What does the crane do if the remote control's battery goes flat?
When transmission stops the receiver releases the relays, the load stays suspended and the brake holds. This is passive stop; a latched command is unacceptable.
The expected behaviour is that when the transmitter stops transmitting, the receiver releases its relay outputs and the movement stops. The load stays hanging in the air, the brake comes in, the crane stays still. A command staying latched is not acceptable behaviour.
Why it has to be this way
A flat battery is the most frequent loss-of-communication scenario on a wireless remote control. In the general machine safety approach, loss of communication counts as a dangerous fault and the system is expected to go to a safe state of its own accord; that is, the moment the receiver stops receiving a valid command it releases its outputs, the contactors drop out and the movement ends. This behaviour, called passive stop, works the same way when the remote control goes out of range; from the point of view of the receiver the two situations cannot be told apart.
This behaviour sometimes strikes the operator as wrong: when the remote control goes quiet with the load in the air, the job is left half done. The alternative, though, is the last command staying latched and the load carrying on moving out of control; there is no choice to be made between the two. For the same reason it is not wanted that the receiver should "remember the last position" and carry on where it left off when the link returns.
The signs before the battery goes flat
A battery does not go flat suddenly; it gives warning over several shifts:
- The range shortens. If a command you give from the same spot no longer gets through, the first suspect is the battery; the range dropping as the battery weakens is an expected result.
- The command holds with a delay or drops out now and then. The operator usually describes this as "the remote control is sticking" and the receiver is suspected first; whereas trying the same remote control with a fresh battery takes a few seconds and clears the suspicion at the outset.
- In the cold the signs become more pronounced; capacity falls at low temperature and a battery that looks full collapses under load.
What to do if the load stays in the air
To lower the load you have to either renew the battery or the charge of the remote control, or use the machine's own wired button panel. On the ST100 and SF100 sets, the manual button being able to work in parallel with the RF remote control is functional in exactly this kind of situation — you can carry on with the button without dismantling the wiring. On other variants confirm the possibility of parallel use from the product page and from the user manual. Do not go under a suspended load and do not intervene without clearing the area.
The preventive side
- The SF100/SF200 remote control runs on 3×AAA cells; keeping spare cells in the shift bag closes the interruption within seconds.
- The ST100/ST200 remote control is Li-Po rechargeable and is charged from the AXI-Link 3-pin industrial connector; make putting it on charge at the end of the shift a routine.
- On critical operations the soundest solution is teaching a second remote control to the same receiver and keeping it as a spare.
- Add the battery and charge state to the start-of-shift checklist; read a shortening range not as a fault but as a battery warning.
Where this behaviour is not enough
Passive stop is a stopping behaviour, it does not take the place of the emergency stop function. When the battery goes flat the movement stops, but that does not mean the wired emergency stop chain of the machine has taken over its duty; that chain has to stay in place. Passive stop is not a function that lowers the load either: the brake holds the load, but the area under the load is not counted as safe just because the brake is holding. Lower a load that will be suspended for a long time to the ground at the first opportunity; and for that the wired control of the machine has to be in working order. Always verify the exact behaviour from the user manual of the product.
The full topic: Wireless Crane Remote Control Selection Guide