Inverter needed for Onan 7500 Generator

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Lawgirl11

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Nov 17, 2013
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I am trying to find an after-market for this inverter. When I googled I found so little companies selling them. Anyone have a secret place they know about to get parts for the generator? :)
 
The Onan QD series generators are very sensitive to being shut down while under a heavy load,, I learned this expensive lesson about 11 years ago to the tune of $1400.00 .>>>Dan
 
Your genset does not have an inverter. It creates and distributes 120VAC @60 CPM here in the U.S.A.
What are you trying to accomplish?
 
Ray-IN said:
Your genset does not have an inverter. It creates and distributes 120VAC @60 CPM here in the U.S.A.
What are you trying to accomplish?
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It has a very expensive Controller/inverter built into it. About $3500 for the part. Hundreds more to have it installed at an Onan service center
 
Ray-IN said:
Please document that statement for my edification. Yes, it has a controller, nowwhere in the specs does it mention an inverter.
reference: Onan 7500 spec sheet. pdf
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The very first sentence on the spec sheet confirms it uses some kind of an inverter, you can't have a constant frequency AC output from a variable speed generator without one.

The variable voltage and frequency output from the generator is rectified to DC (a simple process), then the continuous DC voltage is modulated to 60 Hz AC by the inverter stage.

This doesn't mean you can tack something like a Victron inverter across the output of the generator stage, to simplify the conversion from DC to AC the DC voltage is somewhere in the range of the peak to peak AC voltage, around 340 volts DC.
 
Lou Schneider said:
This doesn't mean you can tack something like a Victron inverter across the output of the generator stage, to simplify the conversion from DC to AC the DC voltage is somewhere in the range of the peak to peak AC voltage, around 340 volts DC.
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AND it's internal, which would make it tough to replace with something else. Mine isn't the same generator, but after my current coach was about six months old the generator failed (under warranty thankfully) and Cummins had to actually remove the generator from the coach to access the failed circuitry inside the generator. I was told it would have been a $1600+ bill if it hadn't been under warranty, and that was in Jan 2017.
 
Ray-IN said:
Please document that statement for my edification. Yes, it has a controller, nowwhere in the specs does it mention an inverter.
Click to expand...
Ray... are you challenging the existence of inverter/generators in general, or the Onan QD 7500 in particular? I can show you Section 10 of the original Onan7500 Service Manual, which is titled Controller-Inverter Service. Or the newer combined 7500/8000 service manual that has a similarly titled chapter 5.1. The 7500/8000 actually uses two inverter modules, one for each leg of the output. That's why their output is dual 120v rather than 240v - the two legs are in phase.

Inverter generator produce DC via an alternator and use an inverter to convert to well-regulated pure sine 120vac. Typically the controls are integrated with the inverter, but that is a design & packaging choice. The Onan 7500 & 8000 do integrate a lot of digital management function into the inverter module.
 
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Larry N. said:
AND it's internal, which would make it tough to replace with something else. Mine isn't the same generator, but after my current coach was about six months old the generator failed (under warranty thankfully) and Cummins had to actually remove the generator from the coach to access the failed circuitry inside the generator. I was told it would have been a $1600+ bill if it hadn't been under warranty, and that was in Jan 2017.
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It’s $4500, now.
Ouch
 
Gary RV_Wizard said:
Ray... are you challenging the existence of inverter/generators in general, or the Onan QD 7500 in particular? I can show you Section 10 of the original Onan7500 Service Manual, which is titled Controller-Inverter Service. Or the newer combined 7500/8000 service manual that has a similarly titled chapter 5.1. The 7500/8000 actually uses two inverter modules, one for each leg of the output. That's why their output is dual 120v rather than 240v - the two legs are in phase.

Inverter generator produce DC via an alternator and use an inverter to convert to well-regulated pure sine 120vac. Typically the controls are integrated with the inverter, but that is a design & packaging choice. The Onan 7500 & 8000 do integrate a lot of digital management function into the inverter module.
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Thanks, pg 29-30 explains the controller turns on the inverter. Now I know the controller interacts with the inverter.
I didn't know how my QD 7500 functioned, just that it does.
As to a challenge, not at all. I merely asked for documentation I could read to educate myself. I've bookmarked that manual for future reference, thanks for that.
 
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Ray-IN said:
I didn't know how my QD 7500 functioned, just that it does.
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The Onan QD 6000, 7500 & 8000 are diesel-powered inverter generators, variants of the same basic machine. They run at variable RPms and produce two "legs" of 120v power, each capable of 1/2 the wattage rating. You cannot get 240v from those models. The QD 10,000 & 12,000 are traditional mechanical generators, running at a fixed rpm and producing 240v power over two legs, i.e. the legs are opposite phases.
 
Sadly you can't just pop a couple of GoPower 3000 watt inverters into the Onan; it's a unique type of inverter designed to work with the output of the Onan DC power generation component. That leaves either a new one or rebuild the existing one (or both - there are two in the Onan7500 & 8000).

Flight Systems has a lot of parts and services for generators and are much less expensive than Onan's own shops. They do offer an Onan HDK inverter repair service that is worth checking out, but I think you have to pull the inverters outyourself and send them in. See 300-6058-02: Repair Service for Onan HDK Inverter
 
Gary RV_Wizard said:
Sadly you can't just pop a couple of GoPower 3000 watt inverters into the Onan; it's a unique type of inverter designed to work with the output of the Onan DC power generation component. That leaves either a new one or rebuild the existing one (or both - there are two in the Onan7500 & 8000).

Flight Systems has a lot of parts and services for generators and are much less expensive than Onan's own shops. They do offer an Onan HDK inverter repair service that is worth checking out, but I think you have to pull the inverters outyourself and send them in. See 300-6058-02: Repair Service for Onan HDK Inverter
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Good find on the Flight Systems inverter repair, Gary! From the illustration on their site you send the whole inverter assembly to them after unplugging it from the generator.
 
It's still an expensive fix, $995 per inverter plus shipping & handling both ways. And you still have to pay for remove & install if you don't have DIY skills & tools. I can readily see a generator shop charging $1500 to R&R the inverter module if they have to pull the generator out of the RV to do it (and that is often required).

Here's another inverter repair service.
 
Gary RV_Wizard said:
It's still an expensive fix, $995 per inverter plus shipping & handling both ways. And you still have to pay for remove & install if you don't have DIY skills & tools. I can readily see a generator shop charging $1500 to R&R the inverter module if they have to pull the generator out of the RV to do it (and that is often required).

Here's another inverter repair service.
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Are there one or two units of the shown per generator? I'd check with Flight Systems but it sounds like the cost is to clean and repair the entire unit, i.e. both inverters if they share the single enclosure.
 
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