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generator/electrical update

I think I've narrowed down why my generator (actually ATS) is puking out when trying to run both A/C units.  My Ch. Engineer gave me a meter to guage the amperage of a circuit while in use.  When I crank up either A/C, after a second or two and for only an instant, they are each drawing around 15.5-17 amps.  They both quickly settle down to around 13.5 (on max cool).  So when one starts and settles in at 13.5 and the other tries to start at 17, the 30+ draw is causing the voltage to drop past the minimum allowed by the ATS...and consequently goodby generator power.  Does not happen on shorepower presumably because there is ample amperage so there is no consequent voltage drop (my theory).  I just got home and found the two hard start capacitors in the mail but I don't think they are correct.  They are for a Coleman unit but the directions say it is for a unit without a start cap or a start relay, which mine has.  This device comes with a something that acts as a start relay but it is supposed to be wired to one side of the run cap and to one side of the start cap.  My start relay is wired to the start cap, the run cap, the overload next to the compressor and somewhere else.  Four wires.  I think I will leave the new relay out and just replace the start cap with the new start cap and see what happens.  I am starting to think that since the run amps are kind of high...perhaps the compressor is the problem and this start cap business is a waste of time.  If that is the case I will be forced to buy at least one new A/C unit.  That way the total amps should not be so high as to drop the voltage enough to trip the ATS.  Here is a photo of existing wiring.  Also a link to what I ended up buying over the phone:
http://cgi.ebay.com/Coleman-RV-AC-Air-Conditioner-Hard-Start-Kit-8333A9021-/390128486286?cmd=ViewItem&pt=LH_DefaultDomain_0&hash=item5ad578478e
Dwayne Keith
1992 U240
3116/MD3060

Re: generator/electrical update

Reply #1 –
Dewayne,

Has either unit ever tripped a breaker when trying to start if not and from looking at the amp readings you took I think the units are OK if they were pulling excess amperage they would trip the breakers feeding the a/c units. You said they worked on shore power I think you have a generator problem regardless of what the tech said. Have you ever had problems with the generator running both units if not I think the generator is the problem not the a/c units.

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Bobby & Norma
1992 GV U280
C8.3 Cummins

Re: generator/electrical update

Reply #2 –
Onan twice now has blessed the generator and our company's Chief Engineer did too.  The units are each on a 20 amp breaker, neither has ever tripped one.  Once they manage to get past the startup without tripping the trasfer switch they continue to run.  It is when the compressor comes on that they need all this amperage (which lowers the votage tripping the transfer switch).  On shorepower there is abundant amperage (at least where I am plugged in) so even though the amps shoot up the voltage doesn't drop so you never know it is happening. 
Dwayne Keith
1992 U240
3116/MD3060

Re: generator/electrical update

Reply #3 –
Have you tried starting just the fan on both units after they are up and running then switch one of the units to cool let it settle down then turn on the second one  this way the fan motors are up and running should help some on the starting amps. I will check the amps on mine tomorrow and see how they compare with the amp readings you got . What size is the generator?
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Bobby & Norma
1992 GV U280
C8.3 Cummins

Re: generator/electrical update

Reply #4 –
Bobby,

That is an excellent idea!

Since all else has failed, let's try putting some logic to this issue.  First, the breakers to the A/C units do not trip.  Second the shorepower connection does not seem to have an issue with the units either.  Third, the ATS switch drops out when one A/C unit kicks in due to low voltage.  We have separate current paths, one from shorepower to the ATS and one from the generator.  The generator path seems to cause the ATS switch to drop out from low voltage.  That would suggest that there could be wiring issues from the generator to the ATS switch.  Dwayne, you might check the wiring connections at the gen set and at the ATS switch for corrosion.  If that seems o.k., look at the wiring under the coach to see if something has damaged it.  I'm guessing that when the checked the gen set they hooked up their loads at the generator and not to the wiring inside the coach, correct?

We are rooting for you!
John Cooper
'91 GV 36'
Oshkosh chassis
Cat 3208T 300HP

Re: generator/electrical update

Reply #5 –
Knowing this is an old subject, Thought would try to simplify this .
First without a peak reading amp meter and a min/max reading AC Volt meter it is a guess at best, I would expect the actual peak amp load on starting the comressor would run closer to 45 amp peak, maybe more depending on the condition of unit. Dont get off track with the 20 amp breaker, for example my home airconditioner has a peak amp load of 156 amps on 240 volt, the breaker is a 40 amp, and it never trips and the running load is 27.3 amp measured by my peak amp reading meter.

