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Onan Generators

Protection of Downstream Loads


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  #1  
Old 01-11-2018, 01:11:25 PM
motion motion is offline
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Default Protection of Downstream Loads

I have a Onan 20.ES and it runs well, I'm curious as to what other members do to protect the loads in the event of over/under current, engine failure, fuel loss, etc. With all of the sensitive electronics in todays stoves, flat screens, A/C, etc. I'm somewhat concerned. Thanks
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Old 01-11-2018, 02:07:02 PM
Augie1 Augie1 is offline
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Default Re: Protection of Downstream Loads

Most will just let the branch circuit breakers protect the circuit from shorts and overloads. In this area I have never seen over/under voltage protection. I suppose it could be done if you wanted to spend the money. Plug a voltmeter in both lines and monitor it seems to work good. I have volt and amp meters connected ahead of the transfer switch so I know what the generator is putting out before I transfer power to the gen.
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Old 01-11-2018, 02:16:57 PM
Ifix71 Ifix71 is offline
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Default Re: Protection of Downstream Loads

I use a computer UPS on my DVR and flat screen , that way it don't
Reboot every Time the lights flicker or you switch power sources.
I did notice during Irma that it don't like a frequency above 61 hertz!
John
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Old 01-11-2018, 03:06:51 PM
motion motion is offline
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Default Re: Protection of Downstream Loads

Quote:
Originally Posted by Augie1 View Post
Most will just let the branch circuit breakers protect the circuit from shorts and overloads. In this area I have never seen over/under voltage protection. I suppose it could be done if you wanted to spend the money. Plug a voltmeter in both lines and monitor it seems to work good. I have volt and amp meters connected ahead of the transfer switch so I know what the generator is putting out before I transfer power to the gen.
I was thinking about the times you may not be standing near the generator i.e. sleeping or away and something goes wrong. I thought about a shunt trip breaker in conjunction with a over/under voltage, phase loss module. but I'd still need power to trip the breaker.
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Old 01-11-2018, 03:21:43 PM
Leon N. Leon N. is offline
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Default Re: Protection of Downstream Loads

Good question! I think if you have a quality product, that is, a generator which is properly maintained you should have little to worry about.

In my situation, I employ a 1960's designed Onan 7500 watt magneciter JB generator. I was concerned like you about under voltage and more importantly under frequency operation and how this would affect not only connected appliances but the generator itself during under frequency operation as would occur should the generator wind down under load.

So without modifying the genuine Onan designed JB, I designed a separate shunt trip circuit which monitors the generator frequency and automatically disconnect the down stream loads should the frequency go low or high.

I never got around to modifying the shunt trip to not only disconnect the downstream loads but also shut down the plant seeing the generator voltage regulator is susceptible to damage should prolong operation occur at a reduced frequency/RPM.

Today, after some 45+ years of reliable JB operation, I have great confidence in the reliability of my unit that I am not in a hurry to modify my shunt trip to not only disconnect the downstream load but also shut down the plant.

If interested I can send you some information on my simple but reliable black box shunt trip design.
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Old 01-11-2018, 04:57:31 PM
Steve Dawkins Steve Dawkins is online now
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Default Re: Protection of Downstream Loads

Quote:
Originally Posted by motion View Post
I was thinking about the times you may not be standing near the generator i.e. sleeping or away and something goes wrong. I thought about a shunt trip breaker in conjunction with a over/under voltage, phase loss module. but I'd still need power to trip the breaker.
I don't think you need to go to that extent of protection, unless you've got a lot of expensive equipment to protect. Since you mentioned phase loss, is your genset configured for 3 phase output?

If your generator is supplying whole house power for 120/240V, single phase operation, a good surge protector on your distribution panel should adequately protect the loads from severe overvoltage and spikes. Should you decide to incorporate a shunt trip system, you can get shunt trip breakers that have 12 VDC coils. Thus, you can use battery voltage to operate the shunt trip mechanism. There are other options available for circuit breakers, such as auxiliary contacts. You could wire this into the generator run circuit to stop the engine if the shunt trip activates.
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Old 01-11-2018, 06:31:07 PM
Wayne 440 Wayne 440 is online now
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Default Re: Protection of Downstream Loads

I have a UPS on my DSL modem, but that is merely for convenience - so I don't have to wait for DSL to resync after a power failure. Other than that, I figure that if some device I have is too "sensitive" to accept power from the RDJC, I should be getting rid of said device anyway.
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Old 01-11-2018, 08:38:07 PM
dracer dracer is offline
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Default Re: Protection of Downstream Loads

Quote:
Originally Posted by Wayne 440 View Post
I have a UPS on my DSL modem, but that is merely for convenience - so I don't have to wait for DSL to resync after a power failure. Other than that, I figure that if some device I have is too "sensitive" to accept power from the RDJC, I should be getting rid of said device anyway.
I have a ups on my computer and modem and the wif , I think the wireless phone is on it also , we used to have a lot of power outs that where on and offs but when the ranger changed and the new one let the power company trim the the trees that was cured
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Old 01-11-2018, 08:50:24 PM
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Jim McIntyre Jim McIntyre is online now
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Default Re: Protection of Downstream Loads

