Using AUX2 to control Air Conditioner

[rwsaustin]

I have a Classic 150 with Rev 2096 firmware. I have an off-the-grid system with about 3.8 kW of solar charging a bank of Concorde AGM batteries. A Xantrex 6048 inverter supplies 120VAC to the house. It gets hot here in Texas, so I recently added a window unit air conditioner. The unit runs fine and produces a good amount of cold air, but it won't run on batteries for long. I would like to use AUX2 in Float High to control the A/C. I want the A/C to run flat-out the entire time the Classic is in Float. AUX1 drives a vent fan in my battery room. I found a Dayton relay with a 12V coil that will switch 30 amps of AC power. I got the system connected, but I am experiencing a problem. The A/C starts with the blower fan on. After a two minute delay, it tries to switch on the compressor, but the surge evidently causes the Classic to drop AUX2 for an instant, the relay opens, and the A/C powers down. A fraction of a second later, AUX2 goes back high and closes the relay and the A/C powers back up with just the blower fan. This cycle repeats. The A/C compressor never starts, so no cold air.

Has anyone experienced a similar problem with AUX2? Is this a bug or a feature? Is there some way to program a time delay on AUX2 to keep it high for a second?

I thought about connecting a capacitor across the relay coil to keep voltage on the coil for a fraction of a second. Is there a down side to this?

[ClassicCrazy]

is that a solid state relay ?  Are the contacts rated for resistive or inductive load ?
There is a discussion on the forum about how you need to use a diode for inductive loads .
I will see if I can find that .
Maybe this discussion will help you
http://kb1uas.com/mnsforum/index.php?topic=3352.0
Larry

[rwsaustin]

Larry,

The relay is mechanical, Dayton 1EJH8. Its contacts are rated for 30 amps resistive, 15 amps inductive. The A/C draws several hundred watts, but I am not sure what the surge current is when the compressor starts. I read that solid state relays generate quite a bit of heat (waste energy) with large loads and require a heat sink, so I chose to go the mechanical route.

You make a good point. My problem could be with the relay instead of the Classic's AUX2. I'll try forcing AUX2 to high on on the front panel of the Classic and make sure that switches on the compressor. If that still doesn't work, I'll try hooking up 12VDC to the coil from a couple of lantern batteries and see if I can turn on the relay and A/C with that. If that doesn't work, the problem is definitely with the relay. If it does work, I'll connect an LED to my AUX2 line to see if it blinks when the compressor switches on. If it blinks, I can video it with my phone to measure how long it goes out (by counting frames 1/30 sec frames). Those tests should isolate the problem and help me design a solution.

[kitestrings]

Hi rw,


It sounds like you've got a robust inverter, but you didn't mention how big the battery bank is.  I'm guessing the in-rush is high on the AC compressor and the voltage is sagging such that you're below the set-point of the aux2.  Have you tried just manually turning it on via the aux2?

~ks

[rwsaustin]

ks,

I have 24 Concorde Sunxtender AGM batteries (don't have model number or AH spec in front of me) wired in 3 strings of 8. This is a 48V system. Batteries are several years old. In a recent load test, I was able to pull 2200 watts of 120VAC load for 2 hours running on battery.  Inverter is Xantrex 6048.

So if the motor start surge drops the battery voltage to less than 0.3 below float, then the Classic would drop AUX2, right?

As I said in my previous reply, my next step is to turn on AUX2 from the front panel of the Classic and see what happens.

Robert

[rwsaustin]

Update:

When I switch AUX2 to high on the front panel of the Classic, the relay works fine and switches on the A/C. Two minutes later, the compressor switches on like it should. So the relay works as it should. I tried again to use AUX2 on Float High to control the relay. Today it got cloudy, and another nasty complication reared its ugly head. The system got into a short cycle mode where the A/C would come on (just the blower), and the Classic would drop out of Float, switch off AUX2 and then immediately go back into Float and switch on AUX2. So the A/C was turning on for a couple of seconds and off for a couple of seconds. It now looks pretty hopeless to use AUX2 Float High directly as a relay controller for my A/C.

Should I try Waste Not High?

