MXR --Max power limited warning anyone else?

[bsatt69]

I have an MXR that I have had a firmware update for the code 103 charger not working, the battery replaced after a code 35. Have 14 hours on it total about 4 with new battery. I have ridden it 3 times with new battery, 2 of those times I have had the warning light come on and display flash max power limited or something similar can't remember wording exactly.

The way it has been rode/charged is: rode until 2-3 bars, then plugged in right away to 240v wall outlet with the rapid charger, charged until 70-100%, ridden and repeated. Both times it happened on the 3rd ride cycle, first time had 2 bars left, last time still had 40% battery left. The bike is in the shade when being charged about 70-80 F. Always in level 4.

It is a bit of a concern both times it happened i didn't notice the light just the loss of power when coming out of a corner trying to clear a triple that requires everything you can get. End up casing and then see the light. I didn't think this should happen with the MXR, has anyone else been having this?

 

[Fog 25]

Yes it comes on when battery gets down to 20% it starts limiting. I believe the computer reads the battery level at each start up and sets it to a new 20% level. I found that the limiting mode doesn’t last long at race pace maybe 4-5 minuets. Your race range 1/3 battery is around what I got at Mammoth MX this year.

 

[strider]

My guess is that it's limiting due to battery temp. It sounds like you ride hard (map 4) which generates heat, then charging at 240V also generates heat, then back to riding, repeat. 70-80F is not very hot but the battery doesn't have much chance to cool down, and without active battery cooling...

 

[Silent But Dirty]

I get that same message on my 17 MX in map 2 when getting a low battery at the end of a hot day.

Like Strider, I thought the battery might be getting over temp from cycling the battery. Yesterday I tried using a spray bottle of water on the battery while it's charging, and it seems to help, as I didn't see the warning at the end of the day.

 

[mxengineer1]

My buddy was riding his Alta MXR this past weekend at local MX track here in Ohio. His last session the battery heated up enough to back the power level down. He said he normally rides in Map 3 but on hot days (>90F) when he rides and rapid charges between sessions his battery has gone into power limit mode a few times. As noted seems to be related to running it hard then charging immediately then running it hard again - no cool down time. Have not felt it on my EXR yet.

 

[Mark911]

Not uncommon and everyone will experience it differently depending on the operating conditions. It's particularly common when the battery is below 20% charged as voltage droop causes more current to be needed for the same power. Current creates heat in the battery cells, inverter and motor, any one can cause the software to intervene and limit.

The only way you'd get consistent performance is to charge the battery full (allowing for balancing) and let it cool to ambient temp before starting your race. Otherwise there's too many variables that can affect things. This is obviously not always possible or desirable. I've argued that Alta should provide its owners with the tools/software to read the important parameters (internal temps, voltages, etc) so we'd know much more accurately what to expect right before we line up. That way if you're gating 10 minutes after coming off charge (or whatever) you'll have a way to calibrate your intensity level and not end up coming up short on some do-or-die double.

 

[bsatt69]

You guys nailed it, combination of riding hard and consecutive ride, charge, ride, charge etc. with no cool down between.

I spoke with Alta today and Kevin said that the R pack is over 2 times better at dealing with the heat than the A pack but if ridden hard, charged and rode without cool down it can happen. He recommended using a fan and a mister to help cool battery and electronics if doing consecutive ride charge sessions.

I also need to pay attention to the warning light on display while riding to know if it is in limiting mode.

 

[Fod]

I'm just going to hit the bike with the track watering hose between riding and charging

 

[Mark911]

Spraying water, icepacks and fans seems so "low tech" for the Alta. The heat path from the cells to the pack housing (radiator) is only as good as the thermal conductivity of the material Alta uses to secure the cells in their honeycomb nesting arrangement. Unfortunately, thermal conductivity, mechanical strength and low weight don't always go together. Alta reportedly used a company in Europe to develop and make its proprietary composite graphite cell support blocks which is fairly cutting edge material but like the cells themselves this material tech is constantly evolving. However, the current material still can't transport enough heat to keep the cells within full performance operating temperatures under demanding conditions. Definitely need some breakthroughs in this respect if Alta intends to keep thermal control passive. Frankly, there's only so much working space and surface area around the tightly packed cells to get the heat out and it's a tough ask for ANY engineering company. Alta's engineers have certainly done much better than anyone else using a passive system that's for sure.
That said, the same limitation applies to "pulling" the heat out through greater delta T gradients (ice packs, etc). Once the pack becomes "heat soaked" its gonna take time to get all that thermal energy out. Without data from the onboard controllers nobody really knows how effective each external cooling technique is. Alta knows of course, but until its published and verified I'm tempted to mount an externally powered TC (thermal couple) somewhere between cell modules to monitor cell temps myself.

 

[strider]

Completely agree and you're right, we won't really know unless Alta exposes that data to us. On the Tesla Roadster, only the battery is liquid cooled. The motor and inverter are air-cooled. On hot days we get power-limited all the time due to inverter over temp. At track days owners will put bags of ice on top of the inverter. It makes a big difference.

I have to believe there's some benefit from dropping the frame and outside pack temps as the thermal transfer will be more efficient due to the higher temp delta.

As I see it there are 2 options for racers. Alta moves to a quick change battery pack setup so you can have a cool pack ready, or they build some kind of jacket or something that circulate coolant around the frame and battery pack while in the pits. I assume as Alta does more racing they'll settle on one method or the other.

A 3rd option would be to liquid cool the battery but that would add a ton of weight.