Electrically operated cooking gas valve?

[treezleef]

Hi,

We are designing and building cooking gas bottles with electronics controlled valves. These are for kids camping chalets. Its purely a safety feature because its kids. As you can tell, there is no big market for this product, its just to get these kids out camping.

System description:
So we have a bottle of cooking gas with a valve which is opened/closed by a small motor. The valve assembly sits on top of the gas bottle. The kid inserts a token (like coin) into a box, and then they get the gas valve opened for 10 mins, then closed again, until another token is inserted. The token box is near to the valve box and is electronically connected to it via a small cable. Which passes though the enclosure walls.
A STM32 micro in the valve assembly contols the valve motor. The micro will be sent to sleep whenever possible. The power to drive the motor comes from a small lithium cell with cell voltage of ~3.6V. There are no SMPS’s in the product. (because we need standby power to be very low). The motor is simply driven directly from the battery. (FET switch, switched by micro). The battery is non-rechargeable, as these have lower leakage current and last longer. The battery voltage is flat at 3.6V for most of its cycle..therefore we cant use battery voltage to sense when the battery is flat. So we intend to do some kind of coulomb counting.
Because its gas, the valve assembly product needs ATEX approval.
When the motor has fully closed (or fully opened) the valve, we don’t want the motor drawing any power, so I guess we need some mechanical latch in there. We can’t use a latching solenoid valve as they draw too much power in operation and in standby. They draw a high current when first actuated, and the ATEX approval means all our currents need to be well limited.
We need to sense when the motor has got to the end position where the valve is fully closed (or fully open)…We are thinking of doing this by sensing the motor current..because when the motor hits the end stop, then its rotor will cease rotation, and thus give no back EMF…so the rotor current will suddenly increase….we will detect this so as to tell us when the motor has reached the end stop.
..However, we were also thinking of adding a double check to this, by way of a Hall Sensor stuck to the rotor…so we can check the motor really has got to the end stop…after all, the user may somehow yank it so the motor stops in the wrong place (valve not fully open/closed). We are also worried that the user may try and somehow force the valve to be always open (so they can get more gas)
Questions, if i may:
1..What type of motor do you think can be used for this? (we aren’t finding such low voltage motors for this). Presumably DC motor is a no-no due to brush sparks and the gas (ATEX approval needed)?
2..Do you know of any kind of existing product on the market anything like this?…even if its not for cooking gas….…we cant find any.
3..Do you have any ideas for low-bias-current current limiters that we will need due to the ATEX approval?
4..Why dont normal gas cookers need ATEX approval?..they must have electronics in them.

 

[sxdave]

Hi,

We are designing and building cooking gas bottles with electronics controlled valves. These are for kids camping chalets. Its purely a safety feature because its kids. As you can tell, there is no big market for this product, its just to get these kids out camping.

System description:
So we have a bottle of cooking gas with a valve which is opened/closed by a small motor. The valve assembly sits on top of the gas bottle. The kid inserts a token (like coin) into a box, and then they get the gas valve opened for 10 mins, then closed again, until another token is inserted. The token box is near to the valve box and is electronically connected to it via a small cable. Which passes though the enclosure walls.
A STM32 micro in the valve assembly contols the valve motor. The micro will be sent to sleep whenever possible. The power to drive the motor comes from a small lithium cell with cell voltage of ~3.6V. There are no SMPS’s in the product. (because we need standby power to be very low). The motor is simply driven directly from the battery. (FET switch, switched by micro). The battery is non-rechargeable, as these have lower leakage current and last longer. The battery voltage is flat at 3.6V for most of its cycle..therefore we cant use battery voltage to sense when the battery is flat. So we intend to do some kind of coulomb counting.
Because its gas, the valve assembly product needs ATEX approval.
When the motor has fully closed (or fully opened) the valve, we don’t want the motor drawing any power, so I guess we need some mechanical latch in there. We can’t use a latching solenoid valve as they draw too much power in operation and in standby. They draw a high current when first actuated, and the ATEX approval means all our currents need to be well limited.
We need to sense when the motor has got to the end position where the valve is fully closed (or fully open)…We are thinking of doing this by sensing the motor current..because when the motor hits the end stop, then its rotor will cease rotation, and thus give no back EMF…so the rotor current will suddenly increase….we will detect this so as to tell us when the motor has reached the end stop.
..However, we were also thinking of adding a double check to this, by way of a Hall Sensor stuck to the rotor…so we can check the motor really has got to the end stop…after all, the user may somehow yank it so the motor stops in the wrong place (valve not fully open/closed). We are also worried that the user may try and somehow force the valve to be always open (so they can get more gas)
Questions, if i may:
1..What type of motor do you think can be used for this? (we aren’t finding such low voltage motors for this). Presumably DC motor is a no-no due to brush sparks and the gas (ATEX approval needed)?
2..Do you know of any kind of existing product on the market anything like this?…even if its not for cooking gas….…we cant find any.
3..Do you have any ideas for low-bias-current current limiters that we will need due to the ATEX approval?
4..Why dont normal gas cookers need ATEX approval?..they must have electronics in them.

I have only a suggestion for the motor to use - hope that helps and that the following is not telling you what you already know. I think small stepper motors may be what you want. Some come with several gears so the rotor rotates many times for a small movement of the output shaft. The rotor is a number of permanent magnets. The only coils to drive are static, creating the rotating magnetic field that drives the rotor. Some work from low voltages and can be driven from some microprocessors that have peripherals designed to drive them. Something I am not sure about is the torque that will be required to operate your valve as this will affect motor size and gearing and ultimately the drive circuitry required.