Jacky Heshi Posted March 28, 2019 Share Posted March 28, 2019 I'm looking to step down the Gotway Tesla's 84V battery pack to 12V for a DIY project. I was thinking of tapping directly into the battery leads in parallel while the wheel is off. I can't seem to find a step-down converter that can handle 84V input and at least 200Watts. Also, would there be any conflict with the battery pack's built-in BMS since I'm bypassing the Gotway's controller board. Any suggestions or advice on how to approach this safely would be appreciated Link to comment Share on other sites More sharing options...
Chriull Posted March 28, 2019 Share Posted March 28, 2019 2 hours ago, Jacky Heshi said: I'm looking to step down the Gotway Tesla's 84V battery pack to 12V for a DIY project. There are many chinese step down converters available on aliexpress and similar sides. 2 hours ago, Jacky Heshi said: I was thinking of tapping directly into the battery leads in parallel while the wheel is off. I can't seem to find a step-down converter that can handle 84V input and at least 200Watts. That's much - 200/12=16A! And with some 5-15% efficiency thats 10 to 30 Watts of dissipated power - very much heating to get out of the enclosed wheel casing! Imo near to impossible - if one does not cut open the case so the the cooling fins from some nice heatsink gets ambient air... or some fancy heatpipe - heat exchanger stuff... 2 hours ago, Jacky Heshi said: Also, would there be any conflict with the battery pack's built-in BMS since I'm bypassing the Gotway's controller board. Afaik no - gotway has _no_ battery pack output protection ... So be sure your DC/DC converter does neither short circuit the pack or discharge any cell below 2.5 Volts 2 hours ago, Jacky Heshi said: Any suggestions or advice on how to approach this safely would be appreciated Link to comment Share on other sites More sharing options...
esaj Posted March 29, 2019 Share Posted March 29, 2019 On 3/28/2019 at 10:36 PM, Jacky Heshi said: I can't seem to find a step-down converter that can handle 84V input and at least 200Watts. Step-down from 84V to 12V at 200W output? How much space do you have? Can you use active cooling? The output power is pretty high, even if the step-down could work at high efficiency of >90%, you'd still be looking at 15-20W of power dissipation (probably worse), so you're likely going to need big heatsinks and maybe fans... and probably custom circuitry, as it's "unusual" voltage, usually you're either looking at AC/DC transform from normal power grid or something like car batteries (around 12V or 24V for bigger trucks), so there probably aren't that many ready-made options. Link to comment Share on other sites More sharing options...
Rehab1 Posted March 29, 2019 Share Posted March 29, 2019 One of the modifications I performed on my ACM 1600 included adding a 84-12v stepdown transformer to power a ventilation fan. I’m not sure if it was 200 watts. Here’s a video. Sorry that the video does not depict the transformer’s final mounting location but it will give you an idea on how I spliced the power wiring. Link to comment Share on other sites More sharing options...
esaj Posted March 29, 2019 Share Posted March 29, 2019 15 minutes ago, Rehab1 said: One of the modifications I performed on my ACM 1600 included adding a 84-12v stepdown transformer to power a ventilation fan. I’m not sure if it was 200 watts. Here’s a video. Sorry that the video does not depict the transformer’s final mounting location but it will give you an idea on how I spliced the power wiring. Most of those fans draw something like 1-5 watts (0.08-0.4A). 200W at 12V would mean about 16.666amps. Link to comment Share on other sites More sharing options...
Rehab1 Posted March 30, 2019 Share Posted March 30, 2019 1 hour ago, esaj said: Most of those fans draw something like 1-5 watts (0.08-0.4A). 200W at 12V would mean about 16.666amps. Yes I believe the fan was 5 watts. @Jacky Heshi what are you mounting to your wheel that requires that much wattage? A stereo system or intense lighting package comes to mind. Link to comment Share on other sites More sharing options...
Jacky Heshi Posted March 31, 2019 Author Share Posted March 31, 2019 On 3/29/2019 at 6:14 PM, Rehab1 said: Yes I believe the fan was 5 watts. @Jacky Heshi what are you mounting to your wheel that requires that much wattage? A stereo system or intense lighting package comes to mind. I'm really into FPV drone racing and would like to use my wheel to continuously charge my batteries when I'm on the field. I said 200w because I will only be drawing 50w and don't want the step down to get too hot to touch. I want the step down to be an external plug and play and not mounted inside the wheel. Link to comment Share on other sites More sharing options...
Jacky Heshi Posted March 31, 2019 Author Share Posted March 31, 2019 On 3/29/2019 at 4:11 PM, esaj said: Most of those fans draw something like 1-5 watts (0.08-0.4A). 200W at 12V would mean about 16.666amps. Just curious why you didn't just tap into the 12v going to the flashlight on your ACM since its only 5w. Link to comment Share on other sites More sharing options...
Rehab1 Posted March 31, 2019 Share Posted March 31, 2019 8 minutes ago, Jacky Heshi said: Just curious why you didn't just tap into the 12v going to the flashlight on your ACM since its only 5w. That would be too easy. Link to comment Share on other sites More sharing options...
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