PWM motor controller replacement for resistor pack

[Unclebob]

I've been testing a PWM motor controller to replace my resistor pack and I'm pretty bloody happy with it. So much more efficient! Now I just have to figure out where to stick it. I gets quite hot running flat stick (not on low like the resistor solution), so I was thinking of trying to fit it in the area the resistor pack currently sits to cool with the blower air. Before I go ripping out my blower, does anybody know how much space I have to play with in there? Dimensions of the controller are roughly 25mm h x 45mm w x 80mm l.

See also Post in thread 'Heater only working at maximum' Heater only working at maximum

 

[Unclebob]

2.86￡ 33% OFF|Pwm Dc Motor Speed Controller Switch Dc 20a Current Voltage Regulator 10-60v Pwm High Power Drive Module 60a 12v 24v 36v 48v - Motor Controller - AliExpress

Smarter Shopping, Better Living! Aliexpress.com

a.aliexpress.com

Cheaper than a new resistor pack!

 

[Robert]

Well done!
I think I was suggesting this method in the past.

PWM is the best speed control method for a DC motor.
But as I already said VW is purposely cutting costs and creates circumstances to make more money.

 

[Unclebob]

11:00AM update - fan has been running at 3A since mid afternoon yesterday with no problems. Heat sinks are warm but nothing concerning. I currently have the vents blowing into the foot well (over the controller) so it's getting some heat dissipation.

Currently 26c and car has been in full sun the whole morning with windows down about level with the bottom of the weather shields. Temp currently 34c inside the car. I do have insulative covers but want to try worst case scenario of being lazy and not putting them up.

Still rather uncomfortable sitting in the front seat due mainly to radiant heat from the dash which would be helped a lot with the covers, but at 34 degrees the wax on my surfboards is plenty safe, the fridge is going to be running a lot more efficient, and it's not going to be doing any damage to my lithium ion batteries.

Hotter temps this afternoon, will check again at 2pm.

I think I'll add a relay to bypass the motor controller to just run the motor directly once it hits about 50% (10A). Judging by the heat the controller is throwing at higher current, it'll be far more efficient and help protect the controller (it's 20A max, so 18A doesn't leave much headroom), and gives some redundancy if either the relay or the controller fails.

 

[Unclebob]

36c at the hottest part of the day (28c outside atm), but I bumped the current up to 4A (got to 38c around 12). I think itd work better if I had vents up the top at the back (at the moment air is going in the foot well then out the front windows). The whole idea of this project was to avoid cutting giant holes in the roof for a maxxfan like contraption, but I guess a couple in the side wouldn't be the end of the world, especially if they can be opened/closed automatically. Unfortunately I can't think of a way to test it without actually cutting holes.

 

[Unclebob]

Today I learnt that there is enough space to fit my pwm motor controller where the resistor pack goes. I also learnt that if I ever meet the arsehole who designed this clusterfuck of a blower, there will be blood. Can't figure out how to get the thing out without removing the entire dash! That's just insane given the access available.

 

[Unclebob]

Apparently sometimes things just work out... 4x30A Anderson powerpoles fit perfectly in the old resistor pack holder. 3.5mm audio jack for the pot and it's off to the races! Couldn't have asked for better!

 

[Unclebob]

Ok, seems I spoke too soon.
There is (unsurprisingly) not enough space behind the old resistor pack socket to fit the other half on the Anderson socket in, so it's now pushed through and hanging down behind, which means less cable in the blower unit, which means I'm cutting the cables anyway if it needs to come back out. I bridged the onboard fuse so it won't blow (don't want to have to do all this again for a fuse!) and after much frustration, I finally got everything in and closed the blower back up, got some cable through to my aux battery fuse box and it works... Sort of.

The issue is that the PWM controller is all backwards - the mosfets are switching the negative side. Not a massive problem but the opposite of what you'd expect in a car. Anyway the real issues is that the pot is drawing current away from the mosfets. Disconnect it entirely and that's full blast. Bridge it, and it's off. That is, unless you run a good meter of small gauge signal wire (or 2m for the round trip) to the pot through an audio jack (known for great current carrying capacity) which adds not insignificant resistance. Long story short, now I can't turn it off without pulling the fuse! And it won't run at less than say a 2.5 on the old scale

Well... f***. Beer time. I'll revisit this when my digital pots show up... At least the fuse is easy to get at

 

[Unclebob]

Digital pots arrived and after much faffing about I discovered my digital pots are 50k, not 100k as advertised I did manage to write my first rust code to control the digi pot using spi though so thats something I suppose.