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+--- Thread: Generator Switch Box (/showthread.php?tid=128)
Generator Switch Box - Darrell Snell - 02-28-2013 16:34
Late last summer we lost power on leg two of our Powertech 15kw generator. At the time I suspected the failure was a result of the extreme current I would see when the front AC would start. The amp meter on leg two would peg out.
I called Powertech and they told me I would need a new genny.
Anyway I got around to looking at it today and found a burnt wire on the T1 terminal of the generator contractor. The wire size on T1 and T3 was 10ga. All other wire size was 6ga!
I replaced the burnt wire and fired up the genny and both legs were hot. Turned on all AC's and noticed the smell and smoke of insulation at the same bad terminal.
Turned genny off, seeked help.
Are these supposed to be rudimentary fuses? Just kidding.
Has any one else seen this?
Darrell
RE: Generator Switch Box - davidbrady - 02-28-2013 16:58
Hi Darrell,
In the Powertech manual (below) there's specs for the stator coil resistance - I have no experience with checking this, but it's recommended in the troubleshooting tips. Also, it looks like 10 gauge wiring at T1 and T3 is factory standard. You may want to check for excessive current draw from the AC's, but it seems that a circuit breaker should also trip. Maybe both a faulty circuit breaker and excessive current draw.
Here's a Powertech Owner's Manual with troubleshooting tips:
http://wanderlodgegurus.com/showthread.php?tid=129
RE: Generator Switch Box - pgchin - 02-28-2013 17:20
Darrell,
David gave you excellent advice on troubleshooting the powertech. I have not seen this before on the bird BUT, I have elsewhere. If it were me, I'd do the resistance check David suggestion and if its good, then rewire again. Keep the AC unit that pegs leg 2 OFF and try and turn on a few things so you can get a 20-30 amp load on both legs, then see where you are at with the new wiring. The only other things I can think of for a SWAG would be the bearing is starting to go but there is no way to check that without tearing the head apart. Take a peak at the voltage regulator if you can and see what kind of shape it's in.......
The AC unit that pegs the meter probably has a bad or weak start motor capacitor or the compressor is shot. I'm willing to bet your Blueberry farm on it!
hashahahahah-just clowin around! Seriously Have seen this MANY times. Climb up on the top of the bus, remove the AC cover (4 screws). Then remove the metal cover that covers the system and forms the air compartments, about 10-12 sheet metal screws. That starter cap should be on the curb side. You can use your ohm meter to see if it's shorted........ very common deal, maybe its causing the genny to overload leg 2? (SWAG) Please BE CAREFUL up there, Donna always hangs around while I'm up there so she can catch me if I fall! If the cap is bad, you can get what you need locally at any appliance parts supply store on the cheap. They will match it up for you. If the compressor is bad,,,,,,,uuhhhhhhhhh use 2 ac's :-) until you save up for a new one! FWIW I have one that's starting to do exactly that and I Know the cap is good so I do not use it anymore and will replace it.......its on my punch list! It's the middle one so the front and rear AC keep the coach comfortable most of the time.
RE: Generator Switch Box - Darrell Snell - 03-02-2013 09:52
(02-28-2013 17:20)pgchin Wrote: Darrell,
David gave you excellent advice on troubleshooting the powertech. I have not seen this before on the bird BUT, I have elsewhere. If it were me, I'd do the resistance check David suggestion and if its good, then rewire again. Keep the AC unit that pegs leg 2 OFF and try and turn on a few things so you can get a 20-30 amp load on both legs, then see where you are at with the new wiring. The only other things I can think of for a SWAG would be the bearing is starting to go but there is no way to check that without tearing the head apart. Take a peak at the voltage regulator if you can and see what kind of shape it's in.......
The AC unit that pegs the meter probably has a bad or weak start motor capacitor or the compressor is shot. I'm willing to bet your Blueberry farm on it!
More info on generator transfer switch.
Thanks to you both for the insight and direction.
Once again I ran all 3 AC's under load (had to set the thermostats at 40F) and observed the amp gages. During normal cycling of the AC's no current spiking was observed. The replacement 10 ga wire didn't get warm, no smell or smoke and my clamp-on amp meter agreed with the coaches. About 12amps per unit under load.
If I manually start an individual unit while there is a demand in that zone I will see a prolonged spike on the meter of which ever leg that unit is wired to. I haven't had the guts to leave it on for more than 3 to 5 seconds and the 20amp breaker doesn't trip. This happens to all 3 units including the center unit which was replaced last spring.
Yes indeed the transfer switch comes from the factory with 10ga wires between both sets of T1 and T3 terminals and one 6ga wire between the T2s (white neutral). The balance of the terminals were wired by BB with 6ga.
Should there be some logic in the AC units or the thermostat that delays engaging the compressor until the motor has started?
Why don't the breakers trip?
I'm pretty sure this condition is what fried the earlier 10 ga wire.
