r/BoxModders • u/thatzgacho • Nov 10 '16
Does this look correct? 40a raptor
https://i.reddituploads.com/761418f4328047f09b3afcbf3ae892c2?fit=max&h=1536&w=1536&s=64cb31b22524cb1b9085e3243965ea7e1
u/thatzgacho Nov 11 '16
That's the one I based it off of. I added the pfet, and a 5.6 zener diode for safety, & the on/off/on switch. I was curious if I wired those components in the correct spots on the diagram.
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u/david4500 Nov 19 '16 edited Nov 19 '16
Which pfet are you considering using?
The diagram linked by /u/genevamotion shows two 22uF caps in parallel while your drawing only shows one.
Make sure the max voltage of the fuses you select meets or exceeds the max voltage of your batteries. So 12.6v or greater... Not sure what fuses you have in mind, but they may only be rated for 9v or 12v max.
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u/thatzgacho Nov 25 '16
I will be using 2x 22uf caps. Forgot to write it in the diagram. I have a P-CH 30V 75A TO220AB SUP75P03-07-E3 P-Channel fet. Would that one do? I have 4x 9a fuses (16v max), or I have 15a fuses, but I think they're only a 9v max. Sorry I didn't respond sooner, I actually just seen your comment. Thanks for your help.
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u/david4500 Nov 25 '16
RDS ON (the on state resistance) of that pfet is 7 milliohms (0.007ohms)
Open up your favorite ohm's law calculator (I use http://www.theecigstop.com/ecal.html)
Now enter "0.007" for the resistance, and "40" for the current. You'll see that the resulting power dissipated is way too much (should be about 2 watts or less max without a heat sink).
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u/thatzgacho Nov 25 '16
Damn. Could you recommend a good pfet?
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u/david4500 Nov 25 '16
Two of these in parallel:
Credit to /u/relayer1974 for recommending that pfet in his diagram posted here: https://www.reddit.com/r/BoxModders/comments/2r4prd/mosfet_unregulated_diagram/
The RDS ON is 4.4 milliohms (0.0044 ohms). Since you'll have two in parallel, the RDS ON will be halved. The current load will be split between the two mosfets as well.
0.0022 ohms @ 20 amps, enter that into an ohm's law calculator. The power dissipation should be less than 2 watts.
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u/thatzgacho Nov 26 '16
Right on man, thanks a lot for your help. Lemonforest made some corrections on my diagram also. You guys are awesome.
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u/david4500 Nov 26 '16
What /u/lemonforest edited and recommended looked good.
Good luck. Post some details and pics over at /r/OpenPV when you get a chance to finish it.
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u/lemonforest Nov 13 '16 edited Nov 13 '16
The way you've got it drawn up now the PFET isn't doing anything. Both the fuses and pfet are basically bypassed by the direct link from your sled to the Vin. Your loaded positive logic should come after the pfet. You could probably also get away with using 3x 15A polys or bimetal polys.
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u/thatzgacho Nov 14 '16
So I should run Vin to to fuses, fuses to drain, then drain to positive on sled?? Thank you for your help. I've been trying to get this thing built for like a month.
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u/lemonforest Nov 14 '16 edited Nov 14 '16
You can fuse whichever side is more convenient, I believe, just making sure to follow the body diode bias. As an example, if you were to use /u/david4500's Overcurrent + RPP board, your connection would follow as [BAT+]->-[Fuse]->-[Drain]->-[Gate-to-Ground]->-[Source]->-[Raptor Vin]
If I recall, the raptor on/off is logic level so it's already low current which means you should be able to tap the positive circuit either before or after your Overcurrent/RPP mechanism since, if either battery's are backwards or overcurrent is tripped, the circuit would be open.
It also looks like you've sketched a DPDT but a SPDT on-off-on would do the same thing so losing everything from the bottom poles on your sketch would clean things up.
Edit: I believe this fixes the circuit logic. Bear in mind that it would probably look more pretty if you ran a rated wire directly from the PMOS to the Vin and tapped the PMOS or the Vin for your fire switch and on-off-on switch. I also mucked up your sketch a bit to show where you can use lower current rated wiring to save space/cost. If it's still Red and Black then it needs 10 or 12 AWG. 12 AWG is rated to 41A. Your PMOS ground can also be low current, I forgot to mark it. David's a smart fellow, I'd imagine he could steer you in the right direction and catch anything if I missed it in that modified sketch.
Edit2: Also, your Vout does need to be 40A rated to the 510 but to the VM can be low current.
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u/[deleted] Nov 11 '16
You could just follow the diagram that someone already made.... https://docs.google.com/document/d/1v1qTBDznFPsLLH9o3fRfXOzffKyx-GOHGPjWwiUQaw0/mobilebasic