Understanding the power PCB design

P

Phoenix

New member
Hi all,

I'm trying to better understanding of design decisions regarding the power PCB eg
( https://github.com/Starsurfer78/TeensyMower-PCBs/blob/main/Power_PCB_v109/charge_pcb.pdf )

is there any chance that someone could tell me what purpose the following components serve

Capacitor C1,
Schottky diode D4
Schottky diode D5
Schottky diodes D6-10

Also is there a reason that d4 is different to the other schottkey diodes?

Are any of these components meant to be for flyback protection, reverse polarity, motors acting as dynamos when manually turned, etc?
 
D3 and D5 are the same. They are designed to limit the flow of current in the right direction.
D1 and D4 I took it from a switching example and they are also intended as simple protection.
D6 -D10 has been added by Bernard
 
The two components that I'm most curious about is D4 and C1.

I'm not an Electrical Engineer so any assumptions of mine are probably wrong. However, my initial assumptions were that D5 serves as reverse polarity protection from the battery source.

It looks like D6-10 also are to protect against reverse polarity - I'd assume the concern is that if a motor was turned manually that it would act as a dynamo and generate electricity - which might cause reverse polarity issues.

As for C1 my guess is that the polarized capacitor combined with D6-10 might act as a filter to smooth out voltage spikes due to the inductive nature of dc motors - capacitors are often bridged across the terminals of brushed DC motors for this reason (Also see the first video below) - that might also explain why there isn't a C2 on the charging side of the circuit? Another possibility is that the capacitor might be some kind of flyback protection for Back EMF - I've seen a few designs online where a Schottky diode is connected in the reverse polarity across the motor terminals or other inductive loads to dissipate that energy ( see https://www.gammon.com.au/motors ).


 
The Switch is similar to this, but with other Components:
www.circuits-diy.com

Arduino High Voltage Driver Circuit Using IRF9540 Power MOSFET

Control current/voltage requirements are often higher than what can be handled directly. Today, we will build an Arduino high voltage driver
www.circuits-diy.com www.circuits-diy.com

Yes C1 is intended as a small filter/spike to smooth the voltage.

The Schottky diodes are intended to prevent one type of dynamo.

But my knowledge of electronics is also very limited and I relied on Samples on the internet.
 
I have another Question concerning the design/function of the PowerPCB (V. 1.09), specifically the part around Q3 and Q4:
I tried to figure it out myself and would like to know, whether my understanding is correct.

So ...
- The "Power Switch J6" is designed as Emergency switch and usually On.
- Accordingly, Battery Voltage is connected to C of Q3 ans S and G of Q4,
- however, both transistors are blocking and there is no voltage to J11/J12, consequently the Teensy (etc.) is off.
- Once Start/J9 is closed/pressed/On the Gate of Q4 is connected to GND Q4 is On, voltage on J11/J122 available, the Teensy starts.
- The teensy activates (via pinBatterySwitch) Q3 and therefore keeps the Gate of Q4 to GND and Q4 ON, even if Start/J9 is open again.
- If the Teensy wants to switch off, it deactivates pinBatterySwitch and cuts off his own power.
Is that correct?

If Yes, this process strongly depends on the power-on-speed of the Teensy, I guess.
Or to put it differently: This will not work with a Raspberry Pi (alternative to a Teensy), which needs several seconds to boot before even being able to switch any PIN high? Would you agree?
 
Sunflare said:
I have another Question concerning the design/function of the PowerPCB (V. 1.09), specifically the part around Q3 and Q4:
I tried to figure it out myself and would like to know, whether my understanding is correct.

So ...
- The "Power Switch J6" is designed as Emergency switch and usually On.
- Accordingly, Battery Voltage is connected to C of Q3 ans S and G of Q4,
- however, both transistors are blocking and there is no voltage to J11/J12, consequently the Teensy (etc.) is off.
- Once Start/J9 is closed/pressed/On the Gate of Q4 is connected to GND Q4 is On, voltage on J11/J122 available, the Teensy starts.
- The teensy activates (via pinBatterySwitch) Q3 and therefore keeps the Gate of Q4 to GND and Q4 ON, even if Start/J9 is open again.
- If the Teensy wants to switch off, it deactivates pinBatterySwitch and cuts off his own power.
Is that correct?

If Yes, this process strongly depends on the power-on-speed of the Teensy, I guess.
Or to put it differently: This will not work with a Raspberry Pi (alternative to a Teensy), which needs several seconds to boot before even being able to switch any PIN high? Would you agree?
Click to expand...
YES all is correct.
Teensy start the init sequence of output in less than 1 second , so push button for 1 second is enough for start process.

Now for PI use:
YES pi take time to start.
But I think It's very complex to use only the PI, you always need other basic MCU for high frequency or safety task, so it's not a real issue.
 
Thank you @Bernard for the very quick response.
For me using only the PI would make it less complex, in fact. Especially concerning adaptions and modification to the great stuff found here and in the associated git-repos.
I really would like to find out, how far I can get with "only a Pi" ;). It's my project for the coming winter.
 
Because this is still about understanding the PowerPCB, I add another question here:
Looking at the charging circuitry with BT1 as power inlet (?) and Q1+Q2 for activating the charging process, I wonder whether there is any monitoring implemented. Usually there is some BMS involved in such a process. The INA266 is not very helpfull without knowing the state of charge.
Or can the original Mower-charger BMS monitor through the circuitry on the PowerPCB?
So what is the strategy to avoid killing the battery.
 
Sunflare said:
Because this is still about understanding the PowerPCB, I add another question here:
Looking at the charging circuitry with BT1 as power inlet (?) and Q1+Q2 for activating the charging process, I wonder whether there is any monitoring implemented. Usually there is some BMS involved in such a process. The INA266 is not very helpfull without knowing the state of charge.
Or can the original Mower-charger BMS monitor through the circuitry on the PowerPCB?
So what is the strategy to avoid killing the batter
Click to expand...
For me :
BMS is mandatory on LI-ion battery but is used to protect battery , and not for management of charge process.
A Li-ion charger is used to power the station and perimeter wire, so the charging process is manage by this unit ,but the issue is that the current consume by of PCB , PI etc.... can false the charging process.
INA226 is used to know the actual sense flowing to battery and allow (or not) mower to start mowing when timer is in use and battery not charged enough.
 
Yes, I agree a BMS is used to protect battery life, but it does that by managing the charge process. The mower, which I want to "optimize" has an
18V NiMH battery (3000mAh). According to what I found in the net it can get quite hot, it it is overcharged and does not really provide a good state of charge indication via its voltage. So maybe I have to exchange it for a Li-ion battery?!
I understand that the currently used cycle is like
  1. Let it mow until battery voltage falls below a certain lower limit
  2. return to the charging point
  3. charge and integrate the charge current with INA266 until a certain Energy is replaced
  4. Go to 1)
Is that correct?
 
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