i finally got around to this after jason at e-bikekits.com called and asked me if i would upgrade one for him. he sent me one which has a different LVC set to 31.5V versus the 30.5V of the others i have. so i upgraded 2 instead.
the older 30.5V LVC controllers have a 330 ohm power resistor in the input to the voltage regulator and this new one has a 200 ohm resistor. other than that there is no apparent difference. even the surface mount resistors in the LVC bridge are the same.
however i did find that the controller labeled with the 31.5 LVC ended up having a 55V LVC after i added the 1.6k ohm bypass resistor to the bridge, and the older model with the 30.5V LVC preset ended up with a 51V LVC after i added the same 1k6R bypass resistor. no idea why.
i used 2 270 ohm 2W power resistors on the newer model controller and the 330R and 200R resistors from the original 2 controllers on the older version. so 540R and 530R input power resistors was really the only difference between them. about 2W total when running under load.
i am fairly certain of my chart from knuckles data since i was able to correctly estimate i would have a 37V LVC when i added the 5k1R bypass resistor on my other controller i modified for the 48V nicads. it was exact, right at 37V! i had expected these 2 new ones would end up at 53V each, so not sure what caused the discrepancy.
i have now determined absolutely that the idle controller current is only 53.3mA and this climbs to about 61.7mA under full load. if i had known this initially, i would have increased the input power resistors from 530-540 ohm to 600ohm because the 12V rail was pulled very high by the 86V input voltage setup. in that case where the idle voltage was 86V, the input to the LM317T was about 54V, with the 12V rail at 19V and the 5V regulated output at 6V. but when it was running under load, the input voltage to the regulator was around 51V, with the 12V rail is around 17V and the 5V output regulated to about 6V but the test points were reading 5.7V, maybe there is a zener clamping the voltage output from the regulator. i decided to leave it since the pack will likely rapidly drop into the 76-77V range where the input to the LM317T is about 48V, and the regulated output drops to 12V and 5V.
at the low end, around the LVC, the voltage regulator still has about 24V input. 12V and 5V on the busses. with 600 ohm in place instead, at 51V for the LVC, the voltage regulator would see 14V input under load.
i soldered up the shunts when i had them exposed and was soldering the bypass resistor in place. i had a bad moment when the LVC bridge capacitor lifted with my soldering iron and i had to reposition it and resolder it in place along with that end of the bypass resistor.
i think the large 100V1000uF caps will make these 75V FETs work at the high voltages of the 72V lifepo4 packs so i am hopeful this is a simple solution, otherwise i will upgrade to 4110s to keep the heat down if these pop.
total cost to upgrade 2 controllers = $4.30 for 6 big caps and 4 resistors.
- my high tech test bed with universal combination data recording device and backup wood stove fire initiator
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- before, 63V 470uF caps
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- caps and power resistors stripped off, 1k6R bypass resistor soldered to base of shunt
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- after, tight fit with the 100V1000F caps, silicon rubber to hold them in place
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- power resistors on the bottom of the pcb, maybe the heat will get to the case more rapidly too
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