New Garage--How to power garage door openers

[Sunking]

The batteries have 32ah at 0C when the battery is new.

Who cares? the battery has a several days of capacity without a charge. The whole thing is overkill.

FWIW AGM batteries DO NOT FREEZE.

[bcroe]

Does the radio unit function when on the 24V battery? If not you'll have to push the wired
button. I found my 120 VAC radios were well under a watt, but they would require modification
to work on battery.

The electric eye could be a pretty efficient pulsed LED system. A continuous on incandescent
will probably use more WH than the motor. Bruce Roe

[Mike90250]

The LED electric eye on my door always appears to be ON, along with the Aim Is Good LED

And AGM batteries can survive being frozen, but you can't use or recharge them while frozen. And I hope to whatever I am never around when it is cold enough to freeze a charged battery.

[Sunking]

The LED electric eye on my door always appears to be ON, along with the Aim Is Good LED.

There two factors to determine the battery and panel wattage. One is the total watt hours used in a day, and the other is the maximum load current on the battery. You have to use the worse case between the two. In this application the motor current is the driving factor.

The motor determines minimum battery size in this application and was specified as 120 watts @ 24 volts DC. That means 5 amps of current to run the motor. AGM maximum discharge rates are C/4, and FLA is C/8. So if one were to use AGM requires 20 AH, or if using FLA 40 AH. Since this is an outdoor application I would go with AGM. That just gives us the minimum battery requirement to just run the door motor. A 24 volt 20 AH AGM battery can operate that door for 2 hours per day. Assuming a 20 second open/close cycle your kid can play with the remote and open/close the door 360 times in a day to 50% DOD. No one is going to allow there kid to do that. In real practice you might open/close 10 times per day, and that only uses. At 10 open/close cycles power consumed by the motor is 120 watts x .055 hours = 6.66 watt hours. So a 24 volt 20 AH battery is grossly over sized to run just the motor.

Want to use FLA? OK they is really overkill to just run the motor, but we can use that to determine minimum panel wattage to provide a minimum C/12 charge current for the battery using a PWM controller. A 40 AH FLA battery at C/12 = 3.33 amps x 18 volts Vmp panel = 59 watts. Let's just call it 60 watts.

Let's make a couple of assumptions and say the owner has a 3 Sun Hour day in winter. The panel can generate up to 60 watts x 3 Sun Hours x 50% efficient = 90 watt hours per day. OK just with the motor load only of 7 watt hours per day our panel wattage is roughly 13 times larger than required, and the battery is 34 times larger if AGM and 68 times larger than required for FLA based on watt hours used in a day. If you use a 40 AH FLA double those numbers

That means the power hog is really the receiver and LED sensor. So how much power do they really use. I would be shocked if more than 2 watts. I think two watts is way over kill but let's run with it. 2 watts x 24 hours = 48 watt hours. Add 7 watt hours for the motor and you have 55 wh per day. That means our panel is now about twice as large as required, AGM battery has over 4 days run time to 50% DOD, and a 24 volt 40 AH you have 8 days to 50% DOD.

With those assumptions the motor run current dictates everything. The actual power consumed in a day can be ignored. The whole system is way over sized to just run the motor 10 times a day which in reality will not likely be used that much.

[Sunking]

And AGM batteries can survive being frozen, but you can't use or recharge them while frozen.

Same can be said of FLA with respect to charge/discharge currents. But with a grossly over-sized system becomes a moot point because neither battery type could likely ever be discharged enough to actually freeze. Possible but very remote chance.

Let me know when Hell freezes over there in California Mike, you can come down here and ride it out with me in Panama. An extremely cold day here is 50 degrees at dawn with rain and a chilly 65 by noon.

[donald]

What's the C/4 rate at 35F?

There are two units, so 98 WH as a standby at 2 watts each. But you have no evidence that these units use 1W baseload. The 8550 is apparently the power champ, sold as a 1W standby unit. But I don't see anywhere that Liftmaster claims the 8500 has that good of power management. I simply suggest he measure, and then design the unit for realistic winter conditions.

A good design assumes multiple days without charging. I agree with the motor current not being important for battery capacity. Part of the motor use will normally be recovered intraday with the excess panel capacity.

[Guest]

I have setup just like this. I bought the battery backup and cut the battery leads off (I needed to use the connectors) I soldered fuses on both ends and used 2 30 ah lawn mower batteries to provide the power.

I used a dual battery charge controller and a 50 watt panel.

It runs 2 separate openers and even over night batteries still have 12.6 charge. Couple cloudy days no problem, I've never seen below 12.4. It's been that way for 6 months with no problems

doors run same speed as when hooked to 120, now my craftsman 12 volt is slow as Christmas, but it works just need a separate battery. I did leave all of the lights out of the equation because they beeped all the time when installed. Works great