Testing running roof air via inverter

Best AC effeciency is to direct motor drive the compressor. Find the optimum BEST TORQUE engine speed then pulley drive ratio from there. I tested a Duo Therm 13.5K in 1993. Trace 2012SB inverter off of 2 8-D batteries. 176 amperes at 12.4 volts.

Lessee that was almost a quarter-century ago.

pianotuna wrote:
Hi howardwheeler,

It is possible to retrofit a mini split air conditioner on an RV, but it costs a bomb.

It's funny you say that. Here in Mexico you can get a one ton minisplit with heat pump for $250. When I checked for my rental in San Antonio, Tx. they were over $750. Don't get it, three companies produce all the compressors and the brands are the same here and there. Only problem is that we weren't allowed to take one to the U.S.

I want one on my TT. Eliminates the noise and vibration of a roof A/C and at only 24ft, a roof air turns the place into a freezer. Would be really nice but I'm leary to take the plunge.

I was going shopping. I did not know how long I would be gone. There would be no point in burning fuel unnecessarily to run the roof air conditioner, so I shut the entire system off. My batteries were not low at all.

If they had designed properly, the cooling fans would run on DC independent of the inverter being on or off and should have a temperature sensor that runs them.

I will say that Magnum stood up to the plate and sent me a replacement unit.

Pianotuna thanks for your time answering my questions just trying to learn/ understand.

In order to invert don't you need 12 volts or do you mean that you ran your batteries down before turning off the inverter causing no power for the fans to run?

From the manual....
Operation
3.9 Inverter Fan Operation
The inverter contains two internal cooling fans that are automatically controlled. The speed of these fans is determined either by the internal temperature of the inverter or by the load on the inverter. The inverter’s fans will come on under the conditions listed below:
• Fans run full speed if the internal transistors (FETS) or the power transformer reaches 80°C (176°F), or the inverter is running at 100% of its rated load.
• Fans run medium speed if the internal transistors (FETS) or the power transformer reaches 60°C (140°F), or the inverter is running at 50% of its rated load.
• Fans run low speed when the inverter is running at 25% of its rated load.
The fans shut down when none of the above conditions are met, or if the battery voltage is below 9.5V (12-volt systems)/19.0V (24-volt systems).The fans shut down when none of the above conditions are met, or if the battery voltage is below 9.5V (12-volt systems)/19.0V (24-volt systems)The fans shut down when none of the above conditions are met, or if the battery voltage is below 9.5V (12-volt systems)/19.0V (24-volt systems)
Whenever the inverter is first connected to the battery, the fans start for about one second. The inverter’s fans will not start based on temperature sensed by the optional BTS.

At times I can here my fans on low with only the batteries powering the system.
Just trying to sort this out in my head or am I missing something?

pianotuna wrote:
Thanks for posting the link to the video.

I see that voltage dropped to 59 when the compressor started up. The lowest I've seen before the Microair installation was about 96. That was enough to concern me.

Yeah, that concerned me as well, which is why I ultimately dropped the idea of powering my 13.5K A/C with my EU2000i and sold the genset. Had I known at the time about the Micro-Air Easy Start soft starter kit I'd have definitely added one to the A/C instead of the SPP6 and likely would have then avoided this excessive voltage drop when the A/C compressor kicked in.

Did you ever try to start the air with the generator in eco mode?

This was several years ago so I don't recall whether I tried initially starting the A/C with the genset in Eco mode but I do know that as the A/C later cycled on/off the genset would most times cope with the load with Eco on. However, the unavoidable problem was that as ambient temperatures rose into the upper 80s F (just when A/C was needed most) the chances of successfully starting the compressor became less and less, even with Eco mode off. It's just speculation on my part but my bet is the Micro-Air would solve this issue and allow the A/C compressor to start repeatedly at temps when A/C would be most required, 'though perhaps with Eco on that may asking too much even of the Micro-Air.

