A Question About The Propeller Project Board USB (#32810)

idbruce

How much amperage can the 8-pin Bridge handle?

WBA Consulting

The trace from the LDO to the bridge will be the determining factor. Judging from photos, it is either a 20 or 25 mil trace. If the top layer is 1/2 oz copper, that puts the current capacity between 0.83 (20mil) and 1 amp(25mil). If the top layer is 1oz, then the current capacity could be between 1.43 and 1.69 amps. In any case, you could run jumpers from the LDO pins to the pwr/gnd 8 pin bridges to gain a little if needed.

https://www.eeweb.com/tools/external-pcb-trace-max-current

idbruce

In the "Guide", Parallax provides the current carrying capacity of the VIN header, and I would imagine that a reasonable person could assume that the current carrying capacity of the 8 pin bridge would be equally important information Unless of course, I am thinking unreasonably

I was hoping that Parallax staff would chime in with an accurate answer. I was going to call them, but thought I would post here because I think it would be handy information for someone else.

If necessary, I will call them for an accurate answer.

In any case, you could run jumpers from the LDO pins to the pwr/gnd 8 pin bridges to gain a little if needed.

Yea.... I need to make four taps off that bridge, and I believe it could get a little messy.

idbruce

Okay... I realize I am asking a very specific question, to which there is a very specific answer. If I ask Parallax "support" to answer my specific question, I want Parallax to answer my specific question, from a person that is knowledgeable about the Parallax products, a person that has full access to give me a valid answer, and additionally a person that has knowledge to answer my specific question accurately.

C'mon Parallax, you are not playing games, and I ain't either. I am designing equipment around your products.

Publison

Bruce, you may want to call tech support. You will get an answer a lot faster. They don't have a chance to go through the 40-50 posts a day here.

Tech Support: 888-997-8267, support@parallax.com

idbruce

Jim

I emailed them..

My last response included this reply:

I'm concluding that the current the vias/pins can handle is going to be anywhere from 0 to 3 amps.

C'mon

Publison

idbruce wrote: »

Jim

I emailed them..

My last response included this reply:

I'm concluding that the current the vias/pins can handle is going to be anywhere from 0 to 3 amps.

C'mon

Ok

idbruce

If it can handle 0 amps.... Might as well throw the board in the trash

EDIT: And the first response was a waste of time and a little annoying. I realize he is probably just a kid, trying to make a buck, but I do not have time to waste.

WBA Consulting

The trace sizes can't handle 3 amps, so that answer cannot be valid. Regardless of what level of detailed answer you are looking for, you can't get past the physics. I will go back to my first reply in that the trace itself will dictate the current capacity as that is the weakest part of the circuit from the LDO output leg and the header installed at the bridge pin location. For an exact answer, someone at Parallax will need to open the design files and calculate against both the trace width/thickness of the positive trace and the combined thermal relief spokes for the ground connections. My opinion is that if you need more than 1.2 amps, don't use the LDO pads.

kwinn

Isn't this a bit of a moot point since the LDO Regulator can only provide a maximum of 1Amp? If 3 amps was available it would be possible to scrape the trace coating off and solder a bit of wire to the copper trace and pads to handle the current.

idbruce

I altered my original question with two more questions about the width and thickness of the trace. He replied with the trace width and the trace width is indeed a 25 mil trace (GOOD GUESS!!!), and I was told he is still searching for the thickness.

idbruce

With a 25 mil trace, I should be in very good shape.

Ken Gracey

idbruce wrote: »

If it can handle 0 amps.... Might as well throw the board in the trash

EDIT: And the first response was a waste of time and a little annoying. I realize he is probably just a kid, trying to make a buck, but I do not have time to waste.

You were exchanging e-mail with Miguel Rodriguez. He's an Electronic Engineer and very adept at searching our design files, accessing the engineers who created the PCB, and getting back to our customers in a timely manner. He stays focused on what he's doing, making sure all of his time is for our customers and not getting distracted by his cell phone going off all day. He's asked to support a lot of products, tools, programming languages and situations.

Not "just a kid, trying to make a buck" and probably provided you with the best answer he could. Stick with him; he's an excellent source.

Ken Gracey

idbruce

Ken

Hmmmmm....

