Lipo's on a switch

[steele42]

Question for you electronics experts. I built a rig

EL GUAPO The Handsome FJ Cruiser

The body is mounted on with 4 screws, so it's not a simple task to get to the battery. Ever sense I put a BEC in my rig the esc power switch isn't sufficient to turn off the rig (because the servo is still receiving power) so you must unplug the battery. Unplugging the battery every time is less than convenient so I thought why not put a switch between the battery and the esc? I could be wrong, but my thinking is that would be just like unplugging the battery. It looks something like this.







Disregard the color of the wires, it's all I had. Basically what I did was make a pigtail to go between the battery and the esc with the POSITIVE cable running through the switch and the negative cable just going straight across. I posted this idea in a local club forum and got told this idea would not work and it would drain my lipo within hours, but no further explanation. I've now had it plugged in this way for over 48 hours with at least 2 hours driving time (5000 mah 2s) and still haven't lowered my voltage enough to reach my cutoff on my esc. This leads me to believe that my switch IS working and cutting off all power when turned off. And it's suuuuuper convenient. What's the theory and is this going to drain my battery over time just sitting on my work bench? (Keep in mind it's not my intention to leave it plugged in for months at a time, just during my days crawling so it can be switched on and off throughout the day. Although I probably will keep it plugged in longer if you guys tell me it's ok to do that.) thanks for your input

[losikid]

You'll probably be fine....there are issues, but with a scaler i wouldn't worry about them.

[losikid]

Why not just wire it so your plug is easy to reach?

[steele42]

Originally Posted by losikid

Why not just wire it so your plug is easy to reach?

That's actually a really good idea. But I've already done this and I really like it. I'll definitely do that if someone can convince me that the switch is bad for my lipo or something. What's the issues you mentioned? Just for learning sake and if someone else stumbles upon this thread looking for info

[ElectroTech]

What's the current rating of the switch? Flipping the switch will be just like unplugging the battery, won't drain the battery at all with the switch disconnected. It will add a few ohms of resistance in the on position though, probably not noticeable. As long as the switch will hold up to the current should be fine. These motors can draw some serious amps inrush current.

[steele42]

Originally Posted by ElectroTech

What's the current rating of the switch? Flipping the switch will be just like unplugging the battery, won't drain the battery at all with the switch disconnected. It will add a few ohms of resistance in the on position though, probably not noticeable. As long as the switch will hold up to the current should be fine. These motors can draw some serious amps inrush current.

It's RadioShack part number 275-602. Toggle switch rated 3A at 125VAC, 1.5A at 250VAC. Sense the amperage rating seems to go up as the voltage rating goes down, I figured it'd be overkill for my scaler. It drives perfect, as much power as I need and no twitching or anything funny. It probably works in my favor that I'm a super slow driver. I don't hardly ever touch full throttle. Thanks for your input

[losikid]

Originally Posted by steele42

That's actually a really good idea. But I've already done this and I really like it. I'll definitely do that if someone can convince me that the switch is bad for my lipo or something. What's the issues you mentioned? Just for learning sake and if someone else stumbles upon this thread looking for info

extra weight, accidental bumps, unreliable...mostly concern for comp rigs

If you put the plug where you could easily get to it, then you could easily charge it as well...

[doublej]

I have always wanted todo this with a dual battery set up. Instead of swapping lipos just switch over to the other one.

[ElectroTech]

Originally Posted by steele42

It's RadioShack part number 275-602. Toggle switch rated 3A at 125VAC, 1.5A at 250VAC. Sense the amperage rating seems to go up as the voltage rating goes down, I figured it'd be overkill for my scaler. It drives perfect, as much power as I need and no twitching or anything funny. It probably works in my favor that I'm a super slow driver. I don't hardly ever touch full throttle. Thanks for your input

So the switch is rated for 375W. Running 2S at 7.4V that's 50A, running 3S it's 33A. Kinda low, depends on what motor/ESC your running. Just kinda example but a Holmes hobbies Torquemaster BR-XL is rated for 80A continuous, so that's around 600W. If you don't ever get into the throttle you should be fine then, just remember if you do the switch may fail.

[steele42]

Originally Posted by ElectroTech

So the switch is rated for 375W. Running 2S at 7.4V that's 50A, running 3S it's 33A. Kinda low, depends on what motor/ESC your running. Just kinda example but a Holmes hobbies Torquemaster BR-XL is rated for 80A continuous, so that's around 600W. If you don't ever get into the throttle you should be fine then, just remember if you do the switch may fail.

Thanks again for your helpful information. My particular setup is an FXR with Tekin 45T hand wound. The good thing is that if my switch ever did fail, all I would have to do is unplug my pigtail, plug the battery right into my ESC like before, and be on my way. I could definitely see how this might be more risk than someone is willing to take during a competition where time is important, but just scaling around with my friends I'll take the convenience of the switch. What's important to me is that the switch is cutting off all power so it's not draining my lipo while not in use. If I do run into any switch problems I will post it back up here so anyone searching the forums for this information will be able to know. Again, thanks for your time and helpful info.

EDIT: Just looking on my electronics wall here at RadioShack and came across a switch that looks physically more capable. It's RS part number 275-0025, rated 50A - 12VDC. Would this switch be more suitable for this aplication? I've got plenty of room where my switch is currently mounted. This toggle lever is a little bit longer, but its still easy enough to flip that I could trim the lever down to the length of my current toggle.

