[SOLVED] Help with emegency shutdown and fuse ratings on circuits

Hi,

So I am making a robot, and I have an 11 volt lipo battery supplying my 12v motors through the roboclaw 30a. I have the logic for the RClaw and an Arduino from a separate 7v battery (to prevent the effects of brown outs and other stuff). What I want is to make all this as safe as possible, so I have an emergency shutoff switch.My problem is I want to connect that emergency shutoff to all power supply of both batteries. How can I have one switch controlling 2 power sources at different power voltage ratings ? Do I have to have the switch connected to relays and the switch turns off both relays when pressed, so the 7 volt has a relay on the +ve, and the 11v has a relay on the +ve. The emergency switch feeds both relays so they remain open. Then someone hits the ESw and the relays drop out and the power is cut. This isn't really an emergency shut off IMO,an EShutoff is turning all the power off instantly to no other components (in case they fail etc). Can anyone help me ?

Also what ratings of fuse do I need for both of these curcuits ? The motors have 20 amp stall rating, but have 2 amp rated-load current. So do I let the current go up to 20Amp (so 20a fuse), or do I blow a fuse at say 5amp ? The Arduino and roboclaw should I put that 7volt circuit on a 1 amp fuse ? This is just the logi of the roboclaw obviously not the motor circuit on the roboclaw.

I got kids and they really love to grab hold of the thing, so I'm trying to make it safe, any other safety advice would also be appreciated !

Thanks

PS my web site is here (being built ... )

**broken link removed**

Marcus

Emergency switch:
You can use the "DPDT Emergency switch" for both circuits. Select the contact rating of switch such that maximum out of two circuits. It will avoid additional circuits like relay.

Fuse:
If you select the fuse for stall current, it provides motor protection under stall conditions and it may not protect the motor from overheating under overload conditions.

It is better to select the fuse based on the 'Rated current' of motor. The fuse rating shall be 150% of rated current of motor. It is suggested to use a time delay fuse based on requirement.

Hi thanks for the repsonse, whats the best way to have a delay on the fuse ? A capacitor ? And if so what rating ? If I have the battery connected to a motor shield and then the motor shield connected to the motor, and I want to do 150% of motor (this will be 3 Amp) I presume I put a fuse between the battery and the motor shield, which line the -ve or the +ve ? Thanks.

marcuso said:

whats the best way to have a delay on the fuse ? A capacitor ? Thanks.

Click to expand...

There is no need for capacitors.

You can use 'Time delay Fuses'. It is (also known as anti-surge / slow-blow) designed to allow a current which is above the rated value of the fuse to flow for a short period of time without the fuse blowing.

Since, your application circuit is motor, it is better to use time delay fuse to avoid the false triggering under inrush/start up conditions. The 'time to response' is to be selected properly to avoid false triggering and it will be in milli-seconds(ms) to seconds based on the motor.

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marcuso said:

I presume I put a fuse between the battery and the motor shield, which line the -ve or the +ve ?

Click to expand...

The fuse should be in series between source_+ve and load.