24Vs and victors

[greencactus3]

i was just wondering.. (note, has nothing to do with FIRST)... using the kit victors, can i use them in a 24V circuit? i know the fans wont like it, so well the easy way to get around that is connecting two fans together in series, so each only gets 12v. but will the victors take 24v? i see in robotcombat.com that they sell the victors at the same price with the only different listing of 12v fans and 24v fans. does that mean the victors itselves are identical? just the fans are different? because they list 36V and 48V victors seperately. but not 24V ones. does anyone know? thanks

[Joe Ross]

I have heard plenty of rumors (enough that I'm fairly certain it's true) that the only difference is the fans. However, you should call IFI to verify.

[sanddrag]

I believe they are different. The IFI Robotics 24V Victor 883 is said to have a max current of 60A continuous while the Innovation First 12V Victor 884 is said to have a max current of 40A continuous. They probably use different transistors.

[dez250]

like sanddrag has said it does seem the V884 is not meant for high voltage uses. If you look on www.ifirobotics.com they sell the V883, V885 and Victor HV's (High voltage up to like 48 volts) and they don't list the 884. It seems that the 884 is a "FIRST Only" part as of now and runs with "Operating Voltage 6V to 15V". if you still really want to use the FIRST Victor 884 at higher voltages contact IFI directly (info can be found on both their consumer and FIRST sites) and ask them.

[sanddrag]

Theoretically you could say that they have no limit on the amount of voltage, but as you increase the voltage, the time period for which they function decreases.

[Joe Ross]

The FIRST Victor 884s specify that they come with a 12v fan and operate from 6-15v

The IFI Victor 883s and 885s specify that the 12v fan operates from 6v-16v and the 24v fan operates from 16-30v.

This site shows what fets the different IFI and Innovation FIRST speed controllers use. http://www.enigmaindustries.com/links.htm Note that they all use different fets, with different maximum currents, however, all of them are rated for 30v.



I believe the 24v fan is bigger then the 12v fan, which makes sense as the fets will get hotter with increased voltage. So, you probably shouldn't just use the 12v fan.

[dez250]

if you follow the links in this post and go towards the bottom of each page you will find the following information for the victors, and not just the fans.

IFI Robotics V883
IFI FIRST V884
IFI Robotics V885
IFI Robotics Victor High Voltage


Operating Voltages:
V883: "Operating Voltage 6V to 30V (does not include the fan)"
V884: "Operating Voltage 6V to 15V"
V885: "Victor Operating Voltage 6V to 30V (does not include the fan)"
V-HV: "Victor Operating Voltage 12V to 42V (36HV) / 12 to 60V(48HV) (does not include the fan)"

As i said before and i will say again, check before you do anything as you dont want to ruin a victor because you didnt spend the few minuets to check with IFI to see if what you want to do will damage the product.

[Mike Betts]

Originally Posted by sanddrag

Theoretically you could say that they have no limit on the amount of voltage, but as you increase the voltage, the time period for which they function decreases.

Sand,

Saying that the voltage has "no limit" is not true... Every solid state device has a maximum voltage. This voltage is extremely well known to the manufacturer and very exact. When you pass that voltage, the voltage potential breaks down the "gate" or "emitter" and the device will fail very rapidly (usually in microseconds).

While there is a small engineering margin an end user like us can expect in a product, it is typically less than 50%.

It is possible that IFI uses the same devices inside all of their products but unlikely. The volume of this kind of a product does not lend itself to that kind of scale of economy. In general, the semiconductor price goes up quite steeply as you increase voltage or current.

Last note to the engineers-in-training out there who take a Victor apart and find 40V or 60V devices in a 12V Victor: The design must accommodate the inductive kick of our motor circuits when the device switches. This kick is not trivial...

Mike

[Al Skierkiewicz]

Originally Posted by Joe Ross

This site shows what fets the different IFI and Innovation FIRST speed controllers use. http://www.enigmaindustries.com/links.htm Note that they all use different fets, with different maximum currents, however, all of them are rated for 30v.

Joe,
Nice find on this site. It not only gives very specific info about the all the controllers available for robot builders, you can follow the links to the exact spec sheets for the FETs used in each.
Now on to answering the other pending questions.
1. 2 12 volt fans in series may or may not work depending on the fan. Brushless DC fans may get very unhappy being in series.
2. As pointed out in the above website, the FETs used on most of the IFI controllers have a breakdown voltage of 30 volts. That would make you guess that 30 volt power supply should allow safe operation but... other things to consider are the interface electronics and internal power regulators may not be able to handle voltage higher than the 6-15 volt range specified by IFI. The FET is not the limiting factor, there is so much more inside those little controllers.
3. Sanddrag, could you elaborate on the time period a little more, I am confused on that one.
4. The overall characteristics of these controllers is a function of the junction temperature (the actual temperature of the solid state material inside the case), load and other things. Having a good fan does not help a device that has a spike in junction temperature, the heat will take too long to conduct to the case and then be removed by the fan. With a fixed load, raising the voltage raises the current supplied to the load and therefore the junction temperature.
5. Safety or design margin is a figure designers calculate to prevent real world circumstances from destroying their products. Knowing the guys at IFI and how some people use their products, I would bet that these devices have a very good margin at 12 volts. At a higher voltage that margin is vastly reduced and failure of components is inevitable. Since each leg of the controller "H" bridge is actually 3 FETs in parallel, the failure of one will bring down the controller as it would provide a short circuit to the other FETs.
6. On the devices used in these controllers, a more important spec is gate to source or gate to drain breakdown which is 16 volts. Assuming the drive electronics run at 5 volts, a power supply of 24 volts would exceed this rating by four volts. When a FET fails it usually creates a short between terminals that is permanent.

[greencactus3]

thanks everyone, so basically am i right in summarizing from what is being said in this thread that the 883s and 885s can take 24v but 884s cannnot? and for the fans, i can always add another circuit for 12v individually so thats no problem.

and yes, i have emailed ifi but still waiting for their reply

[ShorterBorder]

please answer the question, whats the maximum amout of power, and victors you can have on the robot.

[Al Skierkiewicz]

Originally Posted by ShorterBorder

please answer the question, whats the maximum amout of power, and victors you can have on the robot.

You are limited to one power source and that is the ES or EX18-12 battery. Although these are rated as 18 amp hour (that's the 18 in the part number) they are capable of over 400 amps when fully charged for short periods. The number of speed controllers (Victors) are not limited specifically, but you only use one per motor and the motor quantity is limited. BTW all motors are not required to use the controllers, some can be used with Spikes. (Check the robot rule book section 5)

[Mike Hendricks]

Originally Posted by ShorterBorder

and victors you can have on the robot.

As many as your team can afford And like Al said .. one for each of the motors.

Make sure you get one or two spares, just in case. Remember, IFI electronics are exempt from the total cost of the robot.

[Andy A.]

As just a bit of 'real world' experience, I have safely used 884's with up to 16-17 volts, perhaps a little higher. I simply took the fan off to avoid any problems with it. Although the voltage was higher then spec, the current draw was very low, which may help explain why I was able to get away with this.

Your mileage may vary.

-Andy A.