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Old 08-07-2016, 04:32 PM   #1
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Generator Start with loads

There is a general wisdom around here to not start/stop the generator with loads. The transfer switch can be over loaded and perhaps the voltage will spike and cause damage.

However, I want to use my AGS system to keep my pets cool in case of a loss of shore power. Here is a scenario I am facing.

1. On Shore power with AGS ON. The generator will start if an AC load is needed. The transfer switch has configured itself to pass shore power to the house and the generator is not seeing any loads. 2 ACs are on. They cycle on/off as needed. The inverter is on, but with shore power available, it is not doing anything. Batteries are fully charged.

2. Shore power fails.

3. The inverter springs into action and draws power from the batteries to power the residential refrigerator.

4. An hour later, the AC's decide to come on. They might decide to come on at nearly the same time.

5. The AGS system senses the AC needed load and starts the generator. The generator runs for a few minutes and then applies its power to the system.

6. The transfer switch detects gen power and switches itself to pass gen power to the house.

At this point, the generator will be supplying power to 4 major loads;

A. AC1
B. AC2
C. All inverter loads (refrigerator, etc)
D. Charger (which will be in bulk charge mode to start).

The loads will require the following AC AMPS; 15, 15, 3, 10 for a total of 43 amps.

And step 7 is when shore power comes back on. I haven't tested that scenario, but I think the generator will keep running and the transfer switch will ignore shore power.

This is a reality of the problem I am working with. What are the best practices for this kind of situation during a loss of shore power situation?

Also, at this moment, my generator will start with 1 load. However, with the situation described above, the generator will stop supplying AC power after a few seconds. I am trouble shooting this issue and don't know if the generator is shutting down the power or if my transfer switch is.

The AGS functionality is provided by EPLEX and the generator is an ONAN 12.5K
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Old 08-07-2016, 04:44 PM   #2
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FWIW I would be looking into a way to trigger the AGS if the line power failed. Why wait for the battery to run down? You want the house cool for your pets.
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Old 08-07-2016, 04:48 PM   #3
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are you saying that you 'anticipate' a problem, or are you saying that you are already experiencing a problem?
the steps in the scenerio you describe are exactly how the system should work.

and yes, the generator would run until the a/c units reached the prescribed temp, then the restored shore power would be back in control.

sounds good, I also keep my AGS always on as well, but not for a/c's, but for loosing shore power and depleting the batteries...
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Old 08-07-2016, 06:02 PM   #4
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Note that none of this is instant and it all happens in stages. For example, the genset starts but the a/c aren't running yet (no power). Once the genset stabilizes, it starts producing power and the transfer switch flips. The inverter takes a fraction of a second to recognize external power, then it flips too. Assuming the thermostat is calling for cooling, the A/C also goes through its start cycle, but that too takes a couple seconds.

The bottom line is that the ATS is not really switching under load, i.e. relatively little current is passing through the relays at the instant it switches. And that's all that is desirable. A modest amp load so reduce the chance of arcing as the relay changes contacts.

I would also remind everyone that this is not a frequent thing. The ATS is designed to switch with power active, but it's not designed to do it dozens of times daily. Each time it arcs a bit there is some wear & tear, but it can do it dozens or even hundreds of times. Think for a minute about your central air system at home, with a set of "contactors" that close to apply high amp power dozens of times daily during the cooling season. They last for many years, but eventually wear down and need replacement. An ATS is much the same, but gets only a tiny fraction of the usage.
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Old 08-07-2016, 07:53 PM   #5
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>> FWIW I would be looking into a way to trigger the AGS if the line power failed

My ags will trigger upon AC demand. So, when shore power is lost, the generator will remain off until an AC unit needs to start running. Then the AGS will turn the generator on. In my coach, the AGS does not know about the inverter and the devices it supplies. In fact, my AGS doesn't monitor the 12V system at all.

>> are you saying that you 'anticipate' a problem, or are you saying that you are already experiencing a problem?

I am anticipating what happens when starting the generator when loaded. I don't want to damage any systems. I think Gary's comment is best; this is an event that happens infrequently.

And yes, at the moment I do have a transfer switch problem of some kind. My system can start the generator with a 15A load. It fails when the load approaches 40A. I am just beginning to troubleshoot this problem.

I am trying to understand that problems I could face by starting the generator with several power hungry devices turned on.
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Old 08-07-2016, 09:20 PM   #6
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"azSkier"......I think you're anticipating everything starting at once......it doesn't. You have an energy management system that is doing its job along with the major items taking time to start. As stated, when your generator starts, there is no load, once it gets going and up to power it will kick the ATS and then start delivering power.

Turn your A/C units on as a test....they don't immediately turn on. They take a short period with the fan starting and then the compressor.

I think you're worrying about something that is not an issue.
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Old 08-07-2016, 09:38 PM   #7
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Thanks for the comments.

