Buying Guide · Access Control Power
Access control power supply sizing.
A practical sizing walkthrough for access control power supplies — load calculations per door, battery backup math, distribution architecture, and the failure modes that come from undersized supplies.
01 / Per-Device Current Draw Reference
What each piece pulls.
Spec sheets understate inrush current. These are practical field numbers — what installers actually see on a clamp meter, not the marketing minimum.
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OSDP reader 0.15-0.20A 0.30A
Wiegand reader 0.10A 0.20A
Keypad reader 0.20A 0.35A
Maglock (600lb) 0.45A 0.50A
Maglock (1200lb) 0.50A 0.55A
Maglock (1500lb) 0.70A 0.80A
Electric strike (12V) 0.35A 1.00A (1s)
Electric strike (24V) 0.18A 0.50A (1s)
Door controller (1-door) 0.20A 0.30A
Door controller (4-door) 0.50A 0.70A
REX motion sensor 0.05A 0.08A
Push-to-exit (LED illuminated) 0.04A 0.06A
Electric strikes are the inrush trap — they pull 2-3× their holding current for ~1 second on activation. A power supply sized to holding current will sag the bus voltage on every door fire.
02 / Sizing Worked Examples
Three real configurations.
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2 × OSDP reader (0.2A) = 0.4A
2 × 600lb maglock (0.5A) = 1.0A
1 × 2-door controller (0.3A) = 0.3A
2 × REX motion (0.05A) = 0.1A
Continuous load = 1.8A
Battery charging (~0.5A) = +0.5A
Recommended supply = 4A @ 12V
Example B: 4-door retrofit, electric strikes (12V), Wiegand
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4 × Wiegand reader (0.1A) = 0.4A
4 × electric strike (0.35A) = 1.4A continuous
Strike inrush peak (1 fires) = +0.65A briefly
1 × 4-door controller (0.5A) = 0.5A
4 × REX motion (0.05A) = 0.2A
Continuous load = 2.5A
Headroom + charging = +1.5A
Recommended supply = 6A @ 12V
Example C: 8-door multi-tenant, OSDP, maglocks + strikes mix
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8 × OSDP reader (0.2A) = 1.6A
5 × 600lb maglock (0.5A) = 2.5A
3 × electric strike (0.35A) = 1.0A
2 × 4-door controller (0.5A) = 1.0A
8 × REX devices = 0.4A
Continuous load = ~6.5A
Charging + headroom = +3.5A
Recommended supply = 10A @ 12V
(or split: 6A + 6A, 4 doors each)
For sites above 8 doors, default to distributed power — one supply per 4-door cluster, with each cluster on its own battery backup. Single-supply 16+ door installs leave you debugging a sag-induced cascade after a maintenance event.
03 / Battery Backup Sizing
Runtime math, not guesswork.
Sealed lead-acid battery capacity is rated in amp-hours (Ah). Runtime calculation:
Example A (2-door, 1.8A load):
7Ah battery → 7 / 1.8 × 0.7 = ~2.7 hours
12Ah battery → 12 / 1.8 × 0.7 = ~4.7 hours
18Ah battery → 18 / 1.8 × 0.7 = ~7.0 hours
Example C (8-door, 6.5A load):
18Ah battery → 18 / 6.5 × 0.7 = ~1.9 hours
33Ah battery → 33 / 6.5 × 0.7 = ~3.5 hours
Code minimums for commercial access in many jurisdictions: 4 hours of fail-safe operation on emergency egress doors. Practical recommendation: 8 hours for ice-storm regions. Eastern Ontario customers regularly hit 4-6 hour outages in winter; size accordingly.
04 / Common Failure Modes
Power problems that look like other problems.
- Intermittent maglock release — voltage drop on long DC runs. Either step up to 24V or move the supply closer.
- Reader resets on strike fire — undersized supply, inrush sag pulls the reader bus voltage below brown-out. Spec headroom for simultaneous fires.
- Battery won’t take a charge — old SLA after 4-5 years. Replace on schedule, not on failure. Most commercial UPS units don’t notify until the battery is already dead.
- “Maglock hums then drops” — AC ripple on a DC supply with a failing filter capacitor. Replace the supply.
- Strike fires but door doesn’t unlock — wrong polarity, or 12V strike on 24V supply, or vice versa. Verify on the meter before energizing.
05 / Brands We Stock for Access Power
Commercial-grade supplies, sized for security.
Access control power supplies stocked from Altronix, LifeSafety Power, ENS, FUDA; battery backup from Panasonic, Tripp Lite; distribution and accessories from ICC, Snap N Connect. Most stock items deploy within 24-48 hours across Ottawa and Eastern Ontario.
Pair this with the access control buying guide for full door spec walkthroughs.
Power Spec Review
Sizing power for a project?
Send the door count, lock types, controller make/model, and required backup duration. We come back with a sized supply, battery, and distribution layout — verified against the load math, not guessed from a sales sheet.
Equipment Referenced · Access Power
Access power hardware in this guide.
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