Power and Charging Infrastructure for a Robot Fleet

Why This Derails Schedules

Of the deployments we have seen slip, electrical work is the most common single cause and it is almost always avoidable. The pattern is consistent: the robot is specified, quoted and ordered on a six to eight week lead time, and nobody asks about the charging dock until the delivery date is confirmed. At that point a facilities team discovers it needs a dedicated circuit run to a corridor with no nearby panel capacity, which means a licensed electrician, possibly a permit, possibly after-hours work in an occupied building, and a lead time that is no longer inside the robot’s.

The fix costs nothing: treat the dock location and its circuit as a specification item at quote stage, not as an installation detail. Ask for the dock’s electrical requirement in writing before you sign, and have your facilities engineer confirm the circuit exists or can be run, with a date.

Where the Dock Actually Goes

Dock siting is a trade-off between four things, and the one people optimise for is usually the wrong one.

Out of the way, but not far away. The instinct is to tuck the dock into a back-of-house room, which minimises visual intrusion and maximises dead travel. Every minute the robot spends driving to and from the dock is a minute it is not working, and on a short route that overhead can be a meaningful share of capacity. Site the dock near the route’s centre of gravity, not at the building’s edge.

Approach clearance. A dock needs a clear, straight approach — typically a couple of metres of unobstructed floor in front of it, and it must not be at the end of a corridor that people use as a parking spot for carts, laundry bins or floor signage. If the approach can be blocked, it will be blocked, and a robot that cannot dock is a robot that is flat by morning.

Not a fire route, not an egress path, not in front of an electrical panel. A charging robot parked in a corridor is an obstruction, and your fire marshal or safety officer has a view about corridor width that predates your project. Raise it early; retrofitting a relocation after an inspection is expensive.

Thermally sane. Charging generates heat and batteries dislike heat. A dock in an unventilated closet, against a warm wall, or in direct sun through a lobby window will shorten pack life and in hot months may throttle charge rate.

One further point specific to multi-floor buildings: put the dock on the floor where the robot does most of its work, not on the ground floor because that is where the loading bay is. Lift transits are the slowest part of any route and you do not want to spend two of them on charging.

What the Electrician Needs to Know

Give your electrician these six items and the conversation takes ten minutes instead of three site visits:

• Voltage and phase — most service robot docks in North America are single-phase 120V, some 208/240V. Do not assume; larger cleaning machines and lift-capable platforms are more often the latter.
• Continuous current draw and inrush. The nameplate continuous figure determines the circuit; inrush matters for breaker selection and for whether the dock can share a circuit with anything else.
• Whether the manufacturer requires a dedicated circuit. Many do. Where they do, that is not a suggestion — a shared circuit that trips at 2am leaves you with an uncharged fleet and no alarm.
• Receptacle type and mounting height, and whether the dock is floor-standing or wall-mounted. Wall mounting usually needs blocking behind the drywall.
• GFCI requirements, which depend on the location classification — a dock in a kitchen, near a janitorial sink or in any wash-down area is a different question than one in a carpeted corridor.
• Whether the circuit should be on emergency or standby power. Usually no. But in a hospital where the robot carries specimens or medications, ask the question deliberately rather than by default, because the answer changes the panel and therefore the cost.

Have the work done to the electrical code edition your jurisdiction actually enforces, which is frequently not the newest one, and keep the inspection record with the deployment file. If you are in a leased building, check whether the work needs landlord consent — that approval can be slower than the electrician.

Battery Chemistry and What It Dictates

You are unlikely to choose the chemistry — it comes with the platform — but it determines how you can operate, so it is worth understanding what you have bought.

Lithium iron phosphate is the common choice in current service robots and it is the operator-friendly one: long cycle life, tolerant of partial charging, stable thermally, comfortable with frequent top-ups. If you have this, opportunity charging between runs is not merely permitted, it is the right operating pattern.

Other lithium-ion chemistries trade energy density for some of that tolerance. They often want more attention to depth of discharge and to sitting at full charge for long periods.

Sealed lead-acid still appears in older and lower-cost floor-care equipment. It is heavier, has a fraction of the cycle life, dislikes partial charging, and wants a full charge cycle rather than top-ups. If you inherited this, your scheduling constraints are materially tighter and your replacement cost arrives sooner.

Three operational consequences regardless of chemistry. Keep the fleet out of deep discharge as a habit, because it is the fastest way to shorten pack life. Find out the expected cycle life and the pack replacement cost before purchase, because the pack is the largest single consumable on the machine and it rarely appears in a five-year budget that someone else prepared. And ask what happens to the pack at end of life — who takes it, at whose cost, and under what disposal obligation.

Charge Scheduling and Fleet Sizing

The arithmetic here is simple and routinely skipped. You need four numbers: the duration of a full charge, the runtime per charge at your duty cycle rather than at datasheet rating, the length of your operating window, and the work the route requires.

Runtime at your duty is the one that gets misestimated. A machine rated for eight hours of runtime is generally rated on a favourable assumption — flat floor, moderate payload, few stops, no lifts. A real corridor with ramps, a loaded cart, frequent braking for people and two lift transits per trip will draw more. Derate whatever you are told, and confirm it during a trial rather than after.

Two operating patterns follow. Opportunity charging — short top-ups whenever the robot is idle — suits chemistries that tolerate it and routes with natural gaps, and it usually means one machine can cover a longer window. Scheduled block charging suits a machine that works a defined shift and charges through the off-shift, and it is the only real option with lead-acid.

A trap worth naming: if your operating window is close to the sum of runtime plus charge time, you have no margin, and any real-world interruption puts you short. Either accept reduced coverage or plan for an additional machine. Discovering this in month two, when the schedule has already been promised to a client or a ward, is a bad conversation.

Multiple Robots, Shared Docks

Fleets introduce questions a single machine never raises.

Can two robots share a dock, and does the fleet software queue them sensibly or do they deadlock in front of it? Ask to see this behaviour demonstrated rather than described. If docks are one-to-one, the floor space and circuit count scale linearly with the fleet, which changes the electrical budget significantly at four or six machines.

Where a fleet does share, check whether the aggregate draw of simultaneous charging exceeds what the circuit or the panel can carry. This is where several docks on one shared circuit stops being an economy and becomes a nuisance trip at the worst possible hour.

Finally, plan a spare dock position if you expect the fleet to grow. Running one extra circuit while the electrician is already on site and the ceiling is already open is a fraction of the cost of a second mobilisation in eighteen months, and fleets almost always grow.

A Pre-Order Checklist

Eleven items to close out before the purchase order, not after:

1. Dock location agreed, marked on a floor plan, and walked with facilities
2. Voltage, phase, continuous draw and inrush obtained in writing from the manufacturer
3. Dedicated circuit requirement confirmed, and circuit availability confirmed by your facilities engineer
4. Receptacle type, mounting method and any wall blocking identified
5. GFCI and location classification resolved
6. Emergency or standby power question asked and deliberately answered
7. Approach clearance measured, and the corridor obstruction question raised with safety or the fire marshal
8. Thermal environment at the dock assessed
9. Electrical work quoted with a completion date that precedes the robot’s delivery date
10. Landlord consent obtained if the building is leased
11. Runtime at your actual duty confirmed in a trial, pack cycle life and replacement cost documented, and end-of-life disposal responsibility assigned

Nothing on that list is difficult. All of it is cheap to do in the week before you order and expensive to do in the week after the crate arrives, and we would rather raise it early than be the vendor whose robot sat in a corridor for a month waiting for an outlet.