E-max accelerating over 40mph

Update...

I achieved 45 mph (73 kph) exactly on a level roadway, no wind. But as this speed was approached, under power, there was a minor, but distinctive, high-speed "buzzing" vibration, most likely from the motor, but hard to tell. Reducing throttle stopped it.

Pushing envelopes has it's risks.

Yes please post pics as I would like to someday *COPY" your Emax :)

The motor seems no warmer to the touch than before, but I wouldn't expect much since it is seeing only intermittent use - less than 20% of the distance to work, and we've had no hot weather yet.

It won't go very far at 45 mph - especially with only one 20ah booster battery. I hooked up my homemade shunt/mV meter to the 60V circuit and measured 53 amps at 45 mph, compared to about 30-32 amps at 35 mph - you can't get around the air drag increasing as the square of the speed. BTW, this much amperage means that, with the stock controller's 35/70 amp limits, you need to hit the turbo button to get true top speed.

While doing the 60 volt modification on the second scooter, I discovered that the second relay, unused in the 48 volt setup, was sticking closed. If a relay sticks closed, closing the other relay will short the booster battery, and with all that very combustible plastic used in the e-max, probably burn the scooter to the ground unless there is a fire extinguisher nearby. Fortunately, I discovered the problem before wiring it all up and test riding it.

So, it is prudent to add a fuse, circuit breaker, or at least a lower gauge fusible link wrapped in something fireproof to the booster battery circuit. Any guidance on an appropriate measures for, say 200 amp protection?

The simplest solution would be to wire for one SWITCHING relay. This is a very common type of relay. It has three connectors, A, B and C. The middle connector (B) is switched to either A or C, i.e. to A in "off" position and to C in "on". This way you would be mechanically secured against short circuit A to C. If the existing relays can't be wired in switching mode, you could find this type of relays at a car parts dealer. Or truck parts dealer. (Typical car relays have a specified maximum voltage of 50 V, though.) The only drawback would be that you don't get your completely off mode (B not connected to anything). If you need that you could connect a second relay in series with B.

Fusing or making other arrangements for 200A breaker would be expensive and heavy. In this case though, since you know that the current will be either controlled and low (<100A), or immense (>1000A?) you could be less subtle and just put a suitable piece of isolated wire there. Ford cars used to have a short loop (5 cm) of wire for this purpose, just next to the battery terminal. You'll have to do the math yourself, but I am guessing it should be around 6 mm2. And the rest of the wiring substantially thicker, otherwise it won't work.

Rolf,

Thanks for the advice.

I would still need a second relay, since I wouldn't want to leave the controller energized without a second relay to open the circuit. In the auto parts store, I found a 175 amp fuse that is apparently used at the battery connection of a newer model cars. The actual maximum amperage per my earlier mod is between 90 and 100 amps. But the fuse is rated at 32 volts. The actual voltage is 60 volts - but would be 12 volts in the situation of an stuck-relay-caused short-circuit.

What is the effect of using a fuse at a higher voltage than rated? I assume it is power (wattage) that heats the fuse element, so at a higher voltage, will the fuse burn out at a lower than rated amperage?

Paul D.

Here's the pictures I promised. better late than never.

Note the 150 amp safety fuse on the battery, to protect against a short caused by a sticking-closed relay (see the wiring schematic) - A distinct possibility with those cheap Chinese relays.

BTW, I found out that using a fuse at a higher voltage does not affect it's amperage rating. The maximum voltage rating for a fuse is just the maximum voltage that the fuse case is assured of containing the arc and molten metal - so that the blowing fuse itself doesn't start a fire.

Battery Mounting:

Booster Switch Mounting - down 48 volts, middle off, up 60 volts.

Note the battery is simply mounted with an 8-inch hose clamp which is threaded through two slots 7.5 inches apart cut in back of the seat well.

As far as the rear fender, the fender was removed, and the mounting bracket on the rear fork removed using the bending back-and-forth method. The fender was then re-attached to the lowermost and middle battery boxes. The attachment at the middle battery boxes requiring 45 degree bracket.

As far as fasteners, they have to be reasonably smooth with minimal protrusion into the battery boxes flat-head screws, carriage bolts with the head flattened, or pop-rivets - your choice.

The fender is absolutely still needed. Without it, a large bump could cause the tire to jam on the corner of the battery box, resulting in either sudden locking of the wheel or destruction of the tire, loss of control, and bad outcomes. With the fender relocated, you may get an occasional "chirp" when the larger tire contacts the fender on a hard bump. It can be minimized by adjusting the strut springs a couple notches stiffer.

By the way, yesterday, I added a second silicone booster battery and ran it a 60 volts full-time into town on various errands and visits without opportunity charging. Obtained about 27 miles barely limping home - 10 mph or less on any up slope). The real range-killer a 600 feet, 2 mile hill about 5 miles shy of home.

I had gotten 22-23 miles with fair margin of reserve with the single 20AH booster battery and part-time 60 volt operation, so I don't think I got much improvement from the added battery.

The added weight of the extra battery was also noticeable with regard to handling and performance.

So, it appears that the single booster battery, used part-time, seems to be the best compromise until the li-ions come down in price.