cheasy controller upgrade.

I have one of the cheap 24v 15a scooter controllers, I believe it is a single FET as the power wires only go to the one FET on the side. is it possible to find a FET with a similar gate capacitance and voltage and up the shunt to get some more amps out of it?
this is the current FET: http://search.digikey.com/scripts/DkSearch/dksus.dll?WT.z_header=search_go&lang=en&site=us&keywords=fqp70n08&x=13&y=13 i dont think I can drop in a 4110 because its capacitance is about 10x of the current FET and i dont need a 100v fet for 24v. if anybody has any recommendations i would love to hear them, not too knowledgeable about the whole controller thing.

It may not even have a shunt--it may use the voltage drop across the RDSon of the FET to monitor current.

As for the FET, I'd recommend doing something like I did with an old dead ScootNGo controller back a couple years ago for my DayGlo Avenger's friction drive. I just replaced the fried gate transistors and FETs with external ones, on a separate heatsink. I had to do that, as I used much larger FETs than would have fit on the PCB, plus the PCB was burned. I used NTY100N10 FETs, and I'm sure they were way more gate capacitance than the originals, but I also replaced the gate driver transistors with some 4A JFETs I happened to have laying around.

Of course, before I reached that solution I blew up a lot of FETs that couldn't handle the current and/or voltage spikes from switching/etc. :lol:

Some basic info here:
http://www.endless-sphere.com/forums/viewtopic.php?p=231004#p231004
and more details over on my blog in various posts about the friction drive.


I would bet that you could put just about any FET you want to in there, and it would work fine, with the recommendation that you also replace the gate transistor if you find it doesn't have the current drive ability you might need.

I'd chuck an IRLB3034 in there. Pretty similar gate charge, TO220 package, 1.4 mohm Rdson (vs 17 mohm Rdson for the original FET), 195A package limit (343A silicon limit) and 40V max. I use these in my low voltage boat motor controllers and they handle masses of current without even getting luke warm. Only downside is that they aren't that cheap, but if you only need one then it's not so much of a problem.

Jeremy

amberwolf said:

It may not even have a shunt--it may use the voltage drop across the RDSon of the FET to monitor current.

Click to expand...

It actually does have a very small shunt, its probably about the size of a jumbo paperclip and veeery cooked-looking.

i have a 100w controller that i had laying around as a spare controller after i blew my 250w controllers(the 250w controllers were potted so i didnt bother) the small 100w controller that i have isnt potted, so i started modding it, like beefing up traces since i was running a 250w motor and put a better heatsink on it. after i took it out real quick and it wasnt up to par with the other controller, so i wound some copper on the shunt and soldered it up, and i changed out the FET, from a irfz46 to a irf1010e i had salvaged from the blown controllers. i took it out and i went about 0.5 miles until it blew.

so i ripped it back open and replaced the fried FET and added a capacitor and undid the shunt. now im looking for a bigger controller like the 250w i had before(i have a brushed currie 250w chain-drive setup)

so far, what i learned from doing this is, you can polish a turd, but it still is one at the end of the day. maybe because i did it wrong also, i did start really small and try to pull massive power from it. i guess you can get better success if you start bigger.

Jeremy Harris said:

I'd chuck an IRLB3034 in there.

Click to expand...

One of my favorites... I'm putting a IRLB3036 in my LED controller...

The scooter is being built as a super-enduro range scooter. it will have a 6s6p lipo pack for a total of 30 ahr at 24ish volts and the motor is getting drilled and a vent fan is going to be added for some forced-air cooling. i don't want to push any more power, just less controller heat. ok maybe a little

Got the new fet installed, and added a small piece of 16ga copper wire to 1/2 of the shunt, as well as beefing up the traces with a lil more 16ga solid wire and some solder. I wasn't able to find an irlb3034... so i ended up picking out a STP190N55LF3., heres a link: http://parts.digikey.com/1/parts/1668073-mosfet-n-ch-55v-120a-220-stp190n55lf3.html Hopefully i will have it running when the batteries show up tomorrow . but i may try it tonight with the 3 year old stock lead batts and see how much I can make them cry .