STP 75NF20 false alarm. it has 28mohm Rdson

J

John in CR

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Edit- ignore thread. I missed a significant digit and the Rdson is actually 28mohm.

I was poking around trying to find 200V controllers and ran across the STP 75NF20, a 200V 2.8mohm mosfet. I took it a step further and made a price inquiry, and the first response came back at $1.15/ea for just 100. Is there something in the datasheet that I'm missing that make it inappropriate? http://alltransistors.com/pdfview.php?doc=stb75nf20_stp75nf20_stw75nf20.pdf&dire=_st

Now the million dollar question. I realize you guys want the best regardless of cost, but my motors run nice and quiet at much greater efficiency than common motors using trap wave controllers, so economy and durability are at the top of my list. I'm tired of waiting on low priced sine wave controllers. I'm guessing these 75NF20's could be a drop in replacement for 4115's, but with no other changes aren't we still looking at a 32s pack voltage. I'd really like to get to the nice round number of 40s, so just under 170V fresh off the charger or during early regen. Would simply populating a controller board with higher voltage caps and whatever else get me there with these 200V fets, or does a voltage that high present other problems (traces too close together or whatever) that would require an overhaul of the board?

John
 
When I previously asked about replacing FETs in a controller I was advised to compare Rdson and gate charge (Qg?). For the latter, the less it is the faster the switching time (good) but greater the voltage spikes (bad). If it's much greater than the original FETs then the gate drive circuit in the controller may not be up to the job.

The trusty IRF 3077, 4110 and 4115 are getting on a bit and it does seem there are newer and better devices out there.

Can't really advise on track spacing, but I think you'd be all right if the design was originally for ~100V. Mains-powered low voltage adapters have minimum spacings between high and low voltage tracks/components to meet safety standards, but that's to prevent electrocution.

The only potential issue I can think of is with fixed voltages on the board (5V) to power the signal side of things. If a dropping resistor is used to obtain it you may have to replace it with a different value. If a voltage regulator is used you may need one with a higher input voltage rating.
 
Interesting. I recently received a foc from a supplier. I asked my supplier why the FETs weren't 41xx.
They thought I was a bit daft.
Suspect they were right.
 
Buy them and test them :D :D
 
Punx0r said:
When I previously asked about replacing FETs in a controller I was advised to compare Rdson and gate charge (Qg?). For the latter, the less it is the faster the switching time (good) but greater the voltage spikes (bad). If it's much greater than the original FETs then the gate drive circuit in the controller may not be up to the job.

The trusty IRF 3077, 4110 and 4115 are getting on a bit and it does seem there are newer and better devices out there.

Can't really advise on track spacing, but I think you'd be all right if the design was originally for ~100V. Mains-powered low voltage adapters have minimum spacings between high and low voltage tracks/components to meet safety standards, but that's to prevent electrocution.

The only potential issue I can think of is with fixed voltages on the board (5V) to power the signal side of things. If a dropping resistor is used to obtain it you may have to replace it with a different value. If a voltage regulator is used you may need one with a higher input voltage rating.
Click to expand...

I agree with everything but putting "trusty" and 4115 in the same sentence. Yes I have some reliable 4115 controllers, but Zombiess tested and matched the 4115's that went in them. The darn things run a lot warmer than I like, so the far lower Rdson of this mosfet has major appeal. I expect that 24fet controllers with these 75A 75NF20's will be able to handle the same current in real world use as the 100A 4115's due to a much lower thermal derating, and run cooler doing it. Plus they can't get anywhere near a 40s pack voltage. 40s is really where I need to be with either of my Monster motors in mid-drives to dial in incredible efficiency at high power. While the motors could be wound to a higher Kv for the same result at lower voltage, the lower inductance will make them harder motors to drive. Plus I'm set up well for 20s, so 40s is simple.

I'm going to talk to the controller factory about trying some in their 120V controllers, and if that proves successful, I shouldn't have too much trouble pushing for the 150V controllers I really want. Since the motors require 2 controllers, all I need is 120A/160A battery/phase current limits per controller at 40s compared to the 125A/190A I've been running with 4115's, so unless there's some critical spec I don't understand it should work.
 
Oh shlt! Sorry I wasted everyone's time. :oops:

Thanks for catching it Dr Kraut

mods, please just delete the whole thread.
 
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