AP7750 ATS won't run from UPS when on battery

[Anonymous user]

I have an AP7750 automatic transfer switch and it is connected to an RS1500 UPS on source A and directly to utility power on source B. Voltage range is set to wide and sensitivity is set to low.

When I pull the plug on the UPS to go on battery, the ATS instantly switches to source B and the led for source A blinks. The web interface shows source A as 115VAC 60Hz which is well within the published range for 'wide' (106.5 - 135.5VAC), but is says source A is 'Not Ok' and that 'Switchover Not Possible'.

Is the RS1500 not producing a compatible waveform? Or do I have to do something special to get the 'wide' setting to stick?

Model: AP7750
Firmware Revision: 1.10
Firmware Date: 09-15-05
Hardware Revision: 02
Manufacture Date: 09/08/2006

Hardware factory information

[BillP]

i would just make sure that you do not buy a step approximated sinewave or square wave UPS to use with this ATS.

if you have a model of APC UPS you want to know about, you could always ask about it first and if we have one, I can test it out with this ATS. feel free to PM me in order to do that incase i forget to check back here.

[BillP]

i believe it is a problem with the waveform. the Back UPS outputs a step approximated sinewave while on battery. you can try adjusting the ATS sensitivity but I don't think it will make a difference. this ATS is tested and designed to work with UPSs that output a pure sinewave such as a Smart UPS or larger UPS.

[upsguy_apc]

Instead of pulling the plug on the UPS try opening the breaker that feeds it. By pulling the plug you disconnect the neutral and ground input to the UPS.

[Anonymous user]

I replaced my UPS with an SUA1500RM2U and have had better, but not ideal, results. The ATS will now run under UPS battery power (good) but it does switch to source B when the UPS initially goes on battery. It switches back to source A shortly thereafter.

I ran my latest test using a power strip that would only disconnect the hot and leave the ground and neutral connected. The ATS is still set to wide voltage range and low sensitivity.

It appears the time it takes for the UPS to switch to battery is long enough to trip the ATS. But what happens if I lose power to both source B and the UPS input at the same time? I'm hesitant to try that since I have production gear running.

[Anonymous user]

I have an AP7750 automatic transfer switch and it is connected to an RS1500 UPS on source A and directly to utility power on source B. Voltage range is set to wide and sensitivity is set to low.

When I pull the plug on the UPS to go on battery, the ATS instantly switches to source B and the led for source A blinks. The web interface shows source A as 115VAC 60Hz which is well within the published range for 'wide' (106.5 - 135.5VAC), but is says source A is 'Not Ok' and that 'Switchover Not Possible'.

Is the RS1500 not producing a compatible waveform? Or do I have to do something special to get the 'wide' setting to stick?

Model: AP7750
Firmware Revision: 1.10
Firmware Date: 09-15-05
Hardware Revision: 02
Manufacture Date: 09/08/2006

Hardware factory information

[BillP]

hmm the transfer time on the UPS should be closer to 2-4ms where as the ATS takes about 8-12ms typically..

the transfer time should not be the cause here - it seems more about the voltage on the neutral temporarily or something. how long does the ATS switch sources for?

[Anonymous user]

When I disconnect the input to the UPS the ATS instantly switches to source B and remains there for exactly 30 seconds.

02/14/2010 22:56:58 Automatic Transfer Switch: ATS has switched source. Source A is source.
02/14/2010 22:56:28 Automatic Transfer Switch: ATS has switched source. Source B is source.

The source A led remains lit solidly. When the ATS switches back to A (UPS now on battery) everything works just fine.

I measured 0VAC between ground and neutral for both inputs to the ATS so if there's something anomalous with the neutral it must be brief.

Is this something I should worry about? My concern is that the ATS will switch from source A to a dead source B. If that will never happen, or it will switch back to source A within a short number of milliseconds then I shouldn't need to be concerned by this behavior.

--Larkin

[BillP]

i don't suppose anything is reported in the data log? you could also shorten the logging interval on the data log and try it again to see if it records anything about frequency or voltage out of range during the transfer.

are these two UPSs/sources on separate circuits? i understand your concern. if they are on the same circuits and switch at exactly the same time, i would think that the ATS should still see power there of source A goes down even though it switches when source A goes down.

[Anonymous user]

You can see from below that I disconnected power to the UPS shortly after 19:57:51, the voltage dropped slightly to 118 while on battery and I restored power slightly before 20:02:51. The fastest I could set the data logger to was 1min.

02/15/2010 20:03:51 60 60 121 121 1.3
02/15/2010 20:02:51 60 60 120 121 1.3
02/15/2010 20:01:51 60 60 119 122 1.4
02/15/2010 20:00:51 60 60 118 123 1.4
02/15/2010 19:59:51 60 60 118 122 1.4
02/15/2010 19:58:51 60 60 118 122 1.4
02/15/2010 19:57:51 60 60 119 121 1.3
02/15/2010 19:56:51 60 60 120 121 1.3
02/15/2010 19:55:51 60 60 120 121 1.3

The two sources are fed by different circuits (different breakers anyway), but are being fed by the same utility source. I'm 99% sure they're both from the same phase and are definitely off the same transformer.

Message was edited by: llowrey

[BillP]

hm i just had another idea.

on the AP7750, you can hyperterminal directly to the ATS itself, versus the network management card that is inside of it. upon doing that, there are more precise readings and also the last 10 reasons for transferring over. we could crosscheck that log and data while doing the test.

to do this, you need the 940-1000 serial cable. also, inside the NMC you need to reset the ATS microprocessor to defaults to reset the serial port on ATS to 19200 baud rate. it is probably at 2400 now since you have your NMC configured.

if you do these steps, and terminal in at 19200, you should get presented with a user name and password, and you need to enter "apc" all lowercase with both. if you enter passed this without entering a password, you will not get any of the administrator options.

upon doing this, you will have menu options such as measurements, event log, etc and we can look in there for more info.

when you're done, you can choose option 11 for NMC config to put the baud rate back on the serial port to 2400 so you can access the NMC via serial.

by the way, none of this will affect your settings on the NMC, only the actual baud rate on the serial port.

[Anonymous user]

The only noteworthy things I found, while on battery, are in the status screen, it says "Phase Sync - ** ASYNC **", and in the event log which shows:

Event # Event Desciption
-----
-----
1 SOURCE SWITCH
2 SPIKE/DROPOUT

I just loaded up powerchute so I could configure the UPS and found it's voltage range might be the problem. The highest I can get the low voltage threshold is 106VAC. According to the manual, the ATS low threshold for the wide range is 106.5VAC. Could it be that the ATS sees 106.5VAC and trips before the UPS trips at 106VAC? I suppose that the UPS could already be on battery and back above 106.5VAC before the ATS completes it's switch away from the UPS.

Message was edited by: llowrey

[BillP]

that low voltage transfer range means that when the UPS input voltage goes below 106, the UPS will transfer to battery to protect your load. I dont think this has anything to do with it. the threshold for the ATS means that if it sees a voltage below 106.5, it will switch sources if the second source is good.

the ASYNC means that the two input power sources are asynchronous - meaning out of sync.

[Anonymous user · Accepted solution]

I know this thread is a little stale, but did you ever figure out your issue. I'm having similar problems and I believe it's due to the Transfer Range of the UPS vs. the transfer range of the ATS. The highest I can set the lower transfer range of the UPS is 106. But the lower end of the ATS transfer range was actually higher. This means if the utility power had a sag which went below the ATS's transfer range, but above the UPS's transfer range, the ATS would see both sources as unacceptable and simply drop power to the connected devices. It's happened to us on several occasions.