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u/robbiethe1st

r/Motors r/leaf r/graphicscard
▲ 3 r/graphicscard

Looking for a upgrade for a PowerColor Fighter RX 6700XT(low profile)

I have a small form factor build in a unique and completely obsolete case I'd like to keep.

I originally found this GPU a few years ago, and it's pretty small - 228*109*39mm. Works plenty well, though!

I intend on building my wife a PC and swapping this GPU into that, and upgrading for myself.

My requirements are that it's AMD based(for SteamOS), at least 8GB(12-16 preferable) and hopefully a decent jump in performance.

The problem is that I can't find GPUs in the ~110MM height range. And I can't really get it taller in this case.

Length can be maybe 25MM longer. Thicker is fine too.

Any thoughts?

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u/robbiethe1st — 8 days ago
▲ 3 r/Motors

36V to 48V golf cart - what controller?

I got a 50's vintage electric golf cart for free. Of course, it doesn't run and hasn't in 10-20 years.

As you might expect for something of this vintage, it's using a series wound, 36V brushed motor and resistors for speed controller(it has 4 speeds!)

I managed to get it to work by hotwiring it - so I know the motor functions properly.

My plan is to upgrade it for MOAR POWER, and add a modern speed controller.

  1. 48V LFP battery, likely DIY. (I know this part of it, I've done it before). I suspect that going to 48V should work fine with a bump in top speed and torque, at the expense of heat buildup(may need to add a temp sensor/switch?)

  2. Speed controller - Not sure on the amps I'd need. This shows only 40 amps per the nameplate rating. Another, more modern golf cart I worked on would draw over 200A when flooring it from a stop... is it really this low? Or is this just the "at speed" rating and it'll draw a lot more when stopped?

I'm seeing these cheap knockoff controllers that seem like they would work, for $140 or so. https://www.amazon.com/1204-410-1204-412-Controller-5K-0%CE%A9Replace-1204410/dp/B0CGX31KSG?th=1

This would then need a throttle pedal - Ebay seems to have pedal+senders for about $60 - https://www.ebay.com/itm/227033624810

Any reason this wouldn't work?

u/robbiethe1st — 15 days ago
▲ 31 r/Motors

Why can't EV's be flat-towed / can motors be unhooked?

So, this has bothered me for a long time.

Every Hybrid and EV that I've seen cannot be flat towed(or towed with any driven axle on the ground). The manual states it will break things.

I'm trying to understand exactly why, and what the implications are.

So, lets take a simple case - Back axle of a Highlander Hybrid. This is a single-gear, always driven permanent magnet 3-phase motor. It's passively cooled, too.

When you are driving it down the highway, that motor is spinning at X RPM.

If I was to tow the vehicle with that axle on the ground, that motor would also be spinning X RPM.

So, why can't I tow it with that axle on the ground?

My assumption has something to do with motor spinning X RPM -> produces Y volts AC on the 3 legs. This is fine when the inverter is powered, but if it's not, it can't handle those volts being "backfed" into the inverter. This is why it's OK to be in "neutral" coasting down a hill(inverter on), but not towed with the inverter off.

If this is the case, could you just unhook the motor leads before towing? Now, all 3 legs of the motor are floating, the motor should spin freely as no current flows, and everything is fine...right?

Is there something I'm missing here?

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u/robbiethe1st — 24 days ago
▲ 1 r/Motors

Understanding Inductive Kick/spikes with regards to brushed DC motors

First, here's a great video about Inductive Kick - showing that even a small 12V relay can produce negative spikes over 100V: https://www.youtube.com/watch?v=gKWOWx2eNZg

So, I understand that the inductor/coil in a relay will produce a large spike when you disconnect the power, as the current tries to keep flowing due to the magnetic field.

What I want to understand is how this applies to brushed DC motors.

I know that if you take a 12V motor and hook it to power, it will spin.

Take that same motor and keep it spinning, and it will produce +12V (motor becomes a generator)

So if I have a motor and hook it to power, get it spinning and then unhook the power, I wouldn't expect to get a negative spike - it should continue to produce ~12V or so as it still spins.

This is my understanding so far.

What I'm trying to figure out is what happens if the motor is stopped(locked rotor). Do I get a negative spike there on disconnect?

Also, with a brushed DC motor, internally you have a number of windings in the rotor. Each one, in turn gets hooked up to power via the brushes. Once the motor turns and the next pair connects, do you get a negative spike on the winding that is now just disconnected?

Or am I missing something?

I may or may not be explaining this well, so please bear with me.

u/robbiethe1st — 1 month ago
▲ 7 r/leaf

I have a 2011 Leaf with a leaking master cylinder. I got a replacement off Ebay, but it's having the same issue - works, but slowly drips out the "front".

They seem to be expensive / unobtanium to get new/rebuilt, so I need to figure out how to rebuild it myself.

Since I have a spare unit(one I took out), it's basically no risk.

Has anyone done this before? Any leads on what seals I might need?

u/robbiethe1st — 2 months ago