Why Parallel LiPoly

[sjslhill]

Well, I had a nice talk to someone today that races in Canada and at CAFE and I now understand some things better. It seems that amps required to run Fast Electric boats kills NIMH cells, I kinda knew that one.

In order to take full advantage of the power required one needs more ability to feed amps without killing the battery packs. LiPoly packs that are rated 20C should be treated as they will give 10C. By using them at a one half rating you can get up to 200 cycles vs. the 50 cycles of running them at 20C.

So, 2 20C packs is needed in parallel to give the racer longer battery life. The weight will end up close to same as with NIMH

I agree with this but I don't agree with how everything got to this point. But hey, that's just my opinion. Within a year if LiPoly technology does not improve, and I doubt that it will that much more now, you will need 3 packs in parallel in my opinion. Someone will just make a better controller and an even more AMP hungry system

This example above is for N2.

He also went on to say that many of the form factors of today's LiPOly packs will not fit properly in the current hulls that everyone has. So, people I guess wll need to find some different cell shapes or different hulls.

thanks,

Steve

 

[Darin Jordan]

He also went on to say that many of the form factors of today's LiPOly packs will not fit properly in the current hulls that everyone has. So, people I guess wll need to find some different cell shapes or different hulls.

Several guys in our club used paralleled Lipo packs in their hulls last season and they fit just fine... A 2S2P pack takes up about as much space as a normal 6-cell pack... a 4S2P pack can be configured to fit in the same place as a 12-cell pack made up of 2-6-cell packs... If you are talking about M1s/A123 cells, then you are correct... they are oddly sized...

 

[Kevin Whitehead]

I think that you are wrong about the chances of us seeing outrageous controllers any time in the future.

1. The isn't a large enough market to make it profitable. We can barely get the few manufacturers to provide what we have now.

2. At some point, the liability risk (as power handling capability increases) will outweigh the profit potential. I think the fantasy 400A controllers that have been suggested by some are way beyond that point of being too risky.

The controllers are the limiters right now and will most likely remain so.

A rule allowing only commercially available controllers would prevent anyone from working around the limiter by building one-off controllers.

 

[sjslhill]

I agree with the 4S2P pack, he stated that you cannot balance each cell, which is incorrect. A123's would have been a good solution and a safe one, but you guys need too much power to make these work.

thanks,

Steve

He also went on to say that many of the form factors of today's LiPOly packs will not fit properly in the current hulls that everyone has. So, people I guess wll need to find some different cell shapes or different hulls.

Several guys in our club used paralleled Lipo packs in their hulls last season and they fit just fine... A 2S2P pack takes up about as much space as a normal 6-cell pack... a 4S2P pack can be configured to fit in the same place as a 12-cell pack made up of 2-6-cell packs... If you are talking about M1s/A123 cells, then you are correct... they are oddly sized...

 

[JfromJAGs]

The very basic problem is that 1min (1/60 h) of runtime mean a C rate of 60! So for sprint racing 60C cells would be needed. No cell on the market is able to deliver that and even be discharged completely.

To solve this, it does help to increase the available capacity and so leave enough in the pack. Runing the same amps means also only half the C rate @ double capacity - so easier on the cells. I can follow that!

The problem is why should people do that if they can be faster by using more of the available power?

The only real solution to this would be an electronic capacity limiter. Stop the boat after 2000mAh, but let the people have 5000mAh or more in their cells. This is the F5B approach. Do it with energy (capacity * voltage) and you eliminated the advantage of any selecting of cells.

Joerg

 

[Jim Caldwell]

Just got a picture in my mind of somone sitting down and "selecting" a fuse or whatever, from a box of a thousand!! :lol:

 

[JfromJAGs]

Well, it would'nt be a simple fuse. It would be a precise, calibratable, electronic device. Accurate to 0.5% or better. That's so accurate, that the range in inaccuracy would not affect results. That means for a 4min race, the deviation in runtime cutoff should be 1s or less.

 

[Kris Flynn]

JAGs, you are refering to a mAh measurement device, correct? What would happen to the guy who breaks the start, or cuts a bouy (i think in the US a bouycut is an extra lap??)

just curios, but i like the idea of a mAh cut off limit...personally i also like the idea of minimum boat weights h34r:

 

[JfromJAGs]

Kris, this device would measure currents and add these up every 1/10 of a second or faster. So it would sum up the capacity used, and then shut the controller down once you are over the limit, a limit safe for the batteries. It would work similar to the devices known as LiPo savers - which slow down the controller once the LiPo battery voltage is below a lower limit.

A device like that would be a real revolution. Everyone would have the same amount of capacity, selecting batteries for capacity would become more or less obsolete - it would cut racing loose from the battery technology rush. Just not sure if everyone want's that.

Joerg

 

[Kris Flynn]

Very interesting concept. Personally i like it. But as you said, not everyone will. I am all for a level playing field wih NiMh and Li-chemistry.

Here in Australia, we are going through a rule change situation also. BUT our rules are so outdated that NiCad are the only leagal power source (until Jan 1st 07 because NiMh was voted in). LiPo is not being allowed just yet, our opinion was to see what the US did and also for the Li-Po's to get a bit better before allowing them to race.

Is there something available currently that can measure the mAh and then cut off the controller? If we all had a MAX mAh we could use in a race then theoretically everyone should have the same speeds, then driving will be the only factor.

 

[AlanN]

I don't like the idea of a mah limiter.

Another nice reason to have more mah is to run longer.....but I guess that there are too many worried parties out there thinking that we are going to run fantastical setups.

