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Onan Generators

Onan 7.5 JB's Recovery Towards A New Life


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  #61  
Old 01-17-2017, 02:13:04 AM
len k len k is offline
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Default Re: Onan 7.5 JB's Recovery Towards A New Life

sx460 and a resistor $30, but I'ld go with FS Got a better feeling about them.
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Old 01-17-2017, 02:45:13 AM
Ray Lynch Ray Lynch is offline
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Default Re: Onan 7.5 JB's Recovery Towards A New Life

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sx460 and a resistor $30
Definitely an alternative solution. Have no 1st hand experience with it, but other members have with reported good results.
Ray
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  #63  
Old 01-17-2017, 06:49:08 AM
JohnnyC JohnnyC is offline
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Default Re: Onan 7.5 JB's Recovery Towards A New Life

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Originally Posted by Jim Marcozzi View Post
The last one of these that I bought was near $1200
Wow! Out of curiosity does anyone know approximately how much my JB cost new back in 1991 with all the options and accessories it has? That is one piece of information I don't have in the bundle of documentation that came with it.

JohnnyC
New Jersey
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  #64  
Old 01-17-2017, 08:28:06 AM
stretch67 stretch67 is offline
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Default Re: Onan 7.5 JB's Recovery Towards A New Life

Hey JohnnyC when your done painting your JB i can send you my JC to be painted..........so you wont go crazy you know.........

My 1975 vintage set has the non potted board by the way.

There is a thread some place on here about using a different reg board.
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  #65  
Old 01-17-2017, 10:48:22 PM
JohnnyC JohnnyC is offline
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Default Re: Onan 7.5 JB's Recovery Towards A New Life

Tuesday's Update

After work, I spent a few minutes and finished reconfiguring the JB's wiring from a parallel wye 120/208 3 phase to double delta 120/240 single phase and ran my first load test. All went perfect. On one leg I ran 22 amps and the other leg I ran about 25 amps continuous for 15 minutes using heaters. The analog Hz meter showed just slightly over 60 Hz and the voltage was rock solid at 120 volts per leg. While trying to initially load balance the legs I occasionally went past 30 amps per leg and my mini breakers on the power strips tripped as they should. The JB's motor barely flinched. This shows that the JB will crank out those amps.

This completes the initial testing to ensure there are no problems and it performs to spec. Next step is to take the JB apart.

As always, I try to post pictures so here are a few below.

Picture #1) This shows the basic setup for this evening's test. There are 5 heaters and a set of three lights on the yellow pole.

Picture #2) This is the 3 phase meter panel. Since it is no longer wired as a 3 phase genset, only 2 of the amp meters will function and they are circled in red to the right. The Hz meter is also function. When I was reconfiguring the wiring in the box behind the meters, I forgot to wire up the AC volt meter and that is why it shows 0 volts.

Picture #3) In absence of a working analog ac volt meter on the JB's meter panel, I show the voltage using my Fluke meter under the load shown on the amp meters. 120.5 ac ain't bad

JohnnyC
New Jersey
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  #66  
Old 01-17-2017, 10:56:57 PM
Vanman Vanman is offline
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Default Re: Onan 7.5 JB's Recovery Towards A New Life

Since you've already got it in the panel, you could wire the unused third ammeter into the neutral. You know, for the heck of it.
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  #67  
Old 01-17-2017, 11:17:26 PM
JohnnyC JohnnyC is offline
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Default Re: Onan 7.5 JB's Recovery Towards A New Life

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Since you've already got it in the panel, you could wire the unused third ammeter into the neutral. You know, for the heck of it.
Actually I would like to replace the 3rd amp meter with another matching ac volt meter so I can monitor voltage on each leg together without turning the rotary switch. From what I read, only the 3 phase meter panel displays use the rotary switch. I would like to mount a double pole 30 amp breaker in the hole where there is a blank cover on the front panel. I have some other ideas too, but too early to tell which path I will go down, but none the less which ever panel configuration I choose, the wiring behind the panel display will be a double delta configuration.


JohnnyC
New Jersey
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  #68  
Old 01-17-2017, 11:38:56 PM
len k len k is offline
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Default Re: Onan 7.5 JB's Recovery Towards A New Life

Not a bad idea to mount a 2nd volt meter , but it should track the other pretty well. Would be more to check on a failure.
These JB's have pretty large dia wire in the 120V type windings, so not much IR voltage loss.

If your interested in real world voltage variations on a 7 kw NHM there is some test data. Reg was connected to only one 120V winding... post 54
https://www.smokstak.com/forum/showt...=113775&page=3
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  #69  
Old 01-17-2017, 11:54:48 PM
JohnnyC JohnnyC is offline
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Default Re: Onan 7.5 JB's Recovery Towards A New Life

Interesting. On my JohnnyC kilowatt boxes I have two volt meters, one on each leg. The voltages vary between the two legs depending how the leg is loaded, but I have not taken notice if it follows the data shown in post 54 of the link you provided. Next time I pull out my 6.5NH or 5.0 CCK and have time to play, I will check it out.

