UBEC wiring

[alvinlwh 5895]

If I am to wire up a UBEC this way, will the ESC switch still work or will the UBEC power the TX (and servo, etc) even with the ESC switched off? 

[Collin 1956]

yep. unless u use a ubec with switch.

[alvinlwh 5895]

3 hours ago, Collin said:

yep. unless u use a ubec with switch.

Thanks. If I switch the UBEC (on black feed I suppose?), will the ESC continue to suck power if the UBEC is off? 

[LongRat 616]

Yes.  Switching either isn't worth it IMO.  Too much risk for little return.  Better to have no switches and simply unplug the battery.

[alvinlwh 5895]

3 hours ago, LongRat said:

Yes.  Switching either isn't worth it IMO.  Too much risk for little return.  Better to have no switches and simply unplug the battery.

Yes, I know unplugging the battery is best. I am just trying to figure out which item to switch will be best for an emergency stop. My guess will be the ESC since that will cut power to motor right? 

[hIghQ 149]

Especially in an emergency I'd want to unplug the battery instead of using a switch.

[alvinlwh 5895]

4 minutes ago, hIghQ said:

Especially in an emergency I'd want to unplug the battery instead of using a switch.

Getting at a battery will usually require unclipping the body, not that easy when the wheels are spinning at full speed. 

[hIghQ 149]

Spinning wheels without throttle input? I have never seen this happen with an ESC, as they should immediately go to neutral when not getting a signal from the receiver. To me an emergency is more like something went wrong with the battery or wiring and there's smoke or a short-circuit, etc. happening. In these cases a switch is rather useless.

Plus on the cars I own, I can either reach both the switch and the battery cable with the body still attached (e.g. touring car, short course truck, etc.) or neither of them (e.g. buggies - but these are just velcro'd on most racing buggies). Also if something goes wrong with your car while you're up on the drivers' stand and a marshal has to save your car, he'll easily find your battery and where to unplug it, while your little switch could be located just about anywhere, but I know that's racing... 

[alvinlwh 5895]

6 minutes ago, hIghQ said:

Spinning wheels without throttle input? I have never seen this happen with an ESC, as they should immediately go to neutral when not getting a signal from the receiver. To me an emergency is more like something went wrong with the battery or wiring and there's smoke or a short-circuit, etc. happening. In these cases a switch is rather useless.

Plus on the cars I own, I can either reach both the switch and the battery cable with the body still attached (e.g. touring car, short course truck, etc.) or neither of them (e.g. buggies - but these are just velcro'd on most racing buggies). Also if something goes wrong with your car while you're up on the drivers' stand and a marshal has to save your car, he'll easily find your battery and where to unplug it, while your little switch could be located just about anywhere, but I know that's racing... 

NVM, your experience and setup is different from mine and what I am wanting to achieve. And I don't race so no driver's stand or marshal around.

[LongRat 616]

Switching the ESC might get you stopped in some emergency situations, so if it's something you are concerned with then go for it.

My opinion is that these switches lead to a false sense of security that the car is 'off'.  Mistakenly switching off but not disconnecting, with a LiPo connected (if you use one) is more hazard than adding the switch will mitigate.  But that's my view.

[alvinlwh 5895]

1 hour ago, LongRat said:

Switching the ESC might get you stopped in some emergency situations, so if it's something you are concerned with then go for it.

My opinion is that these switches lead to a false sense of security that the car is 'off'.  Mistakenly switching off but not disconnecting, with a LiPo connected (if you use one) is more hazard than adding the switch will mitigate.  But that's my view.

Completely understand that. I just want to stop the spinning wheels first before taking the body off to get at the lipo. I had the experience of setting the wrong memory on the TX or something, turn the car on, wheels went at high/full speed, fingers near to the switch (since just turned it on), so can snap it off instantly before troubleshooting. 

[TurnipJF 9192]

17 hours ago, alvinlwh said:

Completely understand that. I just want to stop the spinning wheels first before taking the body off to get at the lipo. I had the experience of setting the wrong memory on the TX or something, turn the car on, wheels went at high/full speed, fingers near to the switch (since just turned it on), so can snap it off instantly before troubleshooting. 

I think I see what you are trying to achieve. I suppose the ideal would be to switch both ESC and UBEC off at the same time with a single DPDT (double pole double throw) slide switch. These can switch two separate circuits simultaneously, and are typically the same size as a standard Tamiya ESC power switch so you could probably re-use the switch housing and mounting location. 

[alvinlwh 5895]

1 hour ago, TurnipJF said:

I think I see what you are trying to achieve. I suppose the ideal would be to switch both ESC and UBEC off at the same time with a single DPDT (double pole double throw) slide switch. These can switch two separate circuits simultaneously, and are typically the same size as a standard Tamiya ESC power switch so you could probably re-use the switch housing and mounting location. 

Just checking, shouldn't it be a DPST instead? 

EDIT: NVM, it seems that DPST switches are quite hard to find but a DPDT ON-ON will just work as well. Also, will 1.5A @ 240v switches be OK? 

[TurnipJF 9192]

2 hours ago, alvinlwh said:

Just checking, shouldn't it be a DPST instead? 

EDIT: NVM, it seems that DPST switches are quite hard to find but a DPDT ON-ON will just work as well. Also, will 1.5A @ 240v switches be OK? 

DPST will work just as well, but I recommended DPDT due to their easier availability. Just leave the third set of terminals unconnected.

However if the unused terminals bother you, mouser.co.uk have DPST slide switches in stock. Their form factor doesn't appear to match the Tamiya ones though. 

A switch that can handle 1.5A at 240V ought to be able to handle over 40A at 8.4V, so will be fine for this application. 

