I now know that the Dimensions inverter/charger failed due to transistor component failure. The metal oxide varistors (MOV) that Dimensions installs to protect the transistors from electrical spikes were not damaged so a voltage spike could not have damaged the transistors.
I initially believed the inverter/charger failure was caused by the following event: cool weather during our previous early December camp out required us to use the heat pump and we forgot to turn it off when we departed for home. I thought maybe the heat pumps cycling on and off caused an internal spike. Others suggested the inverter/charger probably just failed coincidentally. However, I also found the sleep number bed pump/control board not working so there did seem to be some evidence that a electrical spike from somewhere might have caused some of the motor home (MH) equipment to be damaged. And the "sleep number" mystery is still not resolved.
I connected shore power on 12/27. The weather was warm and stayed warm until January 1st at 73 high and 50 degrees low and the 2nd at 51 high and 34 degrees low. When the MH interior temperatures cooled below the 69 degree heat pump thermostat setting during that two day period the heat pump must have begun it's on and off starting cycle.
When I arrived at the MH on the morning of Wednesday 1/2/08, to turn on the refrigerator and setup for the coming Friday departure, I heard a loud chattering noise. While I stood there the Surge Guard turned power on after its programmed two minute 16 second start up delay (provided to allow head pressure to bleed off the A/C compressor) and then I heard the air conditioning motor starting and then the Surge Guard shortly thereafter shut off, turning off the power. I unplugged the shore power cord and in disbelief went to the central heat/air conditioning system thermostat and found the heat pump switch turned on.
After turning off the heat pump I re-powered. When the power came back on I was standing at the One Place Energy Management System (EMS) panel and there was a LED lamp glowing red: an error message I turned on the inverter and tried to reset it to clear the "over load" error message and then turned the inverter off not realizing or thinking the problem through to the conclusion that the inverter had been damaged. Beside, the Dimensions panel screen showed a 12.0 battery voltage and a 10 amp current draw which at that time indicated to me, incorrectly, that the charger was working. The next day, even with the shore power connected overnight, the battery voltage had dropped to 11.9 and it occurred to me that instead of just 10 amps I should have a larger current draw, at least initially something like 15 to 20 amps. It was then that I realized the charger was probably damaged. Later I was told that not all the transistors were damaged and that was the reason there was still a 10 amp charge and the Dimensions display panel was still operational.
The charger also acts as a "converter" to supply 12 volt power to operate the 12 volt systems. The number of 12 volt systems that are allowed to be used must be monitored by me when limited ampacity is available. I can use the EMS panel that provides the AC line amperage to monitor the amp load. From now on when I plug into a 20 amp circuit I will need to evaluate if I need to manually restrict the charger draw. This can be easily done at the Dimensions panel using the "charger draw" switch and selecting a lower current draw such as 10 amps.
The Surge Guard equipment I installed back in June protected the two A/C (heat pump) air compressors from low voltage startup by shutting off shore power within 810 seconds of reaching the low voltage threshold of 102 volts. RV Products says the minimum voltage is 105 VAC. But the heat pumps only ran on 102 VAC for 8-10 seconds before the Surge Guard shut off the power and no apparent damage occurred. The Surge Guard installation paid for itself many times over considering what it would have cost to replace air conditioner compressors damaged by low voltage.
The Energy Management System (EMS) will shut down the Unit two heat pump within four seconds (per Intellitec) if the current draw exceeds either the 30 or 20 amp threshold. When I went looking on the web for technical support for the EMS panel I found the Intellitec Company. They have apparently assumed ownership of the product line. Intellitec answered my inquiry regarding load shedding the unit two heat pump after it started when using 110 VAC at 20 amps. The technician said the unit two heat pump would shut down in 4 seconds after the magnetically coupled current sensor measured an excess of 21 amps. He also suggested that the heat pump stopping suddenly during start up would not have enough inductive energy to cause a voltage spike.
The Dimensions unit provides some protection against small spikes using metal oxide varistor (MOV) protection. The Dimensions engineering department told me that the MOVs are not used for protection because of their small size but as an indication that a voltage spike occurred. If the MOV is still good then the inverter/charger transistor failure is considered component failure. Per Dimensions their Inverter/charger unit is used by the utility industry on a wide spread basis. They believe that this application provides a rugged environment to proof test their design. Still, maybe there are other inverters that have stronger MOV spike protection components. It's just not something I am familiar with.
