Since the brushless upgrade on my Voltage seems to be functional and not ripping the truck apart, I decided to open up the stock SRS ESC that it came with and see what kind of components ARRMA was using inside this little thing. I didn't take and pictures (sorry!) but it was a very simple board that was absolutely slathered in silicone coating! This thing was so encased in conformal coating that it probably doesn't even need the case to be waterproof, and that is a good thing. The only parts that weren't encased were the pin headers for the external ports, and the tops of the power MOSFETs and LDO's.
Speaking of which, I have no complaints about the main power system ARRMA included in this little ESC. There are 6 power MOSFETs for running the brushed motor: Four Alpha & Omega AOD538's for running the motor forward and two International Rectifier IRFR8314's for reverse. Those are both very respectable parts. The A&O's are 30v, 70A MOSFET's, and the IR's are 30v 179A parts. Now, those amperage ratings are theoretical maximums that no one will ever see in the real world. In reality, they can handle much less continuous current, but you are still probably looking at 30A each for the A&O's, and probably 100A-120A for the IR's. The way they are laid out, you have two AOD538's on the positive side and two on the negative side, and one IRFR8314 each on the positive and negative sides. Now, I have no clue how 'smart' the actual motor controller is, but with two MOSFETs on the positive and negative lines for forward driving it could be doing some current balancing to help spread the heat load between individual parts. It could also just be turning them all on and off at once, which would still spread out the heat load, but not as well. It does look like there is a small transistor being used as a gate drive for each of the six individual MOSFETs, but the traces were too small for my poor eyes to figure out if all six were going to their own pin on the controller, or if they were grouped together. In case you are wondering why there are two massive and awesome MOSFETs for reverse, but four less-aweseome but still very nice MOSFET's for forward drive, I can't say for sure but I do have a guess. There are two things the A&O MOSFETs do better than the IR's: They turn on and off faster, and they shed heat better. I think that second part is why they are used, and why there are twice as many. Well, that and the A&O's cost about half as much as the IR parts, so for the same price as one IRFR8314, you can use two AOD538's! So, assuming the thermal pad that connects the MOSFET's to the heatsink doesn't fail, this little guy should have zero problems meeting it's 40A rating. In fact, if it was a no-name EBay ESC, it would probably be calling its self a 60A model!
The BEC is a bit less amazing: It's just a LM2940 5v low-dropout linear regulator. Actually, there are two LM2940's on the back of the board, but I think one of those is being used as power for driving the gates of the power MOSFET's and the various control chips while the other is exclusively powering the servo/accessory ports. The chips on my ESC were made by UTC, but that doesn't matter a whole lot as a number of places make LM2940's and most of them perform about the same. This particular LDO will typically keep spitting out 5V as long as the battery is putting out around 5.5v or more. In the worst case it could need as much as 5.8v to maintain 5.0v output, but the chip would need to be blazing hot and be putting out a full 1A for that to happen. Basically, it should be perfectly happy pushing 1A at 5.0v all the way down to the low-voltage cutoff of any batteries this ESC supports. The only real downside to this little LDO is that it does start to burn around 0.1A of current at high loads and low voltage differentials. That is really more of an LDO thing in general rather than anything about the particular chip ARRMA chose, so I wouldn't say they made a bad choice. On the up-side these little LDO's are dirt cheap, and require almost no extra components to make them work. You probably could kill one if you added enough extra fans or LED's and consistently started pulling more than 1A, but who does that with a stock Voltage ESC!?
Overall, I was pleasantly surprised when I opened this little guy up. I wasn't expecting the MOSFET's to be nearly as capable as they are, the waterproofing was competent, and even the BEC was better than I expected given that it had a dedicated LDO for the servo rather than making it and the control electronics share one. Kudos to ARRMA for actually putting together a decent little board.
Speaking of which, I have no complaints about the main power system ARRMA included in this little ESC. There are 6 power MOSFETs for running the brushed motor: Four Alpha & Omega AOD538's for running the motor forward and two International Rectifier IRFR8314's for reverse. Those are both very respectable parts. The A&O's are 30v, 70A MOSFET's, and the IR's are 30v 179A parts. Now, those amperage ratings are theoretical maximums that no one will ever see in the real world. In reality, they can handle much less continuous current, but you are still probably looking at 30A each for the A&O's, and probably 100A-120A for the IR's. The way they are laid out, you have two AOD538's on the positive side and two on the negative side, and one IRFR8314 each on the positive and negative sides. Now, I have no clue how 'smart' the actual motor controller is, but with two MOSFETs on the positive and negative lines for forward driving it could be doing some current balancing to help spread the heat load between individual parts. It could also just be turning them all on and off at once, which would still spread out the heat load, but not as well. It does look like there is a small transistor being used as a gate drive for each of the six individual MOSFETs, but the traces were too small for my poor eyes to figure out if all six were going to their own pin on the controller, or if they were grouped together. In case you are wondering why there are two massive and awesome MOSFETs for reverse, but four less-aweseome but still very nice MOSFET's for forward drive, I can't say for sure but I do have a guess. There are two things the A&O MOSFETs do better than the IR's: They turn on and off faster, and they shed heat better. I think that second part is why they are used, and why there are twice as many. Well, that and the A&O's cost about half as much as the IR parts, so for the same price as one IRFR8314, you can use two AOD538's! So, assuming the thermal pad that connects the MOSFET's to the heatsink doesn't fail, this little guy should have zero problems meeting it's 40A rating. In fact, if it was a no-name EBay ESC, it would probably be calling its self a 60A model!
The BEC is a bit less amazing: It's just a LM2940 5v low-dropout linear regulator. Actually, there are two LM2940's on the back of the board, but I think one of those is being used as power for driving the gates of the power MOSFET's and the various control chips while the other is exclusively powering the servo/accessory ports. The chips on my ESC were made by UTC, but that doesn't matter a whole lot as a number of places make LM2940's and most of them perform about the same. This particular LDO will typically keep spitting out 5V as long as the battery is putting out around 5.5v or more. In the worst case it could need as much as 5.8v to maintain 5.0v output, but the chip would need to be blazing hot and be putting out a full 1A for that to happen. Basically, it should be perfectly happy pushing 1A at 5.0v all the way down to the low-voltage cutoff of any batteries this ESC supports. The only real downside to this little LDO is that it does start to burn around 0.1A of current at high loads and low voltage differentials. That is really more of an LDO thing in general rather than anything about the particular chip ARRMA chose, so I wouldn't say they made a bad choice. On the up-side these little LDO's are dirt cheap, and require almost no extra components to make them work. You probably could kill one if you added enough extra fans or LED's and consistently started pulling more than 1A, but who does that with a stock Voltage ESC!?
Overall, I was pleasantly surprised when I opened this little guy up. I wasn't expecting the MOSFET's to be nearly as capable as they are, the waterproofing was competent, and even the BEC was better than I expected given that it had a dedicated LDO for the servo rather than making it and the control electronics share one. Kudos to ARRMA for actually putting together a decent little board.