As for the  volt, it is a 6500 watt and if wired as 120 volt not 120/240e rated load would be 54.16 amp.
Point, it one air conditioner is started then the second I would expect the load on generator to be at least 50+ amp during the start cycle then drop back to about 30 amp for both.  If there is a problem with one of the units or both, their could be a overload whick would drag the generator down.

Why it is soooo important to have test equipment to find what/where the problem is..  For a shop to hunt and peck around guessing what might be, without tools to check, it becomes a guessing game.

Just me opinion after 40+ years , only in the Onan generator game.  as the saying goes "Been there-Done that"
FWIW
Dave M Va

Re: generator/electrical update

Reply #6 –
Dave,

I agree with you hard to trouble shoot something over the internet to many variables but I did check my units just to compare his amp readings mine are close to what he was getting. Duo Therm made 2 models that are rated 13500 BTU at least they did in 1992 Locked rotor amps 50 on the compressor, fan motor 8.8 the other one 60 locked rotor amps compressor, 8.8 fan motor don't know which units he has. Understand about the breakers they are doing what they are designed to do. Duo Therm states in there general information booklet that you can run 2 of these units off of a 5.0 kw generator but like you said age of the units, generator, and other equipment all have a factor in this problem. 
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Bobby & Norma
1992 GV U280
C8.3 Cummins

Re: generator/electrical update

Reply #7 –
I find it interesting that he seems to say that the Coleman compressors
kick in immediately.
On the Dometic it delays about 3 minutes after the fan starts. Never
fails to throw me...
Quote
wg4t wrote:
Knowing this is an old subject,
Thought would try to simplify this .First without a peak reading amp meter and a min/max reading AC Volt meter it is a guess at best, I would expect the actual peak amp load on starting the comressor would run closer to 45 amp peak, maybe more depending on the condition of unit. Dont get off track with the 20 amp breaker, for example my home airconditioner has a peak amp load of 156 amps on 240 volt, the breaker is a 40 amp, and it never trips and the running load is 27.3 amp measured by my peak amp reading meter.As for the volt, it is a 6500 watt and if wired as 120 volt not 120/240e rated load would be 54.16 amp.Point, it one air conditioner is started then the second I would expect the load on generator to be at least 50+ amp during the start cycle then drop back to about 30 amp for both. If there is a problem with one of the units or both, their could be a overload whick would drag the generator down.Why it is soooo important to have test equipment to find what/where the problem is.. For a shop to hunt and peck around guessing what might be, without tools to check, it becomes a guessing game.Just me opinion after 40+ years , only in the Onan generator game. as the saying goes "Been there-Done that"FWIW
Dave M Va
The selected media item is not currently available. Dave Head & Megan Westbrook
Titusville, FL - The Great Outdoors
'98 270 buying this month
Toad is a 2018 F150 XLT

Re: generator/electrical update

Reply #8 –
There may be a very brief delay...ore or two seconds maybe.  I tried changing out the start capacitor but I shouldn't have as the one I bought said that it (and the start relay) was for a unit without those components.  The start capacitor burned up immediately.  I was watching the guage when I turned it on and I saw it spike to 29 amps for a split second.  Strange that the 20 amp breaker didn't trip.  This could be a clue to what's going on.  I always thought a breaker either worked or didn't work.  It is working as it was with the OEM one back in.  I'm either going to order the correct universal hard start unit or just replace one of the A/C units with a new more efficient one that will bring my power consumption down enough not to open that transfer switch when the voltage drops for an instant on compressor start.  They are almost 20 years old and both are running (and starting), on shorepower or generator, at above spec.  Although both run closer to spec on shorepower.  Shorepower start at 14-15 amps for a second (after the pause when just the fan is on) then down to 12.5-13.  They should run at 11-12 and start at 13-14. On generator, add a couple of amps to both.  The front is a little more hungry for power than the rear.  Both cool about the same: 59 degrees at full cool in an 85 degree inside and 95 outside temp.  Very good cooling.  If I wasn't having this surge of amperage on compressor start which drops the voltage enough to open the ATS, I'd love them.  The strangest thing I've noticed is that it is much easier to cause that voltage drop when manually turning the thermostat up rather than allowing the unit to cycle up.  I know about head pressure so I've tested running just the fan with the thermostat all the way warm for fifteen minutes or so then manually moving the thermostat up until it triggers the compressor start.  Doing that is the best way to trip the ATS even more so that just turning the unit from off to on.  In both instances the fan is running prior to the compressor.  Too weird.  Our chief engineer says that these older units probably have worn compressor bearings and the heavy use last summer followed by almost a year of little to no use just has made them that much more inefficient and they've reached the point where their power consumption is past the generator's ability to keep up without tripping the ATS with a little too much voltage drop.  He thinks the generator size vs. the two 13500 BTU A/C units was very tightly matched to begin with, especially after they converted the gasoline generator to propane.  Perhaps the previous owner converting it to vapor made it a little less powerful.  I don't know about that.  I still am not sure as both units acting the same has me worried.  I'd be much more ready to believe it is an A/C problem like Onan and my engineer say if it was just one unit acting up.
Dwayne Keith
1992 U240
3116/MD3060

