply 120V only ( windings in parelle) when starting the compressor
.
 
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Warwagon

Subscriber
Last Subscription Date
05/12/2020
Thank you all for the good advice. For some reason I don't have Thank You buttons showing up.

By the voltage regulator connections it looks like it only sees one leg. I wasn't for sure if that was the case. Is there a known part number for the 240V to 120V transformer that was suggested?

I will check for loose connections. I was only monitoring the voltage of one leg at a time.

Air Compressor is just for testing now. Has a 15 Amp 120v plug. Never gave marketing HP rating fraud a 2nd thought as 15A 120V plug is limited...

I had to bolt the genset down to the enclosure as start/stop had it jump around. 1/4" screen is now #1 on my critical project list. An air deflector is also on my mind for the cooling exhaust to keep hot air from going back in. The bottom grate is for the starting battery.

I have no idea what the genset powered. "Van went to auction" is all I was told.

I would like to power:
1) Fridge 5A 120V
2) Freezer 5A 120V
3) Mini Split AC system, not yet purchased, likely 240V 15K BTU.
4) Microwave
5) A few LED lights.
6) TV. (For watching the bad weather causing the power outage...)

Transfer switch with switched neutral to sub panel with the above critical loads will be installed by an electrician.
 

len k

Subscriber
Last Subscription Date
12/12/2018
For gen testing we like to use resistance heaters, 3-4 hairdriers or space heaters will easily get you to full load, and amp load is more predictable. Use a $20 kill-a-watt meter (home depot) to measure hz, amps, watts, volts.
.
 
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Zephyr7

Registered
By the voltage regulator connections it looks like it only sees one leg. I wasn't for sure if that was the case. Is there a known part number for the 240V to 120V transformer that was suggested?
You could use something like this:
https://www.digikey.com/product-detail/en/triad-magnetics/VPT230-220/237-1331-ND/2090069

You need to find a way to make it physically fit, and satisfy any special requirements of the voltage regulator (like how it wants to be grounded) if you want to try this. Aside from that, all you need to do is convert the full 240v output down to 120v for the voltage regulator. Current needs should be pretty minimal, so you don’t need a particularly beefy transformer.

Air Compressor is just for testing now. Has a 15 Amp 120v plug. Never gave marketing HP rating fraud a 2nd thought as 15A 120V plug is limited...
Then it’s not really 5HP. 5HP is 3,730w. Typical motor power factor at full load might be 0.85, so you get about 4.4 KVA. At only 120v, that’s over 36.5A. Also, code says you can’t use over 80% of a circuits capacity in continuous service, so you’re limited to 12A continuous on a 15A circuit. That works out to a little over 1.5HP that can actually be safely powered continuously by a 15A, 120v plug. Anything claiming more than that is rated by the marketing department, not engineering.

Bill
 

len k

Subscriber
Last Subscription Date
12/12/2018
At steady state a motor at full load draws a minimum of ~ 745 watts per HP (100% efficient). Starting draws extra, ~ 3X. Low power factor (PF) increases amp draw, motor are inductive so have lower PF, I've seen .7, .5, and .3

Technically the UL label means UL company inspected and tested a product and agrees it does what manufacturer claims it does.

"5hp" vac shop vacs with 10 amp 120V plug......read what companies did to get a UL label is: on motor name plate where hp is supposed to be stamped they instead listed something like special contract #123456 instead of actual hp. That gave UL inspectors leeway to put their UL stamp on it, since the 1 hp MOTOR didn't claim it was a 5hp one. Then later manufacturer slaps a 5hp sticker on tank, or whatever hp the marketing dept decides it should be "decorated" with.

But I read now that scam has ~ ended, UL has gotten pressure and is now not playing fast and loose with their rules anymore.
.
 
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Zephyr7

Registered
At steady state a motor at full load draws a minimum of ~ 745 watts per HP (100% efficient). Starting draws extra, ~ 3X. Low power factor (PF) increases amp draw, motor are inductive so have lower PF, I've seen .7, .5, and .3
Motor power factor depends on motor loading, as well as the design of the motor. You can actually see this with a belted blower, different sheave sizes give different motor loads, and you can see it with varying power factor. The 746 w/HP is an ideal case, so you won’t ever see better than that. You may well see less HP per watt.

Technically the UL label means UL company inspected and tested a product and agrees it does what manufacturer claims it does.
Not exactly. UL just tests if the product meets certain UL safety standards. UL doesn’t care if the product does anything useful. I’d imagine you could get a UL listing for a perpetual motion “machine” (mechanical equivalent of snake oil), as long as the device is made with UL listed or recognized materials and meets their various other safety requirements. The US patent office won’t issue you a patent for such a device though, because it’s not useful (well, actually because they won’t issue patents for perpetual motion devices per their policy, but their policy is basically because they won’t patent impossibilities).

But I read now that scam has ~ ended, UL has gotten pressure and is now not playing fast and loose with their rules anymore.
.
I think it was actually a government body that got involved with the misleading marketing claims, similar to what happened years ago with the crazy claimed R values for so-called radiant barrier insulation.

UL has gotten more militant about dealing with falsely UL labeled products, probably due to more Chinese knockoffs being out there than there used to be.

Bill
 

len k

Subscriber
Last Subscription Date
12/12/2018
Didn't know PF varied with load.

Have heard UL tests if product meets certain UL safety standards

I once looked into being UL certified to install bank burglary alarms. It might have been in paperwork I got that I found that UL ALSO checks if product does what manufacturer claims it does. But I did read it somewhere.

In past I checked a shop vac with grand claims of 3-5 hp, on motor nameplate, instead of hp # it said ~ special contract 12345

Read China is now just counterfeiting UL labels.
 

Zephyr7

Registered
Didn't know PF varied with load.
Yep, and power factor is highest when the motor is optimally (fully) loaded, for the most part. That’s how the old gizmo you could buy to make motors more efficient worked — it basically notched out the parts of the waveform that were just going to heat up the motor. As the motor approached full mechanical load, the gizmo saved less less money since the motor was putting more and more of the actual energy into making the shaft go around. I jokingly call that “twirly force” :D

Have heard UL tests if product meets certain UL safety standards

I once looked into being UL certified to install bank burglary alarms. It might have been in paperwork I got that I found that UL ALSO checks if product does what manufacturer claims it does. But I did read it somewhere.
I don’t know about the alarm stuff. I’ve only ever worked with them with electrical stuff, mainly big power switchgear.

No surprise there are counterfeit UL labels. I know UL has sued plenty of places for faking listings.

Bill
 

KPack

Subscriber
Last Subscription Date
04/03/2020
If it were on a bench for testing you shouldn’t have to bolt it down if it’s running right. So something doesn’t sound right having to bolt it down. Are you sure it’s running on both cylinders, have you set the valves to spec ?
 

Warwagon

Subscriber
Last Subscription Date
05/12/2020
If it were on a bench for testing you shouldn’t have to bolt it down if it’s running right. So something doesn’t sound right having to bolt it down. Are you sure it’s running on both cylinders, have you set the valves to spec ?
Only during start up and shut down does it jump.

Runs smooth when running. So the shutdown jump surprised me. Considering I ran the (1800 RPM Onans) on a wagon and it didn't move on them.

That is a good point. With the hours it has on it is there anything I need to give attention to? Esp. with an unknown service history?
 

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