Another component to this electrical puzzle is the 110 VAC shore power circuit. Why didn't the shore power 110 VAC outlet circuit breaker open when the second heat pump unit attempted to start? Adding the second heat pump unit to the shore power line load would have exceeded the 20 amp shore power circuit ampacity. My theory is that because the EMS was in the 30 amp mode EMS could not drop the second unit because the amperage did not exceed 30 amps. So as the amps increased the voltage dropped. When the unit two heat pump tried to start and there was not enough shore power circuit ampacity within seconds the voltage dropped low enough (102 volts AC) to trip the Surge Guard and 8 -10 seconds later shore power was turned off. After a delay of 2 minutes 16 seconds the Surge Guard measured normal voltage and power was turned back on. The start up cycle repeated as long as there was heat pump demand. So even though there was a high ampacity it wasn't sufficient or lasted long enough to generate enough heat to create enough thermal over load to open the circuit breaker. And with the cold weather it would take longer to reach the thermal overload rating (Electrical box furnishing shore power sits outside) so the amperage was able to increase even higher then normal before the circuit breaker opened. Secondly, there were no melted wires to cause the circuit to go to ground and open the circuit breaker. In this situation the circuit breaker had no job to do because the Surge Guard shut down the power before the circuit breaker's shut off threshold was reached.
Did the One Place Energy Management System (EMS) panel also play a part? When I connect to the 110volt/20 amp circuit where we store our MH the EMS panel indicates that "Service Type" is 30 amps which is the default setting when 50 amps (L1, L2 voltage and neutral inputs) are not available. Normally, when I plug into 20 amp service I manually switch the Service Type to the 20 amp setting. I suspect that after analyzing what happened I did not switch to the 20 amps setting. A second error that compounded the first one!
Per the PowerLine 2000 installation and service manual, when in 20 amp service the EMS operates the same as in 30 amp service, just a lower amperage limit. Per the RV Products (heat pump manufacturer) data sheet the unit one heat pump/air conditioner draws about 13.9 amps and both unit one and unit two together draw about 23.2 amps. Heat pump operation always energizes both units but with a 30 second delay between startups.
If the EMS Service Type was in the 20 amp selection, even with no other power demands, the EMS would allow the unit two heat pump to start but in four seconds would prevent unit two from running because the additional amps would exceed the 20 amp limit. There would have been no repetitive startup cycle.
If Service Type was left in the 30 amp mode then it was possible for both heat pump units to start because in the 30 amp mode EMS will be trying to measure for an excess of 31 amps. However, as I mentioned above it was the Surge Guard that repeatedly protected the heat pump equipment by sensing the voltage drop below its minimum 102 VAC threshold when the second unit attempted to start.
So I conclude that the EMS panel did its job as designed.
There is an interesting RV Products aside which I learned about during a discussion with a RV Products engineering technician. He suggested that the heat pumps probably did not cycle the entire time period it was cold. Because I had my LP gas turned on, the LP gas furnace would have been automatically turned on once the heat pump was not able to maintain a 4 degree temperature differential between the thermostat setting and the actual temperature. Once the furnace is turned on it runs on 12 VDC and the heat pumps are shut off. I found this documented in the Winnebago manual under "Appliances & Interior Features - Heat Pump."
The RV Products technician also told me there was a "three strikes and your out" system. That I did not find in the Winnebago manual. But I did find it at the RV Products website in a Service Manual PFD file:
http://www.rvcomfort.com/pdf_documen...408_copy10.pdf. Basically, if the heat pumps can not keep up after the furnace has to provide heating support twice the heat pumps are locked out for two hours and the furnace becomes the primary heat source. The heat pump will return as primary heat source any time the heat pump satisfies the thermostat set point and does not need gas furnace.
In conclusion, in talking with Dimensions they initially believed that the inverter/charger failed because the repeated heat pump starting cycles caused internal voltage spikes or generated too much heat for the inverter/charger transistors to dissipate and they cooked themselves. In the end that was not an accurate assessment. Should I expect the Dimensions design and components to be hardier? Are they less hardier then other inverter designs? In truth, for me it's academic as I elected to have the Dimensions unit repaired. But if you are in the market for an inverter/charger it might be something to think about.
The lesson: I need to be sure that what needs to be off is off. And on the other side of that coin: before I turn on an electrical load I need to think about the electrical system's capacity and its ability to handle the additional electrical load. Incidentally, I have inserted a plug in surge guard into the 110 VAC outlet that powers the Sleep Number pump/control. It may not make sense but it can't hurt!
Winnebago C, 24 V /08 Saturn Vue/2014 Town and Country Van/03 Goldwing (Big Red)Recently triked Roadsmith kit
. The cost of the lesson was $471 
including return shipping. They shipped it Monday and I received it back today. They replaced both boards: main and chg; provided a new panel; installed a new fan. My exisiting panel is good but they said a new panel was required to match the upgraded boards. Will install in the next few days. 
Linear Mode