Gee has any freakin body even thought of running 10 or 15 laps per heat?

Probably not since your so worried about "what if's".

 

[Jeff]

NO,no you don't want to run 10 or 15 laps. That would creat awhirlpool vortex that would suck us down to china. But hey lipos and brushless motors are cheaper there!

Jeff :lol:

 

[Pagemaster]

I don't like the idea of a mah limiter.
Another nice reason to have more mah is to run longer.....but I guess that there are too many worried parties out there thinking that we are going to run fantastical setups.

Gee has any freakin body even thought of running 10 or 15 laps per heat?

Probably not since your so worried about "what if's".

Alan you guys have been running lipo in your club for a while. Did you increase the laps for sprint classes in 2006 or just run hotter setups?

I'm all for longer races, but there isnt to much talk about it.

Steven

 

[brooks93]

I don't like the idea of a mah limiter.
Another nice reason to have more mah is to run longer.....but I guess that there are too many worried parties out there thinking that we are going to run fantastical setups.

Gee has any freakin body even thought of running 10 or 15 laps per heat?

Probably not since your so worried about "what if's".

Alan you guys have been running lipo in your club for a while. Did you increase the laps for sprint classes in 2006 or just run hotter setups?

I'm all for longer races, but there isnt to much talk about it.

Steven

we run on a 1/6th mile for 6 laps.

 

[Pagemaster]

Thats cool Kelly. What are some of the race times with the bigger course and additional lap?

Would you guys consider more laps for sprint? Or is what you have now long enough?

I know myself, I'm shaking and twitching so much, too long at sprint speeds my give me a heart attack!

Steven

 

[JfromJAGs]

I don't like the idea of a mah limiter.
Another nice reason to have more mah is to run longer.....but I guess that there are too many worried parties out there thinking that we are going to run fantastical setups.

Gee has any freakin body even thought of running 10 or 15 laps per heat?

NAVIGA races stepped mono's and hydro's with 7, 12 and 20 cells. Runtimes are 5min for hydro, 6min for mono. Both do in the range of 20-25 laps in that race time, on a cource similar size to the electric oval. Mono 20 cell holds the record with 29 laps in 6min, but the cource becomes to small for that, so people are even talking about eliminating the class. This 29 laps was done using 20 cells of 4200 NiMH in series. A top build 7 cell hydro hits about 60mph, the mono's are more in the 50mph range. It does'nt look slow at all on the cource they run on.

If you'd ask me, I would cut down the mAh limit to 2000mAh for 5 lap sprint (that's still 140A average!), 4000mAh for 4min enduro and the NAVIGA 5-6min classes. 6 laps on 1/6 mile might require different values as well as 1/8 scale. Limit's would be selected to make it safe for the technology. It will for sure make it more equal for the competitors also - but this is the point where I guess not all will like it.

Don't get me wrong, I'm not promoting this idea here, as there are no such devices available (yet). I'm just trying to explain the concept and it's outcome. The competiton plane guys are talking about such technologies though and if they use it, it might be an option to use in the future. The concept would indeed solve many of the problems we face from the technology rush.

Joerg

 

[AlanN]

Joerg,

I dont get your point.

2000mah limit for sprint? I and others have been pulling more than that in our 5 laps 1/8 mi course for the past few years.

We would be moving backwards with those limits.

4000mah for endurance? Aww C'mon we have been doing that (limited by the cells and not paralleling). It's like looking at 20 miles of open highway with a stop sign every 100 feet.

I want to run longer....larger course 1/6th and more laps..I'll settle for 6 sprint laps and a full lap warmup...not that ridiculus fig 9 start.

And for O/S....well there's just a faster 4mins of racing. Not mind blowing speed....just more fun.

 

[Andrewg]

Alan

Actually my loggers say Joerg's 2AH limit is very close (2.2AH would be even closer) for 5 race laps a half course mill and a cool down lap on a 300 meter nitro course. However I have an open mind on a limiter, altho it is interesting.

Why does lipo use less amp hours? Because lipo hold a higher voltage under load than nickel which boosts total energy throughput with negligible heat losses compared to increasing amperes (where heat loss accelerates as amps increase) - Also because the boat is faster it stays out less time.

The latest gen 25C cells are going to turn peoples ideas about Lipo on their head. They are tough, have excellent power, come home cool, are easier to handle than Nickel being lighter and smaller, only needing one instead of 3 nickel packs, are more reliable and dont need parallelling (IME the increased number of connections definitley affect reliability - hey I still use them but it happens).

Anyone who asked me before August about Lipo in boats would have got a dont go there recommendation but not any more.

 

[JfromJAGs]

Joerg, I dont get your point.
2000mah limit for sprint? I and others have been pulling more than that in our 5 laps 1/8 mi course for the past few years.

We would be moving backwards with those limits.

4000mah for endurance? Aww C'mon we have been doing that (limited by the cells and not paralleling). It's like looking at 20 miles of open highway with a stop sign every 100 feet.

I want to run longer....larger course 1/6th and more laps..I'll settle for 6 sprint laps and a full lap warmup...not that ridiculus fig 9 start.

And for O/S....well there's just a faster 4mins of racing. Not mind blowing speed....just more fun.

Well, there's nothing more I can say. You will need to see yourself next year.

 

[TRUCKPULL]

OK who is going to pay for these electronic limiters?? NAMBA , IMPBA For hand out at races???

I don't think so.

Each person buys there own, I see, I think the next persons unit is better then mine, seeing I got mine wet last week, He has to swap his for mine because it is a rule. I don't think so.

Do you see where I am going with this.

Larry