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KV2800 slip ring resistance - when to worry?

slapthecat

New member
KV2800 spec A
After many years of keeping it limping along, a new carb has it running well! But now the Volt Reg is shot (getting 130v at 62hz)

Looking at buying a new Vreg, the pre-install check list says the slip ring resistance should be between 16 and 28ohms - mine is at 40 (I cleaned the slip rings in a previous service around 3ys ago)

I’ve seen talk of running the gennie under heavy load for a while can help clean the slip rings if it’s not bad? Anyone that can speak from experience for or against that idea?!?!

Current thinking that the genset is out of the RV - replaced carb, replacing vreg, should probably clean the slip rings while its out. But if it’s unnecessary, I’d love to know!!!

Thanks for any insight!
 

len k

Subscriber
If you replace reg clean the slip rings. That instruction even comes with new reg. Flight Systems is a good source for very good after market reg at a price much better than Onans, and they have a 2 year warentee,.

This is link to Flight Systems
https://www.flightsystems.com/p-ONAN-305-02.html
https://www.flightsystems.com/pdf/model-305-28-manual.pdf



I'm guessing 40 ohms while a little high , did not kill the reg.

A Staker named Magnatite found reg's internal bismuth "solder" connections between ceramic daughter boards and motherboard of reg had cracked in his similar 6.5 kw NHD. He also found reg's main output "transistor" (IGBT) was dead.

On BGE/NHE BGD/NHD BGM/NHM type gens the rotor resistance is 20.25 - 24.75 ohms. Onan says clean slip rings at 30 ohms between the brushes. Onan also says run gen once a month.

In my testing I've let my 7kw NHM sit outside under a trap for ~ 6-9 months. Then without running it I measured ~ 80 ohms with peaks of 100 ohms as I took readings between brushes, reg unplugged. I turned rotor and stopped to take reading ~ every 5-10 degs.

Before this test I cleaned slip rings with 3M fine scouring pad, pressed it against rings while engine ran. So originally I only read rotor ohms, ~ zero contact resistance.

People with gens that sat a "long" time that had dead regs reported 300 and 700 ohms. But I don;t know if it takes that much to kill a reg. It's possible they sat longer than required to kill it.

For what it's worth I've found after sitting 6-9 months the highest resistance ~ 100 ohms is directly under where the brush sat. So it might be copper/carbon galvanic corrosion cell going on, with humidity or maybe condensation from the air. Although other sections of slip ring had 80 ohms, guessing general surface oxidization of the copper (it's invisible/clear).

Never worked on a KV , but I'ld try to clean the carb. I did on my 7NHM. Seems only the small passageways that are under gasoline level are the ones that plug up ( ethanol/water crud). This is the tiny main jet and any metering jets. I've cleaned 100's of small engine carbs, I re-use all parts, nothing new. Maybe make a new gasket if one between carb and intake can't be saved. Permatex 2 also works with those ripped up gaskets,
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len k

Subscriber
Dang.... I missed that little detail....that the reg WORKED. I just saw reg is shot.
Usually when people post reg is shot gens always makes ZERO volts.


I believe generally acceptable voltage range is ~ +- 10VAC , so that seems ok.

In an Onan manual for ~ 6.5NH gen I think the high acceptable is ~ 135 V even ( at no- load). But it uses a different older design of regulation, internal magnetic saturation.

I have no experience with a KV model, but on another Staker's 7NHM (has similar electronic reg) the voltage was ~ 120 V dead on, and only varied ~ 2.5 V from no to full load.

You might check that reg's voltage sense connections/terminals are tight, clean and not corroded. Typically this is reg pins 2,3 at least that's what my 7NHM is, yours looks similar, page 8-4 of service manual ---crummy quality picture
More readable wire diagram in 981-0518 manual for spec > C, looks like they use reg pins 2, 3 for voltage sense also.

Manual numbers and link to them:
microlite --KV--SERVICE-- (spec A-B) --(3-91)--981-0506
microlite--KV--SERVICE--(begins C spec )--(11-04)---981-0518E
microlite--KV--PARTS--(A-L)---(1-05)--981-0238G
https://www.twinslan.net/~n0nas/manuals/onan/
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Birken Vogt

Email NOT Working
I recently had a job where the inverter was supplying 170 volts +/- to the house in place of 120.

Apart from a blown up power strip and some strange operation of a few electronic devices most everything was working normally, refrigerator, computerized water heater, LED lights, well pump, all were working normally for the few minutes that we could keep the inverter on.

I am sure stuff would have suffered eventually but it caused no immediate damage apart from the power strip.
 

len k

Subscriber
Common for computer power strips to have MOV over-voltage protectors. That's what likely smoked, has caused a fire in a fire station when their gen supplied a sustained over-voltage. I read newer power strips place a thermal fuse next to the MOV to protect against these type fires.

I've seen similar MOVs (without thermal fuses) across the power line in power supplies of VCR's, TVs , and other electronics newer than a VCR
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len k

Subscriber
There are devices that monitor voltage and shut off a power relay if votlage or hz get too far out of line.

From another thread....


