More E-max Controller Mods - Shunt Resistor Trick
I finally got to repairing the original controller that failed due to vibration capacitor's shaking loose. Some of you may recall that 1000 miles on rough streets caused one of the phase filter capacitors to come completely detached from the PC board, and the other two had broken leads. Only one capacitor, used as a filter for the 48V power to the MOSFET sink bus, remained connected - it overheated, bulged and melted and shorted the throttle control wires that were touching it. Suprisingly, no MOSFETS failed. So, with the capaciors replaced and the wires repaired, I now have a working spare controller. The only problem was that the 100V capacitors are a bit too tall for the early-style controller case, I had to grind recesses on the case lid. The capacitors are pretty much tight to the lid with the controller closed, but with a dab of automotive sealant on the capacitor tops, they are secured against shaking and are also have a heat sink...
...But, on one of my scooters, I had worse-than expected degradation in acceleration and hill climbing when switched to bigger tires. So, I couldn't resist the urge and added a 1 1/2 inch piece of 12 ga copper wire to the existing three shunt resistors used for controller's current limiter. The shunt resistors are made of an unknown silver colored metal, probably higher resistance than copper but only about 20% the length of the copper wire I added. Nonetheless, I figured with the extra length I would be decreasing the shunt resistance (and increasing current limit) by about 20%.
With the modified controller swapped onto the "slow" scooter, I took it on a test ride. I think I reduced the shunt resistance by more than 20%. The acceleration and steep-hill climbing non- turbo mode is dramatically improved, and in turbo mode is hang-on tight fast! A 12% hill which the scooter (with the 3.50-10 tires) would do no better than 15 mph in turbo now does 20 to 25 mph in _non_-turbo mode. Turbo mode is not needed for normal riding anymore, and I am concerned about burning something out if I use full-throttle turbo to power-up a steep hill or jackrabbit starts.
As expected, this had little effect on level-ground top speed - maybe a mph faster (36-37 mph) - but it sure gets there quicker. So far, with an easy hand on the throttle, I don't think I am experiencing a dramatic decrease in range. I'm sure this would change with a heavy hand on the throttle. I'm concerned about the effect of all that extra current on controller components. Fortunately this is a spare controller, so I can afford to experiment a bit.
I need to fine-tune this shunt resistance ajustment (use aluminum instead of copper wire?) because I certainly overdid it on my first attempt. Any advice would be welcome.
Good work. It would be nice to measure the current to see where you're at.
You could use thinner wire or a longer piece to reduce the current. Aluminum is bad, you can't solder to it anyway.
With some reverse engineering, it should be possible to put a small adjustable pot somewhere in the circuit to make the limit adjustable. I think I have this figured out for the PowerPack / Crystalyte black box controllers.
Just wondering how hard would it be to for people like me that have an used EMAX scooter, if the stock controller were to go bad, to install or replace it with another one like a programmable one ?? I would like to one day upgrade and do 60 volts for some more speed !!!
Cool! Where do you get your ideas from? Only problem is now I don't know how long I will be able to resist the urge. It wont help the longevity of the motor, controller and batteries. I guess controller components and batteries will take most of the hit.
For fine-tuning the shunt you need to measure the existing one, or find out which material it's made of. Most shunts I've seen were made of copper, maybe it is only nickel-plated? Can you scratch it? For resistors, a metal called "kanthal" is often used. (It's rather a blend of metals, and the name is a trade mark.) Kanthal has a resistivity of 1.45 ohm mm2/m, compared to copper which is 0.0172. At least that sets an upper limit for the resisitivity, all other metals are in between those two.
Other, possible metals:
Aluminium (pure) 0.028
Iron (pure) 0.105
Volfram (tungsten) 0.056
Note that blended metals have a lot higher resistivity than the pure ones.