Re: generator/electrical update

Reply #9 –
Dwayne,
I found this you may want to read it someone had the same problem you are having with the transfer switch taking the generator out.

http://www.smokstak.com/forum/showthread.php?t=62921
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Bobby & Norma
1992 GV U280
C8.3 Cummins

Re: generator/electrical update

Reply #10 –
I'm so confused.  I changed the transfer switch because when turning down the thermostat causing one compressor to go off...the transfer switch would open.  Onan told me generator fine, bad transfer switch.  Seemed logical.  New transfer switch adding in 2nd compressor opens the switch. It doesn't happen every time but enough to make it a problem trying to stay confortable on generator.  Attempting to reduce the compressor start amperage is my best short term solution.  I was checking start and run amps on new A/C and they are not that much less than what I'm seeing.  If I could get that compressor start amp down to 14-15 I'd probably be OK.  It is those 16-17's that are dropping the voltage past the transfer switch acceptable parameters.  Onan says the A/C's are too much for the generator.  The wiring between the generator and transfer switch is a good place to look.  Could be a ground fault.  Electrical problems are like ghosts.  I may never get to the bottom of this.  The only other thing I did before this started was changing out the converter/charger from the 75 amp dumb charger to the 70 amp smart charger.  I've tried turning it and everything else off at the breaker box but still have the same problem so it has to be either generator, wiring from generator to ATS, the ATS itself or one of the A/C units.
Dwayne Keith
1992 U240
3116/MD3060

Re: generator/electrical update

Reply #11 –
If you even suspect a wiring issue between generator and ATS, it is not that difficult to run a new wire between the two.

In the compartment (driver's side) immediately behind the generator is the junction box from generator to house wiring.  Drop the metal wire chases in the basements and pull a new wire.  Use the old wire to fish the new one into the bedroom compartment where the ATS is.

Brett
Brett Wolfe
EX: 1993 U240
Moderator, ForeForum 2001-
Moderator Diesel RV Club 2002-
Moderator, FMCA Forum 2009-2020
Chairman FMCA Technical Advisory Committee 2011-2020

Re: generator/electrical update

Reply #12 –
Thanks.  I may resort to that.  I'd still suspect that a wiring issue would show up in other ways.  Once both units are successfully started and running and even if you add in fridge, blow dryer, microwave...the generator is purring and the volt meter is showing 119-120 and everything is great.  Turn one of the A/C units off, wait 10 minutes or an hour, turn it back on and it is a crap shoot if the ATS will stay closed.  I've observed the volt meter closely during compressor start and I've noticed that as it comes on the volt meter will show a dip to say 105 and everything will be ok if the next second the meter jumps to say 110 then a second later to 118 as it stabilizes.  But when it drops to say 105 and the next second it goes to 108 before back up to 110 or so...then the switch opens.  If it would just stay closed for two milliseconds instead of one everything would be OK.  I'm tempted to call the ATS manufacturer and attempt to get their imput.  I realize these switches have a valuable function but perhaps they are just too sensitive.  I wonder if there isn't a battery or capacitor type device that could go between the switch and the generator that could supply that liitle burst of voltage to compensate what happens when you add a load while under generator power.  Even if everything is off and you start adding in load you see that little dip on the voltmeter for a split second.  This has to be normal as I know Onan observed this as did our Ch.Engineer who say this is just what happens...the generator picks it up and all ishould be well.  I can see why everyone's first guess was bad transfer switch.  It is just incredibly odd that old transfer switch did this when removing load and the new one when adding load.  Has to be an explanation based on this curious fact.
Dwayne Keith
1992 U240
3116/MD3060

Re: generator/electrical update

Reply #13 –
Dwayne,

Ya, your symptoms in your post immediately above do not point to a wiring issue. 