[steele42]

Originally Posted by doublej

I have always wanted todo this with a dual battery set up. Instead of swapping lipos just switch over to the other one.

If you could get a reliably rated switch this could really give you an edge on the competition on those long runs that require a battery change. It would be especially convenient if it was a switch that had the center position "off" and switch each direction for either battery.

[Charlie-III]

Originally Posted by steele42

If you could get a reliably rated switch this could really give you an edge on the competition on those long runs that require a battery change. It would be especially convenient if it was a switch that had the center position "off" and switch each direction for either battery.

You currently have a SPST switch (single pole/connection, single throw....on/off.)
What you're describing is a SPDT (better would be DPDT).
SPDT = Single pole/connection, double throw......on/off/on
DPDT = Double pole/connections, double throw

With a double pole, you could break both battery connections. Typical wiring would be:
Pack-1 to 2 poles on one end of the switch
Pack-2 to 2 poles on other end of the switch
ESC to 2 middle poles of the switch.

Switch in middle, ESC is isolated/packs disconnected.
Switch to one end or the other means one pack is connected to the ESC.

Always check connections of the switch (or read the tech sheet if it comes with one) to verify connections within the switch.

[steele42]

Originally Posted by Charlie-III

You currently have a SPST switch (single pole/connection, single throw....on/off.)
What you're describing is a SPDT (better would be DPDT).
SPDT = Single pole/connection, double throw......on/off/on
DPDT = Double pole/connections, double throw

With a double pole, you could break both battery connections. Typical wiring would be:
Pack-1 to 2 poles on one end of the switch
Pack-2 to 2 poles on other end of the switch
ESC to 2 middle poles of the switch.

Switch in middle, ESC is isolated/packs disconnected.
Switch to one end or the other means one pack is connected to the ESC.

Always check connections of the switch (or read the tech sheet if it comes with one) to verify connections within the switch.

That totally makes sense. Thank you for the good info. This thread has been VERY helpful

[ElectroTech]

Originally Posted by steele42

EDIT: Just looking on my electronics wall here at RadioShack and came across a switch that looks physically more capable. It's RS part number 275-0025, rated 50A - 12VDC. Would this switch be more suitable for this aplication? I've got plenty of room where my switch is currently mounted. This toggle lever is a little bit longer, but its still easy enough to flip that I could trim the lever down to the length of my current toggle.

Yes that's a stronger switch. 50A at 12V is 600W so about double the power handling of the switch your current using.

[steele42]

Originally Posted by ElectroTech

Yes that's a stronger switch. 50A at 12V is 600W so about double the power handling of the switch your current using.

Thanks again for all your help! I hope this thread helps other people with similar questions.

[tozrovr]

I soldered a female deans connector inline on my positive wire from the esc to the battery. I mounted this under my rig where I could access it. I put a loop pigtail on a male Deans plug and just plug it into the female plug underneath. I refer to the male pigtale as the key John Holmes gave me the tip.

[steele42]

Originally Posted by tozrovr

I soldered a female deans connector inline on my positive wire from the esc to the battery. I mounted this under my rig where I could access it. I put a loop pigtail on a male Deans plug and just plug it into the female plug underneath. I refer to the male pigtale as the key John Holmes gave me the tip.

Good idea!

Just as an update in case anyone is wondering, a couple nights ago we did some crawling and I wanted to put the switch to the test with my current setup. Did alot of full throttle blips and full throttle distance runs and no issues at this point. I'll probably install the heavier switch on my other rig that's running 3S, and I'll give an update on that when I do it

[SilmarilS]

Ok, here's a little electrical engineering teaching for you.

You CAN'T calculate the power of a switch with a "wattage" rating!
What matters is that you choose a switch with a sufficient voltage rating to avoid "arcing" between contact poles inside the switch.
So you "can" use a 120V switch on RC component but not the other way around.
Next, the most important part, which is the real way of choosing a switch is the AMP rating of the switch.
The Amp capability of the switch is really important to not melt the switch or cause a fire. For your application a 40-50 amp switch is sufficient. You will have a little trouble finding a bigger than 50A switch. And for RC use, since the load on the switch is not continuous and you don't switch with 50 amp rushing trough it, you could easily power 80 amp for short time without any problems.

I have a setup like your on my helicopter which doesn't have a ESC switch.

[heinie_21]

double post

[heinie_21]

Originally Posted by SilmarilS

Ok, here's a little electrical engineering teaching for you.

You CAN'T calculate the power of a switch with a "wattage" rating!
What matters is that you choose a switch with a sufficient voltage rating to avoid "arcing" between contact poles inside the switch.
So you "can" use a 120V switch on RC component but not the other way around.
Next, the most important part, which is the real way of choosing a switch is the AMP rating of the switch.
The Amp capability of the switch is really important to not melt the switch or cause a fire. For your application a 40-50 amp switch is sufficient. You will have a little trouble finding a bigger than 50A switch. And for RC use, since the load on the switch is not continuous and you don't switch with 50 amp rushing trough it, you could easily power 80 amp for short time without any problems.

I have a setup like your on my helicopter which doesn't have a ESC switch.

Expertise. Love it. How about insight on the Lipo draining itself when plugged into the switch in the off position? Is that possible? With no complete circuit isn't it the same thing as unplugging the Lipo?

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