ZappBots wishes a warm welcome to everyone.

Especially our visitors from
Savage///Circuits and Parallax!!!


Please take a look our new forums, we hope you register and become an active user.

The ZappBots forums are being run on phpBB 3.1.4 software which is different then the vBulletin used on the Savage///Circuits and Parallax forums.
Therefore, things look and work a little different, especially creating posts and uploading images / attachments.


The important thing is we have a place toTalk, Learn and Showcase our projects.

Component selection help

A place to talk about anything about electronics that does not fit in one of the below categories.
User avatar
jknightandkarr
Member
Member
Posts: 223
Joined: Tue May 12, 2015 5:11 pm
Location: Hopelessly lost on the USS-Titanic 968 years from home....
Contact:

Component selection help

Postby jknightandkarr » Fri Oct 16, 2015 6:51 pm

Looking at various stuff for a project n need advice. Its for a relay board. Should. I just use relays, solid state relays, a big transistor, mosfet ect? Now i have 10 to fit in a 3" x 3.5" pcb, so relays probly out... I was thinking of a mosfet, i posted this on savage circuits, but i cant check that, i'd love to have it cover like 20-40 amps. Same range a regular automotive relay would cover.

Joe
Image
My website- Http://titaniceng.altervista.org/

My Facebookhttps://www.facebook.com/TitanicElectronicsGames/

~Owner, Designer & Builder Killer K.A.R.R.
~Starfleet Captain Joe R.
USS-Titanic Registry Number NCC-1513
Launched: Star Date 48509.9 Galaxy Class, Titanic Sub-Class Starship Max Warp: 15.96

User avatar
zappman
Administrator
Administrator
Posts: 120
Joined: Wed May 06, 2015 12:31 am
Contact:

Re: Component selection help

Postby zappman » Sat Oct 17, 2015 6:30 am

jknightandkarr wrote:...i have 10 to fit in a 3" x 3.5" PCB, so relays probably out... I was thinking of a mosfet, ..., I'd love to have it cover like 20-40 amps....
Joe


I have some questions.
1) Is the "20-40 amps" desired, the total current for all 10 relays?
2) Is the "20-40 amps" desired, per relay, so the total current passed through the board is 200-400 amps?
3) "I have 10 to fit in a 3" x 3.5" PCB"at 20-40 amps total for the board. I think this will be hard to fit on the board, but might be possible. What type of board connectors/pins are you going to use?
4) "I have 10 to fit in a 3" x 3.5" PCB"at 200-400 amps total for the board. I think this will be impossible to fit on the board, What type of board connectors/pins are you going to use?
5) Are the 10 individual relays going to be replaceable, or does someone have replace the entire board when they burn up one of the ten sets of relay contacts?
6) What types of loads, will be connected to the relays (be specific)?
Image
butlh ghajbogh nuv'e' yIHo'.
Admire the person with dirt under his fingernails.

User avatar
jknightandkarr
Member
Member
Posts: 223
Joined: Tue May 12, 2015 5:11 pm
Location: Hopelessly lost on the USS-Titanic 968 years from home....
Contact:

Re: Component selection help

Postby jknightandkarr » Sat Oct 17, 2015 10:42 pm

It's upto 40 amps per circuit so be upto 400 amps total. Probly not going to see that much but I wanted to have a good rating for it. as for the loads, its impossable to tell because its for knight rider conversion, so its whatever they hook it up for, but most likely either a) nothing at all or b) mostly small current stuff. i dont see anything major being opperated other then driving lamps.

As for terminals I am either thinking the screw clamp terminals like the h bridge on the ppdb uses or right angle headers.

Digikey got me a mosfet that can take like 80 volts and like 34 amps, and they are small so i should be able to fit them all on with no problems, so I am looking at 340 amps max but probly alot less. Concidering theres a LOT of buttons in any given KITT replica, a vast majority just make DTFM tone n are hooked up to nothing at all, Very few are actually used, but I am offering fully functional incase anyone wants to use them all for stuff.

Joe
Image
My website- Http://titaniceng.altervista.org/

My Facebookhttps://www.facebook.com/TitanicElectronicsGames/

~Owner, Designer & Builder Killer K.A.R.R.
~Starfleet Captain Joe R.
USS-Titanic Registry Number NCC-1513
Launched: Star Date 48509.9 Galaxy Class, Titanic Sub-Class Starship Max Warp: 15.96

User avatar
jknightandkarr
Member
Member
Posts: 223
Joined: Tue May 12, 2015 5:11 pm
Location: Hopelessly lost on the USS-Titanic 968 years from home....
Contact:

Re: Component selection help

Postby jknightandkarr » Sat Oct 17, 2015 10:46 pm

Image
My website- Http://titaniceng.altervista.org/

My Facebookhttps://www.facebook.com/TitanicElectronicsGames/

~Owner, Designer & Builder Killer K.A.R.R.
~Starfleet Captain Joe R.
USS-Titanic Registry Number NCC-1513
Launched: Star Date 48509.9 Galaxy Class, Titanic Sub-Class Starship Max Warp: 15.96

User avatar
zappman
Administrator
Administrator
Posts: 120
Joined: Wed May 06, 2015 12:31 am
Contact:

Re: Component selection help

Postby zappman » Wed Oct 21, 2015 7:27 pm

jknightandkarr wrote:Its for a relay board. Should. I just use relays, solid state relays, a big transistor, mosfet etc? Now i have 10 to fit in a 3" x 3.5" PCB, so relays probably out... I was thinking of a mosfet, ..... It's up to 40 amps per circuit so be up to 400 amps total. Probably not going to see that much but I wanted to have a good rating for it.


