Infineon Controller Power Resistor Calculator

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Infineon Controller Power Resistor Calculator

Postby Kingfish » Mon Jul 19, 2010 1:01 pm

Greetings –

This brief describes how to calculate the resistance of R1 for the various nominal operating voltages between 36V and 74V (10S to 20S) for the Infineon controllers.

There are two presumptions:
    At 36V, R1 = 100 Ohms (2-3W)
    At 72V, R1 = 600 Ohms (3-4W)
It is best to err on conservative and go with the higher wattage resistor for better heat dissipation, though there may be some difficulty in creating room within the controller to fit these components.

Though some utility can still be achieved up to 74V with resistors, for voltages above 60 it is considered more efficient to use a switching DC-DC converter/circuitry if room can be afforded.

LV and HV limits are based upon moderately safe LiPo cell operation ranges.

Formulas:
  • Ohms = ((V / 36) * 500) – 400; slope given as y = 500x – 400
  • LV = (V / Vn) * Vl; (V / 3.7) * 3.0
  • HV = (V / Vn) * Vh; (V / 3.7) * 4.16
    where V = Volts, Vn = Cell-Volts nominal, Vh = Cell Volts-high limit, Vl = Cell-Volts low limit

Table:
Volts	Ohms	LV	HV	LiFePO4	LiPo
36 100 29.19 40.48 x
37 113.89 30 41.6 10S
43 197.22 34.86 48.35 12S
48 266.67 38.92 53.97 x
55 363.89 44.59 61.84 15S
56.8 388.89 46.05 63.86 16S
60 433.33 48.65 67.46 x
64 488.89 51.89 71.96 18S
72 600 58.38 80.95 x
74 627.78 60 83.2 20S
85 780.56 68.92 95.57 24S

Notes:
Some resistance values are difficult to locate. Example: It is pretty common to find two 2W 201-Ohm resistors in parallel to get the ~100 Ohm value on a 36V controller. You may need to get creative to find your best match :)

Citations:
Reviewed and checked by Justin at ebikes.ca. There’s a short topic on the subject just below the Regen section here; scroll to the heading “How do I modify the controller for more than 48 Volts?”

Best of luck, KF

-- Ypedal edit to add Infineon reference.
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Re: Infineon Controller Power Resistor Calculator

Postby Kingfish » Tue Jul 20, 2010 10:08 pm

Addendum:

Image
Example location of R1 relative to the Voltage regulator

Note: Some pc boards have locations for more than one resistorif so then they may be labeled R1A and R1B...

Ypedal, thanks for the help :)
Last edited by Kingfish on Fri Mar 04, 2011 2:20 pm, edited 1 time in total.
* My 2WD Garden Wall
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Re: Infineon Controller Power Resistor Calculator

Postby methods » Wed Aug 18, 2010 10:31 pm

The above recommendations are reasonable, but since this is the Technical Reference Section it should be pointed out that

A) This only applies to the circuit above. Many Infineon controllers have a different 12V regulator design and these values WILL NOT WORK.
**( Case in point - the 18 fet controllers)

B) The values in the table above are really on the ragged edge - it is possible that you could over-volt the LM317 using those values.


Based on the circuit above - one purpose of varying R1 is to limit the voltage drop across the LM317 regulator.
The maximum acceptable voltage drop across the LM317 is 40V, and the above recommendations may result in an over-voltage situation on the LM317

LM317 Datasheet

(note: Vdrop being Calculated by subtracting Vout from Vin)


Specifically for the circuit above:

Vout = 1.25V(1 + R3/R2) + Ia(R3)

R2 = 1.2k
R3 = 10k
Ia = 50uA to 100uA

Vout = 1.25V(1 + 10k/1.2k) + Ia(10k)
Vout = 12.16V to 12.66V

So now we know what Vout is about 12V
(always good to check numbers - right? _Never trust a Chinese schematic :P )

Now lets work an example.

Assuming the following:

Vin = 95.57V (from the table above)
Vout = 12V (from the schematic and my calculations)
I = 50mA (from the linked reference to ebikes.ca and a reasonable rule of thumb)

Vdrop = Vin - VR1 - Vout

VR1 = I * R1 = 50mA * 780ohms = 39V

Vdrop = 95.57 - 39 - 12 = 44.57V

So what this means is that if you implement this resistor choice and your controller current is about 50mA (which is about what it will be) then you will be putting 44.57V across the LM317 which technically puts it into the failure zone.

It is wise to leave a little margin - so generally you would not want to put more than say... 37V across the LM317 worst case. For this example, I think that 900ohms would be more appropriate than 780 ohms. That said - this is all assuming 50mA, so if you assume 60mA then 780ohms would be fine and if you assume 40mA you would be looking at a high likely hood of the expulsion of magic smoke.

In the end, it is the responsibility of the individual who is modding the controller to take responsibility for calculating the correct values to use. The wise individual would measure the actual current draw on the controller in situ and work the formulas from there - since as you can see the controller current draw plays a huge role in the equation.

methods tip of the day: Trust but verify - this goes for everything in life, but especially for magic numbers on the internet. Nothing is as straight forward as it appears in Electronics.

-methods

P.S. Oh yea - Dont forget to run the LVC numbers too to make sure you have sufficient voltage for the LM317 to regulate at 12V - and of course - run the power numbers and add at least 40% margin to your power resistor selection. (I.e. if you come up with 2.4W then run a pair of 2W resistors in parallel) :wink: In this case at 68V 50mA we would still have a sold 17V across the LM317.

P.S.S. Not all controllers draw 50mA !!! Each of the many infineon designs have different components on the board, different accessories, etc. The 12 fet controller that runs a Throttle, ebrakes, Cruise Control, halls, and an LED is going to pull more current (less drop across the LM317) than a 6 fet controller with only a throttle. THAT is why you measure your own current in situ for best results.

P.S.S.S. The honest truth is that just about any of those values will actually work in real life since the LM317 often times has good Margin. On my controllers at home I do stupid things like run 18S on 12S max controllers all the time..... Technically it should not work - but it does :)

P.S.S.S.S. I just wanted to write 4 S's
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Re: Infineon Controller Power Resistor Calculator

Postby Kingfish » Mon May 14, 2012 2:12 pm

ADDENDUM:

It’s been brought to my attention that replacing the Fairchild LM317 having a voltage input up to 40V could be replaced with a Fairchild LM317AHVT which has an input up to 60V. For boards that use the TO-220 package this looks like a good option and an easy inexpensive component to replace, one that would certainly answerable to the extremes of the previously given table posting on Mon Jul 19, 2010 11:01 am.

Credit: ES new member tranquility for the observation :)

LM317 Datasheet: Up to 40V
LM317AHV Datasheet: Up to 60V

Safe travels, KF
* My 2WD Garden Wall
* Current ride: 2WD Disc EBikeKit (9C 2806-equivalent) / Dual Lyen 12FET / 15S6P LiPo when commuting.
* Going to California: 2011: Trip completed 8)
* Club Member: 40-mph & 101. 10k-Club: 11,096 miles-to-date, 5606 as 2WD.

It is by caffeine alone I set my mind in motion.
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