Dave or anyone else, could you review this motor controller...... - Page 1
Forum section: electronics / general

author: AlanR
author_rank: Regular Contributor
timestamp: October 14, 2012, 12:31:46 am
content: I really like to watch your videos, Dave, because you open up all these products to look at what quality, or lack thereof, of each product which helps us as consumers to not get ripped a new one for unreliable products. So I am wondering about a DC motor controller that only works for PM or series wound motors that is made by a company called EVnetics. They call their motor controllers Solitons. I am thinking about purchasing the Soliton Jr. which is supposedly rated at 500 amps continuous at a voltage output of 340 volts. What bothers me though, is the price for the quality. It seems odd to put fans on it that will be exposed to the elements and they use screw terminal blocks for inputs to connect up all sorts of sensors and the throttle sensor instead of a IP rated automotive style connector setup.I am also a member of the DIY electric car forum in which the designer of this product is a member of. He tells us that he has no ability to test his products at max voltage at max current of the controller because he uses a battery bank rather than one of those ultra expensive power supplies that are in the megawatt range, and so he gets major voltage sage. He also never did temperature tests in a simulated environment chamber.Finally, he did not use half-bridge (has no electronic reverse, so no H-bridge) synchronous rectification to catch the back EMF of the motor when the low side switching IGBT slams off (his controller supports a slew rate up to 25,000 amps/sec!!!!!). Instead, he uses diodes paralleled together which seems like a poor design choice since diodes do not all switch at the same time perfectly. So if possible could you get a hold of a Soliton Jr. and do a tear down and maybe a noise analysis? Hopefully, there are not any voltage spikes that exceed the ratings of the IGBT's.Links:http://www.evnetics.com/evnetics-products/soliton-detailed-specifications/

author: tom66
author_rank: Super Contributor
timestamp: October 14, 2012, 12:58:18 am
content: I don't really see how Dave could test a 340V, 500 amp motor controller.Frankly, I don't see how anyone out of a hybrid/electric car development lab could. Even I bet those guys would use power resistors, instead of precision loads, simply because it's very difficult and expensive to build such a load.I have experimented with designing a motor controller (300V, 100A) for electric cars using plasma TV IGBTs (which are quite cheap.) I found that even at 100A (which is "just" 30kW, or "just" 45hp) you cannot simply use fan cooling. No way! Your drive may be 98% efficient but try dumping 600W as heat with fans! It -MUST- be water cooled with a proper cooling system and radiator. Perhaps an old car radiator cooling system would work.Film caps are a good idea but I chose Hitachi AIC high-reliability electrolytics for the bulk decoupling on the design. I think you really need a decent amount of capacitance because you're talking about very high currents and unless you've got your pack very close to the battery that's a lot of inductance which can create lots of problems... but then again, I only used 360V IGBTs on a 300V bus... which might make a big difference.Secondly, there's no problem with using screw terminals if they are fixed properly. They are used often in automotive systems.Thirdly, the 25,000 amps/second isn't really a rise rate, more like a simulated acceleration, it looks from the website. It doesn't mean peak current will be 25,000 amps. It means that if it has a 1000A peak current, it'll reach it in 40ms.

author: AlanR
author_rank: Regular Contributor
timestamp: October 14, 2012, 01:08:18 am
content: Of course it will not be 25,000 amps peak. That is just the slew rate like OP amps have slew rates that can be 100 volts/ sec, but the op amp may only be rated for 5 volts max output. They tested their controller with a motor connected to a hyrdualic dyno. I just want to see build quality and wonder how they got away with not using half-bridge synchronous rectification, yet still have the controller be reliable with no internal destruction with the use of paralleled diodes to capture back EMF. Industrial DC motor drives that use IGBT's intsead of thyristors (not sure what the thyristor types use for back EMF capture) use synchronous rectification.

author: tom66
author_rank: Super Contributor
timestamp: October 14, 2012, 01:28:47 am
content: Quote from: AlanR on October 14, 2012, 01:08:18 amYou can use diodes for regen, and it's what I'd do to be honest. Regen is an event that happens about ~10% of the time, and overall efficiency of the drivetrain isn't great (it's typically 70-80% efficiency for all losses combined - friction, gearbox (?), differential, axle, tyre...) More than likely, they ARE using the IGBTs for synchronous rectification but you need parallel diodes to briefly capture while the IGBTs aren't switched on. Common strategy in power converters.You can parallel diodes if you couple them to the same heatsink and you have matched the diodes well. It's quite possible and done a lot in modern electronics. I don't think it's back EMF they're capturing, it's the motor acting as a generator, I always thought back EMF was the effective voltage source the motor generated in series with the motor which reduces output power. But I only did A-level basic study of AC and DC motors in Physics.

author: AlanR
author_rank: Regular Contributor
timestamp: October 14, 2012, 02:09:33 am
content: Quote from: tom66 on October 14, 2012, 01:28:47 amThe back EMF I am referring to is that of which is cause by the motor's inductance when the IGBT switches off, not the generator voltage which has its polarity in the opposite direction of the of inductive kick voltage. The current circulating through the motor will need a path. If no path is available then the voltage builds up to high levels that will destroy the IGBT device. The freewheel device has to switch fast enough to capture this back EMF to remove any voltage spikes and the freewheeling device needs to be able to handle the current. It would take quite a bit of diodes and the heat of using diodes would be high and lets **hope** they all switch at the same time so you do not blow a diode that has it's current rated exceeded for a long duration. Hopefully, they used diodes all from the same lot and date of manufacture. No way to know for sure as no one has peaked inside these controllers. For $2000 I would expect good quality, but with the fans I am not so sure. It seems kinda odd to use plastic computer case fans that are exposed to the outdoor elements. Automotive devices need to work reliably at -40C to 125C. I just don't see that happening with those fans. So it makes me question the quality of the internals.

author: qno
author_rank: Frequent Contributor
timestamp: October 14, 2012, 02:10:15 pm
content: Hi Alan,I do not know the controller you selected but there are other controller manufacturers.I have worked for DMC in Germany but Curtis and PG are 2 other big ones.These controllers are used in electric forklifts and small utility vehicles.They have to comply to safety regulations so they are build-up more or less the same.There are controllers with H-Bridge outputs. Max voltage used in Forklifts is 72 or 80 volts.The speed control loop of Forklift controllers is optimized for giving you the feel of an internal combustion motor when accelerating / decelerating.With the voltages you specify you run into the realm of the Industrial Inverters. Search for VFD variable frequency drives.These are used for AC motors or Brushless DC. These go up to 500 kW available in 200/400/630 Volt AC. When you skip the rectifier and connect the battery to the DC circuit you can use a 200 V ac on 340 V batteries.