victor 885 parts
 

I know they arent used in first but does anyone have a victor 885 that they could pull a part number off for me if its possibly visible?
I need the part number for the fets used.(these are the parts under the fan)
Thanks so much

Re: victor 885 parts
 

Victor 885's use International Rectifier IRF3703 FETs.

Re: victor 885 parts
 

awesome, thank you so much.
Do you know if they use the same Pic micro controller?
Ive tried to find the microcontroller with some success. Just trying to replace blown parts on one. The microcontroller isnt blown but i wouldnt mind getting a backup to copy the program too.(you never know what could happen)

Re: victor 885 parts
 

I don't know which microprocessor is used in the Victors. I remember locating it on an 883 or 884, but I don't think I went so far as to figure out which model it was. The program is not in the microprocessor, but on a nearby firmware chip. If any of that blows you've got bigger problems than replacing the microprocessor.

Re: victor 885 parts
 

It seems that I remember reading a statement somewhere that the 885 is a different beast than the 884. Besides the fact that it uses the higher voltage FET.

Re: victor 885 parts
 

i didnt notice any firmware chip. The microprocessor has all the built in memory and space to store the program.I see a few voltage regulators, 12 mosfets. A Capacitor. A few small other chips(i dont have one on me right now but i didnt think i saw a firmware chip. Theres also a few little pieces like the frequency chip which i believe runs the mosfets. Altho there are tons of little resistors.

I just have like 6 victors sitting around that are blown and want to fix them. There mostly 883's but thought i may be able to replace the mosfets with higher voltage mosfets to stop them from igniting and burning out. I dont know how well it will work but i think its worth a try. Unless someone else has tried it

Thanks

Craig

Re: victor 885 parts
 

Forget what I said about the firmware chip. I was thinking of another system and confused myself.

There is more to blowing up FETs than their individual ratings. Put too powerful a FET in as a replacement and the rest of the Victor won't be able to handle it.
I agree with Al's comment that the 885's are a different beast. They handle higher power because they are designed for it with features other than "bigger" FETs.

Usually, the FETs short when metal shavings or particles fall into them. Bigger FETs might just release more magic smoke.

Re: victor 885 parts
 

FET's that are rated for higher breakdown voltage and/or for lower on-state resistance will also have higher gate capacitance. A driver circuit that is correctly sized for a lower-rated FET may not provide sufficient gate current to fully saturate a larger FET within the same switching interval; this would result in higher switching losses, so the larger FET might actually run hotter, depending on the chopping frequency. As Mark says, you should not try to soup-up a Victor by simply changing out FETs -- you have to consider the whole circuit.

[edit]666 posts![/edit]

Re: victor 885 parts
 

Not to pile on here,
As Mark has pointed out, FET death is frequently metal shavings related but all too often, teams are running inefficient designs that have extreme current demands (i.e. constant or near constant stall on a Chalupa will draw 129 amps). It is these extreme currents that raise the internal temperature that explodes the case of the FET. (Note that the FETs are not mounted to heatsinks.) Going to a higher breakdown voltage FET will do nothing for that type of failure. In general, a single FET failure is shavings related and will usually be accompanied by smoke damage near the base of the FET. A failure of six at a time is temperature related and will usually result in damage to the circuit board.

Re: victor 885 parts
 

Many competing products to Victors protect themselves from thermal destruction by having the micro onboard the Electronic Speed Controller (ESC) monitor current and/or temp flowing through the ESC.

Back when I was a rabid robot warrior, I thought that I wanted every ounce of performance from the ESC. I reasoned that I would rather replace any dead ESC between matches than loose a pushing match because the ESC was protecting itself.

I have since moderated my views. If everyone has the same constraints, it doesn't really hurt the competition to have everyone with a little less current capability in the ESC -- it's just one more constraint everyone has to live with. The main result of an ESC that protects itself would really just be lower sales of ESCs because fewer die and teams don't have to buy replacement/extra ESCs.

Bottom line, I think it is a good idea for ESC's used in FIRST to have internal thermal protection.

Joe J.

