6 Schottky Diodes, why!?

[Jason Potter]

Just reading a mag and it shows Neil Cragg running 6 diodes.

Why would you do this?
from what I remember each diode drops 0.07 of a volt so that would be close on half a volt loss??

[Remo]

Diodes drops around 0.7V when conducting (forward biased)... but when use in motors they are reverse biased they practically dont conduct (ok a very minute teeny weeny bit of current...) but they wont drop volts for the motor as they are wired in parallel. I cant see why one would need to use several unless one worries one may fail... Frankly crap motor wiring does loads worse.

[Doomanic]

I expect it is a picture taken early in the development cycle of the GT7.
Before Novak revised it by adding an external schottky to the wiring harness it was prone to going pop if loads of external diodes weren't fitted.

[marcoski]

Its an effort to make one big diode out of several, with one fundamental flaw!!! Not all diodes start conducting at exactly the same voltage (0.4 for schottlys, thats why we use them) so the one that conducts first will take most of the current, leaving the other five fairly redundant. You can buy 30A and indeed 60A shcottkys off the shelf as a single diode, if you feel the need! Novak should have drawn on the experience gained with their cyclone, which had a 30A schottky built in!

[PDW]

Agree with Doom on the provenance of the photo. Quite a few Novak drivers did this early last year when the GT7 was released, but few have that number now - Novak seem to be on top of the problem. I wouldn't bother copying this modification, it is probably way out of date.

[super__dan]

I have one of the first update GT7's, with extrenal diode pack. I have had no problems at all with the speedo running as novak suggest, and so with no additional diodes on the motor.

Dan

[colin_jackson]

hi just add a little in,

i was sponsered by novak last year and a lot of the team exsperienced the early speedos going pop when using powerful moters. i had 5 go bang :P in the first half of the year!! not gud ay. we where told to use quite a few diodes on the speedo and most people still did so after novak places a diode between the moter wire. this could be the answer to the picture of neil craggs car.

colin ;D

[dph]

just a simple query, how do you know if you have an early model as mine as just died.

[colin_jackson]

hi dph

the really eary ones came with a casing that you could see through. they changed this after a little while to a pure orange case. the lastest speedos run with a diode that comes factory assembled between the moter wires (+ and -).

colin

[super__dan]

just a simple query, how do you know if you have an early model as mine as just died.


There was a thread about this ages ago and marcus kindly uploaded a pic of mine showing the pack, do a search and you should find it.

The diode also looks like in this pic http://www.teamnovak.com/Buy/ind_buypgs/5638.html
but comes installed with that in the wiring from factory. Looks a little bulky but works perfectly.

Dan

[NumanR]

I run a GT7 in a Schumacher Big 6, Garry does also, so when we heard about this problem the alarm bells were sounding, to there credit Novak sent me two upgrade kits for our cars all the way from the USA FOC. Great customer service I reckon.

[dph]

thanks colin, mine is in an orange case with something heatshrunk in the motor wires, assume this is the diode. mines just died but the power is getting through to the receiver, inside when i removed the small board it appears that there should be six pins but there is only five, the missing pin appears to be the input signal from the receiver, i will have to run some more tests.

[Jason Potter]

Thanks for the answers :)

I believe the picture is from last years Euros, its in Feb04 Racer.

there I was hoping it was some secret weapon to combat motor melting :)

[Terry]

Colin Said:


the really eary ones came with a casing that you could see through. they changed this after a little while to a pure orange case. the lastest speedos run with a diode that comes factory assembled between the moter wires (+ and -).


A translucent see-through case - nice idea - bad idea if you have to do mods on the pcb later... it's all then visible and not nice to look at. Best keep the case sealed and all the bodged bits hidden from view!! ;)

As Marcus says it's a shame they didn't learn from their preveious experience from the 30A internal built-in schottky on their cyclone (ahem, should have known better - experienced engineers designing ESC's know what they're doing don't they?). The external diode in the wires appears to have sorted the problem - the problem that shouldn't have happened in the first place :-

And the moral of all this for ESC designers... when you make your latest speedo as small as possible to gain all the kudos from your admiring public - make sure all the bits you leave out inside to make it small are still wired on the outside so your shiny new speedos don't go pop!!! ;D

The fact that your average racer was soooo impressed with it's mega-smallness has all gone to waste and the kudos is lost :-[

Maybe bigger was better after all??

[PDW]

Terry?, sounds like that nice Mr. Tyree Phillips is working for you now!! ;D ;D LOL!

[rc_jammer]

Hmmm, the 6 diodes were to try and stop the speedo's blowing up.

Did it work??

Well dont mention the worlds