0.86V voltage drop along the +5V line on my supergun - help

I'm currently designing a supergun, and i'm running into a slight problem with the +5 rail of the voltage. I have a external power supply with a 5-pin din connected to it and have it hooked up to my supergun which has a female din input. However, when I turn on the supergun, there is approximently a 0.86 voltage drop between the +5V source (the power supply) to the end of the jamma connector. Sorry I wish I could take a picture of my setup but my friend currently has my camera.

Anyhow, this only occurs on the +5V line. This voltage drop does not occur on the +12V or -5V line at all. When I hook up the +5V line directly to the jamma connector, there is still a voltage drop, but it is much less, about .05V instead of 0.86V.

Is this just the nature of the +5V line or what is the deal?

Hrmm, are you taking these readings under load? As in, with a PCB plugged in and powered up/trying to power up?

You'll always get some drop from the 'unloaded' metered voltage from the PSU as opposed to when it's 'under load', particularly with current hungry boards like large multi slot MVS PCBs or say Capcom CPS-1 & 2 etc. 0.86v is a little high though, but as you've measured it at only around 0.5v drop when you make a direct run to the edge connector, I'd say you need to try and optimise your wiring in order for it to support the voltage/current more effectively. Heavier gauge wiring can help with this and also don’t forget you'll need equally high gauge on the GND run/s as all the other voltage rails combined, as the circuit will be only as efficient as its weakest point. Meaning if you have a huge fat cable to transfer the
+5v, but only a thin cable for the GND run, the amount of voltage/current transferable will be equivalent to the thin cable’s potential not the heavy gauge one!

Also, try not to make your power cables between PSU and SuperGun too long, as the longer you go the more resistance will be added and therefore the greater the voltage drop. If you're registering these voltage drops without the PSU under load then perhaps you've got voltage/current bleeding off somewhere along the line. Have you implemented any circuitry in-line with the PSU and SG? Perhaps something that could contain a minor short or simply add more resistance?

Twould be great to see some pics if you can get your camera back

edit:

Errr...I can't belive I forgot to add this with all my other waffle, but you'll likely need to adjust the +5v up higher at the PSU so that at the edge connector, when under load, it stays at around the 5v mark. This will vary a little from PCB to PCB, but I guess just adjust it for the most current thirsty PCB you have and all the smaller boards you have/may get in the future should be fine also.

If you're using a Jameco PSU I'm not sure if you can adjust this, and if it is possible, how it's done. Someone else may have the key on that front.

Hope this helps

Take a reading at the wire where it hooks into the power connector at the end of the wire from the power supply... Then take another reading where it comes out of the back of the power connector on the supergun...

If your voltage drop is across the connector (which I'm thinking it probably is) then you have a bad connector. It either can't handle the current and is getting cooked or you have some bad contacts on it. I think it's getting cooked since you are only using a 5 pin one...

If you are using a DIN connector you need to use at least 2, preferably at least 3 pins for the +5v line to spread out the current across more pins. I would suggest using an 8 pin DIN setup so you can get more pins in use.

RJ

If it's a reasonable quality 5 pin full sized DIN plug it should handle the current draw from most PCBs without issue. I agree with channelmaniac on the 'more than 1 pin' for 5v, just make sure to have at least as many runs to GND too or having numberous lines transferring the 5v will be pointless.

Hey guys, thanks for all your input and suggestions. And to answer your question, yes I took these measurements under load (when the game was on).

As far as running more +5 lines to the 5 pin din, I cant run more than 1 due to the fact that I need lines for +12 -5 and GND

Right now I have the following setup:

pin1 - +5V
pin2 - +12V
pin3 - -5V
pin4 - gnd
pin5 - gnd

However, the +5V wire that connects the PSU and the male 5pin din cable is extremly thin, like 24 guage or something. I'm going to buy a new cable thats at least 20 gauge.

I'm also going to redesign my PCB to make the +5V and gnd traces 1.02mm thick to carry more current. I'm also going to have 8 seperate lines GND lines into the DB-37 connector I use to connect the jamma harness instead of only having 4 like I had before.

I'm going to make these changes and see if the voltage drop reduces, anything less than ~0.3V is desireable, 0.84 is too much. Also, yes with my current setup, I did crank up the PSU to get near 5V at the edge connector, but I had to crank it up nearly to 5.8V to get 5V at the edge connector, I'm trying to design a supergun where that isnt neccesary.

I'll update when i try out my new setup, but anymore suggestions would be appretiated.

Well even with only single wire runs on the +5v you shouldn't have any problems as long as your cabling is of reasonable guage. Even having only one pin per voltage on the DIN plug/socket shouldn't be an issue as I personally use 3 pin XLR type plugs which have far smaller pins than the full size DIN standard. I use the 3 pins for +5v, +12v & -5v and the outer casing for GND transferral.

I look forward to seeing your setup and good luck with your optimisations!!

Hey, and don't forget to post your work over at SGR!!

FusionITR said:

However, the +5V wire that connects the PSU and the male 5pin din cable is extremly thin, like 24 guage or something. I'm going to buy a new cable thats at least 20 gauge.

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A single 24awg wire for 5v was a crazy idea. If it really has to be a single wire don't use anything thinner than 18awg. But why not use an 8-pin connector with 3 grounds, 3 +5v, 1 +12v and 1 -5v, all with 18awg wires?

