Hello All.
I have been tinkering with this idea for a while, it’s proven to be a good distraction from my E-Gocart project when I needed to step away.
I figured it was about time I posted the project to get some feedback.
Specs/features i'm shooting for. (Dec 29 2017, Several new changes including Isolation and external DAC's)
300W continuous. ( I have tested with 5FETs and a smaller heatsink so it will be easy to do)
Reverse Polarity Protection.
Fully isolated input. This is to mitigate noise issues caused by the Teensy writing to the Screen. It also adds more flexibility to the end user.
20A continuous. (Max 25.5A for my schematic)
External 16/18 bit ADC for Voltage and current measurements.
14/16bit external DAC's. Allowing for sub mA adjustments.
81.96V in max. Resolution = 1.25mV@16Bit and 312.5uV@18Bit
CC/CV/CP and discharge modes for batteries and standard power supplies.
Using an ILI9341 touch screen, 320 x 240 resolution. May use the newer screen Paul mentions here, if it gains traction before I create my first board.
Standard 92mm PWM PC Fan
(2) Rotory Encoders with push bottons(set V and A, select size of range increase/decrease)
(2) Push buttons (Menu, Start/Stop)
3.5 - 28V input power, with monitoring.
New schematic pending
Schematic Oct 8 2017
Schematic Oct 1 2017 and PCB Render
Schematic June 24 2017
Schematic Newest
Schematic New
Schematic Old
Schematic Older
Schematic Oldest
Schematic Older then Dirt
WIP BOM Old
Heatsink/Shroud/Fan mockup (somewhat old)
Cad rending of PCB+Fets+Heatsink+WIP Housing
Updated 5-21-17
Below removed from schematic in favor of using just a standard 4 wire PC fan, circuit should conform to the Specifications of PWM PC Fans.
See below schematic for old fan control scheme's
I am looking at a different setup to drive the fan that would be more efficient at slow speed(300mW savings when at low speed) but it would potentially introduce a lot of noise to the +5V rail.
The below setup will allow the fan to be powered with ~5V when powered up, then once things start getting hot the fan can be PWMed up to 12V, this would ensure there is always enough voltage going to the fan to power the internal hall effect sensor. The 1R resistor and 1u Cap should keep the noise on the +5V rail to a tolerable level. The drawback is that not all fans can actually work at 5V, so some may not function without a kickstart. It will also add noise to both the +12 and +5V rails.
A few answers to questions im sure will pop up.
Updated 11-4
Q. Why are you using a -5V supply?
A. In order to fully turn the FET’s off you really need to push them below 0V. Some OpAmps can push the output close to rail input but most are off enough that the FET’s will never turn fully off.
Q. Why such large sense resistors you could go with much lower values for SMD and maybe just stick them on the bottom?
A. I actually looked at using really low values and sticking them on the bottom of the board, even planned to cool them with a custom made 3D printed heat shroud vent if needed… But the really low resistance would mean really low voltage feedback values. Add to that noise and readings could end up as crap.
Updated 6-22 Q. You have 5 NTC thermistors! Just stick one or 2 on the heatsink and call it a day.
A. It may be more expensive to have 5 instead of 2, but if one of the FET’s gets angry it would be much better to stop before the magic smoke comes out. Preventing a failure is a good thing; it also allows me to dynamically set power limiting based on hottest FET temp. If they are cool you can overdrive it, once they heat up power limiting kicks in. I did an earlier test with 5 FET’s running 300W on a 100x69x36mm Heatsink and the hottest one got to 80C case temp. When I ran out of room on my 100x100mm PCB and went to 150mmx100mm I also increased the Heatsink size to 150x69x36mm, which will give more overdrive room if needed.
Q. Why use LM324’s, they are not super accurate?
A. Correct they aren’t super accurate, but with software control we can calibrate some of the inaccuracy out. I mean we have to deal with 1% resistors… A lot of the chips I looked at claim much better Input Bias values but have max values just as bad as the 324’s
If need be, a better chip can be installed, most manufacturers where smart enough to use the same packages/pinouts.
Update...
Things I need to do at this time.
1. [Fixed in October]The 0805 Footprints that come stock in Kicad for hand soldering are pretty big compared to the Footprints I use in eagle, so I will trim those.
2. I need to go over all the diodes and make sure they are correctly sized, the one leading to the Teensy seems a little big lol.
3. [Fixed in October, now using T3.6] Keep an eye on the Teensy 3++ beta and see if I should incorporate extra features from it. Im using mostly 3.3V anyway and the few place im not could easily get a zener.
