wouldn't there be a miniscule amount of current flowing anyway as standby current? (in the vacuum tube world, nothing beats pulling the power cord 
...that's why I'm still alive)
...that's why I'm still alive)Raptor Flip-Top VV Mod with 20A, 120W dc/dc converter...
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The primary problem with adding another MOSFET, in addition to the reverse polarity MOSFET, is the space required inside the mod for this extra circuitry.
The best solution is a supervisory IC. I was working with that with the OKL2-T20 and what is available for the voltage cutoff we need is teeny tiny (really really teeny tiny) smt parts.
And 20 amp slide switches are pretty big for a master switch...
I'm not sure why a MOSFET with the base driven by a voltage divider, including a zener diode, wouldn't work, but on thinking about it you may not get a sharp cutoff and have too much power dissipation from the MOSFET. A comparator though would provide a sharp cutoff for the MOSFET.
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And 20 amp slide switches are pretty big for a master switch...
You don't need a 20A switch.
We were talking about this at breaktru's and David4500 suggested parallel wiring a DPST or DPDT switch. This would double the current rating and lower resistance of the switch. Gotta love this paralleling stuff.
Plus, as breaktru had said, we're not turning on and off the master switch under load. So just need the switch rated high enough to allow current to pass through without the contacts getting hot or causing an unwanted voltage drop.
Craig also said that the switch's contacts can handle higher amps than what the switch is rated for. He also said you can safely assume that a switch rated for certain amps at a particular voltage can be used for higher amp loads at lower voltages.
So all this gives a larger range of what switches we can use. Good stuff.
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You don't need a 20A switch.
We were talking about this at breaktru's and David4500 suggested parallel wiring a DPST or DPDT switch. This would double the current rating and lower resistance of the switch. Gotta love this paralleling stuff.
Plus, as breaktru had said, we're not turning on and off the master switch under load. So just need the switch rated high enough to allow current to pass through without the contacts getting hot or causing an unwanted voltage drop.
Craig also said that the switch's contacts can handle higher amps than what the switch is rated for. He also said you can safely assume that a switch rated for certain amps at a particular voltage can be used for higher amp loads at lower voltages.
So all this gives a larger range of what switches we can use. Good stuff.
Thanks mamu. I have a few slide switches that should work ok. Just thought something automatic would be cool.
Thanks for the switch ideas...this was what I had considered in an earlier post. I was really hoping to hear that others had also considered and/or tried this
Thanks mamu. I have a few slide switches that should work ok. Just thought something automatic would be cool.
I hear ya. I was really disappointed that the supervisory IC at the cutoff voltage we need is only available in an ant size package and needs a proper PCB to mount on, so I kinda put off searching other ways.
I haven't given up though. I want to do a lipo pack mod with the Raptor like you did, but it freaks me out what you went through. It was a learning experience for both of us. So yeah, we need surety, especially for lipo mods.
I am pretty good at following your step by steps.....
lol
Sometimes I wish someone would give me step by steps. I don't have an electronics background so I learn as I go on an as needed basis. At least my eyes don't glaze over as much nowadays as they did in my first year of modding.
I am really happy with all my lipo pack mods. Even with similar mAh, the high C lipo packs give at least twice the vaping time than the cylindrical cells. Me thinks the mAh ratings on many round cells are exaggerated.
I am really happy with all my lipo pack mods. Even with similar mAh, the high C lipo packs give at least twice the vaping time than the cylindrical cells. Me thinks the mAh ratings on many round cells are exaggerated.
I think so too. I love love what the high drain lipos do for us vs cylindrical. And lipos have much much lower internal resistance than cylindrical, so that helps with longer vape times too.
Mosfet does not bias the zener. Adding a bias resistor does give a non linier region as mamu thought. Mamu is on the right track with a comparator and a mosfet for low parasitic draw. I do have some 70's Era comparators in the "drawers of things" but have surgery in the morning so it will have to wait for me to try it.
What would be way cool would be to figure how the Raptor sets the UVLO at 4.2v and change that to 6.2v or so with a few resistors or what nots. I have no idea if that is even doable, but without a Raptor schematic I wouldn't know where to begin.
Ok I will admit I did only skim threw the last batch of posts.....That said, am I missing something or wouldn't just using mosfet rated for the needed current be the simplest way and still be able to use a non rated switch?
I like switching the negative side since you can use a n-channel mosfet which typically have lower resistance (rdsON).
Here is a basic diagram and instead of going to the atty they would go the Raptor....and I think you should still be able to use the zener diode for low voltage.
I like switching the negative side since you can use a n-channel mosfet which typically have lower resistance (rdsON).
Here is a basic diagram and instead of going to the atty they would go the Raptor....and I think you should still be able to use the zener diode for low voltage.
wouldn't it be possible to also use this for the fire switch, and have the zener diode connected directly from on/off to Vin+?
Ok I will admit I did only skim threw the last batch of posts.....That said, am I missing something or wouldn't just using mosfet rated for the needed current be the simplest way and still be able to use a non rated switch?
I like switching the negative side since you can use a n-channel mosfet which typically have lower resistance (rdsON).
Here is a basic diagram and instead of going to the atty they would go the Raptor....and I think you should still be able to use the zener diode for low voltage.
On your diagram, can I put a 6.2v zener where you have the switch and it would quit draining the batteries when idle if the voltage on the lipo gets below 6.2v?
Specs on the mosfet? All the higher amp mosfets I look at have a 10v gate.
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I just ordered a 16A 88W DC-DC Converter to tinker with.
What drew my interest to it is that it has programmable UVLO - I can set low voltage cutoff to what I want with just a single resistor on the inhibit pin. The converter has a nice low profile and size for being a high amp converter.
I'm already planning my lipo build with it. woot!
What drew my interest to it is that it has programmable UVLO - I can set low voltage cutoff to what I want with just a single resistor on the inhibit pin. The converter has a nice low profile and size for being a high amp converter.
I'm already planning my lipo build with it. woot!
Anxiously waiting for your step by step......I just ordered a 16A 88W DC-DC Converter to tinker with.
What drew my interest to it is that it has programmable UVLO - I can set low voltage cutoff to what I want with just a single resistor on the inhibit pin. The converter has a nice low profile and size for being a high amp converter.
I'm already planning my lipo build with it. woot!
I highly recommend this battery.
http://www.hobbyking.com/hobbyking/...mah_2S_65_130C_Hardcase_Shorty_Lipo_Pack.html
or this, both are shorties and use 4 lipos 2 P then both of those packs in series.
http://www.hobbyking.com/hobbyking/...600mah_2S2P_90C_Hardcase_Lipo_Short_Pack.html
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A little off topic. I've built about 10 raptor boxes using on/off/on switches with the same specs. Is there a certain amp or volt rating I need? Given I would like this part to handle the max of the chip.
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If you are talking about the on off on switch that controls the source to the meter, it does not have to be a high amp switch. The meter uses very little amperage.
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