Genset - Code 27

[Renipladlo]

All - I know this is an ongoing issue, and I get it occassionaly. Since I wanted to know what a code 27 was I ordered a copy of the "Service Manual" for our Genset. So I looked up Code 27 and will try to post it here. Code 27 is a: PMA Sense Lost Fault - Controller unable to sense PMA Frequency. The PMS stands for Permanent Magnetic Alternator (which is a generator with diodes to change it AC). What is happening is the genset never synchronizes up with the load in the coach, so the genset shuts down which is what it's supposed to do. Why it happens, and the various remedies which have been suggested, are; software updates to the Xantrex and Genset. The genset has no computer control that can be updated according to the folks at Onan I talked to. It would be nice if anyone has upgraded their Inverter to Magnum and this problem has disappeared to let us know.

Here is a copy of the Code 27 Fault description.

[KIX]

Could you simply either turn the AC supply breaker off that supplies the inverter/charger wen operating on the genset? Or disconnect the inverter completely to see if this remedies the problem.
maybe I don't understand the issue but after reading the last of your post it seems that this would be a method to troubleshoot the problem.

[Renipladlo]

All - Here is the Fault Code 27 explained.
Code 27 is a: PMA Sense Lost Fault - Controller unable to sense PMA Frequency. The PMA stands for Permanent Magnetic Alternator (which is a generator with diodes to change it AC). The various remedies suggested are; software updates to the Xantrex and Genset. The genset has no computer control that can be updated according to the folks at Onan I talked to. If anyone has changed their inverter to Magnum and the problem has disappeared let us know please.

Code 27 Explained: PMA sense Lost Fault - Code No. 27(Controller unable to sense PMA Frequency)

Logic: If between cranking and run_down, rpm=0 and dc bus voltage present for >2 seconds.
Corrective Action:
1. Check for proper connections between the generator (PMA) stator and the controller assembly and reconnect as necessary.
2. Disconnect the PMA leads from the control. Using inPower, turn on the control starter relay in controller assembly (refer to step 7).
Warning – Do not crank for more than 30 seconds (head could melt starting cable conductor insulation-my words).
3. Connect DMM to PMA leads. While the engine is cranking, measure the voltage between PMA leads T1-T2, T2-T3 and TC-T1 using DMM. Set DMM to AC and range. Do not crank the engine more than 30 seconds.
a. If all of the lease measure > 20Vrms, replace controller assembly.
b. If any of the leads measure <20Vrms, troubleshoot PMA (refer to step 6).
TIP – If values of all leads (T1-T2, T2-T3 and T3-T1) is < 20Vrms, problem is with the rotor.
If value of one/more leads is < 20Vrms, problem lies with stator.
4. After measuring the PMA leads, turn-off control starter relay in controller assembly (Refer Step 7E) using InPower.
5. Run the set again and check if fault is cleared.
PMA Troubleshooting Steps:
A. Check for PMA to ground shorts. Use a digital multimeter to measure resistance between each PMA lead to ground. – Meter will read “Open” if there are no shorts. If meter reads a finite resistance, it indicates a short.
B. Check for an open generator stator winding (p.11-1 of this manual). If winding is open replace the stator.
CAUTION – Ensure actuator is at zero and/or fuel is off.
C. Remove top housing panel, check PMA rotor and integrity of the magnets. Attempt to bar the engine by hand to check for jammed magnets. Replace the rotor if damaged.
Note: If the rotor is damaged, do not replace the controller assembly. Replace the rotor first and check to verity if that solves the problem.

6. Steps for turning on the control starter relay in controller assembly using InPower:
A. Enable the parameter “Starter override Request”.
B. Turn on the Parameter “Starter Override Command”.
C. To Verify, check to see if “Starter Override Status”= on.
D. To switch off starter relay, turn off the parameter “Starter Override Command”.
E. To verify, check to see if “Starter Override Status” =Off.

Comments-mine: I think all the above means is the PMA has some kind of physical electrical short or mechanical issues with the magnets. Our problems stems from interference from some source when the main engine is running or we start the main engine. My Genset always starts and picks up coach load if the ISL-400 is NOT running. If I start the main engine first and then attempt to start the genset, it will not pick up coach load and shuts down. If the genset is running and has picked up coach power, starting the main engine might or might not cause the genset to quit running. I have not tried to turn off the battery charger and then start the main engine, as some reported this will cause the genset to keep running. The Main engine is at that point charging the batteries, not the inverter/charger unit, even though the generator is supplying 120V AC to the coach. My gut feeling is that the Xantrex is causing the problems, and there software might be the issue. Since those inverters are not reparable once they quit, and the replacement does not work with the silverleaf system (if equipped), a magnum inverter is the better choice, plus it is a better quality unit and is component reparable at the site.

[HR-TX]

Wow... very impressive. I recently made a post looking for help with a code 46 on an Onan 8000 QD. Any chance you have similar diagnostic steps for that? I believe I have done all the obvious steps but have gotten nowhere. I have 13V at the battery power to the gen, and it does not drop any when I hit the start button. It never trys to crank, just goes into the flashing code.

