-
Mrathon AC transfer issue
The other day while leaving a campsite I killed most all AC loads, disconnected from shore power, and started the generator. It was quite hot so I turned on all four A/C units, looking at my techlink screen I could clearly see the amperage for the A/C units being supplied by the generator as well as the house batteries being charged, all of which is normal. Upon starting the engine I noticed that now there was a large load on each inverter being supplied from the house batteries and the alternator was supplying a charge matching the load on the inverters, exactly as if I were running two of the A/C units from the inverters with the engine running but no shore or generator power. I shut off the two A/C units that are in the main AC panel and the load on the batteries dropped to near zero and the alternator adjusted down accordingly, and the generator continued supplying current to the other two units but still not to the batteries. Stopped for a pit stop and some lunch, shut down the engine and could see that now the generator was charging the batteries again so I started up the other two A/C units and everything was back to normal, started the engine to leave and back to the same situation with the large draw on the batteries. I have only had this bus for 11 months but have ran all of the A/C units several times from the generator with the engine running and did not have this condition. To sum it up, it seems that with the generator running and upon starting the engine that all loads in the Main AC panel switch to the inverters and the Aux panel continues to run from the generator. It seems that there is a relay or contactor in the transfer panel that is incorrectly switching upon starting the engine.
If Ben or one of the other Marathon electrical guys could point me in the right direction it would be greatly appreciated. After my last trip to Marathon in TX, I have little confidence that they can solve the problem and I am scheduled to leave on a two week family trip next week.
Thank you
Thank you
-
6 Replies
-
This sounds like normal behaviour to me. The coach is set up to run your main panel through the inverters allowing you to run 2 ACs without running the generator when under way. With the engine on, the alternator will supply the current to run the inverters. If you are concerned about cycling the batteries, there should be no net discharge on the batteries thus no cycling. The electrons flow from the alternator to the inverters, no chemical reaction involved.
Now, if you could run all four ACs off the generator while going down the road before, you might want to check your “A/C select” button choice. On my coach I can only select which A/C to run off the inverter. Yours might be different.
-
When I say normal I am just using the way it has been up until last weekend as a baseline for normal, it may really be abnormal. The marathon book that I got with the coach says ” When you start your coach’s generator, power flows to the transfer swithces, which shuttle it directly to the main and auxilary AC breaker panels. At the same time,the generator supplies power to the inverter/chargers to charge the house batteries.” The power from the generator does flow thru the inverters and the remotes say “AC2 in good”, which should put the inverters in charge mode. Maybe you are correct and my condition is normal but it would seem that the main panel loads should only be supplied by the house batteries and the alternator when there is no shore or gen power available.
-
I had a 2001 Marathon XLII and I think that you should be able to run all 4 from the generator and not through the inverters,I think that you should cycle the generator off then on and see if the results change.I think that the contactor for the generator is not pulling in.
-
The reason you saw the inverters power their downstream A/Cs and not charge the batteries is because the voltage regulator on the alternator is always set higher than the battery float voltage. The inverters “saw” the higher voltage and think the battery voltage is too high, they then try to use battery power, and end up inverting in an attempt to maintain the float voltage setting. This feature was integral to the SW-series inverters for the installation with wind or solar power availability. The are simply utilizing the current available from the alternator to run “their downstream loads” rather than utilizing the power from the generator. When you shut the engine off, you noticed that since there was no source charging the batteries above the float voltage setpoints for the inverter, they resumed charging if necessary, and taking generator power to power the A/C’s downstream of them.
Remember, on a Marathon, only two loads can be run from the inverters, the others are powered from the Aux Panel, which has its own transfer switch to select what feeds it, shore or generator directly, not the inverters.
Hope that helps.
Ben Cummings
Parliament Motor Coach
Ben@parliamentcoach.com -
Went out the the bus garage Saturday to do some troubleshooting. Batteries fully charged, same as before, and everything was back to normal. With shore power off and generator running and all 4 A/C units running, everything was running off of gen power and inverters showed float charge on batteries. Start the engine and everything stayed the same, running and charging from generator, unlike the one time before when the inverters were powering the main AC panel loads and batteries charging from alternator with the generator running. I was unable to recreate those circumstances.
According to the schematic I have, Ben is right the Aux panel is transfered directly to the generator when it is running however the main panel is fed by the generator but thru the inverters. When on shore power the main and aux panels are supplied thru the inverters and the aux transfers completly out in the absence of shore or gen power. -
To clarify, with engine at idle, the alternator is only able to put out less than half of its rating. At driving speeds, normally around 1400rpm, the alternator will seem to put out higher voltage because it can now produce its rated output, possibly giving you the results you saw on your last drive. On coaches with bus air, and an isolator between the alternator and battery banks, this was not an issue like when there are two separate alternators with no isolator for each individual battery bank. If you see the “problem” persist on future drives, you may want to consider adjusting down the voltage regulator on the alternator. Doing so below the inverter float setting of 26.6vdc will prevent the inverters from wanting to lower the battery voltage as i mentioned before by inverter the load amps like you observed.
If you would like to discuss further, feel free to give me a call.Sincerely,
Ben Cummings
Parliament Motor Coach
ben@parliamentcoach.com
813-830-8619 (My Cell)
888-571-5755, ext 230 (Office)
Log in to reply.