I have been tinkering with this idea for a while, it’s proven to be a good distraction from my E-Gocart project when I needed to step away.
I figured it was about time I posted the project to get some feedback.
Specs/features i'm shooting for. (Dec 29 2017, Several new changes including Isolation and external DAC's)
300W continuous. ( I have tested with 5FETs and a smaller heatsink so it will be easy to do)
Reverse Polarity Protection.
Fully isolated input. This is to mitigate noise issues caused by the Teensy writing to the Screen. It also adds more flexibility to the end user.
20A continuous. (Max 25.5A for my schematic)
External 16/18 bit ADC for Voltage and current measurements.
14/16bit external DAC's. Allowing for sub mA adjustments.
81.96V in max. Resolution = 1.25mV@16Bit and 312.5uV@18Bit
CC/CV/CP and discharge modes for batteries and standard power supplies.
Using an ILI9341 touch screen, 320 x 240 resolution. May use the newer screen Paul mentions here, if it gains traction before I create my first board.
Standard 92mm PWM PC Fan
(2) Rotory Encoders with push bottons(set V and A, select size of range increase/decrease)
(2) Push buttons (Menu, Start/Stop)
3.5 - 28V input power, with monitoring.
New schematic pending
Schematic Oct 8 2017
Schematic Oct 1 2017 and PCB Render
Schematic June 24 2017
Schematic Newest
Schematic New
Schematic Old
Schematic Older
Schematic Oldest
Schematic Older then Dirt
WIP BOM Old
Heatsink/Shroud/Fan mockup (somewhat old)
Cad rending of PCB+Fets+Heatsink+WIP Housing
Updated 5-21-17
Below removed from schematic in favor of using just a standard 4 wire PC fan, circuit should conform to the Specifications of PWM PC Fans.
See below schematic for old fan control scheme's
I am looking at a different setup to drive the fan that would be more efficient at slow speed(300mW savings when at low speed) but it would potentially introduce a lot of noise to the +5V rail.
The below setup will allow the fan to be powered with ~5V when powered up, then once things start getting hot the fan can be PWMed up to 12V, this would ensure there is always enough voltage going to the fan to power the internal hall effect sensor. The 1R resistor and 1u Cap should keep the noise on the +5V rail to a tolerable level. The drawback is that not all fans can actually work at 5V, so some may not function without a kickstart. It will also add noise to both the +12 and +5V rails.
A few answers to questions im sure will pop up.
Updated 11-4
Q. Why are you using a -5V supply?
A. In order to fully turn the FET’s off you really need to push them below 0V. Some OpAmps can push the output close to rail input but most are off enough that the FET’s will never turn fully off.
Q. Why such large sense resistors you could go with much lower values for SMD and maybe just stick them on the bottom?
A. I actually looked at using really low values and sticking them on the bottom of the board, even planned to cool them with a custom made 3D printed heat shroud vent if needed… But the really low resistance would mean really low voltage feedback values. Add to that noise and readings could end up as crap.
Updated 6-22 Q. You have 5 NTC thermistors! Just stick one or 2 on the heatsink and call it a day.
A. It may be more expensive to have 5 instead of 2, but if one of the FET’s gets angry it would be much better to stop before the magic smoke comes out. Preventing a failure is a good thing; it also allows me to dynamically set power limiting based on hottest FET temp. If they are cool you can overdrive it, once they heat up power limiting kicks in. I did an earlier test with 5 FET’s running 300W on a 100x69x36mm Heatsink and the hottest one got to 80C case temp. When I ran out of room on my 100x100mm PCB and went to 150mmx100mm I also increased the Heatsink size to 150x69x36mm, which will give more overdrive room if needed.
Q. Why use LM324’s, they are not super accurate?
A. Correct they aren’t super accurate, but with software control we can calibrate some of the inaccuracy out. I mean we have to deal with 1% resistors… A lot of the chips I looked at claim much better Input Bias values but have max values just as bad as the 324’s
If need be, a better chip can be installed, most manufacturers where smart enough to use the same packages/pinouts.
Update...
Things I need to do at this time.
1. [Fixed in October]The 0805 Footprints that come stock in Kicad for hand soldering are pretty big compared to the Footprints I use in eagle, so I will trim those.
2. I need to go over all the diodes and make sure they are correctly sized, the one leading to the Teensy seems a little big lol.
3. [Fixed in October, now using T3.6] Keep an eye on the Teensy 3++ beta and see if I should incorporate extra features from it. Im using mostly 3.3V anyway and the few place im not could easily get a zener.
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