I thought I would start to share my project that I am currently working on, Well itís in the initial stage of design/testing .There is a group of us that play around with RC cars and throughout the day we use each others glow plug/rotary starters depending on whoís goes flat first so I got this idea to make one so that it runs of a 12V battery as I have a few 12V 44AH SLA batteries lying around. I did some searching on the net got a few ideas and seen some simple designs and that you can get control panels but the ones I seen where with an analogue gauge or without but I wanted to make sure that I did not apply to much voltage/current to the glow plug and motor so I thought I would and LCD to display all the data with a low main battery voltage warning if the main battery starts to go flat.
I started with the rotary starter first using some mosfetís controlled via PWM found which frequency worked best without the ringing sound. This part is working well I limit the voltage to 8 volts to start with then run the motor it drops to 7.0-7.3 volts depending on how much load was on the motor but found sometimes when the motor stalled so decided to add some feed back so more the load got applied the pwm duty cycle automatically increased to maintain the torque on the motor without burning it out. You can still stall the motor as in the same way s you can with a battery when the engine gets fuel lock up. All this information like current/voltage been drawn gets displayed on the LCD with an added feature if it seeís to much current been drawn for more than a few seconds it cuts the feed off to the mosfetís to prevent you from burning the motor out or causing any damage.
The next stage is to do the same for the glow plug so In principle it should be the same method as for the starter motor but with the voltage been limited to I.5 volts and no more than 4apms max I would say normally 2-3amps is sufficient for the glow plugs, same again this will display the data on the LCD for the user to be able to monitor if drawing to much current to the power off., I think also that it could be used to tell you if you have got a duff glow plug or itís on itís way out. I am in the progress of running some testís on this method.
All this will be controlled by a pic micro (not yet set on which pic chip to use) at the moment Iím using a PIC16F876A as I got some of them lying around. It has a menu system to set it up or make any adjustments, you press and hold the enter key while powering it up menu as follows
1. Calibrate main battery voltage
2. Set the pwm duty cycle
3. Calibrate the output voltage to the motor
4. Calibrate the motor current reading
5. Set the glow plug current
6. Calibrate the glow plug voltage
7. Calibrate the glow plug current
8. Set the max over load current alarm/cut out
9. Set the max glow plug current alarm
You exit by pressing the enter key and this sill store all the values in the EEprom and take you back to the main part of the program. Other stud might get added at a later date like an electric filling fuel pump. Iíve used a couple of op-amps as differential inputs for the voltage/current readings as I found out it was hard to detect the motor voltage when running with a common ground.
By all means this project it not fully completed itís still at the bread board stage as I do not want to design the PCB for it until itís fully completed as each time I progress I make many changes. Most of the values of the resistors will be needed to be finalised.
I know this may be an over kill but having some fun in designing and I think it will be unique in itís self it could also be adapted to run other motorís and stuff like that .
There is a schematic attached for you to have a look at of my design and if there is enough interest I will carry on updating my progress as and when I can with photoís and stuff like that
Please feel free to comment/improvements that could be made
Thatís all for now more will flollow