Kinetic/Ballistic Systems

[lutach]

Originally Posted by NovakTwo

We have never claimed that this current rating applied to the speed control, itself.

This transistor info, (that we have been posting for decades in our BL esc spec chart,) is the transistor rating taken from the technical info sheets provided by the MOSFET manufacturers.

We have never claimed it to be anything other than that. But, I will forward these comments to Bob and Adnan.

Ok, I have attached 2 datasheets that shows the 2 most powerful PolarPAK MOSFETs that I know of and the Vishay shows a 52A rating at 25°C. So lets try going with 6 FETs per phase, that's only 312A (But divide that by 2 since it's a H bridge config). Now here is the thing, if you go by the datasheet it clearly says the package is only limited to 60A, so lets go with that and multiply it by 6 and still only 360A. Now the silicon is limited to 258A, but that really doesn't mean anything if the package is only limited to 60A. Novak still uses the PolarPAK style MOSFET correct? Please have Mr. Novak and Adnan provide some input on why use such a rating if it doesn't apply to the ESC itself. At the moment, I think the Futaba brushless ESC has the most ridiculous rating of all brushless ESCs.

[NovakTwo]

The historical, ridiculous current ratings were why Adnan decided to only publish the objective transistor ratings and not make any claims about the controller itself.

[lutach]

Originally Posted by NovakTwo

The historical, ridiculous current ratings were why Adnan decided to only publish the objective transistor ratings and not make any claims about the controller itself.

Putting it like that is somewhat more ridiculous if it has nothing to do with the ESC. If you want to put a transistor rating, add the datasheet of it to the website and how the 540A rating came to be. It really doesn't make any sense by putting a number out and not explain it to a simple guy like myself.

[BrianG]

Novak, I totally understand your predicament. Many companies are, shall we say, "optimistic" in the their ratings. So, Joe Sixpack looks at two ESCs and brand A looks better on paper because it is rated 1000A. Of course, he doesn't realize that the claim is ridiculous, nor the fact that no motor will pull that kind of current on a regular basis (aside from instantaneous bursts) in a normal setup, not to mention 1000A is beyond the capabilities of just about any normal battery. As I'm sure you are aware, there are many other factors that affect current rating aside from pure FET specs: circuit design, amount of copper, wiring, heatsink area, etc.

Honestly, and no offense here, I think a certain company has the right idea when they rate their controllers as "more than you can handle". As long as the ESC can handle any motor in its class and is used properly (no s-size 6000kv motors running 2s in an 8th scale truggy), it will run fine.

Also, I'm surprised no idiot has tried pulling that 540A on a test bench to see what it would do. I'm pretty sure that would result in a melted controller and an attempted suit for false advertising. Again, I am not dogging on you, just trying to watch out for one of the few US companies.

[NovakTwo]

In the arena of car racing for which we have designed controllers, both brush and sensored brushless, I have never seen, (or read about on forums), any interest in current rating specs.

If anything, about the only spec racers have ever been particularly interested in is on resistance. I'm just speculating here, but maybe these current rating specs have been valued and emphasized more in controllers for air models or non sensored controllers. Especially a few years ago, when European/Asian esc mfgs started re-purposing their airplane controllers for surface vehicles.

Personally, I would be just as content if we deleted all these numbers in our esc spec chart. If the rated/braking current numbers were once meaningful, they no longer are. Years ago, when we began listing only the MOSFET stats, it was because our engineers could never figure out how other companies' garbage ratings were measured; so we selected this alternative method.

[BrianG]

Originally Posted by NovakTwo

In the arena of car racing for which we have designed controllers, both brush and sensored brushless, I have never seen, (or read about on forums), any interest in current rating specs.

If anything, about the only spec racers have ever been particularly interested in is on resistance. I'm just speculating here, but maybe these current rating specs have been valued and emphasized more in controllers for air models or non sensored controllers. Especially a few years ago, when European/Asian esc mfgs started re-purposing their airplane controllers for surface vehicles.

Personally, I would be just as content if we deleted all these numbers in our esc spec chart. If the rated/braking current numbers were once meaningful, they no longer are. Years ago, when we began listing only the MOSFET stats, it was because our engineers could never figure out how other companies' garbage ratings were measured; so we selected this alternative method.

Well, the majority of people probably don't care about the current spec as long as it works without overheating when geared reasonably in the vehicle it was meant. And trying to rate them to match other companies' overzealous methods is just bring you down to their level.

[nitrostarter]

Originally Posted by NovakTwo

In the arena of car racing for which we have designed controllers, both brush and sensored brushless, I have never seen, (or read about on forums), any interest in current rating specs.

If anything, about the only spec racers have ever been particularly interested in is on resistance. I'm just speculating here, but maybe these current rating specs have been valued and emphasized more in controllers for air models or non sensored controllers. Especially a few years ago, when European/Asian esc mfgs started re-purposing their airplane controllers for surface vehicles

I can agree here. I just got into the world of Sensored 1/10th scale systems. The first question I was asked was about the resistance on the controller...

[lutach]

I have an idea. I'll make some phone calls and send some e-mails. It will be good if everything I have in mind works out.

Edit: Two e-mails sent and I'll wait for a reply, but will also make 2 phone calls tomorrow.

Do Li-Fe cells really need a voltage cut off?

[JThiessen]

Not from my experience. You will notice the drop in power - its significant. When you do, its time to shut down. If you keep running them after that, then yes, you can possibly damage a cell.

[JERRY2KONE]

Originally Posted by Erevocanuck

Do Li-Fe cells really need a voltage cut off?

According to all of the info provided by manufacturers a low voltage cut off is not required for LiFe cells. Like Thiessen stated when the LiFe cells are done there is a sharp drop in power and you will know it is time to stop and recharge. From what I have seen there is no real danger with the LiFe cells, and the power provided seems to be very similar or close to the same level as the LIpo cells without worry of catostrophic failure or fire due to over heating the cells.

Seems like a good laternative choice in my opinion over the Lipo technology, but how well they actually stand up against LIpo in performance is yet to be discovered or reported. Some feedback from those who have used them would be nice so we can weigh in on comparison.

[JThiessen]

I used 2S2P A123's in my Revo prior to going Lipo. In the same truck, the performance of the A123's was good - not as good as Lipo, but still a signifcant improvment over Nimh. Just off the top of my head, I would get 15-20 minutes of run time, compared to 20-30 on my lipos. And they charge so fast - 20 minutes or so.....I'd be just rotating packs off my charger and running them. Disadvantage is size - I tried setting them up as 3S2P but they were absolutely huge.

[Unsullied_Spy]

From what I've seen, LiFe cells drop off worse than a NiMH pack. When it's done, you know it.

[snellemin]

Yup when the A123 dump, it's basically empty. As of late I've vented a couple of my A123's from pulling an overdose of amps in my crt.5. It has a funny smell, but there are no fires and whatnot. When they are overheated at around 160F, they lose some capacity. I'm sure lifecycle goes down quite a bit.

I have one 3s1p pack now in the crt.5 that overheated quite a few time. Once cell voltage is lower than the rest. But I still get 1800mah out before the pack loses its marbles. And under max throttle it still puts out 7.3V(nomadio telemetry).

I asked that question because on the novak web site it said something to that effect

Another feature that can be fine tuned via Novak’s new PC interface is the adjustable Voltage Cut-Off parameter. This feature allows drivers to select a cut-off voltage value among a predetermined range of values for 2S Li-Po and Li-Fe battery packs. This voltage cut-off flexibility can improve a vehicle’s performance, while still protecting a driver’s battery investment.

-thats what it says on the link form this thread