Joe, you are NOT going to be able to put 10 circuits each capable of 40 amps, adding up to 400 amps on a 3" x 3.5" PCB, it just won't fit.

jknightandkarr wrote:As for the loads, its impossible to tell because its for knight rider conversion, so its whatever they hook it up for, but most likely either a) nothing at all or b) mostly small current stuff. i don't see anything major being operated other then driving lamps.


Joe, you are the board designer, you have determine the capabilities of the PCB you design. If you are going to sell a product you need to tell your customers how the board works, and what it is capable of doing. You need to test your design, you need to apply the loads you tell you customers the design will handle. If don't you will refunding the cost of your PCB back to your customers, when the PCB does not work as advertised.

jknightandkarr wrote:As for terminals I am either thinking the screw clamp terminals like the h bridge on the ppdb uses or right angle headers.


For each circuit on your board to be capable of handling 40 amps, you are going to have make sure that every component in the circuit that conducts 40 amps is sized properly. Guessing does not work, you need to look at the specification / rating of each component placed on you board. You also need to make sure the copper tracks on your printed circuit board can handle the current.

jknightandkarr wrote:Digikey got me a mosfet that can take like 80 volts and like 34 amps, and they are small so i should be able to fit them all on with no problems, so I am looking at 340 amps max but probably a lot less.


Joe, you are NOT interpreting the MOSFET data sheet correctly. They play games with the maximum ratings listed at the top of the data sheet. You can't put 10 of those MOSFETS on a 3" x 3.5" PCB and pull 34 amps through each circuit with proper heat-sinking.

Here are the notes listed on the MOSFET data sheet.
Datasheet wrote:A. The value of RθJA is measured with the device mounted on 1in2 FR-4 board with 2oz. Copper, in a still air environment with TA=25°C. The Power dissipation PDSM is based on R θJA t ≤ 10s and the maximum allowed junction temperature of 150°C. The value in any given application depends on the user's specific board design.

B. The power dissipation PD is based on TJ(MAX) =150°C, using junction-to-case thermal resistance, and is more useful in setting the upper dissipation limit for cases where additional heatsinking is used.

C. Repetitive rating, pulse width limited by junction temperature TJ(MAX)=150°C. Ratings are based on low frequency and duty cycles to keep initial TJ =25°C.

D. The RθJA is the sum of the thermal impedance from junction to case RθJC and case to ambient.

E. The static characteristics in Figures 1 to 6 are obtained using <300μs pulses, duty cycle 0.5% max.

F. These curves are based on the junction-to-case thermal impedance which is measured with the device mounted to a large heatsink, assuming a maximum junction temperature of TJ(MAX) =150°C. The SOA curve provides a single pulse rating.

G. The maximum current rating is package limited.

H. These tests are performed with the device mounted on 1 in2 FR-4 board with 2oz. Copper, in a still air environment with TA=25°C


jknightandkarr wrote: Considering there's a LOT of buttons in any given KITT replica, a vast majority just make DTFM tone n are hooked up to nothing at all, Very few are actually used, but I am offering fully functional in case anyone wants to use them all for stuff.


I would put 4 relays that will fit on your board along with 6 open collector transistor outputs for your a total of 10 board outputs. You should size the components, including the relay contacts, the PWB traces, and connectors for a realistic current, that will fit on your size limited board.

Also, the MOSFETS you picked are surface mount parts, can you solder them?
Image
butlh ghajbogh nuv'e' yIHo'.
Admire the person with dirt under his fingernails.

User avatar
jknightandkarr
Member
Member
Posts: 223
Joined: Tue May 12, 2015 5:11 pm
Location: Hopelessly lost on the USS-Titanic 968 years from home....
Contact:

Re: Component selection help

Postby jknightandkarr » Sat Oct 24, 2015 7:37 pm

I might need to get rid of the stacked pcb design and have a remotely opperated relay board, which i was trying to avoid cause of the 2 10 pin cables that would be needed.... I wanted to keep the size as small as possable.

I could change my control board design to output the output signals to use with shift registers and have the shift registers on the relay board and just have a 5 pin cable to connect them to the control board. Power, ground, data, enable and clock pins. i could possably make my control board smaller that way too and have the speaker connectable via a small cable.

I was gonna use the copper pour to make directly connected heat sinks for the mosfets, but like i said. normal power probly wouldnt go anyplace near 40 watts * 10 anyhow. theres just not much on the knight replicas that draw that kinda power.

Not by hand but i have an old toaster oven and could just solder them that way. I need new toaster oven anyhow.

Joe
Image
My website- Http://titaniceng.altervista.org/

My Facebookhttps://www.facebook.com/TitanicElectronicsGames/

~Owner, Designer & Builder Killer K.A.R.R.
~Starfleet Captain Joe R.
USS-Titanic Registry Number NCC-1513
Launched: Star Date 48509.9 Galaxy Class, Titanic Sub-Class Starship Max Warp: 15.96


Return to “Electronics: General Discussion”

Who is online

Users browsing this forum: No registered users and 1 guest