...They’re usually called “phase monitors” or similar, and they lock out motors when the power supply gets too far outside of acceptable parameters. Any commercial mechanical supply house should have them, and many electrical supply houses likely will as well. Be sure to get single phase models though since these are much more commonly used in three phase applications to protect against the loss of only one of the three phases (which causes a locked rotor condition which can burn out motors). ....
 

slapthecat

New member
Service manual for my rev says voltage should be between 118 (load) and 126 (no load), and 58hz/62hz respectively. When I cleaned the carb a couple years back and ran through the setup, everything hit right on. The carb clean didn’t fix it, so I just replaced the carb and am getting excessive voltage when I ran the setup. Haven’t tested the gennie output in a while (only use it to run the RV AC when boondocking, which is rare), so I don’t know when it started running high. I found a diode test procedure in the service manual for the Vreg - need to do that - but according to flight systems troubleshooter for he KV, the 130v is indicative of a failed Vreg. (The Vreg housing does have a large crack...) Also says the most common cause of burning out the Vreg is the gennie shutting down under load - that happened quite a bit with the old carb.

Getting to the slip rings on the KV requires a lot of disassembly and flywheel removal! Not fun! But if I’m gonna do it right... dang...
 

Zephyr7

Active member
The usual “good” range for AC power is 110-125v. A little outside of that range isn’t usually a problem. Too low is mostly a problem for motors (overheating), and some low-voltage power supplies (flaky operation of the powered device). Too high a voltage is bad for incandescent lights (shortened lifespan).

I would try to keep line voltage under 130v in all cases, and use about 108v as a low. Inside that range you probably won’t have problems with most devices.

Len is correct about MOVs. 170v AC is about 240v on the sinewave peaks, well above the usual 200-220 or so volt firing voltage of the typical MOV used for surge suppression. I think the usual rated max voltage for typical surge protection MOVs is 170 VAC.

Bill
 

BillMcF

Subscriber
I would try to keep line voltage under 130v in all cases, and use about 108v as a low.
For comparison, I designed an electronic line-voltage thermostat for an electric heater several years ago. To pass UL testing, it had to function correctly at 15% below and 10% above nominal line voltage (e.g., 102-132V, for 120V systems). In addition, the SurgeX SX1115 surge protector for electronics has it's "catastrophic" over/undervoltage shutdown limits set to 90V and 145V. Finally, the EMS-PT30X and EMS-PT50X surge protectors for RVs have their shutdown limits set to 104V (for six seconds) and 132V (no delay).

If I were setting up under/overvoltage protection, I'd probably start with Zephyr7's limits if powering AC motors, or the UL limits otherwise.

Len is correct about MOVs. 170v AC is about 240v on the sinewave peaks, well above the usual 200-220 or so volt firing voltage of the typical MOV used for surge suppression. I think the usual rated max voltage for typical surge protection MOVs is 170 VAC.
FYI, I utilized a V14E275 MOV in the electric heater control. It's rated for 275 VAC (or 350 VDC) continuous. The next closest choice was a 250V MOV, but that didn't meet the UL requirement of 240 VAC plus 10%.

P.S.: Zephyr7 is definitely The Man when it comes to EE topics. I've been an EE for 35 years and still learn many new things from his postings.
 

Zephyr7

Active member
I like to teach about this stuff. It’s fun for me. I can take credit for several of my interns going into the field (EE), and there are a number of electricians I’ve helped with their license upgrades, usually regarding screwy grounding and transformer issues. I don’t ever ask anything in return, I’m just happy to help them improve their understanding of things.

I really like what Richard Feynman, noble laureate and manhattan project physicist said: “any topic in physics should be able to be explained to any regular person without any special knowledge by someone with a good understanding of the concept willing to take the time to explain it”. I’m probably not quoting him exactly correctly, but that’s essentially what he said. His “Feynman lectures on physics” from the early 80s are a good example of his thinking.

I think oftentimes all people need is someone to explain something in a way that works for that particular person asking the question.

Bill
 

HBSaunders

Subscriber
Dumb question, if put a new carb on and getting a little high voltage and frequency would the rpms possibly be a bit high too? Is this an 1800 rpm genset?
 

Zephyr7

Active member
Dumb question, if put a new carb on and getting a little high voltage and frequency would the rpms possibly be a bit high too? Is this an 1800 rpm genset?
High RPM is about the only thing the carb would directly influence. The carb itself has nothing to do with voltage regulation as it is a strictly mechanical-side component.

High RPM can cause high voltage though.

Bill
 

len k

Subscriber
In general, without electronic reg, physics say Higher rpm makes higher voltage.

BUT an electronic reg should instantly reduce it's rotor drive voltage to force gen output voltage to drop back to where it belongs.

Before you buy a new reg check if it's connections to 120VAC lines are clean and not corroded. If you have a bad connection ( high resistance) then as reg draws some current there could be a voltage drop across that resistance, that fools reg into seeing ~ 120V at it's leads, while gen is outputting a higher voltage
 

Zephyr7

Active member
But an electronic reg should instantly reduce it's rotor drive voltage to force gen output voltage to drop back to where it belongs.
An electronic regulator might get a bit confused if frequency is too far off and the volts/Hz function acts. I’ve never tried going overspeed though, only under speed, so I’m not sure how it would behave.

Bill
 

len k

Subscriber
Actual gen responce to high hz is somthing I never really thought. Gov should hold it pretty close. Removing carb might require gov readjustment, read service manual. Might be a good idea to measure your HZ, to see if your way off. 60hz +- 1 or 2 is a typically acceptable range. Kill-o-watt meter can measure hz, ~ $25 home depot, less online.

Reg is likely only looking at voltage level, although it has a voltage roll off as hz get low, to help gen recover from heavy loads ( motor starting). On a JB electronic reg they use Op-amp, cap and resistor filter to do that along with LCR filter feeding it.
 
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