Schlage Connect Keypad lock - Converting to A/C adapter and adding a battery backup

Thread Starter

nicholasalipaz

Joined Jan 22, 2018
8
So I have the Schlage Connect lock and I have experienced low battery life, about 1.5 months overall from the lock. The lock uses 4 AA batteries in series that are placed into a battery tray and then connected to the device via a 9-volt connector that connects to the tray.

Firstly let me tell you I am a computer engineer by trade and have very little circuit design experience.

I have determined I could completely bypass the batteries by simply wiring in a 6V/1000mAh in place of the battery pack. Let me know if that is wrong by am fairly confident it would work. However, the part I am still trying to figure out is wiring in the backup batteries. I was thinking to use the existing battery tray that comes with the lock. I did read over https://www.allaboutcircuits.com/projects/battery-backup-power-supplies/ and it seems doable. I would surmise I need Nimh batteries adding up to 6 volts but noticed I only see 1.2 volt batteries on Amazon. I also believe I would need a 1 kohm resistor. Any help would be appreciated. Thanks
 

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tranzz4md

Joined Apr 10, 2015
310
I suspect your unit. Is it beyond warranty? I've used a few of a competitor's units (Weiser) over the last 20 years and even aging NiCd batteries lasted for nearly a year with daily use.

NiMH cells are 1.2V, NiCd are 1.3 new but taper down over time. Most installations of that mechanism are door mounted so battery power is strongly preferable. Supporting, attaching, and routing wiring across the moving surface, the gap, and the wall don't give a durable and visually appealing result.

1000mA/h is far more current than should be required for that mechanism. Where did that figure and the 1 kohm figure come from?


Oh, incidentally, I'm also on a little personal mission to eliminate the use of a non-existent and entirely needless term (at least among intelligent folk): "doable". (Possible, feasible, practical, and multi-word alternatives abound)
 

tranzz4md

Joined Apr 10, 2015
310
Ah, yes,,, one last observation. If in fact you are really bent on powering that item "from the wall", you should get a wall-wart with 5.0VDC and 5mA output, and wire it to the battery pack, loaded with 4 NiMH cells.

That'll effectively keep a trickle charge on the batteries.
 

Thread Starter

nicholasalipaz

Joined Jan 22, 2018
8
Thanks for the response @tranzz4md and your hilariousness at your disdain for the term "doable". I have similar feelings about words that start with ir-, most especially nonsensical ones like irregardless.

I do understand the feasibility and aesthetic issues surrounding a wire running across the door frame and over to the adjacent wall to be plugged in, however I can deal with that fairly easy and I value the function over form in this. These locks are on a vacation rental property and it is two hours away so it is difficult for me to change the batteries. The unit is in warranty but I have seen many reports of the same issue from other people online so it seems to be fairly normal. Yet I have read accounts of people saying they last a year, and others saying 2 months so who knows at this point.

As to the numbers I am quoting, I am not completely sure on the mAh needed but I figured up to mAh shouldn't hurt since requirements most certainly wouldn't be over that.

The 1 ohm I kind of judged based on the similar details in the linked article but again I could be off base. I am an amateur at this stuff. I do do a lot of home automation stuff using home-assistant and other parts. But most everything is programming based and I don't have to work with a lot of circuitry or if I do I have been able to find guides that tell me most everything I need.
 

Thread Starter

nicholasalipaz

Joined Jan 22, 2018
8
Ah, yes,,, one last observation. If in fact you are really bent on powering that item "from the wall", you should get a wall-wart with 5.0VDC and 5mA output, and wire it to the battery pack, loaded with 4 NiMH cells.

That'll effectively keep a trickle charge on the batteries.
So with that suggestion would I need the resistors or diodes in the setup or just go straight to the battery pack to essentially keep it trickle-charging? I would think that might overcharge the batteries no?
 

tranzz4md

Joined Apr 10, 2015
310
Well, at this hour, and my typical level of solid state electronic control circuit design expertise (or lack thereof),,,, let's see if Crutchow, Max, Dave or another regular will contribute to the question. I'd think 5mA would be just fine,,,, but I doubt you'd ever find one.
 

R.E.

Joined Jul 29, 2017
56
I think you might need 5 cells to get the 6 volts you need. The board uses an Ultra Low Voltage drop regulator and then uses 5 Volt logic for the main board, (At least the last board I looked at did) with 4.8 Volts input I think that when the 6 Volt motor engages to throw the bolt, the increased current draw will cause a very low voltage situation on the logic board. You should be able to wire in an extra cell somewhere or shop around for a smaller NiMH pack, look at some cordless phone packs and see if you find something that fits. Check out this wall wart for a safe and inexpensive power supply
What is being proposed so far will cause issues and not be reliable at all especially when we are talking about locking up a home.