The shunt wires are copper with solder plating. You can measure the shunt resistance with an ammeter and a voltmeter. It also helps to have a power supply that can deliver a constant current. A before and after resistance measurement would allow you to fine tune it. You can also partially bridge between the existing wires with solder to fine tune it.
You'll need a clamp-type current-meter, unfortunately the ones that measure DC are not cheap. Probably around USD 100.
You can use the existing wiring as shunt. Example: let's say the battery current somewhere passes through a 50 cm, 4 mm2 piece of copper cable. The voltage drop for 100A is then 100*0.0172*0.5/4=0.215 V, highly measurable. It won't be very exact, but gives you an indication. I haven't done this on the e-max, so can't tell you which cable to use. And you'll have to translate the example into US units, like inches and "gauge" for the cable section.
The urge is growing stronger. When comparing with the specifications for the new e-max models, you get a feeling that current limits are set primarily to protect the batteries. 90S (42Ah) is limited to 40A/75A, 110S (60Ah) to 50A/90A. The old e-max motor is rated at 2000W, probably the continous (1h) rating. It can take a lot more during shorter times, as long as it is not overheating. We could hope the controller is able to take some more as well, during short accelerations, but it is probably more sensitive. Other components than the transistors suffers as well when current is excessive, such as the capacitors.
Another reflection is that the shunt is a possible explanation for the e-max's weak performance in hot wheather, since the resistance increases with temperature. I always noticed that performance is best just when you pull away after a longer stop.
Looking forward to hearing more about the current measurement. Maybe have to do some on my own, would be interesting to know what the current really is.
I use a chinese ammeter and shunt I got from Allelectronics. I set up the shunt (which is huge) inside a piece of PVC pipe with pigtail wires coming out to ring lugs. I replace one of my battery jumpers with this thing when I want to measure. The meter is a nice analog meter with a 0 to 100 amp scale.
Analog meters behave nicely when dealing with harsh switching transients and are easier to read while riding. See:
Not really cheap either, but way less than a clamp-on digital thing. It's also powered by itself, so it's always on. They also have a 200 amp shunt.
Wiki has some info about gauge wire sizes, but it is based on solid wires:
About the shunt, I am leaning towards that it is made of kantal or something with similar, high resistivity. I am assuming that around 0.2 V would be needed for the control circuit (don't ask me to explain that). I found an old picture of the board, maybe you can confirm the dimensions. Let's say the wires are 2.5 mm diameter, and 50 mm long, each. That means the section is 4.9 mm2, and the resistance of each is 0.0148 ohm, three in parallel are 0.0049 ohm, or 0.49 V at 100 A. Seems reasonable. Also means that power dissipation from each at 72 A is around 8 W. Or 3 mm diameter -> 0.010 ohm (0.0034) -> 0.34 V at 100 A, 6 W at 72 A. A bit high, perhaps. (I am using a resistity value of 1.45 ohm mm2/m, but found similar products with values between 1.0 and 1.3.)
Anyway, when you are connecting a similar diameter stranded copper wire, of 5 times the length, the resistance drops to around 0.001.
The ideal mod to the shunt would be to find the same type of high-resistivity wire, and add one in parallel.
(edit: I have yet to learn how to add comments in the suitable sequence.)
Now I have done some measurements, but they are not what I expected. I measured on the cables in the battery strings, one string at a time. The cables are 5.8 mm outer diameter and marked 6mm2. In string 1, on a 40 cm section I got 59 mV in turbo mode, max throttle. In string 2, a 26 cm section gave 47 mV. With reasonable values on resisitivity (0.0195, which means copper is not perfectly pure, got the value from a product catalogue), it adds up to around 101 A. In economy mode, current was 53 A. There are many errors in this measurement, but I believe they are within +/- 10% exact.