Hi,

Yes, load support works with "weak" shore power supplies. But it does not support the AC voltage. It only draws extra current from the battery bank. I was quite disappointed when I found that out.

The fire happened because I turned off the inverter. That turns off the cooling fans in the Magnum. I.E. the fans only work when there is 120 volt power available. That is an unfortunate design choice. They should have used 12 volt DC fans.

The inverter did not shut down from over heating on the occasion of the fire.

Itinerant1 wrote:
I thought that one of the pluses of the hybrid was if there is "weak power" it can supplement it within the set parameters.

You say "One of the few design faults of the Magnum is that the cooling fans shut off when the inverter or generator are turned off." Unless I misunderstood about the ac/ fridge experience is once you turned off the ac/ fridge that is what you mean turning off the load support. Then when shutting down the generator you still left the inverter on gathering power from the sun to charge your batteries (I'm guessing that you had solar at the time). So unless the batteries where drained beyond the LBCO or you physically turned the inverter off the fans should stay running till the inveter cools off or it would of shut itself down before hand for over heating.

I've just went back into the manual a reread section 3 (operation) of load sharing and fault settings and it just seems there are features to prevent the inverter to operate with in the parameters (preset/ or manually changed) to operate with low voltage or "brown out" as stated in the manual.

The ground fault thing I have not come across since installing the system I've only been in maybe 6 state campgrounds that had power.

pianotuna wrote:
Hi Itinerant1,

When the Magnum is set to load support and there is, for example, a 15 amp shore power supply @ 120 volts, then when more than 15 amps are needed the excess current is taken from the battery bank. I.E. running a 10 amp coffee pot while running a 16 amp microwave. However the output voltage will still sag as the load increases.

On the other hand, if a "weak" 15 amp shore power supply @ 96 volts is being used to attempt to run an air conditioner, then an autoformer can "boost" the voltage up to 108. Without the autoformer the air conditioner would be damaged pretty darn quickly.

One of the few design faults of the Magnum is that the cooling fans shut off when the inverter or generator are turned off. I had been using load support help with the surge from the roof air, and fridge from my Yamaha generator. It was a hot day and so the load was 1900 watts from the AC and 325 watts from the fridge. I decided to go shopping--and so I turned off the load support and then turned off the generator. When I came back an hour later the red fault light on the Magnum remote was on. When I started the generator, no power would pass the Magnum. I bypassed the unit, and I had power again. That is when I noticed the soot marks on the wall above the Magnum.

Earlier in the summer of 2016, I was in a campground and it was hot as Hades. I did not yet own an autoformer. The voltage was only 102 on a 30 shore power feed at the campground. I found out, more or less by accident, that I could force the Magnum to do "voltage support" by dialing down the input amperage to just 11 amps. I do have a modest solar system and that meant I was able to run only the roof air from the (low voltage) shore power supply, without totally draining the battery bank. It did cause the Magnum to become pretty hot (I don't remember the numbers).

I do not recommend forcing the Magnum to do voltage support.

One other oddity is that sometimes the Magnum will not function if there is a ground fault shore power supply. Some it will work just fine with. If I bypass the Magnum the ground fault does not trip--so the issue is something inside the Magnum.

I think I understand what your saying above but as I read it some of it has me wondering why. I'm no rocket scientist here and the brain matter can be in the perpetual state of fog so bare with me on my questions.

The first paragraph makes sense the nature of batteries some will drop faster than others.

Second paragraph is where I start to drift I guess. I thinking of my experience with MSH3012M for the past year, now my system has not been turned off at all whether I was plugged in to shorepower or not. My understanding is that the inverter (load sharing) has built in saftey features and assuming you have the remote settings set properly that it will shut itself down or not let it work (load share) till certian parameters are met. I thought that one of the pluses of the hybrid was if there is "weak power" it can supplement it within the set parameters.

