Rule 6.3 The Link

[jim]

Rule 6.3 The Link

I wish Id bought one of the 180A relays that Maplin used to sell - they were selling them for £9.99. I believe they were sold under the Shark brand name who make lots of cheap car audio accessories. If anyone sees them on sale anywhere please let us know.

180A may not be enough for some modern robots but would do fine for me. As for contacts bouncing open - I have heard several different stories about how likely this is. The biggest problem I expect would be them opening while the controllers are trying to dump energy back into the battery - could cause welding of the contacts and damage to the speed controller.

I agree with Roger about car starter relays or solenoids as theyre often called - theyre not meant to conduct for more than a few seconds.

[ukrobotics]

Rule 6.3 The Link

http://www.albright.co.uk/http://www.albright.co.uk/ sell a wide range of heavy duty DC contactors at reasonable prices. Everything from 80A to 1800A!


Dominic

http://www.ukrobotics.comhttp://www.ukrobotics.com

[Guest]

Rule 6.3 The Link

Theyre quite cheap too!

[roger_plant]

Rule 6.3 The Link

You seem to be mising the point. You do not need to buy a power relay if you use a small relay powered from your receiver power to control the supply to your interfaces or micro switch driven devices.
If the receiver power is missing, the power to the microswitches or interfaces is removed thus removing the power to whatever they were controlling.

[jim]

Rule 6.3 The Link

At some point you need to have a device capable of switching or regulating the power from your batteries to your motors. Normally this is a MOSFET speed controller or weapon-firing relay. Both types are capable of failing in such a way that they will conduct power without any voltage supply to their control inputs, leaving you stuck in forward drive or with a flywheel stuck on.

You may find this risk acceptable, indeed it is fine by the current FRA rules, however, a separate power relay reduces this risk significantly.

[roger_plant]

Rule 6.3 The Link

Jim, it also adds about 0.5 Kg to the robots weight.
We have managed so far without the need for power on/off relays, I dont think it is necessary to add them on to the safety spec now.

[m2xt]

Rule 6.3 The Link

Jim, I would personally never consider building a heavy without the power relays. I have used them once in anger and all the time for the remote kill (when arming / disarming). I accept that I am in a minority and will not form part of the FRA rules but that does not stop anyone from fitting them. I attempt not to compromise safety just to save weight. Its all about taking reasonable precautions and power relays are a reasonable precaution in my book.

Paul

[leorcc]

Rule 6.3 The Link

Ive used relais to shut of the main power from the robot since day one, but never realised it wasnt mandatory till i bought Splinter.

Live and Learn.

I do agree with Paul that it is by far a safer option. I will see if and how i can fit one in Splinter, but i doubt its going to be an Albright, since i dont have the weight to spare on it.