Nice to have the Aqua Hot last night, warm floors too!
D
RE: Generator Switch Box - pgchin - 03-02-2013 10:40
Darrell,
We have different thermostats so we'll David to weigh in here as he has what you have. Two points though, I could never run 3 ac's on the generator. One would always overload the system and automaticity shut one down. When I manually start any of mine, the motor starts first pulling about five amps. Then about five minutes later, the compressor kicks in and a momentary spike of thirty amps happen and the system settles in at 12-15 amps steady state.
RE: Generator Switch Box - Darrell Snell - 03-02-2013 10:59
(03-02-2013 10:40)pgchin Wrote: Darrell,
We have different thermostats so we'll David to weigh in here as he has what you have. Two points though, I could never run 3 ac's on the generator. One would always overload the system and automaticity shut one down. When I manually start any of mine, the motor starts first pulling about five amps. Then about five minutes later, the compressor kicks in and a momentary spike of thirty amps happen and the system settles in at 12-15 amps steady state.
Good stuff
Yours works like I think it should, except the overload condition. Motor starts fan only, compressor pulls in after delay with a little spike.
Mine can be started under a load resulting in a locked rotor!
Not good...
D
RE: Generator Switch Box - davidbrady - 03-02-2013 11:27
Darrell,
The installation manual specs locked compressor inrush at 60A and locked fan motor at 6A. I don't think there's any delay built in to delay compressor startup. I believe this cause there are addons to dometics to insert delays. What are your leg voltages during compressor startup? If the genny is a weak voltage source then voltage will fall more than normal and inrush current will increase above those spec-ed in the manual. I think max inrush would occur only for the first half second or so and quickly disappear and be over within 3s (exponential decay). I have had no problems running three AC's on the genny. The manual specs a minimum generator capacity of 3.5KW per AC unit, so our 15KW units are easily adequate if operating normally.
http://www.dometic.com/1f24ead8-6316-41b6-894c-d01f87ce6bad.fodoc
RE: Generator Switch Box - pgchin - 03-02-2013 11:33
(03-02-2013 10:59)Darrell Snell Wrote:OK,(03-02-2013 10:40)pgchin Wrote: Darrell,
We have different thermostats so we'll David to weigh in here as he has what you have. Two points though, I could never run 3 ac's on the generator. One would always overload the system and automaticity shut one down. When I manually start any of mine, the motor starts first pulling about five amps. Then about five minutes later, the compressor kicks in and a momentary spike of thirty amps happen and the system settles in at 12-15 amps steady state.
Good stuff
Yours works like I think it should, except the overload condition. Motor starts fan only, compressor pulls in after delay with a little spike.
Mine can be started under a load resulting in a locked rotor!
Not good...
D
So I WAS SUPPOSED to be working out in my garage this am on other punch lists, BUT it is so cold, I decided to fire up the puter instead of the phone since I still type like an infant on that thing and kabbits with you guys!
Yeah, I do not know how your thermostat is wired hopefully David can help here, I have the old manual kind. I do know a little about programmable thermostats though, mostly in houses here in Florida for heat pumps and what I can say is there is definitely a compressor delay programmable option in these things. It's either a true software program option located under the technicians password or a hard wire to a certain pin......They messed that up when we had a new system installed recently and the system was behaving like your AC's are, both the compressor and motor started at the same time. As for my overload shutdown, yeah, every time I try and bring up 3, the last one I bring online fires up the motor but won't start the compressor and just shuts down.......been like that since I got the coach, never bothered to troubleshoot it but I did check all the wiring and relays and they are good.Duh, Just saw David's post after I wrote this, Thanks David!!!!! I knew you would have some insight!!!!! :-)
RE: Generator Switch Box - Arcticdude - 03-02-2013 11:48
Pete,
My 96 will run all 3 on the genny. I've got to be a little careful, as the middle and rear are on leg 2, along with a bunch of other stuff. It's really easy to imbalance the two legs. But other than that, I have no issues with the A/C's.
RE: Generator Switch Box - Darrell Snell - 03-02-2013 11:53
(03-02-2013 11:27)davidmbrady Wrote: Darrell,Thanks David
The installation manual specs locked compressor inrush at 60A and locked fan motor at 6A. I don't think there's any delay built in to delay compressor startup. I believe this cause there are addons to dometics to insert delays. What are your leg voltages during compressor startup? If the genny is a weak voltage source then voltage will fall more than normal and inrush current will increase above those spec-ed in the manual. I think max inrush would occur only for the first half second or so and quickly disappear and be over within 3s (exponential decay). I have had no problems running three AC's on the genny. The manual specs a minimum generator capacity of 3.5KW per AC unit, so our 15KW units are easily adequate if operating normally.
http://www.dometic.com/1f24ead8-6316-41b6-894c-d01f87ce6bad.fodoc
I didn't realize the compressor and fan motors were not the same.
I will check the voltage during startup in generator and shore power mode.
D