First box build and need help

[dc99]

MHP-TA15-9-85 TE Connectivity / Raychem | Mouser
These are the ones I use on most parallel boxes.
You are correct in that it really doesn't matter where you tap the positive. I usually solder to the pos on the battery box.
If your going to drive this thing hard you can parallel two mosfets. Still only one resistor. I don't think a heat sink will be necessary but since you are doing the low side you can use the box as a heat sink.
I use 3a 125v switches, at 5v they can handle around 50amps

 

[JimmyDB]

Very good point. Higher amp switches seem to be difficult to come by and if you do, pricy or too large. Does the mosfet serve any other purpose?

You can still make your own switch as I figure you have been for tubes...

I say that the mosfet works as a fuse... but in reality, it can be a fuse that refuses to open in the off-chance it fails closed. They don't work like a relay, so it's different for them to fuse closed... but you can think of it as a fuse as far as simple diagrams are concerned in THIS use case. In more complex electronics they bring much much more to the table though.

 

[JimmyDB]

MHP-TA15-9-85 TE Connectivity / Raychem | Mouser
These are the ones I use on most parallel boxes.
You are correct in that it really doesn't matter where you tap the positive. I usually solder to the pos on the battery box.
If your going to drive this thing hard you can parallel two mosfets. Still only one resistor. I don't think a heat sink will be necessary but since you are doing the low side you can use the box as a heat sink.
I use 3a 125v switches, at 5v they can handle around 50amps

The heat dissipation is to keep the efficiency high and make sure I get the amp output as expected. The datasheets generally show reduced amp output unless you have heat dissipation. YMMV, everything depends on the exact component. I think this is somewhat evident in the sheer number of box mods out there that can't come anywhere near their advertised potential when tested. Sure, they except low ohm coils... sure they maintain a voltage... but the amperage is severely limited.

As far as the switches, I would be interested to check in to them. They seem to be built way above spec. We know the voltage and amperage rating on a switch are related, but independent... i.e., the switch is rated to handle up to 3A at up to 125V... it's not rated to handle 1.5A at 250V nor is it rated to handle 30A at 12.5V... it simply isn't an issue of VAs or Watts. Switch manufacturers would love for that to be the case, then they could just list them for VA or W. Instead, the voltage rating is the max voltage and the current rating is the max current. I have seen many switches used out of place before and well beyond their ratings...

 

[dc99]

I thought about the switch thing so much I ask a friend about it. I have used the slider switches for a while and they always worked but the new thing is to build a box and drive it as hard as possible. His recommendation was to just use the slider switch to turn on a mosfet and use the mosfet as the actual switch. Guess Im a tad behind the times. Guess I stand corrected.

 

[Cfraley]

Completely built the box again today and happy to report it's firing perfectly. Must have over heated my prior mosfet. Also gave me a chance to clean things up. From your suggestions, I raised the source wire up higher where it's nowhere close to the enclosure and shrink wrapped everything. I will be ordering 2 15 amp fuses for my next project. Thanks again to everyone!

 

[rhelton]

Nice job

 

[lucky_x16]

I thought about the switch thing so much I ask a friend about it. I have used the slider switches for a while and they always worked but the new thing is to build a box and drive it as hard as possible. His recommendation was to just use the slider switch to turn on a mosfet and use the mosfet as the actual switch. Guess Im a tad behind the times. Guess I stand corrected.

You and me both!

 

[lucky_x16]

Congrats!! It looks nice and clean.

 

[dc99]

Congrats, glad you got it working.

 

[xPl4guEx]

its hard to tell from your pics but this guy has a very clean easy to build tutorial

https://www.youtube.com/watch?v=9Pmlhm6NkII&index=10&list=FLlqBC9-MN63CNgjJilUTdWA

 

[xPl4guEx]

Didn't catch the last few threads nice job looks great

its hard to tell from your pics but this guy has a very clean easy to build tutorial

https://www.youtube.com/watch?v=9Pmlhm6NkII&index=10&list=FLlqBC9-MN63CNgjJilUTdWA