The R_ds_on is usually much higher on devices with a lower power handling. Each time I have checked, it just didn't make sense to go with several "lesser" instead of a single one that could handle it all.
Also, the parallelled input capacitance usually gets larger with the current handling equivalent amount of "lesser" devices.

Ok, that's true.

The usual failure mode for MOSFETs are D-S shorted, so you'd have to fuse each drain (or source) to keep it running. But... If one blows, the rest have to share the current and if one device died by over-current allready, how long do you think the rest will last? *pop1*, *pop2*, *pop rest*

Ah, yes, and I guess I didn't say that in my post. So far in my experiments, I've found that current overload isn't what did them in, it was a voltage spike, especially from BEMF or worse, accidental disconnection of a motor or battery lead under load, that did them in. In the few times I tried multiple parallel ones, only one or two were taken out, so even if they were shorted and not fused, I could still limp home on motor power by physically cutting the blown MOSFET leads from the controller (mine were externally mounted and individually wired, so much easier to do this than in an enclosed box and soldered to the PCB).

It would not be that easy for someone else to do this, most likely.

But they will have production tolerances, so won't share current completely equally, which might set of the *pop all* in severe cases - there's for and against, the important part is to know all the possibilities and then make an educated desicion.

That is true. I can imagine a Christmas-light-string cascade of failures, and it isn't pretty. :shock:

I totally agree, and for non-critical stuff, it's fine, but I'd never second-hand the parts in the final design of a high power controller.

Well, I don't have any real choice for my own project. I simply suggest the method because some others are also financially challenged, and probably is why they are thinking of making their own controller (it's one of the reasons stated by the OP).

I have to disagree here, as mentioned before.

I guess in what experiences I had with mine, I didn't have to use as much power to drive them. Maybe I wasnt' switching them as fast as they should have been, either (but I didn't have a scope to test that at the time, just a DMM). Now I could probably go back and check, except I've reused most of the parts for various experiments for later versions and other things, and I did not document most of what I did very well.

But that said, If it works for you, I'm all fine with it

Sometimes it did, sometimes not. Perhaps for the reasons you list. At the moment I *am* just using a single giant MOSFET (NTY100N10) that can handle 123A at 100V D-S, in my modified 2QD.

I am not sure for how LONG it will work, but it is even working just driven by a 3904/3906 pair for gate drive. I had my 4-amp JFETs in there doing that at first, but the controller didn't work and I'd removed them in the process of troubleshooting, and never put them back yet. (turned out to be a cat-hair-fine solderbridge I could barely even see between gate and ground, making me feel like an idiot).

 

Helow `im looking for an electrical sheet for an pwm controller from my electrical scooter. it control a 48v motor it has 2 i.c. and 4 big transistors the problem is that the transistors are death and i cant sea wath code are them because the producer of the controller eraised ca codes from all of the pieces ?? any ideees? enybody? or how to bild a new one??? pls?


csorry about my english it bad , i`m from Romania!


Thank you very much , i aprecied your efort!!!