Quote:
Originally Posted by motion View Post
I was thinking about the times you may not be standing near the generator i.e. sleeping or away and something goes wrong. I thought about a shunt trip breaker in conjunction with a over/under voltage, phase loss module. but I'd still need power to trip the breaker.
I think that what you describe, possibly with the addition of an under/over frequency trip could be of some use in preventing damage to some loads under unusual generator operation. Whether it's actually worth the cost, bother, lower system reliability, and inevitable nuisance trips is a question only you can answer. For me, the answer is 'no'.
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Old 01-11-2018, 10:26:37 PM
I like oldstuff I like oldstuff is offline
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Default Re: Protection of Downstream Loads

Keep in mind that a lot of the new electronics (computers, tv's, cable boxes and so on) use a switching power supply that rectifies ac to dc. These will work fine from around 80 volts @~40hZ and up to 250V @100+ hZ. If the power drops off or goes low from your gen these things will just stop making enough dc to power the device. I don't know however if they have any over voltage protection.
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Old 01-11-2018, 10:46:27 PM
rmchambers rmchambers is offline
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Default Re: Protection of Downstream Loads

I have a 3600W Trace/Xantrex inverter and 8 golf cart batteries. I run the loads I want to run from this. (at night it's quiet) the entire output from the generator goes into this device when I fire it up. The inverter will send power through to the loads and charge the batteries up, if the generator stops or gets wiggy, the inverter will drop off the power and work like a UPS and feed the loads.
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Old 01-12-2018, 06:46:01 AM
armandh armandh is offline
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Default Re: Protection of Downstream Loads

Yes you can blow stuff up with a generator

my late friend Tom had one that did this until I fixed it.
Mr "drier outlet back-feed" gave me his old "problem" generator when
he went to a 200A transfer switch and twice as big in generator size.
gave = I paid the $75 late fees on the trailer title transfer and for the new plates.

the problem; it was running out of governor spring under heavy load.
rather than move the working end closer to the pivot
he tightened the adjustment end, but when the load came off,
HZ and V went through the roof, and fritzed goodies. [induction regulated]

I went to a longer softer spring that, after some trial and error, held 60 HZ
from a light load through breaker opening overload without hunting.
and learned a lot about mechanical inverse feed back!

positive feed back [over center spring] or
inverse feed back [above the tangent spring]
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Last edited by armandh; 01-12-2018 at 07:19:10 AM.
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Old 01-12-2018, 07:23:42 AM
motion motion is offline
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Default Re: Protection of Downstream Loads

Thanks for all of the replies. Mine is set up for 208v, three phase, 4wire. As other have said it's not super important but would be nice (belts and suspenders). It's something that I'll think about.
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Old 01-12-2018, 10:17:36 AM
Leon N. Leon N. is offline
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Default Re: Protection of Downstream Loads

With all due respect did you really say this? "the problem; it was running out of governor spring under heavy load."!

What kind of a machine was that? And to try and correct the problem the way mentioned. Wow! Not a good idea. Sounds like it was not set up properly to begin with.
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Old 01-12-2018, 01:32:54 PM
Vanman Vanman is offline
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Default Re: Protection of Downstream Loads

My 6-1/2 kw Kohler came with what looked like a piece of wire twisted around to make a "spring" for the governor. It would go from over 63 cycles to less than 58 when a 5 kw lamp was thrown on the line.

I did pretty much the same thing. Found a suitable spring and adjusted it until it would just not hunt. Problem solved.
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Old 01-12-2018, 03:17:19 PM
Newoldstock Newoldstock is offline
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Default Re: Protection of Downstream Loads

Quote:
Originally Posted by Vanman View Post
My 6-1/2 kw Kohler came with what looked like a piece of wire twisted around to make a "spring" for the governor. It would go from over 63 cycles to less than 58 when a 5 kw lamp was thrown on the line.

I did pretty much the same thing. Found a suitable spring and adjusted it until it would just not hunt. Problem solved.
Moving the spring closer to the fulcrum of the governor arm will increase sensitivity.
If the engine starts to hunt it is too sensitive and a different choice of spring might help.

Long springs have a more constant tension rate short ones are more progressive ( the shorter less likely to hunt the longer ones more )

A dash pot from a different carb might also help with hunting., but this will slow load responds time.

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Old 01-12-2018, 07:04:59 PM
Vanman Vanman is offline
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Default Re: Protection of Downstream Loads

Yes, indeed not having access to factory parts I selected a fairly long spring to ensure that I would be able to adjust the sensitivity to be as sensitive as possible, ie just less than continuous hunting. It works great.
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Old 01-13-2018, 08:05:09 AM
armandh armandh is offline
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Default Re: Protection of Downstream Loads

same thing

a 7.2 KW K-582 powered 1800 rpm generator
1964 vintage and no knowing how many amateur repairs.

when the load went on the spring pulled the throttle open until it fully collapsed
way short of full open throttle, it was probably NOT OEM

finding the right spring at the right angle to give quick response with out hunting
through out the load range took a bit of experimentation.

Quote
Moving the spring closer to the fulcrum of the governor arm will increase sensitivity. if you don't move the other end to the original tangent
If the engine starts to hunt it is too sensitive and a different choice of spring might help.
but if the spring is within the governors ability to pull the throttle closed changing the angle of the fixed end changes sensitivity as well

less inverse feed back = more sensitivity and likely-hood to hunt

as you move the fixed end of the spring above the arc the first part of the governor pull has greater mechanical advantage
photo less/more sensitivity
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__________________
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by using this free advise, you, your heirs, etc
absolve, save, and hold harmless the advisor.
CAVEAT EMPTOR
YMMV

Last edited by armandh; 01-13-2018 at 12:58:24 PM.
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