Ok guys I just wanted to update you.

I've fixed the problem. I redesign the PCB and changed the layout a bit along with having 20 guage wires for the PSU to din connector and now there is only a 0.24V voltage drop, which is very acceptable.

Thanks for the help guys, when Im completely done with the supergun (this may be awhile) I will post pics for you guys.

When you say 'PCB' do you mean you etched your own layout from scratch or just used Prototype/strip board to layout the components?

Just interested as I've tossed around the idea of getting into a bit of etching myself but never seem to find the time to get the equipment etc.

John_Smith said:

If it's a reasonable quality 5 pin full sized DIN plug it should handle the current draw from most PCBs without issue. I agree with channelmaniac on the 'more than 1 pin' for 5v, just make sure to have at least as many runs to GND too or having numberous lines transferring the 5v will be pointless.

Click to expand...

Not to be too much of a stickler, but if you check the specs on one of the component manufacturer's part, it shows the current rating to be 1A at 24VDC on each pin of the 5 pin DIN jack.

If your Neo Geo board is pulling 3A then you need 3 pins for power and 3 pins for ground (preferably more since you need to ground the 12v too)

If you aren't using enough pins you will heat up the connection and burn it up. Hopefully when the pins aren't making good contact and the voltage fluctuates like mad you won't damage anything on the board.

RJ

channelmaniac said:

Not to be too much of a stickler, but if you check the specs on one of the component manufacturer's part, it shows the current rating to be 1A at 24VDC on each pin of the 5 pin DIN jack.

If your Neo Geo board is pulling 3A then you need 3 pins for power and 3 pins for ground (preferably more since you need to ground the 12v too)

If you aren't using enough pins you will heat up the connection and burn it up. Hopefully when the pins aren't making good contact and the voltage fluctuates like mad you won't damage anything on the board.

RJ

Click to expand...

Generally speaking, PCB's including far hungrier boards than the majority of MVS boards will never burn a power connector unless you're plugging and unplugging it under load. The power switch is where you'll have the problems as the internal contacts cop the full shunt when the PCB is powered up. If the wiring and any associated bottle necks are deficient enough to cause issues, all that will result is boards not wanting to boot properly or intermittently resetting due to insufficient voltage/current. You can only pull through the amount of current the wiring/connectors will readily support. Perhaps if the din connector is only just plugged in and the supply voltage can arc across to gap between pin and socket then you could burn the contacts. This is what happens inside an incapable power switch. All the thousands of Jameco SC200 PSU's folks around the forums use all have 5 pin din plugs and easily exceed your stated current rating per pin. Perhaps it varies according to build quality...

If the pins in a connector or the wiring itself are not sufficient to fully supply the required voltage/current, it simply adds potentially unwanted resistance. Notable supply voltage drops are symptomatic of this scenario.

The only other way to fry a power connector is while working in a far higher current environment than we're dealing with here or of course if you have a short somewhere along the line.

Not trying to create a debate here, just the way it tends to pan out.

John_Smith said:

When you say 'PCB' do you mean you etched your own layout from scratch or just used Prototype/strip board to layout the components?

Click to expand...

Correct.

John_Smith said:

Generally speaking, PCB's including far hungrier boards than the majority of MVS boards will never burn a power connector unless you're plugging and unplugging it under load. The power switch is where you'll have the problems as the internal contacts cop the full shunt when the PCB is powered up. If the wiring and any associated bottle necks are deficient enough to cause issues, all that will result is boards not wanting to boot properly or intermittently resetting due to insufficient voltage/current. You can only pull through the amount of current the wiring/connectors will readily support. Perhaps if the din connector is only just plugged in and the supply voltage can arc across to gap between pin and socket then you could burn the contacts. This is what happens inside an incapable power switch. All the thousands of Jameco SC200 PSU's folks around the forums use all have 5 pin din plugs and easily exceed your stated current rating per pin. Perhaps it varies according to build quality...

If the pins in a connector or the wiring itself are not sufficient to fully supply the required voltage/current, it simply adds potentially unwanted resistance. Notable supply voltage drops are symptomatic of this scenario.

The only other way to fry a power connector is while working in a far higher current environment than we're dealing with here or of course if you have a short somewhere along the line.

Not trying to create a debate here, just the way it tends to pan out.

Click to expand...

Eeeek! Sorry about the preachy tone there channelmaniac. I wasn't meaning to be a grumpy aunt. LOL that's the difference between posting at work and then again later at home.

No offense taken...

But as for the connector... I'd much rather over-engineer something to avoid any weak spots in the system.

RJ

FusionITR said:

Correct.

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Fusion, do you by any chance have an EAGLE library or part for the JAMMA edge connector, male or female? I don't know what you're using for your layout, but I can't find anything of the sort for EAGLE, and making one is a pain in the ass.

toodles said:

Fusion, do you by any chance have an EAGLE library or part for the JAMMA edge connector, male or female? I don't know what you're using for your layout, but I can't find anything of the sort for EAGLE, and making one is a pain in the ass.

Click to expand...

Sorry, I use expresspcb for my cading, so I dont have any eagle libraries. However, I dont use the Jamma edge connector on my PCB anyway, I use a DB-37 connector and wire it up to a jamma cable.