Topic: Hacking a BFL Single/25 to 48gh and beyond..... - page 4. (Read 8353 times)

Hm. Does boosting the voltage boost the temps of the FETs on the jalapeno? I wonder because it's usually amps that cause the heat, and if you drive the chips at a higher voltage then the amps should go down or stay the same (maybe). I could see the chip temps going up more, but do the FETs?

I think if I tried this on my 8 chip jalapeno it would catch fire.

Gonna watch this closely.  I have a single that pulls 62Gh at about 64C.  Thinking about replacing the feedback resistor like I did in my jalas to put

about 1.1V into the ASICs.  Wondering if the mosfets can take this though. With the jalas is was a marked improvement with every one. +1Gh and

lower errors but higher temps due to higher clocks.  They only have 2/3 chips.  Do not really want to try this with the already strained DC-DC stage

in the single.

BTW, thanks Lightfoot, for all your effort and information.

And... I took apart the box again and took a look at the existing FETs. Good thing I did because this board has some differences.

First, the driver is not an 1850; it's an ADP 1877. Looks to be a higher power version, which is good since those are taxed. Likewise the FETs are IRFH 5250's and what appear to be 16404's from TI. Both heavier duty components than the little singles.

I also verified that the chokes are the gateways between the power supplies and the 1 volt main lines. So I'm going to order six of each type of FET, and a controller chip. I'll get the 4.7uf electrolytics from my dead jally, and will get the 470uf ones as well, although I think this board has plenty of them.

Then I will try adding 4 chips and see what happens. It's going to be slower going; I have to map out the chips by adding them one at a time and then testing, which requires a lot of heat sinking. Maybe I'll get myself a good temporary sink to run for a few minutes for testing each chip. Once I have 4 I can put on an AL heat sink or something like that.

TO be honest I was temped to toss a chip on there and see what happens. But at the same time I knew I couldn't sink it, so I will wait...

In the meantime, what is the part number for the PCI-e sockets and the fan sockets on this board? I'm probably going to need another fan, and more power input on the 12 volt side rather soon. :-)

Found the other one at Digikey. Not quite sure why they did two totally different models, but I'll give it a go and wait a few days for the chips. I do have the ones from this trashed jally unit here, but since the power supplied blew up I have no idea what kind of shape it is in. Then again I could test them with a 2 volt power supply and a light bulb circuit like I do with my IGBTs; hook it up with the light bulb between source and drain, (a LED would be safer actually) then touch source to gate and the light should go on. Drain to gate should keep the light off. Or maybe you don't need to do that with FETs; with IGBTs the residual charge on the gate is enough to keep it on.

C

Thoughts after looking at the Jalapeno schematics:

I'm guessing the Single schematics are quite similar to the jalapeno, at least in theory. And according to those schematics, it looks like the 1 volt power supply is screaminigly simple: You have a bank of six FETs being gated by a FET driver that picks it's feedback up from resistors and capacitors on the board. All the big caps, and other things are nothing more than filter units, to keep the ripple to a reasonable level.

Which is interesting. The two coils operate one to a set of six FETs; the big capacitors that are flat filter the 1 volt line, and the big capacitors that are round filter the 12 volt line. The chokes are the final stage of the output; I'm guessing they absorb any transients on the line as a result of the switching.

So in theory I should be able to build a quick and dirty 1 volt supply that is isolated from the board by simply putting on the FET driver chip (the 1850), two FETs (one push, one pull), and get a rather noisy 1 volt supply. I still need a filter cap, and if I put the coil on it will hook into the main 1 volt power bus but then I would not be able to measure it in isolation, so I might need to hot wire in a capacitor on the FET side of the coil. Then if I see 1 volt on that side I know the rest of the parts are there. If not, then I'm kind of boned for awhile as not all the supporting tech is in place.

I'll give it a shot. One set of FETs, and a second 1850. Question: Do the FETs have to be different types? One I was able to find at ease at Mouser, the other one was more difficult and I may have the wrong part.

C

First thoughts:

The Single I got was pretty stock. From what I have noticed, the first generation singles had a nasty habit of blowing up the FET drivers. A number of people have posted pictures of the results and they are not pretty. Which is not good. However the reason for this I think is not enough heat sinking on the chips. So when I flashed my unit to stock 1.2.9 software I made sure to include the following heat sinks on the bottom of the board:



Putting these sinks on gives some bottom cooling to the FET chips which I think will help the life.

Next up is to think about how to boost this unit. The normal way to do it is to add chips, and if your board is like this then you can do it pretty easily:



Note how this board has 8 chips to the left, and a full complement of components on the right. All you need to do (I think) is put chips on, as the 1 volt supply line is ready to go.

However if you're like me your board is more like this:



It is going to be a bit more of a problem.

Note how some components are missing. Especially the big capacitors, the smaller surface mount caps, and of course the FETs. And the FET driver. However the supporting small chips all appear to be there, so if we could mount the other stuff we would be in business. Equally important, the solder is there for the components, so it might be fairly non-impossible to add them. Some of the parts are kind of unique, but oddly enough I have a blown up jally sitting here.....

More to follow as I start working on this. You might be able to add a single chip on the right side, but that will probably stress the FETs out beyond their capacity (ie: They go boom). Edit: You can't. The 1 volt supplies on a single board are isolated from each other; the one on the right runs the right chips and so forth. Therefore there is no 1 volt power unless you were to jumper the pads which would be beyond stupid. :-)

More in a bit.

C

Reserved for thoughts and notes.

First thought: The Single board has some more beefy components than the older little_single. I wonder if early singles had the same components and they did an upgrade. I think they did; these FET drivers seem to be much more robust than the ones on the jalapenos. With two full sets of FETs it is almost overkill.

Also cooling is an interesting thing. I don't believe in running the singles open; what I have been doing is putting a speed limiting resostor on the output fan, adding a Noctua 120mm fan on the intake, and right now I'm running two fans on the heat sinks inside. One is blowing air down, the other up.

My thinking is that this take air from the outside, runs it down and to the left over the first sink and the FETs, then continues to run the air up through the second heat sink over the second set of FETs, then out of the unit. Nice wave form, which in my mind is better than sucking air down for the first one, then trying to suck what air is left again down for the second one. Reducing airflow is bad. The result is a nice 73c board temp and warm air coming out the end of it without a whole lot of noise.

I'm currently at 5 chips, might go to a max of six or seven chips because I have a pair that need reballing. 7 is about the limit anyway, going to 8 is a whole nother ballgame on the jallies, so why stress this unit for 4 more gh?

Edit: Went to six chips, 49gh speed, temps of 73c. That's about as far as I need to go; to get to 55-56gh is not really worth it since I have another single to boost, and power/cooling issues tend to snowball at 7-8 chips per side. Overall though a complete success.

C

Ok, I've pretty much taken the Jalapenos to their max limit (32gh, with 6 added chips and a lot of cooling) so now it's time to take on the singles. Much bigger board, has possibilities, but also has some interesting limitations.

My goal is to bring a 25gh single up a bit power-wise, maybe to 48-50gh or so. The unit I will be working with here is a standard single/25 which was bought by me running at 23.5gh tops. Which was a bit slow. In checking it out I found the chips ran slow, and one of the chips was missing from BFGMiner's point of view.

Update: Added two sets of FETs, driver, capacitors, and 5 chips. Hashing very nicely at 48gh and temps of 72c with a speed reducing resistor on the output fan.

If you're curious about the other things I do, check out my jalapeno thread at:

https://bitcointalk.org/index.php?topic=336782.0;topicseen

Here we go....