Robert
rwsaustin

[kitestrings]

You may want someone from MS to confirm, but I would think you'd want to do this task with Aux1 and not Aux2.  Aux2 as I understand it is better suited to a SSR with a load that can except 0 to full power (like a heating element, or I suppose some sort of VSD pump, fan).  When Aux2 is fully active you would be fine, but when it is pulsing it should be hitting a SSR and not a mechanical relay and I can't imagine it is good for the AC unit.  Aux1 would allow you to determine set-point, delay and hold time.  It seems like you want an all (on) or nothing (off) mode for this application.

[rwsaustin]

The Float High is a fully on off signal with no duty cycle. I believe you are referring to PWM (Pulse Width Modulation) which is only used on some of the modes. I am using AUX1 for my vent fan, so I am trying first with AUX2.

Robert

[australsolarier]

i have the same problem with aux float high. when bigger current drawn from battery the float high signal turns off until the high current eases again. try the aux SOC and put in a value that suits your battery.
besides using the float high signal to turn on the aircon, it will drain the battery. the float high signal only turns off when the sun stops shining in the evening. say it is overcast after the midnite goes into float   ......... >>> low charge in battery possible or low volt disconnect or something.

[CDN-VT]

Robert in Austin TX
Howdy
Your 120Vac AC unit , do you know what it draws for power ? I have a mini-split  seer 23 12,500BTU bought from FL for 900.00 $ draws 1200 watt on full in turbo mode , softstart , uses 6-800 watt in normal mode . Being in Canada I set mine to 18* and hope it snows ..
The window units seem to be power hungry  .


VT

I'll edit this so it's EZ , them window ac units are 1800watts run & have a spike till they are let to settle down .
the rest I'll say is not to be posted here .
Im moving into the Euro style fridge & freezers , we in AME are so far behind , it's NUTS .

VT

[ClassicCrazy]

Maybe the it was going out of float ? Bob was just talking about similar issue in this post

http://kb1uas.com/mnsforum/index.php?topic=3384.new;topicseen#new

Larry

[rwsaustin]

As I understand the Classic's Float Hi setting, the Classic will lower the AUX line when the battery voltage drops to 0.3 V below the Float setting, so it should not keep discharging the batteries. When the sun goes down, the system goes from Float to Rest. That was not my issue with Float Hi. My problem was short-cycling. When the A/C compressor would switch on, the surge would cause the Classic to lower the line and cycle the power on the A/C.

Update: I have switched to using AUX1's Waste Not Hi setting to controlling the relay. At some later time, I'll move my vent fan to AUX2, probably using an external relay. The AUX1 has delay settings that should solve my short-cycling woes I faced with Float Hi setting. The Waste Not setting of AX2 is indeed PWM and not compatible with my mechanical relay.

Waste Not Hi has four numbers to set, two voltages offsets and two time delay settings. I think I need to set the turn off "hold" delay to something bigger than the two minute (120 sex) delay of the A/C. I need to pick a number for the turn on delay to prevent short cycling when the sun goes behind a cloud, say a minute. The two voltage thresholds are a mystery to me. These numbers are offsets relative to the Bulk, Absorb and Float settings. The Classic manual seems to imply that these two thresholds should both be negative. I tried setting the High threshold to -0.1 and the Low threshold to -0.3, but the Classic never switched on the A/C even though it was in Float and the array had full sun. Any clues on how to set these voltage thresholds?

My A/C is a Frigidaire 12000 BTU/hr window unit, FFRE12L3S1. It has EER 12. From the definition of EER, it draws about 1000 watts. My inverter happily runs this A/C, and I have enough battery storage to run the A/C for an hour or more and still have charge for my continuous nighttime loads (refrigerator, sewage treatment aerator, smoke l alarms and a few phantom loads). I hope to replace this A/C with one or two ductless mini-split units in a few years. For now, I want to learn what I can do with a single A/C in the bedroom and to find out how many hours a day I can run it with my existing solar array.

[ClassicCrazy]

A whizbang and shunt really give a lot of monitoring capability and control .
But of course you have to give up one of your AUX to use it but there are other ways to turn on a vent fan.

Larry

[CDN-VT]

Agreed , BUT the AC spikes are huge & the MN150 see's a huge drop as the AC unit starts , after a 2 min (120 sec) all is at (so called min WATTAGE ) back to what is reported .
I see these start at 1800 watts on hot . CB's will take the load for the start.

VT

[ClassicCrazy]

That surge is why I went with the recommended 4/0 wires for my 24v  inverter even though seemed like 2/0 would do it okay .

Larry