[alvinlwh 5895]

1 hour ago, TurnipJF said:

However if the unused terminals bother you, mouser.co.uk have DPST slide switches in stock. Their form factor doesn't appear to match the Tamiya ones though. 

I did see the mouser ones but wondered what their postage will be like on just a few switches. So I just looked on ebay instead. The DPDT ON-ON ones will work just fine like a ON-OFF switch by leaving a set of poles unused like you said.

Thanks for the help. 

[KILLorBE 23]

32 minutes ago, TurnipJF said:

A switch that can handle 1.5A at 240V ought to be able to handle over 40A at 8.4V, so will be fine for this application. 

Not really, I'm guessing that you calculated the power first (1.5*240=360) and then divided the power by the voltage (360/8.4=42.86), the switch is most likely rated at 240V AC,  but DC is a different animal, and it's not just about power, more current = beefier switch/thicker cables.

Depending on the motor used, a 40A switch may not be enough, I would probably go for a switch that can handle close to the motors stall current (Which is over 40A for a stock 540 silver can).

@alvinlwh Can't you just switch off the ESC, or is the ESC hard to reach? Is a different ESC an option? Some older ESC's used to have a switch on a wire that you could mount in an easy to reach spot, not sure if there are newer ESC's which also have a switch on a wire.

[TurnipJF 9192]

1 minute ago, KILLorBE said:

Not really, I'm guessing that you calculated the power first (1.5*240=360) and then divided the power by the voltage (360/8.4=42.86), the switch is most likely rated at 240V AC,  but DC is a different animal, and it's not just about power, more current = beefier switch/thicker cables.

Depending on the motor used, a 40A switch may not be enough, I would probably go for a switch that can handle close to the motors stall current (Which is over 40A for a stock 540 silver can).

You are correct about my calculations, however I don't see how the motor comes into play unless you are considering switching the main power cables, which I would not advise due to the high currents involved. Rather, I envisioned a switch that could simultaneously be wired in to replace the ESC's own switch, and the UBEC, neither of which ought to have to handle current in double figures even under heavy load.

[alvinlwh 5895]

1 minute ago, KILLorBE said:

@alvinlwh Can't you just switch off the ESC, or is the ESC hard to reach? Is a different ESC an option? Some older ESC's used to have a switch on a wire that you could mount in an easy to reach spot, not sure if there are newer ESC's which also have a switch on a wire.

Yes, that is the whole point of this post. If I switch off the ESC with a UBEC, what are the effects. 

A different ESC is definitely an option, and will do away with the need of a UBEC as I am only using one because of the low BEC supply on the TBLE. If I am to change to something else, I will get twice the current on the BEC. However, I am also using this as a chance to experiment on things instead of going the easy way out.

[alvinlwh 5895]

1 minute ago, TurnipJF said:

You are correct about my calculations, however I don't see how the motor comes into play unless you are considering switching the main power cables, which I would not advise due to the high currents involved.

I actually thought about switching the battery but will need something like a 400A switch?

[TurnipJF 9192]

2 minutes ago, alvinlwh said:

I actually thought about switching the battery but will need something like a 400A switch?

Not impossible, but heavier, bulkier and more expensive than simply switching the ESC and UBEC with a cheap little slider switch.

Although now that I think about it, if all you want to do is be able to stop the motor from running while you get the shell off to disconnect the battery, it shouldn't matter which one you switch off.

If you switch off the UBEC, the receiver will lose power, so the TBLE's failsafe will kick in and cut the motor. If you switch off the ESC, the motor will also stop. Both scenarios leave a small current being drawn from the battery, so you wouldn't want to leave the car in this state for any significant period, but if all you want is a means of stopping it from spinning up its wheels while you are spending a few seconds disconnecting the battery, either should suffice?

[alvinlwh 5895]

1 minute ago, TurnipJF said:

If you switch off the UBEC, the receiver will lose power, so the TBLE's failsafe will kick in and cut the motor. If you switch off the ESC, the motor will also stop. Both scenarios leave a small current being drawn from the battery, so you wouldn't want to leave the car in this state for any significant period, but if all you want is a means of stopping it from spinning up its wheels while you are spending a few seconds disconnecting the battery, either should suffice?

Good point, I maybe overthinking the problem to start with. I even thought about using a relay to switch the battery. Anyway, I think it will be safer to off the ESC to achieve my goal, although there is no harm in trying out the DPDT idea as well, even if it is just for educational purposes.

My usual practice is to connect the battery and load the cars into my car before driving the 5 minutes to my usual driving grounds. Then, unless the lipo alarm is going off, turn off at the switch and driving home, have dinner, put the kids to sleep before clearing the cars for storage. just about 3 hours in total.

 

[TurnipJF 9192]

2 minutes ago, alvinlwh said:

My usual practice is to connect the battery and load the cars into my car before driving the 5 minutes to my usual driving grounds. Then, unless the lipo alarm is going off, turn off at the switch and driving home, have dinner, put the kids to sleep before clearing the cars for storage. just about 3 hours in total.

Personally I would prefer to connect the battery just before starting my run, and disconnect it again immediately afterwards, but I am perhaps a bit over-cautious. In real-world terms, if you have a LiPo alarm fitted, and you can hear if it goes off while driving home, having dinner, etc, your way of doing things is possibly not much different to mine in terms of risk.

[alvinlwh 5895]

1 minute ago, TurnipJF said:

Personally I would prefer to connect the battery just before starting my run, and disconnect it again immediately afterwards, but I am perhaps a bit over-cautious. In real-world terms, if you have a LiPo alarm fitted, and you can hear if it goes off while driving home, having dinner, etc, your way of doing things is possibly not much different to mine in terms of risk.

Mine is not the best practice I know. In fact, on my first lipo run, I completely forgot about it and left the car in the shed for days (!) and even the lipo alarm sounded weak by the time I got to it. Lesson learnt.