I am beginning to think that the rods are nickel-plated manganin, which is made from 86% Cu, so it might look like copper if you scratch it. Resistivity is 0.43, which gives reasonable values for the voltage drop (pure copper does not). Here is one manufacturer of shunts that uses this material
0.43 ohm*mm2/m is the resistivity of manganin. Dimensions are guesses from looking at a photo. Assuming that the rods are 2.5 mm diameter (4.9 mm2 section), and 50 mm length, the rods will have (0.43*0.05/4.9) 4.4 mOhm a piece, or 1.46 mOhm for all three in parallel. (Lots of uncertainty in that figure.)
According to Wiki, gauge 12 (solid) wire has 5.21 ohms/km resistance, which translates into 0.20 mOhm for 1 1/2 inch (38 mm, is that the same length as the manganin rods?). Anyway, Paul, you might well have reduced the resistance to less than 20% of OEM. Most of the current will go through the copper wire, for sure. I can't tell more exactly, but the conclusion must be: you have disabled the current limiting function more or less. If you want to reduce resistance by only 20%, you need to be more subtle.
And about my measurements, I can't understand what is wrong with them. Possible sources of error are the (chinese) cables might not have the 6mm2 section they claim, or are made of very unpure copper, or my voltmeter doesn't measure correctly, perhaps disturbed by ripple of the current. Or the wires heat up a lot? To get a resistivity of 50% higher than at 20 deg C, temperature must be 150 C. The measured voltage drop was quite stable as well, would have varied a lot if influenced by temperature.
I probably end up buying and installing a shunt, or worse, buying that USD100+ clamp-type DC current-meter I always wanted.
I have now installed a 150A/60mV/0.5% shunt, and here are the results. Max current in normal mode 36.8 A, in turbo mode 69.5 A. I must have been greatly mistaken about something in the earlier measurements. Values are in line with what Paul measured, good work Paul.
Maybe I should also add that this from a rather late 2006 e-max sport, assembled probably around February-March 2006.
According to GAIA germany, a lithium ION manufacturer, the inner resistance of silicone batteries increases during the discharge cycle and reaches a cricital state, where the batteries ability to offer strong surges of power decreases steadily. I have done multiple 20 mile turbo-inundated runs with breaks in between with my E-MAX and can confirm that about a 15-25 min, break is like a miracle for the E-MAX's performance. I do not believe the shunt is accountable for this at all!
When doing this mod, I will probably turn to this supplier
And should it come to rewinding the stator, they have the wire. We'll see.
Would you assume that this shunt mod works for my E-MAX (one of the 2006 batch with the new Manufacturing code...), bought it in June 2006...
Thanks PJD - and, by the way, hows the scoot holding up, any new findings on the affect the mod has on the batteries??
Man these mods are looks more tempting all the time, I’m very curious to see what the E-max can do with the larger wheels and extra current running at 60 volts (maybe melt down the motor, lol). But I’ll probably just start by trying larger wheels. I just picked up 2 more E-max scooters form a dealer getting rid of some stock and I think one going to be dedicated to extreme modding (the other is going to my girl friend). I’m also keeping an eye on the IRFP90N20D. Imagine the E-max controller being able to put out 100amps at 72v or even 96 volts! probably more then enough to melt down the motor.
Also what paint did you use on the asbestos I'm concerned about that also?
2006 E-Max sport @ 60v
Yeah, the larger tires, rewound motor and higher current do sound very promising and looks like the way to go if it works out. But after riding my scooter for a while now with the additional batteries, the weight doesn’t seem to be a problem and the higher voltage does seem to help it accelerate and climb hills a bit better, slightly more then canceling out the problem of the extra weight. Although leaving it at 48 volts would solve the problem of having to use another charger and cutting into your storage space.
So if it works out for you I may just go that route also but in the mean time it’s been great being able to keep up with traffic and zipping around town at the higher speeds. I also just ordered a higher capacity boost battery so I’ll be able to see what the actual range would be in a 60v 40ah pack configuration.
2006 E-Max sport @ 60v
PJD> Nice idea !
You did the mods on an Emax 1500W or on a 2000W ?
Let us know as soon as possible what is your new range with this mod !