Jay Summet via EV wrote:
I have been researching replacement parts for my Curtis 1231c power
board a lot tonight. All of the parts and numbers are listed at this
blog post:
https://www.summet.com/blog/2017/01/11/curtis-1231c-replacement-power-board-components/
I believe I will be able to upgrade the diodes to 600V 75A with the
DIOTEC 7506R.
Don't go by the ratings advertised on the front of a data sheet. They
are usually absolute maximums. The part would soon fail if used at these
limits.
Look *inside* the data sheet for the test conditions. For example, that
"75 amp" diode says it has a 1.35v typical voltage drop at 75 amps.
That's 75 x 1.35 = 101.25 watts of heat.
Now look at the thermal resistance from junction to case. It is 0.8
deg.C/watt. Therefore, the junction temperature rises 0.8 deg.C for
every watt of power dissipation. 0.8 x 101.25 = 81 deg.C.
You don't want a semiconductor junction temperature to exceed 100 deg.C
or its life will be very short. So the only way for the junction to be
at 100 deg.C with an 81 deg.C junction-to-case difference is for the
case to be at 19 deg.C. In other words, you'd have to *refrigerate* the
Curtis internal heatsink for the diodes to survive that current.
A few questions I have with upgrading the capacitors. Is having a higher
capacitance (330 uF instead of the stock 220uF) better (or would I just
suffer from more inrush problems)?
Capacitance does not matter. What matters is the capacitor's ESR (as low
as possible) and its voltage rating (at least 25% more than the maximum
voltage you ever expect it to see).
Electrolytic capacitors have the shortest life of any part in the
controller. As capacitors age, their ESR goes up, and their voltage
rating goes down. At some point, one or the other of these gets bad
enough, and the capacitor fails.
The third option is to just keep the stock caps which appear to be fine
and save myself 100-150$ and a lot of soldering...
Only do this if you have a way to test them to be *sure* they are still
"up to "snuff".
I'm also considering a 250 volt 110A MOSFET (IXTH110N25T) to get the
MOSFET and capacitor max voltages both up to 250.
There is also a marketing "ratings game" with MOSFET specs. You have to
read the data sheet pretty closely to see what they can really do. It's
hard to be sure what part is better just from the data sheet.
Given the Curtis design, the on-resistance of the MOSFET is important.
NOTE: I never plan on running this thing with more than my current 135
volt max battery pack, but I figure having a bit more than 65 volts of
headroom might help keep things from blowing up in the future...
Exactly!
--
Teaching children to program goes against the grain of modern education.
Just imagine the chaos if they learned to think logically, plan, create,
implement, test, and execute!
--
Lee Hart, 814 8th Ave N, Sartell MN 56377, www.sunrise-ev.com
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