[Wil Rathke]

I have always had this problem. I talked to an Onan rep at some rally a number of years ago and he was aware of this problem. He explained that some AC harmonics from the Cummins engine alternator were feeding back through the Xantrex inverter/battery charger onto the AC output of the Onan generator which was slightly distorting its waveform and causing the PMA Sense fault.

I have some success, as you mentioned, by starting the Onan. and letting it take the load before starting the Cummins engine. Turning off the Xantrex battery charger always works for me but I normally have to start the Onan first and then disable the battery charger because the Onan usually shuts down before I can turn off the charger.

[radams]

In my case I had already had the Xantrex software updated when I got my code 27. It turned out to be the stator that had failed.

[Renipladlo]

HR-TX - Code 46 - Inverter Power Supply Fault (Low Battery Voltage or power Supply Device Failure)

Basically it means that incoming start voltage is low, you might be starting the coach engine at the same time, the battery cabels are dirty, or there is a weak spot in the cables. Battery voltage to start motor should be no less than 11.0V. So have the starting batteries load tested, it thay are the same one which start the coach, have those load tested. As a last step change the controller assembly.

[Renipladlo]

Well I have changed the alternator from the Leece Nevill to a Delco Remy, but it still happens, so it must be the xantrex. I will turn off the charger and see if that fixes the problem, if it does then I will know to do that in the future.

[takepride]

My shutting off issue is only when the AGS turns on the genset to start charging first thing in the morning. It runs 30 seconds then shuts off. Three times. Every morning.

If I start it manually, it runs fine.

I recall others having this same complaint.

I have an RS3000 and previously and RS2000 (and previously a Heart Interface).

[Renipladlo]

Yep, mine does that as well. I still think the Xantrex is the root of the problem. A couple of folks have installed the Magnum Inverter, with the silverleaf, and once they get home they might chime in and let us know one way or the other if this fixes the problem.

I think it's some interference from the charger/inverter which causes the genset to shutdown. Solution would be to disable the charger before the genset picks up coach power to see if this then allows it to keep running, say about 5 minutes, and then enable charger to see if it keeps running. The only Fly in that soup, is the AGS starts the genset because the battery voltage has gone below the set voltage threshold, by disabling the charger, this nullifies the AGS having started it at all. Sort of a catch 22 to some degree maybe.

I’m thinking I will check the genset by starting it, then turning off the charger, then start the main engine and see if the genset keeps running. If it does keep running then that proves the issue of two points of charging electricity vying for the same load (although that sounds crazy, but there is the theory of loop flow). If it shuts down regardless, then it still could be the Xantrex because with the charger off, the only thing would be back flow (no diodes) from the alternator feeding the batteries and the inverter is also off so the genset senses a loss of output. I have asked Xantrex about software update, they tell me there are not any for my unit. In APEX coaches, you schedule AGS through the silverleaf, in Alpine and Limited coaches w/o silverleaf; you set AGS though the Xantrex. In your coach and not being apex, then this goes along with above thought as either way, you are really talking to the Xantrex for AGS, at least I think we are. The silverleaf is really a central interface to set/manage all the coach functions, and it (silverleaf) is just the (keyboard sort of) to get to all those functions instead of having different control panels for all the various systems, i.e., HWH leveling & slides, Water pump, charger, inverter, yada, yada, and yada, (hope I said that right). However, the dashboard unit and the TV interface are different, so I will need to read up on those. I like the dah unit for some stuff and the TV for other stuff.

[WeBrzn2]

I too have had code 27 and taken the coach to Cummins West in San Leandro for troubleshooting. The genset faulted at least 5 times in a row at home, but of course, as soon as I got to Cummins West, it would not fault. The service advisor told me he has seen this quite a bit and is generally not considered to be a true issue rather it is more of a nuisance.

[Basil Shannon]

Originally Posted by Renipladlo

...............If anyone has changed their inverter to Magnum and the problem has disappeared let us know please.

Have not seen the problem with my old RS2000 or new (approx 6 months) Magnum.

[Renipladlo]

Today - I started genset, and as soon as genset picked up coach load and started charging batteries, it worked fine. Stopped genset, started main engine, then started genset, waited until GS picked up coach load, then shut off charger quick, genset ran fine, enabled charger, it quit running immediately. There is some kind of interference in the alternator/xantrex system which kills the genset with the main engine running. I have tried it both ways, ISL running then start genset, or the other way, start genset, then ISL, same thing happens both cases. I can have genset running w/o charging batteries, and it runs fine, providing power to the coach going down the road. At least now I know what I have to do to keep it running if I want a/c's or some other system to run while traveling. AGS, can be affected by the state of the batteries (not talking about charge level), but if they are in good shape or not. I think I need new ones, and we are debating wheather flooded cell or AGM now. I don't want to spend the money for what they are asking for AGM's around here, so will wait until fall and then go to the main factory to have them installed, unless we bite the bullet, and just get new flooded ones. I need to do something!

[SC RV'er]

Just got a call from my local Onan/Cummins repair shop today regarding my genset shutting down with a code 27. Would run for several hours and shut down without warning or obvious issues, low oil or coolant. Said inverter was faulty and genset would shut down when no a/c detected. Didn't realize it was a d/c unit and converted to a/c. Who knew. Well at least not me. Hope this helps others.