4/28/2023 0 Comments Momentary switch diptraceBut there is also the risk of some leakage current across the pushbutton or relay contacts, or between tracks on the PCB (which was the topic of a thread quite recently). I have reading about TVS diodes but I am not sure how it would be positioned and if its the tool for the job. (If you spot any other potential disaster in my schematic (other than me!), please let me know). ![]() My concern was some sort of spike coming from the load and possibly blowing the PICAXE. The PCB of the load looks way above much league (those of you who just smiled then, stop it!) and I wouldn't know where to start drawing it up. The load also has a speed up and slow down buttons integrated into it and these "do what they say on the tin". I cant really give much more information about the load other than it has a positive and negative connection block labelled 30V and when powered it starts up a brushless motor which draws around 3-4amps. ![]() I did the schematic from memory and forgot about the transistor for the relay and the "load by pass wire" was another over site by me! I guess that is why I should draw the schematic first and then bread board after! Especially as my computer is several miles from my "laboratory". Nice job! It's been fun watching you get this going! Is the 0.15 mA (150 microamps) critical? Where is it going? Do you care? Should you care!? A 1 amp-hour battery will supply that current for over 6600 HOURS (9 months) before it needs to be recharged.Ĭlean up and complete the schematic, and we'll have another look. This starts to get into weird things like protecting the regulator from the big tantalum cap if you should happen to short the power supply, which is why it's important to show ALL of the components on a schematic (usually). My rule of thumb for low level logic like the Picaxe chip, is at least 1 uF of Tantalum, and the same ceramics as close as possible to the Picaxe V+ pin (within an inch). Probably, at least several hundred microfarads of tantalum on the 30 volt supply, paralleled with a 0.1 uF ceramic and a 0.001 uF ceramic. Again, liberal by-pass capacitors are called for. We'd need to see the details of the motor controller to make any recommendations for suppression or bypassing. They are particularly critical in a high power circuit like this, in which the logic supply is derived from the "high voltage, high current" source. A few relays have the diode built in, but not many.Īlso, I hope you have generous quantities of by-pass capacitors liberally sprinkled around. The coil will generate a huge (sometimes hundreds of volts) surge when it is turned off. It's considered good practice to place a "snubber" or "steering" diode across the relay coil. You may have intended that for "auto-shut-down", or maybe not. It also applies 30 volts to the input of the 7805, providing an alternate input to the switched input to the same regulator. As drawn, when the relay closes, the 30 volt supply is shorted directly through the vertical line directly to the left of the load. (Id like to use a picaxe as I want to integrate "auto off" )Ĭlick to expand.If your circuit is working, then it's not built per your schematic. I have built the circuit shown here and it works! Please can someone tell me if there are any "pitfalls" to using a circuit like this and since my load is a brushless motor controller, what should I use and where should I put it to prevent any reverse spikes from the motor damaging my "picaxe- relay" circuit. So, I am going back to the drawing board (all was not lost as I leaned a lot about PNP, NPN transistors and FETS.) and I am going to make use of Hippies suggestion of using a relay. I've tested it all week and no fires or odd smells! But I have a 0.15 milliamp power flow from the battery when the unit is powered down and I have traced that to a pin on the load PCB that I do need to keep (the pin that is)! ![]() The sad thing is the device works brilliantly and powers up and down without fail. However, having built the circuit and added it to my existing circuit, I am still having problems due to the load sinking the "switch circuit" when it is supposed to be off. I bet everyone thought this had been put to bed. Sorry I have re enlisted the help of this thread again.
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