Turnigy Multistar - lightweight 10C cells

[Ianhill]

I think there is alot of hype over a problem that is few and far between, take precautions when storing and charging them, always check balance before use and your golden.
If a cell fails it's going to be short circuit within itself so depending how well the anode and cathode are connected will depict how bad it let's go, some just get warm and go flat while under storage over a few hours,
Others just go boom on the charger or under high load either way theres lots of cell activity and heat for a big let go, Ideally keep the cells contained at all times with a way of venting so it's not a bomb.

 

[Hillhater]

Hello,
I have a different sort of bike that for various reasons am considering an electric conversion. One battery option I’m considering is to use 96S multistars, 24 x 4S. I believe I need about 30A on average with few second bursts up to 80-90A...
........
Thanks for your insight

Seriously ...you are planning a 400v conversion for a saltwater use jetski !?
I suspect the risk of electricution , shorting, etc far outweigh any inherent risk of a fire caused by cell failure.

 

[rainmaking]

Hello,
I have a different sort of bike that for various reasons am considering an electric conversion. One battery option I’m considering is to use 96S multistars, 24 x 4S. I believe I need about 30A on average with few second bursts up to 80-90A...
........
Thanks for your insight

Seriously ...you are planning a 400v conversion for a saltwater use jetski !?
I suspect the risk of electricution , shorting, etc far outweigh any inherent risk of a fire caused by cell failure.

I am pretty sure I can mitigate these risks, but you do have a valid point.

The battery will be in a sealed enclosure, conductive on the outside but likely isolated from negative(?). I have considered 3D printing this in plastic but it will need to be somewhat larger to achieve the strength. I was planning to mostly isolate each pack from the next by squeezing each brick into its own pocket with silicone foam on all sides. Two well insulated and sealed wires will go to the controller housing attached to an oil filled motor. obviously this stuff needs to seal up pretty well. I guess the battery should have an emergency pressure relief vent. Of course there will also be some low voltage control wiring.

I know it's not the same environment but I plug my Tesla in when its raining all the time and it has a pretty simple plug.

 

[Sunder]

Woah. If you're comparing those two, I'm not sure you understand the risks...

The Tesla plug is just a connector. The power source(s) never risk immersion in water. It's even detailed in its rating - It's IP 65 rated, meaning dust can't get in (6), and low pressure water can't get in (5 - rain, indirect hose). If it was IP67, you could use high pressure spray, or IP68 would be full immersion.

Spray from nearby watercraft would probably be somewhere between low and high pressure water, so at the very least you'd want IP 66. Large waves which could ingress into the battery compartment, might raise that requirement to IP68.

So every box, every wire and every connector needs to be at least IP67, or preferably IP68. The gap between IP65 and Ip68 is a lot higher than you might think. For example, you could use a grommet for IP65. You want silicone on both sides of the cable entry immersion tested, if not pressure tested before it went live as an absolute minimum. When it comes to the lid, an O-ring is unlikely to be enough, you might also need something to provide compression.

Anyway, I'm probably not going to change your mind. So just stay safe, and testing things as thoroughly as you can before you go live.

 

[Hillhater]

Im sure you know you will need all the waterproofing you can think of, ..but i would still reconsider a lower voltage system if it can produce the results you are looking for..30-40kW ?

 

[rainmaking]

Sunder I do understand the risks and the IP rating system. My point with the comparison is that with the Tesla you are even making a wet connection, something I won't need to do on the ski. There is a sealed engine compartment that all this will be in, so spray isn't likely but the design will handle it anyway. The biggest risk is immersion from sinking. I will design the enclosures with that in mind. As I said there are a limited number of penetrations needed so I really don't think sealing is going to be the costliest or most challenging part of the system. Maybe I can even put a cutoff relay in the battery enclosure. Or, maybe it's safer to put the motor drive within the battery enclosure?...needs a little more thought.

Hillhater as you can imagine small and relatively lightweight 40kW capable motors don't exactly grow on trees. I am using an automotive drivetrain component that with liquid cooling is capable of 38 continuous kW at 9500 rpm. I have to step that down with a gear to around 6000 and I really only plan to get into mid-30's on a peak basis. I'm not sure my pump will survive too much of that power level, I was probably around 45hp at the most with the engine setup (on days that it ran). The motor's backemf is ~33v/krpm. I also like not having parallel cells, which I would need an abundance of if I went to a lot lower voltage.

I appreciate the experienced feedback. How about any experience with these multistars? Does anyone get 4-5C peak out of the 20Ah packs?

