Programmable Hotwire Driver FAQ
This FAQ covers the M@gSled Hotwire Driver. Much of what is here applies also to JimmyM's and wquiles' variant, but there are some differences.
What is a Hotwire?
The term Hotwire is generally applied to high power incandescent flashlights, especially ones where the bulb is being overdriven to achieve higher output and efficiency.
What is a Programmable Hotwire Driver?
This is a tiny programmable computer chip controlling a large power transistor (FET) switch that sits between the battery and the bulb. By controlling the switch with PWM (pulse width modulation) it can control the temperature of the filament and the light output of the bulb. This can be used to provide many useful features including voltage regulation, soft start, intensity control and battery protection.
What does it do for my Incandescent Flashlight?
The regulator provides soft-start for the filament to limit inrush current and extend the life of the bulb. It provides regulated voltage levels to make the output level constant regardless of battery condition, and to allow lower levels of output when desired. Lower levels of output make the batteries last longer and reduce heat, making the light far more useful than "maximum only". Using more cells in the battery pack provides more energy and longer runtime. The regulator also monitors battery condition and can shut down before overdischarging the battery. This can allow use of unprotected cells that can deliver higher current. It also monitors temperature inside the flashlight and can shut down the light when high temperatures are reached. The adjustable ceramic bipin bulb socket supports many different available bulbs.
What is the User Interface like?
Since the regulator is programmable the user interface can be changed, and there will be many versions. The software allows the user to tailor the interface to their needs. Just to give a flavor of my own current favorite UI:
click from off to memory level
click from on to off
press from off to lowest level
press while on to ramp the memory level, alternating direction with each press
double click anytime to maximum level
triple click to middle level
What are the Configurable Parameters?
examples of parameters that can be changed by programming the regulator (the following list is not complete):
maximum bulb voltage
minimum bulb voltage
battery chemistry
number of cells
number of clicks to enable/disable lock out
temperature of overtemperature shutdown
See the Programming Thread for more information on this
What is the Lockout feature?
It effectively locks the flashlight off until the unlock sequence is entered.
What are the Voltage and Current Ratings?
Presently estimate 34V battery and 12A bulb current as the maximum rating (subject to change). Some testing has been done but more experience will guide the final rating determination. Absolute Maximum ratings are 40V Peak battery voltage and 15A RMS bulb current. The closer the unit is operated to the maximum values the more likely it will blow the fuse or damage a component. The fuse is 15A, the FET is rated much higher.
What is the relationship between Battery voltage and Bulb voltage?
The battery voltage should be greater than the desired bulb voltage. This regulator cannot increase voltage, it can only reduce it. The ideal situation is when the loaded battery voltage is just higher than bulb voltage. When the battery voltage is twice the bulb voltage the duty cycle will be only 25%, and the peak current and voltage will be twice the bulb rating. The small duty cycle means that change steps in the PWM are larger, as one count is a larger proportion of a smaller duty cycle. For best performance select a battery/bulb combination where the battery voltage under load is about 10 to 30 percent higher in voltage than the bulb. It is not recommended to use battery voltages more than twice the bulb voltage (though it will work).
When will it be Available?
The M@gSled(tm) is shipping starting August.
What will the Regulator Cost?
Prices start under $100. There are a lot of parts some of which are custom and expensive such as the aluminum sled. The parts count (mechanical and electrical) is over 40 in this regulator. (The prices are stated in the Order thread).
How large is the Regulator?
The M@gSled regulator is designed to occupy the same space as the stock switch in a D size Maglite (Maglite is trademarked by Mag Instruments)(We have no affiliation to Mag Instruments, other than using their excellent aluminum flashlight parts to house our switch). It rests against the stop ring in the front, the same as the stock switch. The positive battery terminal sticks out more than the stock switch allowing flat terminal batteries to work properly. The position of the positive terminal places the battery stack approximately 4-5mm further toward the tailcap than a stock M@g, so the spring will need to have enough compliance and space to handle this. This is not a problem in most configurations as there is a lot of room in a stock spring, but some special situations may not have enough room without extending the tailcap.
How is the Regulator installed?
Remove tailcap and batteries. Remove head/reflector/lens assembly. Pry the switch rubber cover out. Using a 3/32 (or size as required) hex wrench through the center of the switch turn counterclockwise and loosen the switch. Push the switch in to the "on" position and slide the switch and bulb assembly out the tail end of the body tube. Remove the pushbutton swtich board from the PHD Sled using needlenose pliers or a loop of wire. Slide the Sled into the body tube against the stop ring. Align the sled with the switch hole. Tighten the lockscrew through the hole in the pc board with the hex wrench. Plug in the switch. Install and clean the bulb. Replace the lens and reflector with high temperature capable units (depending on the bulb power). Install the head assembly. Install battery pack. Test.
