| Author | Message | ||
| Chuck Newman (Chuck_newman)
Registered Member Username: Chuck_newman Post Number: 280 Registered: 1-2005 Posted From: 76.246.254.144 Rating: N/A |
I have designed my AC electrical system such that the front roof air conditioner will be used while driving, as well when parked. It will be powered by either shore power, generator, or 4KW inverter. My question to George xxx, Nick bbb, and other air conditioning guru's is this: Power from any one listed source will transfer to another source within 100 milliseconds, which is six (6) cycles of AC. I think the average roof top compressor (Carrier specifically) can tolerate that short of gap in current supply, BUT will a significant change in phase from one source to the other adversely affect the compressor. If it will, I can insert transfer delay to accommodate compressor equalizing time. What would be the recommended time? I have read some compressors require only 15 seconds while others need two minutes or more. | ||
| Chuck Newman (Chuck_newman)
Registered Member Username: Chuck_newman Post Number: 281 Registered: 1-2005 Posted From: 76.246.254.144 Rating: N/A |
Sorry folks. The post above is an unfinished draft. Please ignore. Was posted by errant fingers and tired brain. | ||
| Chuck Newman (Chuck_newman)
Registered Member Username: Chuck_newman Post Number: 282 Registered: 1-2005 Posted From: 76.246.254.144 Rating: N/A |
My apology, let's try again. I have designed my AC electrical system such that the front roof air conditioner will be used while driving, as well when parked. It will be powered by either shore power, generator, or 4KW inverter. My question to George Todd, Nick Badame, and any other air conditioning guru's is this: Power from any one listed source will transfer to another source within 100 milliseconds or less, which is six (6) cycles (or less) of AC voltage. I think the average roof top compressor (Carrier specifically) can tolerate that short of gap in current supply (let me know if it won't), BUT will a significant change in phase from one source to the other (up to 180 degrees phase angle) adversely affect the compressor while operational? If it will, I can insert transfer delay to accommodate compressor equalizing time. What would be the recommended time? I have read some compressors require only 15 seconds while others need two minutes or more. | ||
| FAST FRED (Fast_fred)
Registered Member Username: Fast_fred Post Number: 549 Registered: 10-2006 Posted From: 66.82.9.56 Rating: N/A |
IF the motor keeps running (I think it wont notice a few milliseconds) there will not be a problem. If it "misses" the head pressure will have to go down ,to avoid a locked rotor start, 2+ min is always a good idea, to lower the restart amps of the any condensing unit. Simply install an on off switch in the line and see how long it takes to miss when you manually switch it off. My guess is 2 seconds or so won't be missed . Load sensing relays are in the Granger catalog. FF | ||
| Tim Hoskinson (Tdh37514151)
Registered Member Username: Tdh37514151 Post Number: 247 Registered: 9-2004 Posted From: 65.25.139.50  Rating: N/A |
Fred is correct. Single phase motors will continue to run in the same direction with a momentary loss of power. The rotation direction is only determined by the phase differential between the main run winding and the start winding. This polarity differential is set up when the start and run winding are connected for the desired rotation direction. The motor would only have a problem if the rotation speed were to reduce to a level at which the start torque of the motor was unable to overcome the head pressure and the motor would stall. At this point it would simply do as Fred stated and go into overcurrent shut down for a predetermined amount of time then reset and start again. Best of luck. Tim | ||
| Nick Badame Refrigeration Co. (Dnick85)
Registered Member Username: Dnick85 Post Number: 258 Registered: 2-2006 Posted From: 75.198.132.212  Rating: N/A |
Hi Chuck, The only problem with harmetic and rotary compressors is that when you drop out the voltage for 100 milli seconds, the start winding will kick back in upon restart and overload your curcuit. I know what you are trying to accomplish! I have tried the same thing on my coach while under construction. When I would transfer from shore to gen or vise versa, the curcuit breaker for the A/C's would trip no matter how hard I researched a solution for it! You are going to need 5 mins for your carrier rotary compressor to equalize the presure in the system before restart. The only compressors that don't require equalizing are 3 phase compressors, and belt driven ones. I don't see a problem with 180 out of phase as long as you can get there ok with in the 100 milisecond. Now, If they would only make DC compressors more affordable...?? Nick- (Message edited by dnick85 on November 23, 2008) (Message edited by dnick85 on November 23, 2008) | ||
| Buswarrior (Buswarrior)
Registered Member Username: Buswarrior Post Number: 1395 Registered: 12-2000 Posted From: 76.69.142.237  Rating: N/A |
Using a Trace 4024, and all sources bow before it, it takes care of these changes between sources. I use the simple manual plug method, shore cord to shore or generator, the batteries are tied to the coach alternator. The Trace aligns the frequencies and carries on within a minute of swapping, no interuption to the device, juts runs on the batteries for that time of synchronizing. Did that make sense to the smarter folks? happy coaching! buswarrior | ||
| Chuck Newman (Chuck_newman)
Registered Member Username: Chuck_newman Post Number: 283 Registered: 1-2005 Posted From: 76.246.254.144 Rating: N/A |
Thank you all for the input. Buswarrior, I thought of that except I have a Magnum 4024. It's basically the same as the Trace and Xantrex, but the Magnum does not utility phase lock or load share. | ||
| George M. Todd (George_mc6)
Registered Member Username: George_mc6 Post Number: 624 Registered: 8-2006 Posted From: 207.231.75.253 Rating: N/A |
Chuck, Nick pretty much said it all, which is that single phase compressors can't start under load. I wouldn't try a changeover like that, just because IF the compressor stops, it can't restart under pressure. So, depending what type of start components it has, something may or may not happen. If it only has one capacitor which does the start and run, it won't restart until the pressure equalizes, which will be at LEAST two minutes. In the meantime, it will draw locked rotor amperage, and either trip the breaker, or trip the internal overload in the compressor, which will reset the first time in a couple of seconds. Each trial will have a longer wait time inbetween, as the motor heats up, going to ten or more minutes between tries. If it has a PTCR in the start circuit, it won't do any better, as the PTCR is open when it is hot, and it stays hot while running normally, its only cold at startup. The only hope is a potential relay with a couple of hundred uf. start capacitor in addition to the run cap, also known as a hard start kit, for obvious reasons. Many caps can't stand 4 or 5 seconds of locked rotor current before a protective device trips. Personally, I would shut the AC off, changeover, and wait 5 minutes before a restart. George | ||
| marvin pack (Gomer)
Registered Member Username: Gomer Post Number: 345 Registered: 3-2007 Posted From: 71.55.230.210 Rating: N/A |
George I found out that when you have like a power blitz you can put in a hard start kit to offset the amp draw to a degree, I prefer tho to have a hard start along with a 1-2 minute delay on the compressor. It makes it start quicker and doesn't drag the power down. Gomer |