Varg Down on power - Thermal Limiting

[willy]

I have a different power issue, I'm riding motos on a sand track. The stark is thermal limiting itself at 7 minutes and by 10 mins is going so slow. The battery is getting hot and putting itself into a limp mode. After a month of testing and lots of emails back and forth with stark. stark admits this is what happens when it's ridden on sand under heavy load, but according to stark the product is not defective because I'm not using it for its intended purpose as they looked at my bikes ride data and said, I'm going from 0% to 100% throttle constantly which they say causes the battery to overheat. I'm no Sebastian tortelli but I was inside the the top 15 mx1 NZ, and their is no way I can get the stark to to a 20 min moto flat out. It just can't handle the jandal.

 

[Chaconne]

I have a different power issue, I'm riding motos on a sand track. The stark is thermal limiting itself at 7 minutes and by 10 mins is going so slow. The battery is getting hot and putting itself into a limp mode. After a month of testing and lots of emails back and forth with stark. stark admits this is what happens when it's ridden on sand under heavy load, but according to stark the product is not defective because I'm not using it for its intended purpose as they looked at my bikes ride data and said, I'm going from 0% to 100% throttle constantly witch they say causes the battery to overheat. I'm no Sebastian tortelli but I was inside the the top 15 mx1 NZ, and their is no way I can get the stark to to a 20 min moto flat out. It just can't handle the jandal, so I sold the thing.

I wonder if there are any mods available to address that? I ride mostly trail and enduro now that I am old, but I would think that 0% to 100% constantly is pretty common for guys riding moto with an E-mxBike --since the throttle is really the complete power delivery system like the clutch and throttle combo on an ICE bike. ICE bikes often fail in rough conditions like mudders because the clutch overheats due to over-modulation in a kind of similar way.

Just out of curiosity what mode were you racing in? Were you using regen? Did you try it without the bash plate and foam liner? Or maybe just without the liner? The battery is air cooled, I wonder if those fins aren't enough for certain heavy load conditions?

Maybe in next gens the battery should be liquid cooled at least for race bikes? The motor is already liquid cooled perhaps that could be re-engineered to provide broader cooling? Also, I wonder if a clutch would allow for more consistent throttle on an E-mxBike if the hard transients are actually the cause of the battery overheat?

Anyway thanks for sharing.

 

[Philip]

I have a different power issue, I'm riding motos on a sand track. The stark is thermal limiting itself at 7 minutes and by 10 mins is going so slow. The battery is getting hot and putting itself into a limp mode. After a month of testing and lots of emails back and forth with stark. stark admits this is what happens when it's ridden on sand under heavy load, but according to stark the product is not defective because I'm not using it for its intended purpose as they looked at my bikes ride data and said, I'm going from 0% to 100% throttle constantly witch they say causes the battery to overheat. I'm no Sebastian tortelli but I was inside the the top 15 mx1 NZ, and their is no way I can get the stark to to a 20 min moto flat out. It just can't handle the jandal, so I sold the thing.

Wow, were you at a motocross sand track in the 80hp mode and able to hold the throttle pinned on all straightaways?

And the bike overheated in just 7 minutes? Wow, again.

What was the ambient temperature on the days when this happened?

 

[willy]

I found that to get the bike to steer with the rear wheel like a gas bike in sand it had to be on 65hp or 67hp anything less it would get to much drive and push high and or go over the berm. Engine braking I found about 35% was good as it settled the chassis in the corner better and carried more roll speed making it smoother when getting back on the throttle. I didn't take the bash plate off as its pretty common to bash things. The first moto was the best at the start of the day, power would last nearly 10 mins before thermal limit, and about 45% to 55% battery consumption. Plug it into the generator 45 mins, then because the battery temperature can't dissipate the heat, in time the second moto it thermal limits much quicker 7 minutes, the the 3rd moto is evan worse 6 mins the forth 5 mins. I agree I think the water cooled gearbox and engine is great but just relying on air to cool the battery is a design problem. The air flow just can't cool it quick enough for the heat it generates. Shame really as the first 5 mins is great fun. But I can't understand how they can advertise that Sebastian tortelli can to a mxgp heat (25 mins) at his pace. What happens if that round is on one of the 6 sands tracks they race on in mxgp, dodgy advertising I reckon

 

[willy]

It's the middle of winter here in New Zealand and the sand is pretty wet, so it will only get worse as the sand gets softer in the summer and the temperature gets warmer

 

[Philip]

