# Thread: My Smartdrive MX2

1. Thanks Bob.

Originally Posted by Bob Sullivan
Now travel distance equals running time ...
Yes, that's what I'm working out. Also I don't charge it every day, so I am still calculating how much charge will remain in various usage/idle patterns. So after 4 km Sunday night, I expect to use it again Tuesday for a short time and will charge overnight then. It doesn't seem to hold reliable charge to trust venturing out after being idle for 4 days.

But what is the discharge rate at different speeds, and what is the discharge rate when it's switched on but not running? If the simple reading of the voltage is irrelevant there should be no meter or the meter should be according to a calculation of - powered distance / use time / use speeds / idle 'on' time / idle 'off' time - made in the circuit board.

2. Originally Posted by mishahu
...It doesn't seem to hold reliable charge to trust venturing out after being idle for 4 days.

But what is the discharge rate at different speeds, and what is the discharge rate when it's switched on but not running? If the simple reading of the voltage is irrelevant there should be no meter or the meter should be according to a calculation of - powered distance / use time / use speeds / idle 'on' time / idle 'off' time - made in the circuit board.
There is optimal motor performance at various speeds for different hub motors, but I haven't found the chart yet. I found that my battery was discharged once when I left the controller turned on even though the motor was not plugged in. Now I disconnect the power and be sure everything is off.

I did find from the e-bike site a good primer on batteries that I'll ref and copy here. https://endless-sphere.com/forums/vi...p?f=16&t=26619

"...4. Batteries

Key concepts in batteries are voltage (V), capacity (amp-hour, or Ah), current (amps, A), discharge rate and charge rate.

Higher V = higher top-end speed.
Higher A = more low-end power (hill climbing).
Power in watts (W) = V * A
Higher capacity = more distance, but also more cost and weight.

Calculate the battery pack capacity you need by
Capacity (in Ah) = km * (Wh/km) / V * 1.25,
where:
• km is max distance in km before recharge,
• (Wh/km) is 10-20 (10 if you pedal, travel mostly on flats, etc; 20 if minimal pedalling, hills, faster speeds, headwinds),
• V is your pack voltage (typically 36 V or 48 V, but whatever you choose),
• the factor 1.25 is to leave 20% unused before recharging, otherwise battery life is reduced. Add another 20% if you plan to keep batteries for a long time, because capacity will decline with battery age.

Charge/discharge rate is expressed in "C", the battery capacity. A rate of 1C is the full battery in one hour. For example, a 10 Ah battery discharged at 10 A would be a 1C discharge, at 20A is 2C discharge (and would last only 0.5 hour).

Lead-acid batteries are old school. Don't go there unless low up-front cost is absolutely key.

LiFePo4 or LiPo are the main choices now. Another possibility is to get batteries from old tool packs etc. sold by some members on E-S.

LiFePo4 is more expensive up front, heavier, no fire risk, theoretically longer life (1000s of charges). pingbattery is one of the best values, but they need a lower C of 1-2C average or battery life is considerably shortened compared with other LiFePo4 choices. So ping batteries (or others with similar C rate) need a higher total capacity to keep the C-rate low enough. E.g. with a 25A controller, get at least 15 Ah.

LiPo is (recently) the cheapest, lightest choice, but needs careful charging or is extreme fire risk (read the Golden Rule and buy LP-Guard or similar fire-containing bags). HobbyKing is the popular source for LiPo right now. Newer quality LiPo can handle >>5C discharge and >2C charge rates; the former means you buy only the capacity you need, the latter means quicker recharges are possible. With LiPo you usually will have to buy several packs and parallel them together for higher Ah (e.g. 2x(5 Ah)), then series connect for higher voltage (e.g. 2 "5S" subpacks for 37 V nominal).

Both LiPo and LiFePo4 packs are sold with terms like "6S2P", which refers to the number of individual cells in series (S) and in parallel (P) within the pack. LiPo cells are nominal 3.7 V each; LiFePo4 cells are nominal 3.2 V each.

Batteries need chargers -- LiFePo4 usually comes with a charger. If LiPo, you should buy a good charger. (Experts sometimes bulk charge directly with a power supply, but "dummies" need one made for LiPo). Popular chargers now seem to be the iCharger 208B+ or 1010B+, or others in the iCharger line, or the Hyperion EOS 1420i. But they (like many chargers) require a separate power supply. Have a look at E-S threads for details, there's too much to explain in a quick guide.

Batteries charge to a fair bit higher than their nominal voltage, and voltage declines as they are discharged. They can be damaged if charged too high, or discharged too low, so they need HVC (high-voltage cutoff) and LVC (low-voltage cutoff) protection. Packs are happier if they are "balanced", i.e. all the cells are have very nearly the same voltage, especially if paralleling subpacks together. Some packs come with a BMS (Battery Management System) computer board built-in to control charging/balancing and protect the batteries from high or low voltage (this is typical with LiFePo4 packs). There are also third-party BMS boards that are sold by E-S members. For LiPo, the charge control/balancing is done by the separate charger, and LVC may be provided during use if desired by add-on monitors (e.g. Battery Medic, Chargery BM6, etc)..."