Does this retain the focussing capability of the M@g?
The focus is adjustable but the fast cam is removed. Coarse adjustments are made by changing the height of the bipin bulb socket using spacers. Fine adjustments are made by turning the head of the light.
What is the Resistance of this Regulator (or How many MilliOhms is it)?
MilliOhms refers to the resistance to current flowing through the regulator. The FET switch is about 5. The fuse is about 5. Not sure yet what the rest is, but it is designed to be very low. The socket probably has more resistance than the regulator. More here later.
What Bipin Bulb Socket is Used?
CPF Member Kiu will not sell us his bipin sockets. A baseline socket will be provided, with the option of the user providing a socket such as a Kiu. Osram sockets will be available as an option.
Does the Regulator get Hot?
The regulator switch is "on" or "off", and does not dissipate much power. It should not get hot. During extended tests it did not get hot, or even warm. The bulb will likely heat the regulator more than the current.
Does the Regulator Shut Down when Overheated?
The default programming configuration uses the cpu's internal temperature sensor to shut the regulator down at approximately 60C to protect both the regulator and the batteries. This value can be changed.
What is PWM?
PWM stands for Pulse Width Modulation. The energy delivered to the bulb is controlled by turning it on and off quickly. Adjusting the duty cycle (percentage of time on) controls the bulb power. The regulator does this about 250 times per second.
What Voltage and Current go to the Bulb?
The switch is very low resistance, when it is "on" the full battery voltage is delivered to the bulb, and the current is determined by the filament resistance. The RMS value of the voltage and current are correct for the bulb's DC values. However the peak voltage and current are higher. The PWM duty cycle controls the power in the filament and delivers the correct RMS values.
What happens when battery voltage is below the desired bulb voltage?
The PWM goes to 100 percent duty cycle (fully on) and the driver becomes direct drive (and is no longer regulating). It still provides soft starting, and if the ramping is used to dim the bulb it may go back into regulation at a lower voltage.
What happens when the battery voltage gets too low?
This depends on the programming in the regulator, but it must reduce the load or go off to protect the battery. The current software in the M@gSled blinks off for 200 milliseconds and then comes back on at half bulb voltage if the battery will support that. If the battery still won't stay above the safe voltage it repeats the cycle, dropping to a lower voltage until either the battery will support the load or the filament voltage drops below minimum and the regulator turns off.
How much power does the Regulator consume?
When the light is on the power consumed by the regulator is approximately 7 mA. When the light is off the power consumed is approximately 300 uA. A 2000 mAH battery pack (such as an AA Eneloops) would take about 270 days to run down at this rate. Loosening the tailcap to lockout the light may reduce or eliminate this leakage current. Note that this current changes with voltage and further changes to these values will occur as the design is finalized.
Does the light Flicker?
At this frequency the thermal inertia of the filament makes any flicker very small and it is not visible.
What is RMS voltage?
RMS stands for Root Mean Square, but that is just the engineering/math term for "effective" voltage. So if we have 10 volts RMS it will produce the same light from the bulb as 10 volts DC.
How can I measure RMS voltage?
Use an AC+DC RMS meter and read it directly, or use a regular average DC meter and make two readings, one of the battery voltage and one of the output average DC voltage. Multiply the battery voltage times the average DC voltage. Take the square root and the result is the RMS voltage. This calculation requires square waves to work properly, so it works best with a light load. Waveform distortion will make the results inaccurate.
My meter has RMS but the values don't agree?
Most RMS meters are AC RMS, not AC+DC RMS. AC RMS meters throw away the average DC part of the reading and cannot be used. Use the DC range and treat it as an average DC value as in the procedure above.
Does the Regulator make Noise?
The regulator is quiet. The pulses in the bulb may make a slightly audible noise, depending on the bulb filament. It is not loud and the noise is reduced at high output levels, increasing at lower voltage outputs (such as when the output is ramped to a low level). The noise level is also a function of the peak current (due to magnetic forces in the filament), so using higher voltage batteries increases the noise level.
Will there be a High Voltage model?
Probably. The parts in the standard models are rated to 40 volts ABSOLUTE MAXIMUM. This includes transients, etc, so we should not go above about 34 volts. There are higher voltage parts available, we need to test those at some point and see if there are any issues with them at higher voltages. They have ratings of about 60 volts MAXIMUM, so that should get us to about 12S or 50 volts. It is also possible for the parts to be changed. The FET, regulator and voltage scaling resistor for the ADC need to be changed to go to a higher voltage range. An application note could be developed to explain this in more detail for those who wish to experiment.
