I've used it for all my commercial stuff for years now (several dozen boards). While it was...umm...interesting, to learn IMO it's a great package for the price. I haven't found any other that gives you that much for the dollar without being just as tough to master.Alan B wrote:Eagle is common but a painful program to learn and use and expensive to do anything commercial with, so I keep looking for other choices.
Alan B wrote:Comparing prices, diptrace is cheaper than eagle for similar capability, though comparisons are not exact.
darkshirikens wrote:You know lately ive been thinking of building a single cell and pack charger for myself and i really didn't know where to really start with the single cell I've read around though i seen things about resistors but which one i don't know , but for the whole pack i was just going to use the light bulb trick to drain the pack. im not electronically inclined and reading parts in this thread gave me a slight headache trying to figure out what i could use for what i need so i need help mainly with the single cell discharger or pack or something that can work for both and what im looking for is like .5c through 5c on a headway pack with 12ah cells.
magudaman wrote:The final specs of a single board:
So if I was to do the process again I would go try to go with a TO-247 package FET so I could use less total devices. The other thing that would greatly simplify the process is getting away from a separate current sense shunt. I should have no problem using a wire based sense resistor though I would give up some resolution. I want to start messing around with surface mount stuff so I don’t have drill the boards but I think silk screens become much more important.
So got all the boards interconnected and have been doing some full discharge test with only one fan. I emptied my A123 to zero volts on accident I pushed that little 12v pack to 140 amps or around 1200 or 1300 watts intermittently. I then did my big headway packs both about 450wh at 50v 20 amps. Everything worked absolutely beautifully. The sink was keeping nice a cool at around 44C to 52C (17C ambient) with the fets at around 60C on the one side and 82c on the other (fan was blowing on one end). With two fans blowing I'll get more balanced air and I'm sure warmer weather shouldn't be a problem even at 1200W. Holds the current perfectly too.
gotta hurry off to work, hopefully I can read over this tonight and figure out what I missed and doesn't make any sense
kfong wrote:Nice work Magudaman, is the based off the national dummy load circuit? Or the CBA. I think I might build one.
That's great news, congratulations!!!
Be careful when using copper wire as a current sense resistor (if I understood you correctly). Their resistance changes MUCH more as they heat up vs. a current sense resistor. Up to 40-50 times more. That will cause your current to drift a lot as the wire heats up.
If the hot-end FETs are about 82C on the outside, they're "case" temperature (measured in the middle of the plate touching the heat sink) is probably about 90C. Are you still using the AOT410L? If so, with a junction-to-case resistance of (worst case) 0.45C/W, the FET junctions are operating at 90C + (110W*0.45C/W) = 140C if at a 110W power level. That's a great temperature to use as the maximum for long-term reliability (80% of the 175C max).
If you can get all the FETs down to 62C (assume 70C "case" temp), that brings your junction temp down to 70C + (110W*0.45C/W) = 120C....very nice.
Assuming 120C junction, and assuming that you're operating each FET at 110W, you have a system thermal resistance of...
120C - 25C ambient = 95C temp rise
110W/FET x 10 FETs = 1100W total
95C / 1100W = 0.0864C/W system thermal resistance
Those FETs have a 175C max temp rating. That's a 150C allowable temp rise at 25C room temp. For max power, 150C / 0.0864 = 1,736W (if you can get all FETs down to 62C in your above described test).
For high reliability, i.e., not operating at max temp, the allowable temp rise = 140C (80% of 175C) - 25C ambient = 115C. For high-rel power, 115C / 0.0864 = 1,330W.
I would expect that you could start discharges at up to 2,000W without problems as long as the power level dropped (as the pack discharged) to below 1700W in, perhaps, 15 seconds or so.
Gregory wrote:Hi Magudaman, great work on this discharger. Good write up too.
How's the software side coming together?
And do you have any thoughts on your plans for this - selling a kit? Open source? Retail?
magudaman wrote:So, I blew up my CBA recently and have found it to be rather undersized for sometime now so I figured it was time to build my own serious discharger.
reagle wrote:I may be a bit late to chime in here, but Dave Jones over at EEVBLOG had a nice tutorial on making constant current loads:
http://www.eevblog.com/2010/08/01/eevbl ... y-testing/
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