But I do have a problem. If I am running on shore power with 2 ACs and turn off the outside breaker (Shore power failure), the AC controllers are still on. If I wait an hour, the house batteries will drain a bit.

Then, I turn on the generator. I have watched the power monitoring system (e-plex) show 120V and then 0. All power goes away... and never comes back!

I think something cannot handle the startup load; inverter(bulk) and 1 or 2 acs.

Since my original post, I have been researching this issue. I have a PD52 transfer switch that is 8 years old. I have seen others on Amazon complain that this switch cannot transfer generator loads greater than a single AC (very similar to what I am experiencing).

from Amazon...
Another thing to note. Technically, you should have the A/C units or any other high power items turned off when starting the generator. But in reality sometimes they were left running when power was disconnected. I have found that if both my A/C units were left on, and I start the generator, when the switch tries to engage the generator power, the relay fails to engage and it repeatedly tries to engage. If I turn off one (or both) A/C units, then the relay engages fine, and I can then turn the A/C units back on.

I am researching the ESCO ES50M-65N ATS as a replacement.

You are probably right about the EMS. However, I have replaced my inverter and it bypasses e-plex. So, my EMS does not have all the information.
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Old 08-07-2016, 11:00 PM   #8
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Yes....the A/C controllers will stay on, they're 12 volt. If they weren't you couldn't run your propane heater without shore power. At some point the controller should come up with an error, when in A/C mode, that says..... power failure.
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Old 08-08-2016, 12:00 AM   #9
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>> I have found that if both my A/C units were left on, and I start the generator, when the switch tries to engage the generator power, the relay fails to engage and it repeatedly tries to engage. If I turn off one (or both) A/C units, then the relay engages fine, and I can then turn the A/C units back on.

This sounds like relay chatter, and indicates a failing relay. The same exact same thing happens to home A/C units just before complete failure of the contactors.


Replacing the relay should resolve your problem..


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Old 08-08-2016, 12:41 AM   #10
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OP you state that your AGS does not monitor 12vdc (battery) power. Is this because you have it setup this way? Not monitoring Battery power is not good because if it gets too low you will not be able to start the generator in the first place. The only exception to this that I know of is an Air start generator and I don't recall them being used on MH's. I have seen them used on Submarines diesel generators, the Fairbanks Morse 8 1/8 Opposed Piston Diesel's but that thing is HUUUUUUGH.
I know the Onan EC 30 Energy Command looks at Battery just for that reason.
Not enough power to start the generator then why have it.
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Old 08-08-2016, 07:27 AM   #11
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>> OP you state that your AGS does not monitor 12vdc (battery) power. Is this because you have it setup this way?

My coach is 11 yrs old and I have been upgrading components. When I upgraded my inverter, the existing AGS logic lost access to the 12V monitoring system.

I need to install the Magnum AGS module, but I have greater priorities at this time.
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Old 08-08-2016, 07:29 AM   #12
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Quote:
Originally Posted by Dutch Star Don View Post
Yes....the A/C controllers will stay on, they're 12 volt. If they weren't you couldn't run your propane heater without shore power. At some point the controller should come up with an error, when in A/C mode, that says..... power failure.
My A/Cs are managed by eplex. I have never seen such a message.
Getting the ACs off eplex is a todo of mine.
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Old 08-08-2016, 10:50 AM   #13
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Generator Start with loads

In the scenario you have laid out (AC mains failure) when the generator starts, there is no load on it! When the shore power fails, the AC units shut down. What the power is restored, whether via shore power or the generator, the AC units do not start immediately. The AC units have a built-in time delay and won't start for a couple of minutes after power is restored. This is to prevent short-cycling the compressor.

If this is NOT happening for you and the ACs attempt to start immediately, the problem likely is not with the generator, but with the time delay circuitry.
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Old 08-08-2016, 02:49 PM   #14
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I am not sure all loads have time delay circuitry. I have an Auqahot as my water heater. The electrical portion of the heater draws about 12 AC amps. When power is lost, the temp will fall. When generator power is restored, it is an instant load.

The AC controllers are 12v systems. With a loss of shore power, It appears to me that the controller has energized the relays for the fan and the compressor. Nothing is happening, but the relays are switched. When the generator starts, my transfer switch (at the moment) fails when I have 2 ACs on and ready to start.

I also think the charger on my magnum inverter starts charging when AC power is present. I checked the magnum manual today and could not find a delay setting.

But, you are right about the generator seeing no load at the very beginning of the start up. When the generator starts, I have seen AC power for a few seconds and then it all goes away.

I hope this works better when I install the new transfer switch.

I think the point of this post now is that the AGS will be able to start the generator even with various loads ready to go. This should be a rare event as it will cause some wear on the contactors.
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