What are the Voltage Ranges?
The regulator has a number of voltage ranges (up to 6) it can operate in, somewhat like changing ranges on a multimeter. These ranges are selected by a combination of jumper and the software. If the jumper is installed the software can select the range that will handle 2, 4 and 8 series connected Li-Ion cells at 4.2 volts per cell. With the jumper out the ranges are 3, 6 and 12 Li-Ion cells at 4.2 volts per cell. NOTE that 12 cells require a special high voltage model of the regulator.
What does 2S, 4S or 8S Voltage Rating Mean?
Lithium Ion cells are generally 4.2V per cell (some are lower). The S rating is for series connected cells, so 4S is 4 cells in series for 4 times 4.2 volts or 16.8 volts. You may also see notations like 4S2P which means 4 cells in series and two stacks in parallel, for a total of 8 cells. Series cells raise the voltage, parallel cells raise the current capacity and ampere-hour ratings.
Will there be a model for the "C" M@glite?
I'm not planning it at this time. JimmyM may do one sometime in the future. It is a tight fit and compromises will likely be required.
Will there be a model for the Surefire M6?
wquiles is working on this.
What type of parts are used in this Regulator?
This regulator uses a mix of standard through-hole and surface mount parts. The early models were entirely through-hole parts. It is not hard to work on and might possibly even be offered as a kit at some point. The other variants from JimmyM and wquiles will most likely use entirely surface mount parts.
What is the difference between this Regulator and JimmyM's?
Jim's variant of this regulator is designed to fit under a KIU base. It is smaller and lower in cost. It will be more difficult to install and reprogram due to its location and the plastic M@g switch will remain. Jim is using a different variant of the CPU so it takes slightly different software, but both are Atmel AVR series chips (and use the same software and programming tools). It uses surface mount parts allowing it to be smaller.
What is the difference between this Regulator and wquile's?
Will's variant of this regulator is designed to fit into a special SF M6 battery pack.
What happens when a bulb blows?
This depends on exactly how the bulb blows. The regulator will not detect that it has happened. If the bulb manages to short and present a really low impedance to the regulator the current spike may blow the onboard fuse, but this is not likely. The FET switch is very robust and can handle large surge currents so it should be fine.
What happens if the fuse blows?
Be thankful that the fuse blew and not the battery pack. After the fuse blows the regulator will no longer get voltage from the battery as the fuse is the first thing in the circuit. It will have to be replaced. To keep it small and low resistance the fuse is soldered to the board. It looks like a green tubular resistor and is located right next to the positive terminal of the battery on the circuit board. Replace it with a 15 amp picofuse. Make sure that the problem that caused the fuse to blow is repaired before returning the unit to operation and double check that the battery positive terminal is not shorted to the sled after reassembly.
What happens if the battery polarity is reversed?
The transistor switch behaves as a high current capable diode when powered in the reverse direction. The battery will be connected to the bulb through this diode. Depending on the choice of battery voltage versus bulb voltage, the bulb may be very bright, or it may instaflash (blow out). The regulator itself is reverse polarity protected so it is not likely to be damaged. Some battery packs have charging jacks in the negative end that may short on the positive battery connector of the regulator, causing high currents, heating and damage to the batteries and battery pack.
What if the Regulator needs repair?
Depot repair will be worked out later. Schematics and software are available on the web for self-repair.
Questions about Programming
For questions about Programming the Regulator see the Programming FAQ:
https://www.candlepowerforums.com/posts/2953206&postcount=2
Links:
Design Collaboration Part I:
http://www.candlepowerforums.com/vb/...d.php?t=186291
Design Collaboration Part II:
http://www.candlepowerforums.com/vb/...d.php?t=209098
Design Collaboration Part III:
http://www.candlepowerforums.com/vb/...d.php?t=220475
Feeler Thread:
https://www.candlepowerforums.com/threads/218506
Review by LuxLuthor:
https://www.candlepowerforums.com/threads/230519
wquiles SF-M6 variant:
http://www.candlepowerforums.com/vb/...d.php?t=215806
JimmyM's D-M@g variant:
http://www.candlepowerforums.com/vb/...d.php?t=216160
Maglite is a trademark of Mag Instruments. This regulator is not produced by Mag Instruments - we have no relation to the company. We just like their aluminum housing. It is a great starting point.
Corrections, suggestions and questions to:
