Battery Backup For Door Strikes

I have a 24VDC power supply running 27 door strikes through a Keyscan door controller. I'd like to do battery backup through a module that can switch to battery power when the input supply fails. As well, it should float charge the battery when input supply is present. The strikes are set to fail lock so the draw is minimal. Anybody have any suggestions?

I take it the strikes are just switched by the controller, not powered by it? If so, is the access system also backup powered?

Do they normally draw power from a big power supply somewhere?

Also, they release when power drops? Because that fail-safe behavior can often be changed in the field in many strikes.

Hi Brian,

Yes they are just switched by the controller. Access system has its own battery backup. The strikes are powered by a separate 24VDC power supply. They don't release when power drops but that's not the intention. The client would like doors to be secure but operational during power outages; they should operate as normal even when power is out. Thus the need for backup batteries.

Brad, instead of having a module failover, couldn't you put the 24DC supply on a UPS?

Apologies if I'm being ignorant...

Typically this would be done with a lock power supply with battery backup built into it, like an Altronix AL600ULX, or a LifeSafety Power. You can add as many pairs of batteries in parrallel (in additional enclosure if need be) to achieve the run time you need.

Thanks for all the responses guys. The dilemma is that the electricians were going to tie this in to the generator but it's maxed out. The PSU for the strikes is already wired in and there's no need to buy another a la the Altronix or similar. 24VDC output on locally stocked UPS seems to be difficult to find.

Possible solution: I'm going to use a 24VDC UPS controller (about 80 bucks) and a couple of 12VDC 7Ah batteries wired in series in an enclosure between the existing PSU and the Keyscan panel. Since the draw on each strike is rated at 190mA and only for about 1/4 sec I should have a pretty reasonable amount of battery backup time. I just need to pick the voltage point on the controller where power switches from main inputs to battery inputs.

Will that controller trickle charge the batteries when mains power is live?

Just for my own knowledge Brad, what did you see as the downsides to using a small line-powered UPS to feed the 24DC PSU?

One downside is that it would be less efficient than the 24V store, due to step down/step up losses. Are there other negatives that you saw?

Cost seems roughly the same.

The main advantage would be simplicity of installation and maintenance and not having to configure and test cutover thresholds.

Again, not being critical, but just wondering if there were some other issues...

Maybe I missed it, but did not one ask if the power supply has a battery charger? I know power supplies without battery chargers exist, but I don't see a lot of them sold these days.

Yes it will recharge them.

2 factors I guess:

1. A UPS with 24VDC output is not a stocked item with any of my distributors.

2. The relative ease of doing things the other way; different voltage thresholds are available

from the manufacturer and delivery is super quick. We have enclosures and

batteries in stock. The installation area would require the UPS to be in an

enclosure much larger than the one for the controller and 2 batteries.

Brad, thanks.

Just to be clear, I'm not suggesting a UPS with a 24V output. I am talking about a standard 120V in, 120v out UPS that you would use to power a NVR or some cameras etc, in the case of power loss.

In this case you would plug your 24v PSU into it. Normally the UPS would just pass thru the AC to the PSU, but if power fails, the UPS would automatically power the PSU and provide energy to the strikes.

As I mentioned before you will lose some efficiency, but depending on the time requirement for off-grid operation, it may not be significant.

As for size, I'm talking about one of those ~10x10x4 APC boxes.

In any event, what you you're considering is more efficient and you seem comfortable doing the work, so it's probably academic at this point.

Thanks again.