I found that to get the bike to steer with the rear wheel like a gas bike in sand it had to be on 65hp or 67hp anything less it would get to much drive and push high and or go over the berm. Engine braking I found about 35% was good as it settled the chassis in the corner better and carried more roll speed making it smoother when getting back on the throttle. I didn't take the bash plate off as its pretty common to bash things. The first moto was the best at the start of the day, power would last 10 to 12 mins before thermal limit, and about 35% to 40% battery consumption. Plug it into the generator 45 mins, then because the battery temperature can't dissipate the heat, in time the second moto it thermal limits much quicker 7 to 10 minutes, the the 3rd moto is evan worse 6 to 8 the forth 5 to 7 mins. I agree I think the water cooled gearbox and engine is great but just relying on air to cool the battery is a design problem. The air flow just can't cool it quick enough for the heat it generates. Shame really as the first 5 mins is great fun. But I can't understand how they can advertise that Sebastian tortelli can to a mxgp heat (25 mins) at his pace. What happens if that round is on one of the 6 sands tracks they race on in mxgp, dodgy advertising I reckon

Thanks for sharing. Here are some battery cooling practices and ideas that worked for the Alta.

Battery Cooling

External cooling of the pack will only help so much. In fact, i plan on doing back to back tests with my mister fan to see how much of an effect on battery temps externally cooling the pack actually makes. @Mark911 said he had cooled wet towels blanketed over the pack when he was having a pro...

electricdirtriders.com

With the Stark, keeping the battery cool should be be easier, I am thinking, because the cell ends touch the outside if the battery casing directly.

 

[Philip]

I found that to get the bike to steer with the rear wheel like a gas bike in sand it had to be on 65hp or 67hp anything less it would get to much drive and push high and or go over the berm. Engine braking I found about 35% was good as it settled the chassis in the corner better and carried more roll speed making it smoother when getting back on the throttle. I didn't take the bash plate off as its pretty common to bash things. The first moto was the best at the start of the day, power would last 10 to 12 mins before thermal limit, and about 35% to 40% battery consumption. Plug it into the generator 45 mins, then because the battery temperature can't dissipate the heat, in time the second moto it thermal limits much quicker 7 to 10 minutes, the the 3rd moto is evan worse 6 to 8 the forth 5 to 7 mins. I agree I think the water cooled gearbox and engine is great but just relying on air to cool the battery is a design problem. The air flow just can't cool it quick enough for the heat it generates. Shame really as the first 5 mins is great fun. But I can't understand how they can advertise that Sebastian tortelli can to a mxgp heat (25 mins) at his pace. What happens if that round is on one of the 6 sands tracks they race on in mxgp, dodgy advertising I reckon

Thanks for sharing. Here are some battery cooling practices and ideas that worked for the Alta.

Battery Cooling

External cooling of the pack will only help so much. In fact, i plan on doing back to back tests with my mister fan to see how much of an effect on battery temps externally cooling the pack actually makes. @Mark911 said he had cooled wet towels blanketed over the pack when he was having a pro...

electricdirtriders.com

With the Stark, keeping the battery cool should be be easier, I am thinking, because the cell ends touch the outside of the battery casing directly.

 

[willy]

Yeah there is lots of people around the world much faster than me, I can't be the only one having this problem. Great bike, alot of fun to ride but when it comes to a race bike it's more of a toy than a tool.

 

[rayivers]

It's too bad the soak-it-or-smoke-it mentality has completely dominated MC cooling methods. I remember forced-air cooling working pretty damn well on all sorts of stuff from Volkswagens to CPU's, guess those days are over (BIG delta-T or nothing!!).

 

[Kurlon]

Air cooling only ever worked 'ok'. If you had those motors pumping out the same HP per CC modern liquid cooled animals are pushing they'd be melting down left and right. (Ignoring that you couldn't build them to the same tolerances as liquid cooled motors 'cause of the thermals...)

 

[willy]

The tesla performance battery's are water cooled, I think if your going to produce a electric motocross bike it has to be built like this in the future, finger crossed honda or ktm capitalise on starks mistake. Not the review I wanted to give the stark, but that's my honest experience and opinion, to many YouTube guys just hyping the thing to the moon.

 

[rayivers]

Air cooling only ever worked 'ok'.

My post was aimed at improving the Stark battery's cooling, not hi-output electric motors or anything else. And I'll take 'ok' over thermal limiting at 7m any day of the week.

 

[Chaconne]

Air cooling only ever worked 'ok'. If you had those motors pumping out the same HP per CC modern liquid cooled animals are pushing they'd be melting down left and right. (Ignoring that you couldn't build them to the same tolerances as liquid cooled motors 'cause of the thermals...)