You say "One of the few design faults of the Magnum is that the cooling fans shut off when the inverter or generator are turned off." Unless I misunderstood about the ac/ fridge experience is once you turned off the ac/ fridge that is what you mean turning off the load support. Then when shutting down the generator you still left the inverter on gathering power from the sun to charge your batteries (I'm guessing that you had solar at the time). So unless the batteries where drained beyond the LBCO or you physically turned the inverter off the fans should stay running till the inveter cools off or it would of shut itself down before hand for over heating.

I've just went back into the manual a reread section 3 (operation) of load sharing and fault settings and it just seems there are features to prevent the inverter to operate with in the parameters (preset/ or manually changed) to operate with low voltage or "brown out" as stated in the manual.

The ground fault thing I have not come across since installing the system I've only been in maybe 6 state campgrounds that had power.

Thanks for posting the link to the video.

I see that voltage dropped to 59 when the compressor started up. The lowest I've seen before the Microair installation was about 96. That was enough to concern me.

Voltage drop now is limited to about 10. I.E. if shore is at 113 then sag is to 103. Then the autoformer 'kicks in' and voltage goes up to 118. It may be that the Kill-a-Watt meter is not "fast enough" to display the start up voltage sag correctly, but I'm certain it is much less with the microair in place.

Did you ever try to start the air with the generator in eco mode?

SoundGuy wrote:
Perhaps this will help - here's a video I made a few years ago powering my Coleman Mach 3+ 13,500 BTU A/C with my EU2000i. A/C was equipped with an SPP6 hard start cap, I wired the thermostat with a Fan HI / Fan LO switch with a centre off position so I could start the A/C compressor only, then manually start the fan a few seconds later once the compressor came up to speed. As you can see voltage drop under full load of the A/C compressor and fan was about 4 volts.

Hi Itinerant1,

When the Magnum is set to load support and there is, for example, a 15 amp shore power supply @ 120 volts, then when more than 15 amps are needed the excess current is taken from the battery bank. I.E. running a 10 amp coffee pot while running a 16 amp microwave. However the output voltage will still sag as the load increases.

On the other hand, if a "weak" 15 amp shore power supply @ 96 volts is being used to attempt to run an air conditioner, then an autoformer can "boost" the voltage up to 108. Without the autoformer the air conditioner would be damaged pretty darn quickly.

One of the few design faults of the Magnum is that the cooling fans shut off when the inverter or generator are turned off. I had been using load support help with the surge from the roof air, and fridge from my Yamaha generator. It was a hot day and so the load was 1900 watts from the AC and 325 watts from the fridge. I decided to go shopping--and so I turned off the load support and then turned off the generator. When I came back an hour later the red fault light on the Magnum remote was on. When I started the generator, no power would pass the Magnum. I bypassed the unit, and I had power again. That is when I noticed the soot marks on the wall above the Magnum.

Earlier in the summer of 2016, I was in a campground and it was hot as Hades. I did not yet own an autoformer. The voltage was only 102 on a 30 shore power feed at the campground. I found out, more or less by accident, that I could force the Magnum to do "voltage support" by dialing down the input amperage to just 11 amps. I do have a modest solar system and that meant I was able to run only the roof air from the (low voltage) shore power supply, without totally draining the battery bank. It did cause the Magnum to become pretty hot (I don't remember the numbers).

I do not recommend forcing the Magnum to do voltage support.

One other oddity is that sometimes the Magnum will not function if there is a ground fault shore power supply. Some it will work just fine with. If I bypass the Magnum the ground fault does not trip--so the issue is something inside the Magnum.

pianotuna wrote:
Hi Itinerant1,

I know about load support. It is not "voltage support". The Magnum can be "forced" to do voltage support by turning down the input amperage. But it does not "like" it. Mine caught on fire.

I use load support whenever I have a 15 amp shore power feed.

I have used it with my Yahama 3000 sIEB inverter generator setting it at 23 amps.

LOL ty MrWizard.

I guess I don't undertand what you mean "voltage support"?
Your the first person that I've heard haveing the hybrid catch fire while load supporting but its not like I've searched for that. I guess tomorrow I'll be searching.