 

[miuan]

I ran 10Ah multistars with 80A peak controller and they did get very warm after a couple aggressive rides. 5C peaks are fine. Just make sure you weed out every suspicious pack. It sure IS a costly decision with such big packs. Also DO reconsider building the battery out of high grade 18650s. They are safer overall, and less trouble on the way.

 

[Ianhill]

 

[rainmaking]

I ran 10Ah multistars with 80A peak controller and they did get very warm after a couple aggressive rides. 5C peaks are fine. Just make sure you weed out every suspicious pack. It sure IS a costly decision with such big packs. Also DO reconsider building the battery out of high grade 18650s. They are safer overall, and less trouble on the way.

miuan,
Yes good point, test all packs and only incorporate ones that balance well. What 18650s could I use to get 5C peaks from? Any way you look at it I need ~5-7kWh capacity and need to hit ~35kW peak discharge.

 

[rainmaking]

I think there is alot of hype over a problem that is few and far between, take precautions when storing and charging them, always check balance before use and your golden.
If a cell fails it's going to be short circuit within itself so depending how well the anode and cathode are connected will depict how bad it let's go, some just get warm and go flat while under storage over a few hours,
Others just go boom on the charger or under high load either way theres lots of cell activity and heat for a big let go, Ideally keep the cells contained at all times with a way of venting so it's not a bomb.

Another point I'd like to make as I have read that someone wants to use 400v on lipo .
Cells have a value for insulation resistance so there a point with voltage where it will leak internally and go bang, plus if a cell let's go it's a dead short and crestes alot of heat and so the more series cells you have it creates the potential for a run away situation where the heat is just moving through the pack destructively destroying and venting the cells as it goes, I wouldnt play with lipo much over 150v your really playing with fire id like to see who has tested the max insulation resistance on the cells before an internal faliure so we know a safe limit for the series string.

Ianhill,
I don't really understand how the insulation resistance plays a part, but it may be my ignorance. The adjacent cells within each brick only see the voltage difference between those adjacent cells and I will arrange each brick as I described earlier in isolation from each other with silicone foam and a rigid wall between.

Also about the run away--if the cell is going short won't the voltage collapse between its adjacent cells, and thus self-lower its ability to heat? Of course as I said I will monitor voltages and this will be a shut-down situation but I thought this was the reason why cells in series are safer than paralleled cells.

 

[Ianhill]

 

[Hillhater]

RC lipo bricks have been used often in high voltage ( 200+v - 400v) packs.
ES member jonesc ran his race bike on a 700v lipo pack.
but , again the risk to life is huge !

 

[Ianhill]

RC lipo bricks have been used often in high voltage ( 200+v - 400v) packs.
ES member jonesc ran his race bike on a 700v lipo pack.
but , again the risk to life is huge !

Does he have a build thread on that 700v pack I'd love to see that from a distance, A 190s pack in a bike even with 40amp discharge it would be 30kw but what type of controller accepts those types of voltages I don't see the need to go over 390v at all even for a performance product.

I feel I need a extinguisher to even talk about it and a chainmail suit to go near it. After 60vdc or so our skin conducts quite well so over 10× that under your chest is a mad idea any fault and instant high speed death without a crash.

 

[skeetab5780]

All I care about is when is the price going to come down on these things, last year I bought for $59.99 now they are $110!!

I keep waiting hoping for a drop one day but they keep going up

 

[rainmaking]

If you check the voltage just before the last cell in the string it's 4.2v lower than the complete pack so the last cell is insulting this value

I still can't get my head around this. The last cell doesn't have the first cell anywhere near it so how is it having to insulate the rest of the string voltage? Of course if the cells were all sitting next to a ground reference it would be different, but they aren't.

 

[rainmaking]

Anyone else have specific experience with the 20Ah multistars?

 

[Hillhater]

Does he have a build thread on that 700v pack I'd love to see that from a distance, A 190s pack in a bike even with 40amp discharge it would be 30kw but what type of controller accepts those types of voltages I don't see the need to go over 390v at all even for a performance product.
.

He used a lot more than 40amps !
I think this is the build thread,..but you may have to dig around to find the pack detail.
https://endless-sphere.com/forums/viewtopic.php?f=10&t=29916

 

[Ianhill]

 

[Addy]

Pass the parcel and it gains amplitude on every pass so more cells bigger the voltage, just because the first cell is not in direct contact with the last doesn't mean it's voltage can not be felt I'm a 20s pack for example I get 4.2v across the last cell but 79.8vdc across the rest of the pack, so that 79.8v has to join hands with the 4.2v walk across the cell and become the 84v on the otherside.
So the first cell is not in direct contact with the last but it s an influence otherwise series packs would have no purpose

The risk here is if the cells aren't insulated properly and they touch ground / pack negative. The cell doesn't know that it's in series with many others and that doesn't change anything in the cell itself.