Ya this true. And you would often get no indication until the bike started to melt down. Back in the day one of my air cooled XRs started losing power and it was too late. It had an oil cooler but it wasn't enough.

Even liquid cooled ICE bike were a mixed bag. I got a mid 2000s WR450 and before I put a fan on it that thing would boil the gas since the radiator and cooling system was right near the gas tank. It was a scarry deal one day when my five year old son called me into the garage to hear a sound and it was the boiling gas in my recently parked WR.

Many generations of ICE bikes had really bad designs of the cooling systems, I rode many early 2000s yz250fs over the years and the first generations of those sucked ass overheating and spitting coolant all the time. Carbs and kickers on 4T mx bikes, I vowed never to ride them again.

 

[Chaconne]

My post was aimed at improving the Stark battery's cooling, not hi-output electric motors or anything else. And I'll take 'ok' over thermal limiting at 7m any day of the week.

Fair enough.

 

[Beagle]

That may be a bit of an extreme case use (sand and national pro level) but they do advertise it for competition.
At least now the limitation is pretty clear, I'm just surprised not to have seen anyone else reporting it?
I guess the other guys riding sand must have been slower than you

France SX tour starts next week, that will be a serious test of the bike as well, not that much sand but it can get pretty heated.

 

[willy]

That may be a bit of an extreme case use (sand and national pro level) but they do advertise it for competition.
At least now the limitation is pretty clear, I'm just surprised not to have seen anyone else reporting it?
I guess the other guys riding sand must have been slower than you

France SX tour starts next week, that will be a serious test of the bike as well, not that much sand but it can get pretty heated.

Read it for yourself emails from stark.
Thank you for contacting Stark.
Sand tracks offer very little traction thus greatly impacting efficiency, as the wheel spins constantly. What you are describing is consistent with derating. That means the operating temperature is reaching the limits and the control units reduce power to prevent any damages. You feel the power coming back after a cool down period. Unfortunately, this isn't something we can fix, per say. We can only continue to work on developing and improving the powertrain efficiency. Keeping your bike up to date will also help prevent derating as we deploy better thermal management strategies with new updates.
Please let us know if there’s anything else we can assist you with at this moment.
The first run will less likely experience this but the next rides will get increasingly worse as the start temperature is already higher. The best advise we can offer is to try and cool it down the battery as much as possible. Use slow charging whenever possible, spray water on the battery casing, get a couple of ventilators blowing on the battery casing, wrap ice packs around the battery, use the active cooling when charging between motos, etc.
We are working on a few solutions ourselves but still in the test stages.


Thank you for your feedback. We understand that our product migh not be up to your expectations. However, unfortunately and as mentioned previously, that doesn't mean the product is defective unless it does not perform as expected within the intended purpose. This is stated in the VARG Owners Manual available at www.starkfuture.com/support.
Your bike's data shows battery derating as the throttle is going from 0 to 100% constantly causing enormous stress on the battery. This is typical behavior on any electric vehicle. As we continuously work to develop and improve the VARG, we hope you will reconsider and we're confident you will love riding the VARG on a motocross track or trails, as it was intended for.

 

[Beagle]

Just surprised I have not really seen many riders witnessing thermal limitation before.
In fact here is the only one I can think of:

Wrapping ice or spraying water on the battery between motos should help, just not sure if that's really convenient

 

[Philip]

The topic of this thread seems to have shifted from power maps to thermal limiting. That's okay. We are going to split this thread into two:

Varg Down on power - Thermal Limiting (This thread)

Varg Down on power? (Ride Modes/Power Maps) <-- The original thread

 

[willy]

Just surprised I have not really seen many riders witnessing thermal limitation before.
In fact here is the only one I can think of:

Wrapping ice or spraying water on the battery between motos should help, just not sure if that's really convenient

Yeah that's the issue, at 18.06 mins in the video, it was ment to be set at 80hp but you can hear and see the bike has thermal limited its self to be slow as hell. Looks like it only took a few laps for these boys.

 

[Beagle]

Yeah that's the issue, at 18.06 mins in the video, it was ment to be set at 80hp but you can hear and see the bike has thermal limited its self to be slow as hell. Looks like it only took a few laps for these boys.

These guys are among the fastest pro sand racers (Touquet), I think the first ride was fine then it got issues for the second run.
Then the guy making the video (average rider) was able to do an entire sand race the next day or so without problem so this shows it's definitely not suited for pro racers on sand tracks.