Re: victor 885 parts
 

i fully agree with the thermal protection idea. i have so many dead victors sitting around just because of over current. I wouldve much rather had the victor limit the current or cut out because of heat then had to replace them. Thermal protection should definately be considered.

I like the overall victor design. but thermal protection would be great.
I know it wouldnt work in first competitions. but i think it would be nice to have a full 2 victor system with mixing capabilitys available for r/c equipment. I like the victors much more than the double esc mixing systems out there

Re: victor 885 parts
 

The thermal rise is so fast that there is no effective way to compensate for that electronically. ( it is likely that the temperature rise is fast enough that even heatsinks would not fix the problem.) At the time that the overcurrent is taking place, the branch circuit breaker was already tripping, several times. A non resetting circuit breaker would cure the damage problem but make it impossible for you to continue to compete. It is essential for teams to measure current in motor circuits while practicing in order to insure no damage to motors or to Victors. Remember that for all intents and purposes, a stalled drive motor (Chalupa, FP, or drill) looks like a dead short to the Victor. A device that is rated at 40 amps cannot sustain a 2.5x overcurrent for very long without damage. You have proved that. P=I^2 * R, with an ON resistance of .002 ohms and assuming that each FET is sharing 1/3 of the load, you have a potential for a junction dissipation of 10 watts. That little piece of silicon can't get rid of the heat fast enough.

Re: victor 885 parts
 

I disagree. Here is a FET* that has internal thermal protection plus current feedback that could be used to implement protection running on the ESC's micro.

Joe J.

*This is just the first FET I found on the IR website as an example. It is not the right FET, but there are many like it that would be suitable for a FIRST ESC.

Re: victor 885 parts
 

Joe,
The 3113 is a very interesting device and has the possibility of some serious applications using current sense, but it is a little beyond what the Victor needs. In comparison with the IRL 3103 FET currently supplied with the 884 it can deliver 64 amps vs. 7 for the 3113. If they were able to handle the current the cost per unit is almost $2 higher than 3103 (single unit quantity) for an added cost per 884 of $24. Even though the 3113 has a pulsed peak current of 100 amps, that is under specific conditions. The internal temperature shutdown is sensed inside the package and shutsdown the circuit while it waits for the temp to cycle down. Since this is not an external control the individual units would be cycling on and off at different times dependent on internal temperature, leaving the remaining online units to share the higher load.

Re: victor 885 parts
 

Now im just going over the design of the victor. Ive got one blown one that im just playing around with trying to figure out exactly how it works. as far as i can tell its basically a microprocessor controlled h-bridge with 3 mosfets per section of the h-bridge circuit. I see a few voltage regulators that im guessing are to run the micro controller and the the gate on each mosfet.

Re: victor 885 parts
 

Cirrus,
I believe there is only one voltage regulator, the other things you see are drive transistors for the FETs. You are correct on the the H bridge design, this is very common in motor controls. If you look closely you will also see the equalizing resistors in series with each FET. These help to equalize the current each shares with the other two in it's string. There are very low resistance so measuring them with a normal DVM won't tell you if they are shorted. The values of these resistors are about the same as the resistance of the leads on the DVM.
Remember that depending on the intial failure of the FET, other devices connected to it may also have been damaged. For instance, a short from gate to drain may have attempted to draw full motor current through the drive transistor until it failed. Power supply traces on the circuit board may also have been damaged by the excessive currents. Use a bright light and a magnifying lens when checking for damage. Post pictures and questions if you have them. I love to see stuff that is blown up.

Re: victor 885 parts
 

Actually the one i was looking at last night was quite blown. Everything else on the board seemed fine except one resistor that i couldnt get a reading thru. but for the most part everything but the fets were fine i believe. I have about 4 blown fets on this one. i pulled one fet off the board already just for curiousity. out of the others that are blown i see one with just a small burn mark on the front casing but not actually blown apart. 3 that the casing split. and one more that i didnt count as burnt, altho it has to be because the gate and the drain have continuity.
The resistors that go to the fets are on the supply then? I figured they were on each gate to make sure that the gates were getting the right voltage. Well victors seem very well engineered. looking at the board (this is just theory, correct me if im wrong) you could technically solder on 3 more fets to the bottom of the board for each string for a total of 24 on board fets aslong as you put a separate resistor for each gate.(i know its not very practical but in theory it would work right?)