The momentary voltage drop upon addition of a heavy load is perfectly normal. 

I am not aware that any ATS was voltage sensitive enough that it will kick out at 105 VAC, but let us know what the ATS manufacturer says. 

Brett
Brett Wolfe
EX: 1993 U240
Moderator, ForeForum 2001-
Moderator Diesel RV Club 2002-
Moderator, FMCA Forum 2009-2020
Chairman FMCA Technical Advisory Committee 2011-2020

Re: generator/electrical update

Reply #14 –
Think I'm going to see if one of our electrical service contractors will rebuild my old switch and see what happens.  Also going ahead with trying to get the right hard start capacitors for the A/C units.  I read through all the posts from the link with the guy who had the same problem and one of the posters thought that the load was ok for the generator and the switch so it must be the wire.  Does the ATS sense a hot overloaded wire and open?  Seems pretty smart for a contactor.  How would I test for this? 
Dwayne Keith
1992 U240
3116/MD3060

Re: generator/electrical update

Reply #15 –
The "right" hard start capacitor actually increased the amps on compressor start.  Dead end.  I have a call into the tech guy at ESCO to ask about the parameters of the 50 amp switch I bought from them.  Our chief engineer is telling me that I just don't want to face the truth that 18+ year old A/C units being way over spec on power consumption is the problem and that I should consider replacing at least one of them with a 13500 BTU energy efficient model that should lower my peak demand to acceptable levels.  Since the front is sucking up about 1.5 amps more than the rear on low or high cool (same on fan only)...I guess that is the one I should junk.  Anyone have any opinion on the Coleman PS?
Dwayne Keith
1992 U240
3116/MD3060

Re: generator/electrical update

Reply #16 –
ESCO says that I could replace my switch with a relay style one that would be more tolerant of low voltage but the simple contactor switch I bought is their most tolerant of contactor based switches and would need 97 volts for a millisecond to open.  He isn't surprised that I'm not seeing anything as low as 97 on the digital voltmeter.  He thinks the old switch opening on removing load makes perfect sense.  Power hungry A/C units running with generator at peak output, take one away and there is a corresponding millisecond of excessively high voltage that caused old switch to open.  The new switch is opening on load up but it is because of the same issue that it drops trying to take on the high load.  He wouldn't say that anything is necessarily wrong with the generator but I kind of got that from the gist of the  conversation.  Despite what Onan says, wouldn't this point to a faulty voltage regulator?  Isn't the regulator tasked with preventing high and low spikes?  I know that there are safeguards (like the ATS) but now I'm back to the generator as the problem.  Power hungry 18 year old A/C compressors are the cause of the spikes but I still think the generator should be dealing with them sufficiently to prevent the ATS from reacting.  Shouldn't excessive demand stall the generator prior to the ATS opening?  Shouldn't a spike high enough to open the old one cause the breaker on the unit or at the power distribution panel to flip first?  Am I expecting too much from the generator?   
Dwayne Keith
1992 U240
3116/MD3060

Re: generator/electrical update

Reply #17 –
Generators rarely / never trip breakers as normaly the voltage will drop long before the amps go high enough and long enough to trip a thermo-magnetic breaker.

When using a 6.5 Onan, that is a very cheap example trying to act like a high class unit. Don't expect miracles.

Why most generators are 7.5 KW diesel or more running 120 volt only and do a great job.

Also have you ever determined if the generator is set up for 120 volt only or is it a 120/240 volt setup??? or unknown ???

Dave M

Re: generator/electrical update

Reply #18 –
I am just disgusted.  I changed out the A/C and only slight improvement.  It may run at under 11 amps but it starts at 15-16 so I am still having the issue though less frequently.  And I know for a fact that these new units don't work as good as the old freon dinosaurs.  I guess this means by process of elimination that it is the generator and Cummins Power South couldn't figure it out.  I know everyone rags on the Onan Emerald Plus but it worked fine last summer!  If they didn't think I was crazy I'd have the new unit taken out and have them put the dinosaur back in.  If it wasn't for the fact that you really can't feasibly repair one once the compressor goes and it is almost 20 years old...I'd do just that.  We're leaving in the morning headed out west.  I guess I'll be fighting with that generator and those A/C units all the way.  I can't wait till I have to drag my wife and daughter out of bed at Flying J at 5 in the morning so I can safely fill the propane tank.  If I knew then what I know now I'd never have bought a rig without a diesel generator and it is really too bad that one cannot be retrofitted in the U-240. 
Dwayne Keith
1992 U240
3116/MD3060