XM-3500LI: BMS and Battery Testing

1. Unless one is not going to worry about this at all, arrange for some safe method to "access" each cell so that all the individual cell voltages can be measured. Since measuring each cell in the "stock" configuration can be difficult or even "impossible", it is usually quite helpful to bring out (CAREFULLY and SAFELY) one wire from the pack minus and one wire from each cell's positive terminal. Best to put fuses in each wire, preferably right at (very near) the connection to the cell. This is a form of Battery Measurement System, not to be confused with the BMS described below.

2. The major indication of "poor" cells is a measuring a voltage that is significantly higher or lower than is "expected".

3. One needs to learn what to expect, and when one can make "significant" measurements. Generally, one wants to see all the voltages (almost) the same, or within about a 0.1 volt range.

4. Learn how to keep cells from overcharging. Usually this means some form of discharging the cells where the voltage has or might become overly high. Methods of charging each cell to one suitable "fixed" voltage are often used. This is the primary function of a BMS (Battery Management System) for "charging" (or regeneration) control.

5. The protection against over-discharging is sometimes included in a BMS, and is usually called LVC (Low Voltage Control). Typically, most batteries will "damage" themselves (usually, losing energy storage capacity) if they are discharged too much. For typical LiFePO4 "3-volt" (really 3.0 to 3.5 volt) cells, a lower-limit value of 2.5 (plus or minus 0.4) volts is often used. While riding, the controller usually stops operating if the pack voltage goes too low. The problem is, some cell will always be "the lowest" cell, and it could get (more) damaged while most the other cells are still high. Usually, this does not happen unless the cells are not well balanced, or a cell is at least a little "weak". But, since it can (and likely will) happen, how to identify the situation before it becomes serious is the issue.

More later:
6. How to get the cells balanced the first time?

7. How to check for balance occasionally?

8. How to re-balance the cells when needed?

I'm definitely no guru, but if I were doing this on the current timeline, I'd take the wait and go with Scenario 3. I REALLY wanted to get an electric maxi-scoot when the xm3500Li came out, despite the discovery of the less-than-optimal specs, but I will admit that if I were doing this now and John was this close to delivering a product like he has coming out from Current, then I definitely would have waited for it. I can almost guarantee from my dealings with him that not only will you get the benefit of a BMS, but you'll likely get a massively better build quality which should more than make up for the price difference. I haven't dealt with his product yet, but having dealt with the man behind it I think it's a safe bet that will be the way to go, IMHO.

I did a search on current motors and could find nothing. I would like to check this out. I'm no expert either but I would say all three are good scenarios . At least you're not shopping for a Hummer:) I'd say if 42mph is fast enough for you're needs the stock xm3500li is pretty good and then I can pretty much guarantee you would end up moving to scenario 2. Then when the better bikes start coming out you'll want one of those. If you can wait that would probably be the best option. If you decide to get an xm3500li google 3500li special and you can get one for $3000 if the deals still going. I know, it's a tough choice but I do know one thing you'll love riding on of these high powered electric scooters, it's feels incredible!

It seems that
www.advancedelectricscooters.com
is offering the XM-3500 for $2999 ...
including shipping to a depot near you, $50 extra to your door (worth it unless you have access to a truck and several strong friends).

Hi Dave,

Personally, I've already placed an order with Current Motors, and I think it's going to be a really good bike. Even if the first few have some design glitches, I trust John to work things out and treat his customers right.

However, John has also mentioned that he's got a local electronics shop building his BMS according to an open source design, and they'll be making more units than he needs. The extras will be available separately, so you could buy one of those and retrofit it to whatever bike you end up with. These aren't available yet, so a wait is still involved, but I think they are coming shortly after the REV-1 starts shipping.

Another alternative to the XM-3500 is the R.Martin EVD. It's slightly higher quality than the 3500 (more like the XM-5000 with a smaller motor), it's set up for more speed but lower torque than the 3500. I just sold mine in anticipation of the REV-1, but I still think it's a pretty good bike. It doesn't come with a BMS either, but you can retrofit one, and it's got a good set of batteries to work with if you want to do mods later. (I'd like to see it with a higher capacity motor, for instance)

I did a search on current motors and could find nothing. I would like to check this out.

Iccarus, Current Motor Company (http://currentmotor.com/rev1.html) is John Harding's new name for his company, and his first units should be shipping around July 1.

Thanks I was wondering if it was Johns company I hadn't heard of it as current motors. I saw the REV-1 on his website before. That looks like a nice machine with all the stuff you need. The seat looks much more comfortable than the XM. Regen braking and a BMS, John could have a busy summer if he gets alot of exposure. I know these things will really take off when people see them alot. If I was buying a bike right now I think I'd go with the REV.