Thanks again

Re: victor 885 parts
 

I do too. Can't wait for these pictures.

Re: victor 885 parts
 

The resistors would normally be in the drain lead. It has been a while since I opened one up, but I seem to remember the gates and sources tied in parallel while the resistors are in series with the drain and then out to the load for the high side FETs and in the source for the low side.
Your idea about added FETs is correct, theoretically adding as many FETs as are needed to make up the current. Some factors might get in the way of success such as turn on time and source to drain "ON" resistance but for the low switching frequency of the Victor the turn on time should not be a problem. Of course the circuit traces are sized for the expected current so you might have to redesign the way power and output leads are treated.

All in all, they are pretty cool little devices for $129.

Re: victor 885 parts
 

Sorry guys that i havent got the pictures up yet.Ive been having major problems with my camera. But out of curiousity. I noticed researching h-bridges that they usually use both p and n channel mosfets. but the victors only use n channel.
Does anyone know the advantages/disadvantages of this?

Also can anyone give me a link or explain how to build all n-channel mosfets into a circuit?

Thanks Again

Craig

Re: victor 885 parts
 

P-channel devices generally cost more and operate less efficiently than N-channel devices.

To control an all N-channel bridge, the gates of the high-side devices must be driven with respect to the motor output terminals, because that's where their sources are connected. So the gate drive circuit must include a power supply that "floats" on the motor terminal. This is often implemented using a special purpose driver IC such as IR2104.

Re: victor 885 parts
 

So basically I need to look at whatever voltage is usually needed on the low side to turn on the mosfet. then take the supply voltage and increase it by this number to run the gate.

For example.
If it takes 8v to turn on the mosfet on the low side.
And my source voltage is 18v

Then i need to run the upper gates with the sum of those voltages.

Required gate voltage(top side) = supply voltage + Required gate voltage(bottom side).

And that ic that was mention is im guessing used to help create this extra voltage?

I think i got it but i may be totally wrong.

Thanks

Craig

Re: victor 885 parts
 

You've misunderstood my use of the word "source". I meant it to indicate one of the terminals of a FET, not a voltage supply. I recall being similarly confused when I first encountered that term, as a sophomore EE student about thirty years ago.

A FET has three terminals called source, gate, and drain. To turn it on [i.e., to get it to conduct with a low resistance called R_DS(on)] you apply about 10V between the gate and source terminals. Please refer to the IRL3103 datasheet, conveniently hosted by FRC 358.

So each of the gate drive circuits for high-side devices in an N-channel FET bridge must be referenced to the respective source terminal. This is accomplished by establishing charge on a capacitor by means of the special purpose IC mentioned in my earlier post.

Re: victor 885 parts
 

Many FET driver IC's need a resistor between the driver output and gate to dampen transients and ringing. This is especially important at higher switching frequencies. These maybe the small resistors you see on the board.

Re: victor 885 parts
 

Yes. Resistors for that purpose, and to limit dv/dt during switching, are indicated in the typical connection diagram at the bottom of the first page of the IR2104 datasheet, linked in my earlier post.

Re: victor 885 parts
 

http://www.chiefdelphi.com/forums/at...tid=4638&stc=1
I know this isnt a picture of the blown up parts. this picture only shows where I removed one Mosfet.
Im still having camera problems so this is a pic from a few weeks ago.
Sorry for the delay. Im workin on more pics

Re: victor 885 parts
 

This is actually a good picture showing the debris carried in by the fan. I have often found metal grit on the board at this point when opening suspect controllers. Teams are shocked by the amount of stuff once I open one of their controllers.

Re: victor 885 parts
 

Very good photo. I have suspected this condition on many occasions; as Al says it is very likely the leading cause of Victor failure.

The moral of this story is: don't make chips and metal dust around the electrical system. You may think you've cleaned it up afterwards, but that's actually somewhere between extremely difficult and totally impossible.