I install these things and I can vouch that in cold weather they can eat batteries much faster than if they were operated in California.
I'd install a power jack in the housing and then charge the pack and disconnect the charger once they were topped up.
Its a great idea but as a system integrator I cannot modify equipment this way or risk getting sued if there was a fire, even if it wasn't my fault.
 

Thread Starter

nicholasalipaz

Joined Jan 22, 2018
8
@R.E. do you think I would need any sort of resistor or diodes in this setup? The link I gave in my first post I was kind of working from that and thought it might be necessary.
 

R.E.

Joined Jul 29, 2017
56
Not at all with the charger that I linked you to as it has a built in microprocessor and detects when the cells are charged, then switches to a trickle charge of 35 ma. It also has built in polarity protection as well. You might even find a 6Volt NiMH battery pack at Home Depot for solar lights or a cordless phone that fits in the lock's battery tray.

The circuit you linked to is for a circuit that takes constant power from a power supply and uses batteries to provide a backup when the power goes out. The diodes are used to prevent current from flowing backwards into the charger and steering current to the regulator when the power goes out. Those are lithium cells which are 3.6 Volts each nominal, the resistor is calculated to trickle charge the batteries at a very low current.

My setup allows you to charge the pack safely and is easy to install. I would put in a power jack in the lock housing, charge the batteries and disconnect the charger. You wish for the charger to be always on so you need something that can monitor the state of your batteries. Simple diodes and resistor circuits are not going to safely do this for you. Check out this page for information about batteries and charging etc. ; https://www.powerstream.com/tech.html
 
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Thread Starter

nicholasalipaz

Joined Jan 22, 2018
8
I think I understand everything, thanks. The only thing I am not quite clear on is whether the wall wart you linked will be safe to leave plugged in. I understand that it switches to a trickle charge when the cells are charged, is that enough to deal with not overcharging the battery pack? Since it switches to trickle charge my understanding is it should be.
 

R.E.

Joined Jul 29, 2017
56
It is designed to be left plugged in, it has a rapid charge feature as well then shifts to a trickle charge when the batteries are full.
With a 2500 ma. battery pack we can trickle charge it between .03 - .05 C (1C = 2.5 amps) safely. At 35 ma. we are far below the safe maximum trickle charge.
 

crutschow

Joined Mar 14, 2008
27,457
Since the average current drain from the batteries is low ( I estimate about 2mA if the AA batteries last about 1.5 months) then you could likely just put the NiMH batteries on a continuous slow trickle charge.
The recommended maximum trickle charge current for NiMH batteries is .05C where C is the ampere-hour capacity. Thus if the battery capacity is 2.5Ah you would set the charge current to no greater than 125mA .
This can be set by an appropriate resistor size (about 30Ω) between a 9Vdc wall-wart and the battery pack for example.
 

Thread Starter

nicholasalipaz

Joined Jan 22, 2018
8
I finally tried the NiMH battery and the charger for this. Initially everything worked before the battery was topped off, however once the battery topped off the lock will not allow me to unlock. The symptoms are strange. I can lock the device using the keypad (single press of the Schlage button), but upon attempting any other function while locked it gives me 3 blinking red lights to indicate the battery level is critically low and it cannot perform it's procedure. How might I go about troubleshooting this?
 

Halfpint786

Joined Feb 19, 2018
12
So I have the Schlage Connect lock and I have experienced low battery life, about 1.5 months overall from the lock. The lock uses 4 AA batteries in series that are placed into a battery tray and then connected to the device via a 9-volt connector that connects to the tray.

Firstly let me tell you I am a computer engineer by trade and have very little circuit design experience.

I have determined I could completely bypass the batteries by simply wiring in a 6V/1000mAh in place of the battery pack. Let me know if that is wrong by am fairly confident it would work. However, the part I am still trying to figure out is wiring in the backup batteries. I was thinking to use the existing battery tray that comes with the lock. I did read over https://www.allaboutcircuits.com/projects/battery-backup-power-supplies/ and it seems doable. I would surmise I need Nimh batteries adding up to 6 volts but noticed I only see 1.2 volt batteries on Amazon. I also believe I would need a 1 kohm resistor. Any help would be appreciated. Thanks
If you use a 9v, 500mA adapter to run the lock (2v over is fine, and actually handy) and put a diode in series with the battery pack, the diode remains reversed biased until the 9v wall adapter fails isolating the battery pack completely. Once the wall adapter cuts out, the 6v battery easily drives the diode into conduction as it is no longer reverse biased. This is how uninterruptable power supplies work. But, you must use new long lasting batteries like energizer lithiums. The reason is the isolation diode will rob you of a .7v drop so a 6v pack fully charged will give 5.3v to the lock (still fine).
 
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