JohnnyC
New Jersey
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  #70  
Old 01-18-2017, 12:08:56 AM
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Jim McIntyre Jim McIntyre is offline
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Default Re: Onan 7.5 JB's Recovery Towards A New Life

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Originally Posted by JohnnyC View Post
Wow! Out of curiosity does anyone know approximately how much my JB cost new back in 1991 with all the options and accessories it has?
A base JB sold for about $1864 in 1979. That inflates to $3500 in 1991. Not sure about the options.
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Old 01-18-2017, 01:16:27 AM
Vanman Vanman is offline
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Default Re: Onan 7.5 JB's Recovery Towards A New Life

This is why the voltage regulator should be 240 volt when regulating a three wire single phase generator. You'll still get differences when one line is loaded more than the other, but you will not get the extremes that you see when the regulator is sensing only one line. I would supply the regulator with a small 240 to 120 transformer.

Quote:
Originally Posted by len k View Post
Not a bad idea to mount a 2nd volt meter , but it should track the other pretty well. Would be more to check on a failure.
These JB's have pretty large dia wire in the 120V type windings, so not much IR voltage loss.

If your interested in real world voltage variations on a 7 kw NHM there is some test data. Reg was connected to only one 120V winding... post 54
https://www.smokstak.com/forum/showt...=113775&page=3
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  #72  
Old 01-18-2017, 01:48:48 AM
yellowlister yellowlister is online now
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Default Re: Onan 7.5 JB's Recovery Towards A New Life

Don't you have the selector switch that will tell each voltage on each leg?
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  #73  
Old 01-18-2017, 02:15:40 AM
len k len k is offline
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Default Re: Onan 7.5 JB's Recovery Towards A New Life

Vanman.... I believe some onan regs do use a transformer to sense off 208 on 3phase .

Believe I seen other gens sense off 240 single phase , this might be better as maybe the 120 voltage deviation could be less. Just thought about this superfluously , without spending a lot of time on it. likely deserves more thought.
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Old 01-18-2017, 06:50:33 AM
JohnnyC JohnnyC is offline
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Default Re: Onan 7.5 JB's Recovery Towards A New Life

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Don't you have the selector switch that will tell each voltage on each leg?
Yes, but I would need to wire it for the current configuration. Not a big deal since I want two ac meters and eliminate the switch.

JohnnyC
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Old 01-18-2017, 01:27:17 PM
len k len k is offline
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Default Re: Onan 7.5 JB's Recovery Towards A New Life

Just for kicks I ran some numbers on the test data in my link.
With 120/240 output and with only one winding fully loaded the voltage difference between 120 windings is ~ 12 VAC, with reg sensing only one 120 winding.

Each windings is 0.327 ohms, full load is 28.3 amps/winding, so IR drop across each winding is 9.2 VAC or ~ 75% of the total voltage drop. That means most of the drop is due to IR resistance of the winding.

Winging gauge looks 2x the size on JB vs NHM , just by eyeballing it. So I'ld estimate IR drop in JB might only be 2.3 volts, ( 1/4 the drop)
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  #76  
Old 01-18-2017, 06:25:10 PM
JohnnyC JohnnyC is offline
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Default Re: Onan 7.5 JB's Recovery Towards A New Life

Quote:
Originally Posted by Jim McIntyre View Post
A base JB sold for about $1864 in 1979. That inflates to $3500 in 1991. Not sure about the options.
So, according to the Cumulative Inflation Calculator, a price of $1864 in 1979 calculates to $6,162.16 for 2016 and that is just the base model. It would be nice to see what the common options available for the J series retail for and the year.

A Chinkorator would retail for much less, but just add up the cost for all the replacement Chinkorators a person would have to buy over the lifespan of just one well made Onan JB (made in the USA) that will continue to run for years to come.

JohnnyC
New Jersey
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  #77  
Old 01-18-2017, 07:02:48 PM
yellowlister yellowlister is online now
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Default Re: Onan 7.5 JB's Recovery Towards A New Life

If they made them that well and simple today I bet they would sell.. people pay 5k for a 6500 watt Honda that has a 2500 inverter.

I mean the kubota with Stamford or marathon generators do
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  #78  
Old 01-18-2017, 07:16:32 PM
JohnnyC JohnnyC is offline
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Default Re: Onan 7.5 JB's Recovery Towards A New Life

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If they made them that well and simple today I bet they would sell.. people pay 5k for a 6500 watt Honda that has a 2500 inverter.

I mean the kubota with Stamford or marathon generators do
I think very few would sell. Today's snowflakes and cupcakes only want cheap, cheap, cheap. They have no clue what quality is since they were only a twinkle in their parent's eyes when quality was going out the window and overseas junky production started. I know many snowflakes and cupcakes that have no expectations of anything lasting long and they will not try to fix anything that breaks. Instead they will immediately throw away the product that failed and buy new junky crap again and not think twice. Talk about waste of resources and these are the same cupcakes and snowflakes that side with the sierra club in their views...

JohnnyC
New Jersey
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  #79  
Old 01-18-2017, 08:02:54 PM
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Default Re: Onan 7.5 JB's Recovery Towards A New Life

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Originally Posted by Vanman View Post
This is why the voltage regulator should be 240 volt when regulating a three wire single phase generator. You'll still get differences when one line is loaded more than the other, but you will not get the extremes that you see when the regulator is sensing only one line. I would supply the regulator with a small 240 to 120 transformer.
agree 100%
my djb would only monitor one leg, and if you had the other leg loaded by itself the voltage would drop.

i guess that's why they say balance the load as best as possible.
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Old 01-18-2017, 10:39:33 PM
len k len k is offline
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Default Re: Onan 7.5 JB's Recovery Towards A New Life

Another thread lists winding resistances for a few JBs in post #4.
https://www.smokstak.com/forum/showt...83#post1353932
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