Where do we stop?
 

This is a somewhat esoteric question but I'm going to ask it anyway.

What do people think the ultimate limit on battery capacity should be for electric racing?

Sooner or later we are going to get to the point where you will need more than one charger to ensure all your batteries are optimally charged, even if you are running just one class at a large meeting. Just because, it takes that long to charge a pack. Of course we can charge at a higher Amperage, but even this has limits and the higher you go the more likely you are to damage or rupture cells.

You could use a battery with less capacity than what is allowed by the rules but this is likely to put you at some disadvantage. Not because you will dump, that doesn't happen any more (unless a pack false peaks), but because larger capacity packs produce a higher voltage output for longer at the beginning of the discharge.

So there has to be some limit to the capacity of batteries we can ultimately use. We are getting close to it now in my opinion.

If you don't like the idea of this then there is only really one alternative. We have fewer races on a day and race for longer. That way there would be more time between rounds to charge the large capacity batteries. Personally I like the idea of that. Some clubs are already going to 6 minute races. It will be interesting to see what happens.

How do people feel about longer races and fewer heats?

As an exercise let us consider the highest capacity battery currently on ROAR's approved list: The LiPo Hobbico Team Checkpoint 5400.

Let us further assume that there is 1 hour between rounds. This may be a little on the short side for a meeting like the Challenge Cup but at say an offroad state title where the classes are split over 2 days this could easily be the case for the finals. This would, of course, be about standard for many club days.

Most people charge their batteries at about 6A, indeed some of the older (but not obsolete) chargers have this as their limit, so we will start by thinking about 6A.

At 6A charging the Hobbico 5400 to it's nominal capacity takes precisely 54 minutes.

This leaves 6 minutes, just enough time to race and we still haven't marshalled or discharged the pack. Ok, many people have a separate discharger so we'll ignore that for the moment but you'll still have to put your next pack on charge before you leave to race; you couldn't put it on when you got back.

Ok, so now let's say you have a CDC version 7.0. This will do up to 8A, but it's also a discharger so, if you're like me, you won't want to buy another discharger.

At 8A charging the Hobbico 5400 to it's nominal capacity takes precisely 40 minutes and 30 seconds. Plenty of time you would think.

But If I race stock then (I'll be generous) I will only have used 3000mAh. This leaves ~2400mAh to discharge which I will do at 20A for the purpose of this exercise (actually, personally I usually discharge at 15A). This takes 7 minutes and 12 seconds.

Rounding up to the nearest minute we've taken 48 minutes charging at 8A and discharging at 20A.

BUT, of course you can only discharge your pack after you get back from marshalling, so there goes at least another 12 minutes. So if you want to discharge your pack before charging the next one that's the full hour. You can do it barely - maybe - not really.

My other option is to get to the track nice and early and start charging my packs ahead of time. But then I have to worry about keeping ahead all day, I want to enjoy my RC racing not go to the track to charge batteries!

This is why I say we are at the limit of the capacity we can support. What happens when the battery capacity increases to 6000mAh? Do we tell people they need to buy at least 2 chargers? Call me a budget racer if you wish but I think that is unreasonable and just a little silly. It certainly won't help bring new people into the sport.

When lipo (or next replacement) becomes more acceptable (assuming it is safe) there isn't the need to discharge batteries. In fact with a lipo (or next gen) you might even be able to run 2 (or more) races on 1 charge without any loss in performance.

I am a budget racer and this is why I'm hoping the newer battery technologies eliminate some need to have to time my battery peaking to the last possible second.

I hope you are right, but people said exactly the same thing about NiMH when they first appeared on the scene so I'm dubious to say the least.

You can have the lipo pack charged from the night before. If you have 2 lipo packs you would easily charge within the parameters you mention. Also unless you completely dump the lipo, your time for charging expectations are way off. You simply keep topping a lipo up, no discharging / equalising required. Probably one battery would do the day for you.

On the other hand, NIMH I agree with you for sure. Too long to get them cooked between heats.

The whole point of lipo is to cut costs and have more run time. If you are running stock and have a 5400 bolted in, then I would suggest staying at home anyway as you are deluded if you think you need that much capacity for a 5 minute stock race.

They are great for practice though and realistically usually arent timed so you have as much time as you need unless at a National where it is easy to TOP UP the pack or charge the day before. Again the whole point of lipo is the new technology to do this sort of thing with faster turn arounds, no cell memory and better voltage, eliminating the need for the best "TEAM Zapped cells" that cost the earth.

Its part of progress and the quicker its adopted the better. If anyone is having problems with understanding lithium-polymer/lithium ion and such lithium based battery technology read the link here

http://www.mpoweruk.com/lithiumS.htm

Pay attention to the advantages but also its disadvantages.

I think in regard to your comments radio active on here and in the challenge cup forum, you profess to know what is best regarding lithium technology and its adoption, but you dont know the facts or advantages or the MAIN reasons for its adoption by ROAR and other RC organizations worldwide (soon enough).

Learn about the cells chemical make up, learn its advantages and disadvantages. Learn why these cells have been adopted in the first place and make an informed choice and give CONSTRUCTIVE comments.