 

[Ianhill]

Pass the parcel and it gains amplitude on every pass so more cells bigger the voltage, just because the first cell is not in direct contact with the last doesn't mean it's voltage can not be felt I'm a 20s pack for example I get 4.2v across the last cell but 79.8vdc across the rest of the pack, so that 79.8v has to join hands with the 4.2v walk across the cell and become the 84v on the otherside.
So the first cell is not in direct contact with the last but it s an influence otherwise series packs would have no purpose

The risk here is if the cells aren't insulated properly and they touch ground / pack negative. The cell doesn't know that it's in series with many others and that doesn't change anything in the cell itself.

Your correct in your first part of thiinking this is dead shorting the two cells but your wrong on the series bit or you could series these upto 1 gazillion volt and you can not.

 

[Addy]

Your correct in your first part of thiinking this is dead shorting the two cells but your wrong on the series bit or you could series these upto 1 gazillion volt and you can not.

You could have a quite a few of these cells in series but that doesn't change what the problems are. With a lot in series it's still an insulation problem, both cell terminals will be at a very high voltage relative to ground. If the cells are well insulated with respect to each other and other parts of the system, then there's no problem.

When you start dealing with very high voltages it can be very difficult to fit enough insulation in dense battery packs, which is one reason you wouldn't bother putting so many in series.

 

[Ianhill]

 

[rainmaking]

I believe you can make a gazillion volt series pack, as long as you mind the insulation resistance between the high potential points in the system...i.e. anything tied to negative needs more and more (insulation) resistance relative to the voltages available up the cell chain. Voltage potential is only valid between any two given points regardless if there is another point somewhere that has a larger potential. An example would be a bird landing on a 300kV transmission wire. The bird doesn't care that it has a huge potential to ground or the other wires if it can't get close enough to it/them to conduct electricity.

In my pack I plan to have at a minimum 5mm of insulating foam around each brick, which should be good for way more than my 400V. Mostly I am doing this for shock load resistance. Of course other areas like my PCB will need to mind the appropriate insulation and gaps.

That bike build thread that Hillhater posted about is interesting! In the video jonesc posted at the end you can see when he pulled the wheelie the bike hit 273A at about 590V
You will not get that kind of racing performance on a small and (relatively) lightweight machine without high voltages like that.

 

[Addy]

I'm not gonna argue with you just try it and find out? Im not talking about the terminals spark gap im talking about internally the insulations resistance to conduct its only rated to go so high after that point it will conduct and fail internally, If you do not agree that a voltage carrys across the cell and the more you place in series the higher the voltage those cells need to insulate against then you have alot to learn.

The voltage across the cell is determined by the cell itself unless you are physically applying some other voltage to it. As I said, it should be well insulated, so that wouldn't be happening.

I did look around a bit and I don't see anyone else saying what you're saying. Please don't spread misinformation. If you have some references about this I would like to see them.

 

[Ianhill]

I believe you can make a gazillion volt series pack, as long as you mind the insulation resistance between the high potential points in the system...i.e. anything tied to negative needs more and more (insulation) resistance relative to the voltages available up the cell chain. Voltage potential is only valid between any two given points regardless if there is another point somewhere that has a larger potential. An example would be a bird landing on a 300kV transmission wire. The bird doesn't care that it has a huge potential to ground or the other wires if it can't get close enough to it/them to conduct electricity.

In my pack I plan to have at a minimum 5mm of insulating foam around each brick, which should be good for way more than my 400V. Mostly I am doing this for shock load resistance. Of course other areas like my PCB will need to mind the appropriate insulation and gaps.

That bike build thread that Hillhater posted about is interesting! In the video jonesc posted at the end you can see when he pulled the wheelie the bike hit 273A at about 590V
You will not get that kind of racing performance on a small and (relatively) lightweight machine without high voltages like that.

Look at the distance between the bird and it's closest potential difference electric doesn't just have to be a ground point to get a zap electric flows to any potential difference, The air gap is huge and air is a good insulator itself,

I wouldn't use foam it's hydroscopic I believe there's alot of risk in your design I just wouldn't be willing to accept either that or you can not see the danger, the foam will help nothing other than mechanical vibration it's internally the cell will fail and short.

Have you trained at all with high voltage I would beg off you please consider what you are doing before its too late and your dead.