Bypass Battery Temperature Sensor and TempComp on Flexmax 100 afci

Discussion about the FM100 AFCI Charge Controller
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mattyxp@yahoo.com
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My RE system: Mate3s
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Flexmax100 afci x 2 units
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Bypass Battery Temperature Sensor and TempComp on Flexmax 100 afci

Post by mattyxp@yahoo.com »

Hi All,

If you have a Mate3s and Flexmax 100 charge controllers and need to bypass the Battery Temperature Sensor (BTS) and Battery Charging Temperature Compensation for any reason and unplugging the BTS sensor from the Flexmax 100 BTS port/jack does not work to turn off the battery temperature reading on the Mate3s, then here is how to fake out the Mate3s correctly and easily so that the Flexmax 100 battery charging temperature compensation is effectively turned off:

***I had to do this because even with my BTS sensor unplugged from the Flexmax 100 BTS port/jack, my Mate3s still was reading/detecting "ghost" temperature signals between 32 degrees F and 450 degrees F even with the BTS sensor unplugged, which Outback can not explain and/or is not willing to fix with a way to permanently disable battery charging temperature compensation for those of us using lithium batteries who obviously need to disable battery charging temperature compensation.

***You'll need to purchase a RJ11 Screw Terminal...I purchased this one that worked great from Amazon:
https://www.amazon.com/AAOTOKK-Terminal ... 886&sr=8-1

- The Battery Temperature Sensor (BTS) ohms at 10,120ohms when the temperature is at 25 degrees Celsius (77 degrees Fahrenheit).
- Pins 1 & 2 and pins 3 &4 are tied together on the BTS sensor port/jack of the Flexmax 100 charge controller.
- Simply solder a 10kohm resistor and a 120ohm resistor together in series and then put one leg in either pin 1 or 2 and put the other leg in either pin 3 or 4 of the RJ11 Screw Terminal. I used 1w resistors but understand that any watt resistor is fine. Make sure to cover any metal on the exposed resistors with electrical tape to prevent any shorting, etc.
- Plug the RJ11 Screw Terminal with the resistors attached into the BTS port/jack in one of the Flexmax 100 charge controllers.
- That's it and the Mate3s will now read a constant 25 degrees Celsius (77 degrees Fahrenheit).
- With the Mate3s now reading a constant/steady 25 degrees Celsius from the BTS port/jack on one of the Flexmax 100 charge controllers, the Flexmax 100 battery charging temperature compensation will be effectively disabled. This is perfect for lithium battery charging with no battery charging temperature compensation.

For my Simpliphi 48v 3.8kwh lithium batteries, I have set the FLexmax 100 Battery Charging Temperature Compensation settings as follows:
Battery Temp Comp Range: Limited (until Outback Power makes way to turn off Temp Comp completely)
Limited: Lower Battery Voltage: 54 VDC (Charge Controller Float setting)
Limited: Upper Battery Voltage: 56 VDC (Inverter Absorb setting...charge controller setting will be .4v higher)
Temperature Comp Slope: 2 mV/C (set to lowest until Outback Power makes turning
off Temp Comp possible, set to 0 if ever possible)

So, with the BTS sensor port on the Flexmax 100 charge controller always being at a steady 25 degree Celsius, the battery charging temperature compensation will always be automatically offset by 0v...perfect for lithium battery charging...effectively no battery charging temperature compensation.

I hope this helps anyone who needs a way around this stupid issue that could be easily fixed by Outback just having an actual on/off setting for battery charging temperature compensation for all of us using lithium batteries with our systems.

Matt :)
Last edited by mattyxp@yahoo.com on Sun Apr 04, 2021 10:02 am, edited 1 time in total.
fcwlp
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Re: Bypass Battery Temperature Sensor and TempComp on Flexmax 100 afci

Post by fcwlp »

Thanks for documenting the work around.
sodamo
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Re: Bypass Battery Temperature Sensor and TempComp on Flexmax 100 afci

Post by sodamo »

So would this work with other components?
David
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Mike Curran
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Re: Bypass Battery Temperature Sensor and TempComp on Flexmax 100 afci

Post by Mike Curran »

sodamo wrote: Sat Apr 03, 2021 2:40 am So would this work with other components?
Yes - all the RTS is, is a thermistor, a component whose resistance changes with temperature. Any Outback component that accepts an RTS input will see this hack as if it were reading a constant 25°C.

PS When I first read the OP, I was surprised the FM100 cannot accept a temperature compensation slope less than 2 mV/°C, because Skybox does accept 0 mV/°C. In fact, without reading the post thoroughly, I'd initially drafted a response saying just set the slope to 0, but re-reading it discovered that was already tried and not possible. With Skybox it's convenient to be able to do this if you still want to track your lithium battery temperature without temperature-biasing the charging voltage .
https://smart.tigoenergy.com/p/pZXn7SZQyO45?date=2021-04-19
https://enlighten.enphaseenergy.com/public/systems/Hctc107221
raysun
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Re: Bypass Battery Temperature Sensor and TempComp on Flexmax 100 afci

Post by raysun »

I'd suggest using precision wire wound resistors instead of carbon or foil units. They will have more stability long term. Also, might want to take a peek at the resistors temperature coefficient to make sure you're not inadvertently creating a thermistor all over again.
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