3. Originally Posted by mishahu
...But what is the discharge rate at different speeds, and what is the discharge rate when it's switched on but not running? If the simple reading of the voltage is irrelevant there should be no meter or the meter should be according to a calculation of - powered distance / use time / use speeds / idle 'on' time / idle 'off' time - made in the circuit board.
Ah, here is the simulator: http://www.ebikes.ca/tools/simulator.html We don't know the brand or model of the SmartDrive motor. But for this purpose it doesn't matter much. Use Ezee brand at 250 rpm because it has to be about that. The speeds shown will be for bike sizes which is what we'd have if the SmartDrive was mounted inside a bike hub. I cannot say I understand what I see yet except it appears these motors do not have a sweet spot. Of course extra weight, load or grade, uphill will draw more power and shorten the battery charge cycle in that trip.

4. I just thought I'd update:
With the MX2 I've been able to resume being a full-time college student! Unfortunately, my switch has broken twice (once was my fault, the second was not) and very recently my battery seems to not be holding a charge like it should. Just sent it out to Max Mobility in the hopes they can repair the switch again (and keep it from breaking in the future) and check everything out with the battery.

5. Originally Posted by betazoidgal
my switch has broken twice.
Switch on the motor or the bluetooth? What happened?

Originally Posted by betazoidgal
battery seems to not be holding a charge
In distance or time travelled directly after a charge or in ability to use it in days after a charge? Please post what the investigation reveals.

6. Originally Posted by mishahu
Switch on the motor or the bluetooth? What happened?

In distance or time travelled directly after a charge or in ability to use it in days after a charge? Please post what the investigation reveals.
First, I just realized how unclear I was, and I apologize. The switch on the drive unit, not on the wristband. The first time, I had the drive on the floor in front of me in the passenger seat of the car. When I went to pull it out, I knocked the switch, and it wouldn't budge the next time I tried to turn the unit on. Max Mobility had me ship it back and they repaired it. The second time, I have no idea... I went to turn it on the other day and it would move, but the unit wouldn't turn on. I don't remember knocking it again and I've been super careful.

Regarding the battery, I meant that it's differed in distance travelled directly after a charge. It's possible I could have been imagining it, or that there are other factors at play. One being that two of my classes this semester are on a part of campus with very steep inclines which could affect it.
I'll definitely let y'all know what the investigation says.

7. The performance of mine isn't even. All I can go by is the lights, and they can drop very quickly after short use or stay glowing after long use. How they are relating to actual usage is anyone's guess. Only once have I allowed it to run dry, described above, but there was an occurrence when I tried to use it after a few days idle and it was out of gas.

Lessons up the hill shouldn't make a huge difference unless you're pushing it ever upwards. After all you're not powering the distance back downhill.

8. Time to update on my experiences. The end of this is that I have a replacement unit which I will talk about in the next post.

After increasingly experiencing unexpected stops / difficult starting I was asked to bring my MX2 to be 'recalibrated'. It hasn't been explained to me what this means but entailed opening up the case, fiddling with dipswitches and running the motor. This improved performance but it slowly deteriorated over about 3 months until it again was recalibrated.

All was going well until one day ...

9. ... I attached the SD in a car park and headed to the elevator. As I approached the elevator I tapped to switch of the motor but it didn't stop. Tap again ... tap again ... motor still running. I quickly did a U-turn and noted that the wrist light turned red when tapped but the motor stayed on. I reached behind and switched the unit off.

In the car park I experimented running the drive and trying to stop but the problem persisted. Even pressing the wristband button didn't stop it. Each time I had to reach behind to switch the motor off.

The thought of this happening in the many of the situations I've used the drive makes my head spin. Roads, wharves, approaching a descent, crowds.

My dealer called in the unit which will no doubt be put under a microscope, and I now have a shiny new one.

From now on I'll start each use with a check in a safe area that everything is working AOK.

Nevertheless I still love SmartDrive-ing and can't imagine how I ever managed without it.

10. Originally Posted by mishahu
.In the car park I experimented running the drive and trying to stop but the problem persisted. Even pressing the wristband button didn't stop it. Each time I had to reach behind to switch the motor off.
I don't know how easily the motor switch would be to reach for a quad, but is that the only emergency stop/off switch? I ask cuz I don't think that would be an option if one needed to immediately stop the SD in an emergency, for anyone, much less a quad.

Also, is there an easy access disengage, if other than the stop switch noted above, so one could manually push the wheels?

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