First reply:

The Product Datasheet has it at a max of 3 amps @16V max.
https://www.parallax.com/sites/default/files/downloads/32810-Propeller-Project-Board-USB-Guide-v3.1.pdf - This product's specifications and related documentation can be found in the Downloads and Documentation section of the Product page.

Second reply:

Yes It's possible. Unfortunately we do not any current testing or rating data for the 8 pin bridge itself. The 8 pin bridge is an output for the LDO which in the schematic its showing a 5V LDO with 1.5A of output current capability. The input voltage for the LDO is coming from Vin which the datasheet states to be no more that 16V and 3 Amps max. I'm concluding that the current the vias/pins can handle is going to be anywhere from 0 to 3 amps. The engineers that created this product are no longer at Parallax and I can't find any documentation that addresses this topic directly.

After the second reply, I respond:

Okay Miguel

Perhaps I am asking you the wrong questions. Could you please tell me the "width" and the "thickness" for the copper trace that makes up the 8 pin bridge?

Third reply:

Here is the width of the trace. The units are in inches. Working on the thickness information.

jmg

idbruce wrote: »

How much amperage can the 8-pin Bridge handle?

'handle' is in itself a pretty vague question, and there are going to be system budgets that matter more.

Some have mentioned the rating limit on the regulator, is less than the bridge, so that already points to a better question...

Even trace current limits are not 'handle' limits, but based on suggested temperature increase. Others might consider 'handle' to be a fusing limit.
Overall, your limits are more likely to be thermal, than any single rating line, but the regulator seems to be the lowest boiler plate number.

In less time than it took to compose all your questions, and your posts about them here, you could have more quickly actually tested this on the bench ?

idbruce

In less time than it took to compose all your questions, and your posts about them here, you could have more quickly actually tested this on the bench ?

In no shape or form did I ever want this thread to become a lengthy discussion. I simply did not want to burn traces off my board which has hours and hours of work put into it.

Buck Rogers

@IDBruce and @"Ken Gracey" I am suitably impressed by all of the discussion here.

I originally bought one from Micro Center back when they were ignoring Parallax items. And I'm still looking for that zebra that my first Prop project would work on it.

Ken Gracey

Bruce, put the board to the test and feel free to burn it up. I'll replace it for you for no charge. Let's see what kind of current it can handle for different periods of time.

Ken Gracey

frank freedman

Maybe find out the copper specifications of the blank PCB from Parallax engineering. Googling for trace thickness gives the following from Sunstone Circuits: https://sunstone.com/pcb-manufacturing-capabilities/detailed-capabilities/copper-weights which gives the thickness of the copper which should be the trace thickness you are looking for after etching. There are many results and nearly all are close to 1.4 mil depening on who rounds up their unit conversion. For 1oz, 35um seems to be consistent answer. Then calculate the current capacity as WBA recommends. If you need more current than your calculations determine, you could always green wire it until you are ready to cut your own custom board.

Found this as well:
https://4pcb.com/trace-width-calculator.html

VonSzarvas

To add more support about the thickness question....

That PCB will have been made with minimum 1oz copper, and based on some of the trace/pad geometry we can see on that board, it seems 99% likely to be no more than 1oz.

Thus, I'd also recommend you'd be best to calculate with that thickness. As WBA, Frank and others have noted.

Use 1oz (or 1.37 mils, or 35 um; whatever units your trace-width-calculator expects), and calculate the maximum current for a 25 mil trace.


I think you got all this by now, but I hope this summary also helps you feel more certain about your experiments.


What current did you want to source from those pins anyway ? More than 1A total ?
If less, than you seem to be good as your are already!

Aside from that...
I think you will find the LDO getting rather hot as you draw closer to it's maximum rating, and it may have it's own thermal shutdown protection.
If you do want to draw 1A (or even up to 1.5A) from the LDO, you will need to get your VIN down as low as possible so the LDO is not creating unnecessary heat from a big voltage drop.

Do you have the part number of the LDO? I wonder what the minimum input voltage is, that you can run the LDO at for whatever current you need. LDO datasheet should have a graph of Vdropout vs current.

idbruce

@VonSzarvas

Based upon the 25mil width, I have already ordered fans that will put me well below the current limit of that trace.

EDIT: However, I would have liked to get the most CFM that allowable amperage could have provided.

Thanks everyone. I now suggest closing this thread.