Firstly my comments on the Challenge Cup thread have nothing to do with my comments here. The comments on the other thread relate specifically to the process of rules adoption we follow in this country. Quite simply, consistency is highly desirable, and for that reason alone it is almost always better to adopt the regulations of a central body wholly.

You are quite right I haven't used LiPo batteries myself yet. Having read the link you directed me to I now have more information. But let me say that I had no objection to LiPo batteries per se before. Now, if all the advantages stated are accurately represented, then all the better.

My previous post suggested that I am apprehensive about believing everything stated by manufacturers about a new technology. This is true. I'm not a Luddite (I have a PhD in physics - which was on polymer nanolithography as it happens). However, as I stated above manufacturers said many of the same things about NiMH cells. That you could store them with any range of capacity in them and just go out and use them without a performance drop off for instance - it turned out not to be true.

Having read the website you directed me to, some of these claims made about LiPo cells seem more credible. I can see how a solid state cell (with no electrolyte) would be less likely to self discharge for instance.

I'm less convinced about the 'flat discharge rate'. Often what a manufacturer means by flat discharge and what the RC industry means are two entirely different things. And as it happens I sat in talks given by academics who were developing polymer based batteries when they were in their early stages. The discharge rate was nowhere near constant. One Professor I spoke to described this as the worst feature of this type of cell. However this was a few years ago now (Wellington PV Workshop 2004) and they have probably solved the problem - though I would be surprised if it had been solved to the extent claimed.

However, if I take the word of a racer I know then these packs do indeed have a near constant discharge rate at 7.2V. Sounds great to me, I'd like it to be true. Yet this same racer says he is much more likely to continue to use NiMH in Stock. Why you ask? Because a good NiMH pack puts out more than 7.2V at the start of its discharge cycle. How long they put out more than 7.2V is directly proportional to the capacity of the battery. So larger capacity batteries are still an advantage in Stock even if we are only using a fraction of that capacity. In fact especially if we are only using a fraction of that capacity. And these are NiMH cells we are talking about so they have all the same quirks. It's true that LiPos are lighter but if your car is close to the weight limit then this is not an advantage, and since nobody is changing the weight limit then it doesn't help.

Just for comparison the highest capacity NiMH approved by ROAR is 4600mAh. Ok, it's not 5400mAh but this is still going to take a bloody long time to charge and this was the point of the thread, not bagging LiPo which might be great for the sport.

It is worth noting also that the ROAR rules don't have provision for saddle pack configuration LiPos. If AARCMCC adopts the ROAR regulations then it will be the same here. So, if like me you drive a car that cannot be modified to take a stick pack like configuration they you're stuck with NiMHs anyway.

where did you find that saddle packs are not supported?

from ROAR

Physical Specs:
8.3.2.2.1 Hard Case & Dimensions A factory encased hard shell pack is mandated for race durability reasons that stem from the vulnerability of Lipo cells to physical damage. Any physical distortion, denting or puncture to
the cells will cause either an immediate or long term safety risk. A hard cased pack reduces this risk significantly by protecting the cells from crash damage, battery ejection, and general wear and tear at the track.

The maximum dimensions are:
Length: 139mm +0mm/-3mm
Width: 47mm +0mm/-2mm
Height: 25.1mm +0mm/-3.0mm
These are in place to standardize pack dimensions in order for chassis manufacturers to now be able to design around a consistent set of fixed dimensions.

Saddle packs fit within these dimensions and they are hard cased. ergo they will be certified

Hi Ben

Are the hard case Trakpower saddles 25.1mm high or less? That's pretty low height expectations for a saddle lipo with decsent capacity to be!

Excerpt from ROAR rule 8.3.2.2.1* ...ROAR defines the "hard case" as a case made of ABS or similar type material. The case shall consist of two (2) halves with each half being constructed from a single mold that is not easily pliable and retains it shape without any exterior or interior support. Both the top and bottom sections of the case must be secured together by glue, double-sided tape or heat seal with a label across the seam stating "ROAR Approved"...

*My italics.

So you are saying that because there are 4 halves in a saddle pack (2 batteries with 2 half cases) that it doesn't comply with the ROAR ruling?

I don't think that's quite what is meant......

But that's exactly what it says. 2 halves, a top and a bottom glued together - that's pretty clear.

For example, each Trakpower battery saddle hard case has a top and bottom half, I haven't pulled one apart to see about glueing, tape etc, but each side complies. It's just that there are x 2.

As you say though there aren't any actually listed on the approved list so you may well be right!;)

Trakpower HARD CASE Saddle packs comply with ROAR specs and ARE legal under their stringent rules regarding the construction of the latest lipo cells.

They are effectively a 1 piece cell (in two halves) if that makes sense in the fact that they are fully contained in the hard case, there is just two of them joined using a plug setup.

Reedy Saddles/LRP etc as well as other s are NOT legal, due to the fact that they are shrink wrapped. They were brought out and into the hands of racers due to racer DEMAND. ROARS stance on this is that most/many clubs in the US do not follow ROAR regulations therefore do not have to follow their rules. International and ROAR sanctioned events are another story. This came from a post from Rick Howhart as did the Hard Case info.

Trakpower Saddle packs ARE LEGAL.

:)

yes